Urinary Session 1- Introduction And Imaging Flashcards
Describe the main functions of the kidney
Regulation- Control concentration of key substances in ECF
Excretion- Excretes waste products
Endocrine- Synthesis of renin, erythropoietin, prostaglandins
Metabolism- Active form of vitamin D, catabolism of insulin, PTH, calcitonin
Define osmolality
Number of osmolality of solute per kg of solvent
Define osmolarity
Number of osmolarity of solute per litre of solvent
In normal conditions what is the osmolality of plasma?
280-310 mOsm/kg or 280-310 mmol/L
Same as interstitial/intracellular fluid
What ions is osmolality mainly determined by?
In ECF- Na+ and Cl- (80%)
In ICF- K+ (50%)
If osmolarity is higher in ECF which way will the water move?
Out of the cell (water moves from low to high osmolarity)
What are the differences in electrolyte composition of ICF and ECF?
ICF- high K+, low Na+, many large organic anions
ECF- low K+, high Na+, main anions Cl- and HCO3-
How are electrolyte differences between ECF and ICF maintained?
Active transport via sodium pumps
What are the consequences if the kidneys fail to control ECF?
Failure to control volume = changes in BP, tissue fluid and cell function
Failure to control osmolarity = cells shrink or swell
What ion in plasma can affect the pH of ECF?
Bicarbonate
How much urine is produced on average per day?
1.5L out of 180L/day that is filtered!
What structure is described as the functional unit of the kidney and how many are there per kidney?
1.5 million nephrons per kidney
Name all the sections of the nephron in the order in which fluid passes through them
Glomerulus Proximal convoluted tubule Loop of Henle Distal convoluted tubule Collecting duct
If all tubes within the urinary system are lined with epithelium, which direction does reabsorption occur in?
From inside the tube back into the body
Which substances are 100% reabsorbed?
Bicarbonate
Glucose
Amino acids
Why are more H+ ions lost in urine than are filtered?
It is actively secreted in the distal convoluted tubule
What blood flow do the kidneys need?
4ml/g/min
What percentage of CO do the kidneys need at rest?
22%
What substances are filtered out of the blood by the glomerulus?
Water, electrolytes and small molecules
What is the glomerular filtration rate determined by and what is the rate?
Afferent and efferent arterioles
125ml/min or 180L/day
What is the main function of the proximal convoluted tubule?
Reabsorption
Which substances are reabsorbed in PCT and how much of each (%)?
60-70% sodium and water
80-90% potassium
90% bicarbonate
100% glucose and amino acids
Is the filtrate isotonic or hypotonic at PCT?
Isotonic
How do reabsorbed materials leave PCT?
Peritubular capillaries
What cellular mechanism allows transport across the epithelium?
Polarised epithelial cells so different membrane properties on luminal and basolateral membranes. Na+/K+ ATPase pumps Na+ across basolateral membrane. Na+ moving down gradient back into lumen provides energy for reabsorption of glucose and other substances.
What is the function of the loop of Henle?
Create a gradient of increasing osmolarity in the medulla (main function) also site for reabsorption of salts
How does the loop of Henle create the osmolarity gradient?
Counter-current multiplication which allows formation of concentrated urine if water has to be conserved
What is the function of the distal convoluted tubule?
Variable reabsorption of electrolytes and water
Is the fluid entering the DCT isotonic or hypotonic?
Hypotonic
Which electrolytes are reabsorbed in DCT?
Sodium and chloride
What is significant about the position of the collecting duct?
It passes through the high osmolarity of the medulla so any water that can cross the epithelium will leave the urine making it more concentrated
Which hormone is responsible for sodium recovery?
Renin angiotensin system- controls ECF volume
Which hormone is responsible for water recovery?
Anti diuretic hormone- controls ECF osmolarity
Which areas of the nephron are affected by ADH and how?
Distal convoluted tubule and collecting
More permeable to water
What are the advantages and disadvantages of X-ray?
Advantages- cheap, contrast depends on tissue density
Disadvantages- ionising radiation
What can X-rays be used for?
Renal stones- follow up, not diagnosis
What is an intravenous urogram (IVU)?
Plain radiograph with contrast- contrast material injected then filtered out through kidneys
What is the advantage/ disadvantage of IVU?
Advantage- cheap
Disadvantage- ionising radiation
Which area of the kidney is IVU good for?
Collecting system
What is an ultrasound?
Uses reflection of sound waves
What are the advantages/disadvantages of ultrasound?
Advantages- non ionising radiation, accessible, cheap
Disadvantage- operator dependant
What are ultrasounds used for?
Can assess flow- good for kidneys and bladder
What is a computed tomography (CT)?
Cross sectional images produced by X-rays
What are the advantages/disadvantages of CT?
Advantages- better resolution, quicker than MRI, can be +/- contrast
Disadvantages- ionising radiation so cannot be used for pregnant women or children
What is CT good for?
Stones, tumour, trauma, infection
What is magnetic resonance imaging (MRI)?
Cross sectional images produced by a magnetic field
What are the advantages/disadvantages of MRI?
Advantages- non ionising radiation, can be +/- contrast
Disadvantages- expensive and timely
What is MRI good for?
Soft tissues
What are the advantages/disadvantages of nuclear medicine?
Advantage- gives functional information
Disadvantage- uses radioactive isotopes (ionising radiation)
What is nuclear medicine good for?
Renal function and obstruction
