L46- blood volume

what are the two major fluid compartment

• extracellular- outside cells (14l)

• intracellular -inside cells ( 28l)

then the plasma (3l) and the interstitial fluid (11l)

describe how volumes in each compartment is maintained

• osmosis controls the volume of water inside and outside cells

• the colloid osmotic pressure and the hydrostatic pressure maintains the volume of water in the interstitial fluid and the plasma ( these only work through the capillaries as its thin enough )

what can failure to maintain fluid compartment lead to

oedema- accumulation of excess fluid in the body

what is osmosis

its the net diffusion of water across a selectively permeable membrane from a region of high water concentration to a region of low water concentration

how is the total number of particles measured

in terms of osmoles

• one osmole=1 mole ( 6.02X10²³ ) of solute in 1L

what is osmotic pressure

its the pressure required to prevent osmosis and its proportional o the number of osmotically active

what is a isotonic, hypertonic and hypotonic

isotonic- the solute concentration/ ions concentration inside and outside of the cell is equal

hypertonic- the solute concentration outside the cell in higher so water moves out and cells shrinks

hypotonic- the solute concentration inside cell is higher so water moves in so cell swells

how is colloid osmotic pressure created

• the capillary membrane is semi-permeable like the plasma and allows ions, water oxygen, nutrients and waste

• not proteins

• the difference in protein concentration between the plasma and the interstitial fluid is what causes the osmotic pressure difference between the two

what is colloid osmotic pressure

its the pressure exerted by the higher levels of protein in the plasma compared to the interstitials fluid

the pressure draws water back into the plasma by osmosis

what is hydrostatic pressure

• its the pressure that’s exerted by the blood upon the capillary walls ( blood pressure )

• it drive blood from the plasma into the interstitial space

• the pressure drops as blood moves through the capillaries

what is the equation for the capillary net filtration pressure

describe the bulk flow of fluid from plasma

• at the start of the capillaries the hydrostatic pressure is highest and forcing liquid out

• but at the venous end colloidal osmotic pressure is highest absorbing water into the capillaries

• this causes a net loss of around 8l of liquid which needs to be removed otherwise it accumulates in the body

• the lymphatic system removes it and takes it back into the blood

what are the two main functions of the lymphatic system

• it drains fluid from the tissues and returning to the cardiovascular system

• maintenance of the immune response

explain the lymphatic system role of drainage

• 8l of fluid passes to the interstitial fluid a day

• the excess fluid passes into lymph capillaries through lymph nodes before passing back to the blood stream at the neck

• the lymph nodes contain valves and fluid is forced along by action of muscles and breathing

• it also collects fats from the liver and the intestines and deposits them into the veins

describe the lymphatic systems role in immunity

• the lymph fluid contains white immune blood cells ( lymphocytes, macrophages, dendritic cells )

• collects antigens ( proteins produced by pathogens )

• antigens recognised by B-lymphocytes in lymph nodes lead to activation of immunity

• b-cell proliferate to produce antibodies. lymph nodes also contain multiple other immune cells.

explain how heart failure leads to odema

• during heart failure there’s excessive kidney retention of water in order to try and increases the blood pressure

• this causes the blood volume to increases so the arterial pressure also increases

• so there’s a net flow of liquid going out of the body on both ends- due to the increased hydrostatic pressure

what can happen if there’s malnourishment

• there’s reduced plasma proteins and there’s loss of proteins in the blood

• this causes a decrease in colloidal osmotic pressure so theres a net movemnt of fluid out of the capillary

describe what happens when the lymph nodes are blocked

the fluid it typically drains accumulates in the area of the lymph node