Lecture: Renal Flashcards
What ions does the kidney regulate?
Na, K. Ca, Cl, and phosphate
What four things do the kidneys regulate in relation to blood?
- Blood pH and osmolarity
- Blood glucose via gluconeogenesis
- Regulation of blood volume by conserving or eliminating water
- Regulation of blood pressure
How do the kidneys regulate blood pressure?
By secreting the enzyme renin or adjusting renal resistance
Which two hormones are released by the kidney
Erythropoietin and calcitriol
How much blood plasma is filtered by the kidneys every minute?
125 mL
How much blood plasma is filtered by the kidneys each day?
180 L
What are the four major physiological functions of the kidneys?
- Filtration
- Reabsorption
- Secretion
- Excretion
What do kidneys perform their actions on?
Blood plasma not blood cells
What percent of a kidney must be damaged in order for it to be evident
More than 75%
Components of the renal corpuscle
Glomerulus: a knot of capillaries where filtration occurs
Glomerular capsule: epithelial cup that collects filtrate
Site of plasma filtration
Renal corpuscle
Site of reabsorption from filtrate and secretion into filtrate
Renal tubules
In which capillaries does blood filtration occur?
glomerular capillaries
Which capillaries carry away substances reabsorbed from filtrate?
Peritubular capillaries and the vasa recta
What is the role of sympathetic vasomotor nerves in the blood supply of the kidney?
Sympathetic vasomotor nerves regulate blood flow and renal resistance by altering the diameter of aterioles
Which cells are hormone receptors found on in the nephron loop?
- DCT cells
- Principle cells of the collecting duct
Which cells are microvilli found on in the nephron loop?
- PCT cells
- Intercalated cells of the collecting duct
What produces the filtration pressure in the glomerulus?
Blood pressure
Fenestrated endothelium filter…
blood cells
Basement membrane (basal lamina) filter…
Large proteins
Podocytes filter…
medium-sized proteins
Total pressure that promotes filtration
Net filtration pressure
Equation for net filtration pressure
Glomerular blood hydrostatic pressure - capsular hydrostatic pressure - blood colloid osmotic pressure
Amount of filtrate formed in all renal corpuscles of both kidneys per minute
Glomerular filration rate
Average glomerular filtration rate in adults
125 mL/min
What happens if the glomerular filtration rate is too high?
The useful substances are lost due to the speed of the fluid passage through the nephron
What happens if the glomerular filtration rate is too low?
Sufficient waste products may not be removed from the body
A glomerular blood hydrostatic pressure lower than ___ stops filtration
45 mmHg
Thickened part of ascending limb of loop of henle
Macula densa
Modified muscle cells that line the afferent arteriole
Juxtagomerular cells
What composes the juxtaglomerular apparatus
Macula densa + juxtaglomerular cells
Contractile cells associated with capillaries
Mesangial cells
Mechanisms that maintain a constant GFR despite changes in arterial blood pressure
- Myogenic mechanism
- Tubuloglomerular feedback
Which form of autoregulation of the GFR causes smooth muscle contraction reduces diameter of afferent arteriole to return the GFR back to its previous level
Myogenic mechanism
Which form of autoregulation of the GFR causes an increase in the blood pressure stretch of the afferent ateriole
Myogenic mechanism
Which form of autoregulation of the GFR raises the GFR by elevating systemic BP in order to rapidly push fluid through the renal tubule
Tubuloglomerular feedback
Which form of autoregulation of the GFR causes afferent aterioles to constrict therefore reducing the GFR
Tubulogolmerular feedback
In tubuloglomerular feedback, what happens when macula densa in the ascending limb detect an increase in Na and Cl?
It inhibits the release of NO (a vasodilator) from the juxtaglomerular appartus
In which mechanism are blood vessels of the kidney supplied by sympathetic fibers that cause vasoconstriction of afferent arterioles
Neural regulation of the glomerular filtration rate
How does vasoconstriction of afferent arterioles occur in neural regulation of the GFR?
Norepinephrine releases from sympathetic postganglionic neurons and binds to the alpha 1 adrenergic receptors
What are the two main functions of the SNS in the neural regulation mechanism of the glomerular filtration rate?
- Override renal autoregulation
- Stimulate renin release from juxtaglomerular cells
At rest, when sympathetic activity is minimal in the kidney, what is the state of the renal blood vessels?
They are maximally dilated
When there is moderate sympathetic stimulation of the kidney, what is the state of renal blood vessels?
The afferent and efferent arterioles are constricted equally
Does the GFR increase or decrease in the presence of moderate sympathetic stimulation?
The GFR decreases slightly
When there is extreme sympathetic stimulation of the kidney, in cases such as exercise or hemorrhage, what is the state of the renal blood vessels?
Afferent arterioles are predominately vasoconstricted
Does the GFR increase or decrease in the presence of extreme sympathetic stimulation?
The GFR decreases substantially
In the presence of extreme sympathetic stimulation, how are urine output and blood flow affected?
Urine output is lowered in order to maintain the blood volume, allowing a greater blood flow to other tissues in the body
Which two hormones contribute to the regulation of the glomerular filtration rate?
- Atrial Natriuretic Peptide
- Angiotensin II
Which hormone increases the glomerular filtration rate?
Atrial natriuretic peptide
What causes a release of atrial natriuretic peptide from the heart?
A high blood volume causes atrial stretching signaling a release of ANP
What is the function of atrial natriuretic peptide?
ANP relaxes glomerular mesangial cells, increasing glomerular capillary surface area and increasing the GFR
Which hormone reduces the glomerular filtration rate?
Angiotension II
What causes the release of angiotensin II?
Angiotensin II is activated by ACE in the lungs which is followed by the release of renin from the juxtaglomerular cells
What is the function of angiotensin II?
Angiotensin II acts as a vasoconstrictor to narrow afferent and efferent arterioles and reduce the GFR
Where does most reabsorption occur?
The proximal convoluted tubule (PCT)
How do small proteins move from the tubular fluid back into blood?
Pinocytosis
What are the two main purposes of tubular secretion?
- Control blood pH by secreting H
- Eliminating waste substances
Difference between tubular reabsorption and tubular secretion
Reabsorption - transfers materials from tubular fluid back into blood
Secretion - transfers materials from blood into tubular fluid
What type of reabsorption is it when the reabsorbed material is moved between cells by diffusion in parts of the tubule?
Paracellular reabsorption
What type of reabsorption is it when the reabsorbed material moves through both the apical and basal membranes of the tubule by active transport?
Transcellular reabsorption
Which membrane does Na/K ATPase pump sodium from the tubule cell cytosol through?
Basolateral membrane
How is water reabsorbed?
Through osmosis
Obligatory water reabsorption is when water is…
obliged to follow solutes being reabsorbed
Facultative water reabsorption is under the control of…
antidiuretic hormone (ADH)
Na symporters
Glucose
Amino acids
Lactic acid
Water-soluble vitamins
The reabsorption of nutrient is…
Isosmotic - meaning that the water follows the solutes
What must the concentration of Na be for reabsorption in the proximal convoluted tubule?
Low intracellular concentration
What do Na antiporters do in relation to secretion in the proximal convoluted tubule?
Secrete acid (H+)
What does drug secretion rely on in the proximal convoluted tubule?
- Organic anion and cation transporters in the basolateral membrane
- MATE (multi-drug and toxin extruder) proteins
- H+ gradient
Which substances have a renal threshold?
All substances that are reabsorbed by nephron cells
Glucose in urine
Glycosuria or glucosuria
What is the glucose renal threshold?
200 mg/dL
Where does osmosis occur in the loop of Henle?
Descending limb
Where does reabsorption of NaCl occur in the loop of Henle?
Thing ascending limg
What is the descending limb permeable to?
The descending limb is permeable to water, but not to NaCl
What is the ascending limb permeable to?
The ascending limb is permeable to NaCl but not to water
The thick ascending limb of the loop of Henle has Na/K/2Cl symporters that reabsorb these ions…
- K moves back into filtrate through K leak channels
- Na is pumped out of the basolateral side
- Cl diffuses across the cell
How do cations move across the vasa recta?
They are drawn to the negative charge in the capillary
What is the early distal convoluted tubule permeable to?
It reabsorbs ions, but is more permeable to water
All water reabsorption until the late distal convoluted tubules is…
obligatory
The two types of cells in the late distal convoluted tubule and collecting duct are…
- Principal cells
- Intercalated cells
What do principal cells reabsorb?
- Na
- If ADH is present, H2O
What do principal cells secrete?
K+
What do intercalated cells reabsorb?
- K+
- HCO3-
What do intercalated cells secrete?
H+
What is the goal of water reabsorption of H2O in the late DCT and CD?
Remove excess fluid from blood by producing dilute urine
Process which produces a progressively-increasing osmotic gradient in interstitial fluid of renal medulla
Countercurrent multiplication
Process which enables oxygen delivery to cells of renal medulla without loss of the osmotic gradient in interstitial fluid of renal medulla
Countercurrent exchange
Two main factors that contribute to building and maintaining the required osmotic gradient
- Permeability differences
- Countercurrent flow
Where are permeability differences present?
Sections of the loop of Henle and the collecting duct
Where is countercurrent flow present?
Within tubular fluid in the descending and ascending loop of Henle
Symporters in the thick ascending limb cells of the loop of Henle cause a buildup of…
Na and Cl in the interstitial fluid of the renal medulla
The descending limb is very permeable to water, but impermeable to solutes except…
urea
What establishes an osmotic gradient in the renal medulla?
Countercurrent flow through the descending and ascending limbs
Osmolarity difference between the outer interstitial fluid of the descending limb and the inner tubular fluid
Osmolarity of the interstitial fluid outside of the descending limb is higher than the osmolarity of the tubular fluid
Why does water move out of the descending limb into the interstitial fluid via osmosis?
Osmolarity differences
