Tubular Reabsorption & Secretion(C)- Exam 3 Flashcards
What affects tubular reabsorption (keeping it relatively constant)?
Glomerulotubular balance Peritubular Capillary and interstitial forces Arterial blood pressure Hormonal control Sympathetic nervous effect
Can reabsorption of solutes be controlled independently?
Reabsorption of some of them can
What does glomerulotubular balance allow?
Increase in reabsorption rate when there is an increase in tubular load (increased tubular inflow); maintains sodium and volume homeostasis; prevents large changes in fluid flow to distal tubules ven though there have been significant changes in MAP
If GFR went from 125 mls/min to 150 mls/min rate of reabsorption in proximal tubule would do what?
80 mls/min (65% of GFR) to 97.5 mls/min (65% of GFR)
What is the normal net force for reabsorption in peritubular capillary?
10 mmHg
What are the 4 peritubular capillary forces?
IN: Pif=6 mmhg; cap oncotic P=32 mmHg
OUT: Pc=13 mmHg; intersti. cap oncotic= 15 mmHg
Filtration coefficient is…
Reabsorption rate/net force; large
124mls/min / 10 mmHg = 12.4 mls/min/mmHg
What affects filtration coefficient?
Transfer surface area and hydraulic conductivity (permeability)
What factors affect peritubular capillary reabsorption?
Peritubular hydrostatic pressure (PHP)
Peritubular oncotic pressure (POP)
Renal interstitial hydrostatic pressure
Renal intersitial oncotic pressures
What happens to reabsorption is peritubular hydrostatic pressure goes up?
Decrease in reabsorption
What happens to reabsorption if peritubular oncotic pressure goes up?
Increase in reabsorption
What affects peritubular hydrostatic pressure?
Arterial pressure
Resistance of afferent and efferent arterioles
Increase in arterial P = __________ in PHP = _________ reabsorption
increase, decrease
Increase in resistance of afferent arterioles = __________ PHP = _______ reabsorption
decrease, increase
What affects peritubular oncotic pressure?
Plasma protein concentration Filtration fraction (GFR/RPF)
Increase plasma protein concentration = ________ plasma oncotic pressure = ________ POP= ______ reabsorption
increased, increased, increased
Increased GFR or Decreased BF causes an _________ filtration fraction
Increased
Increased filtration fraction = _______protein concentration (_____fluid is actually filtered)
increased, more
Increased protein concentration = ___________POP = _______ reabsorption
increased, increased
Decreased capillary reabsorption= ___________ in interstitial solute and interstitial water= _______interstitial hydrostatic pressure and ______ in interstitial oncotic P= ______ net movement of solute/water from tubule to interstitial spaces
Increased, increased, decreased, decreased
Under normal reabsorptive conditions, describe the back flow of water and solute from interstitial spaces to tubular lumen?
Always a back flow; tight junctions not very tight espcially in proximal tubule
Decreased peritubular reabosprtion = ______ solute and water accumulation in interstitial space= _______ backflow of solute and water from interstitial space to tubular lumen
increased, increased
Forces that increase peritubular capillary reabsorption also do what?
Increase movement of solute and water (reabsorption) from the tubular lumen to the renal interstitial spaces
Increased filtration coefficient = _______ Reabsorption
Increased
How does capillary surface area relate to filtration coefficient and reabsorption?
Increased surface area
Increased filtration coefficient
Increased reabsoprtion
How does capillary permeability relate to filtration coefficient and reabsorption?
Increased permeability
Increased filtration coefficient
Increased reabsorption
How much does the filtration coefficient change under most conditions? What can affect it?
Coefficient remains constant under most physiologic conditions. Will be affected by renal disease.
Autoregulation works to keep what constant as pressure changes?
GFR and RBF
Under what pressure range does autoregulation work?
75 mmHg to 160 mmHg
Even though autoregulation is involved, there is a small increase in _______, which results in an increase in _________.
GFR; urine output
Arterial pressure increase = Small ______ in the amount of sodium and water reabsorbed.
decrease
Small increase in peritubular capillary hydrostatic pressure= _______ renal interstitial hydrostatic pressure = _______backflow of solute and water
Increased; increased
Arterial Pressure increases= Angiotensin II ________.
decreased
Decreased Angiotensin II = less stimulation of what?
Sodium reabsorption
Aldosterone production; less stimulation of sodium reasborption
Kidneys must be able to respond to changes in _______ of specific substances without changing ______ of the substances.
Intake; output
What provides the control specificity needed to maintain normal body fluid volumes and solute concentrations?
Hormone secretion
Aldosterone: Site of Action; Effects
Site of Action: Collecting duct/tubule
Effects: increased NaCl, H20 reabsorption
Increased K+ secretion
Angiotensin II: Site of Action; Effects
Site of Action: Proximal tubule; thick ascending loop of henle/distal tubule; collecting duct
Effects: Increased NaCl, H20 reabsorption
Increased K+ secretion
ADH: Site of Action; Effects
site of action: distal tubule; collecting tubule and duct
effects: increased H20 reabsorption
Atrial natriuretic peptide: Site of Action; effects
Site of action: distal tubule; collecting tubule and duct
Effects: decreased NaCl reasborption
Parathyroid hormone: Site of action; effects
Site of action: proximal tubule; thick ascending loop of henle; distal tubule
Effects: decreased PO4– reabsorption
Increased Ca++ reasborption
What secretes aldosterone?
Zona glomerulosa in adrenal cortex
What is the function of aldosterone?
Regulates sodium reabsorption and potassium secretion; very important regularly of [K+]
What is the principal site of action of aldosterone?
Principal cells of cortical collecting tubule; stimulates increased Na-K ATPase activity (basolateral locations)
Increases permeability of luminal side membrane to sodium
What stimulates increased release of aldosterone?
Increased extracellular potassium concentration
Increased angiotensin II levels (sodium/volume depletion or low arterial pressure)
What disease is the absence of aldosterone?
Addison’s disease; adrenal malfunction or destruction
What disease is an excess of aldosterone?
Adrenal tumors; Conn’s syndrome
What is the most powerful sodium-retaining hormone?
Angiotensin II
What causes increased production of angiotensin II?
Low blood pressure and/or low ECF volume
Angiotensin II stimulates the secretion of what?
Aldosterone; resulting in increased sodium reabsorption
What is angiotensin II’s effect on the efferent arterioles?
Constricts efferent arterioles; increased sodium and water reabsorption
What is the purpose of angiotensin II constricting effect arterioles?
Helps ensure that normal exertion rates of metabolic wastes are maintained by helping to maintain normal rates of GFR; able to retain sodium and water without retaining metabolic waste
Angiotensin II directly stimulates sodium reabsorption where?
Proximal tubules, loop of henle, distal tubules, and collecting tubules.
Angiotensin II stimulates which pumps?
- Increased Na/K ATPase activity of tubular epithelial cells (basolateral membrane)
- Na/H exchange in proximal tubule (luminal membrane)
- Na/Bicarb co transport (basolateral membrane)
Angiotensin II affects transport on which membranes?
Luminal and basolateral membranes
Where is angiotensin II “very active”
proximal tubule
What is vasopressin?
ADH
Where is ADH made?
Hypothalamus
Two types of _______ produce ADH.
Magnocellular (large) neurons
Where are the neurons located that make ADH?
Supraoptic (87%) and paraventricular (17%) nuclei (hypothalamus)
What happens to ADH once it is produced?
Moves down the neurones to their tips which are located in the posterior pituitary
Where is ADH released?
Neurons in the posterior pituitary
How is ADH released?
Stimluation of the supraoptic and paraventricular nuclei (increased osmolarity) sends impulses down the magnocellular neurons which stimluates release of ADH from storage vesicles located in the nerve endings
Decreased ADH = ______ water permeability= _______ urine volume and _____solute
decreased, increased, decreased; results in large volumes of dilute urine
ADH stimulates the formation of water channels where?
Across the luminal membrane
What does ADH bind with? What does this do?
Specific V2 receptors; increases formation of cyclic AMP and activation of protein kinases
What does protein kinase activation result in?
Movement of aquaporin-2 to luminal side of cell
Aquaporin-2
intracellular protein
What do aquporin-2’s do?
Come together and fuse with cell membrane to from water channels which increases membrane permeability to water (increases water reabsorption)
What increases the formation of aquaporin-2 molecules?
Chronic increases in ADH
AVP
arginine vasopressin
Where are V2 receptors?
Basolateral membranes
Increased ADH in the plasma results in movement of ADH from where to where?
From peritubular capillaries to renal interstitial space
WHat provides water channels on the basolateral membrane?
aquaporins; no evidence to show that they are affected by [ADH]
What does decreased ADH result in as far as the aquaporin-2?
Movement of the aquaporin-2 molecules back into the cytoplasm which reduces the number of water channels and decreased water permeability
Where is atrial natriuretic peptide secreted?
Cardiac atrial cells when atria distended by plasma volume expansion
What is the action of atrial natriuretic peptide?
Direct inhibition of sodium and water reabsorption (especially collecting ducts)
Inhibits renin secretion (thus inhibits angiotensin II formation)
What is an important response to help prevent sodium and water retention during heart failure?
Atrial natriuretic pepide
What is the most important hormone for regulating calcium?
Parathyroid hormone
What is the action of parathyroid hormone?
Increases calcium reabsorption (distal tubules)
INhibits phosphate reabsorption (proximal tubule)
Increases magnesium reabsorption (loop of henle)
Severe SNS stimulation = _________(constriction/dilation) of renal arterioles= ______ GFR
Constriction of renal arterioles, decreases GFR
Low levels SNS stimulation activate what?
Alpha receptors on renal tubular epithelial cells (proximal tubule, thick ascending limb of loop of henle, maybe distal tubule); receptor activation stimulates sodium reabsorption which decreases water and sodium excretion
SNS stimulates the release of what ?
Renin (angiotensin II) which adds to increase in tubular reabsorption of sodium
Renal clearance
volume of plasma that is completely cleared by kidneys per unit time
Why is renal clearance not realistic?
No volume of blood completely cleared
Renal clearance provides what?
Way to quantify excretory function of kidneys Quantify RBF Quantify glomerular filtration Qunatify tubular reabsoprtion Quantify tubular secretion
What is the equation for renal clearance?
Cs = Us x V / Ps Clearance= urinary excretion rate/ [plasma]
Cs= clearance of solute (mls/min) Us= urine concentration of solute (mg/ml) V= urine flow (mls/min) Ps= plasma concentration of solute (mg/ml)
Clearance of what should be equal to GFR?
Inulin
When is the excretion rate the filtration rate?
Solute is freely filtered and neither reabsorbed nor secreted
How much of creatinine is reabsorbed?
Small amount
How do you make a rough estimate of changes in GFR?
Look at changes in creatinine concentration; a four fold increase in creatinine concentration means the GFR is one-fourth normal
When is clearance rate equal to renal plasma flow?
If a substance is completely cleared
What provides a reasonable estimation of renal plasma flow? What percent?
PAH clearance (90% cleared)
HOw can actual renal plasma flow be calculated?
Dividing the PAH clearance rate by PAH extraction rate
PAH clearance/ 0.9
How can total blood flow be calculated?
Taking the calculated plasma flow and dividing by (1-HCT)
Filtration Fraction equation
GFR/RPF
How to calculate absorption?
Filtered load- excretion rate
How to calculate secretion?
excretion rate- filtered load
If equal to inulin clearance….
Substance is only filtered, not reabsorbed, not secreted
If less than inulin clearance….
Substance must be reabsorbed
If greater than inulin clearance….
Substance must be secreted
