Renal System Flashcards
2 functions of kidney
- blood volume/osmolarity regulation
2. filtration
Micurition Reflex
- stretch of urinary bladder is detected by stretch receptors
- visceral afferent nerves go to sacral spinal cord
- efferent signal, via parasympathetic nerves, cuases contraction of bladder and relaxation of internal urethral sphincter
- conscious control of external urethral sphincter
capillaries and arterioles associated with nephron
2 of each
-countercurrent exchange
kidneys adjust blood composition using 3 fundamental processes
- filtration
- bulk flow of water and solutes from blood into kidney tubules due to hydrostatic - absorption
- transport of substances out fo the tubules and back into the blood - secretion
- transport of substances from the blood into the tubules
blood flow to kidneys
- renal artery has low resistance (short and large diameter)
- branches of renal artery go directly to renal cortex
- afferent arterioles in cortex carry blood to glomerulus
- -the glomeruli are capillaries where filtration of the blood occurs
- efferent arterioles carry blood from glomeruli to peritubular capillaries
- -peritubular capillaries surround the renal tubules and participate in secretion and absorption of substances to and from the tubule
- -loops of the peritubular capillaries descend into the medulla following the tubular loops of Henle. known as vasa recta
- peritubular capillaries carry blood to branches of the renal vein
vasa recta
loops of the peritubular capillaries that descend into the medulla following the tubular loops of Henle
anatomy of a nephron
- bowmans capsule
- proximal tubule
- loop of henle
- distal tubule
- collecting duct
bowmans capsule
- receives filtrate from the glomeruli
- is involved in absorption of nutrients, water, and electrolytes
loop of henle
-involved in creating an osmotic gradient in the medulla that allows absorption of water from the distal tubule and collecting duct
distal tubule
- involved in the fine tuning of Na+ and K+ absorption and secretion
- also involved in absorption of water
collecting duct
- involved in water absorption
- fluid that makes it through the collecting duct into the renal pelvis is urine
Filtration
s
why is blood pressure in the golmerular capillaries high
-efferent arteriole creates significant resistance downstream of the glomerular capillaries
adjustment of blood pressure in the glomerulus
adjusted by constriction and dilation of either the afferent or efferent arterioles
- pressure in the glomerulus can be adjusted by contriction and dilation of either the afferent or efferent arterioles
- pressure in the glomerular capillaires is normally near 50mmHg
- pressur ein the bowmans capsule is normally near 10mmHg
- oncotic pressure in the capillaries is near 25mmHg
filtration pressure
difference between capillary pressure and capsule pressure+oncotic pressure
- ex: FP=50-(10+25)=15mmHg
- small changes in capillary pressure make relatively large changes in filtation pressure
golmerular filtraiton rate
GFR
- determined by filtration pressure
- measured in ml/min
- greater gfr, greater urine volume, increase urine volume, less blood volume
filtration layers
capillary endothelium-fenestrated (holes)
- basement membrane
- podocytes (form the visceral layer of bowmans capsule)
- -filtration slits are between the pedicels of the podocytes
ultrafiltrate
- fluid entering bowmans capsule
- everything in plasma but proteins
- water+all small solutes (Na, K, Cl, Ca, glucose, amino acids, urea, etc)
renal clearnace
clearance of a substance is the volume (ml) of plasma that is cleared of that substance per minute
-measurement of GFR
clearance equation
(V(ml/min)*U(mg/ml))/P(mg/ml)
V=volume of urine produced per minute
U= concentration of substance in the urine
P=concentration of the substance in the plasma
inulin clearance
a measure of the GFR
- insulin is filtered, but not secreted or absorbed, so clearance of inulin=GFR
- absorbed into arteriole
PAH clearance
- measure of total renal plasma flow (RPF)
- PAH is para-aminohippuric acid
- PAH is 100% cleared from renal plasma (no PAH in renal vein)
- total renal blood flow can be determined if CPAH and hematocrit are known
- average hematocrit is 0.45 for males and 0.42 for females
RBF (renal blood flow) equation
CPAH/(1-hematocrit)
clearance of any other substance can be compared to what
GFR and RPF
- if clearance is less than GFR it is being absorbed. If it is completely absorbed the the clearance is zero (glucose)
- if clearance is greater than GFR it is being secreted. if it is completely secreted the clearance=RPF
hematocrit and plasma makeup of blood
hematocrit=45%
plasma=55%
where do all the nutrients get absorbed
the proximal tubule
- glucose, amino acids, lactate, etc
- also about 80% of the Na+ Cl- and H2O
the proximal tubule absorption
- not highly regulated
- fine tuning of absorption occurs further down the tubule
- epithelium is similar to the small intestine epithelium
- leaky epithelium: water goes through tight junctions so isotonic fluid is absorbed
- Na+/K+-ATPase in basolateral membrane provides the primary driving force for the absorption
- Na+/glucose-,Na+/amino acid-cotransporters in luminal membrane
- facilitated diffusion of glucose, amino acids, Cl-
regulated absorption of H2O occurs where
-loop of henle, distal tubule, collecting duct
absorption of H2O process
- loop of Henle creates a hyperosmotic condition in the medulla, which consists of increasing osmotic strength as distance from the cortex increases
- the descending limb is permeable to H2O, so H2O is absorbed (leaves the tubule) as the fluid flows deeper into the medulla. This H2O is carried away by the capillaries of the vasa recta
- the ascending limb is impermeable to H2O and it actively absorbs NaCl, so the solutes tend to stay in the medulla, while the fluid arriving in the distal tubule is hypoosmotic. This process occurring in the loop of Henle is known as countercurrent multiplication
resulting conditions of countercurrent multiplicaiton
- about 12-15 liters/day of 100mOsm tubular fluid reaches the distal tubule
- tissue fluid osmolarity is about 300 mOsm in the cortex
- tissue fluid osmolarity increases from 300 to about 1400 mOsm in the deep parts of the medulla
the collecting duct and distal tubule use the osmotic gradient created by the loop of Henle to regulate the absorption of H2O
- The H2O concentration gradient favors absorption all the way along the distal tubule and collecting duct
- the amount of H2O that is absorbed depends on the permeability of the tubules for H2O
- if H2O permeability is low, little absorption takes place and large volume of dilute urine is produced
- if H2O permeability is high, a lot of absorption takes place and a small volume of concentrated urine is produced
how to control H2O permeability
controlled by antidiuretic hormone (ADH)
-ADH receptors on the distal tubule and collecting duct are linked to the Gs protein and lead to an increase in [cAMP] causes installation of water channels in luminal membranes by exocytosis
negative feedback loop that regulates tissue osmotic strength
- ADH secretion by the neurohypophysis is a part of the negative feedback loop
- hypothalamus has osmotic strength receptors
- increased osmotic strength of the CSF causes increased ADH secretion
- ADH causes decreased urine volume and induces thirst
biggest determinant of water concentration/blood volume
Na+
- controls osmotic strength
- more Na+, ADH conserves H2O, increased [H2O]
- increased BV will increase VR and therefore increase CO and arterial Pressure
kidney anatomy responsible for absorption of Na+?
distal tubule
- absorbs sodium and secretes potassium
- aldosterone increases Na+ absorption and secretion of K+ and H+
- aldosterone is secreted by the adrenal cortex in response to angiotensin 2
- aldosterone causes increased transcription of genes for Na+, K+, and H+ transport proteins
- -Na+/K+-ATPase, Na+/H+-countertransporter
Homeostasis of Body fluids
Renin-Angiotensin-aldosterone system
juxtaglomerular apparatus (JGA)
- JGA secretes renin if any of the following conditions are detected:
- low pressure in afferent arteriole
- large amounts of Na+ in the distal tubule
- low MAP detected by the arterial baroreceptors (vis the sympathetic NS)
renin pathway
an enzyme that cleaves angiotensinogen to angiotensin 1
- angiotensin converting enzyme (ACE) completes activation by conversion to angiotensin 2
- angiotensin 2 increases blood volume and blood pressure several way
ways that angiotensin 2 increases blood volume and pressure
- causes aldosterone secretion from adrenal cortex
- causes vasoconstriction of afferent arteriole, decreasing GFR
- causes increased ADH secretion from neurohypophysis
- causes general arteriole vasocontriction, increasing TPR causes increased thirst
angiotensin 2 receptors are linked to what protein
Gp-protein
atrial natriuretic hormone (ANH)
-stretch of the right atrium, exercise or caloric restriction causes increased release of ANH
-the ANH receptor is a guanylate cyclase receptor enzyme
-[cGMP] rises in the target cell and activates cGMP-dependent protein kinases
the results are:
-vasodilation: causes increased GFR and decreased TPR
-decreased absorption of Na+ by distal tubule (a Na+ channel is phosphorylated by the cGMP-dependent kinase)
-activation of enzymes for lipolysis (fat mobilization)
-most important effect of ANH
-lowering the blood pressure by reducing blood volume
pH
s
three systems interacting to control pH
- buffer system: the major extracellular buffer is bicarbonate
- respiratory system: can influence the bicarbonate buffer system
- renal system: can absorb or secrete H+ or HCO3
what disregulates pH
- metabolic or respiratory influences
- can be differentially diagnosed by observation of the bicarbonate concentration
metabolic acidosis
low pH and low [HCO3]
respiratory acidosis
low pH and high [HCO3]
metabolic alkalosis
high pH and high [HCO3]
respiratory alkalosis
high pH and low [HCO3]
renal handling of H+ and HCO3
absorption of filtered HCO3 is normally the first step (humans tend to be acidotic, and therefore are generally secreting H+ into the urine)
steps of renal handling of H+ and HCO3
- in the proximal tubule cell, CO2 is converted to H+ and HCO3 by carbonic anhydrase
- the H+ is actively secreted into the tubule (H-ATPase or Na/H-exchange)
- the H+ is actively secreted into the tubule (H-ATPase or Na/H-exchange)
- the HCO3 produced inside the cell is transported to the blood in exchange for Cl-
- the net effect of this is that HCO3 disappears from the tubule and appears in the blood, while H+ is removed from the body in the urine
additional secretion of H+ after filtered bicarbonate is recovered
- secreted H+ combines with one of the urinary buffers (amonia or phosphate)
- phosphate is normally found in the tubule fluid. it is co-regulated with calcium. NH3 is made in the proximal tubule cell using glutamine from the liver
- NH4 is one form of nitrogenous waste
- Urea is the other. it is made by the liver: 2NH3+CO2->urea
acidosis
too low pH, increased H+, denatures proteins
alkalosis
pH too high, not enough H+
metabolic acidosis
- something we ate causes increased H+
- reaction goes opposite way, HCO3- decreases, increased CO2
- breathing faster decreases CO2, helps buffer system move faster
- HCO3- is the limiting factor
acidosis reaction
H2O+CO2H+ + HCO3-
only way to eliminate excess H+
kidney excretes
-bicarbonate just binds it
respiratory acidosis
- result of hypoventilation
- increase [CO2], increase H+
- hyperventilation causes alkalosis
Homeostasis of calcium-3 hormones
- parathyroid hormone
- dihydroxycholicalciferol (vitamin D)
- calcitonin
vitamin D (dihydroxycholicalciferol)
- converted to cholecalciferol by the liver, kidney and skin
- it enhances Ca uptake by the small intestine
calcitonin
- causes increased activity of osteoblasts
- it causes increased bone formation and decreased plasma [Ca]
- takes calcium phosphate from bone, phosphate removed from calcium
parathyroid hormone
- most powerful of the three
- causes activation of vitamin D to cholecalciferol
- stimulates osteoclasts, causing mobilization of Ca and PO4 from bone
- it enhances renal absorption of Ca and secretion of PO4
