Question 1

Define Glomerular Filtration Rate (GFR).

Accepted Answer

Glomerular filtration rate is the amount of glomerular filtrate formed in all the nephrons of both the kidneys per minute. In a healthy individual, it is about 125 mL/minute. The glomerular filtrate contains glucose, amino acids, sodium, potassium, urea, uric acid, ketone bodies, and large amounts of water.

Question 2

Explain the autoregulatory mechanism of GFR.

Accepted Answer

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.

Question 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.

Accepted Answer

The given statement is true.The proximal convoluted tubule extends from the Bowman's capsule and help in selective reabsorption in the nephron. Glucose present in the renal blood needs to be absorbed by PCT. It is absorbed actively by the sodium glucose transporter present in the membranes of PCT. The transporter pumps the glucose and sodium inside the PCT and the ions are reabsorbed.

Question 4

Give a brief account of the counter current mechanism.

Accepted Answer

The counter current mechanism operating inside the kidney is the main adaptation for the conservation of water. There are two countercurrent 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 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.

Question 5

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

Accepted Answer

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.

Question 6

Explain micturition.

Accepted Answer

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.

Question 7

Match the items of column I with those of column II:

Accepted Answer

Column I 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

Question 8

What is meant by the term osmoregulation?

Accepted Answer

The regulation of water and solute contents of the body fluids by the kidney is called osmoregualtion.

Question 9

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

Accepted Answer

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.

Question 10

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

Accepted Answer

Juxtaglomerular apparatus (JGA) is a complex structure made up of a few cells of the glomerulus, distal tubule, and afferent and efferent arterioles. It is located in a specialised region of a nephron, wherein the afferent arteriole and the distal convoluted tubule (DLT) come in direct contact with each other.The juxtaglomerular apparatus contains specialised cells of the afferent arteriole known as juxtaglomerular cells. These cells contain the enzyme renin that can sense blood pressure. When glomerular blood flow (or glomerular blood pressure or glomerular filtration rate) decreases, it activates juxtaglomerular cells to release renin.Renin converts the angiotensinogen in blood into angiotensin I and further into angiotensin II. Angiotensin II is a powerful vasoconstrictor that increases the glomerular blood pressure and filtration rate. Angiotensin II also stimulates the adrenal cortex of the adrenal gland to produce aldosterone. Aldosterone increases the rate of absorption of sodium ions and water from the distal convoluted tubule and the collecting duct. This also leads to an increase in blood pressure and glomerular filtration rate. This mechanism, known as the renin-angiotensin mechanism, ultimately leads to an increased blood pressure.

Question 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.

Accepted Answer

(a) Flame cell is a type of excretory and osmoregulatory system. Examples of chordate animal having flame cells as excretory structures are Amphioxus, Flatworms, etc.(b) The cortical portions projecting between the medullary pyramids in the human kidney are the columns of Bertini. They represent the cortical tissues present within the medulla.(c)  A loop of capillary that runs parallel to Henle’s loop is known as vasa rectae. Vasa rectae, along with Henle’s loop, maintain a concentration gradient in the medullary interstitium.

Question 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 constituent as in plasma except ........(d) A healthy adult human excretes (on an average) ..........................gm of urea /day

Accepted Answer

(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.

Chapter 19 : Excretory Products and their Elimination