physiology Flashcards
what two factors need to be known to calculate osmolarity
- molar concentration of the solution
- number of osmotically active particles present
units for osmolality
osmol/kg water
osmolarity units
osmol/l
what is tonicity
effect a solution has on a cell volume
isotonic
no change to cell volume
hypotonic
increase in cell volume
hypertonic
decrease in cell volume
tracer for ECF
inulin
tracer for total body water
3H2O
tracer for plasma
labelled albumin
is there more sodium and chloride ions inside or outside the cell
outside
is there more potassium ions inside or outside the cell
inside
what is fluid shift
movement of water between the ICF and ECF in response to an osmotic gradient
what is regulation of ECF volume vital for
long term regulation of blood pressure
what is electrolyte balance important for
- total electrolyte concentrations can directly affect water balance
- the concentrations of individual electrolytes can affect cell function
what is sodium and potassium balance important for
- major contributors to the osmotic concentrations of the ECF and ICF
- directly affect the functioning of all cells
is sodium a determinant of ECF volume?
yes
a majorrrr one
what happens if there are small leakages or increased cellular up take of potassium
muscle weakness - paralysis
cardiac irregularities - cardiac arrest
functions of the kidney
- water balance
- salt balance
- maintenance of plasma volume
- maintenance of plasma osmolarity
- acid base balance
- excretion of metabolic waste products
- excretion of exogenous foreign compounds
- secretion of renin
- secretion of erythropoietin
- conversion of vitamin D into active form
most common type of nephron
cortical
what is the least common type of nephron
juxtamedullary
which type of nephron has a longer loop of Henle
juxtamedullary
how many capillaries for a juxtamedullary nephron
one
vasa recta
how is the renal tubule a conveyor belt
substances are added or removed as urinary filtrate moves from proximal to distal end
what does the rate of filtration of X =
mass of X filtered into the Bowman’s capsule per unit time
what is the calculation for rate of excretion of X
Vu is urine flow rate
what does it mean if rate of filtration is greater than rate of excretion
net reabsorption has occured
what does rate of reabsorption of X =
rate of filtration of X - rate of excretion of X
what does it mean if the rate of filtration is less than rate of excretion
net secretion of that substance has occured
what are the filtration barriers
- glomerular capillary endothelium
- basement membrane
- slit processes of podocytes
what are the forces that comprise net filtration pressure
- glomerular capillary blood pressure
- bowmans capsule hydrostatic pressure
- capillary oncotic pressure
- Bowman’s capsule oncotic pressure
what is glomerular filtration rate
rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time
what does GFR =
what is the major determinant of GFR
glomerular capillary fluid blood pressure
does the afferent or efferent arteriole have a larger diameter
afferent
what charge is the basement membrane (between bowmans capsule and glomerular capillary)
negative
what are starling forces
the balance of hydrostatic pressure and osmotic forces
what are the two types of regulation of GFR
- extrinsic
- intrinsic (autoregulation)
what happens if there is an increase in glomerular capillary blood pressure
increase in net filtration pressure
increase in GFR
what does vasoconstriction of the afferent arteriole do
decreases glomerular capillary blood pressure
decreases net filtration pressure
decreases GFR
fall in blood volume effect on urine volume
fall in urine volume
what are the two parts of autoregualtion
- myogenic
- tubuloglomerular feedback
what is myogenic regulation
vascular smooth muscle is stretched, it contracts thus constricting the arteriole
what is tubuloglomerular feedback
- involves the juxtaglomerular apparatus
- if GFR rises, more NaCl flows through the tubule of afferent arterioles
what cells sense NaCl content of tubular fluid
macula densa
will someone with diarrhoea have increased or decreased GFR
decreased
calculation for the rate of excretion of X
could be in exam
is inulin absorbed or secreted
no
is inulin metabolised by the kidney
no
can inulin clearance be used clinically to determine GFR
yes
what does it mean is clearance of a substance is less than GFR
substance is reabsorbed
what does it mean if clearance is equal to GFR
substance is neither reabsorbed nor secreted
what does it mean if clearance is greater than GFR
substance is secreted into tubule
what is para-amino hippuric acid
exogenous organic anion
what is PAH used clinically to measure
renal plasma flow
pathway of PAH
- freely filtered at glomerulus
- secreted into the tubule
- completely cleared from the plasma
what should any substance used as a clearance marker be
- non toxic
- inert
- easy to measure
what is the filtration fraction
fraction of plasma flowing through the glomeruli that is filtered into the tubules
what things are reabsorbed in the PT
- sugars
- amino acids
- phosphate
- sulphate
- lactate
what things are secreted in the PT
- hydrogen
- hippurates
- neurotransmitters
- bile pigments
- uric acid
- drugs
- toxins
what is the transcellar route of reabsorption
across the cell wall that makes the nephron
what is the paracellular route of reabsorption
between cells
sodium ions are reabsorbed in sections of nephron apart from where?
descending loop of Henle
at the proximal tubule what percent of glucose and amino acids are reabsorbed
100%
what does sodium reabsorption drive
chlorine reabsorption
function of the loop of Henle
- generates a cortico-medullary solute concentration gradient
- this enables the formation of hypertonic urine
what is the opposing flow in the two limbs termed
countercurrent flow
which limb reabsorbs sodium and chloride
the ascending limb
can the ascending limb reabsorb water
no
can the descending limb reabsorb water
yes
what does the triple co-transporter do
pumps solute from thick ascending limb
what happens after fluid enters the descending limb
what happens in ascending limb
what is the purpose of countercurrent multiplication
to concentrate the medullary interstitial fluid
-this enables the kidney to produce urine of different volume and concentration according to the amount of circulating ADH
where does the vasa recta run
alongside the long loop of Henle of juxtamedullary nephrons
what forms the countercurrent system
the loop of henle and vasa recta
what happens to ensure that blood flow through the medullar doesn’t wash away NaCl and urea
- vasa recta capillaries follow hairpin loops
- vasa recta capillaries freely permeable to NaCl and water
- blood flow to vasa recta is low
osmolality of surrounding interstitial fluid of renal cortex
300 mosmol/l
what hormone increase water reabsorption
antidiuretic hormone
what hormone increases sodium reabsorption and increases potassium and hydrogen secretion
aldosterone
what does atrial natriuretic hormone do
decrease sodium reabsorption
when is ADH released into the blood
when action potentials down the nerves lead to calcium-dependent exocytosis
what is the effect of ADH on water permeability of the collecting duct
triggers cAMP to increase permeability of luminal membrane to H2O by inserting new water channels
what happens to urine and water permeability in high and low ADH
high ADH - high water permeability and hypertonic urine
low ADH - low water permeability and hypotonic urine
presence of maximal ADH what urine is produced
small volume of concentrated urine
in presence of minimal ADH what is urine
large volume of dilute urine
what are the two types of diabetes insipidus
central and nephrogenic
when are the hypothalamic osmoreceptors activated
when you’re thirsty
what does decreased atrial pressure mean for ADH release
increased ADH release
what does stimulation of stretch receptors in upper GI tract do to ADH
exerts feed-forward inhibition of ADH
osmolarity in different parts of the nephron
when is aldosterone secreted
in response to rising potassium or falling sodium in the blood
also when the RAAS system is activated
what does sodium retention do to blood pressure
increased blood volume and pressure
when aldosterone is absent what is that effect on potassium
no potassium is excreted in the urine as aldosterone stimulates the secretion of potassium
when aldosterone is absent what is that effect on potassium
no potassium is excreted in the urine as aldosterone stimulates the secretion of potassium
how do the granular cells in JGA control renin release
- reduced pressure in afferent arteriole
- macula densa cells sense the amount of NaCl in the distal tubule
- increased sympathetic activity as a result of reduced arterial blood pressure
increased RAAS effects on health
- can cause hypertension
- fluid retention which is associated with heart failure
what produces ANP (atrial natriuretic peptide)
the heart
-stored in atrial muscle cells
when is ANP released from the heart
when the atrial muscle cells are mechanically stretched due to an increase in circulating plasma volume
what does ANP promote secretion of
sodium and diuresis
once the urine has been stored by the kidneys what happens to it
it is propelled by peristaltic contractions through ureters to the bladder for temporary storage
what mechanisms is urination controlled by
- the micturation reflex
- voluntary control
how much urine can the bladder hold before the stretch receptors initiate the micturation reflex
250-400ml
