Lecture 2 - Body fluids and membrane transport

Question 1

What is the composition of the average human body? (30 yr old 70kg male)

Answer 1

18% fat
22% lean body mass
60% water (42 litres)

Question 2

What is intracellular fluid?

Answer 2

Makes up 25 litres of the bodys water content
Fluid inside of the cell

Question 3

What is extracellular fluid?

Answer 3

Makes up 17 litres of the bodys water content
Fluid outside of the cell and is split into different components

Question 4

What are the three components that extracellular fluid is split into?

Answer 4

Interstitial fluid
Plasma
Transcellular fluid

Question 5

What is interstitial fluid?

Answer 5

Fluid that fills in the spaces between cells
Makes up 13 litres of the bodys water content
Has no protein
Splits again into
Bulk interstitial fluid (8l), bone (2l) and dense connective tissue (3l)
Has the most sodium and chlorine

Question 6

What is blood plasma?

Answer 6

Fluid in the blood that carries things such as platelets
Makes up 3 litres of the bodys water
Has 1mM of protein

Question 7

What is transcellular fluid?

Answer 7

Water in the body contained within epithelial lined spaces
Makes up 1l of the bodys water content
Features such as protein and sodium are variable

Question 8

What are some features of the plasma membrane?

Answer 8

Highly selective permeability
Lots of transport proteins for uptake and removal of specific solutes

Question 9

What is membrane transport and how is the membrane adapted for its function?

Answer 9

Made up of a phospholipid bilayer which is impermeable to ions and polar molecules
Has membrane proteins that give it its permeability

Question 10

What are the two types of transporters and are they active or passive?

Answer 10

Pumps which are active and channels+carriers which are passive

Question 11

What are the three types of carrier?

Answer 11

Facilitator/Uniport
Cotransporter/Symport
Exchanger/Antiport

Question 12

What is a facilitator/uniport carrier?

Answer 12

Moves one ion in one direction

Question 13

What is a cotransporter/symport carrrier?

Answer 13

Moves two ions in the same direction, and the ions are often one positive and one negative

Question 14

What are exchanger/antiport carriers?

Answer 14

Takes one ion and a different ion in, the two ions are usually the same charge

Question 15

What are some functions of transporters?

Answer 15

Uptake of nutrients, substrates, cofactors
Export of waste products
Regulation of intracellular ions, pH, cell volume
Distribution of water and solutes across membrane

Question 16

What is an example of a function of a transporter?

Answer 16

Transporters help with the distribution of solutes across the plasma membrane
EG, they maintain an asymmetric distribution of K+ which generates a membrane potential
This is done with a pump to maintain this distribution

Question 17

How is water distributed across the plasma membrane?

Answer 17

The distribution is determined by osmosis
It distributes itself so that the osmotic pressures are equal

Question 18

What is the capillary endothelium?

Answer 18

A very thin layer of cells lining the blood vessels
Regulates interstitial fluids
Very permeable in some organs but not others

Question 19

What is the distribution of solutes across the capillary endothelium?

Answer 19

Protein = higher concentration in plasma than interstitial fluid
Small ions and organic solutes = equal

Question 20

What is the distribution of water across the capillary endothelium?

Answer 20

The distribution is decided by hydrostatic and osmotic forces (hydrostatic pressure and colloid osmotic pressure)

Question 21

What is the epithelia?

Answer 21

A layer of cells covering internal and external surfaces of organs and tissues
Acts as a barrier with roles in absorption and secretion

Question 22

How does epithelial transport occur in the intestines and gut lumen?

Answer 22

The apical membrane faces towards the lumen
The basolateral membrane faces away from the lumen
Cells are connected by tight junctions and small molecules can pass between them
Transport proteins are embedded into the membrane to allow transport over tissue

Question 23

What is the distribution of solutes across the plasma membrane?

Answer 23

K+ = Higher intracellular
Na= Lower intracellular
Ca2+ = Lots lower intracellular
Cl- = Lower intracellular
Organic molecules = Higher intracellular
Proteins = Higher intracellular

Question 24

How is water distribution determined across the plasma membrane?

Answer 24

Its decided by osmosis
Water distributes itself so the osmotic pressures are equal