BMS 108 Ch. 17 Renal II Flashcards
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Describe how urea contributes to the medullary osmotic gradient?
- 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
What is the role of urea in urine concentration?
Urea is a waste product of amino acid metabolism and helps maintain medullary osmotic gradient.
What is the role of the collecting duct?
water conservation
Is the collecting duct permeable to salt from the medulla?
no
What does H2O permeability in the CD depend on?
Levels of ADH (antidieuretic hormone)»_space; stimulates the insertion of aquaporins into plasma membrane of the CD
What regulates homeostasis in plasma concentration?
ADH
Describe how ADH maintains homeostasis of plasma concentration.
- Osmoreceptors in hypothalamus sense plasma osmolality
- If high»_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
What else are kidneys responsible for regulating?
Electrolyte and Acid-Base balance
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++?
APs, BP, Blood Volume; APs; Muscle contraction, neurotransmitter release, bones.
What is the role of aldosterone in Na+/K+ balance?
Aldosterone controls Na+reabsorption and K+ secretion in the CD
How much Na+ and K+ is reabsorbed prior to arriving at the DCT?
90%
What happens to Na+ & K+ if aldosterone is not present?
80% of remaining Na+ is reabsorbed in the DCT and cortical CD
When aldosterone is high ____ remaining Na+ is reabsorbed. When would you expect aldosterone to be high?
all; When sodium, BP and Blood volume is low (dehydrated).
Where is aldosterone secreted from? What is it’s effects?
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.
Aldosterone helps regulate blood ________ and _________ through reabsorption and retention of salt (water follows salt).
volume; pressure
What triggers aldosterone release? How?
Low blood volume in the renal artery.
Renin-Angiotensin-Aldosterone System (RAAS)
How does RAAS increase blood volume and thus blood pressure?
Low BP»_space; Juxtaglomerular apparatus»_space; Renin»_space; Angiotensin I»_space; ACE (Angiotensin Converting Enzyme)»_space; Angiotensin II»_space; Adrenal Cortex»_space; Aldosterone»_space; Salt and water retention in kidneys»_space; increase Blood volume»_space; increase BP
What are the two triggers for renin release?
- Low BP on granular cells directly increases renin release (juxtaglomerular)
- Sympathetic input to granular cells increase renin release (B1 adrenergic receptors)
What does inadequate intake of NaCl lead to? How?
decreased blood volume; because lower osmolality inhibits ADH, causing less H2O reabsorption
What is Atrial Natriuretic Peptide (ANP)? What is it’s function?
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
What other system other than the kidneys help regulate acid-base balance?
the respiratory system
How do kidneys regulate blood pH?
by excreting H+ and/or reabsorbing HCO3- (indirectly)
Where does most H+ secretion occur in the nephrons?
PCT in exchange for Na+ (Na+/H+ antiporter)
Why is urine slightly acidic (pH = 5-7)?
because the kidneys reabsorb almost all HCO3- and excretes H+
