Circulation:

Circulation: Last of the transport systems.PRIVATE

Comparative Circulatory Systems: Circulation transports oxygen, nutrients, carbon dioxide and waste.

Sponges: amebocytes in the middle layer carry nutrients from cell to cell.

Gastrovascular Cavities:

A sac like body consisting of a body two cells thick that encloses a central gastrovascular cavity. The cavity serves two functions-- digestion and distribution of substances.

The fluid inside the cavity is continuous with the water outside through a single opening, so both inner and outer layers of tissues are bathed in fluid.

Some organisms have their body cavities lined with flagellated cells that stir and distribute the food and a branched GVC that carries food to various parts of the body (flatworms—planaria).

Open Circulatory System:

In an open circulatory system the blood is free to percolate directly through the tissue. There are no blood vessels. The general body fluid is called hemolymph. The exchange of materials between the fluid and body cells occurs as the hemolymph oozes through sinuses, the spaces surrounding the organs. Hemolymph is circulated by body movements that squeeze the sinuses and by the contraction of the heart and dorsal vessel. The heart pumps the hemolymph through vessels, which opens into a series of interconnected system of sinuses. Arthropods and most mollusks have such systems.

Closed Circulatory System:

In a closed circulatory system the blood is enclosed within blood vessels. Annelids and squids have closed circulatory systems.

Circulation in vertebrates:

All vertebrates have a closed circulatory system with an efficient and centrally located heart.

Circulation Terms:

Atrium: Thin walled heart chamber that empties blood into the ventricle.

Ventricle: Thick walled heart chambers that pumps blood from the heart into arteries (with considerable force).

Arteries: are round and thick walled with smooth muscles and connective tissue. Arteries carry blood away from the heart. The largest artery is the Aorta.

Arterioles: Small arteries.

Capillaries: thin walled vessels that branch from arterioles. Capillaries are the functional units of the circulatory system. Capillaries are the areas of exchange, can be selectively opened, and increase internal temperature of the surface when hot. There are more than 10 billion capillaries at an excess of 25,000 miles.

The walls of the blood vessels are made up of three layers. The outside layer is called the tunica externa or the tunica adventitia. It is made up of the connective tissue collagen and elastin, which allows the blood vessel to stretch and retain the original shape. The middle layer is called tunica media. It is made up of smooth muscles and collagen fibers that bind to the other layers. The inner layer is called tunica intima. It is the endothelial layer. The endothelium is a single layer of flattened cells, which provides a smooth surface that reduces resistance to blood flow. The tunica intima also has an underlying layer of connective tissue that connects it to the tunica media. Arteries have a thicker middle and outer layers. Capillaries lack the middle and outer layer.

In the body, the main artery branches into arterioles, which divide into a greater number of capillary beds. It is in these capillary beds, which are only one cell thick, that oxygen, carbon dioxide, nutrients and wastes are exchanged. Capillaries join to form vennules, which join into veins and enter the heart.

Vennules (small veins): receive the blood from the capillaries. The blood then flows into larger veins and back to the heart.

Veins: thin walled and flattened. They lie near the surface of the skin and carry the blood back to the heart. Veins in mammals have one-way valve that prevent back flow.

Arteries:

There are two types of arteries: Elastic and Muscular.

Elastic arteries/conducting arteries: These are the large arteries in the body with diameters up to 2.5 cm (1 inch). The pulmonary artery, aorta, common carotid, subclavian…are all examples of elastic arteries. The walls of elastic arteries contain a high density of elastin, and a low density of smooth muscle. The elastic arteries can handle a large amount of pressure and pressure changes from the blood.

Muscular arteries/medium sized arteries/distribution arteries: These arteries distribute blood to the body’s organs. They contain a high density of smooth muscle in the tunica media. Their diameters average 0.4 cm in diameter. The superficial muscular arteries can be used as pressure points.

Arterioles: the internal diameter of these smaller arteries is about 30 (m or less. They have poorly defined tunica externa and the tunica media contains only one or two layers of smooth muscle. Arterioles will branch off into dozens of capillaries.

Capillaries: These blood vessels are narrow they are about 8 (m in diameter (close to the size of a red blood cell). Since they are so narrow, the blood flow through capillaries is relatively slow, which allows for a lot of exchange of substances with tissues. There is no tunica externa and tunica media. There are two types of capillaries: continuous and fenestrated.

Continuous: the endothelial cells that make up the lining are bonded together by tight junctions. There is a continuous layer made up a cell. Not only are capillaries one cell thick (in diameter), but they are one cell thick (in their endothelial lining). The substances flow through the endothelial cells by osmosis, diffusion, facilitated transport, through the cell membrane (with fat soluble, lipid soluble substances), and bulk flow. The substances must pass through the cells, not between them. The cells can act as a filter.

Fenestrated: these capillaries contain pores. Substances can move into tissues through pores. These types of capillaries can be found in certain parts of the brain, and are in absorptive areas of the small intestine and filtration sites of the kidneys.

Capillary beds: a single arteriole usually branches off into dozens of capillaries that will eventually join to form a single venule. A precapillary sphincter, a smooth muscle, controls the entrance to the capillary. The muscle contracts and the entrance is blocked. When the muscle relaxes, the entrance is open and the blood can enter.

Veins are classified by size.

Venules: these small veins collect blood from the capillary bends. The average size of a venule is 20 (m in diameter. They usually lack a tunica media.

Medium sized veins: these vessels are 2 to 9 mm in diameter. They contain few smooth muscles in the tunica media.

Large Veins: Examples of these are the inferior and superior vena cava. The blood pressure in these veins is very low, so low that the blood can’t overcome gravity. Your leg muscles help by squeezing the blood along with contractions. Veins also have folds in the tunica intima, called valves that prevent the back flow of blood. If the valves are stretched or damaged, then you can have blood pooling, the vein can stretch (distend) and you can have varicose veins or hemorrhoids (very specific varicose veins).

Circulation in Fish:

Most fish have a two-chambered heart with a single atrium and a single ventricle.

Blood is pumped from the heart into the aorta and carried directly into the blood vessels and capillaries of the gills.

From the gills, where the blood accepts oxygen, the freshly oxygenated blood flows through the body and from there returns sluggishly to the heart. Most of the force it had when the blood left the heart is lost because of high resistance in the capillary beds and gills.

To summarize: Heart to gill (via the ventral aorta) through the gill arches, from the gills to the tissue via the dorsal aorta from the tissues to the heart (via the common cardinal vein). The fish heart pumps deoxygenated blood, however, it must be fed oxygenated blood by a separate blood vessel. This is one giant circuit with smaller circuits branching off of it.

Circulation in amphibians and reptiles:

Both classes of vertebrates pump some blood to lungs and other blood to body tissue. Amphibians have a three-chambered heart while reptiles have a three and one half or four-chambered heart. In both amphibians and most reptiles oxygenated blood mixes with deoxygenated blood.

Blood returning from the body enters the right atrium. From there the blood travels to the single ventricle. In the ventricle, blood is joined with blood from the left atrium, coming from the lungs. In some reptiles, blood goes from ventricle to the lungs and returns to the left atrium and then is pumped into the ventricle and pumped throughout the body. We now see the introduction of two main circuits with other circuits branching off of it.

Both classes of vertebrates have a two-part circulatory system:

1) There is a pulmonary circuit which pumps blood to the lungs.

2) The second system is the systematic circuit which pumps blood to the body.

This is called 'double circulation.' The smaller circuits branch off of this circuit.

Four Chambered Heart:

This heart differs from the three-chambered heart because of a complete septum forming another ventricle. Crocodiles, birds and humans achieve this heart.

Human Circulation:

The human circulatory system has a four-chambered heart along with

Arteries, capillaries, and veins. The heart is a cone shaped organ about the size of a clenched fist (about 12.5 cm or five inches long) with a mass of about 300 g. It is located beneath the sternum, enclosed in a pericardial sac. The pericardium is lined with delicate serous membranes that are divided into the visceral pericardium and the parietal pericardium. There is about 15-50 ml of fluid that separates the two layers. This fluid prevents friction. The heart consists mostly of cardiac muscle tissue, and has two ventricles, two atria and valves separating the two atria from the two ventricles. There is also a septum that separates the two atria and two ventricles.

Circulation through the heart:

In mammals, blood arrives from two major veins (superior and inferior vena cava) to the right side of the heart, the right atrium. The superior vena cava collects the blood from the head, neck, upper limbs, and chest. The inferior vena cava collects the blood from body parts that are below the heart. The superior and inferior vena cava join the heart at the coronary sinus—a large vein that opens into the right atrium, a thin walled muscular chamber. At the coronary sinus there is the foramen ovule. This was an opening that connected the right and left atria. Prior to birth, the blood flows through the foramen ovule, bypassing the lungs. When you are born, the opening closes and is sealed off (within three months of delivery). The fossa ovalis, a small depression, is left behind. The right atrium pumps the blood into the right ventricle. In order to prevent back flow into the atrium the blood passes through a valve called the tricuspid valve (right atrioventricular valve). The blood is then pumped through the pulmonary semi-lunar valve into the pulmonary arteries that carry the blood to the lungs.

Blood from the right and left branches of the pulmonary arteries (the only arteries that carry deoxygenated blood) moves into the arterioles and then capillary beds that surround the alveoli of the lungs. Here gas exchange occurs (due to partial pressure, connect the respiratory system and the circulatory system here). Capillaries join to form venules, which join to become pulmonary veins (only veins to carry oxygenated blood) and return the oxygen rich blood back to the heart, to the left atrium.

The left atrium contracts and the blood is pushed through the bicuspid valve (mitral valve or the left atrioventricular valve) into the left ventricle. The walls of the left ventricle are much thicker and stronger than the right ventricle. This causes the left ventricle to be larger than the right ventricle. The left ventricle must be strong enough to push the oxygenated blood throughout the body. The blood passes through the aortic semi-lunar valve into the aorta, the largest artery in our body.

The aorta branches off into the ascending aorta, the aortic arch, and into the descending aorta.

Arteries (here the other circuits branch off)---> Arterioles--->Capillaries (gas, nutrients exchanged)---> Venules---> Veins---> Superior or Inferior Vena Cava ----> Right Atrium.

At any given time only 5-10% of the body's capillaries have blood flowing in them. Due to the fact that all tissues have so many capillaries, every part of the body is supplied with blood at all times.

Substances can be transferred across the endothelial cells of the capillary wall by endocytosis into the wall and exocytosis out of the wall and into the tissue. Substances can also move by diffusion through the cell or between the cells. Most of the movement is due to BULK FLOW, transport of fluid due to pressure. Fluid is pushed through the leaky endothelial cells by hydrostatic pressure in the capillaries. Few cells lie more than 25 (m (0.005 inches) away from a capillary.

Other Circuits in the Human Circulatory System:

Hepatic Portal Circuit: Vessels from the aorta spread between the intestinal membrane and digestive organs. Food collected and digested is put into the capillaries and venules that go to the liver. In the liver they branch into capillary beds. The liver cleanses blood, and the food is filtered out. The blood returns to the inferior vena cava.

Renal Circuit: Aorta sends right and left branches which turn into the renal arteries, which branch into the kidneys. In the kidneys the nitrogenous wastes, urea, excess water, misc. metabolic by-products, salts, etc. are removed from the blood. Blood returns from the kidneys via the renal veins back to the heart.

Coronary circuit which feeds the heart (blocked coronary arteries and arterioles cause heart attacks—myocardial infarctions. There are circuits that feed the brain, arms, lower body… every part of the body. These circuits feed the body part and join back to the vena cava and start over again.

Each body part has its own circuit. The blood comes off of the aorta, to an artery, that branch into arterioles, which branch into a capillary bed. The capillary bed is in the tissue and substances are exchanged. The capillaries join to form venules, which combine to form medium sized veins that join to the large inferior or superior vena cava and flow back to the heart. There are specific names to the blood vessels, but this gives you the general idea of what happens.

Control of the heart:

Three reasons why the heart muscle is different than other muscles:

1) Striated but uninucleated.

2) The period between contractions is prolonged.

3) Contraction is inherent to the muscle tissue.

The control center is in the medulla of the brain. Sympathetic nerves accelerate the heart rate and the parasympathetic system slows the heart.

Pacemaker:

Origin of the heartbeat is in the right atrium, in the sinoatrial (SA) node. The SA node is located near the point where the anterior vena cava enters the heart. It is made of specialized muscle tissue that acts like both muscle and nerve. It contracts like a muscle, but sends an electrical impulse that travels through the wall of the heart. The impulse travels rapidly and the two atria contract together. This SA node is called the pacemaker; it transmits a signal to the atrioventricular (AV) node.

The stimulation of the SA node causes atrial contraction. The AV node causes ventricular contraction. Impulses from the AV node pass through a strand of specialized muscle in the ventricular septum called the Bundle of His, Purkinje Fibers. This branches to the right and left ventricle and travels to the apex of the heart (where contraction begins). Here are two terms: brachycardia—slow heart rate and tachycardia—high heart rate.

Atria contract simultaneously, filling the ventricles with blood. There is a slight delay in the impulse and then the ventricles contract simultaneously.

The contraction of the SA node is controlled by a variety of cues. There are two sets of opposing nerves that control the SA node. The SA node is also controlled by the hormone epinephrine (the fight or flight response). Body temperature also affects the SA node; a 1oC increase increases the heart rate by 10-20 beats. Exercise also increases the heart rate.

The impulses that travel through the cardiac muscle during the cycle are conducted through the body fluids and to the body surface. Electrodes can pick up these currents, which can be recorded as an electrocardiogram (ECG or EKG).

Heart Sounds: Lubb, Dubb.

The first sound is the sudden closing of the tri and bicuspid valves. The valves shudder under the force of the blood pushing on the valves. The second sound is the sharp sound of the semilunar valves snapping shut. A heart murmur is a hissing sound, caused by blood squirting backwards through faulty valves.

Heart Rate: The heart beats approximately 70- 100 beats per minute.

Cardiac Output: The heart pumps between 5-6 liters of blood per minute. A blood cell circulates the body in about 30 seconds. Blood leaves the aorta at about 30 cm/second. Blood in the capillaries flows at about 0.026 cm/second. If you add up the rate in all of the capillaries, it will equal approximately 30 cm/second.

Heart Pressure/ Blood Pressure: Pressure of blood against the vessels. Systolic/Diastolic (120/80 mmHg) Systolic: The pressure the heart develops to push blood through the body (heart contraction). Diastolic (Ventricles are filling): The pressure the heart must have to keep blood from flowing back into the heart (heart relaxation- between contractions). This is the pressure that the blood exerts on the blood vessels.

Arteries play a large role in the maintenance of blood pressure. Their muscle layer is able to contract and squeeze the blood, which raise blood pressure. When the muscles in the arteries relax, the vessels open and the blood pressure is lowered. If there is a decrease in the diameter of the blood vessel, the heart has to work harder to pump the blood through the body; there is an increase in blood pressure. If there is an increase in blood volume, there is more blood to push, the blood pressure goes up. If there is an increase in the number of blood vessels (capillaries—each pound of fat contains 1 mile of capillaries), then the heart has to work harder to pump the blood, and the blood pressure increases.

We measure blood pressure by determining how hard the heart has to work to pump blood and how much pressure the blood is pushing on the arterial walls. We take a cuff and place it on the left arm (closer to the heart). We are going to measure the pressure in the brachial artery. We will pump up the cuff until the brachial artery is totally collapsed and all blood flow is stopped into the lower arm. The heart is still pumping and trying to get the blood through the artery. We let the air out slowly. The heart is still working to push the blood through. At some point, the heart pumps and forces the blood through the artery—the artery opens and the blood flows through, but between the contractions, the pressure of the cuff collapses the brachial artery again and we can hear an audible click (if we listen with a stethescope). This first click is the DIASTOLIC pressure—the amount of force the heart has to use to push the blood through the body.

The air is still leaving the B.P. cuff and the blood is now being pumped through the brachial artery, but between contractions the artery is still collapsing—you can feel this. At some point in time, the artery is going to be held open by the pressure inside the artery—the pressure of the blood pushing out on the arterial walls. When that happens, the artery won’t close any more and there won’t be any more clicks. The last click you hear is the SYSTOLIC pressure. This pressure measures the amount of pressure the blood uses on the arterial walls.

If you have increased blood volume—more pressure on the arterial walls and the harder the heart has to push to get all this fluid through the body. If an artery or arteries is narrow, the harder the heart has to work. If the arteries are not as flexible—the harder the heart has to work. The more capillaries you have… the harder the heart has to work… If the blood has to work too hard, it can eventually cause congestive heart failure (CHF).

Blood and Lymph:

Blood is a tissue that is composed of several types of cells.

It is a connective tissue with plasma as the matrix. With gentle centrifugation blood divides into three layers:

1) The top layer is plasma.

2) A thin, clear second layer is composed of leukocytes and platelets.

3) The bottom layer is made up of erythrocytes or red blood cells. In males, 45% of volume is red blood cells. This differs from the 43% of red blood cells in females.

Blood cells and cell fragments are collectively called formed elements. A process of hemopoiesis or hematopoiesis produces formed elements. There are two types of stem cells that produce the formed elements: myeloid stem cells or lymphoid stem cells.

Plasma and formed elements make up whole blood. Here are the characteristics of whole blood:

1) Blood temperature is about 38oC (about 100.4oF).

2) Blood is thicker than water, by about five times. Blood is five times as sticky, five times as cohesive, and and five times as resistant to flow.

3) Blood is slightly basic, about 7.35 to 7.45 (average is about 7.4).

4) The adult male contains about 5-6 liters of whole blood. The adult female has about 4-5 liters of whole blood. Your blood volume can be calculated by multiplying 0.07 X mass of your body mass in kg.

Plasma: Ninety percent of plasma is water. Solutes are dissolved in water. The solutes are inorganic salts and are referred to as blood electrolytes. These are ionic compounds that maintain the osmotic balance of blood and fluid. The kidney maintains plasma electrolytes at precise concentration.

Plasma contains various proteins, which are important in maintaining hydrostatic pressure in vessels particularly in capillaries.

Critical plasma proteins maintain the fluid balance.

1) Albumins: About 60% of the plasma proteins are large proteins that bind impurities and toxins in the blood. Albumins also transport fatty acids, hormones, and some steroids.

2) Globulins: About 35% of the plasma proteins are globulins. These include antibodies; transport lipids and fat-soluble vitamins. A type of globulin is apolipoprotein

3) Fibrinogen: important in blood clotting. About 4% of the plasma proteins is fibrinogen.

4) Other proteins that make up the 1%: insulin, prolactin, follicle stimulating hormone, lutenizing hormone, thyroid stimulating hormone.

The liver synthesizes and releases more than 90% of the plasma proteins. This includes the following: most globulins (not antibodies) Ab are produced in the B cells (lymphocyte). Liver problems will lead to a problem with the protein levels of the blood.

The Red Blood Cells or Erythrocytes (RBC):

99.9% of the formed elements are red blood cells. There are 25 trillion cells in five liters of blood. Each red blood cell has a four-month life expectancy. When they are old, they rupture, spilling their hemoglobin into the blood. However, most old red blood cells are phagocytized by macrophages in the spleen and liver. The hemoglobin is stripped of the iron and changed to biliverdin (greenish color of a bruise). The biliverdin is changed into bilirubin. The bilirubin combines with albumin and then which is secreted into the small intestine as bile. If there is too much bilirubin, it can enter the tissues and give the skin a yellowish color—jaundiced. Bilirubin can be changed, by bacteria in the large intestine, into urobilinogens or sterobiliogens (pigments) that is absorbed by the blood. These two pigments color the urine yellow and the feces brown.

The free iron from the dead RBCs is toxic. The iron binds to transferrin, a plasma protein. The transferring drops off the iron in the bone marrow for RBC production. The liver and spleen filter out excess transferrin.

The red blood cell is a biconcave disc. Why is this good? There are three effects of the biconcave shape.

1) It increases the surface area to volume ration. So the RBC can carry more oxygen and carbon dioxide.

2) Enables the RBC to stack together when moving through narrow blood vessels.

3) Allows the RBC to band and flex when entering capillaries.

Hemoglobin (Hb) is a protein that is made up of two alpha and two beta chains. Each chain holds one heme unit. Each heme unit has one iron atom. The iron will interact with the oxygen molecule and become oxyhemoglobin (HbO2). Hemoglobin without oxygen is deoxyhemoglobin.

Each hemoglobin molecule carries four heme units and can hold up to four oxygen molecules (one per group). Carbon dioxide can also bind to hemoglobin, but not the iron group. Instead it bonds to an amino acid of the hemoglobin protein to become carbaminohemoglobin.

Hemoglobin can also bind to nitric oxide (NO), and carbon monoxide. As the RBCs enter the capillaries the oxygen and NO are released. NO relaxes the capillary cells (of the endothelium), and oxygen diffuses into the tissues easily.

Red blood cells lack nuclei when mature. They also lack mitochondria and generate ATP anaerobically. Each red blood cell contains 280 million molecules of hemoglobin. Each red blood cell can carry over 1 billion molecules of oxygen.

Erythrocytes are formed in the red marrow of the bones-- ribs, vertebrate, breastbone and pelvis. Within the bone marrow are PLURIPOTENT STEM CELLS that can develop into any type of blood cell. If tissues are not receiving enough oxygen, the kidney secretes a hormone called ERYTHROPOIETIN, which stimulates production of erythrocytes in the bone marrow. If tissues have too much oxygen erythropoietin is reduced, and erythrocyte production slows.

White Blood Cells or Leukocytes (WBC):

These cells have a nucleus and other organelles, but have no hemoglobin. White blood cells help defend the body against invasion, remove toxins, remove wastes, and remove damaged and abnormal cells. WBCs circulate in the blood for a small part of their lives. WBC can detect damage to surrounding tissues and leave the blood vessel to enter the damaged tissue. There are four characteristics of leukocytes:

1) They can migrate out of blood vessels. Once out of the blood, the WBCs are activated.

2) Leukocytes are capable of ameboid movement.

3) They are attracted to a certain chemical stimuli.

4) Most are capable of phagocytosis.

There are five types of white blood cells: neutrophils, eosinophils, basophils, monocytes and lymphocytes. Neutrophils: 70% of our circulating WBCs are neutrophils, AKA: polymorphonuclear leukocyte. These are highly mobile; in fact, they are usually the first WBC to the site of the injury. They will eat the invader and will release prostaglandins, which causes an inflammatory response. They are very short lived, about 10 hours in the blood, and only 30 minutes if eating invaders. Eosinophils: usually attacks large or multicellular parasite by secreting enzymes and poking holes in the cells. Basophils: these leukocytes migrate to the site of injury and release histamine, which causes an inflammatory response. Monocytes: these WBCs will travel in the blood for about 24 hours and enter the tissue as a macrophage. These are the big cell eaters. Lymphocytes give rise to T and B cells. These cells will produce plasma cells that produce antibodies. All of these are produced by the stem cells. Lymphocytes mature after leaving the marrow in the spleen, thymus, tonsils, adenoids, and lymph nodes.

Platelets: These are numerous tiny structures (2-3μm in diameter), which lack nuclei, are cell fragments, and are active in blood clotting. Clots can form anywhere. If a clot occurs inside the blood vessels it is termed atherosclerosis. Hidden clots can break off and clog arteries, which in turn can cause heart attacks and strokes. They circulate for nine to 12 days and are removed by the spleen.

Clotting: prothrombin and fibrinogen are required.

1) A blood vessel is damaged.

2) Platelets and damaged cells release thromboplastin, an enzyme.

3) Prothrombin + Thromboplastin + Calcium ---> Thrombin.

4) Thrombin + Fibrinogen ---> Fibrin

5) Fibrin along with co-factors (vitamin K and factor 8—don’t forget the hemophiliacs) and damaged platelets form a network that solidifies becoming a clot and stopping the bleeding.

6) The clot contracts pulling the wound together. This prevents bleeding and encourages healing.

Lymphatic System: The Second Circulatory System.

The lymphatic system drains tissue spaces and cavities of fluid that has leaked out of the capillaries because of the high hydrostatic pressure and returns fluids to the blood stream through ducts, which enter the subclavian vein. It is a system consisting of a large number of nodes and thin walled ducts. The fluid that is forced out is cleared at the lymph nodes. The fluid is then returned to the blood to maintain blood pressure.

The Lymphatic system consists of

1) Lymph—a fluid that resembles plasma.

2) Lymph vessels—these begin in the tissues and end at vein connections.

3) Lymph nodes

4) Lymph organs.

The primary function of the lymphatic system is to produce, maintain, and distribute lymphocytes. Lymphocytes protect you from invaders/pathogens.

Lymphatic vessels: These vessels carry lymph from tissues to the venous system. The smallest lymph vessels are the lymphatic capillary. The lymphatic capillary branch through tissues. The endothelial cells of these vessels aren’t tightly bonded together, but they do overlap, and they permit a variety of substances and cells to enter the lymph vessel. Fluids, solutes, large proteins, viruses, bacteria, and cell debris can all enter the lymphatic capillary.

The lymphatic capillaries flow into small lymphatic vessels. These vessels lead to the body trunk. Within these vessels there are valves that prevent back flow. The fluid in the lymphatic system is moved along by the squeezing action of muscles.

Lymphoid tissue: This tissue is basically connective tissue that has a high concentration of lymphocytes. The lymphoid nodule is areolar tissue with a high density of lymphocytes. These average 1 mm in diameter. Each nodule contains a zone called the germinal center, which contains dividing lymphocytes. The following are examples of lymphoid tissue.

MALT: This is a collection of lymphoid tissue that is associated with the digestive system, specifically the intestine. MALT stands for mucosa-associated lymphoid tissue.

Tonsils: These are large lymphoid nodules that are located in the walls of the pharynx. Most people have 5 tonsils. You have a right and left palatine tonsils. These are located in the back of your throat. You have one pharyngeal tonsil (Adenoid). The adenoid is on the superior wall of the nasopharynx. (above the palate). You have a pair of lingual tonsils that are located at the base of your tongue.

Lymphoid Organs: A connective tissue capsule separates lymphoid organs. The lymph nodes, thymus and spleen are lymphoid organs.

Lymph nodes: These range from 1 mm to 25 mm (1 inch) in diameter. Collagen fibers that surround the lymph node will extend into the interior of the node. Blood vessels and nerves also enter the node. They contain a large number of lymphocytes. Many afferent lymph vessels bring lymph fluid to the node, and efferent lymph vessels carry fluid from the node. The fluid is cleansed of foreign particles in the lymph node. The antigens are presented in the lymph node.

Lymph nodes are lymph glands that are scattered through the body. They are concentrated in the neck, armpits, and groin areas. The main function of the lymphatic system is to remove foreign material or invading microorganisms. The lymph nodes enlarge during illness.

Thymus: Located beneath the sternum. The thymus is about 40 grams at puberty and decreases in size to about 12 grams at the age of 50. The thymus is divided into two lobes, which are divided into lobules by the connective tissue. T cells divide and mature in the thymus (after forming in the bone marrow). The T cells take about 3 weeks to mature in the thymus, then they enter the blood to move to various parts of the body.

The thymus also produces thymosin, a hormone that helps with the formation of mature T cells.

Spleen: Contains the largest collection of lymphoid tissue in the body.

Spleen Functions:

1) Removes abnormal cells and other blood components by phagocytosis.

2) Stores iron recycled from dead red blood cells.

3) Stores B and T cells for the humoral and cell mediated response.

Basically, it filters the blood. The lymph nodes filter lymph fluid, the spleen filters the blood.

Anatomy:

It is about 12 cm long and has a mass of about 160 grams. It lies behind the stomach at about the 9th and 11th rib. It is on the left side of the body and is held in place by the gastrosplenic ligament.

The spleen contains red pulp, a high concentration of red blood cells and white pulp, a high concentration of lymph nodules. The 2 pulps have an integrated circulatory system that allows them to integrate. This is how the blood is cleaned.

The spleen can tear easily. If so, internal bleeding can be severe.

Lymphocytes: These are produced by the bone marrow (pluripotent stem cells). Some mature in the bone marrow—B cells. Others move to the thymus and mature there—T cells. These cells are distributed by the blood into lymph nodes, tonsils, spleen, and other tissues. They have a relatively long life, up to 4 years and some can last up to 20 years. Lymphocytes are involved in your immune response.

The lymph system maintains the blood volume. The increased pressure forces the fluid from the blood vessels by bulk flow. The lymph takes that fluid and puts it back into the circulatory system (after cleaning it). If you have high blood pressure, too much fluid is pushed into the lymph system, the lymph system gets overwhelmed, and the fluid will enter your tissues—edema.

Cardiovascular Disease:

Atherosclerosis: plaques develop on the inner walls of the arteries which narrowing the diameter of the vessels. Calcium deposits can infiltrate these plaques, which is arteriosclerosis or hardening of the arteries. The first step of this is an injury to the blood vessel. The blood vessel forms a clot and on top of the clot the deposits form. The blood vessel can be injured in a number of ways—even loud music. The clot and the fatty deposits (usually cholesterol at first and calcium later) decrease the diameter of the blood vessels—increases blood pressure (narrows the pipes).

Hypertension: high blood pressure, which promotes atherosclerosis, increasing the chance of heart attacks and strokes.

One cause is the increase in concentration of LDL, Low-density lipoproteins. These are plasma particles made of thousands of cholesterol molecules and other lipids bound to a protein. High Density Lipoproteins (HDL) reduce the deposits of cholesterol in arteries.

FYI: On chromosome 19 there is a set of genes called the Apolipoprotein genes (APO). There are 4 genes: A, B, C, and E. APOE is the one that we’re going to discuss.

The cholesterol is put into the blood from your diet and transported to the liver by the hepatic portal circuit. The liver takes the cholesterol and processes it for delivery to the cells. Because cholesterol is a steroid it is hydrophobic. The molecule is bonded to a protein—apolipoprotein for delivery to the cell. At the beginning of the journey to the cells, there is a high concentration of cholesterol on the lipoprotein and it is called a VLDL (very low density lipoprotein). The VLDL dumps off some fat and cholesterol and it becomes an LDL (Low density lipoprotein-- the ‘bad’ cholesterol). More and more cholesterol is dumped and it becomes an HDL (high density lipoprotein—the ‘good cholesterol—because all of the cholesterol is gone). The HDL goes back to the liver to get more cholesterol and starts delivery all over again.

APOE and APOB introduce VLDL to the cell receptors that need cholesterol. If APOE and APOB don’t work, then the cholesterol stays in the blood and there is a build up on the walls of the artery. Changes in the cholesterol receptors on cells – hypercholesterolemia—can cause heart problems.

There are three forms of APOE—APOE2, APOE3, and APOE4. If you have two copies of the APOE4 gene that is bad! You see, Alzheimers is associated with APOE4 genes. If you have no E4 genes you have a 20% chance of getting Alzheimers by the age of 84. If you have 1 E4 gene, then you have a 47% chance of getting Alzheimers by the age of 74. If you have 2 copeis of the E4 gene you have a 91% chance of getting Alzheimers by the age of 69. We don’t know why this happens.

The difference between the E4 and E3 genes is a 334 base there is a G instead of an A. The difference between the E3 and E2 genes is at bse 472, there is a G instead of an A.

Blood Clots: Death of other tissue in various parts of the body. Other blood vessels are occluded. This can happen to fingers, toes, eyes,… etc. This is called a Thrombus.

Myocardial Infarction: Death of heart muscle due to a lack of oxygen. The blood vessels that feed the heart are occluded and the blood flow is disrupted. If there is no blood, there is no oxygen, and the muscle dies. This is a heart attack. This is a blood clot in the coronary artery.

Cerebrovascular accident: CVA: Death of brain tissue due to a lack of oxygen. The blood vessels that feed the brain are occluded and the blood flow is disrupted. If there is no blood, there is no oxygen and the brain tissue dies. This is a stroke. This is a blood clot in the carotid artery or brain artery.

Talk about other circulation problems: Shock, Anemia, Congestive Heart Failure…

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