Unit 4 - Kidneys

Question 1

How is the human body continuously challenged in its attempt to maintain homeostasis?

Answer 1

Metabolic processes require fuel

- produces chemical waste

Question 2

What parameters of the body need to be carefully regulated in order for processes to function effectively?

Answer 2

pH of the body’s blood and other fluids

Question 3

What needs to be carefully controlled in the body?

Answer 3

Water

Key electrolytes

Question 4

What is the water permeability of the glomerulus, proximal convoluted tubule and think descending limb of Henle’s loop?

Answer 4

High to extremely high

Question 5

What is the function of the kidneys ?

Answer 5

Kidneys clear our waste products by passing fluid through a filter - glomerulus
Filtered fluid reclaimed by the portion of the nephron known as the renal tubule
Electrolytes, minerals and other critical particles are reabsorbed while leaving waste and excess fluid for excretion
Kidney has the ability to determine water and electrolyte balance while simultaneously removing body’s waste.
Hormones from brain, heart, adrenal gland and other organs which constantly monitor internal state of body regulate this process.
Has to account example for days when we ingest or lose large amounts of water.

Question 6

What is the water permeability of the thick ascending limb of Henle’s loop, and distal convoluted tubule?

Answer 6

Very low

Question 7

What is the function and permeability of the glomerulus?

Answer 7

Function - formation of glomerular filtrate

Water Permeability - Extremely high

Question 8

What is the function and permeability of the proximal convoluted tubule ?

Answer 8

Reabsorbtion of 65% of filtered Na+/K+/Ca2+ and Mg2+; 85% of NaHCO3, and nearly 100% of glucose and amino acids. Isosmotic reabsorption of water.

Water permeability - Very high

Question 9

What is the function and permeability of the Proximal tubule, straight segments?

Answer 9

Secretion and reabsorption of organic acids and bases, including uric acid and most diuretics
Permeability - very high

Question 10

What is the function and permeability of the thin descending limb of Henle’s Loop ?

Answer 10

Passive reabsorption of water

Permeability - High

Question 11

What is the function and permeability of the thick ascending limb of Henle’s loop ?

Answer 11

Active reabsorption of 15-25% of filtered Na+/K+/Cl-; secondary reabsorption of Ca2+ and MG2+
Permeability - Very low

Question 12

What is the function and permeability of the Distal convoluted tubule ?

Answer 12

Active reabsorption of 4-8% of filtered Na+ and Cl-; Ca2+ reabsorption under parathyroid hormone control
Permeability - Very low

Question 13

What is the function and permeability of the Cortical collecting tubule ?

Answer 13

Na+ reabsorption (2-5%) coupled to K+ and H+ secretion

Water permeability - Variable

Question 14

What is the function and permeability of the medullary collecting duct?

Answer 14

Water reabsorption under vasopressin control

Water permeability - Variable

Question 15

What are the three major compartments for water in the body?

Answer 15

Intracellular space (66%)
- inside cells
Intravascular space (11%)
- inside blood vessels
Interstitial space (22%)
- tissue fluid

Question 16

What happens if the intravascular space is overly filled?

Answer 16

Blood pressure increases

Question 17

What happens if the intravascular space is under filled?

Answer 17

Blood pressure falls

- can lead to shock

Question 18

What happens if accumulation of fluid occurs in the interstitial space?

Answer 18

Oedema

Question 19

Which substances does plasma have high concentrations of?

Answer 19

• sodium
• chloride
• bicarbonate
• protein

Question 20

Which substances does interstitial fluid have high concentrations of?

Answer 20

• sodium
• chloride
• bicarbonate

Question 21

What is the difference between plasma and interstitial fluid?

Answer 21

Similar concentrations of ions
Plasma
- high concentrations of protein
Interstitial fluid
- low concentrations of protein

Question 22

What is the Gibbs-Donnan effect?

Answer 22

This effect predicts that the plasma cation levels will be higher than that of interstitial fluid
prevents electroneutrality
The Gibbs-Donnan effect describes the unequal distribution of permeant charged ions on either side of a semipermeable membrane which occurs in the presence of impermeant charged ions.
At Gibbs-Donnan equilibrium,
On each side of the membrane, each solution will be electrically neutral
The product of diffusible ions on one side of the membrane will be equal to the product of diffusible ions on the other side of the membrane
The electrochemical gradients produced by unequal distribution of charged ions produces a transmembrane potential difference which can be calculated using the Nernst equation
The presence of impermeant ions on one side of the membrane creates an osmotic diffusion gradident attracting water into that compartment.
The mechanisms which maintain the resting membrane potential and the mechanisms of the Gibbs-Donnan effect are different phenomena:
The Donnan equlibrium is a completely passive process: i.e. no active transporters are involved in maintaining this equilibrium.
A Donnan equilibrium is an equilibrium, i.e. ion concentrations on either side of the barrier are static.
If the Donnan equilibrium were to become fully established, the increase in intracellular ions would cause cells to swell due to the osmotic influx of water.
At a Donnan equilibrium, the resting membrane potential would be only about -20 mV. This potential would exist even if the membrane permeability for all ions was the same.
The resting membrane potential, in contrast, requires different permeabilities for potassium and for sodium, and is maintained actively by constant Na+/K+ ATPase activity.
Because biological membranes (especially of exciteable tissues) are never at equilibrium, the Goldman-Hodgkin-Katz equation is usually a better choice for explaining their electrochemical behaviour.

Question 23

What is the function of antidiuretic hormone (ADH)?

Answer 23

Osmoregulation

- regulates toxicity of body fluids causing the kidneys to reabsorb solute free water

Question 24

What is the function of aldosterone?

Answer 24

Homeostatic regulation of blood pressure, plasma sodium and potassium
- influences reabsorption of sodium and excretion of potassium
Part of renin Angiotensin system.

Question 25

What is aldosterone also known as?

Answer 25

Mineralcorticoid

Question 26

What is oedema?

Answer 26

Build up of excess fluid in extracellular spaces (interstitial spaces)