Lecture 58 - Collecting Ducts Flashcards
what are the 3 basic renal processes
- glomerular filtration
- tubular reabsorption
- tubular secretion
why is there reabsorption?
because it is impossible and metabolically wasteful to intake the water and electrolytes needed to replenish waste
glomerular capillary bed
- specialized for filtration
- produce ultrafiltrate under high blood pressure
peritubular capillaries
- from efferent arterioles
- associated w renal tubules
- low-pressure and high oncotic pressure
- reabsorption of solutes and water
proximal convoluted tubule
- responsible for the majority of reabsorption
- large # of mitochondria
- microvilli increases surface area
how are tubular cells connected
via tight junction and trans-/para-cellular pathways
what barriers must a transcellular pathway pass between
- luminal membrane of tubular cells
- basolateral membrane of tubular cells
- endothelium of capillary
what is reabsorbed in the PCT
- water
- sodium
- chloride
- bicarb
- glucose
- amino acids
water reabsorption is driven by
starling forces
what stimulates water reabsorption
- high oncotic pressure
- low hydrostatic pressure
glomerulotubular balance
constant fraction of the filtered load is reabsorbed at the proximal tubules
Give examples of increased GFR
constriction of efferent arteriole increases the amount of blood that is filtered
Give examples of increased reabsorption
higher oncotic pressure in the blood in the peritubular capillary will increase the amount of fluid reabsorbed from filtrate to capillary
water moves through
aquaporins
T/F: the resting state of aquaporins can be “open” or “closed”
TRUE
where are aquaporins always open
proximal convoluted tubule
where are aquaporins always closed
collecting ducts
glucose is reabsorbed with ____ in the PCT
Na+
what 2 carrier proteins are required for glucose transport in the renal system
- SGLT-2
- GLUT-2
SGLT-2
Na+ and glucose
Na+ out by APTase
Glucose in due to concentration/electrical gradient
GLUT-2
glucose from cytoplasm to interstitial fluid
passively reabsorbed
what can you give a cat with insulin-non-dependent diabetes
SGLT-2 inhibitor
when glucose exceeds the renal threshold it “spills over” to
urine
T/F: glucose cannot change osmolarity
FALSE
chronic hyperglycemia causes
- poor wound healing
- recurrent infections
- cataracts
Fanconi syndrome
disorder of the PCT where electrolytes and amino acids are not reabsorbed
increased glucose, cystine (AA), and bicarb in urine
How is glucose reabsorbed in the PCT
- glucose is transported from the tubule lumen
- PCT cell via SGLT-2
- from PCT cell to interstitium via GLUT-2
the descending limb is where urine is
concentrated
describe reabsorption in the descending limb
- only water-permeable
- no solute movement
- interstitial osmotic gradient drives
describe reabsorption in the thin ascending limb
- impermeable to water
- permeable to NaCl (passive reabsorption)
where is urine secreted into filtrate
thin ascending limb
describe reabsorption in the thick ascending limb
- impermeable to water
- reabsorption of Na+ (active with symporter and anitporters)
overall the ascending loop is where urine is
diluted
How does the osmolality of ultrafiltrate entering the DCT compare to that in the PCT
ultrafiltrate in entering the DCT has a LOWER osmolality
aldosterone regulates ___ absorption and ___ secretion
Na+; K+
the reabsorption of ___ and secretion of ___ is important for pH regulation
HCO3-; H+
parathyroid hormone regulates ___ absorption
Ca2+
describe the DCT
- macula densa
- less reabsorption than PCT
- fine-tuning of ultrafiltrate
describe the collecting ducts
- collect filtrate from multiple nephrons
- final step of filtrate manipulation
- directs filtrate to ureter
what are the 2 major cell types in collecting ducts
- principal cells
- intercalated discs
principal cells
- more numerous, shorter microvilli
- Na+/urea reabsorption and K+ secretion
intercalated cells
- longer microvilli
- pH regulation
describe the principal and intercalated cells regarding aldosterone
principal = Na+ reabsorption and P secretion
intercalated cells = Cl- reabsorption and HCO3- secretion
why may aniamls with Addison’s have hyponatremia and hyperkalemia
they lack aldosterone
T/F: the aquaporins in collecting ducts are only open with anti-diuretic hormone is present
TRUE
Anti-diuretic hormone (arginine vasopressin)
- peptide hormone produced in hypothalamus and secreted from PP in response to volume or osmolality change
- causes aquaporins to move to surface
ADH ____ urine concentration
increases
what drives resorption in collecting ducts
interstitial osmotic gradient
diabetes insipidus occurs for what 2 reasons
- lack of ADH (central)
- impaired response of kidney to ADH (nephrogenic)
describe tubular secretion
- removing substances that are protein-bound
- removing unwanted substances that were reabsrobed
- eliminating unwanted ions
- controlling H+ and HCO3-
which hormone is responsible for regulating sodium resorption/potassium secretion in the DCT
aldosterone
