Chapter 16: Excretory Products and Their Elimination

Class 11 Biology Chapter 16 Excretory Products and Their Elimination Exercise Questions and Answers :

1. Define Glomerular Filtration Rate (GFR) .

Answer : The amount of filtrate formed by the kidneys per minute is called the glomerular filtration rate (GFR). GFR in a healthy individual is approximately 125 ml/minute, which is equivalent to 180 liters per day. A decrease in GFR can trigger the JG cells to release renin, which, in turn, can stimulate glomerular blood flow and help restore GFR to its normal level.

2. Explain the autoregulatory mechanism of GFR.

Answer : The autoregulatory mechanism of glomerular filtration rate (GFR) in the kidneys is efficiently monitored and regulated by hormonal feedback mechanisms. Osmoreceptors in the body respond to changes in blood and body fluid volume as well as ionic concentration. Excessive fluid loss activates these receptors, leading to the release of antidiuretic hormone (ADH) from the hypothalamus, promoting water reabsorption in the tubules to prevent diuresis. Conversely, increased body fluid volume inhibits ADH release.

Additionally, the juxtaglomerular apparatus (JGA) plays a crucial role. A drop in glomerular blood flow/pressure/GFR activates JG cells to release renin, initiating the Renin-Angiotensin mechanism. Angiotensin II, a potent vasoconstrictor, raises glomerular blood pressure and GFR. It also prompts the release of aldosterone, increasing and water reabsorption, further elevating blood pressure and GFR.

The Atrial Natriuretic Factor (ANF) counterbalances this system by causing vasodilation and reducing blood pressure.

3. Indicate whether the following statements are true or false :

(a) Micturition is carried out by a reflex.

(b) ADH helps in water elimination, making the urine hypotonic.

(c) Protein-free fluid is filtered from blood plasma into the Bowman’s capsule.

(d) Henle’s loop plays an important role in concentrating the urine.

(e) Glucose is actively reabsorbed in the proximal convoluted tubule.

Answer :  (a) True. Micturition, the process of emptying the bladder, is carried out by a reflex.

(b) False. Antidiuretic hormone (ADH) helps in water reabsorption in the kidney tubules, reducing water elimination, and concentrating urine, not making it hypotonic.

(c) True. Protein-free fluid (filtrate) is indeed filtered from blood plasma into Bowman's capsule in the renal corpuscle during the initial stages of urine formation.

(d) True. Henle's loop, especially the descending limb, plays a crucial role in concentrating urine by reabsorbing water while allowing solutes to pass through the tubule.

(e) True. Glucose is actively reabsorbed in the proximal convoluted tubule of the nephron under normal physiological conditions.

4. Give a brief account of the counter current mechanism.

Answer : The counter current mechanism is a key process that enables mammals, including humans, to produce concentrated urine. It primarily involves the interaction between Henle's loop and the vasa recta, which are essential components of the nephron within the kidney.

Below is a brief account of the counter current mechanism :

Opposite Flow in Henle's Loop : The flow of filtrate in the two limbs of Henle's loop (the descending and ascending limbs) is in opposite directions. This forms a counter current, which allows for efficient concentration of solutes.

Counter Current in Vasa Recta : Similarly, the blood flow in the vasa recta, the network of blood vessels surrounding the nephron, is also in a counter current pattern. This helps maintain the osmolarity gradient in the renal medulla, increasing from about 300 in the cortex to around 1200 in the inner medulla .

Role of NaCl and Urea : NaCl (sodium chloride) is transported by the ascending limb of Henle's loop, which is exchanged with the descending limb of vasa recta. The ascending portion of vasa recta returns NaCl to the interstitium. Additionally, small amounts of urea enter the thin segment of the ascending limb of Henle's loop, and this urea is transported back to the interstitium by the collecting tubule.

Interstitium Gradient : The interaction between Henle's loop and vasa recta, along with the movement of NaCl and urea, helps establish and maintain a concentration gradient in the medullary interstitium. This gradient is a key factor in concentrating urine.

Concentration of Filtrate: The presence of the interstitial gradient facilitates the easy passage of water from the collecting tubule, concentrating the filtrate (urine). Human kidneys can produce urine that is nearly four times more concentrated than the initial filtrate formed due to this counter current mechanism .

5. Describe the role of liver, lungs and skin in excretion.

Answer :  The liver, lungs, and skin play important roles in the process of excretion are :

Liver: The liver is the largest gland in the human body and has several crucial functions, one of which is excretion. It secretes bile, a digestive fluid that contains various waste products. These include bilirubin, biliverdin, cholesterol, degraded steroid hormones, vitamins, and drugs. Most of these substances are ultimately eliminated from the body through the digestive system. Bilirubin, for example, gives feces their characteristic brown color. Thus, the liver aids in the removal of metabolic waste products and byproducts of drug metabolism.

Lungs: The lungs are primarily responsible for the exchange of gases, but they also play a role in excretion. During respiration, the lungs help eliminate carbon dioxide () from the body. On average, the lungs remove approximately 200 milliliters of per minute. They also eliminate significant quantities of water vapor. This process helps maintain the acid-base balance in the body and removes excess , a waste product of cellular metabolism.

Skin: The skin, the body's largest organ, also contributes to excretion through its sweat and sebaceous glands. Sweat glands produce sweat, a watery fluid that contains various substances, including sodium chloride (NaCl), small amounts of urea, lactic acid, and other waste products. While the primary function of sweat is to regulate body temperature by providing cooling, it also helps eliminate these waste substances from the body. Sebaceous glands, on the other hand, secrete sebum, an oily substance that contains sterols, hydrocarbons, and waxes. Sebum provides a protective oily covering for the skin and helps eliminate certain waste products through its secretion

6. Explain micturition.

Answer :  Micturition, or urination, is the process of releasing urine from the urinary bladder. It begins when stretch receptors in the bladder wall signal the central nervous system (CNS) due to bladder filling. In response, the CNS sends motor messages to contract the bladder's smooth muscles and simultaneously relax the urethral sphincter. This coordinated action expels urine from the body. An adult typically excretes 1 to 1.5 liters of slightly acidic (pH 6.0), light yellow urine daily. Analyzing urine characteristics aids in diagnosing metabolic disorders and kidney malfunctions, such as detecting glucose (Glycosuria) and ketone bodies (Ketonuria), which indicate diabetes mellitus.

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
(d) ADH	(v) Renal tubule

Answer : The match between the items in column I and column II :

(a) Ammonotelism ----------- (iii) Bony fish

(b) Bowman's capsule ---------- (v) Renal tubule

(c) Micturition ----------- (iv) Urinary bladder

(d) Uricotelism ----------- (i) Birds

(e) ADH --------- (ii) Water reabsorption

8. What is meant by the term osmoregulation?

Answer : Osmoregulation is the physiological process that organisms use to maintain the balance of water and solutes (like salts and ions) within their bodies. It ensures that internal bodily fluids, such as blood or cell cytoplasm, remain at appropriate concentrations, despite changes in the external environment. Osmoregulation is crucial for maintaining internal stability and overall cellular function.

9. Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic,why ?

Answer : Terrestrial animals are typically either ureotelic or uricotelic rather than ammonotelic because ammonia (), the primary nitrogenous waste product in aquatic organisms, is highly toxic and water-soluble. Terrestrial environments pose a challenge for excreting ammonia due to its toxicity and the limited availability of water to dilute it. Urea and uric acid are less toxic and can be excreted with minimal water loss, making them more suitable nitrogenous waste products for land-dwelling animals.

10. What is the significance of juxta glomerular apparatus (JGA) in kidney function ?

Answer :  The juxtaglomerular apparatus (JGA) plays a crucial role in regulating kidney function and maintaining overall homeostasis in the body.

 The significance of juxta glomerular apparatus (JGA) in kidney function : 

Blood Pressure Regulation : The JGA is involved in the control of blood pressure. Specialized cells in the JGA, known as macula densa cells, monitor the sodium chloride (salt) concentration in the filtrate in the distal convoluted tubules. If the concentration is too high, it indicates a higher blood pressure. In response, the macula densa cells signal the adjacent juxtaglomerular cells to release the enzyme renin.

Renin-Angiotensin System : Renin released by the juxtaglomerular cells initiates the renin-angiotensin-aldosterone system (RAAS). This system helps regulate blood pressure by converting angiotensinogen into angiotensin I, which is further converted into angiotensin II. Angiotensin II constricts blood vessels and triggers the release of aldosterone, a hormone that regulates salt and water balance, thus influencing blood pressure.

Volume and Osmolarity Regulation : The JGA helps in regulating the volume and osmolarity of urine. By influencing the reabsorption and secretion of ions and water, the JGA ensures that the body maintains the appropriate balance of fluids and electrolytes.

GFR Regulation : The JGA also plays a role in regulating the glomerular filtration rate (GFR), which is the rate at which blood is filtered by the glomerulus. Through mechanisms like the release of renin, it can help adjust GFR to maintain adequate filtration and avoid excessive loss of essential substances .

11. Name the following:

(a) A chordate animal having flame cells as excretory structures

(b) Cortical portions projecting between the medullary pyramids in the human kidney

(c) A loop of capillary running parallel to the Henle’s loop.

Answer : (a)  A chordate animal having flame cells as excretory structures is Amphioxus, also known as cephalochordate.

(b) Cortical portions projecting between the medullary pyramids in the human kidney: Renal columns (or columns of Bertin) are the cortical portions that project between the medullary pyramids in the human kidney.

(c) A loop of capillary running parallel to the Henle's loop: The loop of capillary running parallel to the Henle's loop is known as the vasa recta.

12. Fill in the gaps :

(a) Ascending limb of Henle’s loop is _______ to water whereas the descending limb is _______ to it.

(b) Reabsorption of water from distal parts of the tubules is facilitated by hormone _______.

(c) Dialysis fluid contain all the constituents as in plasma except _______.

(d) A healthy adult human excretes (on an average) _______ gm of urea/day.

Answer :  (a) Ascending limb of Henle's loop is “ impermeable ” to water whereas the descending limb is “ permeable ” to it.

(b) Reabsorption of water from distal parts of the tubules is facilitated by the hormone ‘‘ ADH ” (Antidiuretic Hormone).

(c) Dialysis fluid contains all the constituents as in plasma except " nitrogenous waste " (waste products e.g. urea and creatinine) .

(d) A healthy adult human excretes (on average) “ 25-30 ” gm of urea per day.