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Kidney drops into pelvis. Why?
- kidneys are retroperitoneal - outside peritoneal membrane
- drop when not enough fat to hold up
which kidney is lower? why?
3 functions of urinary system
- homeostatic regulation
excretion v. elimination
- removal or organic wastes from body fluids
- discharge of waste from body
6 homeostatic functions of urinary system
- 1. regulates blood volume and blood pressure
- 2. regulates plasma ion concentrations
- 3. helps stabilize blood pH
- 4. conserves important nutrients
- 5. assists liver in detoxifying poisons
- 6. gluconeogenesis
what organs produce urine?
what organs make up the urinary tract?
- urinary bladder
process of eliminating urine
result of nephroptosis
kinked ureters/blood vessels
study of urinary system
doctor of urinary system
-what other system?
- also male reproductive system
how does the urinary system regulate blood volume/pressure?
- adjust how much water lost in urine
- release erythropoetin and renin --> stimulates production of angiotensis
the urinary system helps regulate the concentration levels of which ions? how?
- Sodium, Potassium, chloride (control how much lost in urine)
- Calcium (synthesis of calcitriol)
US works with which system to stabilize blood pH? How?
- controls loss of H+ and bicarbonate ions in urine
what product does the US turn to glucose to help regulate homeostasis?
what 3 structures protect/stabilize kidneys?
- fibrous capsule (collagen, covers entire surface)
- perinephric fat capsule (adipose, surrounds renal capsule)
- renal fascia (outer layer, anchors kidneys)
what anchors the kidneys to surrounding structures?
what are the functional units of the kidneys? what occurs here?
- tubular structures in each renal lobe
- -filtration and urine production, secretion/resorption
what occurs in the kidneys during sympathetic innervation?
- -rate of urine formation adjusted by changing blood flow/volume at nephron
- -renin released
What does renin do?
- raises blood pressure
- -Restricts loss of water and salt in urine by stimulating reabsorption at nephron
- -stimulates production of angiotensin II
- -stimulates thirst center
two main parts of nephron and function
- renal corpuscle- filters blood plasma
- renal tubule- converts filtrate to urine
what makes up the renal corpuscle?
- glomerular capsule around it
- -cup-shaped structure
what kind of cell is wrapped around the capillaries of the glomerulus?
- - have "feet" called pedicles
- -"visceral epithelium"
what delivers blood to the glomerulus? What removes it? Where does it go from there?
Afferent arteriole -> glomerulus -> efferent arteriole -> peritubular capillaries -> small venules -> venous system
describe the size of afferent and efferent arterioles and why it is important
- Afferent are wider, efferent smaller
- creates pressure gradient so that filtration will occur
How does high blood pressure affect the glomerulus?
- causes more blood to flow through -> more filtration
- glomerulus is overworked and wears out
what is the fluid called when it's in the renal corpuscle and renal tubule?
What is the glomerulus?
A ball of capillaries where filtration occurs (goes into renal corpuscle)
What is the fluid called once it enters the renal corpuscle?
What can't filter through and is thus not found in filtrate?
Where does filtrate go after leaving the renal corpuscle?
Three functions of the renal tubule
- Reabsorb nutrients from filtrate
- -glucose and water soluble vitamins
- Reabsorb water
- -90% of water in filtrate is reabsorbed
- -Secrete waste products that didn't get into renal corpuscle at glomerulus (drugs, toxins, etc)
What will happen if you don't produce enough ADH/have enough ADH receptors? Resulting disease?
- Reabsorption won't occur
- -> Polyurea
- ->Diabetes insipidus
Why doesn't glucose enter your urine? If it does, what is happening, what is it called, and what disease might you have?
- gets reabsorbed at renal tubule
- Too much glucose in bloodstream -> can't reabsorb it all
- Diabetes Mellitus
- Diabetes Mellitus
What are the three segments of the renal tubule?
Proximal convoluted tubule (PCT)
nephron loop (loop of Henle)
Distal convoluted tubule (DCT)
Where does the most reabsorption of glucose and ions take place?
Proximal convoluted tubule in renal tubule
Once the fluid enters the renal tubule, what is it called?
Tubular fluid passes from PCT -> nephron loop ->DCT -> _________________
function of collecting ducts
- receive fluid from many nephrons
- many collecting ducts merge to become larger papillary duct
Once the fluid enters the collecting ducts, what is it called?
Recap: What are the different names, and associated locations, for the fluid that passes through the urinary system?
- Enters glomerulus: blood
- Renal corpuscle: filtrate
- Renal tubule: tubular fluid
- Collecting duct: urine
The renal corpuscle is made up of the glomerulus and the glomerular capsule around it. What is between the two?
function of descending limb of nephron loop
reabsorption of water from tubular fluid
function of ascending limb of nephron loop
- reabsorption of ions
- -helps make concentration gradient at medulla
Two kinds of nephrons; which is more common?
- Cortical nephrons- 85%
- Juxtamedullary nephrons- 15%
Where does blood go from the efferent arteriole of the nephron loops in cortical nephrons?
In Juxtamedullary nephrons?
in Juxt: to vasa recta
How does aldosterone cause the reabsorption of water?
- Increases number of Na+/K+ antiporters
- -> reabsorbs sodium
- -> water follows
The longer loop of Henle in the Juxtamedullary nephron allows it to do what?
conserve more water
What forms the outer wall of the renal corpuscle?
What drives filtration?
Pressure from heart, size difference between afferent and efferent arterioles
What role do podocytes of the glomerulus play in filtration?
- shaped like an octopus with feet wrapped around capillaries
- feet = "pedicels"
- Between the feet are filtration slits
- -anything smaller than 3 nm can pass through freely into capsular space
Bacterial infection in glomerulus
causes damage to filtration membrane
- allows things that are too big to filter out
Cell that helps control the diameter of the vessel in glomerulus
What kind of capillaries are the glomerular capillaries?
Fenestrated (large pores)
What kind of filtration occurs at the renal corpuscle? What solutes enter the capsular space?
- glucose, free fatty acids, amino acids, vitamins
- -also water
what percentage of solutes that are filtered out end up in urine?
Where does most reabsorption occur?
Proximal Convoluted Tubule
Where is the entrance to the PCT located? What does it have to distinguish it?
- opposite where the afferent and efferent arterioles are
Where do substances that are reabsorbed in the PCT go?
Back to blood
what absorbs materials from tubular fluid and releases them into peritubular fluid?
Peritubular fluid is a kind of ____
what gets reabsorbed at the PCT?
- the good stuff: elecrolytes, fatty acids, amino
- acids, glucose, vitamins
Two segments of each limb of the nephron loop and their function
- Thick segment: reabsorbs solutes
- Thin segment: reabsorbs water
- -ascending and descending limb both have thick and thin segments-
which segment of the nephron loop is absent in the cortical nephron? What does this imply?
- Thin segment
- Cortical loops not as effective at reabsorbing water
Kangaroo rats have more __________, so they can reabsorb more water
Juxtamedullary nephron loops (with thin segments)
what controls reabsorption rates?
- Nephron loop, DCT, Collecting ducts
- Raise blood volume
- Reabsorb sodium, secrete potassium
- --> increase chlorine and water reabsorption (follow sodium)
- Reduce urine volume
Afferent/Efferent arterioles, PCT
- Reduce water loss (raise blood volume)
- stimulates thirst
- stimulates aldosterone and ADH secretion
- Collecting duct
- water reabsorption (inserts aquaporins)
- reduce urine volume
- increase concentration of urine
- Afferent/Efferent arterioles, Collecting duct
- Dilate afferent, constrict efferent --> drive filtration
- Increase GFR
- inhibit renin, ADH, aldosterone
- increase urine, decrease blood volume
- synergistic to parathyroid hormone
- synergistic to parathyroid hormone
- induce renin secretion -> angiotensin II -> raise blood pressure
- -reduce GFR/urine volume
- PCT, DCT, nephron loop
- Promotes calcium reabsorption in loop and DCT
- Increase phosphate excretion by PCT (no crystals)
- promotes calcitriol
What is GFR?
- Glomerular Filtration Rate
- amount of filtrate former per minute by the two kidneys combined
what happens if the GFR is too high?
- fluid flows too rapidly, can't reabsorb enough water/solutes
- excrete more urine, risk dehydration/electrolyte depletion
What happens if GFR is too low?
fluid moves too slowly through tubules, reabsorb waste that should be eliminated
Slit that admits renal nerves, blood vessels, lymphatics, ureter into kidney
part of nephron that filters blood plasma
renal corpuscle (glomerulus and glomerular capsule)
part of nephron that converts filtrate to urine
renal tubule (PCT, nephron loop, DCT, CD)
what part of nephron loop has high metabolic activity and what causes it?
- thick segments (active transport of salts)
- lots of mitochondria
Flow of fluid from formation of glomerular filtrate to urine leaving the body:
- Glomerular capsule
- -> PCT
- -> Nephron loop
- -> DCT
- -> Collecting duct
- -> Papillary duct
- -> Minor calyx
- -> Major calyx
- -> Renal pelvis
- -> Ureter
- -> Urinary bladder
- -> Urethra
4 stages of converting blood plasma to urine
- Glomerular filtration
- Tubular reabsorption
- Tubular secretion
- Water conservation
Compare blood plasma to filtrate
Very similar composition, but filtrate has no proteins
Compare tubular fluid to filtrate
substances are removed/added by tubular cells
What changes does urine undergo once it enters the collecting duct?
Not much- change in water content
What is glomerular filtration anyway?
water and some solutes in blood pass from capillaries in glomerulus into capsular space of the nephron
What is the Glomerular Hydrostatic Pressure (pressure pushing blood out of glomerulus)?
50 (much higher than other capillaries)
COP in glomerular filtrate
not significant --> no proteins
Capsular Hydrostatic Pressure (pushing back on glomerulus)
15 (most ICF pressure is negative i.e. not pushing back)
BCOP in glomerulus (pushing back in)
Why is it important to maintain a net filtration of 10 mm Hg in the glomerulus?
Prevent buildup of toxins
Describe net filtration pressure in glomerulus
- 50 (HP out) - 25 (BCOP in) - 15 (CsHP in) = 10 mm Hg out
- -> just filtrating, not reabsorbing fluid in glomerulus
How much urine is excreted per day?
why is maintaining blood pressure so important in the glomerulus?
Controls the Glomerular Filtration Rate -> ensures that the right amount of filtration/reabsorption occurs
how is the autoregulation of the GFR carried out?
by changing diameters of arterioles/capillaries in response to changes in blood pressure/flow (smooth muscle stretch repsponse)
how is the GFR autoregulated if there is reduced blood flow?
- Create higher pressure gradient
- dilate afferent arteriole and glom. capillaries, constrict efferent
how is the GFR autoregulated if there is increased blood flow/pressure?
- Create lesser pressure gradient
- walls of afferent arterioles are stretched, causing smooth muscle to contract
- ->constrict afferent arterioles, difference with efferent is less -> less gradient, less filtration
what cells release renin
juxtaglomerular cells (JGA)
when afferent arteriole is constricted, the GFR increases/decreases
decreases (less difference in pressure)
Describe results of Renin-Angiotensin-Aldosterone mechanism
- BP drops -> JGA releases renin
- stimulates production of angiotensin II
-vasoconstriction at efferent arteriole raises glomerular BP and GFR (makes sure filtration continues)
-lowers BP in peritubular capillaries -> increases reabsorption of NaCl and water (raise BP)
-stimulates aldosterone (sodium and water reabsorption)
-stimulates ADH (water reabsorption)
-stimulates thirst center
removes useful solutes from filtrate, returns them to blood
*Reabsorption = back to blood
removes wastes from blood, adds them to filtrate
removes water from urine, returns it to blood, concentrates urine
what is the most abundant cation in filtrate?
Why is sodium so important?
- It creates an osmotic and electrical gradient
- Drives reabsorption of water and solutes
Name some things sodium can symport with
glucose, amino acids, lactate
what is pumped out of the cell and into tubular fluid when sodium is pulled in (antiporter with sodium)? What does this do?
Hydrogen (eliminates acid from body fluids)
what hormone activates the Na+/H+ antiporter?
What prevents sodium from accumulating in the epithelial cells?
- Sodium/Potassium pumps (active transport)
- pumps sodium into ICF, returns to bloodstream
what ion follows sodium? why?
chloride, negatively charged, attracted to positive sodium
true or false: the kidney removes all toxic urea from the blood
How does this relate to urea concentration of urine?
- false: removes about half, reabsorbs about half (40-60%)
- reabsorbs 99% of water, so urine has higher concentration of urea
how much creatine is reabsorbed?
None- it is all secreted into the tubule and goes into urine
99% of water is reabsorbed; how much of that occurs in the PCT?
Why does this occur?
What is this called?
reabsorption of solutes/salt there makes tubular cells hypertonic to tubular fluid, water follows (osmosis via aquaporins)
obligatory water reabsorption
Constant rate of water reabsorption, not controlled by hormones
- obligatory water reabsorption
- PCT, descending limb
hormone controlled water reabsorption
- facultative water reabsorption
- DCT and CD
how do water and solutes get reabsorbed into peritubular capillaries?
osmosis and solvent drag
the maximum rate of reabsorption due to limited number of transport proteins is called the ___________
glycosuria is a sign of what disease?
two functions of tubular secretion
- remove wastes from blood (includes drugs/medications)
- maintain acid-base balance
Primary function of nephron loop
generate osmotic gradient that enables the collecting duct that enables the collecting duct to concentrate the urine and conserve water
makes it really dilute- pushes out solutes and brings in water
secondary function of nephron loop
reabsorb Na+, K+, Cl- and water
describe solute concentration at various stages of nephron loop
1) Entering loop
2) descending limb
3) bottom of loop
4) ascending limb
5) entering DCT
what controls reabsorption of water and salts in the DCT and CD?
hormones: facultative reabsorption
what stimulates aldosterone secretion in the DCT?
blood sodium concentration falls, increase of potassium level
4 effects of ANP/BNP
dilate afferent, constrict efferent -> increase GFR
inhibit salt reabsorption
What prompts ADH?
dehydration, rising blood osmolarity
How does ADH raise blood volume?
inserts more aquaporins at collecting duct for more reabsorption
Parathyroid hormone is released in response to high/low blood calcium levels?
What does parathyroid hormone do in the PCT? DCT/thick segment of nephron loop?
- PCT: inhibit phosphate reabsorption
- DCT/thick: increase calcium reabsorption
when urine enters upper CD, it is hyper/hypo/iso-tonic to blood plasma. When leaves it is ______.
- Enters: isotonic
- Leaves: hypertonic (4x more concentrated)
What two things cause water to leave the collecting duct, thereby concentrating the urine?
- ECF is very hypertonic, water leaves via osmosis
- CD is more permeable to water than solutes
Very hypotonic (dilute) urine from drinking a lot of water
What hormone is released when you're dehydrated?
- ADH -increase water reabsorption
- add more aquaporins
What happens to ADH when you're really well hydrated?
Suppressed, aquaporins are removed for less permeability to water/reabsorption
Does increasing the GFR result in more or less urine production? Why? What hormone causes this to happen
- More: less time for reabsorption -> more urine
- --> ANP/BNP
If GFR is low, more time for reabsorption -> less urine
What creates urea?
breakdown of proteins
What creates creatinine?
creatine phosphate is broken down in muscles for extra ATP
What creates uric acid?
breakdown of nucleic acids (DNA, RNA)
What happens if there's a buildup of uric acid/Resulting disease? What is this a result of?
Kidney failure -> buildup -> super saturation -> crystals ->
Is renal threshold higher for glucose or amino acids?
Amino acids in urine
- after high protein meal
what makes pee yellow?
what effect do ACE inhibitors have on BP?
decrease (inhibit Angiotensin II production)
lose proteins that should be reabsorbed -> reduced BCOP -> edema
Where is fluid most concentrated? Most dilute?
Concentrated: bottom of nephron loop and in collecting duct
Dilute: top of nephron loop/beginning of DCT
What happens to filtration/reabsorption rates in kidney/liver failure?
there aren't any proteins so there's a low BCOP to push back in, so filtration is normal but reabsorption rates are low
what two sunstances can be measured in urine to evaluate GFR?
What causes the medulla to have such a high (4x) osmolarity (salt concentration)?
"occurs between two parallel segments of nephron loop"
What does the countercurrent multiplier do (2 benefits)
helps reabsorb solutes and water before tubular fluid reaches DCT/CD
Establishes concentration gradient for water reabsorption in CD
prolonged stimulation of what hormone causes hypokalemia?
aldosterone (pumps Na+ in, K+ out)
why can alkalosis be caused by prolonged aldosterone stimulation?
sodium can be antiporter with bicarbonate -> pump Na+ in, bicarbonate out -> bicarbonate builds up in blood, makes it alkaline
Lack of ADH/ADH receptors -->
- Diabetes insipidus
Polyurea is a sign of ________
what happens to the thirst center with age?
not as sensitive to angiotensin II -> drink less
Two names for urination
what do diuretics target?
ascending loop -> stop reabsorption of solutes -> less osmosis -> lots of clear pee
what is the function of the vasa recta?
returns water and solutes back to blood
what is the normal pH for urine?
4.5-8 (avg 6)
Is reabsorption in PCT active or passive? What does this cause?
- Osmotic water flow out of tubular fluid -> reduce volume of filtrate
In thick ascending limb, is transport of solutes active or passive?
Where does urine go upon leaving the collecting ducts?
- Minor calyx
- Major calyx
- Renal pelvis
- Urinary bladder
what's a pyelogram?
- Tests for kidney function
- inject dye
- check for blockage, kidney stones, cancer
what kind of epithelium do the ureters and urinary bladder have?
transitional epithelium (allows for stretch and recoil)
size difference in male and female bladders
same; females can't expand as much due to uterus
Benign Prostatic Hypertrophy
- Prostate grows and constricts urethra
- -> urine backs up
always feels like you have to pee but can't fully void bladder
what part of the bladder acts as a funnel, channeling the urine from the bladder into the urethra?
two urethral sphincters- voluntary or involuntary?
- Internal urethral sphincter- smooth muscle -> involuntary
- External urethral sphincter- skeletal muscle -> voluntary
what muscle causes the bladder to contract?
- Detrusor muscle
- (in muscularis layer)
how long is the male urethra?
8-20 cm (7-8 in)
3 parts of male urethra
- Prostatic urethra
- membranous urethra
- spongy urethra (in penis)
length of female urethra
3-5 cm (1-2 in)
what act permits micturition?
voluntary relaxation of external urethral sphincter
what part of the brain is responsible for the micturition reflex?
What is the micturition reflex?
- baroreceptors (stretch receptors) in bladder stimulate sensory fibers
- -> pons
- -> efferent nerves of bladder
- -> detrusor muscle contraction
- -> sensation to thalamus
- -> voluntary relaxation of external sphincter causes relaxation of internal sphincter
what causes the relaxation of the internal urethral sphincter?
voluntary relaxation of the external sphincter
what volume of urine in bladder triggers micturition reflex?
why don't infants have voluntary control over micturition?
nerves aren't myelinated yet
inability to control urination voluntarily
what is the first sign of normal incontinence with age? what causes it?
- weakened muscle tone
what can cause incontinence?
Alzheimer disease, stroke, loss of muscle tone
what changes take place in the urinary system with age?
- fewer functional nephrons
- reduced GFR -> less urination
- reduced sensitivity to ADH
- problems with micturition reflex
What four systems are part of the larger excretory system?
- Urinary system
- Integumentary system (sweat)
- Respiratory system (Co2)
- Digestive system
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