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Renal Physiology (Kidney structure/ function (Juxtaglomerular apparatus…
Renal Physiology
Kidney structure/ function
Cortical nephron
80% of nephrons
Short loop of Henle
Juxtamedullary nephron
20% of nephrons
Long loop of Henle
Have vasa recta
Arterioles parallel to descending/ascending limbs
Glomerulus
Loops of capillaries
Endothelial cells internally
Podocytes externally
Juxtaglomerular apparatus
Next to glomerulus
Regulates nephron function
Macula densa
Chemoreceptors for NaCl in distal convoluted tubule
Granular cells
Mechanoreceptors for renin release
Mesanglial cells
Actin-containing constrictor cells
Functions
Water balance
Salt balance
Acid-base balance
Excretion of waste
Secretion of renin/EPO
Filtration
F(x)=[X]plasma*GFR
Measurable
Excretion
E(x)=[X]urine*Vurine
Rate of excretion = rate of filtration + rate of secretion - rate of reabsorption
Measurable
Reabsorption
R(x)=F(x)-E(x)
When F(x)>E(x)
Secretion
S(x)=E(x)-F(x)
When E(x)>F(x)
Loop of Henle
Descending limb
Permeable to water
Impermeable to ions
Ascending limb
Impermeable to water
Permeable to ions
Triple cotransporter
Sodium ions
Chloride ions
Potassium ions
Blocked by loop diuretics
Solute removed from ascending limb
Tubular fluid diluted
Interstitial solute can't enter descending limb
Water leaves descending limb
Descending limb fluid concentrated
Urea adds solute to interstitium
Body Fluid Compartments
Intracellular fluid
Potassium ions
140mM
Negatively charged proteins
67% of total body water
28kg in 70kg male
Extracellular fluid
Sodium ions
140mM
Chloride ions
115mM
Bicarbonate ions
28mM
14kg in 70kg male
Plasma
Interstitial fluid
Lymph
Osmolarity
Concentration of osmotically active particles within a solution (mmol/Kg)
Osmolarity = number of osmotically active particles/ concentration
Tracers
Measures water composition
TBW
3H20
ECF
Inulin
Plasma
Albumin
Volume of distribution = dose/ concentration
Fluid shifts
Movement of water between ECF and ICF
Homeostasis
Gain of water
ICF volume increases
ECF volume increases
Loss of water
ICF volume increases
ECF volume increases
Gain of NaCl
ICF volume decreases
ECF volume increases
Loss of NaCl
ICF volume increases
ECF volume decreases
Gain/loss of isotonic fluid
Change in ECF volume only
Electrolyte balance
Rate of gain = rate of loss
Driven by sodium and potassium ions
90% ECF osmolarity from sodium ions
Potassium ions vital to membrane potential
Hypokalaemia
Paralysis
Cardiac arrest
Glomerular filtration and renal blood flow
Pressures
Glomerular capillary hydrostatic pressure = 55mmHg
Bowman's capsule hydrostatic pressure = 15mmHg
Glomerular capillary oncotic pressure = 30mmHg
Net filtration pressure = 10mmHg
Glomerular filtration rate = Kf x net filtration rate
Normally 125ml/min
Clearance
Rate of cleaning of substance
Clearance = rate of excretion/ plasma concentration
Inulin=125ml/min
Creatinine=125ml/min
Glucose=0ml/min
PAH=650ml/min
GFR measured by measurement of clearance of inulin/creatinine
Renal plasma flow
Rate of flow of plasma within nephron
650ml/min
Measured by clearance of PAH
Completely secreted
Filtration fraction
20%
Percentage of plasma filtered into tubule
GFR/RPF
Renal blood flow = 1200ml/min
Proximal tubule
Facilitated diffusion
Passive movement of a substance down a concentration gradient
Secondary active transport
Active movement of a substance against its concentration gradient in exchange/ coupled with another substance
Transport maximum
Maximum rate of reabsorption of a substance
Renal threshold
Concentration of substance within plasma at which excretion begins to occur
Na+ ion movement
Apical membrane
Na+/Glucose cotransporter
Na+/amino acid cotransporter
Na+/H+ exchanger
Basolateral membrane
Na+/K+ ATPase transporter
Osmolarity does not change as Na+ and H2O absorbed in equal proportions
Distal tubule
Low permeability to H20 & urea
Urea concentrated in tubule
Early
Na/K/Cl transport
Blocked by thiazide diuretics
Late
Ca reabsorption
H+ secretion
Na+ reabsorption
K+ reabsorption
Aldosterone
Increases permeability to urea
Increases K+ secretion
Aldosterone
Secreted by adrenal cortex
Stimulated by high K/ low Na
Na reabsorption
K secretion
Urine production
Hypertonic
High ADH secretion
High urine osmolarity
Low urine volume
Hypotonic
Low ADH secretion
Low urine osmolarity
High urine volume
ADH
Increases permeability of collecting duct to water
Upregulates aquaporin expression on apical membrane
Stimulated by increased plasma osmolarity
Detected by hypothalmic osmoreceptors
Increases intracellular cAMP
Secreted by activation of left atrial stretch receptors
Renin