BMS 108 Ch. 17 Renal II

Question 0

Describe how urea contributes to the medullary osmotic gradient?

Answer 0

• urea diffuses out of the collecting duct into the interstitial fluid of the medulla
• contributes to making the medulla hypertonic
• urea then passes into the ascending limb of the Loop of Henle so it recirculates interstitial fluid in the medulla
• water is reabsorbed by osmosis from collecting duct and descending loop

Question 1

What is the role of urea in urine concentration?

Answer 1

Urea is a waste product of amino acid metabolism and helps maintain medullary osmotic gradient.

Question 2

What is the role of the collecting duct?

Answer 2

water conservation

Question 3

Is the collecting duct permeable to salt from the medulla?

Answer 3

no

Question 4

What does H2O permeability in the CD depend on?

Answer 4

Levels of ADH (antidieuretic hormone)&raquo_space; stimulates the insertion of aquaporins into plasma membrane of the CD

Question 5

What regulates homeostasis in plasma concentration?

Answer 5

ADH

Question 6

Describe how ADH maintains homeostasis of plasma concentration.

Answer 6

• Osmoreceptors in hypothalamus sense plasma osmolality
• If high&raquo_space; they tell the posterior pituitary to increase ADH release
• ADH stimulates the insertion of aquaporins in CD
• Water diffuses out of the CD to the renal medulla due to higher osmolality
• and is reabsorbed by the vasa recta

Question 7

What else are kidneys responsible for regulating?

Answer 7

Electrolyte and Acid-Base balance

Question 8

Kidneys regulate levels of Na+, K+, H+, and HCO3- to control blood plasma levels of these electrolytes. What is control of plasma Na+ important for? K+? Ca++?

Answer 8

APs, BP, Blood Volume; APs; Muscle contraction, neurotransmitter release, bones.

Question 9

What is the role of aldosterone in Na+/K+ balance?

Answer 9

Aldosterone controls Na+reabsorption and K+ secretion in the CD

Question 10

How much Na+ and K+ is reabsorbed prior to arriving at the DCT?

Answer 10

90%

Question 11

What happens to Na+ & K+ if aldosterone is not present?

Answer 11

80% of remaining Na+ is reabsorbed in the DCT and cortical CD

Question 12

When aldosterone is high ____ remaining Na+ is reabsorbed. When would you expect aldosterone to be high?

Answer 12

all; When sodium, BP and Blood volume is low (dehydrated).

Question 13

Where is aldosterone secreted from? What is it’s effects?

Answer 13

secreted by the adrenal cortex (steroid); Aldosterone receptors are inside cell nucleus and works by increasing transcription to produce and insert more Na+/K+ pumps.

Question 14

Aldosterone helps regulate blood ________ and _________ through reabsorption and retention of salt (water follows salt).

Answer 14

volume; pressure

Question 15

What triggers aldosterone release? How?

Answer 15

Low blood volume in the renal artery.

Renin-Angiotensin-Aldosterone System (RAAS)

Question 16

How does RAAS increase blood volume and thus blood pressure?

Answer 16

Low BP&raquo_space; Juxtaglomerular apparatus&raquo_space; Renin&raquo_space; Angiotensin I&raquo_space; ACE (Angiotensin Converting Enzyme)&raquo_space; Angiotensin II&raquo_space; Adrenal Cortex&raquo_space; Aldosterone&raquo_space; Salt and water retention in kidneys&raquo_space; increase Blood volume&raquo_space; increase BP

Question 17

What are the two triggers for renin release?

Answer 17

1. Low BP on granular cells directly increases renin release (juxtaglomerular)
2. Sympathetic input to granular cells increase renin release (B1 adrenergic receptors)

Question 18

What does inadequate intake of NaCl lead to? How?

Answer 18

decreased blood volume; because lower osmolality inhibits ADH, causing less H2O reabsorption

Question 19

What is Atrial Natriuretic Peptide (ANP)? What is it’s function?

Answer 19

a hormone produced by atria due to stretching of walls

an aldosterone antagonist (inhibits aldosterone, promotes vasodilation)

stimulates salt and water excretion

acts as an endogenous diuretic

Question 20

What other system other than the kidneys help regulate acid-base balance?

Answer 20

the respiratory system

Question 21

How do kidneys regulate blood pH?

Answer 21

by excreting H+ and/or reabsorbing HCO3- (indirectly)

Question 22

Where does most H+ secretion occur in the nephrons?

Answer 22

PCT in exchange for Na+ (Na+/H+ antiporter)

Question 23

Why is urine slightly acidic (pH = 5-7)?

Answer 23

because the kidneys reabsorb almost all HCO3- and excretes H+

Question 24

Why is reabsorption of HCO3- in the PCT indirect?

Answer 24

because the apical membranes of the PCT cells are impermeable to HCO3-

Question 25

How does HCO3- get from the filtrate to the blood?

Answer 25

1. H2CO3 + CA&raquo_space; H2O + CO2&raquo_space; diffuse into the PCT cell via apical membrane
2. H2O + CO2 + CA&raquo_space; H2CO3&raquo_space; H+ & HCO3-&raquo_space; diffuse from the PCT cell to blood via basal membrane (permeable to HCO3-)

Question 26

What is Renal Plasma Clearance?

Answer 26

“clearing” substances out of the blood plasma

Question 27

What is the equation for excretion rate?

Answer 27

excretion rate = filtration rate + secretion rate - reabsorption rate

Question 28

Reabsorption ________ renal clearance; secretion ______ renal clearance.

Answer 28

decreases; increases

Question 29

Why is renal plasma clearance important?

Answer 29

important for clearing drugs and assessing renal health