Urinary Flashcards
What are the functions of the kidneys?
-Excrete nitrogenous waste (urea, uric acid, creatine)
-Regulate blood volumes (H2O balance and release of erythropoietin)
-Regulates blood pressure (renin release)
-Regulates chemical composition of blood
-Stabilizes pH
-Converts Vitamin D to active form
What is the flow of blood through the renal blood vessels in the capillary system?
Afferent arteriole > Glomerulus > Efferent arteriole > Pertibular capillaries OR vasa recta
What is the functional unit of the kidney?
The nephron
What are the tubular components of the nephron?
Tubular components: Bowman’s capsule, proximal convoluted tubule, loop of henle, distal convoluted tubule, collecting duct
What are the vascular components of the nephron?
Afferent arterioles, glomerulus (a capillary knot), efferent arterioles, peritubular capillaries (around cortex) , vasa recta (in medulla)
What is the difference between a cortical nephron and a juxtamedullary nephron?
Cortical - in cortex, short loop of Henlea
Juxtamedullary - Glomulerii are deep in cortex and long loop of Henles extends into the medulla
Where is the juxtaglomerular apparatis and what is the purpose of the juxtaglomerular apparatus?
At the beginning of the distal convoluted tubule.
Contains cells that regulate filtration rate and blood pressure
Where are macula densa and what are their purpose?
In JGA, in distal convoluted tubule, contain osmoreceptors (chemoreceptors) that monitor solute concentration (specifically Na+) and flow rate of filtrate
What makes granular cells of JGA granular?
They contain renin
What are the granular cells of the JGA?
Smooth muscle cells in the afferent arteriole that contain barioreceptors that monitor blood pressure, synthesizes and secretes renin
What are the four basic processes of the nephron?
Glomerular Filtration(F), Tubular Reabsorption (R), Tubular Secretion (S), and Excretion (E)
F - R + S = E
What is the main component of the body contributing to osmotic pressure?
Plasma proteins
How often do the kidneys filer the blood plasma?
60x per day
What is filtrate?
Blood plasma minus proteins: everything in the nephron to the tip of the papillary duct
How much of filtrate winds up as urine?
Less than 1%
What is the filtration fraction?
The amount of fluid reabsorbed from filtrate. 20% of fluid from plasma is pushed through the glomerulus, 19% will be reabsorbed
Where is filtrate formed?
Glomerulus
Why is glomerular filtration more efficient at filtration than other capillary beds?
Fenestration makes it more permeable to solutes
Blood pressure is higher due to a wider afferent arteriole than efferent
Higher net filtration pressure
What is the Glomerular Filtration Rate?
The total amount of filtrate formed per minute by the kidneys
125 mL/min or 180L/day
What are the factors that govern filtration rate?
Net filtration pressure
Total surface area available (#of nephrons)
Filtration membrane permeability
What are the forces involves in glomerular filtration?
Glomerular capillary pressure (55mmHg)
Plasma-colloid osmotic pressure (30mmHg)
Hydrostatic pressure in Bowman (15mmHg)
Osmotic pressure in Bowman (mmHg, due to lack of proteins)
What happens if GFR is too high?
Necessary substances cannot be reabsorbed and are lost in urine
What happens if GFR is too low?
Everything is reabsorbed, including wastes
What are the extrinsic controls of the GFR?
Sympathetic nervous system and the renin-angiotensin-aldosterone system
Increased BP increases Glom BP, increases GFR
What are the intrinsic controls of the GFR?
Autoregulation by kidneys, maintains BP between 80-180mmHg
What is myogenic regulation?
Autoregulation of GFR that responds to changes in pressure in renal blood vessels and (constriction and dilation) arteriole smooth muscles
If arteriole pressure increases afferent arterioles constrict or dilate?
They construct, which lowers the GFR
If arteriole pressure is low what happens to the aretioles?
The myogenic mechanism dilates the arterioles to increase GFR
If macula densa cells detect increased NaCl flow what happens?
Releases vasoactive chemicals which cause vasoconstriction of afferent arteriole, decreasing GFR
What is sympathetic control of the GFR?
If blood pressure drops barioreceptors trigger vasoconstriction, less blood flows and lowers GF, which reduces urine volume and conserves plasma volume (which increases blood volume)
What triggers the release of renin?
Reduced stretch of granular cells (MAP below 80)
Stimulation of granular cells by macula densa
Stimulation of granular cella by Beta adrenergic receptors
What are the effects if angiotensin II?
Constriction of arteriolar smooth muscle (increases MAP)
Stimulates reabsorption of Na+
Triggers release of aldosterone from adrenal cortex
Stimulates release of ADH
Activates thirst center
What is tubular reabsorption?
The selective transfer of substances from filtrate back into peritubular capillaries
Note: Rates are very high
What is transepitheleal transport?
A substance is reabsorbed. It crosses the tubule wall, enters interstitial fluid, passes through the wall of the peritubular capillaries, and enters the blood
True or false: Sodium reabsorption is mostly driven by active transport because of the Na+/K+ pump at the basolateral membrane
True
Where is most of Sodium reabsorbed?
67% occurs in the proximal tubule at a constant rate
What is true about the absorption rate of Sodium in the distal tubule?
It varies depending on aldosterone: more or leas is reabsorbed based on the needs of the body
How does aldosterone increase Na+ absorption in the distal collecting tubule?
It increases membrane permeability by promoting additional Na+ channels in the luminal membrane and Na-K pumps in the basolateral membrane
What happens to sodium in the distal convoluted tube if no aldosterone is present?
It gets lost in the urine
What is the effect of ANP on sodium reabsorption?
Inhibits it by acting directly on the ducts to decrease blood volume and lower blood pressure.
It also dilates the afferent arteriole, increasing GFR and decreasing absorption rate
What causes tubular reabsorption of water?
Accumulation of sodium in lateral spaces produces an osmotic gradient that drives water into the peritubular capillaries (water follows)
Where does most water get reabsorbed?
Loop of Henle - 80% occurs via osmosis (no control)
Where does facultative reabsorption of water take place?
Distal tubule and collecting duct: about 20%, based on body’s needs and regulated by ADH
What are the two key hormones for reabsorption?
Aldosterone: sodium
ADH: water
How does ADH affect water reabsorption?
Promotes aquaporin production on luminal membrane, which increases water reabsorption (means concentrates urine)
How are glucose and amino acids reabsorbed?
Secondary active transport. GLUT protein and Co-transported with Sodium on luminal membrane.
What is a transport maximum?
The number of carriers available in a renal tubules: when the carriers are saturated excess is excreted
Note: This is the reason for “sweet urine” in diabetes
What prevents a substance like urea, creatinine, and other nitrogen wastes from begin reabsorbed?
Lack carriers
Water soluble instead of lipid soluble
Too large to pass through pores
What is absorbed in the proximal collecting tubule?
Most reabsorption occurs here.
2/3 of water and Na+
All nutrients, ions, and small proteins
What gets absorbed in the loop of Henle?
Descending Limb: Water
Ascending Limb: Na+, K+, Cl-
What is absorbed in the distal convolutes tubule and collecting duct? What is noteworthy about this absorption?
Reabsorption is hormonally regulated.
Ca2+ (PTH), Water (ADH), Na+ (Aldosterone and ANP)
What is the purpose of tubular secretion?
It speeds up the elimination of substances from the blood by skipping the glomerulus
What is tubular secretion important for?
-Disposing of substances not already in the filtrate
-Eliminating undesirable substances
-Ridding excess K+ ions
-Controlling blood pH
What is the effect of aldosterone on potassium?
Stimulates distal tubule to secrete it and increases excretion
True or false: Potassium is almost entirely reabsorbed in the distal tubule
False. This occurs in the proximal tubule
How is the vertical osmotic gradient eatablished?
The countercurrent system: the movement of filtrate in opposite directions in the ascending and descending loop of Henle
What are the properties of the limbs of the loop of Henle?
Descending: impermeable to solutes, permeable to water
Ascending: permeable to solutes, impermeable to water
Where does the ascending limb of the loop of Henle teansport NaCl?
Into interstitial fluid. Water cannot follow because the limb is impermeable to water, so the fluid becomes hypertonic and is reabsorbed by the descending loop
What is true about blood when it enters the medulla of the vasa recta and when it leaves?
It is isotonic
What hormone signals the production of concentrated urine?
ADH
What changes about the distal convolutes tubule and collecting ducts in the presence of ADH?
Allows them to be permeable to water and 99% is reabsorbed
What are osmotic diuretics?
High glucose levels - Water leaves with glucose
Alcohol - Inhibits the release of ADH
Caffeine - Inhibits Na+ reabsorption
Where is H+ and NH4+ secreted and HCO3 reabsorbed to maintain blood pH?
The proximal convoluted tubule
Where is H+ and HCO3 reabsorbed to maintain blood pH
The collecting duct
What is the term for elimination of the remains in the tubular lumen?
Urine excretion
What is renal clearance?
The volume of plasma cleared of a particular substance in a given time
What are renal clearance tests used to detect?
GFR
Any damage to glmoerulus
The progression of renal disease
True or false: Inulin clearance is equal to GFR
True.
What are the Renal Clearance numbers?
If GFR = 125ml/min
RC < 125 the substance is reabsorbed
If RC = 0 the substance is COMPLETELY rebsorbed
If RC > 125 the substance is secreted (this is true of most drugs)
How does urine leave the kidneys?
Through ureters to bladder, which has stretch receptors that fill until micturition is triggered and urine is forced past the internal sphincter and put the external sphincter (voluntarily)
What is the name of the underdeveloped control center in infants that matures between ages 2 and 3
Pontine control centers.
-Storage - inhibits micturition by inhibiting PSNS and exciting SNS and somatic paths
-Micturition center - promotes micturition by exciting PSNS and inhibiting SNS and somatic paths
