Body Fluids and Membrane Transport - Lecture 2

Question 1

What are the major components of the human body for a 30-year-old 70 kg male, and what is the approximate total body water (TBW)?

Answer 1

○ 18% Fat
○ 22% Lean Body Mass
○ 60% Water (approx. 42 litres)
○ Total Body Water (TBW): 42 litres

Question 2

Main compartments of TBW and their approximate volumes

Answer 2

○ Intracellular Fluid (ICF): 25 litres
○ Extracellular Fluid (ECF): 17 litres

Question 3

Sub-compartments of ECF and their approximate volumes

Answer 3

○ Interstitial Fluid (ISF): 13 litres
○ Plasma: 3 litres
○ Transcellular fluid: 1 litre

Question 4

Examples of transcellular fluids

Answer 4

○ Cerebrospinal fluid (brain)
○ Urine (kidney and bladder)
○ Gastrointestinal secretions (saliva, gastric juice, pancreatic juice, bile)
○ Sweat
○ Aqueous and vitreous humours (eye)
○ Synovial fluid (joints)

Question 5

Concentration of ions in plasma

Answer 5

○ [Na+] = HIGH
○ [K+] = LOW
○ [Cl-] = HIGH
○ [Protein] = 1 mM
○ Osmolality = 290 mOsm

Question 6

Concentration of ions in ISF

Answer 6

○ [Na+] = HIGH
○ [K+] = LOW
○ [Cl-] = HIGH
○ [Protein] = 0 mM
○ Osmolality = 290 mOsm

Question 7

Concentration of ions in ICF

Answer 7

○ [Na+] = LOW
○ [K+] = HIGH
○ [Cl-] = LOW
○ [Protein] = 4 mM
○ Osmolality = 290 mOsm

Question 8

Concentration of ions in TCF

Answer 8

Variable

Question 9

Lining between plasma and ISF

Answer 9

endothelium

Question 10

Lining between TCF and ISF

Answer 10

epithelium

Question 11

Lining between ICF AND ISF

Answer 11

Plasma membrane

Question 12

Functions of the plasma membrane

Answer 12

○ Highly selective permeability
○ Contains many transport proteins for uptake and removal of specific solutes
○ Vital for regulation of the intracellular environment

Question 13

Membrane transport proteins and type of transport

Answer 13

○ Channels - passive transport (driven by gradients)
○ Carriers - passive transport (driven by gradients)
○ Pumps - active transport (ATP hydrolysis)

Question 14

Types of carrier proteins & their roles

Answer 14

○ Uniport (Facilitator): Moves one ion
○ Symport (Co-transporter): Moves oppositely charged ions in the same direction
○ Antiport (Exchanger): Moves ions with the same charge in opposite directions

Question 15

Functions of transport proteins

Answer 15

Uniporter:
- glucose in cell
- urea out of cell
Symporter:
- Na+ & amino acids in cell
- lactate- & H+ out of cell

Question 16

What ions and membrane transport are involved in gradient maintenance?

Answer 16

○ Pump
○ K+ in cell
○ Na+ out of cell
○ 3Na+ for 2K+

Question 17

What ions and membrane transport proteins are involved in regulating volume

Answer 17

○ Volume increase
- Na+, K+, Cl- in cell
○ Volume decrease
- Channel
- K+ and Cl- out of cell

Question 18

What ions and membrane transport proteins are involved in regulating pH

Answer 18

○ Too acidic
- Antiporter
- Na+ in cell
- H+ out of cell
○ Too alkali
- Antiporter
- Cl- in cell
- HCO₃- out of cell

Question 19

How does the asymmetric distribution of K+ affect the membrane?

Answer 19

○ It generates a membrane potential (approx. -70mV)

Question 20

What determines the distribution of water across the plasma membrane?

Answer 20

○ Osmosis
○ Water distributes itself so that the osmotic pressures are equal

Question 21

Characteristics of the capillary endothelium

Answer 21

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

Question 22

Distribution of solutes across the capillary endothelium

Answer 22

○ Small ion & organic solutes = approx equal
○ Protein = LOW in ISF & HIGH in plasma

Question 23

What two forces determine water distribution across the capillary endothelium?

Answer 23

○ Hydrostatic pressure (ΔP) - pushes water out of plasma
○ Colloid osmotic pressure (Δ∏c) - pulls water back in plasma

Question 24

Key functions of epithelia

Answer 24

○ Layers of cells covering internal and external surfaces of organs and tissues
○ Protective/barrier function
○ Important roles in absorption and secretion

Question 25

Epithelial transport in the gut

Answer 25

○ Apical Membrane (faces inwards):
- Symporter: Na+ & glucose into cell
- Channel: Cl- out of cell
○ Basolateral membrane (faces outwards):
- Pump: K+ in cell & Na+ out of cell
- Uniporter: glucose out of cell
- Uniporter: K+, Na+ & Cl- in cell