Anuj's Lectures

Question 1

What is the difference between Osmolarity and Osmolality?

Answer 1

Osmolarity is moles/Litre of solution

Osmolality is moles/Kg of solute

Question 2

What is the difference between tonicity and osmolarity?

Answer 2

Osmolarity refers to if something has a high or low concentration of solutes relative to the cell, tonicity refers to the effect the solution will have on the cell

Question 3

What is the difference between hydrostatic and osmotic pressure?

Answer 3

Osmotic pressure is the pressure required to prevent flow of water across a membrane while Hydrostatic pressure only takes into account the pressure from the water

Question 4

What are the differences between men and women with regards to their body fluids?

Answer 4

Women have a lower percentage of their body mass as water due to their increased adipose tissue (60% in men, 50% in water)

Question 5

What are the relative %s of ECF and ICF?

Answer 5

60% ICF, 40% ECF

Question 6

How is ECF % broken down?

Answer 6

75% Interstitial Fluid
20% Plasma volume
5% Transcellular Fluid

Question 7

What are the relative ion concentrations of cells? adn what is the main mechanism of keeping this assymmetry?

Answer 7

K+ high INTRAcellularly
Na+, Ca2+, Cl- high EXTRAcellularly
This is maintained through transport proteins and the selective permeability of the membranes, the key protein is the Na/K pump

Question 8

What are the differences between the large and small intestine?

Answer 8

The large intestine secretes K+ while the small intestine absorbs it
Most water reabsorption is done by the small intestine

Question 9

What is the mechanism of the Na/H exchanger in the intestines?

Answer 9

1. Na is taken in and exchanged from the lumen by the Na/H antiporter through the high pH of the gut
2. The Na/K pump in the basal side sets up a concentration gradient for Na
3. There is also a Na/H antiporter on the basal side

Question 10

What is the mechanism of the Parallel Na/H and ClHCO3 exchangers in the small intestine?

Answer 10

Similar to the Na/H exchange but the H+ secreted is generated due to a change in intracellular pH which is why this system is used most commonly in the interdigestive state

Question 11

What is the difference between secretory and osmotic diarrhoea?

Answer 11

Osmotic Diarrhoea is caused by inadequate absorption causing an osmotic inbalance as in coelics or lactose intolerance
Secretory Diarrhoea is caused by a change in cellular regulation of secretion as in cholera

Question 12

What makes the bicarbonate buffer an effective buffer solution?

Answer 12

It has a pKa of 6.1, which as blood has a pH of 7.4 this drives the HCO3- reaction allowing it to maintain a high concentration in the blood which can be easily influenced by the lung and kidneys

Question 13

What makes Phosphate an effective buffer?

Answer 13

Acts well in the kidneys as phosphate is concentrated

Tubular fluid also has a slightly lower pH bringing it closer to the pKa of phosphate

Question 14

What makes proteins an effective buffer?

Answer 14

They are an effective intracellular buffer as they have a high concentration, this is where most buffering occurs
They also typically have pKas close to 7.4

Question 15

How does the respiratory system regulate pH?

Answer 15

Changing the respiratory rate can cause a change in CO2 and therefore can induce a change in pH by driving specific reactions in the bicarbonate reaction
An increase in respiratory rate leads to an increase in CO2 blow off and a decrease in pH
A decrease in respiratory rate can lead to an decrease in CO2 and an increase in pH

Question 16

How does the renal system regulate pH?

Answer 16

Secretion of excess H+
Reabsorption of filtered HCO3-
Production of new HCO3-

Question 17

How does the renal system secrete excess H+ in early tubular segments?

Answer 17

In early tubular segments H+ is secreted by secondary active transport where H2O and CO2 from the tubular fluid are reabsorbed and carbonic anhydrase converts these to HCO3- and H+ The H+ is removed by a Na+/H+ antiporter in the apical membrane via the Na+ gradient set up by a basal Na/K ATPase
This also reabsorbs filtered HCO3-

Question 18

How does the renal system secrete excess H+ in late tubular segments?

Answer 18

Secretion is through primary active transport where CO2 is transported from the basal side and carbonic anhydrase converts this to HCO3- and H+, the H+ is then removed by an ATPase

Question 19

How does the renal system generate new HCO3-?

Answer 19

Gutamine can be broken down into two HCO3- and 2 NH4+ molecules in the cell
CO2 can move in through the apical membrane, carbonic anhydrase converts this to HCO3- and H+, the H+ is exchanged for a Na via an apical antiporter while the HCO3- is absorbed into the blood