Heart

The blood is kept in constant circulation through the cardiovascular system. The cardio vascular system consists of two units, a pumping organ called the heart and system of canals consisting of arteries, veins and capillaries. The heart in fact, has two types of chambers, the receiving chamber called auricle (atrium) and the distributing chamber called ventricle. The left auricle receives purified blood from the lungs and empties into the left ventricle.

Valves

1.   Right atrioventricular or tricuspid valve-composed of three cusps, situated in the right ventricle

2.  Left atrioventricular or bicuspid, or mitral, valve-composed of two thick cusps, situated in the left ventricle

The Function of these valves is to prevent flow of blood from ventricles into atria

Semilunar valves. Basically of two types Aortic and Pulmonary and the Function is to prevent flow of blood fron arteries into ventricles

The left ventricle distributes blood to the various organs and tissues through the blood vessels called arteries. These having thick, elastic walls, which can contract. On reaching the concerned organ each artery divides into arterioles of smaller dimensions. Here the blood gives off its nutrients and oxygen and collects carbon dioxide and waste materials from the tissues through diffusion. This is possible because the walls of the capillaries are extremely thin. The blood that has become impure due to the collection of waste materials is now collected from the tissue by a set of blood vessels called veins. Several veins from different organs join to form venous trunks or venae cavae. The two venae cavae empty the deoxygenated blood into the right auricle. From right auricle the blood is passed into the right ventricle, which pumps it to the lungs for oxygenation. The oxygenated blood returns to the left auricle thus the circuit is completed.

Cardiac cycle

Coordinated contraction of cardiac muscle               

1.    Systole-contraction           

2.    Diastole-dilatation            

3.    Rest-quiescent                   

Cardiac cycle, 70-72 per minute

Occupies about 0.8 second

Systolic and rest period each about 0.4  second

Heart Sounds                       

First -caused by closure of atrioventricular valves and contractions of the ventricles

Second-caused by closure of the Semilunar valves.

Pulse Rate: Factors, which influence heartbeat, also influence pulse. Average 65-70 in men and 70-80 in women. Rate of pulse to respiration is about 4 to 1

Blood Pressure                    

Systolic-greatest pressure which contractions of heart cause. A verage systolic pressure in brachial artery of adult, 110-120mm.

Diastolic-lowest point to which blood pressure drops between beats average diastolic pressure in brachial artery of adult, 65-80mm

Blood Pressure is determined by use of sphygmomanometer. Pulse Pressure is  difference between systolic and diastolic pressure

Heart Diseases

They can arise from congenital defects, infection, narrowing of the coronary arteries, high blood pressure, or disturbances of heart rhythm.

Rheumatic heart disease was formerly one of the most serious forms of heart disease of childhood and adolescence, involving damage to the entire heart and its membranes. It usually followed attacks of rheumatic fever. Widespread use of antibiotics effective against the streptococcal bacterium that causes rheumatic fever has greatly reduced the incidence of this condition.

Myocarditis is inflammation or degeneration of the heart muscle.

The major form of heart disease is atherosclerosis. In this condition fatty deposits called plaque, composed of cholesterol and fats, build up on the inner wall of the coronary arteries. Gradual narrowing of the arteries throughout life restricts the blood flow to the heart muscles. Symptoms of this restricted blood flow can include shortness of breath, especially during exercise, and a tightening pain in the chest called angina pectoris. The plaque may become large enough to completely obstruct the coronary artery, causing a sudden decrease in oxygen supply to the heart. Obstruction, also called occlusion, can occur when part of the plaque breaks away and lodges farther along in the artery, a process called thrombosis. These events are the major causes of heart attack, or myocardial infarction, which is often fatal.

The immediate cause of death in many heart attacks, whether atherosclerosis is present or not, is ventricular fibrillation, also called cardiac arrest. This is a rapid ineffective beating of the ventricles. Normal heart rhythm can often be restored by a massive electric shock to the chest, a finding that has led to emergency rescue teams in many cities being trained in this technique.

Severe defects, however, in the sinoatrial node or in the fibers that transmit impulses to the heart muscle can cause dizziness, faintness, and eventually death. The most serious of these conditions is called complete heart block. It can be corrected by insertion of an artificial pacemaker, a device that gives timed electric shocks to make the heart muscle contract in a regular pattern.

Often found among older persons is cor pulmonale, or pulmonary heart disease, which usually is the result of a lung ailment, such as emphysema, or a disease affecting circulation to the lungs, such as arteriosclerosis of the pulmonary artery. Another condition found in older persons is congestive heart failure, in which the ventricles pump much less efficiently. The muscular walls of the ventricles enlarge with the effort to propel more of the blood into the circulation, giving rise to the large, floppy hearts characteristic of this syndrome. Persons with this ailment have a reduced capacity for exercise. Their condition can often be improved with one of the derivatives of digitalis, which increases the pumping efficiency of the heart.

Heart Transplants

In 1967, South African surgeon Christiaan Barnard performed the first such transplant. Because most patients were dying soon after a transplant, however, the number of operations dropped. The major problem was the body’s natural tendency to reject tissues from another individual. In Palo Alto, California, the surgeon Norman Shumway persisted in working on this problem, and in the early 1980s he and his colleagues could report that more than half of all cardiac transplant recipients were living beyond one year. Pharmaceutical aids such as cyclosporine are helping to reduce the immune reaction.

Artificial Hearts

Artificial hearts have been under development since the 1950s. In 1966 Dr. Michael Ellis DeBakey successfully implanted a booster pump for the first time as a temporary measure; at least one such pump continued to work for several years. In 1969 Dr. Denton Cooley implanted the first completely artificial heart in a human, again on a temporary basis. The first permanent artificial heart, designed by Dr. Robert Jarvik, was implanted in 1982 in a patient who lived for three months thereafter. A number of patients have received Jarvik and other artificial hearts since that time, but surviving recipients thus far have tended to suffer strokes and related problems.

BLOOD

Blood is a fluid connective tissue. In a healthy person, about 5.6 liters of blood is present generally, there is about 90 ml of blood per kilogram of body weight. However this volume depends on the age and health of the individual. It has a pH of 7.4 Blood consists of various cells and cell products floating in a watery substances called plasma. The plasma form 54% of the blood volume and the cells 45%. Plasma is straw-coloured fluid, which is composed mainly of water with a large number of proteins called plasma proteins. The plasma proteins help in retaining water, in clotting of blood at the site of injury and in combating disease producing organisms. The plasma also contains sugars, salts, amino acids, oxygen and other substances useful to cells. The waste products of cells such as urea, CO2 and others are also present in plasma.

The formed elements of blood consist of Red Blood Corpuscles (RBC) or erythrocytes, white Blood corpuscles (WBC) or leucocytes, platelets or thrombocytes. The RBCs are more in number in blood. Each cubic millimeter of blood contains about 5 million RBCs. They are produced in bone marrow. By the time they reach the blood stream and lose their nuclei. It gives them a bi concave shape increasing their surface area and consequently the ability to absorb oxygen and carbondioxide. Each RBC is a tiny bag of hemoglobin, which can carry oxygen or CO2. The Camel erythrocytes possess nuclei. The average life span of an erythrocyte in man is about 120 days. The erythrocytes are destroyed by the phagocytic macrophages found in the bone marrow, spleen and liver etc. Most of the Iron of destroyed RBC is retained in the bone marrow to be again incorporated into new erythrocytes. The WBC are less in number about 5000 to 7000 in one cubic millimeter of blood. An increase in the number of leucocytes of blood is known as leucocytosis and fall below is referred to as leucopenia. Leucocytosis is caused by violent exercise, infection, hemorrhage and a high protein diet. Leucopenia results from malnutrition, deficiency of B12, folic acid and pyridoxin. The WBC are formed in bone marrow, lymph nodes and spleen. They are of different types. They protect the body against infection and diseases. The average life span of leucocytes is 48 hours. The leucocytes form antibodies against proteinanceous matter gaining entry into the body. In addition to RBCs and WBCs blood also contains small cell fragments called blood platelets. These blood platelets help in clotting of blood at the site of injury. The life span is very short, only a few days.

Functions of Blood

• Carries oxygen from lungs to tissue

• Carries carbon dioxide from tissues to lungs

• Carries food material to tissues

• Carries hormones and internal secretions

• Carries waste products to organs of excretion

• Aids in maintaining normal temperature

• Aids in maintaining acid-base balance of tissues

• White cells and globulins constitute defense mechanism against infection

• Aids in maintaining internal fluid pressure

• Clots, preventing loss of blood after trauma.

BLOOD GROUPS

When more than 40 percent of the blood is lost over a short period of time the body is usually unable to repair the loss. Some artificial means of replacing the lost fluid must be resorted. The intravenous injection of blood, plasma or serum with the object of restoring the blood volume is called transfusion.

Blood is usually taken from a healthy individual (the donor) and given to a patient known as recipient. However, blood cannot be taken indiscriminately from any person and transferred into any other. Great care must be exercised in the choice of the donor since the blood of the donor and of the recipient may not mix and may result in its clotting and death of the recipient. The types of blood which when mixed behave in this way are termed incompatible.

‘Landsteiner’ and his co-workers divided the entire human population into four major groups according to the reaction of their blood when mixed together. The four types of blood are named A, B, AB and O depending upon the presence of antigen in R.B.C. No antigen is present in ‘O’ blood group. Therefore it is not clotted by any other type of blood group. Since the people having blood group O can donate their blood to any person, therefore are known as universal donor. People with the ‘AB types’ of blood are universal recipients. Anticoagulants are added so that blood does not clot.

The approximate distribution of blood groups among Hindus in India is as follows, A 24%, B 38%, AB 8% and O 30%. A very interesting example of blood groups of human population are natives of Peru. They are cent-percent of group ‘O’.

Rh factors

The Rh factor is a type of blood protein, which was found for the first time in the blood of the rhesus monkey. If the factor is present in the blood, the blood is called Rh positive. If absent then it is Rh negative. If the mother is Rh -ve and the father Rh +ve and the baby is Rh +ve, the Rh +ve factor goes from the body of the baby to the circulation of the mother and causes formation of antibodies against Rh +ve factor. The anti Rh +ve protein enters the baby’s blood which coagulates resulting in the death of the baby. This disease is called erythroblastosis feotalis.

Coagulation of Blood

When a blood vessel is cut or ruptured, the blood coming out of it soon changes into a red gelatinous mass known as the clot. This mass slowly contracts leaving a yellowish fluid known as serum. Serum is fluid left behind after the formation of the clot. If the clot is examined under the microscope its shows agglutinated blood cells entrapped in a fine network of thin fibrillar structure the fibrils.

Fibrin is produced from a plasma protein fibrinogen. Fibrinogen is converted to fibrin by the action of thrombin, which exists in the plasma in the form of prothrombin. Prothrombin is converted into thrombin by the action of thromboplastin and Ca++. The coagulation of blood requires altogether the interaction of thirteen chemically identifiable substances, which have been called blood-clotting factors.

Blood related diseases

Leukemia: This is a form of blood cancer and is characterized by an uncontrolled increase in the number of leucocytes with the appearance of immature forms in the blood stream. Leukemia is accompanied by anemia and is eventually fatal because the bone marrow cell that normally produce erythrocytes are displaced by leukemia cells.

Hemophilia: Hemophilia is characterized by severe hemorrhage even after relatively minor injuries by bleeding in the joints. The times of clotting which is usually 3-6 minutes in normal individuals may extent up to several hours in case of hemophilia patients. Hemophilia is a sex-linked disease and appears exclusively in males. It is carried by the absence of factor VIII (Antihemophilic globulin AHG). The gene for hemophilia is carried by X-chromosome and in the female its action is countered by the presence of the other heterochromosome X. As such hemophilia does not appear in the female but she can transmit it, she is called the carrier. In male the action of hemophilia gene is not counteracted and the individual exhibits hemophilia. The often-quoted example of sex-linked hemophilia patients is the descendants of Queen Victoria of England.

Excretory System

Excretion is the process by which the metabolic waste products formed as a result of anabolism and catabolism are eliminated from the body. Some of these waste products may become toxic if they accumulate beyond a certain concentration An important requisite for the continuation of life therefore is the removal of metabolic waste products such as ammonia, urea etc and the organs concerned with this function are called excretory organs. In addition to the kidney, the skin, lung, intestine and liver also eliminate metabolic waste products directly or indirectly. The removal of carbon dioxide from the lungs is also an e excretory process. Nitrogenous wastes i.e. ammonia, urea and uric acid are derived from catabolism of dietary proteins.

Excretory Mechanism in Humans

Urine formation: The formation of urine involves three processes:

(i)    Glomerular filtration

(ii)   Reabsorption of useful substances back into the blood.

(iii)  Secretion of nitrogenous wastes into the lumen of the tubule.

(i)    Glomerular filtration: The first step in urine formation is the filtration of blood. A large volume of blood flows through the kidneys. The energy for filtration is derived from the hydrostatic pressure of the blood; a severe fall in the blood pressure would reduce renal filtration. The glomerular filtration rate in a normal adult is 120 ml/min. The average volume of fluid filtered from the plasma into Bowman’s capsule is about 170 litres/day. The ultraliltrate has the same composition as the blood minus the cells and proteins. The presence of the RBCs and proteins in the urine indicates a defect in the filtration apparatus.

(ii)   Reabsorption: The cells of the renal tubules are epithelial cells of pyramidal shape with a typical brush border in the proximal convoluted tubule narrowing down to very flat cells in the loop of henle. The proximal convoluted tubules are responsible for the reabsorption of water, glucose, potassium, phosphate, bicarbonate and sodium. Normal urine therefore contains no glucose. The reabsorption of water is partly under the control of antidiuretic hormones (ADH) secreted by the posterior pituitary. When the blood is diluted as by ingestion of large amount of water, the osmoreceptors in the hypothalamic region of the brain detect the decrease in osmolarity of the blood and transmit impulses to the pituitary glands and secretion of ADH is inhibited. The output of the urine is increased and a large volume of water is excreted and vice versa.

The proximal tubule reabsorbs potassium, phosphate, and bicarbonate. The kidney thus, regulates the amount of acid and base in the blood and consequently its pH.

(iii)  Tubular secretion: The loop of henle is active in reabsorbing water and in secreting urea the chief form of soluble nitrogenous waste in man. The concentration of urea is higher than that found in the blood. The distal convoluted tubule is the region where water and sodium are finally reabsorbed against the concentration gradient into their lumen.

Equilibrium of water and salt

The excretion of water is regulated by Altre, whereas the control of sodium excretion depends upon its reabsorption. The reabsorption is controlled by a hormone called rennin produced by the kidney. Animals living in seawater with high salt concentration face the problem of conserving water. They can resist the changes in salt concentration of the seawater by making adjustments. This is called osmoregulation.

Osmoregulation or fluid control in the body: The total amount of body water is maintained with great accuracy. The human body has 50-70% water. The percentage of water forms about 8% of the total body water. Fluid is lost from the body through sweating, respiration, urination and defecation but the major source of fluid loss is urine.

Kidney

Kidney, one of a pair of glands, whose function is the elaboration and excretion of the urine.

Structure

In humans, kidneys are situated in the region of the loins, one on each side of the spine, and are embedded in fatty tissue. They are bean-shaped, possessing a convex outer border and a concave inner border. The inner border presents an indentation, the hilum, at which the blood vessels enter and leave. In front is the renal vein carrying blood from the kidney; behind it lies the renal artery carrying blood to the kidney. Most posterior is the ureter, a tube that conveys urine to the bladder. The hilum arises from a deeper indentation, the sinus of the kidney, in which the ureter dilates to form a small sac, the pelvis. The kidney also embodies glomeruli, aggregations or loops of capillaries enclosed within thin envelopes of endothelial lining called Bowman’s capsules, located at the blind beginning ends of the renal tubules.

Functions of the kidney

(1)   The kidney not only removes the waste products from the body but also plays a very important role in maintaining a constant composition of the blood.

(2)   Urine is acidic in nature, the kidneys perform an important function in selectively filtering out the acidic substances from the blood into the urine and maintain the correct pH balance.

(3)   The kidneys also regulate the loss of excess water from the body.

Diseases of the Kidney

Nephritis, or inflammation of the kidney

Nephrosclerosis, or hardening of the small arteries supplying blood to the kidney, is a disorder characterized by the presence of albumin, casts, and occasionally white or red blood cells in the urine;

Renal calculi, or stones in the kidney, may form in the kidney or renal pelvis from crystals deposited from the urine. They are composed mostly of calcium oxalate. Infection or obstruction may play a part in their formation.

Uremia is a poisoning caused by accumulation in the blood of waste products normally excreted by the kidney.

Pyelonephritis is an infection of the kidney with bacteria.

Of the tumors of the kidney, Wilms’s tumor, a highly malignant form, is most frequent in young children.

In systemic lupus erythematosus, which tends to strike women in their 30s more than other groups, the body makes antibodies that damage the kidney.

Other organs of Excretion in Man

(a)   Skin: The skin acts as an organ of excretion with the help of the sweat glands present in it. These glands remove water, urea and some salts from blood and excrete them on the surface of the skin.

(b)   Lungs: The lungs are the chief organs or respiration; they absorb oxygen and eliminate CO2.

(c)   Intestine: The intestinal epithelial cells plays a minor role on excretion. These cells excrete certain salts for example those of calcium and iron.

(d)   Liver: It may be considered as an accessory excretory organ because it plays only a minor role in excreting waste products directly from the body. Urea the chief introgenous waste material in the human body is formed in the liver.