Physiology Flashcards
define osmolarity
concentration of osmotically active particles in a solution
define osmolality
this is interchangeable with osmolarity for body fluids
osmolarity of body fluids?
300mosmol/L
define tonicity
effect a solution has on cell volume
define isotonic
no change on cell volume
define hypertonic
decreases cell volume, concentrated salt solution
define hypotonic
increases cell volume (lysis) due to dilute solution
what does tonicity also take into consideration?
ability of a solute to cross the cell membrane e.g. urea causes RBC lysis as water follows (sucrose is impermeable so has no effect)
two compartments of total body water
intracellular fluid
extracellular fluid
what does the extracellular fluid consist of?
plasma
interstitial fluid
tracer used to measure TBW
3H2O
tracer used to measure ECF
inulin
tracer used to measure plasma
labelled albumin
inputs in water homeostasis
fluid
food
metabolism
outputs of water homeostasis
insensible losses (no sensible mechanism- skin and lungs) sensible losses- sweat, faeces and urine
what separates plasma and interstitial fluid?
capillary wall
what separates interstitial fluid and intracellular fluid?
plasma membrane
main ions in ECF
Na+
Cl-
HCO3-
main ions in ICF
K+
Mg2+
-ve charged proteins
define fluid shift
movement of water between ICF and ECF in response to an osmotic gradient
is Na+ excluded from ICF?
yes so there is only water movement
what do the kidneys do to ECF
alter composition and volume
why is potassium balance important?
membrane potential (if leakages or increased uptake it can cause paralysis and cardiac irregularities)
why is sodium balance important
ECF concentration and volume
kidney functions
water balance salt balance maintenance of plasma volume acid-base balance excretion of waste secretion of renin, erythopoietin and conversion of vit D
two types of nephron
juxtamedullary (glomerulus near corticomedullary border)
cortical (glomerulus in outer cortex)
glomerular filtration barriers
- endothelium (barrier to RBC)
- basement membrane (basal lamina)
- slit processes of podocytes (glomerular epithelium)
define glomerular filtration rate (GFR)
rate protein-free plasma is filtered from the glomeruli into Bowman’s capsule per unit time
what is normal GFR?
125ml/min
extrinsic regulation of GFR
sympathetic control via baroreceptor reflex
intrinsic regulation of GFR
myogenic mechanism and tubuloglomerular feedback
define tubuloglomerular feedback
GFR rises then more NaCl flows through the tubule causing constriction of afferent arteriole
what senses NaCl concentration in the blood?
macula densa of DCT
calculi effect on GFR?
reduced
diarrhoea effect on GFR
reduced
burns effect on GFR
increases
example of a substance with clearance of 0 (completely reabsorbed)
glucose
example of substance that is partly reabsorbed (clearance < GFR)
urea
example of substance that is completely secreted (clearance > GFR)
H+
what marker can be used to measure renal plasma flow
para-amino hippuric acid (PAH)- exogenous organic anion
normal renal plasma flow
650ml/min
what happens to PAH
it is all secreted from peritubular capillaries
define filtration fraction
fraction of plasma flowing through the glomeruli that is filtered into the tubules
what does the PCT reabsorb?
sugars amino acids phosphate sulphate lactate
what does the PCT secrete?
H+ hippurates neurotransmitters bile pigments uric acids drugs toxins
what channel is used in the PCT for Na+ reabsorption?
Na+/K+ ATPase
define transport maximum (Tm)
point at which increases in concentration of a substance do not result in an increase in movement of a substance across a cell membrane
where is all glucose and amino acids reabsorbed in the nephron?
PCT
what is normal concentration of glucose entering filtrate and whats renal threshold
2mmol/min
10-12mmol/L (consider diabetes)
define the counter-current multiplier
loop of Henle creates a solute gradient allowing formation of hypertonic urine
descending limb role of the nephron
does not reabsorb NaCl but is permeable to water
role of the ascending limb of the nephron
Na+ and Cl- are reabsorbed (thick limb is AT and thin limb it is passive)
impermeable to water
what cycle also contributes to medullary osmolality?
urea cycle
is the DCT permeable to urea?
no
which part of the nephron absorbs urea
collecting duct
where does urea diffuse passively into?
loop of Henle
what is the counter-current exchanger?
vasa recta
what does the blood do in the vasa recta?
equilibrates with interstitial fluid
why are the vasa recta needed?
they provide nutrients for medulla and remove toxins but to minimise removal of needed NaCl and urea for the concentration gradient they have low blood flow and are freely permeable so passive exchange preserves gradient
what hormones influence DCT and collecting ducts?
ADH
aldosterone
ANH/P
PTH
two segments of DCT
early= Na+/K+/2Cl- transporter late= aldosterone
define ADH
octapeptide that is synthesised in the hypothalamus and stored in the posterior pituitary
role of ADH
increases the number of aquaporins
most important stimulus for ADH release?
hypothalamic osmoreceptors
what secreted aldosterone?
adrenal cortex
why is aldosterone secreted
increased K+ or reduced Na+
activation of RAAS
role of aldosterone
stimulates Na+ reabsorption and K+ secretion
what happens in the DCT when aldosterone is absent
rest of K+ is reabsorbed so there is none in the urine
what is renin released from?
granular cells in the JGA
processes that cause renin release
- reduced pressure in afferent arteriole
- low NaCl sensed by macula densa
- increased sympathetic activity in low BP
what produces atrial natriuretic peptides?
atrial cells
what causes ANP release?
atria stretching due to increased blood volume
role of ANP
promotes excretion of Na+ and diuresis
define water diuresis
increased urine flow but not increased solute excretion
define osmotic diuresis
increased urine flow as a result of increased salt excretion
