Urinary Physiology Flashcards
what happens to blood when it filtered
- remove its cells and proteins
- almost everything is reclaimed from filtrate
- specific things are added to filtrate
- filtrate becomes urine
how many times a day does the kidney filter’s the body’s blood plasma volume
60x each day
at rest how much of the body’s oxygen is used by the kidneys
20-25%
filtrate
blood plasma minus its proteins; produced by glomerular filtration
urine
metabolic wastes and unneeded substances; produced from filtrate
3 process of 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% water, and all glucose and amino acids are reabsorbed
- can be active (ATP-requiring) or passive
tubular secretion
process of selectively moving substances from blood into filtrate
3 layers of the 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; blocked all but small proteins
foot processes of podocytes of the glomerular capsule
filtration slits between foot processes, stop all remaining macromolecules
outward pressure
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
- quite high (55mmHg) compared to most capillary beds
- maintained by the smaller size of efferent arterioles 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 (15mmHg)
colloid osmotic pressure in glomerular capillaries (OPgc)
the “pull” of the proteins in the blood (30mmHg)
Net filtration pressure (NFP)
the sum of forces
- 55mmHg forcing out
- 45mmHg forcing in
- Net: 10mmHg of outward force
- NFP is the main controllable factor for determining glomerular filtration rate (GFR)
what pressure is responsible for forming filtrate
net filtration pressure (NFP)
glomerular filtration rate (GFR)
the volume of filtrate formed by both kidneys per minute
- normal GFR = 120 - 125 mL/min
slide 8
regulation of GFR
- GFR is regulated to serve 2 important needs
- the kidneys need a relatively constant GFR to continue making filtrate
- the body needs a relatively constant blood pressure
what happens during an increase GFR
increases urinary output and decreases BP
what happens during a decrease of GFR
decreases urinary output and increases BP
two types of controls
- intrinsic controls
- extrinsic controls
Intrinsic controls
work locally within the kidney to maintain GFR - renal autoregulation
extrinsic controls
neural and hormonal controls that maintain systemic blood pressure
What range of MAP is intrinsic control
- range of 80 to 180mmHg, intrinsic controls maintain a constant GFR
- when MAP is outside of this range, extrinsic controls take over
Myogenic mechanism
smooth muscle contracts when stretched
- increased BP -> muscles stretch -> constriction of afferent arteriole
- decreased BP -> dilation of afferent arteriole
what is the goal of myogenic mechanism
protect the glomerulus from high BP by restricting blood flow, maintain normal NFP and GFR
tubuloglomerular feedback mechanism
directed by the macula densa cells
- responds to NaCl concentration
- GFR increases -> flow of filtrate increases -> decreased time for reabsorption -> higher levels of NaCl in filtrate
response of tubuloglomerular feedback mechanism
the afferent arteriole is constricted -> NFP and GFR are reduced -> increased time for NaCl reabsorption
why do extrinsic controls regulate GFR
to maintain systemic BP
neural control by the Sympathetic nervous system (normal conditions)
renal blood vessels are dilated, intrinsic controls running
neural control by the sympathetic nervous system (abnormal conditions)
(Low BP) norepinephrine, epinephrine are released
- system vasoconstriction to raise BP
- constriction of the afferent arteriole will decrease GFR
- blood volume and blood pressure increase
rening-angiotensin-aldosterone mechanism
the body’s main mechanism for increasing blood pressure
3 pathways to releasing renin from the granular cells
- direct stimulation of granular cells by the SNS
- stimulation of the granular cells by activated macule densa cells – when NaCl concentration in filtrate is low
- reduced stretch of granular cells
anuria
abnormally low urine output (<50 mL/day)
two routes for tubular reabsorption
- transceullular
- paracellular
transcellular
reabsorbed substances travel through cells of the tubule
paracellular
reabsorbed substances travel between cells of the tubule
what is the site of most reabsorption
PCT
what is reabsorbed from the filtrate in the PCT?
- all the nutrients (glucose + Amino acids)
- 65% of sodium + water
- most electrolytes
- nearly all uric acid and 1/2 of the urea
reabsorption 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
reabsorption in the DCT
varies with the body’s current needs – it is hormonally regulated
- most of the 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 decreases 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 secreted in tubular secretion
K+, H+, ammonia, creatinine, organic acids and bases
tubular secretion is important for
- disposing of substances - drugs and metabolites - that are bound to plasma proteins
- eliminating undesirable substances - urea and uric acid - that were passively reabsorbed
- ridding the body of excess K+ - the aldosterone effect
- controlling pH by altering amounts of H+ or HCO3- in urine
urinalysis
the examination of urine for signs of disease – can aid in the detection of illegal substances and help to diagnose disease
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
normal GFR
120 - 125mL/min
chronic renal disease
a GFR < 60 mL/min x 3 months
- rate of filtrate formation decreases, nitrogenous wastes accumulate in blood, pH becomes acidic
- most often seen with diabetes mellitus and hypertension
renal failure
a GFR < 15 mL/min
- formation of filtrate dramatically decreases or completely stops
- uremia
symptoms of renal failure
fatigue, anorexia, nausea, mental status changes, cramps
treatment of renal failure
hemodialysis or kidney transplant
uremia
blood in the urine – ionic and hormonal imbalances, metabolic abnormalities, toxic molecule accumulation
chemical composition of urine
95% water
5% solutes
nitrogenous wastes of urine
- urea
- uric acid
- creatinine
urea
largest solute component; formed from breakdown of amino acids
uric acid
product of nucleic acid and metabolism
creatinine
metabolite of creatine phosphate – found in large amounts in skeletal muscle
normal solutes in urine
urea, Na+, K+, creatinine, uric acid
- Ca2+, Mg2+, HCO3- are occasionally seen in small amounts
abnormal solutes in urine
blood proteins, WBCs, and bile pigments – presence of these can indicate pathology
freshly voided urine (color)
clear - pale to deep yellow
urochrome
pigment that results from the body’s destruction of hemoglobin
more concentrated urine (color)
deeper in color
abnormal colors of urine
- pink, brown, red
- caused by certain foods, medications, drugs, vitamins, presence of bile/blood
what does cloudy urine indicate
UTI
odor of urine
- only slightly aromatic when fresh
- upon standing, develops an ammonia odor as bacteria metabolizes urea
- may be altered by some drugs, foods, and diseases
pH of urine
- slightly acidics (pH = 6, range 4.5-8
- acidic (high protein) or alkaline (vegetarian) diets will alter pH
- prolonged vomiting and UTI can also raise pH
specific gravity of urine
- ratio of the mass of a substance to the mass of an equal volume of distilled water
- urine’s specific gravity ranges from 1.001 to 1.035
ureters
slender tubes that actively carry urine away from the kidneys towards the bladder
as bladder pressure increases what happens to the ureters
the distal ends of the ureters prevent backflow of urine into the ureters
urinary bladder
- smooth, collapsible, muscular sac for temporary storage of urine
- retroperitoneal, on the pelvic floor, posterior to public symphysis
urinary bladder (males)
prostate lies inferior to the bladder neck
urinary bladder (females)
bladder is anterior to the vagina and uterus
trigone
smooth triangular area outlined by the openings for 2 ureters and the urethra
layers of the bladder wall
- mucosa
- muscular layer
- fibrous adventitia
mucosa
transitional epithelial mucosa
muscular layer
thick detrusor muscle with 3 layers of smooth muscle
- inner and outer are longitudinal
- middle layer is circular
fibrous adventitia
superior surface is covered by peritoneum
when urine storage is empty what happens
the bladder collapses and rugae appear
during filling what happens to the bladder
the bladder expands and rises superiorly, but there is no significant rise in internal pressure
moderately full bladder
- 12 cm/5 in long
- 500mL/1 pint of urine
max capacity of urine
1000mL - an overfilled bladder can burst
urethra
muscular tube that drains the urinary bladder
- mucosal lining is largely pseudostratified columnar epithelium – transitional epithelium near the bladder – stratified squamous near the external opening
urethral sphincters
- internal urethral sphincters
- external urethral sphincters
internal urethral sphincters
involuntary/smooth muscle at the bladder-urethral junction – contracts to open
external urethral sphincters
voluntary/skeletal muscle surrounding the urethra as it passes the pelvic floor – relaxes to open
urethra (female)
- 3-4cm/1.5 in long
- tightly bound to the anterior vaginal wall
- external urethral orifice is anterior to the vaginal orifice
urethra (male)
- carries both semen and urine
- much longer – 20 cm/8 in – has 3 named regions
3 regions of male urethra
- prostatic urethra
- intermediate/membranous urethra
- spongy urethra
prostatic urethra
2.5 cm
- within prostrate gland
intermediate/membranous urethra
2 cm
- passes through urogenital diaphragm from prostate to root of penis
spongy urethra
15 cm
- passes through the penis, opens via external urethral orifice
3 simultaneous events of micturition (urination)
- contraction of the detrusor muscle by ANS
- opening of internal urethral sphincters by ANS
- opens via contraction - opening of external urethral sphincters by somatic nervous system
- opens via relaxation
