Urinary system Flashcards
12 functions of the kidneys
regulates blood ionic composition, blood pH, blood volume, blood pressure, blood glucose, total water volume and total solute concentration in water, ion concentrations in ECF, produces hormones, ensures long-term acid-base balance, exercise metabolic wastes, produces erythropoietin, and activates vitamin D
organs of the urinary system
kidneys, ureter, bladder, and urethra
where are the kidneys located?
retroperitoneal and between T12 and L5 (superior lumbar region)
what sits above each kidney?
adrenal (suprarenal) glands
medial and lateral surfaces of kidneys
convex lateral surface and concave medial surface
concave medial surface of kidneys
contains renal hilum which leads to the internal space
what enters and exits at the hilium?
renal vessels, lymphatics, ureters, and nerves
three layers surrounding the kidneys
renal fascia, adipose fat capsule, and renal capsule
renal fascia
outer layer of dense irregular fibrous CT surrounding kidneys that anchors these to the abdominal wall
perirenal fat capsule/ adipose capsule
fatty cushion surrounding kidneys; holds the kidneys in place and provides protection
fibrous capsule/ renal capsule
transparent smooth irregular CT capsule that prevents the spread of infection to kidneys
3 regions of internal kidney
renal cortex, renal medulla, and renal pelvis
renal cortex
outer layer that is granular appearing
renal medulla
deep to cortex layer; composed of cone-shaped medullary pyramids, base, papilla, lobes, and renal columns
what face of pyramid faces the cortex?
the broad base
papilla
the tip of the pyramid that points internally
renal columns
inward extensions of cortical tissue that separate renal pyraminds
lobe
medullary pyramid and its surrounding cortical tissue; there are about eight lobes per kidney
renal pelvis
funnel shaped tube that is continuous with ureter; contains minor and major calcyes
minor calcyes
cup-shaped areas that collect urine draining from pyramidal papillae
major calyces
areas that collect urine from minor calyces; empties into renal pelvis
urine flow beginning in kidneys
renal pyramid, minor calyx, major calyx, renal pelvis, and ureter
how much cardiac output do kidneys receive each minute?
about 1/4 of flow from renal arteries; about 1200 mL
arterial flow of blood to kidneys
renal, segmental, interlobal, arcuate, cortical radiate, afferent arteriole, glomerular capillaries, and efferent arteriole
venous flow of blood from kidneys
cortical radiate, arcuate, interlobar, and renal veins
nephrons simple and 2 main parts
the structural and functional units that form urine; renal corpuscle and renal tubule are the two main parts
how many nephrons per kidney
about 1 million
2 parts of the renal corpuscle
glomerulus and glomerular capsule
glomerulus
fenestrated capillaries that allow for efficient filtrate formation
filtrate
plasma-derived fluid that renal tubules process to form urine; basically blood plasma minus proteins
another name for glomerular capsule
bowman’s capsule
glomerular capsule
cup-shaped, hollow structure that surrounds glomerulus; contains parietal and visceral layer, as well as podocytes, foot processes, and filtration slits
parietal layer cell type in glomerular capsule
simple squamous epithelium
visceral layer in glomerular capsule
clings to capillaries and has branching epithelial podocytes that terminate in foot processes
filtration slits
found in glomerular capsule between foot processes and allow filtrate to pass into the capsular space
foot processes
extend from the podocytes and wrap themselves around the glomerulus to form the filtration slits
podocytes
slits in which fluid that leaves the glomerulus under high pressures passes through and fills up the capsular space
proximal convoluted tubule
where everything leaves from the renal corpuscle; simple cuboidal epithelium that is rich in microvilli and mitochondria
where are juxtaglomerular cells found?
sandwiched between the loop of henle and the afferent arteriole
function of macula densa and juxtaglomerular cells together
help to regulate blood pressure in the kidneys
function of juxtaglomerular cells
help to produce, store, and release renin
renin
an enzyme (sorta hormone) that is involved in blood pressure regulation
where does the basement membrane of the capillary sit?
on the visceral layer of the glomerular capsule
proximal convoluted tubule
cuboidal cells with dense microvilli that form brush borders on apical side; basal side is in contact with capillaries; large mitochondria; function in reabsorption and secretion; are confined to cortex
another name for nephron loop
the loop of henle
nephron loop
U-shaped structure consisting of descending and ascending limbs
descending limb
continuous with the proximal tubule; consists of simple squamous epithelium
ascending limb
thicker than descending limb; cuboidal or columnar cells
what does the ascending limb connect with?
the distal convoluted tubule
distal convoluted tubule
cuboidal cells with very few microvilli; function more in secretion than reabsorption; are confined to cortex
two types of cells in collecting ducts
principal and intercalated cells
principal cells
sparse with short microvilli; function to maintain water and Na+ balance
intercalated cells
cuboidal cells with abundant microvilli; A and B types; function to maintain acid-base balance of blood
collecting ducts
receive filtrate from many nephrons; run through medullary pyramids; ducts fuse together to deliver urine through papillae into minor calyces
2 types of nephrons
cortical and juxtamedullary
cortical nephrons
make up 85% of nephrons; are found almost entirely in the cortex layer
juxtamedullary nephrons
long nephron loops that deeply invade the medulla; important in the production of concentrated urine
what are juxtamedullary nephrons associated with?
vasa recta
what enters and what leaves the glomerulus?
afferent arteriole enters and efferent arteriole leaves
what does the afferent arteriole arise from?
the cortical radiate arteries
what do efferent arterioles feed into?
either peritubular capillaries or vasa recta
why is blood pressure in glomerulus high?
because afferent arterioles are larger in diameter
peritubular capillaries
low-pressure, porous capillaries that are adapted for absorption of water and solutes; cling to adjacent renal tubules in cortex; arise from efferent arteries and empty into venules
vasa recta
long, thin-walled vessels parallel to long nephron loops of juxtamedullary nephrons; arise from efferent arterioles serving juxtamedullary nephrons; function in the formation of concentrated urine
juxtaglomerular complex
accompany each nephron; important for regulating the rate of filtrate formation and blood pressure; includes the distal portion of ascending limb and afferent (sometimes efferent) arteriole
three cells in juxtaglomerular complex
macula densa, granular cells, and extraglomerular mesangial cells
another name for granular cells
juxtaglomerular cells
macula densa cells
tall, closely packed cells of the ascending limb; contain chemoreceptors that sense NaCl content of filtrate
granular cells
enlarged, smooth muscle cells of the arteriole; act as a mechanoreceptor to sense blood pressure in the afferent arteriole; contain secretory granules that contain the enzyme renin
extraglomerular mesangial cells
located between arteriole and tubule cells; interconnected with gap junctions; may pass signals between macula densa and granular cells
how much fluid is processed and formed by kidneys each day?
180 L processed (60x entire plasma volume) but only 1.5 L of urine is formed
three processes that are involved in urine formation and adjustment of blood composition
glomerular filtration, tubular reabsorption, and tubular secretion
glomerular filtration simple
produces cell and protein free filtrate
tubular reabsorption simple
selectively return 99% of substance from filtrate to blood in renal tubules and collecting ducts
tubular secretion
selectively moves substances from blood to filtrate in renal tubules and collecting ducts
glomerular filtration
a passive process in which hydrostatic pressure forces fluids and solutes through filtration membrane into glomerular capsule; no reabsorption into capillaries occurs
the filtration membrane
a porous membrane between blood and the interior of glomerular capsule that allows water and solutes smaller than plasma proteins to pass; consists of three layers
3 layers of filtration membrane
fenestrated endothelium of glomerular capillaries; fused basement membrane; and foot processes of podocytes with filtration slits (repels macromolecules)
how does the filtration membrane work for macromolecules?
macromolecules stuck in filtration membrane are engulfed by glomerular mesangial cells
what can pass through the filtration membrane?
molecules smaller than three nm; water, glucose, amino acids, and nitrogenous waste
why do plasma proteins remain in blood and aren’t filtered?
maintains colloid osmotic pressure; this prevents loss of water to capsular space and proteins in filtrate indicate membrane problem
pressures that affect filtration
outward and inward pressures
outward pressures
forces that promote filtrate formation; associated with hydrostatic pressure in glomerular capillaries; average is 55 mm Hg
hydrostatic pressure in glomerular capillaries
is an outward pressure; is essentially glomerular blood pressure which pushes water and solutes out of blood
inward pressures
forces that inhibit filtrate formation; are hydrostatic pressure in capsular space and colloid osmotic pressure in capillaries
hydrostatic pressure in capsular space
filtrate pressure in capsule; 15 mm Hg
colloid osmotic pressure in capillaries
pull of proteins in blood; 30 mm Hg
net filtration pressure
sum of all forces that is responsible for filtrate formation; outward pressures - inward pressures (HPgc) - (HPcs + OP gc); 10 mm Hg
what is the main factor determining glomerular filtration rate
net filtration pressure
how is glomerular filtration different?
capillaries are long and extensive; mesangial cells can alter surface area; membrane in thin and porous; and glomerular capillary blood pressure is very high
glomerular filtration rate
the volume of filtrate formed per minute by both kidneys; average is 120-125 mL per minute
3 things GFR is directly proportional to
net filtration pressure, total surface area available for filtration; and filtration membrane permeability
what is the primary net filtration pressure?
glomerular hydrostatic pressure
how is total surface area controlled?
mesangial cells control this by contracting and relaxing
why is constant GFR important?
it allows kidneys to make filtrate and maintain extracellular homeostasis
what is the goal of local intrinsic controls
aka renal autoregulation; to maintain GFR in kidneys (important when MAP is in a range of 80-180 mm Hg)
how does GFR affect systemic blood pressure?
increased GFR causes increased urine output which lowers blood pressure (and vise versa)
what is the goal of extrinsic controls?
to maintain systemic blood pressure; nervous system and endocrine mechanisms are the main controls for this
2 types of renal autoregulation
myogenic mechanism and tubuloglomerular feedback mechanism
myogenic mechanism
local smooth muscle contracts when stretched; increased blood pressure causes muscle to stretch, leading to constriction of afferent arterioles that restricts blood flow into the glomerulus (and vise versa)
function of myogenic mechanism
helps to maintain normal GFR despite normal fluctuations in blood pressure
tubuloglomerular feedback mechanism
flow-dependent mechanism that is directed by macula densa cells that respond to filtrate’s NaCl concentration
how does tubuloglomerular feedback mechanism work
is GFR increase, filtrate flow rate also increases; this leads to decreased reabsorption time, causing high NaCl levels in filtrate; feedback mechanism causes constriction of afferent arteriole, which lowers NFP and GFR
what is the purpose of extrinsic controls?
to regulate GFR to maintain systemic blood pressure; these controls will override renal intrinsic controls if blood volume needs to be increased
sympathetic nervous system and renal system at rest
renal blood vessels and dilated and renal autoregulation mechanisms prevail
what happens to nervous and renal system under low blood pressure?
norepinephrine is released, causing systemic and afferent arteriole vasoconstriction, causing blood volume and pressure to increase
where is norepinephrine released from?
the adrenal medulla
purpose of renin
converts angiotensin into its active form
three effects of renin
constricts afferent arteriole, enhances reabsorption of Na+/Cl- in PCT, and stimulates adrenal cortex to release aldosterone
what is the main mechanism for increasing blood pressure?
renin-angiotensin-aldosterone mechanism
renin-angiotensin-aldosterone mechanism
the main mechanism for increasing blood pressure; there are three pathways for the release of renin by granular cells
three pathways for the release of renin by granular cells
direct stimulation of granular cells by SNS; stimulation of activated macula densa cells when filtrate NaCl concentration is low; and reduced stretch of granular cells
the renin-angiotensin system
a hormone system that regulates blood pressure and fluid and electrolyte balance, as well as systemic vascular resistance
when can the renin-angiotensin system be activated?
when there is a loss of blood volume or pressure and a decrease in filtration of NaCl concentration or a decreased filtrate flow rate
when is there a loss of blood volume or pressure?
dehydration or a hemorrhage
what is the loss of blood pressure interpreted by?
baroreceptors in the carotid sinus
when do juxtaglomerular cells release renin?
when blood flow to the juxtaglomerular appartus decreases
what does ANG II act as?
it acts of an endocrine, autocrine, paracrine, and intracrine hormone, as well as a potent vasoconstrictor peptide
how does ANG II act as a vasoconstrictor?
it causes blood vessels to narrow, resulting in increasing blood pressure and secretion of aldosterone
aldosterone role
causes the renal tubules to increase the reabsorption of sodium and water into the blood, while at the same time causing the excretion of potassium (to maintain electrolyte balance)
does ANG II have a larger effect on afferent or efferent arterioles?
efferent
what is the effect of ANG II vasoconstriction?
it causes blood to build up in the glomerulus, increasing glomerular pressure and thus maintaining GFR
what does decreased medullary blood flow through the vasa recta cause?
higher concentration of NaCl and urea (higher concentration of urine) in the medulla which facilitate increased absorption of tubular fluid
how does ANG II cause constriction?
contraction of smooth muscle cells
what are the overall results of ANG II?
reductions in renal blood flow and GFR that preserve ECF and blood pressure
what chemicals can renal cells release?
adenosine and prostaglandin E2; these act as paracrines that affect renal arterioles
what is the effect of cells making their own ANG II?
reinforces the effects of hormonal ANG II
what is the internal space of the kidney called?
the renal sinus
what are heavily modified smooth muscle cells called?
juxtaglomerular cells
what is the difference between cells in distal and proximal convoluted tubules?
distal cells are thinner and have less microvilli; distal cells also function more for secretion than reabsorption
do principal or intercalated cells have more microvilli?
intercalated cells
how is urine delivered into minor calyces?
through collecting ducts fusing together to deliver urine through the papillae
what chemicals cause constriction of vessels?
norepinephrine and epinephrine
what cells release renin?
juxtaglomerular cells
what runs through the medullary pyramind?
collecting ducts; gives them their striped apperance
what is the numerical value of pressure for HSGC?
55 mm Hg; compared to 26 mm Hg which is normal in capillaries
what is the numerical value of pressure for HSCS?
15 mm Hg
what is the numerical value of pressure for COGC?
30 mm Hg
what is average NFP?
10 mm Hg
tubular reabsorption
the process that moves solutes and water out of the filtrate and back into the bloodstream
why is reabsorption ‘re’?
because this is the second time that substances are being absorbed; the first time is when they were absorbed in the bloodstream after a meal
two routes that substances can follow for tubular reabsorption
transcellular and paracellular
types of active transport
pumps/ATPases; secondary active transport; cotransporter; pinocytosis/endocytosis/exocytosis
types of passive transport
simple diffusion; channel proteins; carrier protiens
first step of tubular reabsorption
the passive or active movement of water and dissolved substances from the fluid inside the tubule into the space outside
second step of tubular reabsorption
water and these substances move through the capillary walls into the bloodstream via passive or active transport
transcellular route
solute enters apical membrane of tubule cells and exits through basolateral membrane; it then enters blood through endothelium of peritubular capillaries
what happens when solutes are saturated in tubular reabsorption (and example)?
excess will be excreted in the urine; ex. hyperglycemia leads to high blood glucose levels that exceed Tm, and glucose spills over into urine
paracellular route
water and solutes move between tubule cells through tight junctions in leaky proximal nephorns
what can move via the paracellular route?
water, Ca2+, Mg2+, K+, and some Na+ (only in the PCT)
what is the site of most reabsorption?
the proximal convoluted tubule
what is absorbed in the PCT?
all nutrients (ex. glucose and amino acids), 65% of Na+ and H20, many ions, almost all uric acid, and about half of urea
what can leave in the descending loop?
H2O can leave, solutes cannot
what can leave in the ascending loop?
solutes can, H2O cannot
what is the thin segment of ascending loop passive to?
Na+ movement
symporters in thick segment of ascending loop
Na+ - K+ - 2Cl-
symporter meaning
when two molecules move in the same direction across a membrane
antiporter meaning
when two molecules move in opposite directions across a membrane
antiporters in thick segment of the ascending loop
Na+ - H+ (these transport Na+ into the cell)
where is reabsorption hormonally regualted?
in the DCT and collecting duct
what is ADH released by?
the posterior pituitary gland
ADH
antidiuretic hormone
role of ADH
causes principal cells to insert aquaporins in apical membranes, increasing water reabsorption
what do increased ADH levels cause?
increase in water reabsorption
what does the countercurrent multiplier depend on?
filtrate flow in opposite directions, difference in permerabilities b/w loops, and active transport of solutes out of ascending limb
what are actively reabsorbed in the thick segment of the ascending limb?
Na+ and Cl- (some is passively transported in thin segment)
countercurrent multiplier
the effect of countercurrent exchange with the active transport mechanisms that reabsorb ions from the tubular fluid back into the interstitial fluid; slowly creates a higher solute concentration of interstitial fluid
why does countercurrent multiplier work?
because the limbs of nephron loops are not in direct contact but still close enough to influence each other’s exchange with surrounding interstitial fluid
what is the constant difference between the two limbs of nephron limbs, as well as the ascending limb and interstitial fluid?
200 mOsm
what is the vasa recta highly permeable to?
water and solutes
why does the ascending limb use salty filtrate?
to further raise the osmolarity of medullary interstitial fluid
what three key players interact with the medullary osmotic gradient
the long nephron loops, the vasa recta, and the collecting ducts
what act as the countercurrent multipliers?
the long nephron loops
what preserve the concentration gradient in the medulla?
the vasa recta
how is varying concentrations of urine produced?
the juxtamedullary nephrons create an osmotic gradient within the medulla
where is flow of blood countercurrent?
the loop of nephron and the vasa recta
what is the blood in the vasa recta like relative to the surrounding interstitial fluid
isosmotic
2 ways that the countercurrent exchanger preserves medullary gradient
by preventing rapid removal of salt from interstitial space and by removing reabsorbed water
blood volume at the end of the vasa recta
is greater than at the beginning
movement of water in descending limb (passive or active?)
passive
movement of solutes in ascending limb (passive or active?)
active
highest mOsm of filtrate in nephron loop
1200 mOsm at bend of loop
when is the filtrate the most dilute in nephron loop?
as it leaves (100 mOsm); here it is hypoosmotic to the interstitial fluid
what happens when you are overhydrated
decreased osmolarity of extracellular fluid and ADH production decreases, as well cells swell due to excess H20
what happens when you are dehydrated
increased osmolarity of extracellular fluid and ADH production increases, as well cells lose water and shrink
relationship between gradient and concentration of urine
without the gradient, we would not be able to raise urine concentration
where is the concentration of urine mainly produced?
loop of henle concentrates or diltues by countercurrent multiplication, and then this is finished in the DCT and collecting ducts
how much sodium is reabsorbed in the early DCT?
5%
how much sodium is reabsorbed in the late DCT?
3% (final bit of fine tuning occurs here and determines how much sodium will be excreted)
early DCT and late DCT
have difference in these transporters, as well as the sodium/potassium ATPase that drives reabsorption of calcium and chloride
calcium reabsorption
similar to that of sodium; 99%. reabsorped
phosphate reabsorption
similar to glucose and mainly occurs in the PCT
reabsorption of magnesium
majority occurs in the ascending loop
what is the most abundant cation filtrate?
sodium
how is sodium transported across basolateral membrane of a tubule cell?
primary active transport; Na+-K+ ATPase pumps Na+ into interstitial space
how does sodium enter into peritubular capillaries?
via bulk flow
how does sodium enter tubule cell at apical surface
via secondary active transport (cotransport) or via facilitated diffusion through channels
what is the result of active pumping of sodium at basolateral membrane
more Na+ diffusion into the cell due to low intracellular levels inside, and K+ leaks out of the cell; overall results in a net negative charge inside the cell
what provides energy and means for reabsorbing almost every other substance?
sodium
secondary active transport in tubular reabsorption
the electrochemical gradient created by pumps at basolateral surface gives the push needed for transport of other substances
organic nutrients reabsorption
done by secondary active transport (cotransport with Na+); these are glucose, amino acids, some ions, and vitamins
how is glucose reabsorbed?
Na+-glucose symporter first, then facilitated diffusion, then simple diffusion
how is H+ reabsorbed?
Na + - H+ antiporter
how is HCO3- reabsorbed?
CO2 enters cell and makes H2CO3-, breaks down into HCO3- and enters via facilitated diffusion
how are Ca, K, Mg, Urea, and water reabsorbed?
passive diffusion
osmolarity
the concentration of a solution; expressed in mOsm/L
a higher osmolarity rate says what?
that the concentration of solutes is higher per L
does osmolarity of the interstitial fluid increase or decrease the deeper into the medulla?
increase; this will later facilitate the passive diffusion of water into the interstitial fluid later in the collecting duct
how much water has already been reabsorbed in the early DCT?
80%; it will reabsorb an additional 10-15%, and 5% each of Na+ and Cl-
how does reabsorption of Na+ and Cl- occur in the early DCT?
Na+ - Cl- symporter in the apical membranes
what stimulates the reabsorption of calcium in the DCT?
parathyroid hormone
two mechanisms for water reabsorption
obligatory and facultative
obligatory water reabsorption
occurs anywhere the nephron tube is permeable to water; the PCT and descending limb
facultative water reabsorption
depends on the presence of ADH and ADH-competent principal cells of of terminal DCT and CT
where is aldosternone released from?
the adrenal cortex
what does ANG II act on?
AT1 receptors through binding to them
where are AT1 receptors located?
on luminal and basolateral membranes of proximal and distal nephron segments
what does the activation of AT1 receptors do?
leads to increased activities of the sodium/hydrogen exchanger, the sodium bicarbonate cotransporter, the sodium-chloride transporter, and the epithelial sodium channel
what does aldosterone bind to increase sodium reabsorption?
through binding to the cytoplasmic mineralocorticoid receptor
what does ANG II stimulate?
the release of aldosterone, the release of ADH, Na+/H+ exchangers, and the secretion of potassium back into the tubules
ADH and salt
ADH acts on the CNS to increase an individual’s appetite for salt and the sensation of thirst
where does tubular secretion mainly occur?
in the PCT
substances involved in tubular secretion?
K+, H+, NH4+, creatinine, organic acids, and bases (as well as those synthesised in the tubule cells such as HCO3-)
NH4+
ammonium (ammonia with an extra hydrogen atom)
why is tubular secretion important?
allows for the disposal of harmful substances that are bound to plasma proteins and were passively reabsorbed, rids body of excess K+, and controlling blood pH by altering amounts of H+ and HCO3-
aldosterone effect
causes sodium to be absorbed and potassium to be excreted into the lumen by principal cells
what cells secrete H+?
intercalated cells
how is H+ secreted?
CO2 + H20 forms H2CO3 > H+ + HCO3-; H+ is removed by a proton pump back into the tubule
what happens to H+ once it enters back into the tubule? (buffering)
it bonds with NH3 to form NH4+ or bonds with HPO42- to form H2PO4-
four major fluid compartments of the body
intracellular, extracellular, interstitial, and intravascular
intracellular component
aka cytosol; all fluid contained inside the cells and normally is in osmotic equilibrium
extracellular compartment
the intersital, intravascular and transcellular compartments
interstitial compartment
surrounds tissue cells and is not static (refreshed by capillaries and lymphatic system)
intravascular compartment
blood (includes intracellular fluid inside blood cells and blood plasma)
what fluid compartment holds the most fluid?
intracellular (28 L in males and 22 L in females)
flow of how renin is converted along the line?
prorenin is converted to renin by granular cells; angiotensinogen released by the liver is converted to angiotensin I (by plasma renin); angiotensin I is converted to II by angiotensin-converting enzyme
ACE
angiotensin-converting enzyme
where is ACE found?
on the surface of vascular endothelial cells, predominantly those of the lungs
ions found in electrolytes
sodium, potassium, calcium, magnesium, bicarbonate, chloride, hydrogen phosphate, and sulfate
osmolality
number of solute particles in one kg of H20
two types of countercurrent mechanisms
countercurrent multiplier and countercurrent exchanger
how do the two countercurrent mechanisms work together?
they establish and maintain medullary osmotic gradient from renal cortex through medulla
range of mOsm
300 - 1200
what countercurrent mechanism makes gradient and what preserves it?
multiplier makes, exchanger preserves
where does aldosterone function?
collecting ducts (principal cells) and DCT
what does aldosterone promote synthesis of?
Na+/K+ channels on apical side, and Na+-K- ATPases
why does little Na+ leave the body?
because of Na+/K- channels as a result of aldosterone
atrial natriuretic peptide
reduces blood Na+, resulting in decreased blood volume and pressure
from where and why is atrial natriuretic peptide released?
from cardiac atrial cells when blood volume or pressure is elevated
parathyroid hormone
acts on DCT to increase Ca+ reabsorption; osteoclasts will break down bone in response to this
ADH negative feedback loop
decreased osmolarity of plasma and interstitial fluid detected by osmoreceptors in the hypothalamus activates the posterior pituitary gland to cause principal cells to be more permeable to water
another word for urination
Micturition
what happens when your bladder is at rest?
internal sphincters is passively contracted and external is also contracted (but by skeletal muscle); motor neurons are firing
what is the micturition centre?
in the sacral spinal cord
what happens when your bladder is full?
stretch receptors and parasympathetic neurons fire; sphincters relaxes while detrustor muscle contracts
what do thiazide type blood pressure drugs do?
block symporter for the reabsorption of Na+ and Cl- in the DCT
percentage composition of urine
95% water and 5% solutes
what solutes are found in urine?
Na+, K+, PO43-, SO42-, Ca2+, Mg2+, and HCO3-
what nitrogenous wastes are found in urine?
urea, uric area, and creatinine
what nitrogenous waste is most abundant in urine?
urea
how does urea form?
from amino acid breakdown
how does uric acid form?
from nucleic acid metabolism
how does creatinine form?
a metabolite of creatine phosphate
pH of urine
average is 6, range of 4.5 to 8
what can cause urine pH to drop?
an acidic diet such as protein and whole wheats
what can cause urine pH to rise?
an alkaline diet; vegetarians, lots of vomiting, or UTI’s
specific gravity
the ratio of mass of substance to mass of equal volume
what is the specific gravity of urine?
1.001 to 1.035
what indicates pathology of urine?
high concentrations of any substance, or abnormal levels of blood proteins, WBC’s and bile pigments
what does cloudy urine indicate?
UTI
urochrome
a yellow pigment from hemoglobin breakdown that gives urine its colour
what does abnormal urine colour indicate?
certain foods, bile pigments, blood, and drugs
what happens to urine odor after some time?
it develops ammonia as bacteria metabolise the urea
diabetes urine odor
may have an acetone smell
substances that enhance urination
alcohol, caffeine, drugs for hyperextension or edema, loop diuretics, and osmotic diuretics
why does alcohol increase urination?
it is an ADH inhibitor
why do caffeine and drugs increase urination?
they inhibit Na+ reabsorption
why do loop diuretics increase urination?
they inhibit medullary gradient formation
why do osmotic diuretics increase urination?
the substances are not reabsorbed, so water remains in urine
where do ureters begin?
L2; they are a continuation of the renal pelvis
ureters
slender tubes tubes that convey urine from kidneys to bladder
what happens when bladder pressure increases?
the distal ends of the ureters close, preventing backflow of urine
three layers of ureter wall
mucosa, muscularis, and adventitia
mucosa layer of ureter
consists of transitional epithelium with an underlying lamina propria
muscularis layer of ureter
smooth muscle sheets that contact in response to stretch; this layers propels urine into bladder along with peristalsis; inner long layer and middle circular layer
adventitia layer of ureters
outer fibrous CT
where is the bladder located?
on pelvic floor posterior to the pubic symphysis
male position of bladder
prostate is inferior to bladder neck
female position of bladder
anterior to vagina and uterus
trigone
smooth triangular area outlined by openings for ureters and urethra; where infections persists
3 layers of bladder wall
mucosa, muscular layer, and fibrous adventitia
mucosa layer of bladder
transitional epithelium
muscular layer of bladder
contains thick detrusor muscle that contains three layers of smooth muscle (inner and outer are long and middle is circular)
adventitia layer in bladder
fibrous except on superior surface where it is covered by peritoneum
bladder when empty
collapses and rugae appear
fhow much can a pull bladder hold
500 mL and becomes 12 cm long (rises superiorly when filling)
urethra
muscular tube that drains urinary bladder
epithelium of urethra
mostly pseudostratified columnar but transitional near bladder and stratified squamous near orifice
female urethra
tightly bound to anterior vaginal wall; external urethral sphincter is anterior to vaginal opening and posterior to clit
male urethra
carries semen and urine; has three regions
three regions of male urethra
prostatic urethra, intermediate part of the urethra, and spongy urethra
prostatic urethra
within prostate
intermediate part of the urethra
aka membranous urethra; passes through urogenital diaphragm from prostate to beginning of penis
spongy urethra
passes through penis; opens via external urethral orifice
three events of micturition
contraction of detrusor by ANS; opening of internal sphincter by ANS; opening of external sphincter by SNS
where does active transport energy come from?
ATP hydrolysis
what type of transport is cotransport?
secondary active transport
where does paracellular transport mainly occur?
PCT
what cells insert aquaporins?
principal cells
what do aquaporins do?
increase water reabsorption
ATPase
brings 3 sodium ions out of cell and 2 potassium in; overall negative charge inside cell remains after this
how is blood pH controlled by the urinary system?
by altering the amounts of H+ and HCO3-
H2PO4-
Dihydrogen phosphate (HPO4- + H+)
what ions are more abundant inside the cell?
K+, Mg+, HPO4-, S042-, and protein anions
what ions are more abundant outside the cell?
Na+, Cl-, and HCO3-
what is released when blood pressure is too high
atrial natriuretic peptide which releases Na+ to decrease blood pressure
low calcium levels negative feedback loop
low calcium levels cause parathyroid glands to release parathyroid hormone, causes osteoclasts to degrade bone matrix to bring more calcium into the bloodstream
how are aquaporins formed?
by exocytosis done by principal cells
what maintains electrolyte balance?
renin-angiotensin-aldosterone system
is sodium or potassium concentration higher inside the cell?
potassium
is sodium or potassium concentration higher outside the cell?
sodium
how does metabolism create water?
dehydration synthesis; an extra water molecule is created from two compounds joining
review of negative feedback loop
stimulus is detected by receptor or sensor; info sent along afferent pathway to the control centre; output is send along efferent pathway to an effector; response of effector reduces stimulus
water dissociation theory
H20 > H+ and OH-
water dissociation in reality
H20 + H20 > H3O+ and OH- (this is because protons never really exists alone and in water they bind with water molecules to form hydronium ions
hydronium
H3O+
acids and hydrogen
the stronger the acid, the more readily it donates H+; these combine with OH- to form water
bases and hydroxyl
bases readily donate Oh- ions; these combine with H+ to form water
pH scale
the measure of the concentration of H+ ions in a solution; 0 -14 (water is 7 which is neutral)
buffer systems
convert strong acids/bases into weak ones; ex. the carbonic-acid/bicarbonate buffer system
the carbonic-acid/bicarbonate buffer system
protects your blood plasma from sharp changes of pH; CO2 + H20 > H2CO3 > H + HCO3
sodium bicarbonate
NaHCO3; used as a buffer; can dissociate to HCO3 to increase pH
receptors for decreased blood pH
central chemoreceptors in medulla oblongata and peripheral chemoreceptors in aortic and carotid bodies
control centre for decreased pH
inspiratory area in medulla oblongata
effectors for decreased pH
diaphragm contracts more forcefully and frequently so more CO2 is exhaled; this causes fewer H+ to form as less H2CO3 forms, decreasing H+ concentration
negative feedback loop for decreasing pH levels
H+ concentration is high, receptors in medulla oblongata and heart relay info to inspiratory area in medulla oblongata to increase expiration and ultimately decrease H+ levels in blood
acid-base balance
buffers typically consist of a pair of compounds in a solution, one of which is a weak acid and the other a weak base
most abundant buffer in the ECF
H2CO3 and HCO3 (associated with Na+)
most positively charged electrolyte in ECF
sodium
amount of sodium in ECF
increases blood ECF, determining blood volume and pressure
what forms of Na are mostly reabsorbed in the PCT?
sodium bicarbonate and sodium chloride
when are the most essential substances of the filtrate reabsorbed?
the first half of the PCT
most important reabsorbed substances
glucose, amino acids, phosphate, lactate, and citrate
what enables the reabsorption of bicarbonate?
sodium/proton exchanger
what is fluid entering the late proximal tubule like?
it is depleted of the essential substances
what is the negatively charged ion initially absorbed with sodium?
bicarbonate
chloride/formate anion exchangers
brings chloride into the cell and formate out
gluconeogenesis
production of glucose and this occurs in the kidneys
what hormone do the kidneys produce?
erythropoietin
basolateral side of PCT
highly infolded plasma membrane
