Kidney Function 3 Flashcards
(51 cards)
Where are the osmoreceptors in the brain? (3)
Organum vasculosum lamina terminalis
Median preoptic nucleus
Subfornical organ
What do the osmoreceptors in the brain signal to?
Magnocellular neurosecretory cells in supraoptic and paraventricular nuclei (hypothalamus)
How is ADH synthesised and secreted?
ADH precursor (166aa) synthesised and cleaved to ADH (9aa) in body
Moves down axon to be released from nerve endings in posterior pituitary into blood
What part of the brain is responsible for triggering thirst?
Lateral preoptic area
What is the range of dietary salt intake?
0.05-25g/day
What is the average salt intake per day?
2.3g
What is the total volume of the intracellular fluid?
28L (ECF x 2)
How would low total body sodium affect blood pressure?
Decreased blood volume so decreased blood pressure
How do you calculate the amount of sodium excreted in the urine?
Sodium excreted = sodium filtered - sodium reabsorbed
What two factors are affected to regulate sodium content by the kidney?
GFR
Sodium reabsorption
What does GFR depend on?
Starling forces
Hydraulic permeability
Surface area
What is the aim of extrinsic control?
Maintain arterial blood pressure by affecting GFR
What is the aim of intrinsic control?
Protect renal capillaries from hypertensive damage and maintain a healthy GFR
What does extrinsic control of GFR involve (low bp)? (4)
Activation of sympathetic nervous system (baroreceptor response)
Vasoconstriction of afferent arteriole to decrease hydrostatic pressure
Constriction of mesangial cell smooth muscle to reduce SA
Renin release
What does intrinsic control of GFR involve?
Renal smooth muscle cells surrounding afferent arteriole contract in response to sudden stretch (vasoconstriction)
Tubuloglomerular feedback by juxtaglomerular apparatus controls vasoconstriction (and renin release)
Between what arterial pressures does GFR and renal blood flow remain constant and how?
90-200mmHg
Afferent arterioles constrict or dilate to maintain constant capillary pressure and glomerular blood flow
What sensors are involved in the regulation of sodium reabsorption? (4)
Tubular fluid NaCl concentration receptors - macula densa
Pressure receptors - central arterial tree
Intrarenal baroreceptors - afferent arterioles
Volume receptors - cardiac atria and intrathoracic veins
What are the possible effector pathways involved in sodium reabsorption? (4)
Renin-angiotensin-aldosterone system - stimulates reabsorption
Atrial natriuretic peptide - inhibits reabsorption
Tubuloglomerular feedback - inhibits reabsorption by inhibiting renin release
Dopamine - inhibits reabsorption
How do renal sympathetic nerves cause renin release?
Receives signals from baroreceptors in central arterial tree via cardiovascular centre
Innervate granular renin-containing juxtaglomerular cells (around the afferent arteriole)
How does tubuloglomerular feedback work (high Na/bp)?
Increased NaCl delivery to macula densa (DCT)
Increased Na reabsorption stimulates Na/K-ATPase
Increased rate of adenosine formation so increased interstitial adenosine concentration
Adenosine binds A1 receptors on vascular smooth muscle cells and granular cells
Binding increases calcium concentration in cells resulting in vasoconstriction and decreased renin release
What can cause renin to be released? (3)
Sympathetic stimulation in response to low BP
Decreased Na delivery to macula densa
Decreased wall tension in afferent arteriole (intrarenal baroreceptors) due to decreased BP
(Hypovolemia)
What role does renin have in angiotensin II formation?
Enables rate-limiting step in conversion of plasma angiotensinogen (57aa) to angiotensin I (10aa)
What converts angiotensin I to angiotensin II and where is this found?
Angiotensin converting enzyme
Found on luminal membranes in capillaries of lungs
How many amino acids make up angiotensin II?
8
