Unit 10 - Urinary Physiology Flashcards
(45 cards)
Kidney Function
- regulate water, fluid and electrolyte balance (H+, K+, NA+, electrolyte and water balance)
- regulate blood volume and blood pressure
- regulate acid base balance (H+ & HCO3-)
- Excretion of foreign compounds (drugs, presticides, food additives) and waste products (urea, uric acid, creatinine)
- Secrete hormones
Urinary System consists of
Urine forming organs ( 2 kidneys)
Structures carry urine from kidneys to outside for elimination (2 ureters L slightly longer than R, 1 urinary bladder, 1 urethra) 2 adrenal glands
Renal Structures
Renal cortex: filters blood
Renal medulla: contain 8-12 renal pyramids, empties into cuplike calyx, calyces channel urine into renal pelvis.
Renal pelvis: urine travels from renal pelvis to bladder for storage
Process of urine
Renal pyramid projects into a minor calyx
3 Minor calyces form 1 major calyx
Minor calyx accepts tip of pyramid where urine is dripping off papillary duct in pyramid.
Major calyx empty into pelvis which is at top of ureter
Urine enters ureter
Variability between kidneys
Renal papula
apex of the pyramid and projecting into the calyx
Nephron
Functional unit of the kidney
Filter blood to remove water and substances
Then necessary fluid and electrolytes reabsorbed back into blood
removes unnecessary molecules
approximately 1 million nephrons/kidney
each nephron has two components (vascular & tubular)
Vascular Component
From aorta, each renal artery subdivided into afferent arterioles
1 afferent arteriole supplies 1 nephron -> glomerular capillaries
Glomerular capillaries rejoin to form efferent arteriole
Forms peritubular capillaries
Wrap around tubular structures
Supply renal tissue with blood
Vasa recta
Series of straight capillaries in medulla
Slow rate of blood flow allows concentration of urine
Juxtaglomerular Apparatus JGA
between glomerulus and DCT to regulate function of nephron
Contains:
1. the macula densa, at start of DCT (Sensitive to concentration of NaCl of fluid flowing by
2. Juxtaglomerular cells that secrete renin
3. Extraglomerular mesangial cells (unknown function)
Tubular Component
Blood from afferent arteriole into glomerulus
Fluid that is formed -> proximal convoluted tubule (PCT)
Down descending limb of Henle, which dips into medulla
Urine from DCT to collecting duct->renal pelvis->bladder->elimination
Glomerulus
network of capillaries that sit in bowman’s capsule
Distal Convoluted tubule DCT
ascending limb of Henle returns to cortex
Three steps of Renal Process
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Glomerular Filtration
First step to form urine
20% of blood that enters glomerulus is filtered and goes into BC
Filtered blood components (most of the water, most/all of the salts, glucose and urea
80% of unfiltered blood then travels in efferent arteriole
GFR
Males- 125ml/min
Females- 115ml/min
180 L/day
Three physical forces affect GFR
- Glomerular capillary blood pressure
- Plasma-colloid osmotic pressure
- Bowman’s capsule hydrostatic pressure
Glomerular capillary blood pressure
Pressure exerted by blood in glomerular capillaries
afferent arteriole diameter>efferent diameter
therefore, pressure of blood inside glomerulus is increased
this increased blood pressure forces the components of blood out of glomerular capillaries
elevated pressure favours fluid entering bowman’s capsule (favours GFR)
Plasma-colloid osmotic pressure
caused by more proteins in glomerulus than is BC
water moves from high conc. BC to low conc glomerulus (opposes filtration)
Bowman’s capsule hydrostatic pressure
pressure that pushes fluid out of BC (opposes filtration)
Net filtration pressure (change force favouring filtration, 1 - (2+3)
Regulation of GFR
two major control mechanisms
1. Autoregulation (prevent spontaneous GFR changes) myogenic mechanism, tubuloglomerular feedback TGF
Neuron control aimed at long-term regulation of BP ( SNS effect on afferent arterioles)
Myogenic mechanism (autoregulation)
Increase in BP (afferent arteriole automatically constricts -> decreased dismeter and flow into glomerulus -> less blood filtered and lover GFR)
Decrease in BP (afferent arteriole automatically dilates -> increased diameter and flow into glomerulus -> more blood filtered higher GFR
Tubuloglomerular feedback mechanism
Increased BP increases GFR
Elevation of BP and GFR-> more fluid and salt filtered -> macula densa release ATP and adenosine -> afferent arteriole contricts -> lowers glomerular blood flow and lowers GFR
Reduction of BP and GFR -> less fluid and salt filtered -> less ATP released and adenosine made -> afferent arteriole dilates -> raise glomerular blood flow and raise GFR
Regulatory mechanisms
myogenic and TGF regulations work together
prevent inappropriate fluctuations in GFR and dangerous imbalances of fluid, electrolytes and waste (lose too much water, electrolytes if GFR too high, retain wastes if GFR too low)
Work within MAP 80-180 mm Hg ( changes outside range cause GFR to increase/decrease)
Neural Regulation of GFR
Kidney’s blood vessels also regulated by sympathetic fibers
If blood voume decreased (hemorrhage) -> BP reduced -> baroreceptors -> CV control centre in brain stem -> raise sympathetic stimulation -> vasoconstriction of afferent arterioles that reduces GFR -> less fluid filtered -> lowers urine output -> concerves fluid to help increase BP
