Current Affairs 11th Class

It is a part of venous circulation which is present between two groups of capillaries i.e. starts in capillaries and ends in capillaries. The vein which drains blood into organs other than heart is called portal vein. Types of portal system : It is of following types : (1) Hypothalamo-hypophysial portal system : Present in higher vertebrates (amphibia, reptiles, birds and mammals). Blood from hypothalamus is collected by hypophysial portal vein which ends in anterior lobe of pituitary gland. The superior hypophysial artery which bring blood into circle of willis bifurcate outside the lobe; one branch supplies the lobe itself, but the other one supplies the hypothalamus. The vein that drain the blood from hypothalamus then runs into pars distalis and divide into capillaries. Thus this is a portal vein called hypothalamo-hypophysial portal vein. Function : This portal system enables the releasing factors and inhibiting factors from hypothalamus to reach upto anterior pituitary.     (2) Hepatic portal system : Found in all chordates. In mammals, there is a single vein called hepatic portal vein, formed by the union of six main veins, which drain venous blood from different parts of alimentary canal (digestive system) into the liver. These veins are : (i) Posterior or Inferior mesenteric vein : Collect blood from rectal wall and anal region. This vein possess maximum diluted blood. Posterior mesenteric made up of by joining of 4 small veins that is rectal vein, sigmoid vein, left colonic vein and it opens into the splenic vein. (ii) Anterior or Superior mesenteric vein : Collect blood from wall of colon, caecum and small intestine. This vein possesses largest concentration of nutrients (glucose, amino-acid and vitamins). This vein formed by the joining of right colonic vein, ileocolic vein and appendicular vein. (iii) Splenic vein : Collect blood from spleen and pancreas, splenic vein possess free haemoglobin in large amount. (iv) Right gastric vein : Receives blood from stomach. (v) Left gastric vein : Receives blood from stomach and pancreas. (vi) Cystic vein : Receives blood from gall bladder. Posterior mesenteric vein open into splenic vein and splenic, anterior mesenteric, right gastric fused to form hepatic portal vein, which leads blood in to the liver. In amphibians (example - frog), hepatic portal system is formed of single hepatic portal vein and single anterior abdominal vein. The latter collects blood from leg region and drains it into the left lobe of liver. Significance of hepatic portal system : The hepatic portal system has following significance. (a) The blood which comes from the alimentary canal contains digested food like glucose and amino acids. The excess of glucose is converted into glycogen which is stored in the liver for later use. When an individual feels deficiency of food, the glycogen is converted into glucose and is transferred to the blood stream via hepatic veins. (b) Harmful nitrogenous waste like ammonia is converted into urea which is later removed more...

It is a part of greater circulation which begins in the tissue fluid with lymphatic capillaries which are always terminally closed. This system terminates into venous system near heart. The main components of this system are : (1) Lymph : Lymph can be defined as blood minus RBC's. In addition to the blood vascular system all vertebrate possess a lymphatic system. It is colourless or yellowish fluid present in the lymph vessels. It is a mobile connective tissue like blood and is formed by the filtration of blood. This process involves the diffusion of substances from blood capillaries into the interstitial space which is, thus, the primary site of lymph formation. Two forces bring about a steady filtration of plasma fluid into the tissue spaces : capillary pressure \[(30-35\,\,mm\text{ }Hg)\] and colloid osmotic pressure in tissue fluid (8 mm Hg). After absorption by veins, a small amount of \[C{{O}_{2}}\] and waste material still remains in the tissue fluid which is absorbed in the lymphatic capillaries as lymph. So, we can say that lymph is modified tissue fluid.   Differences between lymph and blood
S.No. Characters Blood Lymph
(1) RBC Present Absent
(2) Blood platelets Present Absent
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The form, structure and function of heart exhibits much variation. The characteristics of heart of fishes, amphibians, reptiles, birds and mammals is presented in the following table. Heart of vertebrates
S.No. Class of vertebrates Characteristics Example Diagram
1.  Pisces (= Branchial heart), Cyclostomata Thick, muscular, made of cardiac muscles, has two chambers (i) auricle and (ii) ventricle. The heart is called venous heart since it pumps deoxygenated blood to gills for oxygenation. This blood goes directly from gills to visceral organs (single circuit circulation). A sinus venosus and conus arteriosus is present. Lung fishes have only one auricles and one ventricle. Labeo Scoliodon  
2. Amphibians, Lung fish Heart consists of : (i) Two auricles (ii) Undivided ventricle (iii) Sinus venosus (iv) Truncus arteriosus (conus + proximal part of aorta) Right auricle receives blood from all the visceral organs (deoxygenated) via precaval and post caval. Pulmonary artery carries deoxygenated blood to more...
A graphic record of electrical events occuring during a cardiac cycle is called Electrocardiogram. The instrument used for recording the heart’s electrical variations is called Electrocardiograph in which the potential differences of heart muscles are recorded by a galvanometer. In ECG, there are 2 types of waves : (1) Depolarisation waves : They represent the generation of the potential difference. These waves appear only when both electrodes of galvanometer are in different fields. When both the electrodes are in same field, there is no deflection and wave drops down to base line. (2) Repolarisation waves : They appear when depolarisation is over and the muscle fibre is returning to its original polarity. When both electrodes are in same polarity (means 100% repolarisation and 100% depolarisation), there is no deflection. A normal ECG has 5 deflection waves \[P,Q,R,S\] and T. Out of them \[P,R\] and T waves are above the base line and are called positive waves. The Q and S waves are below base line and are called negative waves. The part of the base line between any 2 deflections is called Interval. P wave : Indicates impulse of contraction generated by S.A. node and its spread in atria causing atrial depolarisation. The interval PQ represents atrial contraction and takes 0.1 second. QRS complex : Indicates spread of impulse of contraction from A.V node to the wall of ventricles through bundle of His and purkinje fibres causing ventricular depolarisation. This complex also represents repolarization of S.A. node. The RS of QRS wave and ST interval show ventricular contraction (0.3 seconds). QRS is related to ventricular systole. T wave : Indicates repolarisation during ventricular relaxation. Any abnormality in the working of heart alters the wave pattern of ECG. Thus, ECG is of great diagnostic value in cardiac diseases. ECG also indicates the rate of heart beat  

During the completion of one heart beat is called as cardiac cycle. Following events are repeated in a cyclic manner during each heart beat. (1) Auricular systole : The atria contract due to wave of contraction stimulated by S.A. node contraction of auricles drives most of their blood into respective ventricles as the A.V. valves are open. There is no backflow of blood into the large veins as the contraction begins at the upper end and passes towards ventricles and moreover, the valves present at the opening of these veins close. Also, blood is already present in large veins which offers resistance to the blood that may return from the atria. At the end of a atrial systole, there starts the relaxation of auricles (auricular diastole) and contraction of ventricles (ventricular systole) simultaneously. Atrial systole takes 0.1 second while atrial diastole is of about 0.7 seconds. (2) Ventricular systole : The ventricles begin to contract due to a wave of contraction stimulated by A.V. node. Due to ventricular systole, the pressure of blood in ventricles immediately rises above that in the auricles. With this pressure, the bicuspid and tricuspid valves close rapidly to prevent the backflow of blood. This closure of A.V. valves at the start of ventricular systole produces first heart sound called “Lubb” or Systolic sound. The semilunar valves are also close at this time. When the pressure of blood in the ventricles exceeds that in the great arteries, the semilunar valves open and blood enters into the great arteries. This marks the end of ventricular systole which takes about 0.3 seconds. Now the ventricles start relaxing (ventricular diastole which lasts for about 0.5 sec.) (3) Joint diastole : The ventricles and auricles are in the diastolic phase simultaneously. As the ventricular diastole progresses, the pressure in the ventricles falls below that in the great arteries. So, to prevent backflow of blood from great arteries into ventricles, the semilunar valves close rapidly. This rapid closure of semilunar valves at the beginning of ventricular diastole produces second heart sound “Dup” or diastolic sound. The quality of heart sounds indicates the state of the heart valves. Defective or damaged heart valves lead to the backflow of blood either from ventricles to auricles or from aortae to ventricles. Such defects are detectable as abnormal hissing sound called “Murmur”. Defective valves may be replaced or repaired surgically. Syphilis and Rheumatic fever cause Murmur. The instrument used to magnify and record the heart sound is called Phonocardiogram. During joint diastole, blood from great veins and coronary sinus flows into the atria and some blood also passes from auricles into the respective relaxing ventricles due to less pressure in ventricles. This phase takes only 0.4 seconds and is also called as blood receiving period of heart. Thus a cardiac cycle is completed in 0.8 seconds. Cardiac output : Volume of blood pumped from heart (left ventricle) into the systemic aorta in one minute is called cardiac output. It is also called minute volume. It more...

The study of blood vessels is called Angiology. The blood vessels are of following types : (1) Arteries : Thick walled, carrying oxygenated blood (deoxygenated in pulmonary artery) from heart to various parts of body. These blood vessels are grouped as Aorta which branches to form arteries which further divides into thinner branches called arterioles inside the organ. Average diameter of arteriole is \[120\,\,\mu m\] the arterioles further divide into smaller vessels called meta-arterioles \[(70\,\,\mu m)\] which divide into capillaries. At the beginning of capillary, the arterioles posses circular muscles called precapillary sphincter which regulates flow of blood into the capillaries which is called vasomotion. Smooth muscles of arteries innervated by sympathetic fibers, their stimulation control vasoconstriction and vasodilation. Smooth muscles of arteries and arterioles also limit bleeding from wounds by producing vascular spasm during cut. Arteries two types. (i) Conducting or elastic arteries (ii) Distributing or muscular arteries. Elastic or conducting arteries receive blood from heart and do not provide it to any organ rather they provide blood to other atreries and are pressure reservoirs of blood. Muscleless end of meta-arteriole is called thoroughfare channel or preferential channel. The largest artery is dorsal / abdominal aorta (systemic aorta).
  • Anastomosis : If more than one arteries are supplying to one organ then branches of these arteries unite to form a network called Anastomosis. It provides many collateral or alternate pathways of blood supply. So, if there is blocking of any artery, it will not lead to necrosis.
(2) Capillaries : Smallest blood vessels, discovered by Marcello Malpighi (also layered nucleated squamous epithelial cells called endothelium resting on a basement membrane. Diameter of capillary is about 8m. These are also called as exchange vessels as they are the site of exchange of material between blood and tissue because of least barrier in them. The capillaries can be grouped into two categories : (i) Arteriolar capillary : Which supplies nutrition, respiratory gases etc. to the body cells. (ii) Veinular capillaries : Which collect the metabolic wastes from the body cells. Capillaries possess about 7% of total body blood and are present near almost all cells of body in the intercellular spaces. The tissues which are devoid of intercellular spaces are also devoid of capillary. They are called avascular tissues. Capillaries are surrounded by cells of connective tissue called pericapillary cells. Some of these cells are contractile and phagocytic in nature and are called Rouget cells or pericytes. Continuous capillaries are without fenestra/aperture, hence are less permeable. These are present in organs such as lungs, muscles, connective tissues and brain tissues. Fenestrated capillaries possess apertures/fenestra and are found in those organs where there is maximum need of permeability such as endocrine glands, intestinal villi, cavities of brain, kidney, ciliary body of eye. Sinusoids are irregularly dilated capillaries found in organs where there is decrease in flow rate such as liver, spleen, bone marrow, parathyroid, pituitary gland. In liver, sinusoids are branches of venules and open into venules while more...

Blood circulation was discovered by William harvey. In case of vertebrates, blood circulation is of closed type, which can be grouped into two categories : (1) Single circulation                                                                        (2) Double circulation   Differences between single and double circulation
S.N. Single circulation Double circulation
1. Blood flows only once through the heart in a complete cycle. Blood flows in two circuit pulmonary and systemic.
2. Heart pumps only deoxygenated blood, hence called Venous Heart. Heart pumps both deoxygenated and oxygenated blood to lungs and body respectively, hence called arteriovenous heart.
3. Blood is oxygenated in gills. Blood is oxygenated in lungs.
4. Less efficient as gill capillaries slow down the blood flow. more...
The physiology of blood circulation was first described by Sir William Harvey in 1628. The blood circulation in our body is divisible into 3 circuits - (1) Coronary circulation : It involves blood supply to the heart wall and also drainage of the heart wall. (i) Coronary arteries : One pair, arising from the aortic arch just above the semilunar valves. They break up into capillaries to supply oxygenated blood to the heart wall. (ii) Coronary veins : Numerous, collecting deoxygenated blood from the heart wall and drains it into right auricle through coronary sinus which is formed by joining of most of the coronary veins. But some very fine coronary veins, called venae cordis minimae open directly in the right auricle by small sized openings called foramina of Thebesius. (2) Pulmonary circulation : It includes circulation between heart and lungs. The right ventricle pumps deoxygenated blood into a single, thick vessel called pulmonary aorta which ascends upward and outside heart gets divided into longer, right and shorter, left pulmonary arteries running to the respective lungs where oxygenation of blood takes place. The oxygenated blood from lungs is returned to the left auricle by four pulmonary veins. Left auricle pumps this blood into the left ventricle. (3) Systemic circulation : In this, circulation of blood occurs between heart and body organs. The left ventricle pumps the oxygenated blood into systemic arch which supplies it to the body organs other than lungs through a number of arteries. The deoxygenated blood from these organs is returned to the right auricle through two large veins (precaval and post caval). Right auricle pumps this blood into the right ventricle. Thus, the sytemic circulation involves two circuits - Arterial system It involves aorta, arteries, arterioles and meta-arterioles. It supplies oxygenated blood to all parts of the body except lungs. The left ventricle of the heart pumps the oxygenated blood into a single, question marked shaped, long vessel called left carotid-systemic aorta. It is the largest blood vessel of the body. After ascending from the heart, the systemic aotra turns and descends down to the level of lower border of fourth lumbar vertebra. At its distal extremity, it bifurcates into right and left common iliac arteries. The sytemic aorta has following parts - (1) Ascending aorta : It gives off left and right coronary arteries. Brachiocephalic (innominate) : Unpaired, largest branch of the aorta divides into right subclavian towards right side and right common carotid towards left side. Right subclavian gives off vertebral artery (supplies to head and part of right shoulder) and then enters into right arm, now called axillary artery or brachial artery, which divides into ulnar and radial arteries in the region of elbow. The right common carotid, enters into head and divides into external and internal carotids which supply the right parts of head by their branches. Left common carotid : Unpaired artery, enters into head and divides into left external and internal carotids which supply the left parts of the head more...

Human respiratory system is derived from endoderm. Human respiratory system may be divided into two components- (1) Respiratory tract or conducting portion                           (2) Respiratory organs (1) Respiratory tract or conducting portion : It is the passage for the air. In this part gaseous exchange does not takes place. It is also called dead air space. It is divided in following parts*-answer-* (i) Nose (Latin-Nasa) (Greek-Rhine) : Cavity of nose is called nasal cavity. Nasal cavity is divided into two parts by nasal septum called mesethmoid. Each part is called nasal chamber. Each nasal chamber opens out side by external nares. Nasal septum has two part. First part is small and is made of cartilage (hyaline). Second part is major and it is bony. Vomer is the main bone. Each nasal chamber has three region. (a) Vestibular region : Vestibular region also known as vestibule, lined by non keratinized squamous epithelium, it is ectodermal in origin  and have sebaceous gland, sweat gland and hair. Vestibule is also found in inner air larynx, mouth and vagina. It acts like a seive to check the entry of large dust particles and other things. (b) Respiratory region : Middle region lined by respiratory epithelium which is ciliated pseudostratified columnar epithelium. It contains mucus and serous cells. Mucus cells produce mucus and serous cells produce watery fluid. Respiratory epithelium is highly vascular and appears pink or reddish. Respiratory region acts as a air conditioner and makes the temperature of in going air nearly equal to body. It also acts as a filter not give entry to dust particles, flies or mosquitoes. (c) Olfactory region : It is upper region. It is lined by olfactory epithelium. This is also called Schneiderian epithelium. Olfactory region is the organ of smell and detect the odour of inspired air. Inspiration is stopped if odour of air is foul or offensive. According to new researches pheromone receptors are found in nasal cavities. (ii) Nasal conchae : Lateral wall of nasal cavity have three shelves like structures called conchae or turbinate. 3 pairs of nasal conchae are found. Nasal conchae are covered with mucus membrane. They increase the surface of nasal chamber. Both the chambers of nasal cavity open into nasopharynx by their apertures called internal nostrils or conchae. Adjacent to internal nostril there are opening of eustachian tube. Names of these three conchae and names of the bones that form them are given below. (a) Superior conchae : The dorsal most chochae is supported mainly by nasal bone called nasoturbinate. It is the smallest conchae. (b) Middle conchae : Ethmoid bone called ethmoturbinate. (c) Inferior conchae : The ventral most conchae supported by maxilla bone called maxilloturbinate. It is a separate bone itself. (iii) Pharynx : It is the short vertical about 12 cm long tube. The food and air passages cross here. It can be divided in 3 parts - (a) Nasopharynx : Nasopharynx is only respiratory upper part in which internal nares open. There are 5 opening in more...

In men the respiratory organ are a pair of lung. Some snakes have unpaired lungs. Respiration by lungs is called pulmonary respiration. Lungs are found in all vertebrates except fishes. In Lung fishes such as protopterus, neoceratodus and lepidosiren air bladder is found, which is modified lung. Respiration in men and rabbit is pulmonary. Lungs : Lungs lie in thoracic cavity on both side of heart in mediasternum space. Base of lung is attached to diaphragm. Right lung is divided into 3 lobes viz. Superior, Middle, Inferior and left lung is divided into two lobes Superior and Inferior. In rabbit, the left lung is divided into two lobes left anterior and left posterior where as the right lung has four lobes anterior azygous, right anterior, right posterior and posterior azygous. Lungs of reptiles are more complex than those of amphibians. In birds lungs are supplemented by elastic air sacs which increase respiratory efficiency. The narrow superior partion of lung is termed the apex or cupula.     Each lung is enclosed in two membrane called pleura. Pleura are layers of peritonium of thorax. Inner membrane is called the visceral pleuron. It is firmly bound to surface of lungs. The outer membrane is called parietal pleuron. It is attached to chest wall or wall of thoracic cavity. A narrow space exists between the two pleura. It is called pleural cavity. In pleural cavity a watery fluid is found called pleural fluid. Pleural fluid is glycoprotein in nature and secreted by pleura. Pleural fluid lubricate the pleura so that they may slide over each other without friction. This fluids reduces friction bewteen the membrane. When the lungs expand and contract in respiration. Pressure inside pleural cavity is negative - 5 mm Hg. Plurisy is inflamation of pleura and cause collection of fluid in pleural cavity. It results painful breathing (dyspnea). The surface of lung lying against the ribs, known as coastal surface. The mediastinal (medial) surface of each lung contains a region - the hilus, through which bronchi, pulmonary blood vessels, lymphatic vessels and nerve enter and exit.     Pulmonary volumes and capacities The apparatus commonly used to measure the volume of air exchanged during breathing and the rate of ventilation is a spirometer (spiro=breathe) or respirometer. The record is called a spirogram. There are 4 respiratory volumes and capacity. Respiratory volumes (1) Tidal volume (TV) : Volume of air inspired or expired in relaxed or resting position – 500 ml. It consists of 150 ml of dead space volume and 350 ml of alveolar volume. (2) Inspiratory reserve volume (IRV) : By taking a very deep breath, you can inspire a good deal more than 500 ml. This additional inhaled air, called IRV is about 3000 ml. (3) Expiratory reserve volume (ERV) : If you inhale normally & then exhale as forcibly more...



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