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The kidneys regulate
- Vit D3
- erythropoiten; meduallary fibroblasts
- glucose synthesis; gluconeogenisis rivals the liver
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Arcuate arteries
- connect interlobar areteries to interlobular arterioles
- interlobular arterioles lead to afferent arterioles
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Hydrostatic pressure in the renal blood capillaries
- in the glomerular capillaries there is a high pressure to cause rapid filtration and in the peritubular capillaries there is a lower pressure that facilitates absorption
- By adjusting the afferent and efferent resistance pressure can be adjusted correctly
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Connecting tubule
- connects the distal tubule to the collecting duct
- 8-10 connecting tubules empty into 1 collecting duct
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Three types of nephrons
- subcapsular/cortical
- intermediate
- juxtamedullary
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Physical id of the trigone
- its inner mucosa is smooth
- the rest of the inner bladder is rugae. thick folded muscle
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Nerve innervation of the bladder
- para S2-S3
- sympathetics L2, hypogastric nerve, little to do with bladder contraction mostly stimulate the vessels
- external sphincter is from pudendal S2-S3
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Stretch of the ureter
- causes peristalsis
- parasympathetic response
- these peristalsis waves force urine through the normal tone of the detruser muscle which normally keeps the ureters closed
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vesicoureteral reflux
- urine flows retrograde out of the bladder into the ureters
- ureters do not pass all the way into the bladder
- detruser muscle weakness
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Pain in the ureters from blockage
- cause sympathetic reflex to the kidney to constrict the afferent arterial decreasing urine output from that kidney
- Uretorenal reflex
- prevents overflow and pressure from a blocked ureter
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Micturition waves
- intermittent contractions that attempt to signal bladder emptying
- start around 20-50ml and stay constant up until 300-400ml then increase rapidly
- Receptors are mainly in the posterior urethra
- As the bladder fills the contractions last longer and longer, the contraction are self regenerating. The contraction further increases the stretch
- If the contractions become severe the nervous reflex inhibits the pudendal nerve and causes urination
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Matriculation reflex
is completely autonomic in the spinal cord
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Voluntary urination
- person voluntarily contracts there abdominal muscles, this increases bladder pressure
- this pressure stimulates the maturation reflex and also inhibits the external sphincter tone
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Overflow incontinence
- loss of stretch signals from the bladder
- urine leaks out
- usually caused by a crushing injury
- Tabetic dorsalis- fibrosis of dorsal nerve roots by syphilis
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Autonomic bladder
if the spinal cord is injured about the sacral level all bladder control will be reflex
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Uninhibited neurologic bladder
- frequent matriculation
- from partial damage of the spinal cord, inhibitory signals are lost so the brain keeps the sacral region excited causing matriculation with only a small amount of urine
- over excited bladder
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ion concentration in the glomerulus
freely filterd so same as plasma except no proteins
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filtration and absorption
work in unison
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carbonic anhydrase diuretics
if bicarb is not reabsorbed it binds Na in the urine and does not allow it to be reabsorbed
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Advantages of a high GFR
- it allows kidneys to rapidly remove waste products from the body that depend on the kidney for excretion
- allows all the body fluids to be filtered by the kidneys many times per day
- entire plasma volume is filtered 60 times per day
- High GFR allows the kidney to rapidly control the volume and composition of body fluids
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GFR is determined by
- balance of hydrostatic and osmotic pressure
- capillary permiability
- Glomerular capillaries have a high pressure
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Normal filtration fraction of the gomerular capillaries
- 20%
- FF= GFR/renal plasma flow
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Glomerular capillary endothelium
fenistrated
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Basement membrane proteoglycans
- heparin sulfate
- negative change
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All three layers of glomerular filtration
contain negative charges to decrease protein filtration
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Dextran
polysaccharide that can be manufactured as a cation, neutral, or anion
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GFR=
- K x net filtration pressure
- filtration pressure is normally around 10 mmHg
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Osmotic pressure of bowmans capsule
clinically said to be zero since no proteins are filterd
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Normal plasma colloid osmotic pressure
28 mmHg
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Kf in DM and chronic HTN
becomes lover over time due to thickening of the basement membrane
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Normal hydrostatic pressure of bowmans capsule
- 18 mmHg
- urinary stones lead to a higher pressure and a lower GFR
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What is the change in osmotic pressure as plasma flows through the glomerulus
- flows in at 28 mmHg and in the efferent arterioles it is around 36 mmHg
- this is due to a filtration fraction of plasma of 20% deceases the amount of plasma
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Two factors that influence the glamerular capillary colloid osmotic pressure
- the arterial osmotic pressure and the filtration fraction of the plasma
- An increase in arterial colloid osmotic pressure would decrease the GFR
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Blood flow and GFR
- i higher rite of blood flow increases GFR
- A lower rate of flow decreases GFR
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GFR and pressure changes
- increased arterial pressure tends to raise glomerular hydrostatic pressure and raise GFR
- Increased resistance eof the afferent arterial reduced hydrostatic pressure and decreases GFR
- Constriction of the efferent arteriole increases the resistance of outflow from the glomerular capillaries. This raise in pressure increases GFR as long as the constriction does not lower renal blood flow to much
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Severe contraction of the efferent arterioles
- the contraction slows renal blood flow and in turn increases the filtration fraction which increases the colloid osmotic pressure.
- The raise in osmotic pressure exceeds the hydrostatic pressure and decreases GFR
- The decrease in GFR; as the efferent constriction becomes severe constriction increases the protein concentration and causes the donnan effect.
- Donnan effect; As plasma protein concentration increases the osmotic pressure increases non linearly because the proteins negative charge attracts more ions to add to the osmotic pressure
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Efferent arteriole contraction
- is a biphasic effect on GFR
- first increases then decreases
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Kidney O2 consumption
- use oxygen at twice the rate if the brain but have 7 times the blood flow
- High rate of oxygen consumption is due to ATP pumps
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Renal blood flow
pressure difference = flow x resistance
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Most resistance in the renal blood flow
- interlobular arterioles
- afferent and efferent arterioles
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Kidney autoregulation on blood flow
works between 75 and 160
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most blood flow in the kidney goes
- to the cortex
- only 1-2% to the medulla
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renal sympathetic innervation
- T10-L1
- Most important in reducing GFR during severe acute disturbances lasting a few minutes to a few hours such as those elicited by brain ischemia or severe hemorrhage
- does not react to weak influence of barorecptors
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Hormones that reduce GFR, autocoids
- norepinephrine, epinaphrine, sympathetic nervous system
- endothelian ; released from damaged cells. Released during toxemia of pregnancy (preeclampsia)
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Angiotensin II
- Usually released during times of decreased arterial pressure and decreased GFR
- Maintains GFR while increasing extracellular volume
- preferentially constricts efferent arterioles. Raises glomerular pressure and lowers blood flow
- increases GFR but slows flow though the peritubular capillaries which in turn increases Na and water reabsorption
- Thus increases in angiotensin II that occurs with a low sodium diet or hypovolemia helps to preserve GFR and maintain normal excretion of waste products that depend on GFR. at the same time constriction of efferent arterioles increases tubular reabsorption of Na and water helping to restore volume
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Endothelian derived NO
- increases GFR by dilating arterioles
- there is a basil level of secretion
- Drugs that decrease NO production decrease GFR
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After surgery NSAIDs
- stop production of prostoglandins and can lower GFR
- Prostoglandins cause vasodilation and increase renal blood flow
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Main function of autoregulation in the kidneys
- to maintain GFR
- in other tissues it is to control nutrient delivery and waste excretion
- 60-180 mmHg
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Two reasons changes in arterial pressure have a small effect on urine volume
- renal autoregulation prevents large changes in GFR
- additional adaptive mechanisms in the renal tubules allow them to increase reabsorption when GFR rises. Glomerulotubular balance
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Glomerulotubular balance
an increases in GFR causes an increase in Na and water reabsorption
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Tubuloglomerular feedback
- Links changes in Na at the macula densa to renal arteriolar resistance
- Directed to stabalizing Na concentration in the tubules
- two mechanisms; sfferent arterial feedback mechanism and efferent arteriole feedback mechanism
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Decrease in Na at the macula densa , tubuloglomerular feedback cont.
- A decreased GFR slows the flow rate at the TAL allowing more time for Na reabsorption
- decreased Na at the macula densa has two effects.
- It decreases resistance to blood flow in the afferent arterioles increasing glomerular hydrostatic pressure increasing the GFR
- increases renin secretion
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Myogenic mechanism
- individual blood vessels resist stretching
- respond to increased pressure and stretch by contracting
- stretch of the vascular walls allows increased movement ov calcium ions into the cell causing contraction
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High protein intake on GFR / increased blood glucose
- high protein intake increases both GFR and renal blood flow
- Can be due to growth of the kidney
- High amount of filtered AA causes a high absorption in the proximal tubules, this is by secondary active transport which causes an increase in Na reabsorption.
- The increase in Na reabsorption causes less Na to be delivered to the macula densa and a release of renin. Increased GFR and blood flow through the dilated afferent vessels
- Not only absorbs the extra AA but with increased AA breakdown there is an increase in Urea, the increase in GFR allows for an increase in Urea excretion
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Increased Na at macula densa
- tubuloglomerular feedback
- causes vasoconstriction which decreases renal blood flow and decreases GFR
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Urine flow rate
=GFR - Reabsorption rate
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