osmoregulation 4 Flashcards
proximal tubule function
- most solute, salt, nutrient, and water reabsorption
- excretion of most toxins
- cells abundant with mitochondria and microvilla, specialized for energy-dependent solute transport
loop of henle descending limb function
-water reabsorption
loop of henle ascending limb
-solute reabsorption
distal tubule
-reabsorption completed for most solutes, plus K+, H+ secretion
collecting duct
- drains multiple nephrons
- carries urine to renal pelvis
- final osmotic balance
what compounds are filtrated back out after reabsorption?
H+, NH4+, toxins, drugs, K+
proximal tubule filtrate
- Na’s active transport out of prox tube cells allows cotransport of nutrients against their gradients out of lumen and into prox tube cells, with water following by osmosis
- 2/3 of water and NaCl are filtered by the proximal tubule; remaining filtrate is relatively high in wastes, low in nutrients, and reduced in volume
loop of henle purpose
descending and ascending each differential create a countercurrent multiplier for reabsorption of both water at solutes
- accomplished via descending being permeable only to water, decreasing volume of urine and making it more concentrate (still a net loss of water back into body)
- ascending limb impermeable to water, and the concentrated urine allows reabsorption by diffusion gradient in ascending limb in lower portion, while solutes are actively transported in upper part, resulting in primary urine becoming more dilute
countercurrent multiplier of loop of henle
- concentrated urine from water reabsoprtion at the descending limb allows reabsorption of solutes by diffusion gradient on the ascending limb
- this also results in low osmolarity near cortex, and high osmolarity deep in medulla
distal tubule process
- hormones control final absorption of electrolytes and water, and final conc of urine in collecting ducts
- leaves mostly urea and other wastes in filtrate
distal tubule hormones
- parathyroid hormone
- aldosterone
- vasopressin/ADH
aldosterone
increases K+ secretion (Na/K ATPase, K channel; active if Na+ blood levels are low, causes reabsorption of NaCl into tissues, with water following by osmosis, reducing urine volume
parathyroid hormone
increases Ca2+ reabsorption
vasopressin/adh
-increases water reabsorption during dehydration by activating aquaporin expression
struture of distal tubule and collecting duct
principal and intercalated cells, the latter containing microvilli, which maintaion acid-base regulation through excretion of H+ and bicarbonate
collecting duct
- drains multiple nephrons
- carries urine to renal pelvis
- final osmotic balance
- further regulation of ion and water balance
- reabsorption of Na+
- K+ absorption or secretion
- pH balance
- urea reabsorption
excretion/micturition
- after urine is produced, it leaves kidney and enters urinary bladder via ureters
- urine leaves bladder via urethra; schincters of smooth muscle control flow of urine out of bladder, which are controlled by spinal cord reflex arc
hormones affecting kidney function
- steroids from adrenal gland, such as aldosterone, are slow response
- peptide hormones from hypo-pit axis like vasopressin are rapid response
dietary factors that affect urine output
- diurectics=stim excretion of water
- antidiuretics=stim water reabsorption
glomerular filtration rate
-determined by pressure across glomerular wall
-three forces: glomerular capillary hydrostatic pressure
2. bowman’s capsule hydrostatic pressure
3. oncotic pressure=osmotic pressure due to PROTEIN CONC. in blood
(pg 508)
glomerular cap hydrostatic pressure determined by
cardiac output
systemic bp
efferent artery vasoconstriction
bowman’s caopusle hydrostatic pressure is caused by
glom cap hydrostatic pressure
oncotic pressure caused by
osmotic pressure due to protein conc in blood
intrinsic regulators of GFR
- myogenic regulation
- tubuloglomerular feedback
- mesangial control
- pressure natriuresis
myogenic regulation
- constriction/dilation of afferent arteriole via smooth muscle cells:
- -as blood flow increases, bp increases, and there is increased hydrostatic gradient
- in response afferent arteriole constricts, decreasing GFR, creating a -ve feedback loop to regulate GFR, as pressure is increased to increase GFR when it is lowered
tubulorglomerular feedback
- juxtaglomerular apparatus (afferent arteriole); macula densa cells (distal tubule) controls diameter of afferent arteriole
- they are positioned sidebyside so dilation/contriction of distal tubule will affect afferent arteriole
mesangial control
- special smooth muscle cells regulate blood flow through caps
- increased flow causes stretching, which increases permeability of the filter
- results in changes in GFR independent of vascular effects
pressure natriuresis
- small number of vessels penetrate the medulla of kidney without passing through a glomerulus
- when BP increases, pressure of these vessels increases, renal interstitial hydrostatic pressure increases, reducing ability of tubule to recover solutes and water from primary urine, leading to more urine excretion and lowering of bp
- thus creates a negative feedback loop on blood pressure and renal arterialpressure/filtration
longterm mechanisms of GFR
- baroreceptor activation at SNS decreases MAP causes vasocontriction of aff/eff vessels, decreased GFR and increased recovery of Na+, water conservation and increase blood volume
- decreased renal circ=increased peripheral resistance=increased MAP
- endocrine hormones also control bf and gfr
endocrine hormones involved in blood flow and GFR
angiotensin 2= vasoconstrictor, decreases GFR
-prostoglandin=vasodilator, increases GFR
