Renin Angiotensin Aldosterone System and Erythropoietin

Question 1

explain how the renin angiotensin aldosterone system works (5)

Answer 1

1. the liver produces angiotensinogen
2. in response to a stimulus, the kidney releases renin into circulation, which cleaves 10 amino acids from angiotensinogen; those 10 AAs are angiotensin I
3. angiotensin-converting enzyme then removes 2 AAs from angiotensin I, leaving the 8 AA long angiotensin II
4. angiotensin II then causes vasoconstriction of systemic and glomerular arterioles (preferentially constricting the efferent arterioles), and increases renal Na+ absorption
5. additionally, angiotensin II stimulates the adrenal glands to secrete aldosterone, a steroid hormone that increases renal Na+ absorption and K+ secretion

Question 2

what are the 3 key roles of the renin angiotensin aldosterone system in health and disease?

Answer 2

1. regulates blood pressure, fluid volume, and electrolyte balance in health
2. combats systemic arterial hypotension in during blood loss, dehydration, and circulatory shock
3. has an important, but adverse role in kidney disease, heart disease, and systemic renal hypertension

Question 3

explain how the renin angiotensin aldosterone system regulates sodium balance, extracellular fluid volume, and blood pressure (3)

Answer 3

angiotensin II is

1. a potent vasoconstrictor in systemic and glomerular arteries that increases systemic vascular resistance and therefore raising systemic arterial blood pressure within seconds; its preferential vasoconstriction of efferent arterioles also increases glomerular capillary pressure to increase or maintain GFR during renal hypoperfusion
2. promotes circulating volume expansion by increasing sodium reabsorption in the proximal, distal, and collecting tubules as well as stimulating thirst, appetite, and secretion of ADH
3. stimulates aldosterone secretion which increases Na+ reabsorption (plus K+ and H+ secretion) in the distal nephron

Question 4

how does aldosterone increase blood volume? list one additional function of aldosterone

Answer 4

1. its primary function is to promote renal Na+ reabsorption and K+ excretion; so by promoting Na+ retention, it promotes water retention, which will increase blood volume and gradually raise systemic arterial blood pressure over a few days
2. contributes to acid-base balance by influencing the activity of the intercalated cells in the distal tubule and collecting duct

Question 5

how is aldosterone release by the adrenal glands regulated? (2)

Answer 5

1. increased concentration of angiotensin II in the ECF greatly increases aldosterone secretion
2. increased K+ concentration in the ECF greatly increases aldosterone secretion

Question 6

identify the main functions of the renin angiotensin aldosterone system and its components

Answer 6

main function of the system: help preserve GFR in low-volume states with simultaneous increases in renal Na+ and H2O reabsorption to maintain circulating volume

does this by increasing total body Na+ and water which increases ECF and increases blood pressure and also by improving vascular tone which increases systemic vascular resistance which also increases blood pressure

Question 7

list the stimuli (3) for activation of the renin angiotensin aldosterone system and conditions (3) in which this system is activated

Answer 7

stimuli: decreased systemic arterial pressure (less afferent stretch), decreased Na+ delivery to the macula densa, and increase sympathetic stimulation of the JGA

these stimuli can occur in conditions of dehydration, systemic hypotension, and sodium depletion

Question 8

predict changes in glomerular filtration rate and electrolyte balance caused by activation or inhibition of the renin angiotensin aldosterone system

Answer 8

activation would increase/maintain GFR and leads to Na+ reabsorption and K+ secretion

inhibition would decrease GFR and decrease Na+ reabsorption, as well as INCREASE BLOOD BUN AND CREATININE!!! (endogenously produced substances that are eliminated by renal filtration will increase in concentration in the blood when GFR decreases)

Question 9

identify the stimuli (3) for erythropoietin release, its target tissue, and main function

Answer 9

stimuli: decreased red blood cell count, decreased availability of oxygen to blood or increase tissue demand for oxygen

kidney (plus a little bit from liver) release eyrthropoietin, which stimulates red bone marrow to enhance erythropoiesis, increasing RBC count and increasing the oxygen-carrying capacity of blood