Urinary System Flashcards
Describe the alterations to the filtrate as it travels along the nephron:
Filtration occurs at glomerulus, pressure is maintained by specialised circulation. In PCT reabsorption occurs via peri tubular capillaries but filtrate remains isotonic. Further reabsorption and countercurrent multiplication occurs in the loop of Henle allowing the formation of concentrated urine. DCT continues reabsorption of water and electrolytes to produce a hypotonic secretion. In the collecting duct water can be further reabsorbed by inserting Aquaporins using ADH.
Describe the development of the kidney from the intermediate mesoderm of the trilaminar disc:
Pronephros develops pronephric duct which drives development.
Mesonephros develops caudally and mesonephric duct sprouts ureteric bud to induce development = embryonic kidney.
Metanephros develops in caudal region (definitive kidney), differentiation driven by ureteric buds action on metanephric blastema.
Ascent of metanephric kidney from pelvic region crossing arterial fork formed by vessels returning blood to placenta.
What is the urogenital ridge?
Region of intermediate mesoderm gives rise to the embryonic kidney and the gonad
What causes renal agenesis?
Ureteric bud fails to interact with the metanephric blastema causing oligohydramnios.
What is a Wilm’s tumour?
Nephroblastoma, malignant tumour containing metanephric blastema, stroma and epithelial derivatives.
What is the cloaca?
Single structure where GI, urinary and reproductive tracts end in region of the hind gut.
What is the urachus?
Fibrous remnant of canal that drains foetal bladder (allentois) that becomes median umbilical ligament.
How is the male urethra formed?
The mesonephric ducts make independent openings in the urogenital sinus and the prostate and prostatic urethra are formed.
What are the functions of the kidneys?
Regulation and control of concentrations of substances in extracellular fluid
Excretion of waste products
Endocrine- synthesis of renin, erythropoietin, prostaglandins
Metabolism- activation of vitamin D, catabolism Of insulin, PTH and calcitonin
Regulation of acid-base balance
Describe the alterations to the filtrate as it travels along the nephron:
Filtration occurs at glomerulus, pressure is maintained by specialised circulation. In PCT reabsorption occurs via peri tubular capillaries but filtrate remains isotonic. Further reabsorption and countercurrent multiplication occurs in the loop of Henle allowing the formation of concentrated urine. DCT continues reabsorption of water and electrolytes to produce a hypotonic secretion. In the collecting duct water can be further reabsorbed by inserting Aquaporins using ADH.
Describe the development of the kidney from the intermediate mesoderm of the trilaminar disc:
Pronephros develops pronephric duct which drives development.
Mesonephros develops caudally and mesonephric duct sprouts ureteric bud to induce development = embryonic kidney.
Metanephros develops in caudal region (definitive kidney), differentiation driven by ureteric buds action on metanephric blastema.
Ascent of metanephric kidney from pelvic region crossing arterial fork formed by vessels returning blood to placenta.
What is the urogenital ridge?
Region of intermediate mesoderm gives rise to the embryonic kidney and the gonad
What causes renal agenesis?
Ureteric bud fails to interact with the metanephric blastema causing oligohydramnios.
What is a Wilm’s tumour?
Nephroblastoma, malignant tumour containing metanephric blastema, stroma and epithelial derivatives.
What is the cloaca?
Single structure where GI, urinary and reproductive tracts end in region of the hind gut.
What is the urachus?
Fibrous remnant of canal that drains foetal bladder (allentois) that becomes median umbilical ligament.
How is the male urethra formed?
The mesonephric ducts make independent openings in the urogenital sinus and the prostate and prostatic urethra are formed.
What are the functions of the kidneys?
Regulation and control of concentrations of substances in extracellular fluid
Excretion of waste products
Endocrine- synthesis of renin, erythropoietin, prostaglandins
Metabolism- activation of vitamin D, catabolism Of insulin, PTH and calcitonin
Regulation of acid-base balance
How is the female urethra formed?
The mesonephric ducts regress and the ureteric bud opens into the urogenital sinus, the female urethera is formed by the pelvic part of the urogenital sinus.
How are external genitalia formed?
By the genital tubercle, folds and swellings. In males the GT elongates and the folds fuse to form the spongy urethra, in females there is no fusion and the urethra opens into the vestibule.
What is a fistula?
Abnormal connection between two hollow spaces e.g. Urorectal fistulae.
What causes hypospadias?
Direct fusion of urethral folds so urethra opens onto ventral surface rather than the end of the glans
What is meant by a renal corpuscle?
Primitive renal tubule derived from ureteric bud grows into primordium of true kidney and envelops the glomerulus.
What makes up the bowman’s capsule?
Simple squamous parietal and visceral layers and pod oxygen with food processes and filtration slits that share a basement membrane with the capillary endothelium.
What epithelium is used in each part of the nephron?
PCT- simple cuboidal with brush border Descending Loop of Henle- simple squamous Thick ascending limb-simple cuboidal DCT- simple cuboidal Collecting duct- simple cuboidal
What makes up the juxtoglomerular apparatus?
Macula densa, juxtaglomerular cells of afferent arteriole, extra glomerular mesangial cells
What are the differences between cortical and juxtamedullary nephrons?
The loop of Henle in juxtamedullary nephrons is longer and these nephrons have vasa recta instead of peri tubular capillaries.
Explain the pressures acting on the filtrate at the glomerular tuft:
Hydrostatic pressure in capillary forcing filtrate out
Hydrostatic pressure of bowman’s capsule forcing filtrate back in
Oncotic pressure difference forcing filtrate back in
Explain what is meant by autoregulation?
Keeps GFR normal limits (80-180mmHg).
Myogenic- smooth muscle reacts to being stretched by constricting
Tubular glomerular feedback- macula densa acts as a sensor, concentration-dependent salt uptake through NaK2Cl cotransporters. Increased GFR leads to increased sodium and chloride delivery which stimulates the JGA to release adenosine for vasoconstriction and prostaglandins for vasodilatation.
How are solutes and water reabsorbed in the PCT:
Sodium moves down its concentration gradient into the apical cells using the gradient established by the sodium-potassium-ATPase. Sodium and glucose are also reabsorbed via a cotransporter.
What transporters are used to reabsorb sodium in the nephron?
PCT- Na-H antiporter, Na-glucose symporter
Loop of Henle- NaK2Cl symporter
DCT- NaCl symporter and ENaC
How does secretion occur in the nephron?
By transepithelial transport using an Na-H antiporter driving the cation exchanger and passive carrier-mediated diffusion down favourable gradients.
What is the filtration fraction?
Proportion of the substance that is actually filtered
What is meant by renal clearance?
The volume of plasma that is completely cleared of a substance by the kidneys per minute
How is renal clearance calculated?
(Substance concentration in urine X volume of urine) / concentration of urine in plasma
What features must a substance have to be used to determine GFR?
Freely filtered
Detectable
Unable to be secreted/reabsorbed
How would you calculate eGFR?
(140-age) X mass(kg) X constant // serum creatinine
What is the filtered load?
Amount of substance that is freely filtered that enters the renal tubule. Calculated as plasma conc X GFR
What is the renal threshold?
Plasma concentration of a substance at which transport maximum (Tm) is reached and the substance spills into urine
What is glomerulotubular balance?
Blunting of Na+ excretion in response to GFR changes so if GFR spontaneously increases the rate of sodium and water reabsorption increases proportionally.
How are solutes reabsorbed along the loop of Henle?
Paracellular uptake of water in descending limb leading to high concentration of solutes in filtrate at loop. Sodium is reabsorbed passively paracellularly in the thin ascending limb. In the thick ascending limb there is active sodium and chloride uptake through the NaK2Cl channel but it is impermeable to water so fluid leaving the loop is hypo-osmotic.
What cotransporters are in the DCT that allow reabsorption of sodium and therefore water?
NCC transporter on apical membrane
NCX exchanger on basolateral membrane
Gradient established by sodium-potassium ATPase
What are the effectors of change in volume control?
Changes in osmotic pressure and hydrostatic pressure causing changes in GFR.
Sodium reabsorption in PCT stimulated by RAAS
Principle cells of CD and DCT affected by aldosterone
What is the RAAS?
RAAS is responsible for long term regulation of blood pressure.
Renin released from granular cells of JGA, stimulated by NaCl delivery, reduced perfusion pressure or sympathetic stimulation.
Renin converts angiotensin to angiotensin I which is then converted to angiotensin II by ACE present on epithelial cells.
Angiotensin II stimulates aldosterone release.
What are the actions of angiotensin II?
Vasoconstrictor, causes ADH, aldosterone and noradrenaline release, stimulates sodium reabsorption via Na-H exchanger.
What is the action of aldosterone?
Acts on principal cells to stimulate sodium and water reabsorption via ENaC channels and stimulates sodium-potassium-ATPase
What is the effect of sympathetic stimulation on the kidney?
Causes vasoconstriction thus decreasing GFR and sodium excretion. Activates the Na/H exchanger and basolateral sodium-potassium-ATPase. Stimulates release of renin from JGA.
What are natriuretic peptides?
Synthesised and stored in atrial myocytes released in response to stretch and low pressure volume sensors in the atria.
Decreased ECV inhibits release of ANP to increase BP.
How do NSAIDs affect the kidney?
Inhibit cyclo-oxygenase pathway that results in prostaglandin formation (vasodilators).
How does dopamine affect the kidney?
Formed locally in kidney from circulating L-DOPA causing vasodilation and increased renal blood flow thus reducing sodium chloride reabsorption by inhibiting NH exchanger in principal cell membranes
How does renovascular disease lead to hypertension?
Renal artery stenosis causes decreased perfusion so increased renin.
How does renal parenchymal disease lead to hypertension?
Early loss of vasodilator substances and later sodium and water retention due to inadequate glomerular filtration
What is Conn’s syndrome?
Aldosterone secreting adenoma
How would you manage a patient with chronic hypertension?
ACE inhibitors, angiotensin II receptor antagonists, thiazides/spironolactone, vasodilators and potentially beta-blockers
Where are osmoreceptors located exactly?
The organum vasculoum of the lamina terminalis (OVLT) anterior and ventral to the third ventricle in the hypothalamus
What is the effect of ADH on plasma osmolarity?
ADH receptors when activated cause the change of ATP to cAMP by adenylyl cyclase which then activates PKA to insert AQP2 channels into the apical membrane of the collecting duct thus increasing retention of water.
What are the consequences of ADH?
Vasoconstriction that reduces GFR
Increased solute reabsorption in thick ascending limb
Increased water reabsorption and potassium secretion
Increased water and urea reabsorption in the medulla
What is diabetes insipidus?
Pituitary gland does not produce enough ADH/acquired ADH insensitivity