Current Affairs 11th Class

The fluid and dissolved waste substances excreted by the kidneys constitute urine. Quantity : An adult man normally passes about 1 to 1.8 litres of urine in 24 hours. The volume of urine depends upon (i) the fluid intake, (ii) level of physical activity, (iii) type of food taken and (iv) environmental temperature increase urine output. Less fluid intake and profuse sweating due to heavy physical work and high temperature reduce urine output. Certain substances, such as tea, coffee and alcohol, increase urine output. These are said to be diuretic. Physical properties : Urine is transparent yellowish fluid, but becomes turbid (cloudy) on standing, its colour depending on its concentration. Its colour is due to a pigment urochrome derived from the breakdown of haemoglobin from the worn-out RBCs. Colour of the urine is altered by certain materials taken such as beet, vitamin B complex and some drugs diseases. It is hypertonic to blood plasma. Its specific gravity ranges between 1.001 to 1.035, being slightly higher than that of water. Its pH is 6. It depends on the diet. High protein food and fruits increase acidity whereas vegetables increase alkalinity. Urine has a characteristic unpleasant odour. If allowed to stand, urea is degraded by bacteria to ammonia which imparts a strong smell to urine. Chemical composition : Urine consists of water and organic and inorganic substances. Water alone forms about 95% of it, other substances form only 5%. The organic substances are mainly nitrogenous organic compounds include urea, uric acid, creatinine and hippuric acid. Of these, urea is the principal component of human urine. The non nitrogenous organic compounds include vitamin C, oxalic acid, phenolic substances include ammonia, and mineral salts such as chlorides, sulphates and phosphates of sodium, potassium, calcium and magnesium. Sodium chloride is the principal mineral salt of the urine. Urine also contains some other substances, such as pigments and drugs, and some epithelial cells, leucocytes, mucin, enzymes, and hormones. Abnormal materials : Presence of proteins (albumins), bile salts, bile pigments, ketone bodies, blood, pus, microbes and more than a trace of glucose in the urine is pathological condition. Presence of glucose, protein, blood, ketone bodies and pus in the urine is called glucosurea, proteinuria, haematuria, ketonuria and pyuria respectively. Renal threshold : A negligible amount of glucose is present in the urine. The highest concentration of a substances in the blood upto which it is fully reabsorbed from the glomerular filtrate is called its threshold. If its concentration in the blood exceeds its renal threshold, some of the filtered out substance is not reasborbed and is excreted in the urine. For example, the renal threshold of glucose is 180 mg. per 100 ml. of blood. If its blood level exceeds 180 mg., some of the filtered out glucose is not reabsorbed and is passed in urine. Conduction of urine and Micturition : Urine is produced and drained continuously by the nephrons into the renal pelvis. From here, it is carried down the ureters by peristaltic waves into more...

Major nitrogenous excretory substance in frog, rabbit and human is urea, i.e. these are ureotelic animals. The excretory physiology in these animals may be considered under two phases, viz urea synthesis and formation and excretion of urine.     Synthesis of urea in liver : Urea is formed in liver by two processes. (1) Deamination                               (2) Ornithine cycle (1) Deamination : The amino acid is oxidised using oxygen. This result in removal of the amino group \[(N{{H}_{2}})\] and leaves pyruvic acid. the pyruvic acid can enter the Krebs cycle and be used as a source of energy in cell respiration. The amino group is converted to ammonia \[(N{{H}_{3}})\] during deamination. Deamination is also known as oxidative deamination.     \[\underset{\left( \text{Amino}\,\,\text{acid} \right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}{\mathop{\begin{array}{*{35}{l}} C{{H}_{3}}  \\ |  \\ CH-N{{H}_{2}}+\frac{1}{2}{{O}_{2}}  \\   |  \\ COOH  \\\end{array}\xrightarrow{{}}}}\,\underset{\left( \text{Pyruvic}\,\text{acid} \right)}{\mathop{\begin{array}{*{35}{l}} C{{H}_{3}}  \\ |  \\ CO+N{{H}_{3}}  \\ |  \\ COOH  \\\end{array}}}\,\]   With the help of a number of enzymes and energy of A.T.P. two molecules of ammonia are combined with \[C{{O}_{2}}\] to form urea according to the ornithine cycle. (2) Ornithine cycle (Kreb-Henseleit cycle) : In liver one molecule of \[C{{O}_{2}}\] is activated by biotin and combines with two molecules of \[N{{H}_{3}}\]in the presence of carbamyle phosphate synthatase enzyme (C.P.S.) and 2 ATP to form carbamyle phosphate and one molecule of \[{{H}_{2}}O\] release. Carbamyle phosphate react with ornithine and form citrulline. Citrulin combines with another molecule of ammonia and form arginine. Arginine is broken into urea and ornithine in the presence of an enzyme arginase and water. \[2N{{H}_{3}}+C{{O}_{2}}\xrightarrow{\text{Arginase}}\underset{\text{(Urea)}}{\mathop{N{{H}_{2}}-CO-N{{H}_{2}}+{{H}_{2}}O}}\,\] Liver cells, thus, continuously remove ammonia and some \[C{{O}_{2}}\] from blood and release urea into the blood. Kidneys continuously remove urea from the blood to excrete it in urine.     Urine formation : Urine formation occurs in the kidneys. It involves three processes glomerular filtration, reabsorption and tubular secretion. (1) Ultra filtration (Starling’s hypothesis) (i) It is passive process which takes place from the glomerulus into the Bowman's capsule. The glomerular epithelium has various micropores (diameter\[=50100\,\,nm\,\,or\text{ }0.050.1\,\,\mu m\]) which increase the rate of filtration. (ii) The non colloidal part of the plasma as urea, water, glucose, salts, vitamin, minerals, nitrogenous waste are forced out from the glomerular capillaries into the Bowman's capsule by the high pressure of the blood in the glomerular capillaries. The pressure and resistence is high because the glomerular capillaries are narrower than the afferent renal arteries. Glomerular capillaries are about 50 times more permeable than capillaries elsewhere. Pressure highest in glomerular capillaries than in capillaries else where, produce more filtrate.     (iii) The effective filtration pressure that causes ultrafiltration is determined by three pressures.     (a) Glomerular blood hydrostatic pressure (G.B.H.P.) : Hydrostatic pressure is force that a fluid under pressure exerts against the walls of its container. \[G.B.H.P.=+70\,\,mm\text{ more...

The regulation of solute movement, and hence, water movement, which follows solutes by osmosis, is known as osmoregulation. Osmosis may be defined as a type of diffusion where the movement of water occurs selectively across a semipermeable membrane. It occurs whenever two solutions, separated by semipermeable membrane (the membrane that allows water molecules to pass but not the solutes) differ in total solute concentrations, or osmolarity. The total solute concentration is expressed as molarity or moles of solute per litre of solution. The unit of measurement for osmolarity is milliosmole per litre (mosm\[{{L}^{1}}\]). If two solutions have the same osmolarity, they are said to be isotonic. When two solutions differ in osmolarity, the solution with higher concentration of solute is called hypertonic, while the more dilute solution is called hypotonic. If a semipermeable membrane separates such solutions, the flow of water (osmosis) takes place from a hypotonic solution to a hypertonic one. Osmoconformers are the animals that do not actively control the osmotic condition of their body fluids. They rather change the osmolarity of body fluids according to the osmolarity of the ambient medium. All marine invertebrates and some freshwater invertebrates are strictly osmoconformer. Osmoconformers show an excellent ability to tolerate a wide range of cellular osmotic environments. Osmoregulators, on the other hand, are the animlas that maintain internal osmolarity, different from the surrounding medium in which they inhabit. Many aquatic invertebrates are strict or limited osmoregulators. Most vertebrates are strict osmoregulators, i.e. they maintain the composition of the body fluids within a narrow osmotic range. The notable exception, however, are the hagfish (Myxine sp., a marine cyclostome fish) and elasmobranch fish (sharks and rays). Osmoregulators must either eliminate excess water if they are in hypotonic medium or continuously take in water to compensate for water loss if they are in a hypertonic situation. Therefore, osmoregulators have to spent energy to move water in or out and maintain osmotic gradients by manipulating solute concentrations in their body fluids.

Hormonal controls of the kidney function by negative feedback circuits can be identified : (1) Control by antidiuretic hormone (ADH) : ADH, produced in the hypothalamus of the brain and released into the blood stream from the pituitary gland, enhances fluid retention by making the kidneys reabsorb more water. The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the osmolarity of the blood above a set point of 300 mosm \[{{L}^{1}}.\] In this situation, the osmoreceptor cells also promote thirst. Drinking reduces the osmolarity of the blood, which inhibits the secretion of ADH, thereby completing the feedback circuit. (2) Control by Juxtaglomerular apparatus (JGA) : (Low Blood pressure triggers the Reninangiotension pathway) JGA operates a multihormonal Renin-Angiotensin-Aldosterone System (RAAS). The JGA responds to a decrease in blood pressure or blood volume in the afferent arteriole of the glomerulus and releases an hormone, renin into the blood stream. In the blood, renin initiates chemical reactions that convert a plasma protein, called angiotensinogen, to a peptide, called angiotensin II, which works as a hormone. Angiotensin II increases blood pressure by causing arterioles to constrict. It also increases blood volume in two ways - firstly, by signaling the proximal convoluted tubules to reabsorb more \[NaCl\] and water, and secondly, by stimulating the adrenal gland to release aldosterone, a hormone that induces the distal convoluted tubule to reabsorb more Na+ and water. This leads to an increase in blood volume and pressure, completing the feedback circuit by supporting the release of renin.     (3) Parathormone : The hormone increases blood \[C{{a}^{++}}\] (Hypercalcium) and decreases \[P{{O}_{4}}\] accordingly, it increases absorption of \[C{{a}^{+}},\]increases excretion of \[P{{O}_{4}}.\] (4) Thyrocalcitonin : It increases excretion of \[C{{a}^{++}}\] in the kidney. (5) Prostaglandin : The renal pyramids produce fatty acids of prostaglandins (P.G.) which participates in blood pressure regulation. (6) Erythropoeitin : It is secreted by juxtaglomerular apparatus and plays an important role in erythropoeisis (blood production).   Differences between Rennin and Renin
S.No. Rennin Renin
1. It is secreted by peptic (zymogen) cells of gastric glands into the stomach. more...
By continuously eliminating metabolic wastes and other impurities, and even the surplus quantity of useful materials from blood plasma in the form of urine, kidneys play a vital role in homeostasis. Kidneys also operate certain other homeostatic regulatory mechanisms. Proper maintenance of the internal environment is knows as homeostasis. All regulatory functions of kidneys can be enumerated as follows - (1) Osmoregulation : Being the universal solvent, water is the actual vehicle in ECF to transport materials between various parts of body. Water volume in ECF tends to vary considerably due to several reason, such as drinking, perspiration, diarrhoea, vomiting, etc. As described in previous pages, the kidneys maintain the water balance in ECF by diluting or concentrating urine. (2) Regulation of osmotic pressure : Osmolality of cytoplasm is mainly due to proteins and potassium and phosphate ions, whereas that of the ECF is mainly due to sodium, chloride and bicarbonate ions. Inspite of marked difference in chemical composition, the two fluids - intracellular (cytoplasm) and extracellular (interstitium) - must be isotonic, because if ECF becomes hypotonic, cells will absorb water, swell retaining apropriate number, mainly of sodium and chloride ions, kidneys maintain the normal osmolality of ECF. (3) Regulation of pH : Concentration of hydrogen ions \[(Na{{H}_{2}}P{{O}_{4}})\] in ECF is to be regulated at a constant value usually expressed as pH (minus log of\[{{H}^{+}}\]). The normal pH of ECF is about 7.4. A low pH, i.e. a high \[{{H}^{+}}\] concentration causes acidosis, while a high pH, i.e. a low \[{{H}^{+}}\] concentration causes alkalosis. Both of these conditions severely affect cellular metabolism. Several special control systems, therefore, operate in the body to prevent acidosis and alkalosis. These system are called acid-base buffer system. Kidneys play a key role in maintenance and operation of these systems. Further, the kidneys regulate hydrogen ion concentration in ECF by excreting acidic or basic urine. (4) Regulation of electrolyte concentrations in ECF : The kidneys regulate, not only the total concentrations of water and electrolytes in ECF, but also the concentrations of individual electrolytes separately. This regulation is complex and is accomplished by tubular reabsorption and secretion under the control of hypothalamic and adrenal hormones. (5) Regulation of RBC-count in blood : In oxygen deficiency (hypoxia), kidneys secrete an enzyme into the blood. This enzyme reacts with plasma globulin to form erythropoietin. The latter substance stimulates bone marrow to produce more RBCs for enhancing \[{{O}_{2}}-\]intake in lungs. (6) Regulation of renal blood flow : See (R.A.A.S.).

Mammalian (human) urinary system consists of a pair of kidneys, a pair of ureter, a urinary bladder and a urethra. (1) Kidneys : The kidneys are dark-red, bean-shaped organs about 11 cm long, 5 cm wide and 3 cm thick, each weight about 150 gm in an adult male and about 135 gm in adult female. They are placed against the back wall of the abdominal cavity just below the diaphragm, one on either side opposite the last thoracic and first three lumber vertebrae. The 11th and 12th pairs of ribs protect them.     The kidneys are covered by peritoneum on the front (ventral) side only. Thus, they are retroperitoneal. The right kidney is attached more anterior than the left in rabbit. This asymmetry is just the reverse of that found in man. In man left kidney occurs at a slightly higher level than the right one, because right side has prominent right liver lobe. In rabbit the condition is little differ due to quadropedilism i.e. left kidney is in normal position while the right kidney shift ahead to provide place for stomach below it. In mammals, the kidney is concavo convex. The center of concave inner surface is called as hilum or hilus which gives out a ureter. From this hilus surface the renal artery enters into the kidney, the renal vein comes out and the renal nerves enter into the kidney.   (i) Structure of kidney : The kidneys are metanephric in mammals. The kidney is divisible into two parts outer-cortex and inner-medulla. Three layers of tissue surround each kidney. (a) The innermost, renal capsule made up of fibrous connective tissue. (b) The intermediate layer, adipose capsule of fatty tissue. (c) The outermost, renal fascia of dense connective tissue.  Renal pyramids or medullary pyramids : The medulla is subdivided into 8 to 18 conical masses - the renal pyramid, each having broad base towards the cortex and a narrow end called renal papilla towards the pelvis.     Path of urinary drainage : Collecting duct\[\to \]Papillary duct in renal pyramid\[\to \]Minor calyx\[\to \]Major calyx\[\to \]Renal pelvis\[\to \]Ureter\[\to \]Urinary bladder Renal columns of bertini : Between the pyramids, the cortex extends into the medulla or renal columns of bertini. Calyx : Each renal papilla projects into the cavity of a minor calyx, minor calyx join to form major calyx. The major calyx open into a wide funnel like structure, the pelvis. The latter leads into the ureter. In rabbit, the pelvis is unbranched hence, it is without calyx. In frog ventral surface of each kidney has many ciliated funnels called nephrostomes. They drain wastes from body cavity (coelom) and connect to renal veins in frog or to uriniferous tubules in tadpoles.   (ii) Histology of kidney : Histologically a kidney is made of innumerable thin, long, much convoluted tubular units more...

(1) Protozoans : In protozoans like Amoeba and Paramecium carbon dioxide and ammonia are mostly excreted out by diffusion through general body surface. It is considered that the contractile vacuoles also play some role in the removal of excretory products.   (2) Sponges : In sponges, the nitrogenous metabolic waste (ammonia) leaves the body in the outgoing water current by diffusion. Most of the sponges are marine and have no problem of surplus water in their cells. A few sponges lie in hypotonic fresh water and have contractile vacuoles in most of their cells.     (3) Coelenterates : Hydra also lacks special excretory organs. The nitrogenous waste products like ammonia are removed through the general surface of the body by diffusion. Some nitrogenous waste products are also thrown along with indigestible matter through the mouth.   (4) Platyhelminthes : Planaria, liverfluke and tapeworm possess a large number of excretory cells called the flame cells (solenocytes) or protonephridia and long excretory ducts (also called canals of vessels). The flame cells open into the ductules which in turn open into the excretory duct.       (5) Nematoda : The round worms such as Ascaris have H-shaped excretory system. It is made up of a single Renette cell. in entire length of body. It consists of two longitudinal excretory canals connected anteriorly by a network of transverse canals. A short terminal duct opens outside via excretory pore. Ascaris is excretes both ammonia and urea.     (6) Annelids (Earthworm) : In earthworm excretory system also known as nephridial system, which consist of 3 types of nephridia Pharyngeal, septal, and integumentary nephridia. All nephridia commonly called micronephridia. Earthworm excrete 40% urea, 20% ammonia, 40% amino acids. Earthworm mainly ureotelic. Chloragogen cells found in coelomic fluid also excretory in nature. Blood gland in earthworm found in 4, 5, 6 segment, serves for excretion, manufacture of blood corpuscles and Hb.     (7) Arthropods : The excretory system of the adult Prawn (crustacean) consists of a pair of antennary or green glands, a pair of lateral ducts and a single renal sac. Insects, centipedes, millipedes and arachnids like scorpion and spider posses Malpighian tubules as their principal excretory organs. In the Malpighian tubules bicarbonates of potassium and sodium, water and uric acid are formed. A large amount of water and bicarbonates of potassium and sodium are reabsorbed by the cells of Malpighian tubules and then transferred to the blood (haemolymph). Uric acid is carried to the alimentary canal of the insect and is finally passed out through anus. Spiders and scorpions possess Malpighian tubules and coxal glands both for excretion.     more...

(1) Pyelonephritis : It is an inflammation of renal pelvis, calyces and interstitial tissue (G.pyelos = trough, tub; nephros = kidney; it is = inflammation). It is due to local bacterial infection. Bacteria reach here via urethra and ureter. Inflammation affects the countercurrent mechanism, and the victim fails to concentrate urine. Symptoms of the disease include pain in the back, and frequent and painful urination. (2) Glomerulonephritis : It is the inflammation of glomeruli. It is caused by injury to the kidney, bacterial toxins, drug reaction, etc. Proteins and R.B.Cs pass into the filtrate. (3) Cystitis : It is the inflammation of urinary bladder (G.kystis = bladder, - it is = inflammation). It is caused by bacterial infection. Patient has frequent, painful urination, often with burning sensation. (4) Uremia : Uremia is the presence of an excessive amount of urea in the blood. It results from the decreased excretion of urea in the kidney tubules due to bacterial infection (nephritis) or some mechanical obstruction. urea poisons the cells at high concentration. (5) Kidney stone (Renal calculus) : It is formed by precipitation of uric acid or oxalate. It blocks the kidney tubule. It causes severe pain (renal colic) in the back, spreading down to thighs. The stone may pass into the ureter or urinary bladder and may grow, and cause severe pain of blackade. When in bladder, the patient experiences frequent and painful urination and may pass blood in the urine. Surgery may be needed to remove stone and relieve pain. (6)          Kidney (Renal) failure (RF) : Partial or total inability of kidneys to carry on excretory and salt-water regulatory functions is called renal or kidney failure. Result kidney failure leads to (i) uremia, i.e., an excess of urea and other nitrogenous wastes in the blood (G.ouron = urine, haima-blood); (ii) Salt-water imbalance; and (iii) stoppage of erythropoietin secretion. Causes : Many factors can cause kidney failure. Among these are tubular injury, infection, bacterial toxins, glomerulonephritis (inflammation of glomeruli) arterial or venous obstruction, fluid and electrolyte depletion, intrarenal precipitation of calcium and urates, drug reaction, heammorrhage, etc. Artificial kidney Artificial kidney, called haemodialyser, is a machine that is used to filter the blood of a person whose kidneys are damaged. The process is called haemodialysis. It may be defined as the separation of small molecules (crytalloids) from large molecules (colloids) in a solution by interposing a semipermeable membrane between the solution and water (dialyzing solution). It works on the principle of dialysis, i.e. diffusion of small solute molecules through a semipermeable membrane (G. dia = = through, lyo = separate). Haemodialyser is a cellophane tube suspended in a salt-water solution of the same composition as the normal blood plasma, except that no urea is present. Blood of the patient is pumped from one of the arteries into the cellophane tube after cooling it to 0oC and mixing with an anticoagulant (heparin). Pores of the cellophane tube allow urea, uric acid, creatinine, excess salts and excess H+ ions to diffuse from more...

(1) Skin : Many aquatic animals, such as Hydra and starfish, excrete ammonia into the surrounding water by diffusion through the body wall. In land animals, the skin is often not permeable to water. This is an adaptation to prevent loss of body's water. Mammalian skin retains a minor excretory role by way of its sudoriferous, or sweat glands and sebaceous, or oil glands. (i) Sweat gland : Sweat glands pass out sweat. The latter consists of water containing some inorganic salts (chiefly sodium chloride) and traces of urea and lactic acid. It also contains very small amounts of amino acids and glucose. (ii) Sebaceous glands : Oil glands pass out sebum that contains some lipids such as waxes, sterols, other hydrocarbons and fatty acids.  (2) Lungs : Carbon dioxide and water are the waste products formed in respiration. Lungs remove the\[C{{O}_{2}}\]and some water as vapour in the expired air. Lungs have access to abundant oxygen and oxidise foreign substances, thus causing detoxification and also regulate temperature. (3) Liver : Liver changes the decomposed haemoglobin of the worn-out red blood corpuscles into bile pigments, namely, bilirubin and biliverdin. These pigments pass into the alimentary canal with the bile for elimination in the faeces. The liver also excretes cholesterol, steroid hormones, certain vitamins and drugs via bile. (4) Large intestine : Epithelial cells of the colon transfer some inorganic ions, such as calcium, magnesium and iron, from the blood into the cavity of the colon for removal with the faeces. (5) Saliva : Heavy metals and drugs are excreted in the saliva. (6) Gills : Gills remove \[C{{O}_{2}}\] in aquatic animals. They also excrete salt in many bony fish.

Circulatory system in various groups of animals can be classified as follows : (1) Intracellular circulation : Occurs inside the individual cells where the distribution of substances is through cyclosis of cell cytoplasm. Example – Protozoans. (2) Extracellular circulation : When the distribution of the substances occurs inside the body through extracellular or intracellular fluids. This is of following types – (i) Extra organismic circulation : Canal system in porifera, water vascular system in Echinoderms and gastrovascular system in coelenterates. (ii) Intra-organismic circulation : It involves circulation of body fluids. It is of following types – (a) Parenchymal circulation : In platyhelminthes, the fluid filled spaces present in the mesodermal parenchyma tissue between body wall and internal organs are used in the distribution of substances. (b) Coelomic circulation : Coelomic fluid is concerned with the transport of substances. Example – pseudocoelomic fluid in the roundworms and haemolymph in Arthropods. (c) Blood vascular system : It contains blood and a pumping structure (heart) for circulation of materials inside the body. It is open circulatory system and closed circulatory system.   Differences between open and closed circulatory system
S.N. Open circulatory system Closed circulatory system
1. In open circulatory system blood flows through large open spaces and channels called lacunae and sinuses among the tissues. In closed circulatory system blood flows through a closed system of chambers called heart and blood vessels.
2. Tissues are in direct contact with the blood. Blood does not come in direct contact with tissue.
3. more...



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