Homeostasis & Excretion

Question 1

What is homeostasis?

Answer 1

The maintenance of a constant internal environment, providing a degree of independence from the external environment.

Question 2

What are comformers and regulators?

Answer 2

Regulators maintain a constant internal environment despite changes in external environment.

Conformers allow their internal conditions to fluctuate in response to external environment.

ectotherms vs endotherms

Question 3

How does skin regulate internal temperature

Answer 3

1. Subcutaneous fats > Insulation
2. Arterioles dilate/constrict > More/less blood flows to skin capillaries > Increase/decrease Heat loss by radiation, conduction, convection through skin
3. Hairs stand on end > trap layer of air > air poor conductor, insulation
4. Sweat glands secrete sweat > latent heat is removed when sweat evaporates

Question 4

What are the corrective mechanisms when body temperature falls

Answer 4

• Sweat glands produce less sweat
• Increased metabolic rate —> more heat released by cellular respiration
• Shivering-involuntary spasmodic contraction of skeletal muscles released heat
• Arterioles constrict –> less blood sent to skin capillaries –> less heat is lost by radiation, conduction, convection through skin

Question 5

Where does ultrafiltration take place? Explain the process of ultrafiltration.

Answer 5

Ultrafiltration takes place at the renal corpuscle

As afferent arteriole is wider than efferent arteriole, there is a high
hydrostatic blood pressure in the glomerulus

As the glomerular capillaries is partially permeable, small molecules
(glucose, amino acids, mineral salts, urea) are filtered out

Large surface area of glomerular capillaries produces large volume of glomerular filtrate ~ 10% blood plasma

Question 6

Where does selective reabsorption take place? Explain this process

Answer 6

Selective reabsorption takes place in the renal tubules.

Glucose, amino acids, and mineral salts are reabsorbed via diffusion and active transport from the proximal convoluted tubule into the capillaries, while water is reabsorbed via osmosis.

At the loop of Henle, distal convoluted tubule (structure X) and collecting duct, some water and salts are reabsorbed from the filtrate in the tubule as the filtrate becomes more dilute.

Question 7

What is the effect of anti-diuretic hormone?

Answer 7

• ADH transported in blood to kidneys where it:
• Makes cell in walls of the the proximal distal tubule and collecting ducts more permeable to water
• Increase amount of water reabsorbed