The Genitourinary System

Question 1

What are the functions of the kidney?

Answer 1

Homeostasis - of bodily fluids, electrolytes and acid base balance

Excretion - of metabolic products e.g. uria uric acid, creatinine

Excretion- of foreign substances, eg drugs

Regulates - blood pressure

Secretes - hormones eg. Erythropoietin and renin

Question 2

What is the structure of the kidney ?

Answer 2

Outer cortex

Inner medulla

Vasculature: renal artery, renal vein

Drains into ureter, first from the minor calyx, then the major calyx then into ureter

Question 3

What is the schematic of the renal blood supply?

Answer 3

Renal artery ->

Segmental artery ->

Interlobar artery ->

Arcuate artery ->

Interlobular artery ->

Afferent arteriole ->

Glomerular capillaries ->

Efferent arteriole ->

Peritubular capillaries ->

Interlobular vein ->

Arcuate vein ->

Interlobar vein ->

Renal vein

Question 4

What is the structure and function of different parts of the bladder and urethra?

Answer 4

Bladder sits above urethra

Detrusor muscle - contracts to build pressure in the urinary bladder to support urination

Trigone - stretching of this triangular region to its limit signals the brain about the need for urination

Internal sphincter - involuntary control to prevent urination

External sphincter - voluntary controlled to prevent urination

Bulbourethral gland - produces thick lubricant which is added to watery semen to promote sperm survival

Question 5

What is the structure of the nephron (functional unit of kidney) ?

Answer 5

Glomerulus - blood vessels

Now mans capsule - sits around blood vessels

Proximal convoluted tubule - epithelial cells are rich in mitochondria

Thin descending loop of henle

Thin ascending loop of henle - both thin loops have a low conc of mitochondria

Thick ascending loop of henle - epithelial cells are rich in mitochondria

Distal convoluted tubule - epithelial cells rich in mitochondria

Collecting duct - principal cells (low mitochondria). Intercalated cells (high mitochondria)

Question 6

What are the types of nephron?

Answer 6

Superficial nephron - glomerulus and convoluted tubules in cortex, loop of henle only goes into outer medulla. Ten times more of these than other type

Juxtaglomerular nephron - glomerulus and convoluted tubules in cortex. Loop of henle goes all the way into inner medulla

The many loops of henle gove the medulla of the kidney it’s striated appearance

Question 7

What is the structure and function of the juxtaglomerular apparatus?

Answer 7

Macula densa - part of distal convoluted tubule, regulates glomerular contraction rate through tubulo glomerular feedback mechanism

Juxtaglomerular cells - on afferent arteriole, renin secretion for regulating blood pressure

Extraglomerular mesangial cells

Question 8

What is the schematic/order of the renal processes?

Answer 8

Afferent arteriole - blood in

Glomerulus - glomerular filtration

(Efferent arteriole - blood out)

Proximal DCT -> collecting duct - reabsorption (selective), secretion and excretion

Different substances under oof different combination of these processes

Question 9

What is glomerular filtration?

Answer 9

Passive process: fluid is driven through the semipermeable glomerular capillaries into the Bowmans capsule space by the hydrostatic pressure of the heart

The filtration barrier (size and charge dependant): Highly permeable to fluids and small solids. Impermeable to cells and proteins

In the capillaries of the glomerulus there are fenetstrae

On the bowmans capsules there are epithelial podocytes. These have slits between them, and slit diaphragms that cross these slits. This is another layer of filtration to get water and small solutes through

Question 10

What are the pressures that contribute to glomerular filtration?

Answer 10

Hydrostatic pressure (pushing): exerted by fluid. Solute and fluid molecules pushed out

Oncotic pressure (pulling): solute (eg. Proteins) exert this. Fluid molecules drawn in across a semipermeable membrane

Question 11

What is the net ultrafiltration pressure?

Answer 11

HPgc = hydrostatic pressure in glomerular capillaries

HPbw = hydrostatic pressure in bowman capsule

(Pi)gc= oncotic pressure of plasma proteins in glomerular capillaries

(There is no pi bw because no large solutes will be present in it so it’s negligible)

Puf = net ultrafiltration pressure

Puf = HPgc - HPbw -Pi gc

Question 12

What is the glomerular filtration rate (GFR)?

Answer 12

The amount of fluid filtered from the glomeruli into the Bowmans capsule per unit time (mL/min)

Some of filtration rate of all functioning nephrons

GFR = Puf x Kf

Where Kf is an ultrafiltration coefficient (membrane permeability and surface area available for filtration)

Any changes in filtration forces or Kf will result in GFR imbalances

Healthy male and female: 90-140 mL/min and 80-125 mL/min respectively

A fall in GFR is the cardinal feature of renal disease, with a buildup of excretory product in the plasma

Question 13

What are the two mechanisms for regulation of GFR?

Answer 13

1. Myogenic mechanism

2. Tubulo glomerular feedback mechanism

Question 14

How does the myogenic mechanism of regulation of GFR work?

Answer 14

Arterial pressure increases ->

Afferent arteriole stretches (maybe due to BP) ->

Arteriole contracts ->

Vessel resistance rises ->

Blood flow reduces ->

GFR stays the same

Question 15

What is the tubulo glomerular feedback mechanism?

Answer 15

Increase/decrease in GFR ->

Increased/decreased NaCl in loop of henle ->

Change detected by macula densa ->

Increased/decreased ATP and adenosine discharged ->

Afferent arteriole constricts/dilates ->

GFR stabilises

Question 16

What is renal clearance?

Answer 16

Renal clearance is the number of litres of plasma that are completely cleared out of the substance per unit time

Renal clearance is only concerned with the excretory role played by the kidneys, i.e. rate of removal of a substance X from the blood and excretion through urine

Therefore, this concept finds its use in the calculation of GFR, renal plasma flow and to understand the excretory route of a substance

C = U x V / P mL/min

U is concentration of urine, V is rate of urine production, P is concentration of substance in plasma

Question 17

What is the practical determination of GFR?

Answer 17

If a molecule is freely filtered and neither reabsorbed nor secreted in the nephron than the amount filtered equals the amount excreted. Thus GFR can be measured by measuring renal clearance of this molecule

Ideal molecule: inunlin:

Plant polysaccharide. Freely filtered and neithe reeabsorbed or secreted. Not toxic. Measurable in urine and plasma. However not found in mammals so has to be transfused

Commonly used: creatinine:

Waste product from creatine in muscle metabolism. Amount released is fairly constant. If renal function is stable, so is amount of creatinine. Low creatinine clearance or high plasma creatinine may indicate renal failure. It is not a prefect molecule as although it is freely filtered and not reabsorbed, a small amount is secreted into the nephron

Question 18

What is renal plasma flow and filtration fraction?

Answer 18

If the total amount of the molecule entering the kidney equals the amount excreted, then the renal clearance of this molecule equals the renal plasma flow

PAH (para aminohippurate) is used as all the PAH is removed from the plasma passing through the kidney through filtration and secretion

The ratio of the amount of plasma which is filtered and which arrives by the afferent arteriole is defined as the filtration fraction (FF). It’s value ranges from 0.15-0.20 normally. A value of 0.15 suggests that 15% of the plasma has been filtered

FF = GFR/RPF

Question 19

What are the main methods of transport of molecules?

Answer 19

Passive: diffusion, osmosis, electrical gradient difference

Active:

Primary - active transport, endocytosis

Secondary - co transport (symport/anti port)

Question 20

Please can u note bank all of the specific transport mechanisms of ions?

Answer 20

Okay