Physiology Flashcards
Define osmolarity
Concentration of osmotically active particles present in a solution
What is the osmolarity of most body fluids?
300mosmol/l
Define tonicity
Effect a solution has on cell volume
What is the effect of a hypotonic solution?
Causes a cell to swell and increases cell volume
What is the effect of a hypertonic solution?
Causes a cell to shrink and decreases cell volume
What percentage of the body weight is total body water?
50-60%
What are the two components of total body water?
Intracellular and extracellular
What makes up the extracellular fluid?
Plasma
Interstitial Fluid
What separates the intra/extracellular fluid?
Cell membrane
How can the distribution volume be calculated?
By use of a tracer - titrated water, inulin, labelled albumin
Describe the ionic differences between ICF and ECF
ICF - high potassium
ECF - high sodium, chloride, bicarbonate, magnesium, negative proteins
Define fluid shifts
Movement of water between ICF and ECF in response to an osmotic gradient
What is the effect of water loss from ECF?
Increase in ECF osmotic concentration water will move out of the ICF and into the ECF so cells will shrink
What is the effect of water gain to the ECF?
Decrease in ECF osmotic concentration water will move out of the ECF into the ICF so cells will swell
Describe the effect of gain/loss of NaCl
Sodium excluded from ICF, if ECF gains salt osmolarity will increase so water will leave ICF to ECF
Loss of salt will increase ICF volume as ECF osmolarity will decrease
Other than salt/water changes what else can cause a fluid shift?
Change in volume - gain/loss of isotonic fluid, only change in ECF volume
Define an electrolyte
Any substance that dissociates into free ions when dissolved
Name two key ions that contribute to osmotic concentrations
Sodium - ECF
Potassium - ICF
What detrimental changes can occur due to changes in potassium?
Muscle weakness and paralysis
Cardiac irregularities and arrest
What is the recommended salt allowance?
6g/day
Name the function of the kidneys
- water balance
- salt balance
- maintain plasma volume
- maintain plasma osmolarity
- acid base balance
- excretion of metabolic waste
- excretion of exogenous compounds
- secretion of renin
- secretion of erythropoietin
- conversion of vit D to its active form
What percentage of blood is filtered by the glomerulus?
20%
Name the three components of the glomerular filter
- glomerular capillary endothelium
- basement membrane
- slit processes of podocytes
Name the four forces that result in glomerular filtration
Glomerular capillary BP 55mmHg towards tubule
Capillary oncotic pressure 30mmHg towards capillary
Bowman’s capsule hydrostatic pressure 15mg towards capillary
Bowman’s capsule oncotic pressure towards tubule 0mmHg
What is the net filtration pressure?
10mmHg
Define GFR
Rate at which protein free plasma is filtered from the glomeruli in to Bowmans capsule per unit time
What is the normal GFR?
125ml/min
How is GFR regulated extrinsically?
Changes to vessel shape alter the GFR
Describe the effect of a fall in blood volume
- Decreased blood pressure
- Detected by baroreceptors
- Increase in sympathetic activity
- Vasoconstriction
- Decreased GFR
- Decreased urine volume (compensates for reduced blood volume)
What is the effect of auto regulation on GFR?
Prevents short term changes in systemic arterial pressure affecting GFR
Describe myogenic auto regulation
If vascular smooth muscle is stretched it contracts, constricting the arteriole
Describe tubuloglomerular auto regulation
Involves juxtaglomerular apparatus
If GFR rises more salt will through flow the tubule leading to constriction of afferent arterioles
What senses NaCl content in the tubular fluid?
Macula densa
Name three pathologies that can alter GFR
Kidney stones, increases bowmans fluid pressure, decreases GFR
Diarrhoea increases bowman oncotic pressure, decreases GFR
Severe burns decrease bowmans oncotic pressure and increases GFR
Define plasma clearance
Measure of how effectively the kidneys can clean the blood of a substance
Describe the clearance/GFR of inulin
Clearance = GFR as it is freely filtered and not reabsorbed or secreted
Describe the clearance/GFR of glucose
Filtered, completely reabsorbed and not secreted
Clearance = 0
Describe the clearance/GFR of urea
Filtered and partly reabsorbed but not secreted so clearance
Describe H+ clearance/GFR
Filtered and secreted but not absorbed
Clearance > GFR
All filtered plasma is cleared and some peritubular plasma too
State three things a clearance marker should be
Non-toxic
Inert
Easy to measure
Name some substances that are reabsorbed
- sugars
- amino acids
- phosphate
- sulphate
- lactate
Name some substances that are secreted
- hydrogen ions
- hippurates
- neurotransmitters
- bile pigments
- uric acid
- drugs and toxins
Name two methods of reabsorption
Transcellular
Paracellular
State three methods of transport of a substance
Primary active
Secondary active
Facilitated diffusion
Describe primary active transport
Energy directly required to move the substance against the gradient
Describe secondary active transport
Molecule is transported, coupled to the concentration of an ion
Describe facilitated diffusion
Passive carrier mediated transport down the concentration gradient
Describe three methods of sodium reabsorption
- Sodium potassium pump on basolateral membrane
- Co-transport with glucose/amino acids
- Sodium/hydrogen exchanger using hydrogen ions produced by carbonic anhydrase
How do water and chlorine leave the tubule?
Paracellular reabsorption
Standing osmotic gradient moves water by diffusion
As sodium leaves the lumen becomes more negative which causes chloride ions to leave
How is glucose reabsorbed?
Co-transported with sodium into the epithelial cell, it then leaves via facilitated diffusion
What is the renal threshold for glucose?
10-12mmol/l
What is the function of the loop of henle?
Generates a cortico-medullary solute concentration gradient which enables formation of hypertonic urine
Describe the movement of substances in the loop of henle
- Solute is removed from the ascending limb
- Tubular fluid is diluted and osmolality of interstitial fluid increases
- Water leaves the descending limb via osmosis
- Fluid in the descending limb is concentrated
Describe the gradient created by countercurrent multiplication
The horizontal gradient has been multiplied into a large vertical gradient
How is urea managed in the distal tubule?
Distal tubule is impermeable to urea so as water is removed it becomes more concentrated
What happens to urea in the medullary collecting duct?
It is absorbed as transporters are activated by vasopressin as a result this drives water reabsorption from the descending limb
What transporters are activated by vasopressin?
UTA3
A3
Name the blood vessel that supplies the medulla
Vasa Recta
How does the vasa recta prevent all the solute being washed away?
- hairpin loops
- capillaries are permeable to NaCl and water
- low blood flow
Name four hormones that control body fluid
- antidiuretic
- aldosterone
- atrial natriuretic hormone
- parathyroid hormone
What ions are reabsorbed in the early distal tubule?
NaCl (NaK2Cl transport)
What ions are reabsorbed in the late distal tubule?
Calcium
Hydrogen
Sodium
Potassium
Describe the late collecting duct
Low ion permeability
Permeability to water and urea influenced by ADH
Where is antidiuretic hormone synthesised?
Hypothalamus
State the shape of antidiuretic
Octapeptide
What signals to the hypothalamus to release ADH?
Osmoreceptors
Atrial volume receptors
When is ADH released?
When action potentials down the nerves lead to calcium dependent exocytosis
How does ADH increase the permeability to water?
Binds to receptor to turn ATP to cAMP
Increased the permeability by inserting new aquaporins to the luminal membrane
What happens to water in the presence of ADH?
Moves from the collecting duct lumen along the osmotic gradient and into the medullary interstitial fluid
Describe the effect of high/low ADH
High - small volume of concentrated urine
Low - large volume of dilute urine
What extra-renal features can impact ADH level?
GI stretch receptors inhibit ADH
Nicotine stimulates ADH
Alcohol inhibits ADH
Where is aldosterone secreted?
Adrenal cortex
When is aldosterone secreted?
In response to increased potassium or decreased sodium in the blood
What is the effect of aldosterone?
Increases sodium reabsorption and potassium secretion
State the steps of the RAAS system in response to decreased salt, ECF or ABP
- Angiotensinogen converted into angiotensin I by renin
- Angiotensin I is converted into angiotensin II by ACE
- Angiotensin II causes vasoconstriction, thirst and ADH release
Thirst increases fluid uptake
ADH increases water reabsorption
How does aldosterone act as part of RAAS?
Increases sodium reabsorption and chlorine follows this leads to osmotic hold of water and thus conservation of water
Where is renin released from?
Granular cells in the juxtaglomerular apparatus
What signals for renin to be released?
- Reduced pressure in afferent arteriole
- Macula dense cells ones the amount of NaCl in distal tubule
- Increased sympathetic activity due to decreased ABP
Where does atrial natriuretic peptide come from?
Produced in heart and stored in the atrium
When is ANP released?
When atrial muscle cells are stretched due to increased plasma volume
How does ANP decrease plasma volume?
- decreases sodium reabsorption
- decreases RAAS
- vasodilation
- reduces sympathetic activity
What is micturition governed by?
Micturition reflex
Voluntary control
What is the average pH of blood?
7.4
Where can hydrogen ions come form?
Carbonic acid formation
Inorganic acids produced in breakdown of nutrients
Organic acids from metabolism
What is the difference between a strong and weak acid?
Strong - completely dissociates in solution
Weak - partially dissociates in solution
What is a buffer?
Pair of substances;
one can yield free hydrogen ions
one can bind free hydrogen ions
What is the key physiological buffer?
CO2, HCO2 Buffer
How is carbonic acid formed?
By the hydration of carbon dioxide by carbonic anhydrase
How does the kidney control bicarbonate concentration?
Variable reabsorption of filtered bicarbonate
Addition of new bicarbonate to the blood
What does control of bicarbonate depend on?
Hydrogen ion secretion
Describe the reabsorption of filtered bicarbonate
Carbon dioxide moves into the epithelial cell and is hydrated to carbonic acid to produce
hydrogen ions - exchanged for sodium and move into tubule
bicarbonate - move into interstitial with sodium
What happens to the bicarbonate in the filtrate?
It binds to hydrogen ions forming carbonic acid which can be broken down and moved into the epithelium
What is the purpose of new bicarbonate formation?
Used to regenerate buffer stores depleted by an acid load
If bicarbonate ion decreases how is new bicarbonate produced?
Hydrogen ions combine with phosphate to form HPO42- this combines with another hydrogen ion to form HPO4-which is excreted in urine. However the bicarbonate is still formed by hydration of carbon dioxide
What is titratable acid?
Measure of strong bade (NaOH) added to titrate the urine back to 7.4
How does ammonia contribute to acid base balance?
Glutamine form the liver leads to NH3 in the tubule which mops up the hydrogen ions forming NH4+ that can be secreted in the urine
Define compensation
Restoration of pH irrespective of what happens to bicarbonate and carbon dioxide
Define correction
Restoration of pH and bicarbonate and carbon dioxide to normal
What is immediate buffering?
Dilution of acid/base in ECF, blood and ECF buffers respond very quickly but stores are quickly depleted
What is respiratory acidosis?
Retention of carbon dioxide by the body
What causes respiratory acidosis?
Lung diseases
What happens to the equilibrium in respiratory acidosis?
Driven to the right to produce hydrogen ions and bicarbonate
How does the body compensate for respiratory acidosis?
All bicarbonate is reabsorbed and hydrogen ions excreted with titratable acid
What is needed to correct respiratory acidosis?
Ventilation
What is respiratory alkalosis?
Excessive removal of carbon dioxide by the body
State the causes of respiratory alkalosis
Panic attack
Hyperventilation
Altitude
Describe the effect on the equilibrium of respiratory alkalosis
Moves to the left meaning both hydrogen ion and bicarbonate concentration fall
How does the body compensate for respiratory alkalosis?
Reduces hydrogen ion secretion and bicarbonate is excreted in urine.
No titratable acid or new bicarbonate is generated
What is metabolic acidosis?
Excessive hydrogen ions from any other source other than carbon dioxide
What can cause metabolic acidosis?
Ketoacidosis
Diarrhoea
Ingestion
How does the body compensate for metabolic acidosis?
Decreased pH stimulates chemoreceptors which increase ventilation to blow off CO2 and lower H+ and bicarbonate
How is metabolic acid corrected?
Filtered bicarbonate is low and readily reabsorbed and new bicarbonate is generated
Hydrogen ion secretion continues and acid is excreted in the urine
Ventilation can then be normalised
What is metabolic alkalosis?
Loss of hydrogen ions or addition of a base causes bicarbonate to rise
How does the body compensate for metabolic alkalosis?
Increased pH is detected by chemoreceptors which slows ventilation to retain carbon dioxide and increase hydrogen and bicarbonate ions
How is metabolic alkalosis corrected?
Filtered bicarbonate is so large that not all of it is reabsorbed, no titratable acid is generated so bicarbonate is secreted and falls back to normal