Homestasis

Question 1

What is homeostasis?

Answer 1

The maintenance of steady states within the body

Question 2

What are the three basic features?

Answer 2

1) A control system with sensors which allow the monitoring of factors
2) Departure from set point = corrective mechanism put in place
3) Involvement of a negative feedback system to prevent overcorrection

Question 3

What are the two types of control and what do they control?

Answer 3

1) Nervous control e.g. Temperature

2) Hormonal e.g. blood glucose level

Question 4

What does homeostasis provide/prevent?

Answer 4

Provides - optimum conditions for enzyme action

Prevents - osmotic issues

Question 5

Describe the two important functions of the kidney

Answer 5

1) Excretion - removal of the toxic waste of metabolism. e.g. Urea and Creatinine
2) Osmoregulation - control of the water potential of body fluids.

Question 6

Describe the structure of the urinary system.

Answer 6

Blood travelling from aorta reaches Renal artery at high pressure, leaves by the Renal vein whereas the waste products and excess water pass to the ureter as urine.

Question 7

What are the two main zones of the kidney? and what is its functional unit?

Answer 7

Cortex - Outer region
Medulla - Inner region

Functional unit - Nephron

Question 8

What is the first function of the kidney?

Answer 8

Excretion

Question 9

Describe the two processes of excretion.

Answer 9

1) Ultrafiltration - The filtration of plasma and substances below a certain size into the Bowman’s capsule
2) Reabsorption - Filtered useful products are REabsorbed back into the bloodstream.

Question 10

What does the high hydrostatic pressure cause and how is it created?

Answer 10

The blood entering glomerulus has a high hydrostatic pressure because:
1) Short distance from the heart
2) Afferent > efferent
3) Coiling of the capillaries in the glomerulus restricts
blood flow thus increasing pressure.
High pressure means small molecules (glucose, amino acids, salts, urea) are forced out of capillaries into Bowman’s capsule. Larger ones are not able to be forced out.

Question 11

How is ultrafiltration aided?

Answer 11

3 layers separate the plasma from the filtrate: Capillary ENDOthelium, basement membrane and the inner layer of the Bowman’s capsule. Two of these are v. porous:

1) The ENDOthelium of the capillaries - a single layer of squamous endothelial cells with pores between them.
2) Podocytes - extend in two planes have foot like processes which surround the capillaries but have spacious gaps called filtration slits between them.

Question 12

What does the basement membrane do?

Answer 12

It is an extracellular matrix which acts as the effective filter.

Question 13

What is glomerular filtrate?

Answer 13

similar to blood except with no blood cells or proteins.

Question 14

What is filtration force?

Answer 14

Water potential in the blood plasma must be more negative than the water potential in the glomerular filtrate.

Question 15

What are the two components of water potential?

Answer 15

Pressure potential and solute potential. The pressure potential of the blood is much greater than the back pressure created by the filtrate.

Question 16

What is the solute potential?

Answer 16

Represented by plasma proteins as the are only plasma proteins in the blood NOT the filtrate. Filtrate is less negative. Although the difference in solute potential opposes filtration, it is INSIGNIFICANT when compared to the differences in hydrostatic pressure.

Question 17

Describe reabsorption (PCT)

Answer 17

Useful products SELECTIVELY REABSORBED. Glucose and amino acids travel along the PCT and are selectively reabsorbed via facilitated diffusion and active transport. 70% of water then follows via osmosis. Pinocytosis of small proteins. The Cuboidal epithelial cells have a high level of metabolic activity. At the end of the PCT all glucose and amino acids will have been reabsorbed. Flow of filtrate maintains concentration gradient.

Question 18

Describe reabsorption (DCT)

Answer 18

Depending on permeability some water may also be absorbed.

Question 19

Describe the role of the Loop of Henlé.

Answer 19

Enable mammals to produce a hypertonic urine, significant role in water reabsorption.

Question 20

Descending limb and ascending limb

Answer 20

Descending - Thin and permeable to water

Ascending - Thick and impermeable to water

Question 21

What does the loop of Henlé do?

Answer 21

Ascending limb secretes Na+ and Cl- ions into the medulla. NaCl builds up in the interstitial fluid creating a v. negative solute potential. Due to negative water potential in the medulla water is drawn out of the descending limb via osmosis. Thus causing the filtrate in the descending limb to become more concentrated. Solution at the bottom becomes hypertonic to the blood.

Question 22

What is the concurrent multiplier effect

Answer 22

Osmotic differences between Descending and Ascending limb are small but the cumulative effect of the million nephrons is large.

Question 23

What is the effect of a longer loop of henle

Answer 23

More water can be absorbed

Question 24

Kidney function 2 - Osmoregulation

Answer 24

The homeostatic process that controls water balance in the body. Controlled by the Antidiuretic hormone (ADH)

Question 25

Where is ADH produced and stored. and how is the solute potential monitored.

Answer 25

Produced - HYPOTHALAMUS
Stored - POSTERIOR LOBE OF THE PITUITARY GLAND

Monitored by osmoreceptors in the hypothalamus

Question 26

What happens when you sweat on a hot day/ not drinking water

Answer 26

• Osmoreceptors detect solute potential becomes MORE negative
• Posterior lobe of the pituitary gland releases MORE ADH into the blood
• MORE aquaporins in the DCT and collecting duct open making it become MORE permeable
• MORE water is reabsorbed
• Solute potential returns to normal, smaller volume of MORE concentrated hypertonic urine produced.
• Negative feedback prevents overcorrection