Exam 4 Flashcards
Kidney Primary Function
filter waste from blood + return valuable resources to blood
Renal System Components
kidneys, nephrons, ureters, urinary bladder, and urethra
Urine Flow
kidney, ureter, bladder, urethra, leaves body
Overview of Kidney Functions
Regulation of Blood Ionic Composition
Regulation of blood pH and osmolarity
Regulation of blood glucose and volume
Regulation of blood pressure
Release of erythropoietin and calcitriol
Excretion of wastes and foreign substances
4 Main Physio Functions for Kidneys
- Filtration
- Reabsorption
- Secretion
- Excretion
True or False: Kidneys perform their actions on blood cells
False, they perform it on blood plasma
True or False: No replacement occurs to injured kidneys or nephrons
True
What is increased kidney size associated with?
increased size of individual nephrons
Renal Corpuscle
Site of plasma filtration
A. Glomerulus: a knot of capillaries where filtration occurs
B. Bowman’s Capsule: a double-walled epithelial cup that collects filtrate
Renal Tubule
Site of reabsorption from filtrate and secretion into filtrate
A. PCT
b. Loop of Henle
c. DCT
one or more DCTs drain into a collecting duct –> Papillary Duct –> Renal Pelvis –> Ureter
Blood Vessels Around the Nephron
Glomerular Capillaries form between the afferent and efferent arterioles
Efferent arterioles give rise to the peritubular capillaries and vasa recta
Glomerular Capillaries
Where filtration of blood occurs
Peritubular Capillaries and Vasa Recta
carry away substances reabsorbed from filtrate
Sympathetic Vasomotor Nerves
regulate blood flow and renal resistance by altering diameter of arterioles
vasoconstriction and vasodilation of afferent and efferent arterioles produces large changes in renal filtration
Microvilli are found on:
PCT Cells + Intercalated Cells of the CD
Which cells are the most common?
Cuboidal Cells
Squamous Cells are found in:
Parietal layer of the glomerular capsule, Loop of Henle Descending Limb, Loop of Henle Thin Ascending Limb
Hormone Receptors are found on:
DCT Cells + Principal Cells of the CD
Rate of Excretion Formula
Rate of Glomerular Function + Rate of Secretion - Rate of Reabsorption
Net Filtration Pressure: total pressure that promotes filtration
GBHP - CHP - BCOP
True/False: Homeostasis does not need a constant GFR
False
If it is too high, useful substances are lost due to the speed of fluid passage through the nephron
If it is too low, sufficient waste products may not be removed from the body
True/False: NFP depends most heavily on BCOP
False, it depends most heavily on GBHP
Macula Densa
thickened part of the ascending limb of loop of Henle
Juxtaglomerular Cells
modified muscle cells that line afferent arteriole
Messangial Cells
Contractile cells associated with the capillaries
Macula Densa + Juxtaglomerular Cells
Juxtaglomerular Apparatus
2 Mechanisms of Autoregulation of GFR
- Myogenic Mechanism
- Tubuloglomerular Feedback
Myogenic Mechanism
Faster
Systemic increases in BP stretch the afferent arteriole
Smooth Muscle Contractions reduce the diameter of the afferent arteriole
–> returns GFR to its previous level in seconds
Tubuloglomerular Feedback
Slower
Elevated systemic BP raises the GFR so that fluid flows too rapidly through the renal tubule
–> Na, Cl, and water are not reabsorbed
Macula Densa in ascending limb detects increased Na and CL
–> inhibits release of a vasodilator from juxtaglomerular apparatus
Afferent arterioles constrict –> reduce GFR
Neural Regulation of GFR
Blood vessels of the kidney are supplied by sympathetic fibers that cause vasoconstriction of afferent arterioles
SNS will override renal auto-regulation
SNS will also stimulate renin release from the juxtaglomerular cells (see hormonal regulation)
NR of GFR @rest
renal blood vessels are maximally dilated (sympathetic activity is minimal)
NR of GFR w/ moderate sympathetic stimulation
both afferent and efferent arterioles constrict equally
GFR decreases slightly
NR of GFR w/ extreme sympathetic stimulation
(exercise/hemorrage) vasoconstriction of afferent arterioles predominates
GFR decreases substantially
lowers urine output to maintain blood volume
permits greater blood flow to other tissues
2 Hormones that Contribute to regulation of GFR
Atrial Natriuretic Peptide (ANP)
Angioetensin II
ANP
increases GFR
High blood volume causes atrial stretching which causes hormonal release from the heart
ANP relaxes glomerular mesangial cells, increase glomerular capillary surface area and increasing GFR
Angiotensin
reduces GFR
activated by ACE in the lungs following the release of renin from juxtaglomerular cells
potent vasoconstrictor that narrows both afferent and efferent arterioles reducing GFR
Tubular Reabsorption
transfers materials from tubular fluid back into the blood
Nephrons must reabsorb 99 percent of the filtrate
Most reabsorption occurs in the PCT
Rest of the nephron does fine tuning of the filtrate
How does reabsorption occur?
solutes reabsorbed by active and passive processes
water follows solutes by osmosis (if it can)
small proteins move across into blood by pinocytosis
Tubular Secretion
transfers materials from blood into tubular fluid
- helps control blood pH via secretion of H+ ions
- eliminates certain substances
Paracellular Reabsorption
50% of reabsorbed material moves between cells by diffusion in some parts of the tubule
Transcellular Reabsorption
materials moves through both apical and basal membranes of tubule cell by active transport
Reabsorption in PCT
Na+ symporters help reabsorb materials from tubular filtrate
-Glucose, amino acids, lactic acid, water-soluble vitamins
Rely on low intracellular sodium ions
intracellular sodium levels kept low by Na/K pumps on basolateral side
By end of PCT, filtrate is still isotonic to blood
Secretion in the PCT
Na+ antiporters help secrete acid (H+)
-Rely on low intracellular Na+
- Intracellular sodium levels kept low by Na+/K+ pumps on basolateral side
Renal Thresholds
Renal Symporters have limits on rate of transport (threshold is based on blood cxn of substance when it starts to be removed to urine)
-If exceeds renal threshold, transport is limited
-Exists for all substances reabsorbed by nephron cells (nutrients, electrolytes, vitamins)
Reabsorption in the Loop of Henle
STUDY!!!!
Reabsorption of Na+ and Cl- in Early DCT
STUDY!!!
Reabsorption of Na+ and secretion of K+ in Late DCT and Collecting Duct
STUDY!!!!
Reabsorption of H2O in Late DCT and CD
STUDY!!!
Formation of Dilute Urine
Blood Plasma = 300 mOsm/L
Filtrate osmolarity increases as it moves down descending loop of Henle
Filtrate osmolarity decreases as it moves up ascending loop of Henle
Filtrate osmolarity decreases in collecting duct –> dilute urine
Water Deprivation
Increased blood osmolarity
Stimulate ADH release
ADH causes more aquaporin channels in apical membranes of principal cells
2 Things that Countercurrent Mechanisms Involve
a. countercurrent flow of fluid through a tube
b. an osmotic gradient in fluid surrounding the tube
Countercurrent Multiplication
process which produces a progressively increasing osmotic gradient in ISF of renal medulla
Countercurrent Exchange
process which enables oxygen delivery to cells of renal medulla without loss of the osmotic gradient in ISF of renal medulla
2 main factors that contribute to building and maintaining the required osmotic gradient
Permeability Differences (in different sections of loop of Henle and collecting duct)
Countercurrent Flow ( tubular fluid through the descending and ascending limbs of the loop of Henle)
Permeability Differences
Descending Limb of Loop of Henle: very permeable to water
Thin and Thick ascending limb of loop of Henle: impermeable to water, but permeable to solutes
Late DCT and CD: only permeable to water in the presence of ADH
Countercurrent Flow
descending and ascending limbs of the loop of Henle carry tubular fluid in opposite directions
ADH Effects on Osmotic Gradient
- stimulates symporter activity in thick ascending limb of loop of henle (builds osmotic gradient)
- ADH stimulates facultative reabsorption of water in upper collecting duct
- ADH stimulates water reabsorption and urea recycling in lower collecting ducts (builds osmotic gradient)
Go through steps of Countercurrent Multiplication
4 Steps
Go through concurrent exchange!1
g
Countercurrent Multiplication vs. Exchange
-Vasa recta provides oxygen and nutrients to renal medulla without washing out the osmotic gradient
-Loop of Henle establishes osmotic gradient in renal medulla (via concurrent multiplication)
- Vasa recta maintains the gradient to the best extent possible as it delivers nutrient to nephron cells (via concurrent exchange)
What do ADH actions lead to?
the formation of concentrated urine
Principal Cells
reabsorb Na+. secrete K+ and reabsorb H2O
Intercalcated Cells
Reabsorb K+ and HCO3 and secrete H+
Effects of Aldosterone on Principal Cells
increases Na+ and water reabsorption and K+ secretion by stimulating the synthesis of new pumps and channels in principal cells
Effect of ADH on principal cells
Increases water permeability of principal cells in collecting duct, by triggering insertion of aquaporin channels into apical membrane
Water molecules will move more rapidly from tubular fluid into ISF –> blood
Actions of Intercalated Cells
help regulate pH of body fluids by secretion of H+ (via proton pumps) and absorption of HCO3 (via Cl-/HCO3 antiporters)
Urine Storage
Sympathetic
Detrusor Muscle: relaxation
Trigone Muscle: contraction
Micturition
Parasympathetic
Detrusor Muscle: Contraction
Trigone Muscle: relaxation
Highlight the Micturition Reflex
!!
How many ureteral and urethral openings in the trigone?
2 ureteral
1 urethral
Diuretics
Substances that slow renal reabsorption of water and cause diuresis (increased urine flow rate)
Caffeine
Inhibits Na+ reabsorption
Alcohol
Inhibits secretion of ADH
Intercalated Cell Actions when Blood pH is high and low
!!!
