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describe urine formation
- filtration
- reabsorption
- secretion
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describe the steps in filtration
blood pressure forces water and solutes across walls of glomerular capillaries
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describe reabsorption
- removal of water and solutes across tubular epithelium
- reabsorbed substances re-enter the blood
- [passive (water) or active (carrier proteins)]
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describe secretion
cells produce and then discharge substances directly into the urine
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what are the characteristics of normal urine
- 180L filtrate produced per day
- 99% reabsorbed
- pH 4.5-8
- 93-97 % water
- 700-2000ml per day produced
- clear, yellow, sterile liquid
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how is glomerular filtrate governed
governed by balance between hydrostatic pressure and colloid osmotic pressure
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what are fenestrations
large - even plasma proteins can pass through
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what are basement membrane
only small proteins can pass through
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what is hydrostatic pressure
fluid pressure
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what is colloid osmotic pressure
pressure due to materials in solution on either side of the capillary walls
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what is HPgc
the pressure in the glomerulus capillaries
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what is OPgc
the pressure exerted by proteins in the blood
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what is HPcs
is the pressure resulting from restiance of filtrate already in the nephron and collecting system
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what is creatinine clearance used to estimate
used to estimate GFR
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what is GFR
the amount of filtrate produced by the kidneys per min
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what is autoregulation of GFR
subtle changes to diameters of afferent, efferent and glomerular capillaries
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decrease in renal BP - hormonal regulation
renin-angiotensin-aldosterone system
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what is autonomic regulation
- sympathetic activation triggered by acute decrease in BP
- causes vasoconstriction of afferent arterioles
- decreases GFR, slows production of filtrate
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what can shock, haemorrhaging and dehydration lead to
can lead to acute renal failure
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what does low renal BP cause
causes release of renin from kidneys
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what does renin convert angiotensinogen into
converts angiotensinogen to angiotensin
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what is angiotensin converted to by angiotensin converting enzyme (ACE)
converted to angiotensin II
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what does angiotensin II cause
- causes increase in sympathetic activity, resorption of Na and CL ions and water, excretion of K ions and vasoconstriction
- induces release of aldosterone from adrenal cortex
- induces release of ADH from pituitary gland
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what are ureters
pair of muscular tubes extending from kidneys to bladder
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describe the openings of the ureteral
they are slit-like openings
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what does the slit-like openings do
helps prevent backflow of urine towards ureter and kidneys when bladder contracts
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what is the urinary bladder
hollow, muscular organ which acts as a reservoir for urine
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what does the neck of the bladder contain
- contains internal urethral sphincter
- involuntary control over release of urine
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what happens when layers of muscle contract
when layers of muscle contract the bladder compresses and urine is expelled into the urethra
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describe the urethra
- extends from neck of bladder to exterior
- males 18-20 cm
- females 3-5 cm
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describe the external urethral sphincter
- voluntary control
- must be relaxed to allow urination
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what does micturition reflex do
micturition reflex coordinates urination
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if the bladder exceeds what volume the bladder will contract
exceeds 500 ml
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when the stretch receptors in the bladder are stimulated where is a message relayed
message is relayed to cerebral cortex
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what are some age related changes in the renal system
- decrease in number of functional nephrons
- reduction of GFR
- reduced sensitivity to ADH
- problems with micturition reflex
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