Regulation of the fluid compartments and the Lymphatic System

Question 1

Two major fluid compartments

Answer 1

Extracellular and Intracellular

Intracellular = 28L
Extracellular = 14L
- Plasma (3L)
- Interstitial (11L)
Total = 42L

Question 2

Failure to regulate fluid compartments leads to

Answer 2

oedema
Burn or friction blister
Surgery for testicular cancer

Question 3

What is Osmosis?

Answer 3

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)

Question 4

Osmolarity is…………of molecular weight

Answer 4

independent

Question 5

Cellular membranes

Answer 5

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)

Question 6

What is the osmotic pressure ()?

Answer 6

Osmotic pressure = pressure required to prevent osmosis
∝ conc. of osmotically active particles in solution

Question 7

Balance of ions is maintained by

Answer 7

active transport

Question 8

ISOTONIC

Answer 8

no change
Extracellular =
300 mOsm/L
Transfer of fluid is rapid across cell membranes

Question 9

HYPOTONIC

Answer 9

cell swells
Extracellular =
200 mOsm/L
from 300 intracellu;ar
Transfer of fluid is rapid across cell membranes

Question 10

HYPERTONIC

Answer 10

Cell shrinks
400 mOsm/L

Transfer of fluid is rapid across cell membranes

Question 11

What is the colloid osmotic pressure?

Answer 11

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

Question 12

Hydrostatic Pressure

Answer 12

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)

Question 13

Overall movement across capillary membrane determined by

Answer 13

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

Question 14

Capillary Net Filtration Pressure varies between the arterial and venous end of the capillaries

Answer 14

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

Question 15

Lymph system———-

Answer 15

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

Question 16

Lymphatic system : Drainage

Answer 16

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

Question 17

Lymphatic system : Immunity

Answer 17

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)

Question 18

Increased Capillary Hydrostatic Pressure (both ends)

Answer 18

Heart Failureexcessive kidney retention of waterincreased arteriolar resistance
high venous pressure

Question 19

Decrease in colloid osmotic pressure

Answer 19

Reduction in plasma proteins
loss of proteins in urine (kidney failure)
loss of protein in denuded skin areas (burns)
malnutrition

Question 20

Blockage of lymph nodes

Answer 20

Cancer
Infections
Surgery

Question 21

Intracellular oedema

Answer 21

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

Question 22

There is a net flow of fluid (bulk flow) from

Answer 22

the plasma into the interstitium within the capaillaries which is returned to the plasma via the lymphatic system

Question 23

Breakdown in the regulation of fluid compartments leads to

Answer 23

oedema (swelling)

Question 24

The size of the plasma and interstitial compartments is determined by

Answer 24

by hydrostatic pressure and the colloid osmotic pressure (blood protein levels)