Body Fluid & Membrane Transport

Question 1

What percentage of a 30-year-old 70 kg male’s body is water?

Answer 1

60%

This is approximately 42 litres.

Question 2

What is the total body water (TBW) volume for a 30-year-old 70 kg male?

Answer 2

42 litres

Question 3

What are the two main compartments of total body water?

Answer 3

• Intracellular fluid (ICF)
• Extracellular fluid (ECF) = split into the Plasma, Interstitial fluid (ISF) and Transcellular fluid (i.e. urine, sweat, joint fluid etc)

Question 4

What is the volume of intracellular fluid (ICF) in a 30-year-old 70 kg male?

Answer 4

25 litres

Question 5

What is the volume of extracellular fluid (ECF) in a 30-year-old 70 kg male?

Answer 5

17 litres

Question 6

What is the volume of interstitial fluid (ISF)?

Answer 6

13 litres

Question 7

What is the volume of plasma in the body?

Answer 7

3 litres

Question 8

What are examples of transcellular fluids?

Answer 8

• Cerebrospinal fluid
• Urine
• Gastrointestinal secretions
• Sweat
• Aqueous and vitreous humours
• Synovial fluid

Question 9

What is the role of the plasma membrane?

Answer 9

Highly selective permeability

Lots of transport proteins for uptake and removal of specific solutes

Vital for regulation of the intracellular environment

Question 10

What types of molecules can the phospholipid bilayer of the plasma membrane not permeate?

Answer 10

Ions and polar molecules

Question 11

What provides permeability in the plasma membrane?

Answer 11

Membrane proteins (transporters)

Question 12

What are the categories of transport proteins?

Answer 12

• Channels = passive transport
• Carriers = passive transport
• Pumps = active transport (ATP hydrolysis)

Question 13

What drives passive transport?

Answer 13

Gradients

Question 14

What is the energy source for active transport?

Answer 14

ATP hydrolysis

Question 15

What are the types of carriers in membrane transport?

Answer 15

• Uniport = facilitator
• Symport = co-transporter
• Antiport = exchanger

Question 16

What are the functions of transport proteins?

Answer 16

• Uptake of nutrients, substrates and cofactors
• Export of waste products
• Regulation of intracellular ions, pH, cell volume

Question 17

Fill in the blank: The asymmetrical distribution of _______ generates a membrane potential.

Answer 17

K+

Question 18

What is the approximate membrane potential generated by K+?

Answer 18

-70 mV

Question 19

What determines water distribution in the body?

Answer 19

Osmosis

Question 20

True or False: Capillary endothelium is uniformly permeable across all organs.

Answer 20

False

Question 21

What are the two forces that decide water distribution across capillary endothelium?

Answer 21

• Hydrostatic pressure
• Colloid osmotic pressure

Question 22

What is the role of epithelia in the body?

Answer 22

• Protective/barrier function and roles in absorption and secretion
• Allows production of selective fluids
• Layers of cells covering internal and external surfaces of organs and tissues
• Important role in absorption and secretion

Question 23

What are the components of epithelial transport in the kidney?

Answer 23

• Apical membrane - Inside intestinal epithelial cell
• Basolateral membrane - outside intestinal epithelial cell, has uniports
• Tight junction - impermeable

Question 24

What is the capillary endothelium?

Answer 24

• Very thin layer of cells lining blood vessels
• Highly permeable in some organs but not in others (e.g. the brain)
• Important role in regulation of the interstitial fluid