Urinary Physiology Flashcards
how much filtrate is made each day
180 L (47 gallons)
how much of that filtrate is urine
1.5 L
filtrate
blood plasma minus its proteins; produces by glomerular filtration
urine
metabolic wastes and unneeded substances; produced from filtrate
3 processes involved in urine formation
- glomerular filtration
- tubular reabsorption
- tubular secretion
glomerular filtration
produces cell and protein-free filtrate
tubular reabsorption
process of selectively reclaiming substances from filtrate and moving them back into blood
- typically 99% of water and all glucose and amino acids are reabsorbed
tubular secretion
process of selectively moving substances from blood into filtrate
3 layers of filtration membrane
- fenestrated endothelium of glomerular capillaries
- basement membrane
- foot processes of podocytes of the glomerular capsule
fenestrated endothelium of glomerular capillaries
allows all blood components except cells to pass
basement membrane
allows solutes; blocks all but the smallest proteins
foot processes of podocytes of the glomerular capsule
filtration slits between foot processes, stop all remaining macromolecules
outward pressures
forces that promote the formation of filtrate
hydrostatic pressure in glomerular capillaries (HPgc)
glomerular blood pressure
- chief force pushing water, solutes out of blood across the filtration membrane
- 55 mmHg
- maintained by the smaller size of efferent arteriole versus the afferent arteriole
inward pressures
forces that inhibit the formation of filtrate
hydrostatic pressure in the capsular space (HPcs)
pressure exerted by the filtrate in the glomerular capsule
- 15 mmHg
colloid osmotic pressure in glomerular capillaries (OPgc)
the “pull” of the proteins in the blood
- 30 mmHg
Net filtration pressure
the sum of forces
- 55 mmHg forcing out
- 45 mmHg forcing in
Is a NFP net outward or inward force
110 mmHg of outward force
GFR
the volume of filtrate formed by both kidneys per minute
What 3 things determine GFR
- NFP
- total surface area available for filtration
- permeability of filtration membrane
Normal GFR
120 - 125 mL/min
Why is GFR important
- the kidneys need a constant GFR to continue making filtrate
what does a increase of GFR do
increases urinary output and decreases BP
what does a decrease of GFR do
decreases urinary output and increases BP
2 control of GFR
- intrinsic controls
- extrinsic controls
intrinsic controls
work locally within the kidneys to maintain GFR - renal absorption
extrinsic controls
neural and hormonal controls that maintain systemic blood pressure
What is an appropriate MAP range for intrinsic controls to be in control?
80 to 180 mmHg
Myogenic mechanism
smooth muscle contracts when stretched
what happens when BP increases during myogenic mechanism
muscle stretches -> constriction of afferent arteriole
what happens when BP decreases during myogenic mechanism
dilation of afferent arteriole
what is the goal of myogenic mechanism
protect the glomerular from high BP by restricting blood flow, maintain normal NFP and GFR
tubuloglomerular feedback mechanism
directed by the macula densa cells
What happens during tubuloglomerular feedback mechanism
- responds to NaCl concentration
- GFR increases -> flow of filtrate increases -> decreased time for reabsorption -> higher levels of NaCl in filtrate
what is the response of tubuloglomerular feedback mechanism
the afferent arteriole is constricted -> NFP and GFR are reduced -> increased time for NaCl reabsorption
neural control by the sympathetic nervous system
- normal conditions: renal blood vessels are dilated, intrinsic controls running
- abnormal conditions: norepinephrine, epinephrine are released
how does the neural control alter BP
- systemic vasoconstriction to raise BP
- constriction of the afferent arterioles will decrease GFR
- blood volume and blood pressure increase
3 pathways to releasing renin from the granular cells
- direct stimulation of granular cells by the SNS
- simulation of the granular cells by activated macula densa cells – when NaCl concentration in filtrate is low
- reduced stretch of granular cells
What are some things that are reabsorbed in tubular reabsorption
almost all organic nutrients: reabsorption of water and ions is hormonally regulated and adjusted as needed
which portion of the renal tubule conducts the most reabsorption
the PCT is the site of most reabsorption
What is reabsorbed in the PCT
- glucose + amino acids
- 65% of sodium + water
- most electrolytes
- nearly all uric acid
what is reabsorbed in the nephron loop
reabsorption of water is no longer coupled to solute reabsorption
- descending limb: water can leave, but solute cannot
- ascending limb: solute can leave, but water cannot
what is reabsorbed in the DCT
reabsorption in the DCT varies with the body’s current needs - it is hormonally regulated
- most of water and solutes have already been reabsorbed
Anti-Diuretic Hormone (ADH)
released by the posterior pituitary gland, can cause an increase in reabsorption of water
Aldosterone
increases blood pressure and decreased K+ levels by promoting the reabsorption of Na+
Atrial Natriuretic Peptide (ANP)
released by cardiac atrial cells, decreases blood volume and blood pressure by reducing the reabsorption of Na+
Parathyroid Hormone
increases reabsorption of Ca2+ by the DCT
What is tubular secretion
- the reverse of tubular reabsorption
- occurs entirely in the PCT
- selected substances are moved from the peritubular capillaries, through the tubule cells, and back into the filtrate
what is typically secreted in tubular secretion
- K+
- H+
- Ammonia
- Creatinine
- organic acids and bases
renal clearance
the volume of plasma that the kidneys can clear of a particular substance within a given time
- can determine GFR, detect glomerular damage, and follow the progress of renal disease
treatment options for renal failure
hemodialysis or kidney transplant
normal solutes in urine
- urea
- K+
- Na+
- creatinine
- uric acid
abnormal solutes in urine
blood proteins, WBCs, and bile pigments - presence of these can indicate pathology
review physical characteristics of urine (SLIDE 25)
trigone
smooth triangular area outlined but the openings for the 2 ureters and the urethra
what is the max capacity of the bladder
1000 mL
compare and contrast the male/females Urethra (slide 32)
internal urethral sphincter
involuntary/smooth muscle at the bladder-urethral junction - contracts to open
external urethral sphincter
voluntary/skeletal muscle surrounding the urethra as it passes the pelvic floor - relaxes to open
micturition 3 simultaneous events (1)
contraction of the detrusor muscle by the ANS
micturition 3 simultaneous events (2)
opening of internal urethral sphincters by ANS
- opens via contraction
micturations 3 simultaneous events (3)
opening of external urethral sphincters by somatic nervous system
- opens via relaxation
