Heart
The heart (Latin cor) is a hollow, muscular organ that pumps blood through the blood vessels by repeated, rhythmic contractions. The term cardiac means "related to the heart", from the Greek kardia for "heart"

Structure
In the human body, the heart is normally situated slightly to the left of the middle of the thorax, underneath the sternum (breastbone). It is enclosed by a sac known as the pericardium and is surrounded by the lungs. In normal adults, its mass is 250-350 g, but extremely diseased hearts can be up to 1000 g in mass. It consists of four chambers, the two upper atria (singular: atrium) and the two lower ventricles.

A septum divides the right atrium and ventricle from the left atrium and ventricle, preventing blood from passing between them. Valves between the atria and ventricles (atrioventricular valves) maintain coordinated unidirectional flow of blood from the atria to the ventricles.

The function of the right side of the heart (see right heart) is to collect deoxygenated blood from the body and pump it into the lungs so that carbon dioxide can be dropped off and oxygen picked up. This happens through a process called diffusion. The left side (see left heart) collects oxygenated blood from the lungs and pumps it out to the body. On both sides, the lower ventricles are thicker than the upper atria.

Oxygen-depleted or deoxygenated blood from the body enters the right atrium through two great veins, the superior vena cava, which drains the upper part of the body and the inferior vena cava that drains the lower part. The blood then passes through the tricuspid valve to the right ventricle. The right ventricle pumps the deoxygenated blood to the lungs, through the pulmonary artery. In the lungs gaseous exchange takes places and the blood releases carbon dioxide into the lung cavity and picks up oxygen. The oxygenated blood then flows through pulmonary veins to the left atrium. From the left atrium this newly oxygenated blood passes through the mitral valve to enter the left ventricle. The left ventricle then pumps the blood through the aorta to the entire body. Even the lungs take some of the blood supply from the aorta via bronchial arteries.

The left ventricle is much more muscular (1.3 - 1.5 cm thick) than the right (0.3 - 0.5 cm thick) as it has to pump blood around the entire body, which involves exerting a considerable force to overcome the vascular pressure. As the right ventricle needs to pump blood only to the lungs, it requires less muscle.

Even though the ventricles lie below the atria, the two vessels through which the blood exits the heart (the pulmonary artery and the aorta) leave the heart at its top side.

The contractile nature of the heart is due to the presence of cardiac muscle in its wall, which can work continuously without fatigue. The heart wall is made of three distinct layers. The first is the outer epicardium, which is composed of a layer of flattened epithelial cells and connective tissue. Beneath this is a much thicker myocardium made up of cardiac muscle. The endocardium is a further layer of flattened epithelial cells and connective tissue which lines the chambers of the heart.

The blood supply to the heart itself is supplied by the left and right coronary arteries, which branch off from the aorta.

The cardiac cycle
The function of the heart is to pump blood around the body. Every single beat of the heart involves a sequence of events known as the cardiac cycle, which consists of three major stages: atrial systole, ventricular systole and complete cardiac diastole. The atrial systole consists of the contraction of the atria and the corresponding influx of blood into the ventricles. Once the blood has fully left the atria, the atrioventricular valves, which are situated between the atria and ventricular chambers, close. This prevents any backflow into the atria. It is the closing of the valves that produces the familiar beating sounds of the heart, commonly referred to as the "lub-dub" sound.

The ventricular systole consists of the contraction of the ventricles and flow of blood into the circulatory system. Again, once all the blood empties from the ventricles, the pulmonary and aortic semilunar valves close. Finally complete cardiac diastole involves relaxation of the atria and ventricles in preparation for refilling with circulating blood.

Regulation of the cardiac cycle
Cardiac muscle is self-exciting. This is in contrast with skeletal muscle, which requires either conscious or reflex nervous stimuli. The heart's rhythmic contractions occur spontaneously, although the frequency or heart rate can be changed by nervous or hormonal influences such as exercise or the perception of danger.

The rhythmic sequence of contractions is coordinated by the sinoatrial and atrioventricular nodes. The sinoatrial node, often known as the cardiac pacemaker, is located in the upper wall of the right atrium and is responsible for the wave of electrical stimulation (See action potential) that initiates atria contraction. Once the wave reaches the atrioventricular node, situated in the lower right atrium, it is conducted through the bundles of His and causes contraction of the ventricles. The time taken for the wave to reach this node from the sinoatrial nerve creates a delay between contraction of the two chambers and ensures that each contraction is coordinated simultaneously throughout all of the heart. In the event of severe pathology, the Purkinje fibers can also act as a pacemaker; this is usually not the case because their rate of spontaneous firing is considerably lower than that of the other pacemakers and hence is overridden.

Other physiological functions
The heart also secretes ANF (atrial natriuretic factor), a powerful peptide hormone, that affects the blood vessels, the adrenal glands, the kidneys and the regulatory regions of the brain to regulate blood pressure and volume.

Diseases and treatments
The study of diseases of the heart is known as cardiology. Important diseases of the heart include:

Coronary heart disease is the lack of oxygen supply to the heart muscle; it can cause severe pain and discomfort known as Angina.
A heart attack occurs when heart muscle cells die because blood circulation to a part of the heart is interrupted.
Congestive heart failure is the gradual loss of pumping power of the heart.
Endocarditis and myocarditis are inflammations of the heart.
Cardiac arrhythmia is an irregularity in the heartbeat. It is sometimes treated by implanting an artificial pacemaker.
Congenital heart defects.
If a coronary artery is blocked or narrowed, the problem spot can be bypassed with coronary artery bypass surgery or it can be widened with angioplasty.

Beta-blockers are drugs that lower the heart rate and blood pressure and reduce the heart's oxygen requirements. Nitroglycerin and other compounds that give off nitric oxide are used to treat heart disease as they cause the dilation of coronary vessels.

Lecture II

Circulatory system

The circulatory system or cardiovascular system is the organ system, which circulates blood around the body of most animals.

It consists of Heart - Aorta - Arteries - Arterioles - Capillaries - Venules - Veins - Venae cavae - Pulmonary arteries - Lungs - Pulmonary veins - Blood

AORTA:
The largest artery in the human body, the aorta originates from the left ventricle of the heart and brings oxygenated blood to all parts of the body in the systemic circulation.

The course of the aorta
The aorta is usually divided into several segments. The portion above the diaphragm (in the thorax) is called the thoracic aorta and is sometimes further subdivided into the ascending aorta, aortic arch and descending (thoracic) aorta. The portion below the diaphragm (in the abdomen) is known as the abdominal aorta.

Thoracic aorta
The initial part of the aorta, the ascending aorta, rises out of the left ventricle, from which it is separated by the aortic valve. The two coronary arteries of the heart arise from the aortic root, just above the cusps of the aortic valve.

The aorta then arches back over the right pulmonary artery. Three vessels come out of the aortic arch,

Brachiocephalic artery,
Left common carotid artery, and
Left subclavian artery.
These vessels supply blood to the head, neck, thorax and upper limbs.

The aorta gives off several paired branches as it descends in the thorax. These includes the

Bronchial arteries,
Esophageal arteries and
Intercostal arteries.

ABDOMINAL AORTA
The abdominal aorta travels down the posterior wall of the abdomen, the abdominal aorta runs on the left of the inferior vena cava, giving off major blood vessels to the gut organs and kidneys. There are many recognized variants in the vasculature of the gastrointestinal system. The most common arrangement for the abdominal aorta is to give off (in order) a

Celiac artery,
Superior mesenteric artery and
Inferior mesenteric artery.
The renal arteries usually branch from the abdominal aorta in between the celiac artery and the superior mesenteric artery.

The aorta terminates by dividing into two branches, the left and right common iliac arteries that branch to supply blood to the lower limbs and the pelvis.

Features
The aorta is an elastic artery, and as such is quite distensible. When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure during diastole, as during this time the aorta contracts passively.

Diseases
Aneurysm of sinus of Valsalva
Aortic aneurysm
Dissecting aortic aneurysm
Aortic coarctation
Marfan’s syndrome
Inborn cardiovascular defects

ARTERY

Arteries are muscular vessels that carry blood away from the heart to the tissues and organs of the body (The vessels which return blood to the heart are veins).

The circulatory system is extremely important in sustaining life. Its proper functioning is responsible for the delivery of oxygen and nutrients to all cells, as well as the removal of carbon dioxide, waste products, maintenance of optimum pH, and the mobility of the elements, proteins and cells, of the immune system. In First World countries the two leading causes of death, myocardial infarction and stroke, are each direct results of an arterial system that has been slowly and progressively compromised by years of deterioration.

Description
The arterial system is the higher-pressure portion of the circulatory system. Arterial pressure varies between the peak pressure during heart contraction, called the systolic pressure, and the minimum, or diastolic pressure between contractions, when the heart rests between cycles. This pressure variation within the artery produces the pulse which is observable in any artery, and reflects heart activity.

Anatomy
Arteries are composed of distinct layers of tissue; The innermost layer, which is in direct contact with the flow of blood is the tunica intima, commonly called the intima. This layer is made up of mainly endothelial cells. Outside this layer is the tunica media, or media, which is made up of smooth muscle cells and elastic tissue. The outermost layer is known as the tunica adventitia or the adventitia, and is composed of connective tissue.

Types of arteries:
There are several types of arteries in the body:

Pulmonary arteries
The pulmonary arteries carry oxygen deficient blood that has just returned from the body to the lungs, where carbon dioxide is exchanged for oxygen.

Systemic arteries
Systemic arteries deliver blood to the arterioles, and then to the capillaries, where nutrients and gasses are exchanged.

The Aorta
The aorta is the root systemic artery. It receives blood directly from the left ventricle of the heart via the aortic valve. As the aorta branches and these arteries branch in turn, they become successively smaller in diameter, successively down to the arteriole. The arterioles supply capillaries, which in turn empty into venules.

ARTERIOLES
Arterioles, the smallest of the true arteries, help regulate blood pressure and deliver blood to capillaries.

Arterioles and Blood Pressure
Arterioles have the greatest collective influence on both local blood flow and on overall blood pressure. They are the primary "adjustable nozzles" in the blood system, across which the greatest pressure drop occurs. The combination of heart output (cardiac output) and total peripheral resistance, which refers to the collective resistance of all of the body's arterioles, are the principal determinants of arterial blood pressure at any given moment.

Capillaries
Though not considered true arteries, the capillaries are where all of the important action happens in the circulatory system:

Functions of capillaries
These vessels have no smooth muscle surrounding them and have a diameter less than that of a red blood cell; a red blood cell is typically 7 micrometers outside diameter, capillaries typically 5 micrometers inside diameter. The red blood cells must distort in order to pass through the capillaries.

This small diameter of the capillary provides a relatively large surface area for the exchange of gases and nutrients.

What are the functions of capillaries:

In the lungs, carbon dioxide is exchanged for oxygen
In the tissues, oxygen and carbon dioxide and nutrients and wastes are exchanged
In the kidneys, wastes are released to be eliminated from the body
In the intestine nutrients are picked up, and wastes released

Lecture III

Blood pressure
Systemic arterial pressures, are generated by the forceful contractions of the heart's left ventricle.
Healthy resting arterial pressures, are relatively low, mean systemic pressures typically being under 100 mmHg, about 1.8 lbf/in², above surrounding atmospheric pressure (about 760 mmHg or 14.7 lbf/in² at sea level).
To withstand and adapt to the pressures within, arteries are surrounded by varying thicknesses of smooth muscle, which have extensive elastic and inelastic connective tissues.

The pulse pressure, i.e. Systolic vs. Diastolic difference, is determined primarily by the amount of blood ejected by each heart beat, stroke volume, versus the volume and elasticity of the major arteries.
Over time, elevated arterial blood sugar (see Diabetes Mellitus), lipoprotein cholesterol, and pressure, smoking, and other factors are all involved in damaging both the endothelium and walls of the arteries, resulting in atherosclerosis. Diabetes Mellitus also leads to capillary damage.

Arteriole
An arteriole is a blood vessel that extends and branches out from an artery and leads to capillaries.

Arterioles have thick muscular walls and are the primary site of vascular resistance. The mean blood pressure in the arteries supplying the body is a result of the interaction between the cardiac output (the volume of blood the heart is pumping per minute) and the vascular resistance, usually termed total peripheral resistance by physicians and researchers.

The up and down fluctuation of the arterial blood pressure is due to the pulsatile nature of the cardiac output and determined by the interaction of the stroke volume versus the volume and elasticity of the major arteries.

The muscular contraction of arterioles is targeted by drugs that lower blood pressure (antihypertensives), for example the dihydropyridines (nifedipine and nicardipine), which block the calcium conductance in the muscular layer of the arterioles, causing relaxation. This decreases the resistance to flow into peripheral vascular beds, lowering overall systemic pressure.

Capillary

The word capillary is used to describe any very narrow tube or channel through which a fluid can pass. See capillary action for details.

Capillaries are the smallest of a body's blood vessels, measuring 5-10 μm. They connect arteries and veins, and most closely interact with tissues. Capillaries have walls composed of a single layer of cells, the endothelium. This layer is so thin that molecules such as oxygen, water and lipids can pass through them by diffusion and enter the tissues. Waste products such as carbon dioxide and urea can diffuse back into the blood to be carried away for removal from the body. Capillary permeability can be increased by the release of certain cytokines.

The endothelium also actively transports nutrients, messengers and other substances. Large molecules may be too big to diffuse across endothelial cells. In some cases, vesicles contained in the capillary membrane use endocytosis and exocytosis to transport material between blood and the tissues.

In an immune response, the endothelial cells of the capillary will upregulate receptor molecules, thus "catching" immune cells as they pass by the site of infection and aiding extravasation of these cells into the tissue.

The "capillary bed" is the network of capillaries supplying an organ. The more metabolically active the cells, the more capillaries it will require to supply nutrients. The capillary bed usually carries no more than 25% of the amount of blood it could contain, although this amount can be increased through autoregulation (e.g. active muscle cells) by constricting smooth muscle.

Venule
A venule is a small blood vessel that allows blood to return from the capillary beds to the larger blood vessels called veins. Venules have three layers: An inner endothelium composed of squamous epithelial cells that act as a membrane, a middle layer of muscle and elastic tissue and an outer layer of fibrous connective tissue. The middle layer is poorly developed so that venules have thinner walls than arterioles.

Vein
In biology, a vein is a blood vessel, which returns blood from the microvasculature to the heart. Veins form part of the circulatory system. The vessels carrying blood away from the heart are known as arteries.

Veins have one-way valves to prevent backflow caused by gravity.

In systemic circulation, de-oxygenated blood from the capillary blood vessels is taken by veins to the right part of the heart. Differently, in the pulmonary circulation oxygenated blood from the lungs is taken to the left part of the heart by pulmonary veins. Another special case is portal circulation where the portal vein transports blood rich in products of digestion from the intestines to the liver.

NAMES OF IMPORTANT VEINS:

Pulmonary veins
Portal vein
Superior vena cava
Inferior vena cava
Femoral vein
Great saphenous vein

Veins are used medically as points of access to the blood stream, permitting the withdrawal of blood specimens (venipuncture) for testing purposes, and enabling the infusion of fluid, electrolytes, nutrition, and medications. The latter is called intravenous delivery. It can be done by an injection with a syringe, or by inserting a catheter (a flexible tube).

If an intravenous catheter has to be inserted, for most purposes this is done into a peripheral vein (a vein near the surface of the skin in the hand or arm, or less desirably, the leg.) Some highly concentrated fluids or irritating medications must flow into the large central veins, which are sometimes used when peripheral access cannot be obtained. Catheters can be threaded into the superior vena cava for these uses: if long term use is thought to be needed, a more permanent access point can be inserted surgically.

The precise location of veins is much more variable from person to person than that of arteries.

VENAE CAVAE
The superior and inferior venae cavae are the veins that return the blood from the body into the heart. They both empty into the right atrium.

The inferior vena cava travels up alongside the abdominal aorta with blood from the lower part of the body.

The superior vena cava is above the heart, and forms from a convergence of the left and right brachiocephalic veins that contain blood from the head and the arms. The vena cava carries blood from the body to the right atrium of the heart.

PULMONARY ARTERIES

The pulmonary arteries carry blood from the heart to the lungs. They are the only arteries (other than umbilical arteries in the fetus) that carry deoxygenated blood.

In the human heart, the pulmonary trunk begins at the base of the right ventricle. It is short and wide - approximately 5 cm (2 inches) in length and 3 cm (1.2 inches) in diameter. It then branches into two pulmonary arteries, which connect to the base of each lung.

Role in disease
Pulmonary hypertension occurs alone and as a consequence of a number of lung diseases. It can be a consequence of heart disease (Eisenmenger's syndrome) but equally a cause (right-ventricular heart failure); it also occurs as a consequence of pulmonary embolism and scleroderma. It is characterized by reduced exercise tolerance. Severe forms, generally, have a dismal prognosis.

PULMONARY VEINS

The pulmonary veins carry oxygen rich blood from the lungs to the left atrium of the heart. They are the only veins in the adult human body that carry oxygenated blood.

There are four of them:

Right inferior
Right superior
Left inferior
Left superior

MAJOR BLOOD VESSELS

HEAD ARTERIES: carotid - common carotid - internal carotid (ophthalmic, retinal, anterior cerebral, middle cerebral, posterior communicating) - external carotid (facial, maxillary, superficial temporal artery) - posterior cerebral - anterior communicating - basilar - circle of Willis - middle meningeal | VEINS: jugular - vein of Galen

ARMS: ARTERIES: axillary (superior thoracic, thoracoacromial, lateral thoracic, subscapular, anterior circumflex humeral, posterior circumflex humeral) - brachial - radial - ulnar - dorsal scapular.

VEINS: axillary - brachial - radial - ulnar - median cubital - basilic - cephalic.

THORAX: ARTERIES: aorta - brachiocephalic - bronchial - thoracic (lateral thoracic, internal thoracic) - subclavian - vertebral - axillary - pulmonary | VEINS: venae cavae (superior - inferior) - brachiocephalic - subclavian - portal - ductus venosus - azygos - pulmonary.

ABDOMEN: ARTERIES: celiac artery - marginal - artery of Adamkiewicz - gastroduodenal - gastroepiploic - left gastric - umbilical - mesenteric (superior - inferior) | iliac (common - external - internal) - Internal pudendal - renal - hepatic - common hepatic - splenic | VEINS: mesenteric (inferior, superior) | iliac (common - external) - renal - hepatic - splenic.

LEGS ARTERIES: dorsalis pedis - femoral - peroneal - popliteal - profunda femoris - tibial (anterior, posterior) | VEINS: femoral - saphenous (great, small) - peroneal - popliteal - profunda femoris - tibial (anterior tibial, posterior tibial)

Lecture IV

BLOOD

Blood is a circulating tissue composed of fluid plasma and cells (red blood cells, white blood cells, and platelets). Medical terms related to blood often begin in hemo- or hemato- (BE: haemo- and haemato-) from the Greek word "haima" for "blood".

The main function of blood is to supply nutrients (oxygen, glucose) and constitutional elements to tissues and to remove waste products (such as carbon dioxide and lactic acid). Blood also enables cells (leukocytes, abnormal tumor cells) and different substances (amino acids, lipids, hormones) to be transported between tissues and organs. Problems with blood composition or circulation can lead to downstream tissue dysfunction.

Anatomy of blood
Blood is composed of several kinds of corpuscles; these formed elements of the blood constitute about 45% of whole blood. The other 55% is blood plasma, a yellowish fluid that is the blood's liquid medium. The normal pH of human arterial blood is approximately 7.40. Blood is about 7% of the human body weight [1], so the average adult has a blood volume of about 5 liters, of which 2.7-3 liters is plasma. The combined surface area of all the erythrocytes in the human anatomy would be roughly 2,000 times as great as the body's exterior surface.

The corpuscles are:

1. Red blood cells or erythrocytes (96%). In mammals, these corpuscles lack a nucleus and organelles, so are not cells strictly speaking. They contain the blood's hemoglobin and distribute oxygen. The red blood cells (together with endothelial vessel cells and some other cells) are also marked by proteins that define different blood types.
2. White blood cells or leukocytes (3.0%), are part of the immune system; they destroy infectious agents.
3. Platelets or thrombocytes (1.0%) are responsible for blood clotting (coagulation)

Blood plasma is essentially an aqueous solution containing 96% water, 4% blood plasma proteins, and trace amounts of other materials. Some components are:

Albumin
Blood clotting factors
Immunoglobulins (antibodies)
Hormones
Various other proteins
Various electrolytes (mainly sodium and chlorine)
Together, plasma and corpuscles form a non-Newtonian fluid whose flow properties are uniquely adapted to the architecture of the blood vessels.

PHYSIOLOGY OF BLOOD

Production and degradation
Blood cells are produced in the bone marrow; the process is termed hematopoiesis. The proteinaceous component is produced overwhelmingly in the liver, while hormones are produced by the endocrine glands and the watery fraction maintained by the gut and the kidney.

Blood cells are degraded by the spleen and the Kupffer cells in the liver. The liver also clears proteins and amino acids (the kidney secretes many small proteins into the urine). Erythrocytes usually live up to 120 days before they are systematically replaced by new erythrocytes created by the process of hematopoiesis.

Diagnosis
Blood pressure and blood tests are amongst the most commonly performed diagnostic investigations that directly concern the blood.

Pathology

Problems with blood circulation and composition play a role in many diseases.

1. Wounds can cause major blood loss (see bleeding). The thrombocytes cause the blood to coagulate, blocking relatively minor wounds, but larger ones must be repaired at speed to prevent exsanguination. Damage to the internal organs can cause severe internal bleeding, or hemorrhage.
2. Circulation blockage can also create many medical conditions from ischemia in the short term to tissue necrosis and gangrene in the long term.
3. Hemophilia is a genetic illness that causes dysfunction in one of the blood's clotting mechanisms. This can allow otherwise inconsequential wounds to be life-threatening, but more commonly results in hemarthrosis, or bleeding into joint spaces, which can be crippling.
4. Leukemia is a group of cancers of the blood-forming tissues.
5. Major blood loss, whether traumatic or not (e.g. during surgery), as well as certain blood diseases like anemia and thalassemia, can require blood transfusion. Several countries have blood banks to fill the demand for transfusable blood. A person receiving a blood transfusion must have a blood type compatible with that of the donor.
6. Blood is an important vector of infection. HIV, the virus which causes AIDS, is transmitted through contact between blood, semen, or the bodily secretions of an infected person. Hepatitis B and C are transmitted primarily through blood contact. Owing to blood-borne infections, bloodstained objects are treated as a biohazard.
7. Infection of the blood is bacteremia or sepsis. Malaria and trypanosomiasis are blood-borne parasitic infections.

Treatment
Blood transfusion is the most direct therapeutic use of blood. It is obtained from human donors by blood donation. As there are different blood types, and transfusion of the incorrect blood may cause severe complications, crossmatching is done to ascertain the correct type is transfused.

Other blood products administered intravenously are platelets, blood plasma, cryoprecipitate and specific coagulation factor concentrates.

Many forms of medication (from antibiotics to chemotherapy) are administered intravenously, as they are not readily or adequately absorbed by the digestive tract.

As stated above, some diseases are still treated by removing blood from the circulation.

Jehovah's Witnesses
Jehovah's Witnesses are prohibited from eating blood and accepting transfusions of whole blood or any of red cells, white cells, platelets or plasma. They are permitted to accept fractions, and the acute normovolemic hemodilution (ANH) and autologous blood salvage (cell saver) procedures.

Lecture IV

RED BLOOD CELL

Red blood cells are the most common type of blood cell and are the vertebrate body's principal means of delivering oxygen from the lungs or gills to body tissues via the blood.

Red blood cells are also known as RBCs or erythrocytes (from Greek erythros for "red" and kytos for "hollow," nowadays translated as "cell"). A schistocyte is a red blood cell undergoing fragmentation, or a fragmented part of a red blood cell.

Blood diseases involving the red blood cells include:

Anemias (or anemias) are diseases characterized by low oxygen transport capacity of the blood, because of low red cell count or some abnormality of the red blood cells or the hemoglobin.
Iron deficiency anemia is the most common anemia; it occurs when the dietary intake or absorption of iron is insufficient, and hemoglobin, which contains iron, cannot be formed.
Sickle-cell disease is a genetic disease, which leads to mis-shaped red blood cells.
Thalassemia is a genetic disease that results in the production of abnormal hemoglobin molecules.
Spherocytosis is a genetic disease that causes a defect in the red blood cell's cytoskeleton, causing the RBCs to be small, sphere-shaped, and fragile instead of donut-shaped and flexible.
Pernicious anemia is an autoimmune disease wherein the body lacks intrinsic factor, required to absorb vitamin B12 from food. Vitamin B12 is needed for the production of hemoglobin.
Aplastic anemia is caused by the inability of the bone marrow to produce blood cells.
Hemolysis is the general term for excessive breakdown of red blood cells. It can have several causes.
The malaria parasite spends part of its life-cycle in red blood cells, feeds on their hemoglobin and then breaks them apart, causing fever. Both sickle-cell disease and thalassemia are more common in malaria areas, because these mutations convey some protection against the parasite.
Polycythemias (or erythrocytoses) are diseases characterized by a surplus of red blood cells. The increased viscosity of the blood can cause a number of symptoms.
In polycythemia vera the increased number of red blood cells results from an abnormality in the bone marrow.
Several blood tests involve red blood cells, including the RBC count (the number of red blood cells per volume of blood) and the hematocrit (percentage of blood volume occupied by red blood cells). The blood type needs to be determined to prepare for a blood transfusion or an organ transplantation.

WHITE BLOOD CELL

White blood cells (also called leukocytes or immune cells) are a component of blood. They help to defend the body against infectious disease and foreign materials as part of the immune system. There are normally between 4x109 and 11x109 white blood cells in a litre of healthy adult blood - about 7 000 to 25 000 white blood cells per drop. In conditions such as leukemia this may rise to as many as 50 000 white blood cells in a single drop of blood. As well as in the blood, white cells are also found in large numbers in the lymphatic system, the spleen, and in other body tissues.

There are three major types of white blood cells.

Granulocytes
Granulocytes are a category of white blood cells, characterized by the fact that all types have differently staining granules in their cytoplasm on light microscopy. There are three types of granulocytes: neutrophils, basophils, and eosinophils (named according to their staining properties).

Lymphocytes
Lymphocytes are much more common in the lymphatic system, and include the so-called "killer T-cells". The blood has three types of lymphocytes: B cells, T cells and natural killer cells. B cells make antibodies that bind to pathogens to enable their destruction. CD4+ (helper) T cells co-ordinate the immune response (they are what becomes defective in an HIV infection). CD8+ (cytotoxic) T cells and natural killer cells are able to kill cells of the body that are infected by a virus.

Monocytes
Monocytes share the 'vacuum cleaner' function of neutrophils, but are much longer lived as they have an additional role. They present pieces of pathogens to T cells so that the pathogens may be recognized again and killed, or so that an antibody response may be mounted. Monocytes are also known as macrophages after they leave the bloodstream and enter tissue.

Diseases
Leukopenia is a disease symptom defined as a lower than normal number of white blood cells in the blood.
Leukocytosis refers to an increase in the number of white blood cells in the blood.
Leukemia and lymphoma are two types of cancer in which white blood cells multiply out of control.

Other tissue cells
Histiocytes, found in the lymphatic system and other body tissues, but not normally in blood:
Macrophages
Dendritic cells
Mast cells

PLATELETS

Platelets or thrombocytes are the blood cell fragments that are involved in the cellular mechanisms that lead to the formation of blood clots. Low levels or dysfunction predisposes for bleeding, while high levels - although usually asymptomatic - may increase the risk of thrombosis.

Production
Platelets are produced in the bone marrow; the progenitor cell for platelets is the megakaryocyte. This large, multinucleated cell sheds platelets into the circulation. Thrombopoietin (c-mpl ligand) is a hormone, mainly produced by the liver, that stimulates platelet production. It is bound to circulating platelets; if platelet levels are adequate, serum levels remain low. If the platelet count is decreased, more thrombopoietin circulates freely and increases marrow production.

Circulation
The circulating life of a platelet is 9-10 days. After this it is sequestered in the spleen. Decreased function (or absence) of the spleen may increase platelet counts, while hypersplenism (overactivity of the spleen, e.g. in Gaucher's disease or leukemia) may lead to increased elimination and hence low platelet counts.

Function
Platelets are activated when brought into contact with collagen (which is exposed when the endothelial blood vessel lining is damaged), thrombin (primarily through PAR-1), ADP, with receptors expressed on white blood cells or the endothelial cells of the blood vessels, among other activators. Once activated, they release a number of different coagulation factors and platelet activating factors, they also provide a catalytic phospholipid surface (with the charge provided by phosphatidylserine and phosphatidylethanolamine) for the tenase and prothrombinase complexes. The platelets adhere to each other via adhesion receptors or integrins, and to the endothelial cells in the wall of the blood vessel forming a haemostatic plug in conjunction with fibrin. The high concentration of myosin and actin filaments in platelets are stimulated to contract during aggregation, further reinforcing the plug. The most common platelet adhesion receptor is glycoprotein (GP) IIb/IIIa this is a calcium dependent receptor for fibrinogen, fibronectin, vitronectin, thrombospondin and von Willebrand factor (vWF). Other receptors include GPIb-V-IX complex (vWF) and GPVI (collagen)

Activators
There are many known platelet activators. They include

1. Collagen, especially with von Willebrand factor which is exposed when endothelial blood vessel lining is damaged and binds to GPVI on the platelet,
2. thrombin primarily through cleavage of the extracellular domain of PAR1 and PAR4,
3. Thromboxane A2 (TxA2) which binds to TP,
4. ADP through creation of TxA2, and it can be blocked by conversion of ADP to cAMP,
5. Human neutrophil elastase (HNE) cleaves the αIIbβ3 integrin on the platelet surface,
6. P-selectin which binds to PSGL-1 on endothelial cells and white blood cells, and
7. Convulxin (a purified protein from snake venom) which binds to GPVI.

Inhibitors
Prostacyclin opposes the actions of Thromboxane A2
Nitric oxide
Clotting factors II, IX, X, XI, XII
Nucleotidases by breaking down ADP

Role in disease
High and low counts
A normal platelet count in a healthy person is between 150 and 400 (x 109/L of blood).

Both thrombocytopenia (or thrombopenia) and thrombocytosis may present with coagulation problems. Generally, low platelet counts increase bleeding risks (although there are exceptions, e.g. Immune heparin-induced thrombocytopenia) and thrombocytosis (high counts) may lead to thrombosis (although this is mainly when the elevated count is due to myeloproliferative disorder).

Low platelet counts are generally not corrected by transfusion unless the patient is bleeding or the count has fallen below 5 (x 109/L); it is contraindicated in thrombotic thrombocytopenic purpura (TTP) as it fuels the coagulopathy. In patients having surgery, a level below 50 (x 109/L) is associated with abnormal surgical bleeding, and regional anesthetic procedures such as epidurals are avoided for levels below 80-100.

Note however that the actual platelet count is only part of the story, since they may not all be functioning normally. For example, aspirin irreversibly prevents platelets from working correctly and so normal hemostasis may not return until the aspirin is ceased and the affected platelets have been replaced by new ones, which may take over a week.

Diseases
Disorders leading to a reduced platelet count:
Thrombocytopenia
Idiopathic thrombocytopenic purpura
Thrombotic thrombocytopenic purpura
Drug-induced thrombocytopenia, e.g. heparin-induced thrombocytopenia (HIT)
Gaucher's disease
Aplastic anemia

Disorders leading to platelet dysfunction or reduced count:
HELLP syndrome
Hemolytic-uremic syndrome
Chemotherapy
Disorders featuring an elevated count:

Thrombocytosis, including benign essential thrombocytosis (elevated counts, either reactive or as an expression of myeloproliferative disease); may feature dysfunctional platelets

Disorders of platelet adhesion or aggregation:
Bernard-Soulier syndrome
Glanzmann's thrombasthenia
Scott's syndrome
von Willebrand disease

Disorders of platelet metabolism
Decreased cyclooxygenase activity, induced or congenital
Storage pool defects, acquired or congenital

Transfusion
Platelets are separated from donated blood using an apheresis blood separator. This is necessary because platelets will not survive at the low temperatures used to store red blood cells, so they must be stored separately using porous storage bags that allow oxygen to flow in and carbon dioxide to flow out. Typical storage is between 20 and 24 °C and continuously agitated to promote gas exchange. Because of the higher risks of bacterial growth at this temperature, platelets are generally only stored for up to 5 days.

A bag of platelets can be separated from multiple bags of whole blood or from a single donor connected to the separator for less than two hours. By drawing and returning blood repeatedly, a bag of high quality platelets can be prepared in about 90 minutes. Platelets collected from a single donor can reduce the infection rates of blood-transmitted diseases.

People with few platelets or platelets that are dysfunctional may benefit from a platelet transfusion, however patients with autoimmune disorders that affect platelets may not.

Neutrophil granulocytes
Neutrophil granulocytes, generally referred to as neutrophils, are a class of white blood cells and are part of the immune system.

Neutrophils are active phagocytes, capable of only one phagocytic event, expending all of their glucose reserves in an extremely vigorous respiratory burst. Low neutrophil granulocyte counts are termed "neutropenia". This can be congenital (genetic disorder) or due to acquired factors. It can also be a side-effect of medication, including chemotherapy.

Eosinophil granulocyte
Eosinophil granulocytes, commonly referred to as eosinophils (or less commonly as acidophils), are white blood cells that are responsible for combating infection by parasites in the body.

Eosinophils make up about 2.3% of the all white blood cells, and are about 10-12 micrometers in size.

Eosinophils play a role in fighting viral infections, which is evident from the abundance of RNAses they contain within their granules.

Eosinophils also play a role in the allergic response, and in fibrin removal in inflammation. Eosinophils are considered the main effector cells in asthma pathogenesis and are associated with disease severity.

Basophil granulocyte
Basophils are the least common of the granulocytes, representing about 1% of circulating leukocytes. Basophils tend to appear in specific kinds of inflammatory reactions, particularly those that cause allergic symptoms.

AF

Atrial fibrillation.

AS

Aortic stenosis.

ASD

Atrial septal defect.

A-V

Atrioventricular.

BP

B/P, blood pressure.

CABG

Coronary artery bypass graft.

CAD

Coronary artery disease.

CCU

Coronary/cardiac care unit.

CHD

Coronary heart disease.

CHF

Congestive heart failure.

CPK

Creatine phosphokinase.

CVP

Central venous pressure; normal range: 0 to 9 cm of water.

DOE

Dyspnea on exertion.

DSA

Digital substraction angiography.

DVT

Deep venous thrombosis.

ECC

Extracorporeal circulation.

ECHO

Echocardiogram.

EKG

Electrocardiogram (also ECG).

ETT

Exercise tolerance test.

HDL

High density lipoprotein.

LDH

Lactic dehydrogenase.

LDL

Cholesterol, low-density lipoprotein cholesterol.

LV

Left ventricle.

LVH

Left ventricular hypertrophy.

PAC

Premature atrial contraction.

PDA

Patent ductus arteriosus.

PND

Paroxysmal nocturnal dyspnea.

PTCA

Percutaneous transluminal coronary angioplasty.

PVC

Premature ventricular contraction.

SA

Sinoatrial node.

TPA

Tissue plasminogen activator.

VLDL

Very low density lipoprotein.

VSD

Ventricular septal defect.

VT

Ventricular tachycardia.