Regulation of the fluid compartments and the Lymphatic System Flashcards
Two major fluid compartments
Extracellular and Intracellular
Intracellular = 28L
Extracellular = 14L
- Plasma (3L)
- Interstitial (11L)
Total = 42L
Failure to regulate fluid compartments leads to
oedema
Burn or friction blister
Surgery for testicular cancer
What is Osmosis?
Osmosis: net diffusion of water across a selectively permeable membrane from a region of high water concentration to one that has a lower water concentration (low particle concentration to high particle concentration)
The total number of particles in a solution is measured in terms of osmoles.
One osmole (osm) = 1 mole (6.02 x 1023 ) of solute particles in 1L, eg.
1 M glucose = 1 Osm
1 M NaCl = 2 Osm1 M MgCl2 = 3 OsmIntracellular/Extracellular particles = 300 mM = 300 mOsm
Osmolarity is independent of molecular weight
1 molecule albumin (MW 70000) = 1 molecule of glucose (MW 180) = ½ molecule of NaCl (MW 58)
Osmolarity is…………of molecular weight
independent
Cellular membranes
Permeable to water
Impermeable to solutes (ions) such as Na+, Cl-, K+ etc
Osmosis determines distribution of water (i.e. size of intracellular and extracellular compartments)
What is the osmotic pressure ()?
Osmotic pressure = pressure required to prevent osmosis
∝ conc. of osmotically active particles in solution
Balance of ions is maintained by
active transport
ISOTONIC
no change
Extracellular =
300 mOsm/L
Transfer of fluid is rapid across cell membranes
HYPOTONIC
cell swells
Extracellular =
200 mOsm/L
from 300 intracellu;ar
Transfer of fluid is rapid across cell membranes
HYPERTONIC
Cell shrinks
400 mOsm/L
Transfer of fluid is rapid across cell membranes
What is the colloid osmotic pressure?
Capillary membrane is semi-permeable
- Permits diffusion of ions, water, oxygen, nutrients and waste
NOT PROTEINS
pressure exerted by the higher levels of protein in the plasma compared with the interstitial fluid
draws water back into plasma by osmosis (absorption)
28mmHg (plasma) – 3mmHg (interstitium)
= 25mmHg
Hydrostatic Pressure
is the force exerted by the blood upon the capillary walls i.e. blood pressure
Hydrostatic pressure drives blood from plasma into interstitial space
Pressure drops as the blood moves through the capillaries (35mmHg to 15mmHg)
Overall movement across capillary membrane determined by
Capillary Net Filtration Pressure (NFP)
NFP= (Pc + πif) – (Pif + πc)
Pc-capillary hydrostatic pressure
Pif-interstitial fluid hydrostatic pressure
πc-osmotic force due to plasma protein concentration
Pif-osmotic force due to interstitial fluid protein concentration
Capillary Net Filtration Pressure varies between the arterial and venous end of the capillaries
Arterial end
(Pc + πif) – (Pif + πc)
(35 + 3) – (0 + 28) = 10mmHg
Net OUTWARD Filtration
Hydrostatic Pressure Dominates
Venous end
(Pc + πif) – (Pif + πc)
(15 + 3) – (0 + 28) = -10mmHg
Net INWARD Filtration
Colloid Osmotic Pressure Dominates
Lymph system———-
Lymph system is parallel vascular system with two major functions:
Draining fluid from the tissues and returning to the cardiovascular system
Maintenance of the immune response
Lymphatic system : Drainage
Fluid (plasma) passes (8l/day) from blood into the interstitial area (surrounds cells in the tissues)
Excess fluid passes into lymph capillaries, through lymph nodes (detection of infection) before passing back to blood stream at the neck (largest is thoracic duct that drains into subclavian vein)
Lymph vessels contain valves and fluid is forced along by action of muscles and breathing (respiration). Larger lymph vessels are surrounded by smooth muscle that contract spontaneously and driven by pacemaker cells (~ heart)
Collects fats from the intestines/liver and deposits into veins
Lymphatic system : Immunity
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 leading to activation of immunity.
B-cell proliferate to produce antibodies. Lymph nodes also contain multiple other immune cells (swelling can occur)
Increased Capillary Hydrostatic Pressure (both ends)
Heart Failureexcessive kidney retention of waterincreased arteriolar resistance
high venous pressure
Decrease in colloid osmotic pressure
Reduction in plasma proteins
loss of proteins in urine (kidney failure)
loss of protein in denuded skin areas (burns)
malnutrition
Blockage of lymph nodes
Cancer
Infections
Surgery
Intracellular oedema
Intracellular oedema
Depression of metabolic systems of the tissues and lack of adequate nutrition to the cells eg. ischaemia: reduced activity of Na+ pumps leads to accumulation of Na+ in cells, causing osmosis of water into cells
There is a net flow of fluid (bulk flow) from
the plasma into the interstitium within the capaillaries which is returned to the plasma via the lymphatic system
Breakdown in the regulation of fluid compartments leads to
oedema (swelling)
The size of the plasma and interstitial compartments is determined by
by hydrostatic pressure and the colloid osmotic pressure (blood protein levels)
