Excretion and Osmoregulation

Question 1

Define excretion and explain its importance.

Answer 1

Excretion is the removal from the body of waste compounds produced during the metabolism of cells. It is essential because the chemical reactions of metabolism produce byproducts that may be toxic if they accumulate.

Question 2

Define osmoregulation

Answer 2

Osmoregulation is the maintenance of a proper balance of water and dissolved substances in the blood. i.e. the maintenance of water and blood potential

Question 3

State the parts that make up a kidney. (3 parts)

Answer 3

Each kidney consists of an outer cortex and inner medulla, with millions of nephrons located part in the cortex and part in the medulla.

Question 4

Describe the parts that make up a nephron.

Answer 4

1. The first part of the nephron is formed into a cup-shaped Bowman’s capsule and the capillary network there is known as the glomerulus. Collectively, the Bowman’s capsule and the glomerulus is known as the Malpighian body. The Malpighian body occurs in the cortex.
2. The proximal convoluted tubule links the Bowman’s capsule to the loop of Henle. It is located partly in the cortex and partly in the medulla.
3. The loop of Henle links the proximal convoluted tubule to the distal convoluted tubule. It largely occurs in the medulla.
4. The distal consulted tubule links the loop of Henle to the collecting ducts. It occurs partly in the medulla and partly in the cortex.
5. The collecting duct largely occurs in the medulla.

Question 5

State the 5 stages of urine formation and the region of the nephron where each stage occurs.

Answer 5

1. Ultrafiltration occurs at the Bowman’s capsule
2. Selective reabsorption occurs at the proximal convoluted tubule
3. Water conservation occurs at the loop of Henle
4. Blood pH and ion concentration regulation occurs at the distal convoluted tubule.
5. Water reabsorption occurs at the collecting duct.

Question 6

Describe what happens during ultrafiltration.

Answer 6

During ultrafiltration, the arteriole supplying blood to the glomerulus is wider than the arteriole leaving the glomerulus, hence blood pressure at the glomerulus is high. This causes water and small molecules to pass out of the glomerulus into the lumen of the Bowman’s capsule. Large molecules are retained in the glomerulus as they are too large to pass through the glomerulus.

Question 7

Describe what occurs during selective reabsorption.

Answer 7

Selective reabsorption occurs in the proximal convoluted tubule, all of the glucose, amino acids, and most of the mineral salts in the glomerular filtrate are reabsorbed into the capillary network via diffusion and active transport.
Most of the water in the filtrate is reabsorbed by osmosis.

Question 8

Describe the processes in the nephron that result in the formation of urine, starting from the proximal convoluted tubule.

Answer 8

Selective reabsorption occurs in the proximal convoluted tubule, all of the glucose, amino acids, and most of the mineral salts in the glomerular filtrate are reabsorbed into the capillary network via diffusion and active transport.
Most of the water in the filtrate is reabsorbed by osmosis. Water is reabsorbed from the filtrate through osmosis at the loop of Henle. Ions and salts are reabsorbed from the filtrate by selective reabsorption in the distal convoluted tubule. The remaining filtrate containing urea, excess water and mineral salts will enter the collecting duct and into the ureter, forming urine.

Question 9

Describe how anti-diuretic hormone (ADH) changes the permeability of the collecting duct?

Answer 9

When we drink a lot of water, the hypothalamus detects the high volume of water in our body above the norm and stops the pituitary gland from secreting anti-diuretic hormone (ADH). Thus the walls of the collecting ducts are less permeable to water, the medulla absorbs less water from the collecting ducts as a result. Hence a large volume of dilute urine is formed.

When we take in too little water/ sweat excessively/ eaten salty food, the hypothalamus detects the low volume of water in our body below the norm and stimulates the posterior pituitary gland to secrete ADH. The walls of the collecting ducts are more permeable, thus the medulla absorbs more water from the collecting duct. Hence a small volume of concentrated urine is formed.