renal system L11-13 Flashcards
juxtamedullary nephrons
involved in making concentrated urine
no. nephrons per kidney
1 million
~80% cortical
renal distribution of blood flow
93% cortex
7% medulla
1% papilla
afferent arterioles
feed into glomeruli
efferent arterioles
leave glomeruli and wrap around nephron
vascular supply to nephrons pathway
afferent arterioles > glomeruli> efferent arterioles > peritubular capillaries/ vasa recta> renal veins> inferior vena cava
kidney functions
homeostatic regulation of water/ ion content of blood
metabolic waste product excretion
hormone production
hormones produced by kidney
erythropoietin (RBC synthesis)
renin (sodium balance)
vit D activation
prostaglandins and kinins (renal blood flow)
what’s filtered at glomerular filtration?
all plasma constituents except proteins >67kDa
as filtration barrier filters on size/ charge
glomerular filtration fraction
~20%
glomerular filtration rate (GFR)
~180 litres/ day
filtration barrier layers surrounding
capillary lumen
filtration barrier
capillary endothelium
basement membrane
bowman’s capsule epithelium
pressures controlling glomerular filtration
hydrostatic p of blood through glomerular capillaries (~55mmHg)
colloid (30mmHg)
hydrostatic p of fluid in Bowman’s space (15mmHg)
colloid osmotic pressure
caused by proteins in blood, favouring fluid retention in capillaries
net glomerular filtration pressure
55-30-15=10mmHg
afferent arteriole resistance effect on blood flow to glomerulus
^R decreases blood flow
decrease in R ^blood flow
efferent arteriole resistance effect on blood flow to glomerulus
^R increases blood flow
decrease in R decreases blood flow
GFR /RBF control
maintained relatively constant over range of arterial pressure as a protective mechanism (autoregulation)
neural control
tubuloglomerular feedback
autoregulation local control mechanisms
myogenic response
tubuloglomerular feedback (fluid flow influences arteriole resistance/ GFR
why does the nephron loop back in on itself
so ascending limb of henle loop passes between afferent/ efferent arterioles
macula densa cells function
sense distal tubule flow/ release paracrines that affect afferent arteriole diameter
tubuloglomerular feedback
GFR/ tubule flow ^ so ^macula densa flow^ and Na+/Cl- conc sensed
paracrine factors released from macula densa (adenosine/ ATP/ nitric oxide)
afferent constricts and afferent r ^
GFR decrease
urine formation process
filtration
reabsorption
secretion (at proximal convoluted tubule)
amount excreted
amount filtered - amount reabsorbed + amount excreted
reabsorption
movement of solutes/ fluid out of filtrate and into capillaries via epithelial transport mechanisms
epithelial transcellular transport
substances cross apical and basolateral membranes of tubule epithelial cells
paracellular transport pathway
substances pass through cell-cell junction between 2 adjacent cells
passive transport
diffusion (membrane-permeable)
leak channels
paracellular transport
active transport
membrane channels
transporters
co-transporters
pumps
carriers
PCT functions
reabsorption (microvilli on apical surface maximise sa)
secretion
interdigitations of basolateral membrane shorten distance to mitochondria for active transport
Na+ reabsorption at PCT-1
Passive at apical membrane (down echem gradient)
co-transport w essential solutes
water reabsorption at PCT-1
paracellular route via osmosis
ion reabsorption
paracellular/ transcellular along echem gradient
glucose at PCT-2
co-transport at apical membrane and carrier at basolateral membrane
urate at PCT2
anion transporters/ paracellular/ passive/ transcellular/ secretion
Tm
max transport rate
renal threshold
plasma conc of substrate at Tm
diabetes mellitus
excessive glucose conc saturates carrier no. and therefore appears in urine
PCT secretion
peritubular capillary transfer to tubule actively
isosmotic fluid leaving (300mOsm)
nephron osmolarity changes
descending limb ^ conc (permeable to water/ impermeabe to ions)
ascending limb > hypoosmotic fluid (impermeable water)
H2O reabsorption in urine formation
ADH^ collecting duct permeability to water
countercurrent systems maintain osmotic gradient in medullary interstitium
urine formation countercurrent system multiplier
enhanced by active transport of solutes maintaining osmotic gradient
acidosis in renal adjustment
A intercalated cells in collecting ducts excrete H+ and reabsorb HCO3-
alkalosis in renal adjustment
B intercalated cells in collecting duct excrete HCO3- and reabsorb H+
diuresis
removal of excess water from urine
what controls permeability in collecting duct?
vasopressin
ADH
reabsorption passivelycvia osmotic gradient in medullary interstitium
ADH cellular action
- binds to basolateral membrane receptor
- adenlyl cyclase stimulation > cAMP generation and protein kinase activation
- aquaporin 2 insertion into apical membrane
- ^ permeability
ADH release control
osmoreceptors
ADH release
produced by cells in supraopitc/ paraventricular nuclei of hypothalamus
stored in vesicles in p pituitary gland
normal plasma osmolarity
~290mOsm
ADH half-life/ removal
~15 mins
removed by liver and kidneys
physio ADH release stimuli
stress
high temp
exercise
pain
alcohol effect on ADH release
inhibits
inappropriate ADH release stimuli
post-operative pain
intracranial disease/ injury
ectopic ADH production
opiates
MDMA/ nicotine
pneumonia/ TB
nocturnal enuresis
delay in normal circadian rhythm of ADH development
MdMa effect on body
^ thirst reflex/ ADH secretion/ circulatin g volume
hyponatraemia
diabetes insipidus
polyuria
ADH secretion deficiency
nephrogenic diabetes insipidus (nephrons don’t respond to ADH)
Na+ reabsorption
free filtration at glomerulus
~67% PCT reabsorption
none from henle thin ~35% from thick
renin-angiotensin-aldosterone axis
renin release from kidney
stimulates angiotensin> angiotensin I> angiotensin II> aldosterone> ^Na+rebasorption/ extracellular fluid
renin release
stretch receptors in afferent arteriole sense low BP and NaCl at macula densa
^renal symp nerve stimulation
aldosterone cellular action
binds to cytoplasm receptors and initiates txn
^ENaC channels in apical surface
^Na+/Cl- pumps
^Na+ reabsorption (^Cl- and K+ secretion)
aldosterone production
steroid hormone synthesis in adrenal cortex
aldosterone function
stimulates angiotensin II
promotes Na+ reabsorption promotion via principle cells in final third of DCT/ Cortical collecting duct
^ blood vol and decreases NaCl/water excretion
angiotensin II function
stimulates aldosterone release from adrenal cortex
^thirst/ vasoconstriction
^norepinephrine release from symp postganglionic fibres
atrial natriuretic peptide
produced by atria in response to stretch
regulates plasma vol
nephrolithiasis symptoms
nausea
renal colic
sweating
blood in urine
nephrolithiasis
renal calculi formation due to build up of ion/solute conc in filtrate in nephron loop/ distal tube/ collecting system
risk factors of nephrolithiasis
dehydration
obesity
diet
micturition
emptying urine from urinary bladder
* up to 500ml
2 sphincter muscle rings
internal (smooth muscle)
external (skeletal muscle controlled by somatic motor)
neurones/tonic CNS stimulation maintains contraction
micturition process
stretch receptors fire
para neurones fire and motor stop firing
smooth muscle contracts/ internal sphincter passively pulled open, external sphincter relaxes
