Excretion In Humans

Question 1

Definition of excretion

Answer 1

Excretion is the process by which excretory products are removed from the body of an organism

Question 2

Ultrafiltration and selective reabsorption

Answer 2

1. Blood flow from the afferent arteriole into the glomerular then the efferent arteriole.
2. The afferent arteriole has a larger lumen than the efferent arteriole—> this creates a high hydrostatic blood pressure—> that forces water and small molecules eg. Glucose, amino acids, mineral salts and nitrogenous waste products
   Out if the glomerulus and into the bowman’s capsule
3. At the proximal convoluted tubule, most mineral salts, all of the glucose & amino acids are reabsorbed through the walls of the tubule into the surrounding blood capillaries. (Diffusion+active transport ) *it is highly selective, only those substances required by the body are reabsorbed readily. Most water is reabsorbed by osmosis

Question 3

Definition of osmoregulation

Answer 3

It is the control of H2O and solute concentrations in the blood to maintain a constant water potential in the body.

Question 4

Role of anti-diuretic hormone (ADH)

Answer 4

Stimuli: water potential in blood plasma decreases

1. It stimulates the hypothalamus in the brain.
2. Pituitary gland releases more ADH into the bloodstream there will always be a small amount of ADH in the bloodstream
3. Cells in the walls of the collecting ducts become more permeable time water—> more water is reabsorbed by the collecting ducts into the blood capillaries
4. Smaller volume of urine produced—> it will be more concentrated.

Question 5

How does a dialysis machine work?

Answer 5

1. Blood is drawn from the vein in the patient’s arm and is to be pumped into the dialysis machine via the dialysis tubing.
2. The dialysis tubing contains special controlled dialysis fluid and it is partially permeable.
3. The dialysis tubing allows small molecules such as excretory products to diffuse out into the dialysis fluid while precluding blood cells from exiting the dialysis tubing.
4. The filtered blood is then returned to a vein in the patient’s arm.