Wednesday, April 11, 2012

Human Biology: Unit 3 Compilation


Table of Contents

Chapter 5: The Skeletal System
5.1 – The Skeletal System consists of Connective Tissue
5.3 – Mature Bone undergoes Remodeling and Repair
5.4 – The Skeleton Protects, Supports, and Permits Movement
5.5 – Joints form Connections between Bones

Chapter 6: The Muscular System
6.1 – Muscles Produce Movement or Generate Tension
6.2 – Individual Muscle Cells Contract and Relax
6.4 – Cardiac and Smooth Muscles have Special Features

Chapter 7: Blood
7.1 – The Components and Functions of Blood
7.2 – Hemostasis: Stopping Blood Loss
7.3 – Human Blood Types

Chapter 8: Heart and Blood Vessels
8.1 – Blood Vessels Transport Blood
8.2 – The Heart Pumps Blood through the Vessels

Chapter 9: The Immune System and Mechanisms of Defense
9.1 – Pathogens cause Disease
9.2 – The Lymphatic System Defends the Body
9.3 – Keeping Pathogens Out: The First Line of Defense
9.4 – Nonspecific Defenses: The Second Line of Defense
9.5 – Specific Defense Mechanisms: The Third Line of Defense
9.6 – Immune Memory Creates Immunity
9.7 – Medical Assistance in the War Against Pathogens
9.9 – Inappropriate Immune System Activity Causes Problems

Chapter 10: The Respiratory System: Exchange of Gases
10.1 – Respiration takes Place Throughout the Body
10.2 – The Respiratory System Consists of Upper and Lower Respiratory Tracts
10.3 – The Process of Breathing Involves a Pressure Gradient
10.4 – Gas Exchange and Transport Occur Passively
10.5 – The Nervous System Regulates Breathing
10.6 – Disorders of the Respiratory System

The Skeletal System
The human body is an amazing thing. We can climb to the tallest mountain, throw a football across an enormous field, and thread a needle. Each action, individually, might not seem like much, but when you consider that we are capable of all of them, the human body is remarkable.

The Skeletal System Consists of Connective Tissue
The skeletal system consists of these three connective tissues:

  • Bones - These are the hard elements of the skeleton that most people are familiar with.
  • Ligaments – Consists of dense, fibrous connective tissue that bind the bones together.
  • Cartilage – A specialized connective tissue, made of collagen fibers and ground substance (an elastic gel-like fluid). Cartilage has several functions, among them are reducing friction in joints.

Bones are the hard elements of the skeleton
Bone is really a living tissue, although it is mainly made of nonliving extracellular crystals of calcium minerals. It contains several types of living cells, as well as nerves and blood vessels.

Bone has five different functions. Some are more familiar than others. They support our ability to sit and stand. They protect organs such as the spleen, liver and lungs. And the attachment of bone to muscle allows for movement. Cells in certain bones are the only source of new red and white blood cells and platelets for blood. Without this function, the human body would expire within months. And bones also store two minerals, calcium and phosphate.

Haversian Canal/newscenter.lbl.gov/accessed 4/11/12
Bone contains living cells 
Compact bones are made of calcium phosphate enclosing and surrounding living cells called osteocytes. The osteocytes are arranged in rings in a cylindrical structure called an osteon or Haversian system. The osteocytes nearest the center of an osteon receive nutrients via diffusion from blood vessels that pass through the Haversian cannal. The osteocytes remain in contact with one another via thin canals or canaliculi. They exchange nutrients via the gap junction, so that all osteocytes are supplied with nutrients. And waste product from the osteocytes is removed in the opposite direction by  blood vessels.

In spongy bone, which is less dense than compact bone, osteocytes do not need a central canal. The trabecular structure gives each osteocyte access to blood vessels in red bone marrow.

Ligaments hold bones together
Ligaments hold bone to bone. They are an array of packed collagen fibers, all facing the same direction, with a few fibroblasts in between. (Fibroblasts are cells that produce and secrete the proteins that make up collagen, elastic and reticular fibers). They give strength to certain joints while still allowing movement of the bones in relation to one another.

Cartilage lends support
Cartilage is smoother and more flexible than bone. You find it where support is needed when pressure is exerted and where some movement is necessary. There are three types of cartilage.

Fibrocartilage – consisting of thick bundles of collagen fibers. It withstands pressure and tension. It is found in intervertebral discs between vertebrae and knee joints.

Hyaline cartilage – is smooth and glass-like, thin collagen fibers. They form embryonic structures that become bone later as well as covering mature bones at the joint, creating a low-friction surface.

Elastic cartilage – are elastin fibers, which are very flexible. They help structure in the outer ear and epiglottis.

Mature Bone Undergoes Remodeling and Repair
Even though the bones stop growing longer, bone tissues still undergo constant replacement, repair and remodeling. This is due in part to osteoclast bone cells. There are three more cells that help facilitate bone development – chondroblasts, osteoblasts, and osteocytes.

Bones can change in shape, size, and strength 
The remodeling of a bone happens at a compression site, where stress is a constant, for instance, jogging or weight bearing exercise. The constant force causes electrical currents in the bone, which stimulates osteoblasts. So new bone is formed in regions of high compressive stress and bone is reabsorbed in areas of low compressive stress. Trained athletes tend to have an increase in bone mass and strength. Homeostasis of bone structure depends on the balance of osteoclasts and osteoblasts. Osteoporosis happens when these two cells are out of balance, which happens over time.

Bone cells are regulated by hormones  
To maintain calcium homeostasis, the rate of activity in osteoblasts and osteoclasts are regulated by hormones in adults. If calcium falls below a certain point, PTH, or parathyroid hormone, stimulates the osteoclasts to secrete more bone-dissolving enzymes. This releases calcium and phosphate into the bloodstream. If calcium levels rise, then calcitonin, another hormone, stimulates osteoblasts, causing calcium and phosphate to be removed from blood, back to bone.

Bones undergo repair Bone Remodeling Video
When you break or fracture a bone, blood vessels bleed into that bone producing a hematoma., usually accompanied by pain and swelling. Within days, the repair process begins as fibroblasts enter the area. Some of these cells actually become chondroblasts and together they begin to produce a callus (a tough fibrocartilage) between the two broken ends. Then osteoclasts arrive and start to move dead fragments of the original bone and blood cells of the hematoma. Osteoblasts come next and deposit osteoid matrix (a mixture of proteins), which encourages crystallization of calcium phosphate minerals, turning the callus into bone. Over time, this bone becomes thick and hard again. It is very rare for a bone to break in the same place twice, because repaired bone is usually thicker than normal.

The Skeleton Protects, Supports, and Permits Movement
The skeleton consists of 206 bones and various connective tissue. The bones are classified into four types: long (including limbs and fingers), short (wrist bones), flat (including cranial, sternum, and ribs), and irregular (hip or coxal and vertebrae, for example). There are three important functions of the skeleton, It is a structural framework for support of soft organs. It protects some organs from injury. And third, it allows movement and flexibility due to the way they are joined. Further, the skeleton is organized into the axial and appendicular skeleton.
Axial Bones/wikipedia.org/accessed 4/11/12

The axial skeleton forms the midline of the body
The axial skeleton consists of the skull or cranium and includes the mandible and maxilla, sternum, ribs, and vertebral column, (including the sacrum).

The cranium consists of over two dozen flat bones that protect the brain and form the structure of the face.   

Vertebral Column/academic.kellogg.edu/accessed 4/11/12
The vertebral column is the body’s main axis and consists of the backbone and spine. It supports the head, protects the spinal cord, and is the site of attachment for our four limbs and various muscles. This column has 33 irregular bones called vertebrae that extend from the skull to the pelvis. The vertebral column is broken down into five regions: cervical (7 vertebrae), thoracic (12 vertebrae), lumbar (5 vertebrae), sacral (5 fused vertebrae), and coccygeal (4 fused vertebrae). (Insert pic with labels here)

The ribs and sternum protect the chest cavity. There are 12 ribs in all. One end branches from the vertebral column. The upper seven pairs attach to the sternum via cartilage. Ribs 8-10 are indirectly joined to the sternum via the seventh rib by cartilage. And ribs 11 and 12 are floating ribs, meaning they do not attach to the sternum.

The ribcage is made of the ribs, sternum and vertebral column and forms a protective barrier around the heart, lungs, and other organs of the thoracic cavity. Muscles between the ribs lift slightly when we breathe, expanding the cavity and inflating the lungs. And the base of the sternum is attached to the diaphragm, which is critical to breathing.

The appendicular skeleton: Pectoral girdle, pelvic girdle, and limbs
The appendicular skeleton consists of the arms, legs, and the pectoral and pelvic girdles.

The pectoral girdle helps with flexibility with the upper limbs. It is a supportive frame and consists of the left and right clavicles and the left and right scapulas.

There are 30 bones that make up the arms and hands. The humerus is the long bone of the arm and attaches at one end to the scapula and the other to ulna and radius (your forearm). The other end of the ulna and radius attach at the carpal bones, which are made up of eight small bones of the wrist. Then there are five metacarpals that form the palm of the hand and 14 phalanges, which are your thumb and fingers.

All of this allows for a great range of motion, but at times we do pay a price for this. The flexibility is also somewhat unstable, and if you fall, this makes it easy to dislocate or break a bone.  And overuse can also cause problems with inflammation and swelling.

The pelvic girdle consists of two coxal, or hip, bones, the sacrum, and coccyx of the vertebral column. The coxal bones attach to the sacral area of the vertebral column in the back. They curve towards the front and are joined by cartilage. This forms the pelvis. Its primary function is to support the weight of the upper body against gravity. It also protects organs inside the pelvic cavity and is the site of attachment for the legs.

Pelvic girdle/skillbuilders.patientsites.com/accessed 4/11/12
The pelvic girdle is broader and shallower and the pelvic opening is wider in women than men. This is to allow childbirth. During puberty, the sex hormones trigger the process of bone remodeling that shapes the pelvic girdle and prepares it for pregnancy and birth.

The femur, or thighbone, is the longest and strongest bone in the body. It attaches to the coxal at one end and the knee joint, at the other. It intersects with the tibia and fibula of the lower leg at the knee joint also. The patella, or kneecap, protects the knee joint and provides stability. At the other end of the tibia and fibula, they join at the ankle with seven tarsal bones, making up the ankle and heel. There are five metatarsals that form the foot and 14 phalanges that form the toes, similar to the fingers.

Joints Form Connections between Bones
Joints/jointsjoints.com/accessed 4/11/12
The structures that hold the skeleton together are joints, ligaments and tendons. The joints or articulations, are the points of contact between bones. Ligaments and tendons are made of connective tissue and they help to stabilize these joints.
    
Joints vary from immovable to freely movable
Joints can vary from totally immovable to being able to move freely. The following are three types: fibrous, cartilaginous, and synovial.

Fibrous joint – are immovable. They protect the brain and skull at birth. If you have ever seen a “soft spot” on a babies head, this is the fibrous connective tissue, or fontanels between the flat bones of the skull. This allows for brain development and growth and eventually these harden and become sutures between skull bones.

Cartilaginous joints – are hyaline cartilage and slightly movable allowing a small amount of flexibility. These include joints that connect vertebrae in the backbone and attachments between the lower ribs to the sternum.

Synovial joints – are freely movable and filled with a fluid cavity. They are joined together and supported by ligaments. The interior is lined with a synovial membrane which secretes fluid to lubricate the joints. The articulating joints are also covered by hyaline cartilage to reduce friction further. There are different types of synovial joints that move in different ways: the hinge joint, which moves like a door hinge, in one direction and the ball-and-socket joint, which allows movement in all directions.

Ligaments, tendons, and muscles strengthen and stabilize joints
Synovial joints can withstand a tremendous amount of pressure. This is because they are held together by ligaments, as we stated above. But then the ligaments are further stabilized by tendons, which attach bone to muscle. The ligaments and tendons contain collagen, which makes them strong and flexible, much like a twisted nylon rope. At certain joints, muscle contractions also help to strengthen just at the moment of movement, when the support is needed the most.

Muscles/ngureco.hubpages.com/accessed 4/11/12


The Muscular System
We have muscle cells in every organ in our bodies that contribute to movement. They make up almost half of our body mass. There are three types of muscle: skeletal, cardiac and smooth. The skeletal muscles sculpt our bodies and give us strength and mobility, the cardiac muscle pumps blood through our bodies, and smooth muscle accomplishes several things, such as propelling a child through the birth canal or regulate blood flow to every cell in our bodies. Lets take a closer look…


Muscles Produce Movement or Generate Tension
There are voluntary muscles, which we have conscious control over and involuntary muscles, which are beyond our control, for the most part. They both produce and resist movement. And our muscles actually produce heat, which is crucial to our bodies homeostasis.

The fundamental activity of muscle is contraction
There are certain features that all three types of muscles have in common: they respond to chemical and/or electrical signals from other organ systems, they contract or shorten, and they relax, returning to their original position.

Skeletal muscles cause bones to move
We have over 600 skeletal muscles and they interact with the skeleton, causing bones to move or not move. Most are organized in pairs or groups. Muscle groups that work together to create a motion or movement are synergistic muscles. Muscles that oppose one another are antagonistic muscles. Each muscle is joined to the skeleton in a way that produces very specific movement of one bone to another.

A muscle is composed of many muscle cells
A single muscle is made of a group of muscle cells with the same origin, insertion and function. They are arranged in bundles, or fascicles and enclosed in a sheath, or fascia. Each cell contains more then one nucleus, just under the cell membrane. Most of the cell is occupied with myofibrils (long, cylindrical structures arranged parallel). When myofibrils contract, the muscle cell shortens.

Myofibril/imperial.com/accessed 4/11/12
The contractile unit is a sarcomere
Sarcomeres are what cause contraction of the muscle cell and the whole muscle. This is a segment of a myobril from one Z-line (a dark line within the myobiril) to the next. One single myofibril within one muscle cell may contain over 100.000 sarcomeres, end to end. The sarcomere consists of two proteins, myosin and actin.

Individual Muscle Cells Contract and Relax
There are four keys to understanding what makes a skeletal muscle cell contract and relax:

  • Nerves activate skeletal muscles – Motor neurons stimulate muscle cells to contract. They secrete a neurotransmitter called acetylcholine, which activates a skeletal muscle.

  • Activation releases calcium – Inside the muscle cell, an electrical impulse runs down what is called a T tubule to the sarcoplasmic reticulum (membrane chambers). The arrival of the electrical impulse causes the release of calcium ions. The calcium diffuses into the cell cytoplasm, come into contact with the myofibrils and sets in motion a chain of events which lead to contraction.

  • Calcium initiates the sliding filament mechanism – When thick and thin filaments slide past one another, the sarcomeres shorten. This process is called sliding filament mechanism. The thin filament consists of the protein actin. And the thick filaments are made of the protein myosin. When a muscle is relaxed the myosin does not touch the thin filament of actin. When they do touch, it is this act that causes calcium to be released. So when they do not touch, calcium is inhibited, which inhibits muscle contraction. In other words, calcium has to be present for muscle contraction to take place.

  • When nerve activation ends, contraction ends – Relaxation happens when the nerve impulse ends. No nerve activity means no more calcium being released. Any calcium released prior, is transported back via active transport to the sarcoplasmic reticulum.

Muscles require energy to contract and to relax  Muscle Contraction Video
Muscles use a great deal of ATP energy to contract. Myosin acts as an enzyme when it is exposed to calcium, which splits ATP into ADP and inorganic phosphate. This action releases the energy necessary to do the work. Once the nerve impulse ends, energy from the ATP breakdown is used to transport the calcium back to the sarcoplasmic reticulum allowing relaxation of the muscles.  Muscle cells store just enough ATP for approximately 10 seconds’ worth of activity. Once this is used up, more ATP must be produced.

Cardiac and Smooth Muscles have Special Features
Most muscle mass is made from skeletal muscle. But cardiac and smooth muscle have very unique features that suit their function.

How cardiac and smooth muscles are activated
Both cardiac and smooth muscle are considered involuntary muscles, because we do not generally have conscious control over them. They can act on their own, without nerve stimulation. In the cardiac muscle, it is the pacemaker cell that sets the pace for activity, with the rest of the cells following. Due to the gaps of the intercalated discs (where muscle cells are joined), one cell can stimulate another. Smooth muscle cells also have gaps that allow cells to activate one another. However, both cardiac and smooth muscle can respond to nerve activity also. Your heart rate increase when you exercise is an example of nerve activation for the cardiac muscle.

Speed and sustainability of contraction
As for speed, smooth muscle is very slow, cardiac muscle moves at a moderate speed, and skeletal muscle is the fastest.

Smooth muscle is partially contracted all of the time. Yet it almost never fatigues because it contracts so slowly that ATP usage is less than ATP production. Smooth muscle is key to the homeostasis of blood pressure, maintaining the diameter of the blood vessels indefinitely.
Cardiac muscle cells go through cycles of contraction and relaxation, necessary so the muscle does not fatigue.

Arrangement of myosin and actin filaments
Smooth muscle filaments are arranged in bundles that attach at various angles to the cell membrane. The thick and thin filaments slide past each other and the attachment points are pulled towards each other, so the cells get shorter and fatter. It looks smooth because of the bundled filaments, rather than the sarcomeres of skeletal and cardiac muscle, which look striated.
 


Blood drop/hometownstation.com/accessed 4/11/12

Blood
The circulatory system is the system by which cells can maintain oxygen levels, supply nutrients, eliminate waste, and keep concentrations of every essential molecule and atom within acceptable limits. It consists of the heart, blood vessels, and blood, which moves through them.



The Components and Functions of Blood
Blood is a special connective tissue, consisting of specialized cells and fragments of cells suspended in a watery solution made of molecules and ions. Blood has three crucial tasks:

  • Transportation: transports all substances needed everywhere within the body, including oxygen, nutrients, hormones, and waste.

  • Regulation: helps regulate body temperature, water volume, and pH within the body.

  • Defense: contains defenses within the cells to help protect your body from infections and illness and has the ability to prevent excessive blood loss via clotting.

On average, blood makes up about 8% of your body weight. It is thicker, stickier, and denser than water. Bloods components fall into two main categories: plasma (or liquid components) and formed elements (red and white cells, and platelets). The formed elements are denser than plasma and sink to the bottom in a rotation device, Red cells are on the very bottom and white blood cells and platelets are just above the red cells, appearing as a thin, grayish white layer.

Plasma consists of water and dissolved solutes
Plasma is the transport for blood cells and platelets. It appears pale yellow and is about 90% water. The other 10% is made of dissolved proteins, hormones, ions, and more than 100 different molecules (including amino acids, fats, carbohydrates, vitamins, and waste).

Red blood cells transport oxygen and carbon dioxide O2 Blood Transport Video
Erythrocytes (or red blood cells) primary function is to carry oxygen and carbon dioxide. They have an unusual shape – doughnut-like with a flattened center. This allows flexibility, so they can fit through small blood vessels. They have no nucleus and basically no organelles. They are fluid-filled plasma bags, crammed with almost 300 million molecules of hemoglobin (an oxygen-binding protein).

Hematocrit and hemoglobin reflect oxygen-carrying capacity
Hematocrit is the term used for the percentage of blood that consists of red blood cells. Hematocrit and hemoglobin levels measure the oxygen-carrying capacity of the blood. When this falls too low or is too high, it can be cause for concern. Low numbers might indicate anemia, and high numbers could indicate polycythemia. Small shifts in hematocrit and hemoblogin are normal and temporary.

Adult Human Breast Stem Cell/scienceblogs.com/accessed 4/11/12
All blood cells and platelets originate from stem cells
Stem cells are located in the red marrow of certain bones. They divide constantly throughout our lives, producing immature blood cells. These develop into platelets and various types of mature red and white blood cells……insert a chart here….

RBCs have a short life span
Stem cells first produce immature red blood cells, called erythroblasts. Within a week’s time, these become filled with hemoglobin and develop into mature red blood cells. Mature red blood cells only live approximately 120 days. During that time, they make nearly 3,000 round-trips a day, through your body. Because they have such a short life-span, they produce at a rate of more than 2 million per second just to keep the hematocrit steady.

RBC production is regulated by a hormone
If oxygen levels fall for any reason, the kidneys kick in and produce a hormone called erythropoietin. Erythropoietin is transported to the red bone marrow, which stimulates stem cells to produce more red blood cells. Once oxygen levels have returned to a normal level, the cells cut back on production.

White Blood Cell/wikipedia.org/accessed 4/11/12
White blood cells defend the body
White blood cells, or leukocytes, are larger then red blood cells and make up approximately 1% of whole blood. There is only one WBC for every 700 RBCs, but they play a crucial role in the bodies defense. There are two main categories for white blood cells: granular and agranular. They have a short life-span, some dying within a few hours to nine days.

Granular leukocytes:
  • Neutrophils – most abundant WBCs, the first to combat infection. They target bacteria and some fungi. 
  • Eosinophils – the first to defend against large parasites, they surround the parasite and release digestive enzymes. They also release chemicals to counteract severs allergic reactions. 
  • Basophils – are the rarest white blood cells. They initiate the inflammatory response of the body with histamine.

Agranular leukocytes: Immune Response Video

  • Monocytes – the largest WBC, can leave the bloodstream and take up residence in body tissue, becoming macrophages that eat up invaders and dead cellular debris. They also stimulate lymphocytes to defend the body. 
  • Lymphocytes – are classified further into B and T lymphocytes. They reside in the bloodstream, tonsils, spleen, lymph nodes, and thymus gland. B’s produce antibodies that fight against microorganisms. And T’s destroy bacteria, viruses, and cancer cells.
 
Platelets are essential for blood clotting
Platelets are not living cells and only last five to nine days. They come from megakaryocytes (large cells derived from stem cells). They take part in the clotting process and participate in the repair process of damaged tissue, releasing a protein that promotes growth and repair. 

Hemostasis: Stopping Blood Loss
Hemostasis is the natural process of stopping the flow of blood, or blood loss. This happens in three stages:

Vascular spasms constrict blood vessels to reduce blood flow – this minimizes the damage and prepares for the later steps.

Platelets stick together to seal a ruptured vessel – they swell and clump together, forming a plug.

Blood Clotting/creationwiki.org/accessed 4/11/12
A blood clot forms around the platelet plug – blood changes from a liquid to a gel. Chemical reactions produce a meshwork of protein fibers. These wind around the platelet plug and holds the platelets, blood cells and molecules against the opening. This initial clot can form in less than a minute and reduces or stops blood flow at the site of injury. Then the platelets contract and tighten the clot, pulling the walls together. The entire process takes less than an hour.

Human blood types
For over a century, physicians have been playing with blood transfusions (taking one persons blood directly into another persons bloodstream). Some attempts were successful and others were not. Now we know that the reason is due to blood type. This is based on an ABO blood group system. Our cells have certain proteins that our immune system recognize as “self”. Foreign cells carry a different protein and our immune system recognizes this as “non-self”, or antigen. When an antigen comes along, it stimulates the immune system to defend itself. And as part of this defense, it produces another protein, or antibody.

ABO blood typing is based on A and B antigens
It is the interactions of antigens and antibodies that were hugely responsible for failed blood transfusions in the past. We fall into one of four types of blood groups: A, B, AB, or O. Type A has A antigens, type B has B antigens, type AB has both A and B antigens, and type O has neither. We also have circulating antibodies and the ability to make more against surface antigens that are not our own. Type A has B antibodies, type B has A antibodies, type O has both A and B antibodies, and type AB has neither. When antibodies attack foreign antigens, they damage the RBCs with those antigens, causing them to agglutinate, or clump together. If this becomes extreme, it causes organ damage and even death. It can also cause kidney failure.

So, when it comes to blood transfusions, if you have type A, you can only have transfusions from A or O because neither of these have the B antigen. If you are type B, you cannot have transfusions with anything that has A antigens (A or AB). People with AB can generally receive transfusions from all types, but can only donate blood to AB individuals. And if you are type O, you can donate to all types (universal donor), but you can only receive from type O.

Pregnant Mother/ehow.com/accessed 4/11/12
Rh blood typing is based on Rh factor
Rh factor is another surface antigen in red blood cells, called this because it was first discovered in rhesus monkeys. 85% of Americans are Rh positive and 15% negative for this antigen. This antigen is a critical factor in pregnancy. If a mother is Rh negative, which I happen to be, and a father is Rh positive, there is a risk of the child being Rh positive. When this occurs, usually right at childbirth, a small amount of the fetus’s blood leaks into the mother’s bloodstream. This causes the mother to produce anti-Rh antibodies that attack the fetus. This can result in HDN (hemolytic disease of the newborn), which can lead to mental retardation and even death. The risk is usually much greater for the second pregnancy. It takes days and sometimes weeks for the mother to produce antibodies. If the leak happens at childbirth with the first pregnancy, there is only a slight chance of exposure. It is when the second pregnancy comes along that the risk of HDN is so high. To prevent this an injection of anti-Rh antibodies is given to the mother at 28 weeks of gestation and again, no later than 3 days after childbirth.

Blood typing and cross-matching ensure blood compatibility
Blood typing is done by adding plasma containing small amount of anit-A and aniti-B antibodies to drops of diluted blood. If the blood agglutinates, then it contains the antigens that match the antibodies. Universal recipients were AB+ individuals because they can give to the other types. And universal donors were O- because they could give to the other blood types. However, there have been a few transfusion reactions even after blood typing was done. Because of this, those terms are no longer used. The reaction happens on rare occasions because there are over 100 other, less common blood antigens in humans. Medical laboratories now generally test not only for blood typing, but they cross-match as well to make sure you can combine blood types. If agglutination does not occur, it is assumed that it is a good match.


Heart Scan/dailymail.co.uk/accessed 4/11/12
Heart and Blood Vessels
The cardiovascular system consists of the heart and blood vessels. The heart moves, or pumps, the blood through the vascular system, which is a network of branching conduit vessels through which the blood flows. We would not have life without it.

Blood Vessels Transport Blood
The network of blood vessels that carry blood throughout our bodies is so extensive that if you laid it all out end to end, they would stretch for 60,000 miles! They are classified into three types: arteries, capillaries, and veins.

Arteries transport blood away from the heart
Arteries are thick-walled and muscular. The larger ones transport blood away from the heart. The further they move away from the heart, the smaller they get. They have to be large by the heart in order to withstand the pressure generated by the heart. They have three distinct layers:

The endothelium - a thin, smooth layer of squamous epithelial cells, which promote smooth blood flow.

The middle layer – made of smooth muscle with elastic fibers of connective tissue. This layer is the thickest. They help to resist high pressure from within.

The outer layer – tough, connective tissue made mostly from collagen. This layer anchors vessels to tissue and helps protect them from injury.

Arterioles and precapillary sphincters regulate blood flow
The largest artery, or aorta, is approximately 2.5 centimeters wide, while the smallest arteries, or arterioles, are 0.3 millimeters or less in width. Where the arteriole joins a capillary, there is a smooth muscle band called a precapillary sphincter. This sphincter acts as a gateway, controlling blood flow into capillaries. Vasoconstriction (contraction of smooth muscle) of the arterioles and precapillary sphincter reduces their diameter, which reduces blood flow. Vasodilation (relaxation of the smooth muscle) does just the opposite, increasing their diameter and blood flow. There are internal and external factors that control vasoconstriction and vasodilation, including nerves, hormones and environmental conditions.

Capillaries/fphoto.photoshelter.com/accessed 4/11/12

Capillaries: Where blood exchanges substances with tissue
Arterioles connect to capillaries (the smallest blood vessels). Capillaries are thin-walled vessels, on average only one-hundredth of a millimeter in diameter. They have an extensive network throughout your body. Because of the branching design and their thin, porous walls, they allow blood to exchange oxygen, nutrients, carbon dioxide, and waste with tissue cells.  They are the only blood vessel that can exchange materials with the interstitial fluid (the fluid that surrounds every living cell). So basically, capillaries function as a biological strainer, permitting selective exchange of substances.

Lymphatic system helps maintain blood volume
Lymphatic capillaries are blind-ended vessels, branching throughout our body tissues and are considered part of the lymphatic system. They pick up excess plasma fluid and return it to the cardiovascular system. They can also pick up larger objects in the interstitial fluid that are too big to diffuse into capillaries, including lipid drops and invading organisms. The lymphatic system plays a crucial role in maintaining blood volume and interstitial fluid.

Veins return blood to the heart
Blood flows back to the heart via veins and venules (small veins). They consist of three layers, just like arteries, only not as thick. Veins do not have near the pressure that arteries do, which is why they are thinner. Veins are also a reservoir for blood volume for the cardiovascular system. Almost two-thirds of the blood in your body is located in your veins.  The three mechanisms that help veins return blood to the heart are contractions of skeletal muscle, one-way valves inside the veins, and pressure associated with breathing.

The Heart Pumps Blood through the Vessels How the Heart Works Video
Your heart pumps about 75 times per minute, not including the times of exertion or stress. Over a 70 year period, this adds up to approximately 2.8 billion heartbeats, which is rather impressive. Under normal circumstances, your brain controls the rate of pumping. However, the heart can also beat on its own, without any instruction from the brain.

The heart is mostly muscle
The heart sits behind the sternum, or breastbone. It is enclosed with the pericardium, a tough fibrous sac that protects it, anchors it, and prevents it from blood overflow. The space between the pericardium and heart is called the pericardial cavity. This cavity contains a lubricating fluid, which reduces friction when the heart contracts. The heart consists of three layers, just like the vessels.

Heart Muscle Layers/vascularconcepts.com/accessed 4/11/12
Epicardium – thin, outermost layer.

Myocardium – thick, middle layer.

Endocardium – thin, innermost layer.

The heart has four chambers and four valves
There are two chambers on top, called the atria, and two chambers on the bottom, called the ventricles. Then there is a muscular partition, the septum, that separates left and right. Blood returning to the heart from the tissues enters the right atrium and passes through a valve to the right ventricle. Blood returning from the lungs, enters the left atrium, then through a valve to the left ventricle.

The four heart valves enforce the one-way flow pattern and prevent blood from flowing backwards. The right and left atrioventricular (AV) valves prevent blood from flowing back into the atria when the ventricles contract. The two semilunar valves (pulmonary and aortic), prevent backflow into the ventricles from the main arteries leaving the heart when the heart relaxes.

Pulmunary Circuit/images.vintagemedstock.com/accessed 4/11/12
The pulmonary circuit provides for gas exchange
The heart pumps blood through the pulmonary circuit, or lungs, and through they systemic circuit (all cells in the body). Blood that returns to the heart is deoxygenated, giving it all to tissue cells and taken up by carbon dioxide.  Once the blood reaches the pulmonary capillaries, blood gives up carbon dioxide and receives fresh oxygen from our inhalation. Deoxygenated blood on the right side of the heart never mixes with oxygenated blood in the left.

The systemic circuit serves the rest of the body
Once blood enters the left ventricle, it begins the systemic circuit, which takes it to the rest of the body. The left ventricle pumps blood through the aortic semilunar valve into the aorta. From there, it travels through the arteries and arterioles to the capillaries, giving oxygen and nutrients to all the tissues and organs and removing waste. Then, fro the capillaries, it flows to the venules, veins, and back again to the atrium.

Because the heart is so thick and hard-working, it has its own set of coronary arteries and its own set of cardiac veins.
 


The Immune System and Mechanisms of Defense
The world is swarming with bacteria, a living organism too small to see with the naked eye. We even have some nonliving entities – viruses and prions.  They are everywhere, doorknobs, money, clothing. You name it, they live there. Some are beneficial to us, some are harmless, and some are deathly or cause disease. We call these pathogens. Pathogens come from outside our bodies, but we also have challenges from within, such as mutations to our DNA’s cells.

We have several mechanisms to help defend ourselves, including barriers to entry or ways of expelling and neutralizing pathogens, nonspecific defenses that help our bodies respond to tissue damage, and specific defenses which recognize and kill specific bacteria and other foreign cells. Our bodies have several ways in which to protect us – this is our immune system.

Pathogens cause disease
Bacteria, viruses, fungi, a few protozoa, and possibly prions, are all considered pathogens. And even some larger parasites, such as worms can also be pathogens, although they are rare in industrialized areas.

E. Coli Bacteria/microbeworld.org/accessed 4/11/12
Bacteria: Single-celled living organisms
If you go by the variety and numbers of bacteria living on earth, they are one of the most successful organisms on the planet. They use ATP as a direct source of energy and amino acids for making protein. They also store carbohydrates and fats. And they obtain these raw materials anywhere they can. Some bacteria breakdown raw sewage and cause decomposition of dead animals and plants, which plays an essential role in recycling energy. Others get nutrients from soil and air. We have learned how to harness some bacteria to produce things like hormones, antibiotic drugs, etc… But some of the bacteria are pathogens that rely on living human cells as their source of energy. They cause pneumonia, tuberculosis, syphilis, Lyme disease, and a boat load of other diseases and illnesses.

Viruses: Tiny infectious agents
There is some debate as to whether or not viruses are a living organism or not. They are extremely small, have no organelles, and cannot reproduce on their own. However, once they enter a living cell, they take over and use the cell’s organelles to make more viruses. Some of the diseases caused by viruses are AIDS, hepatitis, encephalitis, and rabies. Some less harmful, but annoying viruses are colds, warts and chicken pox. Not every human reacts the same way to a virus either. For some, they can shake it off in a matter of days, while for others, it could kill them.

Prions/findingnew.com/accessed 4/11/12
Prions: Infectious proteins
You’ve heard of mad cow disease (called this because it was first observed in cattle), right? Well, what caused it was a prion. Prions are misfolded forms of a normal brain cell protein. And they trigger the misfolding of other normal proteins as well. Once they enter a nerve cell, they begin to propagate until eventually there are so many infected brain cells, that the cells die and burst, which releases even more prions to other brain cells. These creatures, if you will, are resistant to cooking, freezing, and drying. There is no known cure. The infection in humans seems to come from eating contaminated beef. Since banning the use of mammalian meat and bone meal as cattle feed, the incidence of mad cow disease has dropped drastically.

Transmissibility, mode of transmission, and virulence determine health risk
The Plague/dweelingintheworld.wordpress.com/accessed 4/11/12
Some pathogens are clearly more dangerous to humans than others. There are three factors that determine the danger – transmissibility (how easily it passes from one person to another), mode of transmission (how it spreads), and virulence (how damaging the resulting disease is). On occasion, there have been diseases that were highly transmissible and highly virulent. This caused deadly epidemics back in 1348-1350, as bubonic plague, a bacteria, killed 25-40% of the European population. And in 1918, an influenza outbreak that caused 20 million deaths worldwide. More recently, is the Ebola virus in Africa in 1976. And this one is still a threat today, killing 80% of an exposed population in less than two weeks. Pathogens are obviously continuing to be a challenge to the human population.

The Lymphatic System Defends the Body
The lymphatic system works closely with the cardiovascular system. It has three important functions:
  • helps maintain blood volume in the cardiovascular system
  • transports fats and fat-soluble vitamins absorbed from the digestive system to the cardiovascular system
  • defends the body against infection.

The basic components of the lymphatic system and functions are listed below.

  • Lymphatic vessels transport lymph – lymph is a milky fluid containing white blood cells, proteins, fats, and the occasional bacterium and virus. There structure allows them to take substances too large to enter a blood capillary. They also have valves that prevent backflow of lymph.
  • Lymph nodes cleanse the lymph – lymph nodes are responsible for removing microorganisms, cellular debris, and abnormal cells from the lymph before it returns to the cardiovascular system.
  • The spleen cleanses blood – the spleen helps fight infection and controls the quality of circulating red blood cells by removing old and damaged ones.
  • Thymus gland hormones cause T lymphocytes to mature – they thymus gland secretes two hormones, thymosin and thymopoeitin. These hormones cause T cells to mature. T cells are crucial in the bodies defense mechanisms.
  • Tonsils protect the throat – the tonsils and adenoids are a mass of lymphatic tissue that help to filter out microorganisms that enter the throat in air and food.

Keeping Pathogens Out: The First Line of Defense
Skin: An effective deterrent
The skin is the most important defense or barrier that we have for pathogen entry. It has four crucial attributes that make it so effective:

  • It’s structure – keratin, a fibrous protein, forms a tough barrier on the surface of our skin.
  • The fact that it is constantly being replaced. – dead cells are constantly shed, along with any pathogens, and are replaced by new cells.
  • It’s acidic pH – the relatively low pH of healthy skin is a detriment to many microorganisms.
  • The production of an antibiotic by sweat glands – the sweat glands produce an antibiotic peptide called dermicidin that can kill a range of bacteria.

Impeding pathogen entry in areas not covered by skin
Successful pathogens enter the body through mucous membranes that line the digestive, urinary, respiratory and reproductive tracts. They thrive in the moist surface having direct contact with living cells. They can also enter through the eyes and ears. Fortunately, our body also has defenses in these areas.

  • Tears and saliva can wash away particles, kill bacteria, rinse away harmful microorganisms. They both contain lysozyme, and enzyme that kills bacteria.
  • Earwax traps small particles and microorganisms.
  • Mucus, a thick-like gel, trap microorganisms.
  • Digestive and vaginal acids can kill pathogens. Digestive acid is so strong, it can kill almost every pathogen. There is only one strain of bacteria that can thrive in this acid, helicobacter pylori.
  • Vomiting, urination, and defecation are also effective ways to get rid of  toxins or infection.
  • Resident bacteria that live in the mucous membranes of the vaginal and digestive tracts helps to control population levels of more harmful bacteria by competing for food.

Nonspecific Defenses: The Second Line of Defense
We call the second line of defense nonspecific because once pathogens get through the first line of defense, our bodies kick in without regard to what the target is to destroy the pathogen.

Phagocyte Eating Bacteria/foodmedicaleponyms.com/accessed 4/11/12
Phagocytes engulf foreign cells
Phagocytes are white blood cells that destroy foreign cells through phagocytosis. Neutrophils and macrophages digest and destroy bacteria, some fungi, viruses, and bacterial parasites. (Macrophages also serve as clean up duty and they release chemicals that stimulate production of more white blood cells). Eosinophils kick into action when invaders are too big to be engulfed by phagocytosis. They bombard and digest large parasites and some foreign proteins.

Inflammation: Redness, warmth, swelling, and pain
The inflammatory response is triggered by any type of tissue injury, whether infection, burns, chemicals, or physical trauma. The four outward signs are redness, warmth, swelling, and pain. These outward symptoms, although uncomfortable, prevent damage from spreading, dispose of cellular debris and pathogens, and begin the process of tissue repair.

Natural killer cells target tumors and virus-infected cells
NK cells are lymphocytes that release a chemical that breaks down the foreign cells membrane, creating holes. Then the nucleus disintegrates quickly. They target tumors and cells infected by viruses. They also secrete a substance that helps with the inflammatory response.

The complement system assists other defense mechanisms
The complement system consists of at least 20 plasma proteins that circulate in the blood assisting other defense mechanisms. It works much like a domino effect, with one protein activating another.

Interferons interfere with viral reproduction How Interferons Work Video
When cells become infected by viruses, they release a group of proteins called interferons. These interferons diffuse to nearby healthy cells, bind to their membranes, and stimulate production of proteins that intefere with the synthesis of viral proteins. This makes it much harder for the virus to infect the protected cells. (Some interferons are being produced in laboratories and show some promise of assisting in the fight against certain viral diseases).

Fever raises body temperature
We have one final weapon, a high body temperature. Normal range is 97-99 degrees. When macrophages detect and attack bacteria, viruses, and other foreign substances, they release a chemical call pyrogens into the bloodstream. This causes your brain to set your thermostat to a higher temperature. This makes it more difficult for pathogens. It increases the metabolic rate of body cells, which speeds up the defense mechanisms and tissue repair.

Specific Defense Mechanisms: The Third Line of Defense
This third line of defense targets very specific pathogens or foreign substances. It has a “memory” which is capable of storing information from past exposures, enabling your body to respond to later invasions more quickly. And it protects your entire body – your immunity is not limited to the site of infection.

Your immune system targets antigens
Your immune system responds to each unique antigen by producing a specific antibody to attack and inactivate the antigen and the cell carrying it. We have what are called major histocompatibility complex proteins (MHC) that are considered self-markers. They work much like a password. If your immune system reads the password, it leaves it alone. If there are cells that do not have this, the immune response kicks in.

T Lymphocyte/daviddarling.info/accessed 4/11/12

Lymphocytes are central to specific defenses
The two types of lymphocytes are B and T cells, getting their names based on where they mature. B cells mature in bone marrow. They are responsible for antibody-mediated immunity. Meaning they produce proteins that bind with and neutralize specific antigens. This line of defense works for viruses, bacteria, and foreign molecules.

T cells mature in the thymus gland. They are responsible for cell-mediated immunity. Some T cells attack foreign antigens directly, while others release a protein that helps to coordinate the immune response. Cell-mediated immunity helps to protect us from parasites, bacteria, viruses, fungi, cancerous cells, and foreign cells.

B cells: Antibody-mediated immunity
B cells have unique surface receptors that allow them to recognize specific antigens. They travel through the bloodstream and take up residence in the lymph nodes, spleen and tonsils. Here they remain inactive until they sense a foreign cell with that particular antigen. B cells multiply after they encounter an antigen and bind to it. Most of these clone cells are plasma cells. Plasma cells secrete antibodies into the lymph fluid and eventually into blood plasma. Other clone cells become memory cells. These cells store the information about the pathogen, which allows your body to respond much quicker with future encounters.

The five classes of antibodies
Gamma globulins is the class of blood plasma proteins that antibodies belong to. You will see the term immunoglobulin used frequently due to their crucial role in immunity.

  • IgG – is 75% of immunoglobulins. These antibodies are found in blood, lymph, intestines, and tissue fluid. They activate the compliment system and neutralize toxins. They are the only antibody that cross the placenta during pregnancy to pass on the mother’s acquired immunity to the fetus.

  • IgM – is 5-10% of immunoglobulins and are the first antibody to be released during an immune response. These are found in blood and lymph and activate the compliment system also. They can also cause foreign cells to agglutinate (ABO blood cell antibodies belong to this class).

  • IgA – makes up 15%. They enter areas of the body where mucous membranes reside. They neutralize infectious pathogens. They are also present in breast milk and are transmitted to an infant during breast-feeding.

  • IgD – is less than 1%. These antibodies are in blood, lymph, and B cells. There function is not clear yet, but they may play a role in activating the B cells.

  • IgE – approximately 0.1%, these are the rarest immunoglobulins. They reside in B cells, mast cells, and basophils. These activate the inflammatory response by triggering the release of histamine. They also play a part in allergic responses.

Antibodies’ structure enables them to bind to specific antigens
All antibodies share the same basic structure, having four linked polypeptide chains arranged in a Y shape. Each of these chains has a region that forms a trunk and two branches. There is a variable region where the antigen binds. Each variable region has a unique shape that fits only one antigen.

T cells: Cell-mediated immunity Immune Response Video
There are several types of T cells, determined by the surface protein they develop (CD4 or CD8).  CD4 T cells will become either helper or memory cells and CD8 T cells will become cytotoxic and suppressor cells.

Immune Memory Creates Immunity
The presence of memory cells, created from B and T cells, are the basis for immunity from disease. Memory cells are long-lived. Some lasting a lifetime in their ability to generate a secondary immune response. This system is so effective, that many times you may not even realize you have been exposed to the pathogen again. You may wonder why we have trouble with colds and flu…this is because there are hundreds of viruses that cause this ailment. These viruses actually adapt and change so rapidly, that they are different almost every year.  Fortunately, we have an awesome immune system to combat this.

Medical Assistance in the War Against Pathogens
Though our bodies have an incredible defense against pathogens, we have taken matters into our own hands by developing the science of medicine.

Vaccine/historyofvaccines.org/accessed 4/11/12
Active immunization: An effective weapon against pathogens
The process of activating the bodies immune response in advance, before it encounters the pathogen, is called active immunization. This involves administering an antigen in the form of a vaccine. Some are created from dead or weakened pathogens and others from live pathogens.

However, there are concerns with vaccines. There are issues with safety, time, and expense. There is the risk of the pathogen actually causing the disease that it was supposed to prevent. Typically a vaccine only targets one pathogen, so a different vaccine  is needed for every virus. And they do not cure an existing disease.

Passive immunization can help against existing or anticipated infections
Passive immunization involves giving a person antibodies from a human or animal donor that has immunity from that illness. It is usually given in the form of a gamma globulin shot. It can be given to someone who has already been exposed to a pathogen. It is not as long-lasting as active immunization though, disappearing from circulation fairly quickly. It has been effective against some viral infections like hepatitis B and measles, bacterial infections such as tetanus, and Rh incompatibility. Passive immunization also happens naturally across the placenta and through breast-feeding.

Monoclonal antibodies: Laboratory-created for commercial use
Monoclonal antibodies are produced in a lab from cloned descendants of a single hybrid B cell. They can be produced fairly inexpensively and are considered somewhat pure. They are proving useful in research and testing, as well as in cancer treatments preparations. They are working on the possibility of delivering monoclonal antibodies directly into cancer cells, sparing the nearby healthy tissue.

Antibiotics combat bacteria
The first antibiotics were derived from molds and fungi, but today are mostly synthesized by pharmaceutical companies. Some antibiotics combat only certain types of bacteria, while others are considered broad-spectrum, effective against several groups of bacteria. But they are not effective against viruses.

Inappropriate Immune System Activity Causes Problems
Allergies: A hypersensitive immune system
An allergy is an inappropriate immune response to an allergen. The allergen is not a dangerous pathogen, but the body reacts as if it were. These reactions can be mild to severe, some even life threatening. Exposure to an allergen causes a primary immune response…B cells produce the IgE antibody. The antibody binds to mast cells and to circulating basophils. Then the second exposure the mast cells and basophils to release histamine, which results in an inflammatory response.

Autoimmune disorders: Effective recognition of “self” Autoimmune Diseases Video
On occasion, the bodies ability to distinguish self from non-self fails. The immune system produces antibodies and cytotoxic T cells that target its own cells. This is an autoimmune disorder. There is currently no cure for autoimmune disorders, which include multiple sclerosis, type I diabetes mellitus, lupus erythematosus, and rheumatoid arthritis.


The Respiratory System: Exchange of Gases
The primary function of the respiratory system is to exchange oxygen and carbon dioxide (gases) with the air. We can survive for days without water or nutrients, but would die within minutes if denied oxygen. So I would say the respiratory system is pretty important.

Respiration takes place throughout the body How Respiration Works Video
Respiration involves four processes: breathing or ventilation, external respiration, internal respiration, and cellular respiration. Breathing is through the respiratory system and its associated bones, muscles, and nerves. External respiration takes place within the lungs. Internal and cellular respiration take place in the tissues throughout the body.

The Respiratory System Consists of Upper and Lower Respiratory Tracts
The upper respiratory tract filters, warms, and humidifies air
Respiratory System/scribd.com/accessed 4/11/12
The upper tract consists of the nose, nasal cavity, and pharynx. When you inhale, air enters through your nose or mouth and then flows into the nasal cavity. Air is filtered partially by nose hairs before entering the cavity. The cavity is lined with epithelial tissue and blood vessels. The blood vessels help to warm the air and the tissues secrete mucus, which humidifies the air. Next, the air enters the pharynx or throat. From here, air heads to the lower respiratory tract.

The lower respiratory tract exchanges gases
The lower respiratory tract includes:

The larynx  - maintains an open airway, routes food and air to appropriate channels, and assists in the production of sound.

The trachea - transports air down to the left and right bronchi.

The bronchi – and bronchioles (smaller branches), not only transport air, but clean it, warm it to body temperature, and saturate it with water vapor before it reaches the lungs.

The lungs – are the organs of gas exchange. They occupy most of the thoracic cavity. There is a left and a right lung, separated by the heart. The gas exchange itself, takes place in the alveoli. The lungs are a network of branching airways that end in 300 million tiny air-sacs called alveoli. The combined surface area is nearly 800 square feet, 40 times the area of our skin.  It is this surface area and the thinness of the epithelium that facilitate gas exchange with capillaries. Pulmonary capillaries come into very close proximity to the air-filled alveoli. Only two living cells separate blood from air at this point. A series of veins and venules collects the oxygenated blood from the pulmonary capillaries and returns the blood to the left side of the heart. From there, it is transported to all parts of the body. (The close contact between air and blood in the lungs is turning out to be an alternative way to administer medications).

The Process of Breathing Involves a Pressure Gradient
Inspiration brings in air, expiration expels it
Inspiration pulls air into the respiratory system as lung volume expands. The diaphragm contracts  - flattening and pulling the center downward.  While this is happening, the intercostal muscles contract, pulling the ribs upward and outward. These two actions increase the volume of the pleural cavity and lowers the pressure within the pleural space. This expansion reduces air pressure within the lungs relative to the atmosphere, which allows air to rush in.

In expiration, the muscle contraction ends. As they relax, the diaphragm returns to its domed shape, the ribs move downward and inward, and the pleural cavity becomes smaller. The lungs become smaller, so the pressure rises relative to the atmosphere, and air flows out.

Lung volumes and vital capacity measure lung function
Tidal volume represents each breath of air or approximately 500 ml. (Only about 350 ml reach the alveoli. The rest remains in the airways, referred to as dead space volume). The maximal volume that you can exhale after a maximal inhalation, is called vital capacity.  Your vital capacity is about 4800 ml, which is almost 10 times your normal tidal volume at rest. A spirometer can measure lung capacity. This is useful when diagnosing various lung diseases.

Gas Exchange and Transport Occur Passively
Gases diffuse according to their partial pressures
The primary gases of earth’s atmosphere are nitrogen (78%), oxygen (21%), trace amounts of carbon dioxide (0.04%), and less than one percent of all other gases combined. In this mixture of gases, each exerts a partial pressure proportional to its percentage of total gas composition. The pressure is not noticed by us because the pressure inside our lungs is the same as the atmospheric pressure when we are resting between breaths.

External respiration: The exchange of gases between air and blood
Alveoli/shutterstock.com/accessed 4/11/12
Most of the air in our lungs is “old” air that has already undergone some gas exchange. When venous, or deoxygenated, blood arrives from the pulmonary arteries to the pulmonary capillaries, O2, or oxygen, diffuses from the alveoli into the capillaries, and CO2, or carbon dioxide, diffuses in the opposite direction. This results in partial pressure of oxygenated, or arterial, blood leaving the lungs rising to 100 mm Hg (millimeters of mercury) and the partial pressure of carbon dioxide falls to 40 mm Hg. Then oxygenated blood is carried to the pulmonary veins to the heart and throughout the body in the arterial blood vessels. The CO2 that diffused into the alveoli is exhaled along with water vapor.

Internal respiration: The exchange of gases with tissue fluids
Both internal and external respiration occur via diffusion. Your body’s cells get O2 for cellular respiration from the interstitial fluid around them. Because your cells are constantly drawing this oxygen from the fluid, the partial pressure of oxygen is lower than that of arterial blood. Then as blood enters the capillaries, O2  diffuses into the interstitial fluid, which replenishes the O2 that has been used by the cells. CO2, again, diffuses the opposite direction and goes from cell, to interstitial fluid, to capillary blood. Partial pressure gradients permitting diffusion are maintained by breathing, blood transport, and cellular respiration. The effect being that homeostasis of O2 and CO2 in your cells is well maintained.

Hemoglobin transports most oxygen molecules
One of the most important functions of blood is to carry oxygen from the lungs, to the tissues. It is transported either by binding to hemoglobin in red blood cells, or by dissolving in blood plasma. Because O2 is not very water soluble, only about 2% is dissolved in plasma.  The other 98% binds to hemoglobin molecules. Without hemoglobin, we would not receive enough oxygen to sustain life.

Most CO2 is transported in plasma as biocarbonate
The metabolism in our tissues is constantly producing CO2 waste. It diffuses easily from tissues to the bloodstream. Once it hits our blood, it transports either by dissolving in blood plasma, binding to hemoglobin, or converting to biocarbonate. In fact, 70% of CO2 converts to biocarbonate. When biocarbonate is produced, CO2 combines with water (H2O) to become carbonic acid (H2CO3). This is catalyzed by an enzyme called carbonic anhydrase. The carbonic acid quickly breaks apart into bicarbonate and hydrogen ions. The formation of bicarbonate from CO2 occurs in red blood cells because this is where carbonic anhydrase is located. But bicarbonate diffuses quickly from the red blood cells into plasma, where it returns to the lungs.

The Nervous System Regulates Breathing
A respiratory center establishes rhythm of breathing
Skeletal muscle contractions are what allows our breathing and these contractions are activated by motor neurons. This means that respiration is controlled by our nervous system. The rate at which we breathe is controlled by the medulla oblongata at the base of our brains. A group of nerves called the respiratory center, generate electrical impulses every 4-5 seconds. The impulses travel along the nerves to the diaphragm and intercostal muscles, which then contract. As they contract, the rib cage expands, the diaphragm pulls downward, and we inhale. We have stretch receptors in our lungs that send input back to our respiratory center, which monitors the degree of and limits inflation, and starts exhalation. Once the nerve impulse ends,  the muscles relax, the rib cage  returns to normal size, the diaphragm move upward again, and we exhale.

Chemical receptors monitor CO2, H+, and O2 levels
Our bodies regulate rate and depth of breathing in order to maintain homeostasis. This centers mainly on the regulation of CO2, H+, and O2 levels. It is through the detection of H+ concentrations that CO2 levels are detected. The medulla oblongata does this via the cerebrospinal fluid (interstitial fluid surrounding the cells in the brain). The rate and depth of normal breathing is set by the need to get rid of CO2, not to obtain O2.

Conscious Breathing/thinklifebalance.com/accessed 4/11/12
We can exert some conscious control
There is one other way we can regulate our breathing and that is through conscious control. This control resides in our higher brain centers in the cortex. Our ability to control breathing is what enables us to speak, sing, hold our breath, and even hyperventilate for a short time. Eventually, though, our automatic regulatory mechanisms kick back in and our conscious control is overpowered. This could not be more demonstrated as when we try to hold our breath.

Disorders of the Respiratory System
There are many factors that can lead to disorders of the respiratory system:

  • Reduced air flow or gas exchange impedes respiratory function – Anything that impedes air flow between the atmosphere and the alveoli or diffusion of gas exchange between the alveolar and capillary walls will impede respiratory function. These include:

      • Asthma – spasmodic contraction of the bronchi
      • Emphysema – in which alveoli become permanently impaired
      • Bronchitis – inflammation of the bronchi
      • Cystic fibrosis: an inherited condition

  • Microorganisms can cause respiratory disorders – The lungs are particularly susceptible to infection due the their moist lining, which microorganisms love. Some of these conditions include:

      • Colds and flu: common respiratory infections
      • Pneumonia: an infection that inflames the lungs
      • Tuberculosis: a bacterial infection that scars the lungs
      • Botulism: poisoning by a bacterial toxin

  • Lung cancer is caused by proliferation of abnormal cells – Cancer cells crowd out normal cells and impair not only airflow, but gas exchange as well. Lung cancer accounts for one-third of all cancer deaths in the U.S. It takes years to develop and is highly preventable. 90% of lung cancer is caused by smoking or exposure to secondhand smoke. The other 10% is caused by either radon gas exposure or chemical exposure such as asbestos.

  • Pneumothorax and atalectasis: A failure of gas exchange – Pneumothorax refers to the collapse of one or more lobes of the lungs and can be life-threatening. The most common cause is a penetrating wound to the chest, which allows air into the pleural cavity around the lungs.

Atlectasis refers to  a lack of gas exchange within the lungs which results from alveolar collapse or buildup of fluid in the alveoli. This means there is no exchange of gases between the atmosphere and the blood. This can be caused by a compilation of surgery.

  • Congestive heart failure impairs lung function – Though congestive heart failure starts as a heart disorder, it can end by impairing lung function. It causes fluid to build up in the interstitial spaces between capillaries and alveoli and sometimes within alveoli themselves.  This reduces diffusion of gases. Treatment for this focuses on reducing the fluid buildup and improving the hearts pumping action.

In summary, our body systems all have to work together to maintain life. We are probably the most complicated, incredible machine in existence today. When it works the way it was designed, we function at full capacity and our abilities are bar none, off the charts. When things do not work properly, even then, we have been given the ability to correct a great deal. In my opinion, we are truly blessed, just by being human. The following article is one on little tricks, if you will, on how to maintain a healthy lifestyle.
http://exercise.about.com/od/healthinjuries/a/healthylifestyl.htm 

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