Urinary S1 - Introduction Flashcards
How much ultra filtrate do kidneys produce daily?
~180L
The kidneys produce ultra-filtrate. What is ultra filtrate?
Plasma after blood cells and large proteins have been removed.
How efficient are kidneys at filtering plasma?
They filter ~20% of plasma volume at each pass through the kidneys
What are the names and order of kidney areas?
Glomerulus Proximal convoluted tubule (PCT) Loop of Henle (intermediate tubule) Distal convoluted tubule (DCT) Collecting duct
Where does filtration occur?
In the glomeruli of the nephron, in the cortex
Describe the glomeruli
Specialised circulation maintains filtration pressure
Afferent and efferent arterioles
Determines glomerular filtration rate
Describe the PCT
Major reabsorption site
Filtrate remains isotonic
Reabsorbed materials leave by peritubular tubules
What is re absorbed from ultrafiltrate in the PCT?
~60-70% of Na and H2O
~80-90% of K
~90% of bicarbonate
100% of glucose and amino acids
Why does filtrate remain isotonic after the PCT?
Water follows ions so only so much water leaves as ions are reabsorbed
In what circumstance would <100% of glucose be reabsorbed?
In patients with diabetes, blood glucose may be high so some glucose may not be re absorbed from the ultrafiltrate, resulting in polydipsia and polyuria
What does it mean when we say a cell is polarised?
The membranes of opposite poles (ie basolateral vs luminal membranes) of that cell may have different properties
This allows transport across an epithelium
How is sodium transport involved in reabsorption in the PCT?
Na is pumped out from the basolateral membrane
Na enters cell through luminal membrane down concentration gradient
Energy from this drives reabsorption of other substances eg glucose
Water follows electrolytes osmotically
Describe the loop of Henle
Site of further salt reabsorption which dips into and out of the medulla
Uses counter current multiplication to create a gradient of increasing osmolarity in the medulla
This allows formation of concentrated urine if water needs to be conserved
Describe the DCT
Major site of variable reabsorption of electrolytes and water in cortex
Actively secretes hydrogen ions to maintain pH balance
What is diuresis and how does it occur?
It is large volumes of dilute urine
Occurs when water does not follow reabsorption of electrolytes in the DCT
Describe the collecting duct
Passes through the high osmolarity environment of the medulla (created by the loop of Henle) to the renal pelvis
Water moves down its osmotic gradient to produce a low volume of concentrated urine if possible
If now, urine remains dilute
Describe the variable reabsorption of Na
Occurs in the distal nephron
Controlled by a hormone system: the renin-angiotensin system
This controls ECF volume
Describe the variable reabsorption of water
Occurs in the distal nephron
Controlled by hormone system: ADH
ADH controls permeability of DCT and collecting duct to water
His controls ECF osmolarity
Describe and explain the metabolic demands of the kidney
Very high O2 and glucose demand
Require 4ml/min/g
Use 25% of cardiac output at rest
Due to kidney function being highly metabolically demanding (>99% of filtered plasma is reabsorbed)
Describe kidney locations
Between T12-L3
Right kidney slightly lower due to liver
Describe kidney size
~11-12cm long
~5-7.5cm wide
~2.5-3cm thick
Describe the blood vessels of the kidney
Renal veins and arteries come directly off the IVC and aorta and enter the kidney in the hilar region
NB it’s not unusual for there to be extra accessory arteries supplying the kidney
What is the cause and the common sites of renal colic?
Caused by kidney stones becoming lodged in the ureter
Common locations are: the pelviuretic junction, the pelvic brim and the entry through the bladder wall
During what surgery are the ureters particularly vulnerable?
Hysterectomy
