3C Flashcards
What do the kidneys do?
- filter blood so it doesn’t become toxic
- removes waste products and coverts filtrate into the urine
- regulates the composition of blood through reabsorption and secretion including ion levels and acid/base composition
- maintains blood volume and pressure through the reabsorption and secretion of water
What waste do the kidneys remove?
Urea, creatine
What ions do the kidneys regulate?
Na, K, H, HCO3
What do the ureters do?
transport urine from the kidneys where it is produced to the urinary bladder where it is stored
What does the bladder do?
expandable muscular sac that stores up to one liter of urine
What does the urethra do
-eliminates urine from the body
-males have longer urethra since it travels through the penis
What are the two types of nephrons?
cortical nephron
juxtamedullary nephron
What percentage of nephrons are cortical nephrons?
approximately 85%
What percentage of nephrons are juxtamedullary nephrons?
approximately 15%
What does the juxtamedullary nephron do?
-establishes osmotic gradient medulla from 300-1200 mOSm
- conserves H3O
-allows for the secretion of hypertonic urine
How does blood flow through the Nephron?
- arcuate artery
- interlobular artery
- glomerulus (capillary knot of renal corpuscle)
- efferent arteriole
- peritubular capillary (surrounds renal tubule)
- Vasa recta (surrounds nephron loop) adjusts absorption and secretion
- Interloular Vein
Which way does secretion move through the nephron?
blood to tubular fluid
Which way does reabsorption move through the nephron?
tubular fluid to blood
What drives filtration?
passive, pressure-driven process?
How do materials move through the renal corpuscle?
glomerular capillaries across the filtration membrane, into capsular space forming filtrate
What is the filtration membrane include?
the cells that form the wall of the glomerulus and associated podocytes
What is the relationship between the blood pressure in the renal corpuscle and systemic capillaries?
- bp is higher in the glomerulus compared to other systemic capillaries bc it is both fed and drained by arterioles and afferent arteriole has larger lumen than efferent tubule
When does filtrate become tubular fluid?
- once it exits the capsular space and enters the renal tubule
What happens in the renal tubule?
- composition of the tubular fluid is modified because of reabsorption and secretion
- has a fenestrated endothelium of the glomerulus and associated basement membrane and a little leaky so-formed elements (RBC, WBC, platelets) have large proteins that can’t cross membrane
What is the filtrate in the Renal Corpuscle?
- H2O, glucose, amino acids, ions, urea, some hormones, vitamins, B+C, ketones, small amounts of proteins
What is glomerular hydrostatic BP?
force that pushes H2O and some solutes out of the glomerulus and into the capsular space driving filtration force
What forces oppose glomerular hydrostatic BP?
- blood colloid osmotic pressure
- capsular hydrostatic pressure
- glomerular filtration rate
What is blood colloid osmotic presure?
osmotic pressure exerted by dissolved solutes in plasma
What is capsular hydrostatic pressure?
pressure in glomerular capsule due to filtrate already present
What is glomerular filtration rate?
the rate the glomerulus filters blood in ml/min
What is a normal glomerular filtration rate?
180l/day
What is the relationship between net filtration pressure and glomerular filtration present?
-directly correlated
-increase in NFP increases GFR
Can NFP be negative?
NO
How is GFR regulated?
- changes in the luminal diameter of the afferent arteriole
- altering SA of the filtration membrane
- intrinsic controls
-extrinsic controls
Why is GFR regulated?
to help kidneys control urine production based on physiological conditions
How does change in luminal diameter of afferent arteriole influence GFR?
- increase in diameter= increase in blood flow and GFR
- decrease in diameter= decrease in blood flow and GFR
How does altering the surface area of the filtration membrane influence GFR?
-increase in SA= increase in GFR
- decrease in SA= decrease in GFR
What are the intrinsic controls of GFR and what do they do?
- renal autoregulation by myogenic mechanism and tubuloglomerular feedback
- this maintains a constant GFR in spite of systemic arterial BP changes
What is an extrinsic control of GFR?
Neural (sympathetic) response and hormonal control (ANP)
What happens when there is insufficient urine production?
- afferent arterials move to max dilation
- glomerular bp and GFR go down
- if extremely low cesation of waste elimination in urine
- we want to increase blood flow and GFR
What happens when there is a normal production of urine due to the myogenic mechanism?
myogenic mechanism maintains renal autoregulation by compensating for systemic BP changes by causing constriction or dilation of the afferent arteriole wall
- allows for intrinsic control of GFR levels
What do we want GFR to be?
180
What happens when there is excess urine production?
-arterioles go to max constriction
- we want to decrease blood flow and increase GFR
-urine formation increases
- too much filtrate could cause too much blood flow
What happens if there is a decrease in systemic bp?
- less stretch of afferent arteriole which results in smooth muscle cells of afferent arteriole relaxing (vasodilation )
- this increases blood flow into the glomerulus and compensates for lower systemic pressure
What happens if there is an increase in systemic bp?
- a stretch of afferent arteriole which stimulates the contraction of smooth muscle cells in afferent arteriole (vasoconstriction)
- this decreases blood flow into the glomerulus and compensates for high systemic BP
What does the tubuloglomerular feedback mechanism do?
- acts as a backup for the myogenic mechanism in response to high bp
- an increase in NaCl of tubular fluid is detected by macula densa cells in the distal convoluted tubule of the juxtaglomerular apparatus
-macula densa cells signal the granular cells in the afferent arteriole of the juxtaglomerular apparatus to release the renin-angiotensin-aldosterone mechanism causing a cascade effect - too much NaCl increases bp triggering the release of renin decreasing GFR
What are the extrinsic controls of GRF through the sympathetic nervous system?
- decreasing GFR through Sympathetic stimulation of the kidneys
-contraction of Mesangial cells - granular cells of JG increase renin release
- increase in angiotensin 2 production
What does decreasing GFR through sympathetic stimulation of the kidneys do for extrinsic GFR control of the sympathetic nervous system?
vasoconstriction of afferent arteriole results in decreased blood flow
What does contraction of the mesangial cells do for extrinsic control of the sympathetic nervous system?
-specialized contractile cells positioned in between the glomerular capillary loops pull loops closer together and decrease filtration surface area therefore decreasing gfr and reducing filtration
What are mesangial cells?
specialized contractile cells that impact SA at glomerulus
Summarize sympathetic control of GFR?
- nervous system triggers sympathetic fight or flight which decreases GFR while maintaining blood volume and pressure
- granular cells stimulate the release of renin stimulating the constriction of mesangial cells and decreasing surface area
- uses intrinsic mechanisms but overrides their messages because we wanted to change GFR instead of keeping it constant
What is the result of the extrinsic GFR control through the sympathetic nervous system?
- vasoconstriction of afferent arteriole decreases blood flow into the glomerulus and contraction of mesangial cells decreasing filtration surface area
- decrease gfr and filtrate, more fluid retained in blood maintaining blood volume
How is GFR extrinsically controlled by ANP
- increases GFR through atrial natriuretic peptide
- stimulus is an increase in blood volume or pressure that causes atrial wall of heart to stretch and release ANP
-renin release from granular cells of JG apparatus inhibited
-decrease in angiotensin 2 produciton
How is GFR extrinsically controlled by ANP?
- increases GFR through atrial natriuretic peptide
- stimulus is an increase in blood volume or pressure that causes the atrial wall of the heart to stretch and release ANP
-renin release from granular cells of JG apparatus inhibited
-decrease in angiotensin 2 production - vasodilation of the afferent arteriole increases blood flow
- relaxation of messengial cells increases surface area and therefore increases gfr and filtration
What is the result of anp on extrinsic control of GFR?
- vasodilation of afferent arteriole increases blood flow into the glomerulus and relaxation of the mesangial cells increases the surface area
- increase in gfr increases filtrate, more fluid eliminated in the urine, decreases blood volume and pressure
Summarize ANP control of GFR
ANP is released from the atrial wall increasing blood pressure and volume inhibiting renin , mesangial cells relax increasing surface area and GFR
- increases GFR, filtrate, decreases blood pressure and volume
What happens in the proximal convoluted tubule?
- collects the filtrate from the renal corpuscle which is now referred to as tubular fluid
- the majority of reabsorption happens here
What happens in the descending nephron loop?
-receives tubular fluid from the proximal convoluted tubule
-permeable to H2O facilitating a large amount of water reabsorbtion
What happens in the ascending limb of the nephron loop?
- receives tubular fluid from descending limb
- impermeable to water, permeable to salts facilitating reabsorbtion
What happens in the distal convoluted tubule?
-receives tubular fluid from the ascending nephron loop
-tubular fluid adjusted in response to hormones
What happens during reabsorbtion?
materials move from the filtrate into the renal tubule lumen into the blood
What happens during secretion?
materials that weren’t filtered move from the blood into the renal tubule lumen
-whatever stays in filtrate renal tubule lumen becomes urine
What is the pressure in the peritubular capillary?
low hydrostatic pressure, high colloid pressure
What are examples of transport proteins?
channels, carriers, pumps
What is paracellular transport?
movement of substances between epithelial cells
What is transcellular transport?
movement of substances across an epithelial cells
What is transport maximum
-maximum rate of substance that can be reabsorbed or secreted across tubule epithelium per a certain time
- depends on the number of transport proteins in the membrane when facilitated diffusion, primary or secondary active transport involved
- open more doors to let more people out
What are normal glucose mg of glucose?
- greater than 375 mg = excess glucose excreted in urine (abnormal)
- less than 375 mg= glucose n tubule all reabsorbed
What % of glucose, Na+, H20, HCO3 are reabsorbed into the proximal convoluted tubule?
100% glucose
35% water and Na
80-90% HCO_3
What % of glucose, Na+, H20, HCO3 remain in tubular fluid
0% glucose
65% water and Na
10-20% HCOS
What is the concentration gradient in urea recycling?
-present in interstitial fluid surrounding the nephron
- established by various solutes (Na, Cl) and urea
-progressively increases in osmolarity as you move deeper in the medulla
What is the urea recycling process?
-urea is filtered and becomes part of the tubular fluid at the PCT
- urea exits the tubular fluid at the collecting ducts and re-enters the tubular fluid at the thin segment of the nephron loop
- urea levels are high in the deepr medulla (makes of 50% of solutes here) contributing to the higher osmolarity of the interstitial tissue found in this region
What happens in the descending limb of countercurrent exchange?
- descending limb is permeable to water, and impermeable to salts so H2O moves out
- tubular fluid becomes more concentrated as water is being re-absorbed from descending limb (H2O moves from tubule to vasa recta)
What happens in the vasa recta?
blood travels in opposite direction (countercurrent) to tubular fluid of adjacent nephron loop
What happens in the ascending limb during the counter-current exchange?
-impermeable to H2O, permeable to salts, so ions move out
- no aquaporins for transcellular transport
- tubular fluid becomes less concentrated as it moves through the ascending limb due to active movement of Na, K+ out of the tubular fluid and into the interstitial fluid and vasa recta
What does the distal convoluted tubule contain?
type a and b intercalated cells
principle cells
What do type A intercalated cells do?
secrete H+ in order to raise pH and reabsorb/ replace HCO3-
-occurs in response to acidic blood
What do type B intercalated cells do?
reabsorb H+ in order to lower PH
-occurs in response to basic blood
What do principle cells do?
reabsorb Na+, H2O, Ca, secretes K+ at varying rates
- responds to ADh Aldoseterone, PTH
What does ADH cause in principle cells?
- increases number of aquaporins resulting in an increase of H2O absorption
What does aldosterone do to principle cells?
- aldosterone is regulated by the renin-angiotensin mechanism which increases Na+ H2O reabsorption and K+ secretion
- increases the number of N+ channels, Na/K+ pumps leading to an increase in Na+ reabsorption
What does PTH do to principle cells?
-inhibits reabsorption of phosphate in PCT
- stimulates reabsorption of Ca2+ in DCT resulting in an increase in the blood calcium levels
-PTH= parathyroid hormone secreted in response to low blood calcium levels acting to increase them
What is the overall urine pathway
- kidneys
- nephrons form filtrate from the blood at the renal corpuscle and adjust the tubular fluid composition throughout the renal tubule and collecting ducts/ tubules
- no more changes occur after collecting tubules drain into renal papillae and renal pyramids, it is now considered urine
- urine drains from renal papillae t the minor calyx to the major calyx to the renal pelvis - ureter transports urine from kidneys to the urinary bladder
- bladder stores up to 1 l of urine for controlled release through the urethra (internal sphincter under autonomic control and external sphincter under somatic control
- urethra excretes urine from body
What sphincter do we have control over
We gain control of the external sphincter when we get potty-trained
What is the micturition reflex?
responsible for the expulsion of urine from the bladder and out of the body through the urethra
What regulates the micturition reflex?
-parasympathetic signals
How does the micturition reflex work?
- when the bladder is distended and baroreceptors in bladder wall are activated which results in a reflex that causes the detrusor muscle to contract.
- signals are sent to the brainstem, parasympathetic response (involuntary) allows for the internal urethral sphincter to relax
- relaxation of external sphincter requires voluntary (somatic) muscle control
- we gain control of external sphincter when we get potty trained
