Urinary System Flashcards
Describe the position of the kidneys (2)
- Paired retroperitoneal organs
- Lie either side of the vertebral column between T12 and L3
Explain why the two kidneys are not perfectly horizontal with each other (2)
- Right kidney is pushed upwards by position of the liver
- Left kidney is pushed downwards by position of the heart
Name 4 functions of the kidneys (4)
- Regulation of key substances in ECF
- Excretion of waste products e.g. Urea
- Endocrine function (renin, prostaglandins, erythropoietin)
- Metabolism e.g. active form of vitD, PTH etc.
Which portions of the nephron are in the kidney medulla?
- Loop of Henle
- Collecting duct
Where is the site of ultrafiltration?
Glomerulus in the kidney cortex
What is filtered out of the blood at the glomerulus?
- Water
- Electrolytes
- Small molecules e.g. Glucose, AA
Why is the oncotic pressure of the Bowman’s capsule lower than that of the capillary oncotic pressure?
- Proteins are too large to be filtered out of the capillaries
- The protein composition of the filtrate relative to that of the capillary is therefore very low
Where is the major site of reabsorption of filtrate?
Proximal convoluted tubule (PCT)
What determines GFR and how is this maintained?
- Capillary filtration pressure in glomerulus
- Maintained by the difference in lumen sizes between the afferent and efferent arterioles
Explain how the osmolarity of the filtrate is maintained during selective reabsorption (2)
- Ions (mainly Na+ and Cl-) are reabsorbed from the filtrate using specialised iron channels into the interstitium, therefore the osmolarity of the filtrate in the nephron decreases (filtrate is hypertonic)
- Water follows ions and moves down an osmotic gradient out of the filtrate into the interstitium, therefore the osmolarity of the filtrate increases - solution remains ISOSMOTIC
Where is the majority of Na+ reabsorbed?
PCT (60-70%)
What is normally reabsorbed at the PCT?
- 100% Glucose and AA
- 60-70% Na+ and water
- 80-90% K+ and HCO3-
Which pump is mainly responsible for setting up the Na+ gradient at the PCT and where is this located? (2)
- Na+/K+ ATPase
- Located on the basolateral membrane
Explain how glucose is reabsorbed at the PCT (3)
- Na+/K+ ATPase transported 3Na+ out of the tubule cell and into the interstitium therefore the [Na+]i decreases
- This sets up a gradient and Na+ moves from the filtrate into the tubule cell from a high to low concentration
- Na+/Glucose symporter utilises the passive transport of Na+ to actively transport Glucose into the cell via secondary active transport
How much fluid does the glomerulus filter in a day?
~180L
What is a renal corpuscle?
Structure formed from the glomerular tuft and the Bowman’s capsule
Embryologically, how is the Bowman’s capsule formed?
Ureteric bud extends from minor calyces and dilates at end, wrapping around the glomerular tuft and enclosing it in a double membrane (parietal and visceral)
What kind of epithelia lines the Bowman’s capsule?
Simple squamous
Which two membranes form the filtration barrier of the glomerulus?
- Capillary endothelium
- Visceral layer of the Bowman’s capsule
Explain how the composition of the filtration barrier aids in the filtration of the blood through the glomerulus (3)
- Fenestrated capillary endothelium = very leaky!
- Podocytes invest in capillary endothelium using foot processes and produce filtration slits between processes
- Shared basement membrane minimises resistance to filtration
Describe the histological appearance of the PCT (3)
- Simple cuboidal epithelia arranged in circles
- Pronounced BRUSH BORDER on luminal/apical surface to increase surface area for reabsorption
- Centrally positioned nuclei
What type of cells line the limbs of the loop of Henle and how can they be distinguished from other structures? (2)
- Simple squamous epithelia line the thin descending limb (looks like small capillary but no RBC)
- Simple cuboidal epithelia line the thick ascending limb (but no brush border like PCT)
How does the DCT differ histologically from the PCT? (3)
- Larger lumen
- Nuclei positioned towards the apical/luminal surface
- NO BRUSH BORDER
Where does the DCT make contact with the glomerulus?
Juxtaglomerular apparatus