Genitourinary system Flashcards
What is the outer region of the kidney?
The cortex
What is the inner region of the kidney?
Renal medulla
What is located within the renal medulla?
Renal pyramids separated by renal columns
What does a renal pyramid produce?
Urine
Where does the urine from the renal pyramid terminate into?
Renal papilla
The Renal papilla drains urine into what?
Minor calyx
Multiple minor calyces drain into what?
Major calyx
What do major calyces drain into?
Ureter
What are the 5 main functions of the kidney?
1) Excretion: Excretion of metabolic products; urea; uric acid and creatine
2) Excretion of foreign substances e.g drugs
3) Homeostasis of body fluids,electrolytes and acid-base balance
4) Regulation of blood pressure
5) Secretion of hormones e.g renin and erythropoietin
How is blood pressure regulated by the kidney?
Function to control blood pressure through the production of renin by the juxta-glomeruluar cells
Which hormone secreted by the kidney regulates erythropoiesis?
Erythropoetin
Which enzyme catalyses the secondary hydroxylation of vitamin d?
1-alpha-hydroxylase
which artery does the afferent arteriole arise from?
Interlobular artery
Which artery does the glomerular capillaries arise from?
Afferent arteriole
Which vessels does the efferent arteriole arise from?
Glomerular capillaries
Which arteriole does the peritubular capillaries arise from?
Efferent arteriole
What is the main blood supply to the kidney?
Renal artery
What is the main blood outflow of the kidney?
Renal vein
What are the three main processes of the nephron?
Filtration
Reabsorption
Secretion
Which artery distributes blood towards the glomerulus?
Afferent arteriole
Where does ultrafiltration occur within the kidney?
Bowmans capsule
What does the Bowman’s capsule produce?
Filtrate
Which network of capillaries are enclosed within the bowman capsule?
Glomerulus
Where is the filtrate reabsorbed within the kidney?
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
How is blood filtered within the Bowman’s capsule?
Filtered firstly by the glomerular basement membrane which allows water,ions and small proteins to pass.The epithelial podocytes in the Bowman’s space are the 2nd filter.
What cells cover the glomerular capillaries and assist with filtration?
Podocytes
What role is performed by podocytes?
Allow water and small solutes to pass through slits between podocytes
What is the filtration barrier?
Filtration barrier (size & charge dependent): Highly permeable to fluids & small solutes; impermeable to cells and plasma proteins.
What is the diameter to which water, ions and small proteins can pass through?
70nm diameter
Which type of pressure within the glomerular capillaries forces fluid outwards into the Bowman’s capsule?
Hydrostatic pressure
Which type of pressure is exerted by plasma proteins?
Oncotic pressure
What is oncotic pressure?
Osmolarity generated produces a tendency for water to be drawn inwards along water potential gradient, across semipermeable membrane
What type of pressure is exerted by the interstitial fluid with Bowman’s capsule?
Exerts a hydrostatic pressure
What is the net ultrafiltration pressure?
HPgc = Hydrostatic pressure in glomerular capillaries
HPbw = Hydrostatic pressure in bowman’s capsule
πgc = Oncotic pressure of plasma proteins in glomerular capillaries
𝑷𝒖𝒇=𝑯𝑷𝒈𝒄 −H𝑷𝒃𝒘−𝝅𝒈𝒄
What is GFR?
Glomerular filtration rate: The volume of fluid filtered from the glomeruli into the Bowman’s capsule per unit time (ml/minute)
Sum of filtration rate of all functioning nephrons
What is the equation for glomerular filtration rate
𝑮𝑭𝑹=𝑷𝒖𝒇 𝒙 𝑲𝒇
What is the ultrafiltration coefficient?
Product of membrane permeability and surface area available for filtration; changes in Kf will result in GFR imbalances, reduction in GFR characteristic feature of renal disease, accumulation of excretory products within the plasma
What is the GFR range for males?
90-140ml/min
What is the GFR range for females?
80-125ml/min
What is arteriole myogenic control of GFR?
Myogenic mechanism regulating afferent arteriole blood supply into the glomeruli and nephron is dependent on smooth muscle characteristic contractions.
Increasing blood pressure Smooth muscle cells within the arteriole wall are stretched (activation of mechanoreceptors) vasoconstriction occurs to resist the pressure. Vasoconstriction of the afferent arteriole acts to reduce excess filtrate formation, maintain normal NFP and GFR; reduction in arteriole diameters increases resistance and decreases subsequent blood flow.
Vasodilation of afferent arteriole Increases declining filtrate formation, increases GFR to standard level.
Which nerves provide sympathetic innervation to the kidney for GFR?
Coeliac plexus and splanchic nerves
How does sympathetic activity control the kidney GFR?
Kidney innervated by sympathetic neurons via the coeliac plexus & splanchnic nerves. Reduction of sympathetic stimulation results in vasodilation and increased afferent arteriole blood flow. Increased action potential frequency Vasoconstriction Decreases GFR (adrenaline on alpha-1 receptors from adrenal medulla).
Which part of the loop of Henle is permeable to water?
The thin descending limb
Which ion channels permits the water transfer within the loop of Henle?
Aquaporin channels
How does the fluid entering the descending limb compare with plasma concentrations?
Isotonic with blood
Why is the thick descending loop of Henle impermeable to water?
There is an absence of aquaporin channels.
Why doe cells of the thick ascending limb of the loop of Henle have a high mitochondrial density?
Supplies ATP for Na/K ATPase pump, the pumps actively remove sodium ions from tubular cells into the juxtamedullary fluid
Which ions generate a solute concentration gradient within the interstitial fluid?
Chloride and sodium ions
Describe the variance in osmolarity of the juxtamedullary fluid?
Hyperosmolar progressively downwards
Why do the tubule cells of the thin descending limb have a low mitochondrial density?
Hyperosmolar juxtamedullary fluid in comparison to the thin descending limb of Henle, thereby enables water to leave into the fluid by osmosis (descending limb is permeable to water due to aquaporins). Osmosis is a passive process, thus epithelial cells associated with the descending limb have a low mitochondria density.
The presence of which type of junctions makes the ascending limb impermeable to water?
Tight junctions, decreases paracellular transport of water
Which part of the ascending limb does sodium chloride passively diffuse out?
Upon hairpin bend
Explain the Na+/K+ ATPase pump on the Loop of Henle?
Na+/K+ ATPase pump: Na+ actively transported into the interstitial space subsequently reduces the solute concentration within the tubule cells. Assists with luminal resorption of sodium via symporter into epithelial cell, powers secondary active transport of chloride & potassium. Passive flow Supplies energy for secondary active transport.
What is the effect of the Na/Cl/K symporter?
Na+/K+/Cl- Symporter: In apical membrane passively allows ions to enter into cytoplasm from the lumen of the loop down a concentration gradient created by the pump.
What is the purpose of Potassium ion entry via symporters in the loop of Henle?
+ entry into the cell via the symporters returns to the lumen, passively along the concentration gradient through channels present in the apical membrane. This action creates a negative charge in the interstitial fluid, attracting cations from the lumen to the interstitial space and vasa recta by paracellular routes.
What are the two main roles of the Loop of Henle ATPase?
convoluted tubule
Pumping of Na+ into interstitial space generates a hyperosmotic interstitial fluid environment in the kidney medulla.
What are superficial nephrons?
Loops of Henle do not penetrate the inner medulla.
What are juxtamedullary nephrons?
: Loops of Henle penetrate deeper into the medulla.
What is the ratio of superficial: Juxtamedullay nephrons?
10:1
What is responsible for the granular appearance of the renal cortex?
Glomeruli reside within the cortex, the glomerulus is associated with the early distal convoluted tubules
Why is there a striated appearance within the renal medulla?
Striated appearance due to collecting tubules and Loops of Henle
Where are JG cells located?
Located within the afferent arteriole
Which cells stimulate the JG cells?
Macula densa
Which adrenoreceptors are located on JG cells are respond to sympathetic innervation?
Sympathetic innervation to beta-1 adrenoreceptors on juxtaglomerular cells sig
Where are Macula densa cells located?
Reside within the distal convoluted tubule
What stimuli do the macula densa cells respond to?
Renal perfusion pressures
Changes to sodium concentration
What effect does the GFR have on renin?
Increasing GFR reduces the amount of time NaCl to be reabsorbed in the proximal convoluted tubule, this causes a hyper osmotic filtrate, increased fluid movement deflects cilia on macula densa cells - this allows greater flow in DCT activates cells by releasing ATP and adenosine - causes JG cells to release renin - this causes vasoconstriction to decrease GFR
What is the definition of renal clearance?
Renal clearance is the number of litres of plasma that are completely cleared of the substance per unit time
What Is the calculation of renal clearance?
𝑪=(𝑼 𝒙 𝑽)/𝑷 𝒎𝒍/𝒎𝒊𝒏
U= Concentration of substance in urine | V= Rate of urine production | P= Concentration of substance in plasma.
What does freely filtered mean?
If a molecule is freely filtered and neither reabsorbed nor secreted in the nephron, then the amount filtered is equal to the amount excreted. Therefore GFR can be measured by evaluating renal clearance of this molecule.
𝑮𝑭𝑹=𝑪=𝑼𝑽/𝑷
If a molecule is freely filtered how can the renal clearance of the molecule be evaluated?
Equal to GFR.
Why is inulin used to calculate GFR?
Inulin is non-endogenous, thus a specified mass is injected into circulation for GFR measurements Indicator of GFR considering it is freely filtered (neither reabsorbed nor secreted through the peritubular capillaries). Hence, the amount of inulin cleared through the urine is indicative of the amount of plasma filtered by the glomeruli.
Urine concentration refers to the inulin in a sample of urine. Flow refers to the amount of urine produced in a given time period, and plasma concentration refers to the concentration of inulin in blood plasma after intravenous administration.
What are the main advantages of inulin?
Non-toxic, plant polysaccharide, free filtered, measurable in plasma & urine.
What are the disadvantages of inulin?
Must be infused for a short period of time.
Why can creatine be used to determine GFR?
Waste product from creatine phosphate in muscle metabolism; the amount of creatine released is relatively constant. Stable renal function confers for stable creatine level in urine. Minor proportion of creatine is secreted by the efferent arteriole, although the estimation of creatine in the blood and urine can account for that to enable GFR calculations.
Low creatine clearance or high plasma creatine indicative of renal failure.
Which substance is secreted and filtered by the kidney?
PAH
What is a symport mechanism?
Moves multiple substances in the same direction simultaneously
What is an antipode mechanism?
Movement of multiple substances in opposite directions across the cell membrane
Which transports involve the movement of glucose and sodium ions into the PCT tubule cells?
SGLT-2 symport protein
Where are SGLT-2 symport proteins integrated within the PCT tubule?
Apical membrane
How are sodium ions reabsorbed into the tubule cells?
Sodium-potassium ATPase pump on basilar surface, sodium ions are actively transported extracellular at the base surface into the interstitial space and subsequently into the peritubular capillaries
How does glucose leave the PCT tubule cells?
By the GLUT-2 cotransporter proteins on basal membrane
How is acid-base balance maintained within PCT cells?
Recovery of bicarbonate (HCO3-) is essential to the maintenance of acid-base balance; catalysed by carbonic anhydrase activity on the apical membrane of PCT cells. Within the lumen of the PCT, HCO3- combines with hydrogen ions to form carbonic acid Enzymatically catalysed into CO2 & water, diffuses across apical membrane into the cell.
Water osmotically moves across the phospholipid bilayer membrane due to embedded aquaporin water channels.
Intracellularly, reverse reaction occurs whereby the water and carbon dioxide form carbonic acid dissociates into H+ and HCO3- .The HCO3- ions are co-transported with Na+ across the basal membrane to the interstitial space.
Na+/H+ NHE3 antiporter excretes H+ into the lumen, recovering Na+.
Which hormone regulates the amount of sodium reabsorption into circulation by increasing the translation of NHE3-Na/H anti porters?
Angiotensin-II
Which hormones controls the calcium renal reabsorption within DCT tubule cells?
Parathyroid hormone (PTH) Vitamin D
What role does PTH have on calcium renal reabsorption?
Induces insertion of calcium channels on luminal surface
Influx of calcium intracellularlly
Calcitrion induces calcium binding proteins that transports calcium into the cell , assets with exocytosis of calcium across the basolateral membrane
Why is there no water reabsorption within the early distal convoluted tubule?
There are no aquaporins present, thus there is no water reabsorption
Explain chloride ion absorption within the early DCT?
Apical Na+/Cl- symporter, passive diffusion of Na+ along concentration gradient established by the Na+/K+ ATPase basal membrane pump; energy released through passive diffusion enables transporter of Cl- into the distal convoluted tubule cell. Cl- leaves the cell into the interstitial space through concentration gradient into the peritubular capillaries.
What is the role performed by principal cells?
Sodium reabsorption & potassium secretion. Principal cells have a low mitochondrial density due to the passive diffusion of sodium ions intracellularly, and potassium efflux.
Aldosterone regulates Na+ reabsorption by increases apical Na+ channels & basolateral Na+-K+ ATPase pumps.
Anti-diuretic hormone (ADH) regulates water reabsorption by increasing apical aquaporins (Present within intracellular vesicles, ADH signals increased vesicle fusion to embed aquaporins).
What are intercalated cells?
Intercalated cell: Secretes or absorbs acid/bicarbonate Regulation of blood pH. Intercalated cells reabsorb K+ & HCO3-, while secreting H+. This function reduces the acidity of the plasma, and subsequently increases urine acidity; this mechanism is achieved by carbonic anhydrase activity.
Mitochondrial rich
What are alpha intercalated cells?
HCO3- reabsorption & H+ secretion.
What are beta intercalated cells?
HCO3- secretion & H+ reabsorption.
What is the trigone area?
Stretching of this triangular region to its limit signals the brain about the need for urination
What does the detrusor muscle do?
Contracts to build pressure in the urinary bladder to support urination
What is the internal sphincter?
Involuntary control to prevent urination
What is the external sphincter?
Voluntary control to prevent urination
What is the bulbourethral gland?
Produces thick lubricant which is added to watery semen to promote sperm survival.
What is the filtration fraction?
GFR/RPF,usually 0.15-0.2
When does the renal clearance equal RPF?
If the total amount of a molecule entering the kidney equals the amount excreted.
