RS: Renal Mechanisms

Question 1

What part of the kidney nephrons is responsible for bulk reabsorption?

Answer 1

Proximal convoluted tubule

Question 2

What part of the kidney nephrons is responsible for fine control of filtrate content?

Answer 2

Distal convoluted tubule and the collecting ducts

Question 3

What region of the kidney nephrons is responsible for the concentration of urine and water recovery?

Answer 3

The loop of Henle

Question 4

What is the countercurrent mechanism?

Answer 4

Occurs when adjacent vessels contain8ng fluid, flowing in opposite directions, use energy to create a concentration gradient. Allows the regulation of urine concern with production of dilute urine which can be concentrated in the presence of ADH.

Question 5

What are the 2 renal countercurrent mechanisms?

Answer 5

1. Countercurrent multiplication mechanism

2. Countercurrent exchanger mechanism

Question 6

What happens during the countercurrent multiplication mechanism?

Answer 6

generation of an osmotic gradient from the renal cortex (isotonic) to the tip of the renal medulla (hypertonic) by juxtamedullary loop of Henle. Energy consuming process that produces a small osmotic difference between descending and ascending limbs of the loop of Henle that allows the control of water reabsorption, as required, to generate highly concentrated urine.

Question 7

What happens during the countercurrent exchanger mechanism?

Answer 7

Vasa recta capillaries are highly permeable to sodium, chloride, urea and water. Descending blood loses water and gains NaCl as it descends, whereas ascending limb progressively gains water and loses NaCl to ensure water doesn’t dilute hypertonic medulla. No net gain or loss of water of NaCl salt.

Question 8

What is the role of the countercurrent exchange mechanism?

Answer 8

Generated by the vasa recta capillaries supplying the renal medullas. Prevents the corticomedullary gradient from dissipating. Passive process; does not require ATP.

Question 9

What are the 3 structures in the loop of Henle?

Answer 9

1. Descending loop
2. Thin ascending loop
3. Thick ascending loop

Question 10

What is the structure of the descending loop of Henle?

Answer 10

Thin cells with few mitochondria. Membrane is permeable to water and minimally permeable to ions and solutes.

Question 11

What is the structure of the thin ascending loop of Henle?

Answer 11

Impermeable to water but permeable to sodium ions.

Question 12

What is the structure of the thick ascending loop of Henle?

Answer 12

Cells are thick and rich with mitochondria. Impermeable to water but permeable to sodium ions. Sodium ions are actively pumped into the medullary matrix via NKCC2 membrane transport proteins.

Question 13

What contributes to the hyper osmotic gradient in the ascending loop of Henle?

Answer 13

Urea reabsorption contributes to the hyperosmotic gradient in the ascending loop of Henle, to allow the further movement of ions out of the filtrate. ADH can also promote facilitated urea transport out of the CD.

Question 14

Where is renin released from?

Answer 14

Cells in the juxtaglomerular apparatus (JGA); granular cells and macula densa cells.

Question 15

Where are granular cells and macula dansa cells found?

Answer 15

Granular cells are mainly found within the walls of the afferent arterioles whereas macula dansa cells are found within the walls of the distal convoluted tubule where it enters the renal cortex.

Question 16

What are the 3 pathways by which renin secretion is regulated?

Answer 16

1. Afferent arterial baroreceptors
2. Beta-adrenergic receptor mechanisms
3. Macula dansa cell mechanisms

Question 17

Describe the afferent arterial baroreceptor pathway for the regulation of renin secretion

Answer 17

Decreased blood volume (and pressure) is detected by renal afferent baroreceptors which stimulate the release of renin from granular cells

Question 18

Describe the beta-adrenergic receptor mechanism for the regulation of renin secretion

Answer 18

Decreased blood volume (and pressure) is detected by carotid artery receptors and triggers increased sympathetic innervation which stimulates renin release from granular cells

Question 19

Describe the macula densa cell mechanism for the regulation of renin secretion

Answer 19

Macula densa cells detect low levels of NaCl in the distal convoluted tubule filtrate and the decreased blood volume (and pressure) which leads to a decreased GFR. Stimulates macula densa cells to release prostaglandins (PGI2) which cause renin release by granular cells.

Question 20

What cells in the juxtaglomerular apparatus are responsible for renin secretion?

Answer 20

Granular cells

Question 21

What is renin?

Answer 21

Renin is a proteolysis enzyme that converts angiotensinogen to angiotensin I

Question 22

How is angiotensin I converted to angiotensin II?

Answer 22

By action of ACE (Angiotensin Converting Enzyme)

Question 23

What does angiotensin II do?

Answer 23

Angiotensin II is a potent vasoconstrictor which helps to increase systemic blood pressure. Angiotensin II also activates the thirst centre in the hypothalamus and triggers the production and release of ADH. Angiotensin II also promotes aldosterone biosynthesis.

Question 24

Where is aldosterone synthesised?

Answer 24

In the adrenal cortex

Question 25

What is the role of aldosterone?

Answer 25

Aldosterone stimulates the reabsorption of water and sodium ions, in exchange for potassium or hydrogen ions, from the urine, ultimately increasing blood pressure.