Renal Physiology Flashcards
What are the three main kidney functions
Regulation of water electrolyte balance
Removal of waste
Secretion of hormones
What 3 hormones are secreted from the kidney
Erythropoietin (RBC synthesis)
Renin
1,25 dihydroxyvitamin D (bioactive form)
What is the function of the lower urinary tract (ureters, bladder and urethra)
Urine collection, storage and excretion
What are the blood vessels connected to kidney
Renal artery and renal vein
What makes up the cortex of the kidney
Glomeruli
What makes up the medulla of the kidney
Renal tubules, collecting ducts, blood vessels and medullary pyramids
What are the important features of the renal system
Kidneys have excellent blood supply (20% of cardiac output) enabling them to work with the cardiovascular system in an intergrated manner by processing plasma of blood (control blood volume)
What is a nephron
Functional unit of kidney
What are the 2 functional components of the nephrons
Vascular component (contains blood) and tubular component (contains urine)
What does the mechanisms of the kidneys depend on
The relationship between the vascular and tubular components
What is the the pattern of blood flow from the aorta to the kidney and back to the heart
Aorta- renal artery- afferent arterials- glomerulus- efferent arteriole- peritubular capillaries- renal vein - inferior vena cava
What are the two main components of the nephron
Golmerulus and tubule
What is the function of the glomerulus
Forms a protein free filtrate from blood
What is the function of the tubule
Processes the filtrate to form urine
What are the 4 segments of each tubule
Proximal tubule, loop of Hemel, distal tubule and collecting ducts
Where does filtration occur
The glomerulus
Where does water and solute reabsorption occur
PCR, loop of henle, DCT and collecting ducts
Where does secretion occur
PCT, DCT and collecting ducts
Where does the golmerular filtrate drain into
The bowman’s capsule
What is the function of the pores in the capillary endothelium of the glomerulus
Enables small molecules to pass into the bowman’s capsule but not larger proteins and RBC
What stops plasma proteins from entering the tubular fluid
The negative charge of podocytes and the basement membrane of the glomerulus
Why does ca2+ not pass through into the capsule
50% is bound plasma proteins
What is the glomerular filtrate rate
180l/day
What is the function of glomerular filtration
Regulate the composition of extracellular fluid
What two things control glomerular filtrate rate (GFR)
The diameters of afferent and efferent arterioles
Why causes high hydrostatic pressure at glomerular capillaries
Short, wide afferent arteriole and and long, narrow efferent arteriole
What regulates the diameter of the efferent and afferent arterioles/ GRF
Sympathetic vasoconstrictor nerves, ADH and RAAS
What is the function of the peritubular capillaries
Provide nutrients for tubules and receive the fluid that the tubules have reabsorbed
Why does reabsorption not filtration occur in the peritubular capillaries
As oncotic pressure is greater than hydrostatic pressure
Why must reabsorption of fluid in the peritubular capillaries occur
As we filter 180L/day but only excrete 1-2l/day of urine
Where does most reabsorption of nutrients, ions, water and urea occur
The proximal convoluted tubule
How are glucose, AA, phosphate ions and chloride ions reabsorbed in the proximal tubules
Coupled with Na+ and transported down electrochemical gradient for Na+, requiring energy
Gradient established by Na+/K+- ATPase
Move across basolateral membrane by passive or facilitated diffusion into peritubular capillaries
How are peptides reabsorbed in proximal tubules
Taken up by pinocytosis and degraded by cells to AA so they can cross the basolateral membrane
What is the Tm
Maximum transport capacity of transporter proteins in tubules
What happens if the maximum transport capacity is exceeded
Excess nutrient is excreted in urine, which is useful for disease detection
Why do amino acids have a high maximum transport capacity
Because we need to preserve as many as possible
How is Na+ absorbed in the tubules
By active transport mechanism instead of a Tm mechanism, basolateral ATPases establish the gradient for Na+ to cross the tubule wall
Na+ ions move down this concentration gradient via Na channel proteins
Cl- follow Na+ to maintain an electrochemical gradient
How does the reabsorption of Na+ affect the fluid in the tubules
Becomes more concentrated as H2O follows Na+ due to osmotic gradient
How is glucose reabsorbed in the tubules
Apical- Na+/ glucose cotransporter (SGLT) down Na+ conc gradient, requiring Na+/k+-ATPASE
Basolateral- glucose transporters (GLUTS) down concentration gradient
How are amino acids reabsorbed in the tubule
Apical- Na+/ amino acids cotransporter (SGLT) down Na+ conc gradient, requiring Na+/k+-ATPASE
Basolateral- passive diffusion down concentration gradient
How is K+ reabsorbed in the proximal convoluted tubule
Reabsorbed in promximal convoluted tubule
Passive via K+ selective ion channel following movement of Na+ and fluid
Where is K+ secreted
Cortical collecting ducts
How is K+ secreted into the cortical collecting ducts
Via active transport of K+ across basolateral membrane and passive exit across apical membrane into the tubular fluid
What controls K+ excretion
RAAS mediated Na+ absorption
Why is K+ regulation important
Too high (from 4 to 5.5 moles/l) = hyperkalaemia (ventricular fibrillation and death)
Too low (from 4 to 3.5 mmoles/l)= hypokalaemia (hyperpolarise= arrhythmias and paralysis and death)
What maximises K+ excretion when it is too high
Medullary trapping of K+ in the PCT
Describe the osmoraility is the glomerular filtrate after the PCT
Isotonic with the plasma
What is the main function of the loop of Henley and collecting ducts
Absorption of water and sodium chloride
What does absorption of water and sodium chloride in the loop of henle and collecting ducts facilitate
Fine tuning of urine according to the body’s needs
What is the counter current exchange
The relationship between permeability of the descending thin limb and ascending thin limb to Na+
How is Na+ removed from the ascending thin limb
Actively transported into interstitial fluid surround limb
What regulates the cyclical movement of Na+ throughout the loop of helpless
ADH (increases water permeability)
What occurs in the descending limb of the loop of henle and how does this affect filtrate osmorality
Water reabsorbed, increasing the osmorailty
What occurs in the ascending limb of the loop of henle and how does this affect filtrate osmorality
Active solute reabsorption, decreased filtrate osmorailty
What is the vasa recta
Blood vessel that removes water leaving the loop of henle
What occurs in the descending limb of the vasa recta and how does this affect filtrate osmorality
Water reabsorption and solute uptake, increased blood osmorailty
What occurs in the ascending limb of the vasa recta and how does this affect filtrate osmorality
Water reabsorption
Descreased blood osmorailty
What is the descending limb of the loop more permeable to
H20
What is the descending limb of the loop less permeable to
Na+ and Cl-
What is the descending limb of the loop impermeable to
Urea
What does not happen in the descending limb of the loop
Active transport of solutes
What happens to the osmorailty of the extracellular fluid surrounding the descending limb of the loop from the PCT
Progressively increases
What does high osmorailty mean
More concentrated
What is the ascending limb of the loop less permeable to
H20
What is the ascending limb of the loop moderately permeable to
Urea
What is the ascending limb of the loop more permeable to
Na+ and Cl-
What happens in the ascending limb of the loop of henle
Na+ diffuses from tubules to extracellular fluid surrounding both limbs
Urea enters tubules down concentration gradient
Thick ascending limb reabsorbs Na+ from extracellular fluid via apical Na+-K+-ATPase. Cl- diffuses across basolateral membrane
Describe the countercurrent multiplier exchange in the loop of henle
Filtrate entering the descending becomes progressively more concentrated as it loses water (increased osmolarity of filtrate)
Blood in the vasa recta removes water leaving the loop of henle and the descending limb of the vasa recta uptakes Na+, Cl- and K+ (increased osmorality so the ascending limb can reabsorb more water (decreased osmorality)
The ascending limb pumps out Nat, K+, and Cl- and filtrate becomes hyposmotic (decreased osmolality of filtrate)
What is the function of the collecting ductsm
Runs through hyper osmotic (high osmorality) medulla to drain into renal pelvis and uterers
Water moves down osmotic gradient to extracellular fluid to produce concentrated urine
What controls Na+ reabsorption at the collecting ducts
Tight epithelium junctions and aldosterone (from RAAS)
How is membrane permeability to water increased in the collecting ducts
ADH activates adenylate cyclase and cAMP to increase the permeability of the apical membrane to water
What are the macula densa
Specialised region of cells in DCT (in close proximity to bowman’s capsule) that sense Na+ in glomerular filtrate
What happens if the macula densa sense low Na+ in glomerular filtrate
Cells on afferent arteriole within the juxtaglomerular apparatus (JGA), includes JG cells that secrete renin, help regulate renal blood flow, GFR and also indirectly, modulates Na+ balance and systemic BP
Describe the role of ADH in the collecting duct
Changes in plasma osmolality (in carotid artery) detected by osmoreceptors in hypothalamus.
Stimulates release of anti-diuretic hormone from posterior pituitary (reduce osmolality decreases ADH)
ADH receptors present on basolateral membrane, ADH binds, G protein activated, adenylate cyclase activated, ATP converted to cAMP, protein kinase A (PKA) activated, PKA phosphorylates target proteins causing endosomes containing aquaporins to fuse with membrane, increase incorporation of aquaporin channels into apical membrane
Due to high Na+ in extracellular fluid in medulla water moves from CD tubule into the medulla (concentrating urine)
What do juxtaglomerular apparatus cells (within afferent arteriole) secrete
Renin
How is urea reabsorbed
Passively
When is urea reabsorption greatest
When urine volume per minute is small (concentrated urine)
What is urea recycling
Urea is toxic at high levels but useful in small amounts, recycling causes a build up in inner medulla which helps create the osmotic gradient for water reabsorption at the loop of henle
What can cause more urea/more concentrated urine
High protein diet
What is the function of urea
Concentrating urine
What is the role of angiotensin in DCT and glomerulus
Increase Na+ and water retention, increase extracellular fluid and increase blood pressure via vasoconstriction in arterioles
What causes efferent arteriole vasoconstriction
Low dose of Angiotensin II
What causes afferent arteriole vasoconstriction
High dose of angiotensin II
What is the function of renin
Stimulates release of angiotensin from liver into blood to stimulate vasoconstriction
What is the function of aldosterone
Aldosterone stimulates Na+ uptake on the apical cell membrane in the distal convoluted tubule and collecting ducts
What causes the secretion of aldosterone from adrenal cortex
Angiotensin II
How is chronic kidney disease identified
Chronic kidney disease is identified by a blood test for creatinine. Higher levels of creatinine indicate a lower GFR and as a result a decreased capability of the kidneys to excrete waste products
What is normal blood pH
7.35-45
How does the kidney regulate blood pH
via the active transport of H+ ions into the filtrate
What is associated with high GRF
aff art dilation and eff art constriction
What is the pH of urine
4-8
How is plasma pH buffered in the kidney
CO2 actively transported out of peritubular capillaries
CO2 combines with water to form HCO3- and H+
Secretion of H+ either slows or increases until the pH returns to normal
Excess H+ buffered by HCO3-
