Renal - Physiology (Hormones)

Question 1

What are 3 stimuli that cause the release of renin? Which structures are responsible for detection of these stimuli?

Answer 1

Kidney; (1) Decreased BP (JG cells) (2) Decreased Na + delivery (macula densa cells) (3) Increased sympathetic tone (Beta 1-receptors)

Question 2

What releases renin? What function does renin serve?

Answer 2

Kidney; Converts angiotensinogen to angiotensin I

Question 3

What releases Angiotensinogen?

Answer 3

Liver

Question 4

What releases ACE? What functions does it serve?

Answer 4

Lungs and kidney; (1) Converts angiotensin I to angiotensin II (2) Bradykinin breakdown

Question 5

What 6 functions does angiotensin II have?

Answer 5

(1) Acts at AT I receptors on vascular smooth muscle –> Vasoconstriction –> Increase BP (2) Constricts efferent arteriole of glomerulus –> Increase FF to preserve renal function (GFR) in low-volume states (i.e., when RBF decrease) (3) Triggers release of Aldosterone (from adrenal gland) –> Increase Na+ channel and Na+/K+ pump insertion in principal cells, Enhances K+ and H+ excretion (upregulates principal cell K+ channels and intercalated cell H+ ATPases) –> Creates favorable Na+ gradient for Na+ and H2O reabsorption (4) Triggers release of ADH (from posterior pituitary) –> Increase H2O channel insertion in principal cells –> H2O reabsorption (5) Increase proximal tubule Na+/H+ activity –> Na+, HCO3-, and H2O reabsorption (can permit contraction alkalosis) (6) Simulates hypothalamus –> Thirst

Question 6

What effect does angiotensin II have on vasculature, and how? What ultimate effect does this have?

Answer 6

Acts at AT I receptors on vascular smooth muscle –> Vasoconstriction –> Increase BP

Question 7

What effect does angiotensin II have on the glomerulus? What consequence does this have?

Answer 7

Constricts efferent arteriole of glomerulus –> Increase FF to preserve renal function (GFR) in low-volume states (i.e., when RBF decreases)

Question 8

What effect does angiotensin II have on the adrenal gland? What consequence does this have?

Answer 8

Aldosterone (adrenal gland) –> Increase Na+ channel and Na+/K+ pump insertion in principal cells; Enhances K+ and H+ excretion (upregulates principal cell K+ channels and intercalated cell H+ ATPases) –> Creates favorable Na+ gradient for Na+ and H2O reabsorption

Question 9

What effect does angiotensin II have on the posterior pituitary? What consequence does this have?

Answer 9

ADH (posterior pituitary) –> Increase H2O channel insertion in principal cells –> H2O reabsorption

Question 10

What effect does angiotensin II have on the proximal tubule? What consequence does this have?

Answer 10

Increase proximal tubule Na+/H+ activity –> Na+, HCO3-, and H2O reabsorption (can permit contraction alkalosis)

Question 11

What part of the brain does angiotensin II affect? What consequence does this have?

Answer 11

Stimulates hypothalamus –> thirst

Question 12

What is the main purpose of ATII, and how does it mainly accomplish this?

Answer 12

Affects baroreceptor function; limits reflex bradycardia, which would normally accompany its pressor effects. Helps maintain blood volume and blood pressure.

Question 13

From where is ANP released, and in response to what?

Answer 13

Released from atria in response to increased volume

Question 14

What impact can ANP have on the renin-angiotensin-aldosterone system?

Answer 14

May act as a “check” on renin-angiotensin-aldosterone system

Question 15

What effect does ANP have on vasculature, and how? What consequences does this have?

Answer 15

Relaxes vascular smooth muscle via cGMP, causing increased GFR, decreased renin.

Question 16

What is the primary function of ADH? To what does it respond?

Answer 16

Primarily regulates osmolarity; also responds to low blood volume states.

Question 17

What is the primary function of Aldosterone? To what does it respond?

Answer 17

Primarily regulates ECF Na+ content and volume; Responds to low blood volume states.

Question 18

What does “Juxta” mean? What is contained in the juxtaglomerular apparatus? Name and define these parts.

Answer 18

Juxta = close by; Consists of JG cells (modified smooth muscle of afferent arteriole) and the macula densa (NaCl sensor, part of the distal convoluted tubule)

Question 19

What is the act of JG cells? In response to what 3 things does it act?

Answer 19

JG cells secrete renin in response to (1) decreased renal blood pressure, (2) decreased NaCl delivery to distal tubule, and (3) increased sympathetic tone (Beta 1).

Question 20

What end goal does the JGA accomplish, and how?

Answer 20

JGA defends GFR via renin-angiotensin-aldosterone system.

Question 21

How do Beta-blockers work in the kidney?

Answer 21

Beta-blockers can decrease BP by inhibiting Beta1-receptors of the JGA, causing decreased renin release

Question 22

What releases erythropoietin? To what is it released in response?

Answer 22

Released by interstitial cells in the peritubular capillary bed in response to hypoxia.

Question 23

What relation does vitamin D have to the kidney? Which part of the kidney is involved?

Answer 23

Proximal tubule cells convert 25-OH vitamin D (inactive form) to 1,25-(OH)2 vitamin D (active form)

Question 24

What enzyme converts 25-OH vitamin D to 1,25-(OH)2 vitamin D, and where? What stimulates this enzyme?

Answer 24

1 alpha-hydroxylase; Proximal tubule cells; PTH

Question 25

What secretes renin, and in response to what?

Answer 25

Secreted by JG cells in response to decreased renal arterial pressure and increased renal sympathetic discharge (Beta 1 effect).

Question 26

How are prostaglandins secreted, and what effect do they have?

Answer 26

Paracrine secretion vasodilates the afferent arterioles to increase RBF

Question 27

By what mechanism do NSAIDs work? What effects can they have?

Answer 27

NSAIDs block renal-protective prostaglandin synthesis –> constriction of afferent arteriole and decreased GFR; this may result in acute renal failure

Question 28

Name 5 hormones acting on the kidney.

Answer 28

(1) Angiotensin II (AT II) (2) Atrial natriuretic peptide (ANP) (3) Parathyroid hormone (PTH) (4) Aldosterone (5) ADH (vasopressin)

Question 29

In response to what is AT II synthesized?

Answer 29

Synthesized in response to decreased BP.

Question 30

What direct effects does AT II have on the kidney? What is the net effect?

Answer 30

Causes efferent arteriole constriction –> increased GFR and increased FF but with compensatory Na+ reabsorption in proximal and distal nephron. Net effect: preservation of renal function in low-volume state (increased FF) with simultaneous Na+ reabsorption (both proximal and distal) to maintain circulating volume.

Question 31

In response to what is ANP synthesized?

Answer 31

Secreted in response to increased atrial pressure.

Question 32

What direct effects does ANP have on the kidney? What is the net effect?

Answer 32

Causes increased GFR and increased Na+ filtration with no compensatory Na+ reabsorption in distal nephron. Net effect: Na+ loss and volume loss.

Question 33

In response to what is PTH secreted?

Answer 33

Secreted in response to decreased plasma [Ca2+], increased plasma [(PO4)3-], or decreased plasma [1,25-(OH)2 vitamin D].

Question 34

What direct effects does PTH have?

Answer 34

Causes increased [Ca2+] reabsorption (DCT), decreased [(PO4)3-] reabsorption (PCT), and increased 1,25-(OH)2 vitamin D production (increased Ca2+ and (PO4)3- absorption from gut via vitamin D)

Question 35

In response to what is Aldosterone secreted?

Answer 35

Secreted in response to decreased blood volume (via AT II) and increased plasma [K+]

Question 36

What direct effects does Aldosterone cause?

Answer 36

Causes increased Na+ reabsorption, increased K+ secretion, and increased H+ secretion.

Question 37

What is another name for ADH? In response to what is it secreted?

Answer 37

ADH (vasopressin); Secreted in response to increased plasma osmolarity and decreased blood volume.

Question 38

What direct effects does ADH (vasopressin) cause, and how?

Answer 38

Binds to receptors on principal cells, causing increased number of water channels and increased H2O reabsorption.

Question 39

Where in the kidney do each of the following hormones mainly act: (1) AT II (2) ANP (3) PTH (4) Aldosterone (5) ADH (vasopressin).

Answer 39

(1) Glomerulus (2) Glomerulus & DCT (3) PCT & DCT (4) Collecting tubule (5) Collecting tubule.