Excretory Products and their Elimination

Q1 Define Glomerular Filtration Rate or GFR

Ans.

Explanation:

Glomerular Filtration Rate or GFR is the rate at which the kidneys form the filtrate in a minute.

For a healthy individual, the GFR is about 180 L/day, that is 125 ml in a minute.

The Glomerular filtrate contains various organic and inorganic molecules like glucose, amino acids, ketone bodies, sodium, potassium etc.

Q2 Explain the autoregulatory mechanism of GFR

Ans. The mechanism by which the kidney regulates the glomerular filtration rate is autoregulative. It is carried out by the juxtaglomerular apparatus. Juxtaglomerular apparatus is a microscopic structure located between the vascular pole of the renal corpuscle and the returning distal convoluted tubule of the same nephron.

It plays a role in regulating the renal blood flow and glomerular filtration rate. 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.

Q3 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.

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

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

Ans. (a) The act of passing the urine is called as micturition. It is a reflex reaction. Distension stimulates the stretch receptors located in the wall of the bladder and the reflex activity is carried out. Hence, the statement is true.

(b) ADH (Anti diuretic hormone) is produced by the hypothalamus and secreted by the neurohypophysis (posterior pituitary gland). ADH increases the re-absorption of water in the collecting ducts and reduces the formation of urine. Hence, the statement is false.

(d) The counter current multiplication in the loop of Henle plays is responsible for concentrating the urine. Hence, the statement is true.

(e) Glucose and sodium are absorbed by the proximal convoluted tubule and returned back to the blood by active transport. Hence, the statement is true.

Q4. Give a brief account of the counter current mechanism.

Ans.

Q5 Describe role of Liver, lungs and skin in the process of excretion.

Ans. Liver, lungs, and skin also play an important role in the process of excretion.

Role of the liver: Liver is the largest gland in the human body. It changes the decomposed haemoglobin pigment into bile pigments called bilirubin and biliverdin. It helps in the excretion of cholesterol, steroid hormones, vitamins, drugs, and other waste materials through bile. Urea is formed in the liver. Ammonia is quickly changed into urea in the liver and then eliminated from the body.

Role of the lungs: Lungs help in the removing waste materials such as carbon dioxide and water as vapour in expired air.

Role of the skin: Skin has has two types of glands which help in excretion of waste products – sweat and sebaceous glands. (i) Sweat glands are highly vascular and tubular glands that excrete excess salt and water from the body in the form of sweat. Sweat helps in thermoregulation. (ii) Sebaceous glands are branched glands that secrete an oily secretion called sebum. It prevents the drying up of skin.

Q6 Explain Micturition

Ans. Micturition is the process by which the urine from the urinary bladder is excreted. As the urine accumulates, the muscular walls of the bladder expand. The walls stimulate the sensory nerves in the bladder, setting up a reflex action. This reflex stimulates the urge to pass out urine. To discharge urine, the urethral sphincter relaxes and the smooth muscles of the bladder contract. This forces the urine out from the bladder. An adult human excretes about 1 – 1.5 litres of urine per day.

Q7 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

(d) Uricotelism (iv) Urinary bladder

(d) ADH (v) Renal tubule

Ans.

Column I Column II

(a) Ammonotelism (iii) Bony fish

(b) Bowman’s capsule (v) Renal tubule

(d) Uricotelism (i) Birds

(e) ADH (ii) Water reabsorption

Q8. What is meant by the term osmoregulation?

Ans. The process by which an organism regulates the water balance in its body and maintains the homeostasis of the body is called osmoregulation. It includes controlling excess water loss or gain and maintaining the fluid balance and the osmotic concentration, that is, the concentration of electrolytes. In humans, the Kidney is the osmoregulatory organ.

Q9 Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic, why ?

Ureotelic - : excreting nitrogen mostly in the form of urea.

Uricotelic - : excreting nitrogen mostly in the form of uric acid birds are typical uricotelic animals.

Ammonotelic - excreting ammonia as the main nitrogenous waste: characteristic of freshwater fishes and many aquatic invertebrates.

Ans. Terrestrial animals are either ureotelic or uricotelic, and not ammonotelic. This is because of the following two main reasons:

(a) Ammonia is highly toxic in nature. Therefore, it needs to be converted into a less toxic form such as urea or uric acid.

(b) Terrestrial animals need to conserve water. Since ammonia is soluble in water, it cannot be eliminated continuously. Hence, it is converted into urea or uric acid. These forms are less toxic and also insoluble in water. This helps terrestrial animals conserve water.

Q10 What is the significance of juxta glomerular apparatus (JGA) in kidney function?

Ans. Juxta glomerular apparatus is a group of specialized cells from afferent arteriole and distal convoluted tubule of a nephron. They help in maintaining the blood pressure and glomerular filtration rate through renin angiotensin system.

Juxta glomerular cells secrete renin based on the stimulation of stretch receptors in the walls of arterioles. They result in aldosterone production and thus regulate the salt absorption from the filtrate and regulate the blood pressure.

Q11 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

Ans.

A. Amphioxus is an example of a chordate that has flame cells as excretory structures. Flame cell is a type of excretory and osmoregulatory system.

B. The cortical portions projecting between the medullary pyramids in human kidney are known as Columns of bertini. They represent the cortical portion between medulla.

C. Vasa recta is a loop of capillary running parallel to henles loop. They together help in maintaining the osmotic gradient in the kidney.

Q 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 _______.

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

Ans.

(a) Henle's loop consists of three parts: Descending limb, Ascending limb, Hair pin bend. Descending limb is permeable to water and impermeable to salt or ions. Ascending limb is impermeable to water and permeable to salt or ions.

Hence, Ascending limb of Henle's loop is impermeable to water whereas the descending limb is permeable to it.

(b) Vasopressin (Antidiuretic hormone, ADH) is secrted by the posterior pituitary. It increases the permeability of the distal convoluted tubules, increasing water reabsorption.

Hence, Reabsorption of water from distal parts of the tubules is facilitated by hormone Vasopressin.

(c) The fluid and solutes in a dialysis process that simply flows through the dialyzer and does not pass through the semipermeable membrane, gets discarded along with removed toxic substances after they flow back out of the dialyzer. It contains sodium, potassium, calcium, bicarbonate, magnesium, chloride and glucose.

Hence, Dialysis fluid contain all the constituent as in plasma except nitrogenous waste.

(d) About 95% of nitrogen is excreted as urea through urine. A healthy adult person normally excretes about 25 - 30 grams of urea per day.