Urinary System Reading Flashcards
Outer Renal cortex contains
- Capillary tufts
- Convoluted tubules
Inner Renal Medulla contains
- Renal pyramids seperated by renal columns
Acute renal failure
Sudden loss of kidney function
Associated with shock or intense renal vasoconstriction that lasts from a few days to weeks
Cystitis
Inflammation of bladder
Hematuria
Blood in urine
Hemodialysis
Method of clearing waste products from blood
Nocturia
Night urination while asleep
Oliguria
Urinary volumes of less than 500 ml/day
Uremia
Retention of urinary constituents in the blood, owing to kidney dysfunction
Nephron consists of
- Glomerulus
- Bowmans capsule
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule
- Collecting duct (1 collecting duct serves several nephrons)
Glomerulus
- Network of 50 capillaries
- Endothelial lining has circular fenestrations
- Highly permeable
Bowmans capsule
- Double walled
- Composed of squamous epithelium
- Outer layer is continous with epithelium of proximal tubule
- Inner layer is composed of podocytes that are closely associated with glomerular capillaries
Proximal convoluted tubule
- Continous with epithelium of bowmans capsule
- Consists of a single layer of cuboidal cells containing microvilli
- Many mitochondria, energy for active transport
- Terminates at descending limb of loop
Loop of Henle
- Has descending ascending thin limbs and thick ascending portion
- Thin segments- flat squamous cells that lack microvilli
- Thick- cuboidal cells lack microvilli, runs between the afferent and efferent arterioles
Distal convoluted tubule
- Begins at macula densa, a amss of specialized epithelial cells of tubule wall, next to afferent arteriole
- Shorter than proximal
Glomerular filtration
Filtrate passes through
- Filtrate must pass through
- Capillary endothelium
- Fenestrations
- Basement membrane
- Unusually thick with type 4 collagen
- Podocytes
- Primary and secondary extensions (pedicles)
- Capillary endothelium
Glomerular filtration membrane regulates prevents and permits
- Prevents passage of blood cells and most plasma proteins
- Permits movement of water, metabolic wastes, ions, glucose, fatty acids, vitamins other solutes out of blood
- Valuable solutes reabsorbed by PCT
3 major functions of nephrons
- Glomerular filtration
- Creates plasma like filtrate of blood
- Tubular Reabsorption
- Removes useful solutes from filtrate, return to blood
- Tubular secretion
- Removes additional waste from blood and adds to filtrate
Glomerular Filtrate
- Fluid and solute in blood plasma of glomerulus pass in glomerular capsule
- Called Glomerular Filtrate
- Normal GF output 180L/day
Mechanisms that cause glomerular filtration
- High hydrostatic pressure of blood in glomerulus
- Large number and size of pores
Glomerular filtrate contains
- Contains water, elctrolytes and glucose
- Excludes RBC WBC, plasma proteins, platelets bc too large
- If protein and RBC are present then its a sign of hydrostatic pressure being too high and a defect in glomerular membrane
Glomerular Filtration Rate (GFR) normal
Regulation
- Total amt of filtrate formed per min by kidney
- Healthy 125 ml/ min
- Regulated by vaso dilation or constriction of Afferent arteriole due to
- Extrinsic (sympathetic)
- Intrinsic (locally produced chemicals)
Result on GFR from vasodilaltion and constriction
- Afferent vasodilation increases blood flow into glomerulus
- Increases glomerulus capillary BP
- Increases net filtration
- Increases GFR
- Afferent vasoconstriction decreases blood flow
- Dcreases BP in glom cap
- Dec Net filtration
- Dec GFR
Equation for GFR
GFR (ml/min)= Urine vol(rate of urine form) (ml/min) X Inulin concentration in urine (mg/ml) / Inulin concentration in plasma (mg/ml)
What would happen if filtration was too high or too low, what influences it?
- Too high
- 250 ml/min
- frequent urination
- Increase in protein and glucose bc cant be reabsorbed
- Too low
- Dilute urine
- Reabsorb too much
- Influenced
- diameter of blood vessels that feed system
Tubular reabsorption def
- Transfer of fluid and solutes out of lumen of nephron through interstitial space and into peritubular capillaries
How much filtrate is actually secreted
180 L/day of filtrate is made and only 1-2 L secreted
99% of filtrate i reabsorbed from renal tubules
Tubules reabsorption capacity
Tubules have high reabsorptive capacity for essential substances and little to non for those of no value
Only excess amounts of valuable substances are excreted
Where does tubular reabsorption take place
- Throughout renal tubules
- Primarily in Proximal Convoluted Tubule
Sodiums reabsorption
- Majority of sodium is reabsorbed Actively
- Most in PCT (needed for glucose and AA reabsorption)
- Loop of henle (role in kidneys ability to make dilute or concentrated urine)
- Distal tubule (subject to hormonal control, aldosterone)
Aldosterone and sodium reabsorption
- Aldosterone regulate reabsorption of sodium in Distal and collecting duct
- Renin-angiotensin aldosterone system
Glucose reabsorption
- 100% of glucose filteres is reabsorbed in Proximal tubule
- Carrier-mediated transport of glucose displays the property of saturation
- Concentration of transported molecules needed to saturate the carriers and achieve maximal transport rate is called Transport Maximum
- Tm for glucose is 375 mg/min filtered
- Normal glocose concentration in plasma is 100mg/100ml of plasma
- Glucose levels above Tm will not be reabsorbed and will appear in urine–> diabetes
Reabsorption of glucose normal and diabetic
- 1 mg/ml glucose in blood
- 1 mg.ml X 125 ml/min=125 mg/min
- Tm is 375 mg/min so no glu in urine
- 3.5 mg/ml glucose in blood
- TL: 3.5 X 125= 438 mg/min
- Law of kidney= filtration-Reabsorption + secretion=Excretion
- 438 mg/min - 375 mg/min= 63 mg/min in urine
Tubular Secretion
- Active transport secretion of substances from
- Peritubular capillarie–> Kidney tubules–> excretion in urine
- Involves trans-epithelial transport (reverse of reabsorption)
What are the most imp substances secreted by tubules
- Hydrogen ions, potassium ions, penicillin, organic anions
- H+ secretion important for acid-base balance and can be secreted in all tubular regions
- Potassium is reabsorbed in PCT and actively secreted in DCT
- K secretion is coupled to Na reabsorption and stimulated by Aldosterone
Acidosis
- Ratio of CO2 and HCO3 in extracellular fluid is increased
- Net result is H ions are excreted and Na and HCO3 ions retained
Alkalosis
- Ratio of HCO3 increases as pH rises
- Net result is H ions are retained and bicarbonate ions are excreted
- Kidneys help regulate the pH of fluids between 7.37-7.45
What are the 2 mechanisms the Kidneys reg urine concentration
- Producing an osmotic gradient between tubular lumen and surrounding interstitial fluid
- By amount of ADH secreted from posterior pituitary
Why does osmolarity increase deep to medulla (5)
- This Ascending limb actively transports neg Cl- OUT of tubular fluid into medullary interstium, Na follows bc of charge
- Ascending limb impermeable to H2O
- Fluid in ascending becomes more dilute (100 mosm/L) as it passes–> cortex
- Ions (Na, Cl) are actively transported into interstium from collecting duct, urea passively diffuses out of collecting duct into interstium
- Peritubular capillaries contain 1-2% of renal blood flow, as result carries only a min amuont of medullary interstitial solutes are carried away from renal medulla
- Net result- high osmolarity in medulla 1200-1400 osmos/L
Low ADH
- Distal tubules and collecting ducts become impermeable to water
- No water reabsorbed, excess water eliminated
- NaCl is still being pulled out and despite the high osmotic gradient, little H2O is pulled out into medulla
- Producing Large vol of DiLUTE urine (100 mosm/L)
High ADH
- ADH increases permeabi;ity of distal and collecting duct
- More water is reabsorbed, less water lost in urine more water returned to blood
- H2O is pulled out bc of high osmotic gradient in interstium
- Producing small vol of CONCENTRATED urine (1200 mosm/L)
Juxtaglomerular Apparatus
- Kidney plays imp role in BP regulation
- Renin-Angiotensin-Aldosterone-System
- Renin is made and secreted from Juxta App
- Where distal CT contacts affernt arteriole near Bowmans capsule
Decrease in BP in afferent arteriole…
or
Increased Na, Cl concentration of fluid in Distal CT
- Dec in BP in affernt is sensed by
- J cells
- Inc in NaCl in DCT is sensed by
- Macula densa
- Both result in release of renin from J cells
Macula densa histo
- Tall densely packed cells
- Contain Osmoreceptors which sense drop in blood osmotic pressure, change in [Na}
Renin secreting Juxta cells histo
- Modified smooth muscle cells
- Mechanoreceptors line wall of afferent arteriole
- Sense pressure changes due to tension in arterial wall
Renal function step 1. glomerulus, 2. PCT
- Glomerulus
- Filtrate produced at renal corpuscle
- Same comp as blood plasma minus plasma proteins
- PCT
- Active removal of ions and organic substrates
- Produces osmotic water flow out of tubular fluid
- Reduces vol of filtrate
- Keeps solutions inside and outside tubule isotonic
- Active removal of ions and organic substrates
Renal function 3. PCT and Descending 4. Thick ascending
- PCT and Descending Limb
- Water moves into peritubular fluids leaving highly concentrated tubular fluid
- Reduction in volume occurs by obligatory water reabsorption
- Thick Ascending Limb
- Tubular cells actively transport Na and Cl out of tubule
- Urea accounts for higher proportion of total osmotic concentration
Renal function 5. DCT and Collecting ducts
- DCT and collecting ducts
- Final adjustments in composition of tubular fluid
- Osmotic concentration is adjusted thru active transport (reabsorption or secretion based on ADH)
- Urine production ends wehn fluid enters renal pelvis
Urination Signaling
- Stretch receptors in bladder send impulses to sacral spinal cord
- Sensory neurons snd impulse to brain
- Parasympathetic nerve impulses stimulates detrusor muscle and the internal urethral sphincter
- Dertrusor muscle contracts and internal sphincter relaxes–> have to pee really bad now!
- To preevent use voluntary contraction of external urethral sphincter
- To urinate, external urethral sphincter is relaxed, detrusor contracts
