Body Fluids and Membrane Transport - Lecture 2 Flashcards
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)?
○ 18% Fat
○ 22% Lean Body Mass
○ 60% Water (approx. 42 litres)
○ Total Body Water (TBW): 42 litres
Main compartments of TBW and their approximate volumes
○ Intracellular Fluid (ICF): 25 litres
○ Extracellular Fluid (ECF): 17 litres
Sub-compartments of ECF and their approximate volumes
○ Interstitial Fluid (ISF): 13 litres
○ Plasma: 3 litres
○ Transcellular fluid: 1 litre
Examples of transcellular fluids
○ Cerebrospinal fluid (brain)
○ Urine (kidney and bladder)
○ Gastrointestinal secretions (saliva, gastric juice, pancreatic juice, bile)
○ Sweat
○ Aqueous and vitreous humours (eye)
○ Synovial fluid (joints)
Concentration of ions in plasma
○ [Na+] = HIGH
○ [K+] = LOW
○ [Cl-] = HIGH
○ [Protein] = 1 mM
○ Osmolality = 290 mOsm
Concentration of ions in ISF
○ [Na+] = HIGH
○ [K+] = LOW
○ [Cl-] = HIGH
○ [Protein] = 0 mM
○ Osmolality = 290 mOsm
Concentration of ions in ICF
○ [Na+] = LOW
○ [K+] = HIGH
○ [Cl-] = LOW
○ [Protein] = 4 mM
○ Osmolality = 290 mOsm
Concentration of ions in TCF
Variable
Lining between plasma and ISF
endothelium
Lining between TCF and ISF
epithelium
Lining between ICF AND ISF
Plasma membrane
Functions of the plasma membrane
○ Highly selective permeability
○ Contains many transport proteins for uptake and removal of specific solutes
○ Vital for regulation of the intracellular environment
Membrane transport proteins and type of transport
○ Channels - passive transport (driven by gradients)
○ Carriers - passive transport (driven by gradients)
○ Pumps - active transport (ATP hydrolysis)
Types of carrier proteins & their roles
○ 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
Functions of transport proteins
Uniporter:
- glucose in cell
- urea out of cell
Symporter:
- Na+ & amino acids in cell
- lactate- & H+ out of cell
What ions and membrane transport are involved in gradient maintenance?
○ Pump
○ K+ in cell
○ Na+ out of cell
○ 3Na+ for 2K+
What ions and membrane transport proteins are involved in regulating volume
○ Volume increase
- Na+, K+, Cl- in cell
○ Volume decrease
- Channel
- K+ and Cl- out of cell
What ions and membrane transport proteins are involved in regulating pH
○ Too acidic
- Antiporter
- Na+ in cell
- H+ out of cell
○ Too alkali
- Antiporter
- Cl- in cell
- HCO₃- out of cell
How does the asymmetric distribution of K+ affect the membrane?
○ It generates a membrane potential (approx. -70mV)
What determines the distribution of water across the plasma membrane?
○ Osmosis
○ Water distributes itself so that the osmotic pressures are equal
Characteristics of the capillary endothelium
○ 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
Distribution of solutes across the capillary endothelium
○ Small ion & organic solutes = approx equal
○ Protein = LOW in ISF & HIGH in plasma
What two forces determine water distribution across the capillary endothelium?
○ Hydrostatic pressure (ΔP) - pushes water out of plasma
○ Colloid osmotic pressure (Δ∏c) - pulls water back in plasma
Key functions of epithelia
○ Layers of cells covering internal and external surfaces of organs and tissues
○ Protective/barrier function
○ Important roles in absorption and secretion
Epithelial transport in the gut
○ 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
