Renal Physiology 5 - Checked and Complete

Question 1

Describe short-term, medium-term, and long-term BP regulation

Answer 1

Short-term: Secs-mins during postural change, exercise, etc…

**Medium-term: **Mins-Hours with renin production

**Long-term: **Changing salt/H20 in body, change blood volume

Question 2

Describe Short-term BP Regulation in detail

Answer 2

** Controlled by brain stem nuclei called the vasomotor center**

1) BP sensors in the carotid arteries and aortic arch report arterial BP to the brain stem.

2) BP sensors in the atria and pulmonary vasculature report venous BP to the brain stem

rain stem then sends signals to the heart and blood vessels to regulate BP via the autonomic nervous system

Question 3

Describe Medium-term BP Regulation in detail.

Answer 3

JGA cells in kidney sense renal afferent arteriolar pressure; can’t send signals to the brainstem, only can receive

Renin released by granular cells in response to sympathetic system or decreased afferent arteriole pressure

Renin cleaves angiotensinogen to form angiotensin I; Angiotensin-converting enzyme (ACE) then cleaves angiotensin I to form angiotensin II (a potent circulating vasoconstrictor)

Thus, low BP = renin secretion = vasoconstriction = increased BP

Question 4

How might the macula densa sense a change in BP?

Answer 4

Less BP = less GFR = low tubular flow and low NaCl leaving the thick ascending loop of Henle = renin release

Question 5

Describe Long-term BP Regulation

Answer 5

90% of ECF osmolarity accounted for by Na and Cl

Helps hold or release water in the long term

Question 6

Define natriuresis

Define pressure natriuresis

Answer 6

excretion of excess Na+ in the urine

Natriuresis because of increased renal arterial pressure

Question 7

What should we know about pressure natriuresis?

Answer 7

**1) it is driven by physical/hemodynamic factors; NOT sensors or circulating factors **

2) it is largely a proximal nephron phenomenon

3) Would not control water/sodium well alone

Question 8

Describe where aldosterone is produced and how it works.

Answer 8

Angiotensin II stimulates aldosterone release from the adrenal cortex

Aldosterone acts on the collecting duct to increase sodium/water reabsorption

Is the “fine-tuning” of kidney sodium output and blood pressure

Question 9

If aldosterone only controls 2% of sodium reabsorption, how can it really affect BP?

Answer 9

**Total Na filtered per day = GFR (per day) x PNa = 180 L/day x 145 mmoles/L = 26,100 mmoles/day **

2% of 26,100 = 522 mmoles/day or about ~30 grams of table salt

Question 10

How does aldosterone work molecularly?

Answer 10

Aldosterone crosses the principal cell membrane and combines with mineralocorticoid receptors in the cytoplasm

Then, the bound-receptor moves to the nucleus where it promotes gene expression and synthesis of new mRNA.

**The mRNA is for proteins that increase the activity or number of, 1) apical Na+ channels and 2) basolateral NaK-ATPase pumps. **

Sodium reabsorption increases and water follows

Question 11

What are some other mechanisms that can pathologically contribute significantly to sodium/BP regulation?

Answer 11

Atrial Natriuretic Peptide (ANP)

Antidiuretic Hormone (ADH)

Estrogen

** Growth hormone**

** Estrogen**

** Thyroid hormone**

Question 12

Describe atrial natriuretic peptide

Answer 12

Distension of the atria triggers ANP release

ANP relaxes the afferent arterioles to increase filtration

** ANP inhibits Na+ reabsorption in the collecting duct**

ANP also inhibits RAAS (inhibition of renin release & ang-II stimulation of aldostrone production)

Sodium is EXCRETED

Question 13

How does ADH work?

Answer 13

1) Increases H2O permeability of the collecting duct by inserting aquaporins at apical membrane of collecting duct

2) Increases Na+ reabsorption by the cortical collecting duct

3) At high concentrations, ADH has vasocontricting effect to increase peripheral resistance; also constricts renal afferent arterioles which reduces GFR and water loss

Question 14

Compare proximal vs distal kidney factors

Answer 14

Proximal factors generally well suited to deal with changes in iso-osmotic body fluid volume

Distal factors are well suited to deal with balancing Na+ excretion with Na+ ingestion.

Both can influence BP because of the intimate relationship between Na+ , osmolarity, volume and BP.

Question 15

Which baroreceptors signal ADH secretion?

Answer 15

** Carotid sinus**

** Aoric arch**

Atrium

Question 16

How/where is osmolarity sensed?

Answer 16

** Sensed in hypothalamus and communicate with neurons to secrete ADH**

Increased osmolarity triggers more ADH release

Question 17

What are minor inputs which affect ADH inadvertently?

Answer 17

**Fear, Pain, Alcohol **

Question 18

Calculate free water clearance

Answer 18

**C_OSM = (U_OSM x V)/P_OSM **

** C_H20=V - C_OSM**

Positive C_H2O means that excess H₂0 was excreted - urine is hypo-osmotic

Negative C_H2O means that H₂0 was retained by the body - urine is hyperosmotic

Question 19

Aldosterone is released from WHICH part of the adrenal gland?

Answer 19

CORTEX