Renal Physiology Lecture Powerpoint Flashcards
9/9/19
Kidney homeostatic functions (6)
- filters blood plasma eliminating waste, free radicals and drugs
- regulates blood volume and pressure
- regulates osmolarity of body fluids
- secretes renin
- secretes erythropoietin
- Activates vitamin D
Kidney shares this homeostatic function with the liver and this function with the lungs
Liver: Detoxification (obvi) but also gluconeogenesis (a small amount)
Lungs: regulates acid base balance
Renin definition
Major component of the RAAS which allows the kidneys to control the body’s BP by regulating fluid volume
Erythropoietin definition
Hormone released in response to low plasma o2, acts on hemocytoblasts to convert them into erythrocytes to increase the number in circulation
Vitamin D3 activation by the kidney
Kidney functions to convert vit D3 to active form vit D2
Where is the kidney in relationship to the peritoneum?
Retroperitoneal - behind the peritoneum
Urine flow pathway from collecting duct to exit
- Collecting duct
- Renal papilla
- Minor calyx
- Major calyx
- Renal pelvis
- ureter
- bladder
- urethra (prostatic, membranous, spongy in men, just urethra in women)
Renal pyramids and renal columns definition
Renal pyramids are the triangles pointed toward the center of the kidney that are composed of the renal medulla
Renal columns are the projections that fill the space between the renal pyramids
2 types of nephrons and their definition
1) cortical - short nephron loops that have a shorter loop of henle that dips into the outer medulla
2) Juxtamedullary - long nephron loops with longer glomeruli that dip into the deeper medulla and are extremely important in maintaining a salt gradient as well as conserving water
How many nephrons are there in a kidney?
Approx 1 million
Components of a renal corpuscle (2)
- Glomerulus
- Bowman’s capsule
The afferent arteriole entering the glomerulus typically has ___ hydrostatic pressure relative to the efferent and is thus vaso____
higher, vasodilated
Portions of the nephron from glomerulus to collecting duct
- Glomerulus
- proximal convoluted tubule
- Descending loop of henle
- ascending loop of henle
- distal convoluted tubule
- collecting duct
Glomerulus definition and function
A tuft of blood vessels from the afferent arteriole that allow for fluid filtration of the blood into the proximal convoluted tubule before the capillaries converge and exit as the efferent arteriole
Bowman’s capsule definition and function
Visceral and parietal epithelial cell layers surrounding and below a basement membrane of the glomerulus containing podocytes where fluid can pass onward into the proximal convoluted tubule from the glomerulus
Podocytes definition and function
Cytoplasmic extensions that wrap around capillaries of the glomerulus from bowman’s capsule, have openings called filtration slits that limit the substances that can be filtered through relaxation and contraction
Type of capillaries located in the glomerulus
Fenestrated
Filtration membrane of the glomerulus definition, and the 3 layers that make it up
Filtration membrane is the thickness between the endothelium of the capillary to the space of bowman’s capsule, the 3 layers are the 1)fenestrated endothelium, 2)basement membrane, and 3)filtration slits of the podocytes
Blood pathway through the kidney from renal artery to renal vein
- renal artery
- interlobar arteries traveling up columns of the kidney
- arcuate arteries that travel across pyramids of the kidney
- interlobular arteries that travel into the cortex
- afferent arterioles
- glomerulus
- efferent arterioles
- peritubular capillaries surround tubular portion of nephron capturing and reabsorbing substances
- interlobular vein
- arcuate veins
- interlobar veins
- renal vein
Juxtaglomerular apparatus definition and function
A specialized structure composed of macula densa, juxtaglomerular cells, and mesangial cells that functions to rregulate filtrate formation and systemic BP
Macula densa defnition and function
epithelial cells in the distal convoluted tubule adjacent to juxtaglomerular cells part of the juxtaglomerular aparatus. Senses changes in solute content of filtrate (decreased Na+) in lumen and secretes paracrine messenger to sitmulate JG cells
Juxtaglomerular cells definition and function
Modified smooth muscle cells that form a cuff around the afferent arteriole as it moves to the glomerulus part of the juxtaglomerular apparatus. Contains renin granules and are stimulated to release by acting as mechanoreceptors that directly sense BP in afferent arterioles
Mesangial cells definition and function
Cells between the afferent and efferent arterioles and among capillaries of the glomerulus part of the juxtaglomerular apparatus. Thought to mediate communication between juxtaglomerular cells and macula densa (i.e. macula densa at distal tubule sends paracrine signals thru messangial cells to reach JG cells to release renin)
Renal plexus definition and function
sympathetic division ANS nerves that follow the renal artery and function to regulate the rate of bloodflow thru the kidneys by regulating diameter of arterioles, can very quickly adjust blood flow
3 general processes in the formation of urine
1) glomerular filtration
2) tubular reabsorption into peritubular capillaries from nephron
3) tubular secretion from renal capillaries to nephron
Some drugs such as ___ and ____ are secreted via tubular secretion
NSAIDS, cephalosporins
Glomerular filtrate is similar to ___ in content
Plasma
How much renal filtrate is reabsorbed into the blood stream?
As much as 99%
Net filtration pressure is formed from these three components
- Blood hydrostatic pressure going into the proximal convoluted tubule (largest, variable)
- Colloid osmotic pressure pulling fluid into the efferent arteriole
- Capsular pressure pulling fluid into the efferent arteriole
Glomerular filtration rate definition (GFR)
Amount of filtrate formed by kidneys in 1 minute
Typical GFR for adults
100-125mL/min
In a 24 hr period blood passes thru the kidneys at least ___ times
36
How much of the GFR measured in ml/min is voided? What happens to the remaining 100-125mL/min
1ml/min voided, remaining is reabsorbed
Increased arterial BP in the kidneys ___ GFR
Increases
How much urine is excreted per day
1 to 2 liters
Autoregulation of arterial pressure by kidneys definition
Refers to intrinsic ability of kidney to continually adjust to keep GFR constant over a wide range of arterial pressure (90-190mmHg)
Blood flow (Q) formula
Q= deltaP/R
deltaP=pressure gradient
R=resistance
When there is increased BP, the kidney will ___ afferent arteriole and ___ efferent arteriole
Constrict, dilate
When there is decreased BP, the kidney will ___ afferent arteriole and ___ efferent arteriole
Dilate, constrict
Constriction of a vessel causes ___ pressure upstream and ___ pressure downstream
Increased, decreased
3 mechanisms of renal autoregulation of GFR
1) myogenic mechanism
2) tubuloglomerular feedback
3) RAAS
Myogenic mechanism of renal autoregulation of GFR definition
Increased systemic BP causes afferent arteriole constriction due to vascular smooth muscle response to stretch, lowering glomerular BP and preventing it from rising too high and reducing GFR
Tubular feedback mechanism of renal autoregulation of GFR definition
JG cells sythesize, store, and release renin stimulated by hypovolemia or decreased renal perfusion
The macula densa detects flow or changes in filtrate at the distal convoluted tubule (decreased Na+) due to decreased GFR and stimulate paracrine messengers causing JG cells to relax dilating and increasing GFR to normal
How does angiotensin II cause increase in GFR
It acts as a potent vasoconstrictor of efferent arterioles at low concentrations
Autoregulation of renal system is unable to handle extremely ___ BP about ___mmHg, causing GFR to ___
low, <45, stop
Nervous overriding of renal autoregulatory mechanisms
During extreme stress when blood must be shunted to heart, brain, and skeletal muscle at expense of kidneys and to conserve water (to maintain BP), the SANS releases epi and NE that strongly constrict afferent arterioles decreasing GFR greatly
The SANS can stimulate ___cells under extreme stress which activates the ___ system and causes increased vasoconstriction of both ___ and ____ arterioles. When this happens, there is…
JG, RAAS, afferent, efferent
…no blood coming in or going out of the kidney
3 hormones that cause vasoconstriction, decreasing renal blood flow and GFR
1) epi
2) norepi
3) angiotensin II
Complete cessation or extremely low flow to kidneys can cause….
…renal failure
Prostaglandins (PGE-2 and PGI-2) impact on GFR
Cause vasodilation increasing renal blood flow and GFR
Explain how NSAIDS and ASA in high enough dosages can cause renal failure
-Prostaglandins that act as vasodilators are released by endothelium in arterioles, if formation and release inhibited blood flow may become too low due to excessive constriciton of the vasculature
Renin angiotensin aldosterone system mechanism of action
- JG cells release renin in response to reduced stretch caused by drop in BP or by macula densa stimulation due to decreased Na+ in filtrate or via sympathetic stimulation
- Liver constantly secretes angiotensinogen into blood stream
- Renin splits angiotensinogen to angiotensin I
- Angiotensin I is converted to Angiotensin II by ACE found primarily in lungs (activated when agiotensin I moves thru pulmonary circulation)
- Angiotensin II causes predominant constriction of efferent arteriole but in high conc can impact afferent as well
- Angiotensin II sitmulates release of aldosterone by adrenal cortex causing Na+ retention at the collecting duct, H2O follows
- BP returns to normal
Angiotensin II action on hypothalamus
Increase thirst
Atrial natriuretic peptide mech of action (ANP) (Note that it has action on vessels, sodium conc, and other hormonal systems)
- Polypeptide produced by atrial heart muscle
- stimulated for release due to atrial distension (hypervolemia)
- Increases vasoconstriction of efferent arteriole
- Dilation of afferent arteriole
- Increases Na+ loss
- Inhibits aldosterone and renin
Reabsorption in the proximal nephron mechanism of action
- In the tubular cells, the luminal side faces toward the nephron has several Na+ energy dependent cotransporters (glucose, AA, etc) to bring in and reabsorb nutrients (as well as water that follows
- This Na+ transport moves down its conc. gradient because of low Na+ conc. in the cell because on the basal side facing toward the interstitial space and thecapillary has many Na+/K+ pumps that actively pump out Na+
Aldosterone mech of action
-Increases reabsorption of Na+ ions and excretes K+ ions by increasing Na+ K+ ATPase activity in distal and collecting tubule cells
Solvent drag definition
Tendency for water absorbed by osmosis to carry other solutes with it
The proximal convoluted tubule reabsorbs the ____ of chemicals
Greatest variety
Transport maximum definition
The upper limit to the rate of how much substance a cell can transport across its membrane per unit time due to saturation of the transport proteins, dependent on how many transport proteins are available, varies for each substance
ADH/vasopressin mech of action (include where it is produced and stored)
- Produced in hypothalaus
- stored in posterior pituitary
- drop in pressure directed by baroreceptors in aorta and carotids or dehydration stimulate hypothalamus
- hypothalamus stimulates posterior pituitary
- ADH increases water absorption by binding the distal convoluted tuble and collecting duct and allowing aquaporin activation to decrease urine volume
Approx __% of urea in filtrate is reabsorbed
50
Creatinine reabsorption and why is it useful?
Not reabsorbed so useful measurement of GFR and glomerular function
Substances that undergo tubular secretion from blood into renal tubules (3)
-ammonia
H+ ions
-K+ ions
Countercurrent mechanism of loop of henle components (2)
- Loop of henle
- Vasa recta (derived from peritubular capillary and surround the loop of henle)
Countercurrent multiplier of loop of henle mech of action
- As water moves down descending loop of henle, osmolarity continues to rise from 300 to 1200 mOsm in the interstitial space, drawing out more and more H2O
- The more water that leaves the descending limb, the saltier the remaining fluid in the tubule
- At the ascending limb, the ions are pumped into the interstitial fluid while it remains impermeable to water at this point
- The more salt that is pumped out of the ascending limb, the saltier the interstial space is for the water
- Vasa recta descending capillaries see water diffuse out of blood and NaCl diffuse into blood
- Vassa recta ascending capillaries see water diffusing into blood and NaCl out of blood, encouraging much greater water retention
Items absorbed in the proximal tubule, loop of henle, distal tubule, and colelcting duct
Proximal - Na+ maority, gluose, amino acids, K+, urea
Loop of henle descending - H2O reabsorption
Loop of henle ascending - Na+ reabsorption, impermeable to water
Distal - very little
Collecting duct - H2O mainly
___% of water is reabsorbed from the proximal tubule and descending loop of henle, this is called ____ reabsorption
75, obligatory
Diabetes insipidus is a deficiency of….
What 2 symptoms does this cause?
…ADH
Polyuria, polydipsia
Inhibitor of ADH release
alcohol
Aldosterone functionally decreases this ion and increases this ion both in blood levels.
It is what kind of hormone?
K+, Na+
Steroid
Caffeine mech of action as a diuretic
Dilates afferent arteriole, increases cardiac output driving blood flow to kidney resulting in increased GFR
Lasix mech of action as diuretic
get back to me on this one Tav
Vit D2 function
Active form of vitamin D that causes increased absorption of Ca2+ and phosphorus in small intestine
Simple explanation of kidney acid base balance regulatory function
- Acidic blood causes more H+ secretion into filtrate and more HCO3- ions reabsorbed into blood
- Basic blood causes less H+ reabsortpion into blood and more HCO3- secretion into filtrate
Trigone definition, what can inflammation of it cause?
Little space between ureters and urethra on base of bladder that can become inflamed and cause interstitial cystitis
Internal urethral sphincter is __ muscle part of the ___ muscle and external is ____ muscle
Smooth, detrusor, skeletal
How much urine triggers sensation of need to micturate?
200-300mL
How much fluid can a full bladder hold?
800mL
The short length of the female urethra can make it easy to have this infection occur
Bacterial cystitis
Micturition reflex
- stretch receptors upon 200mL of urine in bladder send signal to spinal cord (S2, S3)
- Parasympathetic reflex arc from spinal cord stimulates contraction of detrusor muscle
- relaxation of internal urethral sphincter
- sensory fibers also go up to brain in pons and allow it to analyze and keep external muscles tight preventing urination
