Biology Chapter 19 Excretory Products And Their Elimination

The fall in the glorular filtration rate (GFR) or the fall in the glomerular pressure or blood flow results in secretion of renin from the JG cells.

During winter, the surrounding temperature will be very low. There is no sweating, there are no evaporation losses. To keep the body temperature constant, the blood capillaries in the skin are constricted and the blood pressure is increased. In order to maintain the blood pressure normal, the excess water along with the wastes is excreted mostly in the form of urine resulting in frequent urination in winter.

Excretion : It is the process by which the nitrogenous wastes is eliminated from the body.

Nitrogenous waste products : Ammonia , urea, uric acid are some nitrogenous waste products excreted by our body. 

1. Ammonia : It is formed by the deamination of amino acids during the protein metabolism. Ammonia is highly toxic. It is highly soluble in water and needs a large amount of water for its excretion. The animals which excret ammonia are called ammonotelic organisms. For expmple bony fishes , aquatic amphibians and insects.
 2. Urea : It is less toxic than ammonia. Most mammals, fishes and amphibians excrete their nitrogenous waste products in the form of urea. Process of excretion of urea is called ureotelism and such animals are called ureotelic. It needs less water for excretion, hence helps in the conservation of water. Animals like mammals, terrestrial amphibians and marine fishes excrete urea. 

3. Uric acid : Reptiles and birds excrete uric acid and are called uricotelic. The uric acid is is excreted in the foprm of pellet and paste with minimum loss of water. 

Sponges : Ammonia is the main excretory product in sponges. It diffuses from cells into the water filling the canals and surrounding the sponge. From the canal system, the waste matter is carried away by the outgoing current of water. 

Coelentrates : Coelentrates have no excretory organs. They pass out metabolic waste by diffusion from all cells. They are ammonotelic i.e. their excretory product is ammonia. The waste water entering coelentron leaves when its water is renewed.

A nephron is the functional unit of the kidney.
Each nephron compreises of two parts – the glomerulus and the renal tubule.
 
The different parts of a nephrons are : 
Glomerulus - is a tuft of capillaries formed by the afferent arteriole – a fine branch of renal
artery. Blood from the glomerulus is carried
away by an efferent arteriole.
Renal tubule - The renal tubule begins with a double walled cup-like structure called Bowman’s capsule, which encloses the glomerulus.

Malphigian body - The Glomerulus alongwith Bowman’s capsule, is called the malpighian body or renal corpuscle.
PCT - The tubule continues further to form a highly coiled network – proximal convoluted tubule 

Loop Of Henle - A hairpin shaped Henle’s loop forms the next part of the tubule which has a
descending and an ascending limb.
DCT - The ascending limb continues as another highly coiled tubular region called distal
convoluted tubule (DCT).
Collecting Duct - The DCTs of many nephrons open into a straight tube called collecting duct, many of which converge and open into the renal pelvis through medullary pyramids in the calyces.
The Malpighian corpuscle, PCT and DCT
of the nephron are situated in the cortical
region of the kidney whereas the loop of Henle
dips into the medulla. 
Peritubular capillaries - The efferent arteriole emerging from the glomerulus forms a fine
capillary network around the renal tubule called the peritubular capillaries.
Vasa recta - A minute vessel of this network runs parallel to the Henle’s loop forming a ‘U’ shaped vasa recta. 

Nephron : A nephron is a structural and functional unit of kidney. It is differentiated into four regions Bowman's capusle, proximal convoluted tubule, loop of Henle and distal convoluted tubule (DCT).

Fig. Uriniferous tubule
(i) Bowman's capsule : It is a double walled cup containing bunch of parallel capillaries called glomerulus. The glomerulus rests on basement membrane. It is a continuous layer. The Bowman's capsule and glomerulus together are called renal corpuscle or malpighian body. The endothelial cells lining the glomerulus have pores  between them. The cells of inner wall of Bowman's capsule are called podocytes have gaps called slit pores 25nm wide between them.

The glomerulus is supplied by an afferent arteriole and is drained by a relatively narrow efferent arteriole. The latter forms peritubular capillary network around the rest of nephron.

(ii) Proximal convoluted tubule (PCT) : It starts from the neck of the Bowman's capsule.

(iii) Loop of Henle : It is a U-shaped segment of the nephron located in the renal medulla. It consists of two straight parallel limbs.

(iv) Distal convoluted tubule (DCT) : Like PCT, it is greatly twisted and lies in the renal cortex. DCT continues into a collecting tubule.

Collecting tubes or ducts : These are larger tubes, each receiving the collecting tubule of several nephrons. They join each other forming larger ducts of bellini. These open into calyces, which lead into the pelvis.

1. Ultrafiltration : It is the filtration which occurs under high blood pressure. The afferent arteriole supplies blood to glomerulus and efferent arteriole collects blood from glomerulus. The afferent arteriole has more breath than the capillaries of glomerulus. Therefore, the pressure in glomerulus is two and half times more than ordinary capillary bed. Thus smaller molecules of glucose, water, salts, ammonia etc. diffuse from glomerulus into Bowman's capusle. And this process is called ultrafiltration. 

2. Selective reabsorption : It is the process by which useful materials are absorbed by the blood from glomerular filtrate. The tubular  epithelial cells in different segments of nephron perform this either by active or passive  mechanisms. For example, substances like glucose, amino acids, Na+, etc., in the filtrate are reabsorbed actively whereas the nitrogenous wastes are absorbed by passive transport. Reabsorption of water also occurs passively in the initial segments of the nephron

3. Selective secretion : The metabolic waste products like ammonia, creatine, H⁺ ions etc. present in the blood diffuse into distal convoluted tubule DCT. This process is called selective secretion. The tubular cells secrete substances like H+, K+ and ammonia into the filtrate. Tubular secretion helps in the maintenance of ionic and acid base balance of body fluids.

Antidiuretic hormone (ADH) or vasopressin hormone : Urine output is inversely proportional to ADH. It is secreted by hypothalamus and released through posterior lobe of pituitary gland.
If there is excess of water in body then ADH is secreted in less amount so that urine output is increased and if there is less amount of water in the body then ADH is secreted more, because osmoreceptors in hypothalamus detect an increase in osmolarity of blood above a set point of 300 mosml^–1, so that urine output is decreased. In this condition osmorecptor cells promote thirst. Drinking reduces osmolarity of blood. Those substances which increase urine output are called diuretics e.g. alcohol, tea, coffee and all type of non-alcoholic drinks etc. Control of ADH is a negative feed back circuit.

Functions of kidney :

1. Excretion : Kidneys pass out metabolic waste products.

2. Regulation of pH value : Kidneys help in the removal of excess of acids from the blood and thus help in regulating pH value.

3. Osmoregulation : Kidneys help in the maintenance of the osmotic balance in the body.

4. Secretion of renin : The kidneys secrete renin which converts angiotensinogen into angiotensin. It stimulates the limbs of uriniferous tubules to absorb Na⁺ ions from blood.

5. Elimination of excess of salts : The kidneys elminate excess of salts from blood and thus help in regulating blood pressure.

6. Regulation of blood pressure : By controlling the fluid balance in the body, kidney nephron regulates blood pressure.

7. Homeostasis : As kidney removes various unwanted material from the blood, it helps in keeping the internal environment of the body constant.

8. Elimination of other substances : Kidney removes toxic substances like drugs, pigments etc. from the blood.

Composition of urine :

Nature : Urine is acidic in nature and its pH varies between 4.5 to 8.0.

Colour : Urine is pale yellow due to the presence of urochrome, a pigment.

Odour : Urine has a faint odour due to bad smelling urinod. On standing, urea changes to ammonia and produces a strong offensive pungent smell.

Quantity : A normal adult excretes about 1 to 1.8 litre of urine in 24 hours.

Chemical composition : An analysis of urine shows that urine contains 95% water, 5% nitrogenous metabolic waste products like urea, hippuric acid, creatinine etc. and non-nitrogenous waste products like oxalic acid, excess of vitamin etc.

Abnormal constituents of urine are :

1. Proteinuria : e.g. When albumin and globulin are present in urine.

2. Glycosuria : When glucose is present in urea.

3. Hematuria : It is the presence of blood in urine is called hematuria.

4. Ketouria : The presence of ketone bodies causes ketouria.

5. Albuminuria : Presence of albumin in urine is callcd albuminureu.

The skin, lungs, liver and large intestine in vertebrates are  the accessory excretory organs.

1. Skin : Human skin possesses sweat glands and sebaceous glands. Sweat is an aqueous fluid containing sodium chloride, lactic acid, urea, amino acids and glucose. It serves mainly as a cooling process. Sweat contains 99.5% of water. The volume of sweat varies from negligible amount to 142 ml. a day depending upon activity and temperature. Sebum also contains excretory products like waxes, sterols and fatty acids. It also keeps skin oily.

2. Lungs : Lungs remove large volume of carbon dioxide produced in the body along with which  some moisture is regularly excreted. Human living removes 182 ml. of C0₂/hr. and 400ml. of water per day in normal resting conditions volatile materials are also eliminated by lungs.

3. Liver : Liver is the principal organ for the excretion of cholesterol pigments (bilirubin and biliverdin) and inactivated products of steroids, hormones, some vitamins and many drugs.

ADH (Aniti diuretic hormone) - is released when the there is loss of water, it facilitates water reabsorption from latter parts of the tubule, thereby producing hypertonic urine. An increase in body fluid volume can switch off the osmoreceptors and suppress the ADH release to complete the feedback. 
Aldosterone - also causes reabsorption of water from the distal part of the tubule thus producing hypertonic urine. When the level of the aldosterone is low, water absorption is less and hence hypotonic urine is produced. 
The counter current mechanism helps in the maintenace of the intestinal gradient. The intestinal gradient helps in easy passage of water from the collecting tubules thereby concentrating the urine. 

Osmoreceptors in the body are activated by changes in blood volume, body fluid volume and ionic concentration. 

Artificial kidney or Haemodialysis : It is the artificial removal of the nitrogenous wastes from the body. It is used in those patients whose kidney tubules do not function properly so that the metabolic wastes start accumulating in the blood and they need to be eliminated frequently. It can be explained in following points.

1. In the process, the blood of the patient is pumped from one of the main arteries and cooled to 0°C.

2. It is then mixed with an anticoagulant heparin and passed through cellophane tube.

3. This cellophane tube is a semipermeable membrane which allows only small molecules like urea, uric acid, creatinine and mineral ions to pass out but the macromolecules like proteins are not able to pass through it.

Fig. Diagram of Artificial Kidney

4. This cellophane tube is suspended in a salt solution which is isotonic with the blood plasma. Now, as the blood flows through this tube metabolic wastes are filtered out of the blood in the salt solution.

5. The purified blood is mixed with antiheparin to restore its normal coaguability and is then pumped into the body through a vein.

Haemodialysis is the artificial process by which urea is removed from the body of the patient.
i. Blood drained from an artery is
pumped into a dialysing unit after the addition of anticoagulant like heparin.
ii. The unit contains a coiled cellophane tube surrounded by a dialysing fluid having the same composition as that of plasma except the nitrogenous wastes. 

iii. The porous cellophane membrance of the tube allows the passage of molecules based on concentration gradient. As nitrogenous wastes are absent in the dialysing fluid, these substances
freely move out, thereby clearing the blood.
iv. The cleared blood is pumped back to the body through a vein after adding anti-heparin to
it. This method is a boon for thousands of uremic patients all over the world.

Juxta glomerular Apparatus (JGA) has a complex regulatory role and it controls multihormonal Renin-Angiotensinogen System (RAAS). It responds to decrease in blood pressure in afferent arteriole of glomerulus. Afferent arteriole's cells release an enzyme called renin into blood stream.

Renin converts angiotensinogen present in plasma into angiotensin II peptide. Functions of Angiotensin II :

1. Angiotensin II is a hormone which increases B.P. by causing arterioles to contract.

2. Angiotensin II also increases blood volume in following two ways.

(a) It signals the PCT to absorb more H₂0 and more NaCl.

(b) It also stimulates adrenal cortex to release aldosterone which induces the DCT to absorb Na⁺ and water.

Therefore, B.P. and blood volume is increased and it completes the feed back circle.

ANF is released by walls of atria or auricles. ANF (Atrial Natiuretic Factor) is secreted in response to increase of B.P. or blood volume.

ANF checks the secretion of renin-angitensin mechanism, and thus inhibits reabsorption of NaCl by collecting duct and also stops release of aldosterone. ANF is a vasodilator whereas the Angiotensin II is a vasocontrictor. 

A kidney stone is formed by the precipitation of uric acid or oxalate.

Symptoms :

1. It blocks the kidney tubule.

2. It may pass into the ureter or urinary bladder and may grow, and cause severe pain or blockage.

3. When, the stone is in bladder, the patient experiences frequent and painful urination and may pass blood in urine.

Kidney failure is the partial or total inability of kidneys to carry on excretory functions.

Symptoms :

(a) Kidney failure leads to uremia i.e. an excess of urea and other nitrogenous wastes in the blood.

(b) Salt-water imbalance.

Causes : Many factors can cause kidney failure. Among these prominent are

1. tubular injury

2. infection

3. bacterial toxins

4. glomerulonephritis.

5. fluid and electrolyte depletion

6. internal precipitation of calcium and urates

7. haemorrhage.

Kidney transplantation is the transfer of a healthy kidney from one person into the body of a person who has little or no kidney function. A functioning kidney is used in transplantation from a donor, preferably a close relative, to minimise its chances of rejection by the immune system of the host. 

First kidney transplant was performed by a Washington Surgeon, Dr. Charles Hufnagel. In India, first transplant was performed on a 35 yrs old Shaninughan at CMC, Vellore on December 1, 1971.

Immunosuppression : It means to suppress the immune response of recipient to prevent transplant rejection.

This is done before or at time of kidney transplantation. The therapy is done with the help of drugs which destroy ‘T’ cells (which are responsible for providing immunity to the body. These T-cells produce antibodies against the foreign graft or transplant and result in the rejection of the transplant. Hence, the immune system of the patient is suprresed so that the transplant is not rejected.

Glomerular Filtration Rate (GFR) is the amount of the filtrate formed by the kidneys per minute. GFR for a healthy individual is approximately 125 ml/minute. i.e. 180 litres per day. 

The kidney regulates the glomerular filtration rate by an autoregulative mechanism carried out by the juxtaglomerular apparatus.
The Juxtaglomerular apparatus is a special sensitive microscopic structure formed by cellular modifications in the distal convoluted tubule and the afferent arteriole at the location of their contact. 

When there is a fall in the glomerular filtration rate, it activates the juxtaglomerular cells to release renin. This stimulates the glomerular blood flow, thereby bringing the GFR back to normal. Renin brings the GFR back to normal by the activation of the renin-angiotensin mechanism

The counter current mechanism operating inside the kidney is the main adaptation for the conservation of water. There are two counter current mechanisms inside the kidneys. They are Henle's loop and vasa rectae.

Henle's loop is a U-shaped part of the nephron. Blood flows in the two limbs of the tube in opposite directions and this gives rise to counter currents. The Vasa recta is an efferent arteriole, which forms a capillary network around the tubules inside the renal medulla. It runs parallel to Henley's loop and is U-shaped. Blood flows in opposite directions in the two limbs of vasa recta. As a result, blood entering the renal medulla in the descending limb comes in close contact with the outgoing blood in the ascending limb.
The osmolarity increases from 300 mOsmolL -1 in the cortex to 1200 mOsmolL -1 in the inner medulla by counter current mechanism. It helps in maintaining the concentration gradient, which in turn helps in easy movement of water from collecting tubules. The gradient is a result of the movement of NaCl and urea.

Organs like lungs , liver and skin also play a role in excretion.
Lungs - Lungs remove large amounts of carbon dioxide and significant amount of water everyday. 
Liver - The liver helps in the excretion of cholesterol, steroid hormones, vitamins, drugs, and other waste materials through bile. Urea is formed in the liver by the ornithine cycle. Ammonia - a toxic substance - is quickly changed into urea in the liver and thence eliminated from the body. Liver also changes the decomposed haemoglobin pigment into bile pigments called bilirubin and biliverdin.
Skin - Skin plays a major role in excretion of water, NaCl and small amounts of urea, lactic acid, etc. The sebaceous glands in the skin help eliminating substances like sterol, hydrocarbons, and waxes through sebum.  

Micturition is the process of the discharge of urine from the urinary bladder.
The urinary bladder stores urine temporarily. the streching of the urinary bladder initiates a signal from the stretch receptore to the Central nervous system. The CNS then passes on the signal to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral spincter resulting in the release of the urine. 
Usually an adult human excretes on an average 1 to 1.5 litres of the urine per day. 

Osmoregulation is the maintenance of the ionic and tconcentration and amount of water and salts in the body of the organism. It is the regulation of the osmotic pressure of an organism's body fluids to maintain the homeostasis of the organism's water content and the concentration of salts and ions. 

Teresstrial animals live in drier conditions as compared to others. They always are in the grave dangers of excessive loss of water. 
Excretion of urea and uric acid requires less amount of water as compared to the excretion of ammonia which requires a large amount of water. In order to avoid water loss they are ureotelic or uricotelic and not ammonotelic. 

The juxta glomerulus apparatus is plays a major role in the regulation of the rate of the glomerular filtrate. It is a special sensitive region formed by the cellular modifications in the distal covuluted tubule and afferent arteriole at the location of their contact. 
The JGA plays a complex reulatory role. It regulates the complex mechanism called the renin-angiostensin mechanism. The JG cells are activated when there is a fall in the glomerular blood flow or GFR. On actibations these cells release renin which converts the inactive angiotensin to angiotensin- I and further to angiotensin-II. 
Angiotensin-II is a powerful vasocontrictor and thus increase the glomerular blood pressure thereby the GFR. It also activates the adrenal cortex to release the hormone aldosterone. 
Aldosterone directs the reabsorption the Na⁺ and water from the distal parts of the tubule. The reabsorption leads to increase in the blood pressure anf the GFR. 

Amphioxus

Vasa recta

impermeable

permeable

B.

Hepatic vein

Urea is synthesised in the liver. So, maximum amount of urea of urea is present in hepatic vein and minimum in Renal vein.  

A.

A - adrenal gland - located at the anterior part of kidney. Secrete catecholamines, which stimulate glycogen breakdown

A - adrenal gland, B - Renal pelvis, C - Medulla, D - cortex.

C.

Proximal convoluted tubule

From the Bowman's capsule, the glomerular filtrate enters the proximal convoluted tubule (PCT). PCT is surrounded by a network of peritubular capillaries and is the seat of reabsorption. About 75% of glomerular filtrate is normally reabsorbed in PCT before reaching the loop of Henle. The reabsorbed materials include glucose, amino acids, vitamins, hormones, sodium, potassium, chlorides, phosphates, bicarbonates, most of water and some urea etc. 

A.

Increase in aldosterone levels

The increase in aldosterone levels cause and increase in sodium reabsorption is DCT. It is secreted by outer, layer of adrenal gland when aldosterone is present in the blood, all the Na⁺ in the filtrate is reabsorbed. Retaining Na⁺ raises the osmotic pressure of the blood and reduces the water loss from the body.

C.

On the basis of nitrogenous metabolic waste the animal are of four types:
(i) Ammonotelic: Excreted ammonia, e.g., aquatic animals, bony fishes, frog, toad and crocodile, etc.
(ii) Aminotelic Excreted amino acid, e.g., Mollusca and echinoderms.
(iii) Ureotelic Excreted urea, e.g., frog, toad and mammals.
(iv) Uricotelic  Excreted uric acid, e.g., insects, land reptiles and birds.

A.

Juxtra glomerular cells to release renin

Juxtaglomerular apparatus consists of macula densa and juxtaglomerular cells. The apparatus becomes active when there is decrease in renal blood pressure or decrease in glomerular filtration rate. There is increased absorption of NaCl in ascending limb or loop of Henle. The decreased NaCl content of filtrate activates cells of macula densa to increase secretion of renin from juxta glomerular cells. Renin convert angiotensinogen to angiotensin peptides.

D.

Ureotelic mode of excretion

Most animals convert toxic ammonia into less toxic urea and excreted it, e.g., adult frog and man. 
Four-chambered heart is present in human but two-chambered in frog.
Nucleated RBCs are found in frog but not in human.
Fertilization is internal in human but external in frog. 

A.

more diluted urine

The removal of proximal convoluted tubule from the nephron results in lack of reabsorption of high threshold substance from renal tubules and obligatory reabsorption of water is also affected leading to more diluted urine. Since, proximal convoluted tubule is mainly associated with reabsorption of much water by osmosis, reabsorption of glucose and amino acids by secondary active transport and other salts and ions as Na⁺, K⁺, vitamins act by primary active transport. 

C.

Actin and Myosin filaments do not shorten but rather slide pass each other

Sliding filament theory is explained as actin and myosin filaments do not shorten but rather slide pass each other. 
Two groups of workers, i.e. Andrew Huxley and Ralph Niedegerke (1954) and Hugh Huxley and Iean Hanson (1954) proposed the sliding filament theory. It has essential feature as follows:
(i) During musocle contraction the thin myofilaments show sliding inward towards H-zone. 
(ii) The sarcomere shortens, without changing the length of thin and thick myofilaments. 
(iii) The cross bridge of thick myofilaments connect with portions of thin myofilaments. These cross bridges move on the surface of the thin and thick myofilaments over each other.
(iv) The lengths of thick and thin myofilaments don't change thin filament (actin) during muscle contraction. 

C.

Renin

Renin secreted by JGA regulates the glomerular filtration rate by inducing multihormonal system i.e. RAAS (Renin Angiotensin - Aldosterone System). Activation of this system increase the reabsorption rate of sodium (Na⁺) and water, making the urine more concentrated. 
Alcohol decreases vasopressin level which lowers reabsorption of water thus making urine more dilute. ANF causes vasodilation and acts as check on RAAS

D.

Podocvytes - create minute spaces (slit pores) for the filtration of blood into the Bowman's capsule

Podocytes or cvisceral epithelial cells are the cells in Bowman's capsule in the kidneys that wrap around the capillaries of glomerules. They create minute pores (slit pores) for the filtration of blood into the Bowman's capsule.

A.

Convoluted tubules

The convoluted tubule is the highly convoluted segments of the nephron in the renal labyrinth of the kidney. It is made up of the proximal tubule leading from the Bowmans capsule to the descending limb of Henle's loop and  the distal tubule leading from the ascending limb of Henle's loop to a collecting tubule.

C.

comparatively more permeable to K⁺ ions and nearly impermeable to Na⁺ ions

Neurones are excitable cells because their membrane is in a polarised state. Different types of selectively permeable channels are present on the neural membrane. When a neurone is not conduction any impulse, i.e. resting, the axonal membrane is comparatively more permeable to potassium ion (K⁺) and nearly impermeable to sodium ion (Na⁺)

D.

When someone drinks lot of water ADH release is supposed 

When someone drinks a lot of water which is not required by the body, the osmolarity of the blood will decrease. The decrease in osmolarity will inhibit the release of ADH.

C.

Nearly 99 percent of the glomerular filtrate is reabsorbed by the renal tubules

The plasma fluid that filters out from glomerular capillaries into Bowman's capsule of the nephron is called glomerular filtrate. A comparison of the volume of the filtrate formed per day (180 L /day) with that of the urine release (1.5 L), suggested that nearly 99 percent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption

D.

in the liver, but eliminated mostly through the  kidneys

In humans, the principal nitrogenous excretory compound (i.e, urea) is synthesised in the liver by ornithine cycle. In liver, one molecule of CO₂ is activated by biotin and combines with two molecules of NH₃ in the presence of carbamyl phosphate synthetase enzyme and 2ATP to form carbonyl phosphate reacts with ornithine and forms citrulline. Citrulline combines with another molecule of ammonia and forms arginine that is broken into urea and ornithine in the presence of an enzyme arginase and water. 

Urea is eliminated mostly through kidney as a nitrogenous excretory product.

D.

(1) and (2)

To prevent graft (Kidney transplant) rejection, the principle is to use chemicals, which inhibit the enitre activity of the immune system. when this occurs graft rejection is delayed. It has been show that immunosuppression may make the patients more preeen to develop cancers.One way of overcoming the problems of radiatin and immunosuppression is to suppress only the cells responsible for rejection, normally the killer T- cells .In this way, the rest of the  patients immune system would continue to function normally. The most promising approach is to treat the patient with monoclonal antibodies that recognize and destroy the killer T-cells. A monoclonal antibody has been developed, which is very effective at preventing rejection of transplanted kidneys.

A.

Arteries are thick -walled and have narrow lumen as compared to veins

Arteries are the blood vessels which carry blood away from the heart. In comparison to veins, arteries have a narrow lumen and more muscular thick walls to bear the pressure of pumping action of the heart.
Angina is constricting chest pain caused due to reduced blood supply to the heart wall.
Persons with blood group- AB are universal acceptor, while those with blood group -O are a universal donor. 

C.

Urine will continue to collect normally in the bladder

The urinary bladder is a pear-shaped, hollow muscular organ situated in the pelvic cavity, which is made up of smooth and involuntary muscles. The lumen of the urinary bladder is line by transition epithelium, which has great power of stretching. If stretch receptors of urinary bladder wall are totally removed, the urine will continue to collect normally in the bladder.

B.

Basophils

The basophils are probably like mast cells connective tissue. They release heparin, histamine and serotonin. Their nucleus is usually three-lobed and their granules take basic stain strongly.
Monocytes are largest of all types of leucocytes.Their nucleus is bean-shaped.They are motile and phagocytic in nature. They engulf bacteria and cellular debris.Generally, they will change into macrophages after entering tissue spaces.

A.

more sodium in his urine

The normal concentration of sodium in the blood plasma is 150 mEq/L. If this level drops below 120 mEq/L, the result may be lethargy, coma or death. Unlike deficiencies of other important fluid constituents, the most common cause of this drop in sodium concentration is not a nutritional deficit of sodium, but rather an excess of water.

C.

liver cells

Angiotensinogen is a plasma protein produced and secreted by the liver cells. Renin secreted from juxtaglomerular cells and acts enzymaticaly on angiotensinogen to release 10 amino acid peptide angiotensin I.
Macula densa is actually a plaque in wall at the end of thick assending limb of nephrons.

A.

The ascending limb of loop of Henle is impermeable to water

Descending limb of loop of Henle is permeable to water but impermeable to electrolytes while ascending limb is impermeable to water but permeable to electrolytes.

B.

1. Ultrafiltration refers to filtration of very fine particles having molecular weight less than 68,000 daltons through malpighian corpuscle.
2. Concentration of urine refers to water absorption from glomerular filtrate as a result of hyperosmolarity in the medulla created by counter-current mechanism in Henle's loop.
3. Urine is carried from kidney to bladder through ureter.
4. Urinary bladder is concerned with storage of urine.

B.

cholecystokinin

Cholecystokinin Pancreozymin (CCK-PZ) is the hormone secreted from mucosa of the small intestine. It stimulates the pancreas to release enzymatic (Pancreatic) juice and gallbladder to eject bile.

B.

ammonia and urea

Omithine cycles remove both ammonia and urea from the blood. It converts ammonia into urea (in the liver) and transports it to kidneys by the blood. Hence, it plays a key role in the detoxification of our blood. This cycle occurs in the liver.

B.

Liver

The formation of urea from NH₃, and CO₂ Occurs in the liver. Through Ornithine cycle or Krebs Hansleit cycle. All the steps of this cycle are enzymatic and can be visualized as follows.

C.

Pelvis

The term 'pelvis' is common to both kidney and skeleton in mammals. In relation to the kidney, it can be described as a chamber in the kidney into which the urine drains from renal tubules before passing to the ureter. For skeleton, it is related with a pelvic girdle or hip girdle.

B.

Allantois

Allantois is an extraembryonic membrane developed as an outgrowth from hindgut. In the eggs of reptiles and birds, it functions as a urinary bladder and stores the waste excretory products. It also provides oxygen (in reptiles, birds and mammals) and food (in mammals) to the embryo.

A.

Stomach and Duodenum

Pyloric sphincter guards are the opening between the pylorus of a stomach and the duodenum of the small intestine. It periodically permits partially digested food to leave the stomach and enter the duodenum.

B.

Birds

Birds are uricotelic organisms which excrete uric acid to reduce their weight.

C.

Anuria

The terms anuria, oligonuria, polynuria and dysuria are used for the absence of urine, scanty urine, large amounts of urine, and painful urination respectively. Deamination is the removal of amino (NH) group frequently from an amino acid by transaminase enzymes.

D.

Platyhelminthes

Solenocytes (also called flame cells) are meant for excretion and osmoregulation in Platyhelminthes. Annelids have metanephridia for excretion, Molluscs have kidneys (although different from vertebrate kidneys) for excretion. In echinodermates, no special excretory organs are found for excretion. In them, excretion takes place through diffusion or osmosis or through active transport.

B.

Helminths

Sponges possess an extensive system of interconnected cavities called canal system, which typically consists of in current canals, radial canals, excurrent canals and spongocoel. The system is useful for nutrition, respiration and excretion.

A.

20 mm Hg

Kidneys help in the formation of urine, from the blood flowing through glomerular capillaries. About 20% of plasma fluid filters out into the Bowman's capsule through a thin glomeular- capsular membrane due to a net or effective filtration of about 10 to 15 mm Hg.

B.

Urea

Urea is the main nitrogenous excretory product of ureotelic animals. It is produced by liver cells from deaminated excess amino acid via urea cycle or Omithine cycle. Urea is released outside the body in the form of urine through the kidneys.

A.

uric acid

Urea is the main nitrogenous excretory product of ureotelic animals. It is produced by liver cells from deaminated excess amino acid via urea cycle or Omithine cycle. Urea is released outside the body in the form of urine through the kidneys.

A.

kidney

Urine formation takes place in kidney. It includes glomerular filtration (ultrafiltration), selective reabsorption and tubular secretion. Urine is stored temporarily in urinary bladder.