formation of urine Flashcards
what processes in the nephron form urine
glomerular filtration
tubular reabsorption
tubular secretion
filtrate contains
same concentration of all substances except for proteins and blood cells
urine
waste that leaves the body.
- contains urea, creatinine, uric acid
- metabolic waste including
sodium, potassium, chloride and excess water.
where does glomerular filtration occur?
renal corpuscle
glomerular filtration is a…
passive process where hydrostatic pressure forces fluids and solutes through the membrane
glomerular filtration produces filtrate that:
includes: water, glucose, amino acids and nitrogenous wastes.
excludes: proteins and RBC
endothelium of filtration membrane includes:
1st layer.pores, 2nd layer. basement membrane and 3rd layer. membrane of glomerular capsule.
what wraps around the capillaries to form the filtration membrane
fenestrations or pores and podocytes
pores allows passage of..
plasma components excluding BCs and proteins
basement membrane restricts..
all but small protiens, and allows other solids to pass
membrane of glomerular capsule is made up of ____ and has __________ between their processes
podocytes, filtration slits
forces that drive fluid and solutes out of blood across glomerular capillary membrane
hydrostatic pressure favours filtration as efferent arteriole is smaller than afferent –> feeds into glomerular space
opposing filtration
capsular hydrostatic pressure and blood colloid osmotic pressure.
tubular reabsorption occurs
predominantly in the PCT loop of Henle and DCT
what is the net filtration of glomerular filtration
10+ millimetres of mercury mmHg
PCT - tubular reabsorption
PTC cells are most active reabsorbers.
reabsorb glucose amino acid sodium potassium and water via osmosis.
PTC cells absorb nearly all uric acid and half of the urea, these waste products are later secreted back into filtrate
what is reabsorbed back into the blood stream?
99% of water, glucose, amino acids, sodium and chloride ions,
tubular reabsorption occurs as…
filtrate traveling through renal tubule is reabsorbed back into blood stream via peritubular capillaries
the reabsorption of sodium creates an osmotic gradient across the tubule which drives..
water absorption through aquaporins.
WATER REABSORPTION IS DEPENDANT ON SODIUM REABSORPTION
DCT and collecting duct - tubular reabsorption
fine tuning of electrolyte reabsorption
- 10% sodium and 20% of water remain in tubules.
- ADH controls water reabsorption–> makes collecting ducts more permeable to water via aquaporins
- aldosterone controls fine tuning of sodium and potassium
- ANP inhibits sodium reabsorption at collecting ducrts = reduces blood sodium conc. =decrease bp and volume
- PTH acts on DCT fine tuning of calcium and phosphate ions
loop of henle- tubular reabsorption
produces highly concentrated or very dilute urine.
descending –> concentrates filtrate by removing water to peritubular blood via osmosis (impermeable to solutes)
ascending–> impermeable to water no aquaporins, removes solutes like sodium and chloride.
sodium reabsorption provides the energy for..
for the reabsorption of most other solutes ect. glucose, amino acids, vitamins
substances are not reabsorbed if..
- lack carriers or channels
- are not lipid soluble
- too large to pass through membrane pores
- urea, creatinine and uric acid most important non reabsorbed substances
micturition
prices of emptying urine from the bladder, also known as urination
micturition process
kidney produce urine, collected by renal pelvis, travels to ureter, bladder then released by ureters
bladder has three layers:
mucosa- inner, detrusor -middle and adventitia- outer
three things must happen simultaneously for micturition to occur
contraction of detrusor muscle (autonomic)
internal urethral sphincter (smooth muscle) involuntary must OPEN (autonomic involuntarily)
external urethral sphincter (skeletal muscle ) must open (voluntary)
Steps of micturition reflex (children no voluntary control
- Bladder wall distends as urine accumulates
- Stretch receptors are activated
- Sends signals to sacral region of spinal cord, stimulates parasympathetic neurons, causing detrusor muscle contraction
- Internal urethral sphincter will open, inhibits the sympathetic neurons to the internal urethra sphincter which helps it to open
Within the brain–> pons, two centres participate in the control of micturition:
PONSTINE STORAGE CENTRE –> inhibits
PONTINE MICTURITION CENTRE –> promotes reflex
PONTINE STORAGE
- Neural fibres from stretch receptors in bladder get relayed to pons and higher brain centres (provide consciousness of full bladder)
- Small bladder activates pontine storage centre
- Inhibits urination= SUPRESSES PARASYMPATHETIC and ENHANCES SYMPATHETIC output to bladder.
- Person chooses to not void/empty bladder
- Bladder contraction subside temporarily
- Bladder fills
- External urethra sphincter is VOLUNTARY we choose to keep it closed
PONTINE MICRUITION
- Urine added to bladder, stretch receptors activate pontine micturition
- Parasympathetic activity is promoted and sympathetic activity decreased
- Open internal urethral sphincter.
- Decreased somatic activity to the external urethral sphincter, opening it.
Urine exits.
