lecture 17 - urinary Flashcards
example of symporter
Na/glucose symporter
example of antiporter
Na/ H antiporter
two types of Na transporters
Na symporters
Na antiporters
Na symporters function
help reabsorb substances from tubular filtrate (glucose, amino acids, lactic acid)
Na antiporters function
reabsorb Na and HCO3, and secrete H
maintain homeostasis of pH
concentration gradient of solutes causes
CG of solutes at the beginning of teh PCT causes solutes to diffuse to peritubular capillaries
this drives water reabsorption
urea and NH3 are filtered at ______ and secreted by _______
glomerulus, PCT
NH3 is
poisonous and quickly binds to H to form ammonium (NH4)
how is NH3 secreted through the apical membrane
through Na/H antiporters
NH3 subs for H
how much fluid has been reabsorbed by the time tubular fluid reaches the nephron loop
60-70%, and 99% of organic components and ions
after most of teh water has been reabsorbed by the PCT, the nephron loop will reabsorb how much of the water left + ions
50%, and 2/3 of remaining ions
osmolarity in PCT
constant with blood at ~ 300 mmHg
thin descending limb is permeable to:
what does this do
water, but not many solutes
this drives osmolarity up
osmolarity of thin descending loop
increases from 3-900
thick ascending limb is permeable to:
what does this cause
permeable to ions via symporters, impermable to water
this causes a drop in osmolarity
osmolarity of thick ascending limb
drops from 900-150 due to being impermeable to water, but ions can leave via symporters
reabsorption in the thick ascending limb
Na/K/Cl symporters are here (apical membrane)
after symporter brings 3 ions in:
Na = Na/K pump to get Na into blood
Cl = leak channel into blood
K = leak channel into tubular fluid
relative negativity from Cl in the thick ascending limb drives:
reabsorption of cations thru gap junctions
when the tubular fluid reaches teh DCT, there is
less vol and low solute conc
only 15-20% of initial filtrate vol reaches the DCT
these substances represent a significant portion of remaining solute in the tubular fluid in the DCT, why?
urea, other organic waste
because none of it is reabsorbed
how does reabsorption of Na and Cl continue in the DCT
Na/Cl symporters
major site where PTH stimulates reabsorption of Ca
DCT
reabsorption in early DCT (apical/basal membrane, PTH stimulation)
apical membrane
- Na/Cl symporters that absorb both of these into the tubular cells
basal
- Na/K pumps
- Cl leak channels
- absorbs into capillaries
PTH hormone
- stimulates Ca reabsorption
what % of solutes and water are removed form fluid that reaches teh end of teh DCT
90-95%
what cells are located in late DCT and collecting ducts
principal cells and intercalated cells
these cells make final adjustments to volume and osmolarity of fluid
principal cells fucntion
have ADH and aldosterone receptors
increase water reabsorption (ADH)
reabsorb Na / secrete K (Aldosterone)
intercalated cells function
pH regulator located in late DCT and collecting duct
reabsorb HCO3/secrete H OR vice versa depending on the needed change
reabsorb K as well
angiotensin 2 functions (3)
decreases GFR via vasoconstriction of afferent arteriole
enhance reabsorption of Na/Cl/water in PCT vai stimulating Na/H antiporters
stimulates aldosteroen release from adrenal cortex
- aldosterone stimulates principal cells that increase Na/K pumps in collecting ducts
- increase Na reabsorption/K secrtion
- results in water reabsorption
anti diuretic hormone functions (3)
AKA vasopressin
released by pos pituitary
increases water permeability of principal cells in collecting duct
- does this by stimulating insertion of aquaporin-2, a water channel
increases facultative water reabsorption
controls whether urine is dilute or concentrated
- low ADH - dilute
- high - concentrated
without ADH, apical surfaces of principal cells are
poorly permeable to water whihc leads to more urine vol
negative feedback loop for ADH
receptor:
osmoreceptors in hypothalamus detect increase in plasma osmolarity
control centre:
stimulate ADH release
effectors:
principal cells become more permeable to water and reabsorb
response:
plasma osmolarity decreases
Atrial natriuretic peptide is released when
large increasein blood vol stretches atrial cells
ANP functions
inhibit Na and water reabsorption in PCT and collecting duct to lower blood vol / BP
suppresses secretion of aldosterone and ADH (water/”solutes that water follows” producing hormones)
overall decreases blood vol and pressure by stimulating increases urine output and increases Na secretion in urine
when is dilute urine produced
in teh absence of ADH
when is concentrated urine produced
in the presence of ADH
dilute urine means
the body is normally hydrated
concentrated urine means
body is dehydrated or large amounts of fluid are lost
ADH regulation requires
what is this driven by/
an osmotic gradient
driven by
- difference in solute/water pemeability and reabsorption in sections of tubule
- urea recycling
- counter current flow of fluid thru tubule
types of counter current mechanisms
countercurrent multiplication
counter current exchange
countercurrent multiplication
involved juxtaemdullary nephrons (due to long loop)
osmotic gradient generated in ISF ( in medulla) thru Na/Ca/water movement in nephron loop
increases concentration in medulla
this osmotic gradient is essential to production of concentrated urine when ADH is present
how to test kidney function (3)
urinalysis
- measure characteristics of urine
blood tests
- blood urea nitrogen test measures urea in blood
renal plasma clearance
- measure speed of how fast substance is removed form blood
how is the kidney capable of compensation (2)
nephrons can increase in size and workload
removal of one kidney causes enlargement of the other, and total kidney functions remains at 80%
at what % is kidney dysfunction evidnet
under 25%
how does piss get thru the ureters (3)
peristaltic contractions
hydrostatic pressure
gravity
ureter wall histology - mucosa
- urothelium
- lamina propria with elastic fibres
- has mucus to prevent cells from getting piss on them
ureter wall layers
mucosa
muscular layer
adventitia
ureter wall histology - muscular layer
opposite of GI tract
- inner longitudinal and outer circular
- peristalsis
ureter wall histology - adventitia
loose CT anchors ureters in place
contains lymphatic and blood vessels
location of urinary bladder in males/females
male - anterior to ass hole
female - anterior to vag, inferior to uterus
avg urinary bladder capacity
7-800 ml
trigone
smooth flat triagular area in flood of bladder
internal uretral orifice
entrance to urethra
layers of urinary bladder
mucosa
muscularis (detrusor muscle)
adventitia
serosa
urinary bladder mucosa
deepest
- covered in mucus
- urothelium and lamin propria
- has mucosal folds called rugae to bladder can expand
urinary bladder muscularis (detrusor muscle)
three layer of smooth muscel
- inner longitudinal, middle circular, outer long
- internal urethral sphincter - circular fibres near urethra opening
- external urethral sphincter - skeletal muscle
urinary bladder adventitia
outermost layer
- areolar CT on posterior and inferior surfaces
- covers the parts without serosa
urinary bladder serosa
covers superior surface
visceral peritoneum
urethra length in males/female
female - 4cm
male - 15-20 cm
female urethra path
posterior to pubic symphysis, orifice between clitoris and vag
male urethra pathway/regions
tube pass thru prostate and penis
contains regions
- prostatic, membranous, spongy
histology of urethra
urothelium to non K strat sq, ahs lamina propria with elastic fibres and circular smooth muscle
micturition
pissing
micturition reflex
filling of urinary bladder causes sensation of fullness that triggers desire to urinate before reflex occurs
sensed by stretch receptors, activated at 2-400mls
impulses are sent to sacral spinal cord (s2/3) to trigger the reflex
parasympathetic fibres ause detrusor muscle to contract and internal sphincter to relax. inhibition of somatic motor neurons cause external one to relax
cerebral cortex can initiate urination of delay for a limited time
