2 - Body fluids and membrane transport

What is the TBW in an average 70Kg male?

42 L

What is the Total body water (TBW) comprised of?

• ICF - Intercellular Fluid (25L)

• ECF - Extracellular Fluid (17L)

What is the ECF split into?

• Interstitial fluid (13L)

• Plasma (3L)

• Transcellular fluid (1L)

What is Interstitial fluid?

Bathes cells/tissues

What is plasma?

Liquid component of the blood

What is transcellular fluid?

Passes over an epithelium to be created

E.g. Urine, sweat, cerebrospinal fluid, saliva

What is the main electrolyte in plasma and Interstitial fluid?

Sodium

How do the ion levels differ from ICF to ECF

ICF - ion levels in plasma and IF are similar

ECF - Lower sodium, lower Chlorine, higher potassium

What are the osmolality for ICF and ECF

Always the same. 290

Is there protein in plasma, IF, and ICF?

Plasma - Yes - 1

IF - No - 0

ICF - Yes - 4

Features of the plasma membrane

• Phospholipid bilayer

• Transport proteins - removal of specific solutes, uptake of water

• High selective permeability

• Vital for intercellular regulation

What types of carrier protein are there?

Uniport - facilitator

Symport - cotransport

Antiport - exchanger

What types of transport proteins are there, and are they active or passive?

Channels - passive

Carrier - passive

Pumps - active (against a conc gradient)

What are the functions of transport proteins?

• uptake of nutrients, substrates, cofactors

• Export of waste products

• Maintain internal metabolism

• Regulate pH

• Regulate volume of water

How is the membrane potential created?

Asymmetric distribution of K+

• Negative inside cell (high conc of K inside cell)

• K+ attract negative anions, trapped inside cell

• Membrane potential 70mV

What do water and ions move through in cells?

Aquaporins

Are capillaries permeable in the brain?

No

What regulates interstitial fluid?

Capillaries

What is the usual level of permeability in capillaries?

High

What are the two layers of epithelia in the gut?

• Apical membrane (faces into the gut)

• Basolateral membrane

What are epithelial cells connected by?

Tight junctions

What happens in the gut with Cholera?

Chloride channel on apical membrane, remain open, uncontrolled chloride movement into gut and water follows

What are epithelia and what purpose do they serve?

• Layers of cells covering internal and external surfaces of organs and tissues

• Protective/barrier function

• Important roles in absorptions and secretion

Description and roles of capillary endothelium?

• Very thin layer of cells lining blood vessels

• Highly permeable in some organs

• Important role in regulation of the interstitial fluid

What are the distribution of solutes across the capillary endothelium?

• Small ions and organic solutes - approx equal

• Protein - Low in IF, High in plasma

Water distribution and hydrostatic and osmostic forces across capillary endothelium

• Hydrostatic pressure - From plasma to IF

• Colloid osmotic pressure - From IF to plasma