Urinary System Flashcards
What is the predominant cation and anion in the extracellular fluid?
cation is sodium and anion is chloride
How do the kidneys affect the intra-cellular composition of ions?
By directly affecting the concentration of ions and small molecules in the ECF
How is ultra-filtrate different to plasma?
Ultra-fitrate doesn’t contain cells and large organic molecules that are found in plasma
What are the 5 main functions of the urinary system?
Control the concentration of substances in the ECF and therefore control the osmolarity of the ECF. Also, to control pH, excrete waste products and control the volume of ECF.
These then impact on blood pressure, cell function and cell size
From what type of mesoderm does the urinary system originate?
Intermediate mesoderm
What are the 3 embryological types of kidney systems and how are they different?
Pronephros is initial one, in cervical region. Never functions in humans but does involve nephrotomes and develops alongside a duct which runs from cervical region to cloaca.
Next is Mesonephros which develops caudally to pronephros. This is the embryonic kidney. It’s duct is functional but can’t conserve water so can’t concentrate urine. It also sprouts the ureteric bud which drives the development of the final stage.
Metanephros is last one, which starts off as metanephric blastema. This develops into the true kidney. The ureteric bud makes conact with the blastema and eventually develops into calyces and the renal pelvis
Through what developmental error, can there by duplication of the ureter?
By complete splitting of the ureteric bud
What are the three parts of the urogenital sinus?
Bladder part, pelvic and phallic sections
What are the four parts of the male urethra?
pre prostatic, prostatic, membranous and spongy
How many litres, roughly, of ECF are there?
About 15 litres
Roughly at which vertebral level, are the kidneys located?
T12-L3
Which are the three most common sites of blockage caused by kidney stones?
Junction of renal pelvis and ureter
Where ureter crosses pelvic brim
Where ureter enters bladder wall
What are supernumerary renal arteries?
Where there’s more than one renal artery going to one kidney
What parts of the nephron are located in the medulla?
Loop of Henle and collecting duct
What is the average GFR?
Roughly 125 ml/min
What are the two main sections of the renal corpuscle and what are they made up of?
Vascular pole - afferent and efferent arterioles and the glomerulus
Urinary pole - Bowman’s capsule
What makes up the filtration barrier of the renal corpuscle?
The visceral layer of bowman’s capsule (podocytes) and capillary endothelium (v leaky + fenestrated)
Where in the nephron is lined by simple squamous epithelium?
Glomerulus parietal layer and endothelium
Thin descending and ascending limb on loop of Henle
Everywhere else is simple cuboidal
Where in the loop of Henle does active transport not take place?
Thin limbs
What makes up the juxtaglomerular apparatus?
Macula densa
Juxtaglomerular cells of afferent arteriole
Extraglomerular mesangial cells
Compare the appearance of the collecting duct to the thick ascending limb
Both have simple cuboidal but collecting duct lumen is larger and less regular
Describe the path that collecting ducts take through the renal medulla
Ducts merge to form larger ducts. First form ducts of bellini, then renal papillae and then exit into calyx
What layers of smooth muscle are there in the urinary bladder?
2 Circular layers and 1 longitudinal
How does the diameter of glomerular arterioles contribute to filtration?
Diameter of afferent arteriole is always slightly bigger than the efferent arteriole so pressure of blood inside the glomerulus is increased so there’s increased hydrostatic pressure so filtration is promoted
What are the 3 forces involved in plasma filtration?
Hydrostatic pressure in cappilary
Hydrostatic pressure in capsule
Osmotic gradient between capillary and tubule
What types of sodium channels are found on apical membranes in different parts of the tubule?
PCT - Na-H antiporter and Na-GLucose symporter
Loop of Henle - Na-K-2Cl symporter
Early DCT - Na-Cl symporter
Late DCT and collecting tubule - ENaC
What is the Transport maximum?
Renal threshold for glucose = 200mg/ml
Point at which further increases in concentration do not result in increased filtration/excretion
How is clearance calculated?
(urine flow rate x amount in urine)/ arterial plasma concentration
What is the reference range for GFR in men and women?
Men = 115-125 ml/min Women = 90-100ml/min
How is renal plasma flow calculated?
Plasma makes up about 55% of renal blood flow. = 0.55 x rbf = 0.55 x 1.1 = 605ml/min
How is filtration fraction calculated?
= gfr divided by renal plasma flow
What is the autoregulatory response to decreased BP?
Dilation of afferent arteriole to increase hydrostatic pressure in capillary
What is the tubular glomerular feedback response to increased NaCl concentration?
GFR needs to decrease so juxtaglomerular apparatus is stimulated to release adenosine to cause vasoconstriction of afferent arteriole
What happens to ECF volume if sodium excretion is less than sodium uptake?
Sodium is retained, primarily in ECF so water leaves the nephron which increases ECF volume. There is therefore an increase in blood volume and arterial pressure and there may subsequently be oedema
What channels are there apically in Section 1 of the PCT?
Sodium/glucose co transporter
Na/H exchanger
Contransport of sodium with amino acids/ carboxylic acids/ phosphate
also aquaporin channels
What electrolyte transport occurs apically in S2/S3 of PCT?
Na/H exchange
paracellular and transcellular chloride transport
What are the driving forces behind water reabsorption of PCT?
Oncotic force of peritubular capillary
Osmotic gradient between tubule and interstitium
Hydrostatc force in intersitium
Describe sodium reabsorption in descending limb of loop of Henle
Doesn’t absorb sodium but instead has no tight gap junctions so there’s paracellular uptake of water
Describe sodium reabsorption of ascending limb
Descending limb concentrated filtrate so there’s reabsorption of sodium through NaKCC2 channel and secretion of potassium via ROMK channel.
Describe sodium reabsorption of DCT
Early DCT isn’t very permeable to water to is very diluting. Sodium is reabsorbed via Na/Cl- symporter. There’s also calcium reabsorption
Describe action of principle cells of collecting duct
70% of cells in CD are principal cells.
Reabsorb sodium through ENaC but this sets up electrical gradient in lumen for paracellular chloride uptake. Also variable uptake of water through aquaporin 2 channels, sensitive to ADH
What are the four neurohormonal factors that control blood pressure?
RAAS
Natriuretic peptide hormone
ADH
sympathetic nervous system
How does the sympathetic nervous system act to increase blood pressure?
Acts on alpha1 receptors to cause vasoconstriction of afferent and efferent arterioles to decrease renal blood flow and so GFR. This stimulate reabsorption of sodium via NHE of PCT. Also stimulates renin release
Also acts on beta1 receptors to increase rate and force of heart contraction
How does atrial natriuretic peptide act to control blood pressure?
Release from atrial myocytes in response to stretch (increased BP) cause vasodilation of afferent arteriole of glomerulus to increase sodium excretion by increasing GFR
When is renin released?
Due to reduced perfusion pressure at baroreceptors in afferent arteriole of kidney.
Also due to reduced NaCl concentration at macula densa. Granular cells of juxtaglomerular apparatus is sympathetically stimulated to release renin
How does renin lead to angiotensin 2 production?
Renin cleaves angiotensinogen into angiotensin 1. this is cleaved into angiotensin 2 by ACE
What actions does angiotensin 2 have?
Breaks down bradykinin to reduce vasodilation
Acts on vascular smooth muscle to cause vasoconstriction of arterioles
Acts on PCT to increase sodium reabsorption.
Acts of principal cells of collecting duct to stimulate sodium reabsorption via ENaC channels
Stimulates release of noradrenaline
Stimulates release of ADH from hypothalamus
What action does ADH have?
Inserts aquaporins into apical membrane of principal cells in collecting duct to increase water retention
Stimulates NaK2Cl in thick ascending limb to increase sodium reabsorption
Why are prostaglandins important in blood pressure control?
Have vasodilation action and locally act to enhance glomerular filtration and decrease sodium reabsorption. Act as a buffer to excessive vasoconstriction caused by SNS and RAAS
Why are NSAIDs dangerous to give to patients with renal/cardiovascular disease?
Inhibit formation of prostaglandins so in renal disease, cause further vasoconstriction so further reduction of GFR and can cause acute renal failure.
Can exacerbate heart failure and hypertension by increasing sodium and so water retention.
What are some adrenal causes of secondary hypertension?
Conn’s syndrome - aldosterone secreting adenoma
Cushing’s syndrome
Phaeochromocytoma - tumour of adrenal medulla
How does renovascular disease cause hypertension?
Occlusion of renal artery decreases perfusion pressure in that kidney so renin is stimulated to be released from JGA cells causing vasoconstriction and increased sodium reabsorption in other kidney
How can hypertension be treated?
ACE inhibitors
Thiazide diuretics - inhibit Na/Cl cotransporter in DCT but can cause hypokalaemia
Beta blockers to decrease heart rate and contractility
vasodilators - alpha1 blockers reduce sympathetic tone
calcium channel blockers reduce entry into smooth muscle cells
What is the steady osmolality of body fluid?
275-295 mOsm/kg
Where are changes in osmolarity detected?
By osmoreceptors in Organum Vasuloum of the Laminae Terminalis in the hypothalamus
What maintains the concentration gradient set up by the loop of Henle and counter current multiplication?
Counter current exchange by Vasa Recta
Where is ADH released from?
Posterior pituitary gland
What effects does ADH have on different parts of the nephron?
Vasoconstriction of afferent arteriole
Increased Na, K and Cl reabsorption in TAL
Increased water reabsorption in late DCT and CD
Increased K+ secretion in cortical CD
Increased urea reabsorption in Medullary CD
How does ADH increase water reabsorption?
Causes insertion of Aquaporin 2 channel on apical membrane, via a GPCR. There are always aquaporin 3 and 4 present so water enters cell and leaves across basolateral membrane. AQP2 is then retrieved by endocytosis in absence of ADH
What happens in SIADH syndrome?
Loss of negative feedback of ADH secretion so there’s massive water retention, causing big drop in blood osmolarity and so causes hyponatraemia
In plasma, in what forms does calcium exist?
45% as free ionised calcium
45% protein bound (80% of which bound to albumin)
10% complexed to citrates/phosphates etc
How is intestinal absorption of calcium controlled?
By vitamin D.
Where in the nephron is calcium reabsorbed?
65% in PCT
25% in loop of Henle
10% in DCT
Where is vitamin D produced?
D2 is absorbed in the gut and D3 is synthesised in the skin in the presence of UV light
How is vitamin D activated?
Hydroxylated in liver to calciferol then it travels to the kidneys where it’s hydroxylated to calcitriol, it’s activa form
What actions do calcitriol and PTH have on calcium?
Calcitriol binds to calcium in the gut, increasing its absorption
PTH Increases conversion of calciferol to calcitriol. It also increases reabsorption of calcium from kidney and increases its release from bone and decreases reabsoprtion of phsophate and bicarbonate