Flashcards in BIOL 0800 Reading- Chapter 14 Deck (137):
Where does gluconeogenesis occur?
In the kidneys
What are the three main hormones/enzymes secreted by the kidneys?
Erythropoeitin, 1,25 dihydroxyvitamin D, and renin
What are the two components of the nephron?
Renal corpuscle and the tubule
What is the renal corpuscle?
The initial filtering component of the nephron: Bowman's capsule and the glomerulus
What happens in the Bowman's space?
Where protein-free fluid is filtered from the blood in the capillaries of the glomerulus
What is a podocyte?
The epithelial cells on the visceral layer of the Bowman's capsule
What parts of the nephron are in the renal cortex vs medulla?
In the cortex: the renal corpuscles; in the medulla: varying lengths of the loops of Henle
What are peritubular capillaries?
The capillaries that run alongside the renal tubules
What is the blood flow through a nephron?
From afferent arteriole into glomerular capillaries into the efferent arteriole into the peritubular capillaries into the veins
What are the two types of nephrons?
Juxtamedullary and cortical
What are juxtamedullary nephrons?
Renal corpuscle is close to the cortical-medullary border, and tubule dips deep into the medulla: useful for reabsorption of water; lined by vasa recta
What is the vasa recta?
The long capillaries that line that juxtamedullary nephrons
Do all cortical nephrons have loops of Henle?
No: involved in reabsorption and secretion, but don’t contribute to hypertonic medullary interstitium
What is the juxtaglomerular apparatus?
Where the macular densa and JG cells combine between the afferent and efferent arterioles
What is the macula densa?
The patch of cells in the wall of the distal convoluted tubule
What are JG cells?
On the wall of the afferent arteriole; secrete renin
What is the formula for amount of substance excreted?
Amount filtered (in glomerulus) + amount secreted (in tubules) - amount reabsorbed (in tubules)
Why are proteins not included in the fluid filtered through the nephrons?
Because they're too big, and because the filtration pathways in the corpuscular membranes are negatively charged and oppose plasma protein movements
Why aren't plasma calcium and fatty acids filtered?
Because they're usually bound to proteins in the plasma
What does glomerular capillary hydrostatic pressure favor?
Filtration of fluid out of the capillaries into Bowman's space
What does the Bowman's space hydrostatic pressure favor?
Opposition of filtration of fluid from capillaries into Bowman's space
What does the osmotic force of the GC favor?
Opposition of filtration of fluid form capillaries into Bowman's space; wants the fluid to stay in the GC
What does the osmotic force of Bowman's space favor?
Nothing: there is no osmotic pressure in Bowman's space because there aren't any protein particles
What is the formula for net glomerular filtration pressure?
(P gc) - (P bs) - (pi gc)
What determines GFR?
Net filtration pressure, permeability of corpuscular membranes, and surface area available for filtration
How does afferent arteriole constriction affect GC hydrostatic pressure?
Decreases (P gc), decreases GFR
How does efferent arteriole constriction affect GC hydrostatic pressure?
Increases (P gc), increases GFR
How does mesangial cell activity affect GFR?
Contraction of mesangial cells (surround glomerular capillaries) reduces SA of capillaries; decreases GFR
What is filtered load?
The amount of any nonprotein/bound substance filtered into Bowman's space: = (GFR)(concentration in plasma)
What are the two main methods of tubular reabsorption?
Diffusion and mediated transport
Tubular reabsorption by diffusion is dependent on reabsorption of what?
Water: reabsorption of water increases the concentration of the substance in the tubular lumen, causing it to diffuse into the peritubular capillaries
Mediated tubular reabsorption is often coupled to reabsorption of what substance?
Na+: sodium goes downhill, driving the uphill diffusion of other substances
What is the transport maximum?
The limit to the amount of material that can be transported per unite time by the mediated transport reabsorptive systems
What are the two most important substance secreted by tubules?
H+ and K+
Tubular secretion is usually coupled to reabsorption of what substance?
What part of the nephron is a big source of solute secretion?
What parts of the nephron are a big source of reabsorption?
Proximal tubule and loop of Henle
What is clearance?
The volume of plasma from which that substance is completely removed: Mass secreted per unit time / plasma concnetration
What is the formula for clearance?
(urine concentration of S)(volume of urine per unit time) / (plasma concentration of S)
What must occur if the clearance of any substance is greater than the GFR?
Substance must undergo tubular secretion: more volume has been cleared of substance than the volume that underwent filtration: something beyond filtration (secretion) is helping clearance
What is micturition?
What is the detrusor muscle?
Smooth muscle in the bladder that contracts to produce urination; stemmed by internal urethral sphincter and skeletal muscle of external urethral sphincter
What kind of neurons innervate the detrusor muscles?
Parasympathetic: causes contraction
What kind of neurons innervated the internal urethral sphincter muscles?
Sympathetic: causes contraction
What kind of neurons innervate the external urethral sphincter muscles?
Somatic: causes contraction
Why do Na+ and water have high reabsorption?
Because they easily filter due to low molecular weight and are unbound
Where is major hormonally-controlled reabsorption of Na+/water?
Distal convoluted tubules and collecting ducts
Where does the majority of Na+ and water reabsorption occur through bulk flow?
In the proximal tubule
What is a generalization about sodium reabsorption?
Active process; occurs in all tubular segments except descending Henle
What is a generalization about water reabsorption?
By osmosis; dependent on sodium reabsorption
Does transport of Na+ across the luminal membrane vary along tubule segments?
Yes: but transport across basolateral membrane doesn’t: still the active pump
Active Na+ reabsorption occurs on what membrane?
What kind of channel makes membranes permeable to water?
What is the water permeability of the proximal tubule?
What portion of the nephron is highly water permeable?
What portion of the nephron has water permeability that is highly variable based on physiological control?
Cortical and medullary collecting ducts
What hormone controls water reabsorption?
What is vasopressin?
Peptide hormone, posterior pituitary
What second messenger is involved in aquaporin fusion?
What protein kinase is involved in aquaporin fusion?
What happens after vasopressin binds to basolateral membrane receptors?
cAMP triggers PKA to fuse AQP2 with the luminal membrane
How does water passively reabsorb?
ADH triggers cAMP and PKA to fuse more AQP2 to the luminal membrane, and then it passes through AQP3 and AQP4 on the basolateral membrane
What is water diuresis?
Increased urine excretion resulting from low ADH
What is osmotic diuresis?
Increased urine flow as the result of a primary increase in solute excretion
What causes diabetes insipidus?
Failure of posterior pituitary to release ADH or inability of kidneys to respond to ADH: low water permeability
Where does urinary concentration take place?
Medullary collecting ducts
How does medullary interstitial fluid compare to tubule fluid?
Why is medullary interstitial fluid hyperosmotic to the tubular fluid of medullary collecting ducts?
Countercurrent anatomy, NaCl reabsorption in the ascending Henle; water impermeability in ascending Henle; trapping urea in the medulla; hairpin vasa recta loops
How does NaCl reabsorption occur along the upper and lower segments of the ascending Henle?
Lower: thin, simple diffusion; Upper: thick, active transport
How permeable to water is the ascending Henle?
NOT: that's why the interstitial medullary fluid is so hyperosmotic
How permeable to water is the descending Henle?
Very, but not to solute!
As tubular fluid passes through the distal convoluted tubule, how does osmolarity compare to the interstitial fluid?
The distal convoluted tubule: permeability to NaCl and water? Why is this important?
Actively permeable to NaCl, but not to water: makes fluid more hypoosmotic by allowing NaCl out, but keeping water in
How does the vasa recta "hairpin" prevent the multiplier countercurrent effect from washing away?
Any diffusion that occurs in the descending hairpin is reversed by the ascending hairpin
What is the equation for sodium in the renal system?
Na excreted = Na filtered - Na reabsorbed
Are there receptors to detect Na+ changes?
No specific receptors, just the cardiovascular baroreceptors
How can baroreceptors detect changes in Na+?
Since Na+ is a huge component of ECF solutes, changes in total-body sodium can cause changes in ECF volume, which also affects plasma volume
What is the main direct cause of the reduced GFR?
Reduced net glomerular filtration pressure
What is usually the cause of an increased GFR?
Increased neuroendocrine inputs when an increased total body sodium level increases plasma volume
What is the major factor determining the rate of tubular sodium reabsorption?
Which was more effect on long term regulation of sodium excretion, GFR or Na reabsorption control?
Sodium reabsorption control
Where is aldosterone produced?
Adrenal cortex; steroid hormone
Where does aldosterone affect the nephrons?
Distal convoluted tubule and cortical collecting ducts
What happens with high aldosterone to the sodium reabsorption?
Most sodium reaching the distal convoluted tubule and the coritcal collecting ducts Is reabsorbed
Which acts more quickly, vasopressin or aldosterone?
Vasopressin because it's a peptide, whereas aldosterone is a steroid: induces changes in gene expression and protein synthesis
When can aldosterone become high?
When the person ingests a low-sodium diet or becomes sodium depleted
What controls aldosterone secretion?
Angiotensin II: acts on the adrenal cortex to stimulate aldosterone secretion
What is angiotensin II?
Component of renin-angiotensin system
What is renin?
Enzyme secreted by JG cells of JG apparatuses in the kidneys
What is angiotensinogen?
Produced by the liber; precursor to angiotensin I and II
How does angiotensin I turn into angiotensin II?
By ACE: angiotensin converting enzyme
Where is Ace found?
Luminal surface of capillary endothelial cells
What are the most important effects of angiotensin II?
Stimulation of aldosterone secretion, constriction of arterioles
What is the rate-limiting factor in angiotensin II formation?
Plasma concentration of renin
What is the chain of events in salt depletion?
Increases renin secretion > increased plasma renin concentration > increased plasma angiotensin I > increased plasma angiotensin II> increased aldosterone release > increased plasma aldosterone
What are the three distinct inputs to JG cells?
Renal sympathetic nerves, intrarenal baroreceptors, macula densa
How do renal sympathetic nerves affect JG cells?
Directly innervate: increased activity stimulates renin secretion; reflexively activated by baroreceptors if low sodium/volume causes low blood pressure
Why are JG cells intrarenal baroreceptors?
Because they're located in the walls of the afferent arterioles and are sensitive to pressure: if BP decreases, cells stretched less and secret more renin
Where is the macula densa located?
Near ends of the ascending loops of Henle
What does the macula densa do?
Sense sodium concentration in tubular fluid; decreased salt releases paracrine factors to the JG cells: causes renin release
How does the renin-angiotensin system balance arterial blood pressure?
Controlling Na reabsorption and thus blood volume; AND vasoconstriction
What do ACE inhibitors do?
Reduce angiotensin II production: keep blood pressure lower
What do angiotensin II receptor blockers do?
Prevent angiotensin II from binding to receptors on target tissues: vascular smooth muscle and adrenal cortex; treat hypertension
What is ANP?
Atrial natriuretic peptide: secreted by atria; inhibit Na reabsorption; increase GFR for increased Na excretion
When does ANP secretion increase?
Because of expansion of plasma volume that accompanies increased body sodium: increased atrial distension
How does arterial pressure affect sodium reabsorption?
Increased arterial pressure inhibits Na reabsorption: increases Na excretion through pressure natriuresis
What is the formula for water excretion?
Volume filtered through GFR MINUS volume reabsorbed
Secretion of what hormone is the biggest determinant of total body water?
Why do changes in water excretion have little effect on extracellular volume?
Water distributes through all body fluid compartments, with two-thirds intracellular like NA
What sensory receptors initiate reflexes controlling vasopressin secretion?
Osmoreceptors in the hypothalamus, when conditions are due to water gain or loss
How does increased/decreased water ingested affect osmoreceptor firing and vasopressin secretion?
Increased water: decreased osmolarity, decreased firing, decreased vasopressin, increased water excretion; Decreased water: increased osmolarity, increased firing, increased vasopressin, decreased water excretion
How do baroreceptors control water excretion?
Through receptors to vasopressinergic neurons in the hypothalamus; decreased pressure decreases baroreceptor firing: increases vasopressin secretion
How does decreased ECF volume affect renin-angiotensin system and vasopressin secretion?
Decreased ECF causes increased aldosterone secretion from RAS, and increased vasopressin secretion
How do alcohol and nausea affect vasopressin secretion?
Alcohol (inhibits vasopressin, increased water excretion); Nausea (stimulates vasopressin, decreased blood flow to GI)
What brain area recognizes thirst?
Hypothalamus: triggers for thirst are similar to controls for vasopressin : osmoreceptors and baroreceptors in hypothalamus
What is the most abundant intracellular ion?
True or false: K+ is freely filterable in the glomerulus
What part of the nephron can secrete K+?
Cortical collecting duct
How is K+ secreted by the cortical collecting ducts?
Pumped into cell across basolateral membrane by NaK pumps (so associated with Na reabsorption)
What is the most important factor for K+ secretion?
Increased K+ ingestion
How does aldosterone affect K+ secretion?
Aldosterone stimulates K+ secretion from the cortical collecting ducts
How does K+ concentration affect aldosterone secretion?
Directly: increase K+ stimulates adrenal cortex to product aldosterone to bring K+ concentration back down
What controls calcium and phosphate balance?
PTH and 1,25 (OH)2D
Where does most calcium reabsorption occur?
In the proximal tubule; very efficient because we NEED calcium
How does PTH function in the kidneys?
In response to low calcium, opens calcium channels in the proximal tubule to increase reabsorption; also activates production of 1,25 (OH)2D to increase Ca and 1,25 (OH)2D reabsorption in the GI tract
How does PTH affect phosphate ion reabsorption in the kidneys?
Decreases phosphate ion reabsorption in the proximal tubule
What is the major extracellular buffer to control pH?
What is the renal response to alkalosis?
Increased excretion of bicarbonate
What is the renal response to acidosis?
Increased reabsorption/production of bicarbonate
What is the formula for bicarbonate excretion?
Excreted = filtered + secreted - reabsorbed
What does bicarb reabsorption depend on?
How does bicarb reabsorption occur?
Carbonic acid dissociates in the tubular epithelial cells; bicarb diffuses into interstitial fluid and H+ diffuses into lumen to recombine with filtered bicarb; filtered bicarb plus H+ reforms water and CO2 to eb reabsorbed; the original bicarb remains in the interstitial fluid
How does the renal system produce extra HCO3- to respond to acidosis?
Secreted H+ combines with a buffer (HPO4--) into H2PO4-; this allows a net gain of bicarb into interstitial fluid
How does ammonium secretion affect bicarb production for H+ secretion?
Tubular epithelial cells turn glutamine into NH4+ and bicarb; NH4+ actively secreted with a NH4+/Na+ pump; net gain of bicarb
What is respiratory acidosis?
Respiratory system fails to eliminate CO2 as fast as it is produced
What is respiratory alkalosis?
Respiratory system eliminates CO2 faster than it is produced