Regulation

Question 1

What is excretion?

Answer 1

Excretion is the removal from the body of waste products of metabolism.
Many wastes produced by the body are toxic.
Excretory organs include the lungs, sweat glands, alimentary canal (bile pigments) and the kidneys.

Question 2

Is faeces considered excretion?

Answer 2

Generally, faeces (not counting bile pigments) is not considered excretion.
Most of the faecal content is undigested material. It is not waste product PRODUCED by the cells.
Generally, defaecation is called elimination.

Question 3

What is needed to maintain water balance?

Answer 3

In order to maintain optimum osmotic pressure (concentrations):

Fluid input = Fluid output

Question 4

What is intracellular and extracellular fluid?

Answer 4

Intracellular= fluid inside cells.
Extracellular= fluid outside cells.

Extracellular fluid may be either interstitial (intercellular) fluid, or plasma.

Question 5

Explain the role of antiduretic hormone (ADH) in regulating urine concentration and volume?

Answer 5

1 Concentration of water in the blood decreases.
2 Increase in the osmotic pressure of body fluids, this stimulates osmoreceptors in the hypothalamus.
3 Hypothalamus signals the posterior pituitary gland to release antiduretic hormone.
4 The blood carries ADH to the kidneys.
5 ADH causes the distal convoluted tubules and collecting ducts to increase water reabsorption by osmosis.
6 The urine becomes more concentrated, and urine volume decreases.

Question 6

Explain the negative feedback loop associated with a change in osmotic pressure.

Answer 6

1 Stimulus- Change in osmotic pressure
2 Receptor- Hypothalamus
3 Modulator- Hypothalamus
4 Effector- Cells lining tubules in nephron (DCT and collecting duct)
5 Response- Change in amount of water reabsorbed by nephron.
6 Feedback- Change in osmotic pressure.

Question 7

What is the function of the renal corpuscle?

Answer 7

• Water dissolved substances and small molecules such as glucose, amino acids, urea, and Na+ are filtered out of the glomerulus under high pressure.
• The filtrate is captured in the Bowman’s capsule.
• The afferent vessel is wider than the efferent.

Question 8

What is the function of the proximal convoluted tubule?

Answer 8

• Passive reabsorption of amino acids, glucose, and urea.
• Active reabsorption of Na+, hence the concentration of Na+ increases in the peritubular capillaries causing water to move out passively by osmosis.

Question 9

What is the function of the descending tubule, loop of henle, and ascending tubule?

Answer 9

-Active reabsorption of Na+ continues in the ascending tubule, hence the concentration of Na+ increases in the peritubular capillaries causing water to move out via passive osmosis from the descending tubule.

Question 10

What is the function of the distal convoluted tubule?

Answer 10

• Active secretion of larger molecules (e.g. drugs- penicillin) from the blood.
• Aldosterone produced by the adrenal cortex causes active reabsorption of Na+ and secretion of K+. The concentration of Na+ increases in the peritubular capillaries causing water to move out by osmosis (passive)

Question 11

What is the function of the collecting duct?

Answer 11

• Passive reabsorption of urea. Is impermeable to water.
• Antiduretic hormone secreted from the posterior pituitary causes the collecting duct to become permeable to water and hence promotes active reabsorption of water.

Question 12

Describe what thermoregulation is.

Answer 12

• Humans are endotherms, and lose heat to the environment.
• To maintain a constant (optimal) body temperature, the amount of heat produced must be exactly the same as the amount of heat lost.

Heat input = Heat output

-Thermoregulation is a classic feedback system which involves the same stimulus, receptors and modulator.
Stimulus= change in body temperature.
Receptors= Thermoreceptors
Modulator= Hypothalamus
-The effectors, response and feedback however will be different.

Question 13

Give some detains regarding thermoreceptors.

Answer 13

• Are peripheral.
• Found in the skin and mucous membranes.
• Some are heat receptors, some are cold receptors.
• Central- in the hypothalamus, spinal cord and abdominal organs.
• All thermoreceptors relay information to the hypothalamus (modulator)

Question 14

What are some ways we can lose or gain heat?

Answer 14

When we lose or gain heat it can occur in several ways:

• Conduction: Through one SOLID to another.
• Convection: Through FLUIDS (liquids and gases).
• Evaporation: Change in STATE removes heat (e.g. sweat evaporating)
• Radiation: Through SPACE

Question 15

What changes to the body occur in COLD conditions?

Answer 15

IN COLD CONDITIONS:
To decrease heat loss:
-Peripheral vasoconstriction of blood vessels.
-Reduction in sweating
-Behaviour (jumper)
-Reduction of surface area (curling into a ball)

To increase heat production:

• Shivering
• Increase in voluntary activity (moving)
• Increased metabolic rate by increased secretion of thyroxine and adrenaline.

Question 16

What changes to the body occur in HOT conditions?

Answer 16

IN HOT CONDITIONS:
To increase heat loss:
-Vasodilation of blood vessels in the skin.
-Sweating
-Behaviour (fan)
-Increase surface area.

To decrease heat production:

• Decrease voluntary activity.
• Decreased metabolic rate by decreased thyroxine secretion and adrenaline.