Excretory Products &Their Elimination

Excretory Products &Their Elimination 1. 16 Chapter Define Glomerular Filtration Rate (GFR) Ans: The amount of glomerular filtrate which is formed by the kidneys in a minute is known as glomerular filtration rate, which is about 125ml per minute. It is used to check the amount of blood passing through the glomeruli. 2. Explain the Autoregulatory mechanism of GFR. Ans: The regulation of GFR through the kidney is autoregulatory and it is regulated by the juxtaglomerular apparatus, which is a microscopic structure located between the renal corpuscles and distal convoluted tubules of the same nephron. GFR helps in the regulation of renal blood flow and glomerular filtration rate. Fall in GFR activates juxtaglomerular cells which releases renin. By the reninangiotensin mechanism, the reabsorption of sodium and water takes place with increased blood pressure which brings GFR back to normal. 3. Indicate whether the following statements are true or false: 1. Micturition is carried out by a reflex. 2. ADH helps in water elimination, making the urine hypotonic. 3. Protein–free fluid is filtered from blood plasma into the Bowman’s capsule. Henle’s loop plays an important role in concentrating the urine. 4. Glucose is actively reabsorbed in the proximal convoluted tubule. 1 Ans: 1. Micturition is carried out by neutral mechanisms which cause contraction of smooth muscles and relaxation of the urethral sphincter which is known as micturition reflex therefore the given statement is True. 2. ADH release takes place when an excessive fluid loss takes place from the body. This ADH helps in water reabsorption and also prevents diuresis. Therefore the given statement is False. 3. The blood plasma with proteins passes through the lumen of Bowman's capsule whereas the rest of the plasma without proteins passes through the membrane of Bowman's capsule, therefore the given statement is true. 4. The important part of the nephron is the Henle's loop as it helps in maintaining the ionic balance of fluid and also in concentrating the urine therefore the given statement is true. 5. The proximal convoluted tubule has a large surface area for reabsorption of nutrients, water, and minerals therefore the given statement is True. 4. Give a brief account of the countercurrent mechanism. Ans: The Henle's loop and vasa recta help in the concentration of filtrate through counter current mechanism because the limbs of Henle's loop carry filtrate and the limb of vasa recta carry blood in opposite directions. ● The counter-current between the Vasa recta and Henle loops helps in maintaining the osmolarity from 300 mOsmol per liter in the cortex to 1200 mOsmol per liter in the inner medulla. ● The NaCl in the ascending loop of Henle's gets exchanged with the descending loop of the vasa recta and then after getting returned into the interstitium by the vasa recta through its ascending portion. ● The transportation of urea takes place through collecting tubules to the interstitium. ● The production of urine takes place four times more concentrated than initial 2 filtrate in humans. 5. Describe the role of the liver, lungs, and skin in excretion. Ans: Liver is one of the most important organs of our body as it helps in passing out digestive wastes along with other substances like bilirubin, biliverdin, vitamins, etc. Lungs carry gases from the atmosphere to the inside and remove carbon dioxide from the body with small quantities of water with them. The skin consists of both the sweat gland and sebaceous gland which help in the excretion of sweat in the form of watery fluid with NaCl along with urea and lactic acids. The sebaceous gland helps in the excretion of sterols, hydrocarbons, and waxes. 3 6. Explain micturition. Ans: The excretion of urine from the urinary bladder by contraction and relaxation of smooth muscles of the bladder is known as micturition. When urine accumulates in the urinary bladder, a voluntary signal passes out from the CNS which leads to the excretion of urine. Accumulation of urine leads to the passage of signals from stretch receptors to CNS by which the motor neuron initiates the contraction and relaxation of smooth muscle and release of urine. On average a healthy adult can excrete 1 to 1.5 liters of urine per day. 7. Match the items of Column I with those of column II: Column I Column II (a) Ammonotelism (i) Birds (b) Bowman’s capsule (ii) Water reabsorption (c) Micturition (iii) Bony fish (d) Uricotelism (iv) Urinary bladder (e) ADH (v) Renal tubule Ans: (a) Ammonotelism is a process where the excretion of ammonia takes place. It takes place mainly in aquatic animals like amphibians, bony fishes, and insects. (b) Bowman's capsule is the part of the renal tubule which encloses the glomerulus. (c) Micturition is the process of passage of urine from the urinary bladder. 4 (d) Uricotelism is the process where the release of uric acid takes place to prevent water loss from the body. Examples are birds, reptiles, insects, etc. (e) ADH helps in water reabsorption and it releases when excess loss of water takes place from the body. 8. What is meant by the term osmoregulation? Ans: The regulation of optimum temperatures of waters and salts in tissues and body fluids is known as osmoregulation. It helps to maintain the internal temperature of the body by balancing the water- ionic concentration. 9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why? Ans: The main reasons behind the terrestrial animals being ureotelic and uricotelic is as follows: 1) Due to the high toxicity of ammonia, the body of terrestrial animals converts it into less toxic forms like urea and uric acid. 2) Terrestrial animals conserve water to regulate the body temperature and ammonia is water-soluble, so to resist the continuous elimination of water it gets converted into less water-soluble urea and uric acid. 10. What is the sign ificance of juxtaglomerular apparatus(JGA) in kidney function? Ans: Juxtaglomerular apparatus (JGA) is formed by modifying the distal convoluted tubule and afferent arteriole. It is located where the afferent arteriole and the distal convoluted tubule (DLT) come in contact. It contains juxtaglomerular cells which are the specialized cells of the arteriole and also contain an enzyme that regulates blood pressure and this enzyme is called renin. Fall in glomerular filtration rate activates the juxtaglomerular cell which causes the release of renin. Renin stimulates the glomerular blood flow by which the glomerular filtration rate comes to normal. Angiotensin gets converted into Angiotensin I with the help of renin and further conversion into Angiotensin II takes place. Angiotensin II increases the glomerular filtration rate by an increase in glomerular blood pressure. It also releases aldosterone by activating the adrenal cortex. The mechanism of renin and angiotensin is known as the Renin-Angiotensin mechanism. 5 11. Name the following: 1. A chordate animal having flame cells as excretory structures. 2. Cortical portions projecting between the medullary pyramids in the human kidney. 3. A loop of capillary running parallel to Henle’s loop. Ans: 1) The flame cell is a specialized cell that helps in osmoregulation and excretion and it is present in the amphioxus which is an example of Cephalochordata. 2) The columns of Bertini are the cortical portion that projects between the medullary 3) Vasa recta are the loop of capillaries that runs parallel to the loop of Henle's. 12. Fill in the gaps (1) Ascending limb of Henle's loop is ________________ to water whereas the descending limb is _____________ to it. Ans: Impermeable, Permeable (2) Reabsorption of water from the distal part of the tubules is facilitated by hormone_______________. 6 Ans: Vasopressin (3) Dialysis fluid contains all the constituents as in plasma except ______________. Ans: The nitrogenous waste (4) A healthy adult human excretes an average ___________ gm of urea per day. Ans: 25 -30 7