renal physiology test 3 Flashcards
how does the renal system regulate pH?
by retention of HCO3
remember excretion of HCO3 is bascially the same as adding 1 Hydrogen
-kidneys also produce new HCO3 by metabolizing gluatamine, which makes NH4 and HCO3
what are some other renal functions?
production of erythropoietin=more RBCs
Gluconeogenesis, particularly during a fasting state
what are the two basic parts of the kidney?
renal cortex and renal medulla(innermost)
what do we find within the medulla?
renal pyramids that contain nephrons
each pyramid is connected to what?
renal pelvis or urine drainage tube, by a papilla
the kidney is supplied with blood via the renal artery which enters the organ at the hilum. This branches into what?
afferent arterioles, which feed capillary beds known as glomerular capillaries.
why are glomerular capillaries important?
supply the nephrons with blood
this is where filtration occurs
glomerulo capillaries feed into what?
efferent aterioles which form a secondary capillary network called the peritubular capillaries.
where does reabsorption/secretion occur?
at the peritubular capillaries
is the hydrostatic pressure higher in the glomerular capillaries or the peritubular capillaries?
the glomerular capillaries (60 mmHg) peritubular capillaries (13 mmHg)
what regulates the hydrostatic pressure?
changes in the afferent/efferent arterioles
when the glomerulus is covered by epithelial cells what is it called?
bowman’s capsule
list the order of tubes in the nephron
bowman’s capsule ->proximal tube->loop of henle->distal tubule->collecting duct->renal pelvis and ureter
where does reabsorption and secretion occur within the nephron?
proximal tube
loop of henle
distal tube
**peritubular capillaries
where does filtration occur?
bowman’s capsule/bowman’s capsule
**glomerular capillaries
what are the two types of nephrons
cortical nephrons-cortex region (70%)
juxtamedullary nephrons-medulla (30%)
how is the blood supply different between cortical nephrons and juxtamedullary nephrons?
- cortical nephrons: peritubular capillaries are tightly associated with loop of henle
- juxtmedullary nephrons: efferent arterioles extend part of the way down the loop of henle and form vasa recta
what is the formula for urinary excretion rate:
(filtration rate-reabsorption)+secretion=excretion
-what comes out into proximal tube, minus what gets taken back out into peritubular, plus what comes out of peritubular.
are waste products generally filtered or reabsorbed?
filtered, Thus a high Glomerular filtration rate (GFR) ensures rapid removal form the blood
T/F for most substances, filtration rates and reabsorption rates are very high compared to the proportion which is excreted. Thus small changes in filtration or reabsorption translate to large changes in excretion?
True
how much water do we excrete per day usually?
1 liter
how much sodium do we excrete per day?
150 mmol
how much glucose do we excrete per day?
0 g
how much creatinine do we excrete per day?
1.8 g
the glomerular capillary membrane is selective for what?
small positively charged molecules
what are the three layers of the glomerular capillary membranes?
endothelium
basement membrane
specialized epithelial cells called podocytes
endothelium
has small fenestrea
negatively charged
basement membrane
serves to fuse the endothelium to the podocyte cell layer
podocytes(foot cells)
form slit pores which size and charge restrict filtrate
Glomerular filtration rate =Kf x net filtration pressure. What does this mean?
- K the glomerular capillary filtration coefficient (surface area)
- net filtration pressure: the sum of the colloid and hydrostatic pressures across the glomerular capillaries
why is filtration favored in the afferent arteriole?
the glomerular hydrostatic pressure is higher than the bowman’s capsule pressure
why is anti-filtration favored at the efferent arteriole?
glomerular colloid osmotic pressure is greater than the bowman’s capsule pressure
what will constriction of the afferent arterioles do to GFR?
decrease it because the hydrostatic pressure will decrease due to the increased velocity of blood flow
what will minor constriction of the efferent arterioles do the GFR?
increase GFR due to a build up of blood in the glomerulus
major constriction of the efferent arteriole will cause what to the GFR?
decrease GFR because proteins will build up thus increasing the colloid osmotic pressure.
sympathetic nervous system regulation of GFR?
decrease of GFR due to vasoconstriction of afferent and efferent arterioles
catecholamine (norepinephrine) regulation of GFR?
decrease GFR due to vasoconstriction of afferent and efferent arterioles
Angiotensin II regulation of GFR?
prevents a decrease in GFR by constricting efferent arteriole
prostoglandin/NO regulation of GFR?
increase in GFR due to vaso dialation of afferent and efferent arterioles.
what is the tubuloglomerular feedback
links sodium chloride concentration in distal tubule with the constriction state of the afferent and efferent arterioles
what is the macula densa?
it is in the distal tubule and detects forms the juxtaglomerular complex with the walls of both the afferent and efferent arterioles.
**detects a decrease in NaCl concentration, which indicates a decreased renal flow (GFR)
what happens when the macula densa senses a decrease in NaCl?
dilation of afferent arterioles and causes an increased release of renin, which increases angiotensin I and II which causes constriction of efferent arterioles thus restoring GFR.
when osmolarity in the body is high (body water is low) what kind of urine will you have?
more concentrated urine
* inverse is also true for low osmolarity body fluid
what is the primary active transporter?
Na/K ATPase
why is the primary active transporter important?
sets up gradients for secondary active transport
active transport of Na is linked to reabsorption of many things including?
glucose and H ions
Co-transport with Na
glucose follows Na from tubule back to the blood
What is excreted by counter-transport with Na?
Hydrogen ions
The proximal tubule is involved with reabsorption of what?
water through passive diffusion throught the tight junctions of the tubules linked to Na gradients
65% of what is reabsorbed in the proximal tubule?
water and Na
also Cl is reabsorbed with the Na(mostly at the distal end of the proximal tube)
the cells bordering the proximal tube have what characteristics?
tons of mitochondria for active transport
brush border to increase surface area
at the more proximal end of the proximal tubule what are preferentially reabsorbed with Na?
glucose and AAs and HCO3
why does the amount of Na decrease as you move along the tubule but not the concentration?
because water is leaving with it
the thin descending segment of the loop of henle is permeable to?
water because of aquaporins
20% of water filtered here
the thick ascending segment is not permeable to water but has tons of what?
active transporters and thus is heavily involved in reabsorbing Na, Cl, K. 25% of these ions are absorbed here.
also Ca, Mg, and HCO3 are reabsorbed here.
what type of cells are in the distal half of the distal tube?
principal cells
intercalated cells
what do principal cells do?
reabsorb Na and water from the lumen and secretes K into the lumen.
-favors outward Na flow
intercalated cells do what?
reabsorb K and HCO3 and secrete H ions and can therefore regulate pH
the permeability of the late distal tube is controlled by what hormone?
anti-diuretic hormone
in absence of ADH the late distal tube is more or less permeable to water?
less, causing urine to be more dilute.
ADH increases permeability of water thus making more concentrated urine
collecting ducts
- reabsorb 10% of the filtered water and Na
- regulated by ADH
- Have same cells as late distal tube
- medullary collecting cels efficient at pumping H ions into lumen (pH control)
- **permeable to urea letting some out into medullary interstitium
Urea is passively reabsorbed where?
how does ADH affect urea?
- proximal tubule and collecting duct
- When ADH is high the ducts are permeable to water thus letting more urea out
how is the vasa recta associated with the juxtamedullary nephrons important for maintaining the medullary interstitial hyperosmolarity?
- blood flow is very slow, preventing solute washout
- long U bend shape allows it to act as a countercurrent exchanger, maintaining the steep concentration gradient
