Intracellular, Extracellular Compartments, and Oedema

A & M

Water Water is the major constitute of body fluids 60% of body weight or 42 L Daily water intake:1- ingestion accounts for about 2100 ml/day2- a result of oxidation of carbohydrates accounts for about 200 ml/dayDaily water output:1- insensible water loss: evaporation from respiratory tract and skin about 700 ml/day2- sensible water loss: in sweat (about 100 ml/day), in feces ( about100 ml/day), and as urine (about 1.4 L/day)

There is balance between water intake (2500 ml/day) and output (2500 ml/day)

Category Water

Men 60%

women 50%

Newborn babies 70-75%

water percentage decreases as the person gets older (Why?)

Women have low water percentage compared to men (Why?)

Body fluid compartments

- Total body fluid is distributed into 2 compartments:1- Intracellular compartment

2- Extracellular compartment: interstitial fluid and plasma 1- Intracellular compartment: represent about 28 L from total 42 L (40% of body weight) The fluid inside the cells

2- Extracellular compartment: the fluid outside the cells. divided into:A- the Plasma : about ¼ , 3 L of ECF B- the interstitial fluid: about ¾ , 11 L of ECF

Composition of ECF and ICF:ECF: the plasma and interstitial fluid have the same ionic composition (Why?)- ECF composition is maintained by the kidneys - Interstitial fluid composition= plasma

composition(true or false and why?)

ICF: is separated by cell membrane from ECF

- It contains small amounts of Na and Cl and almost no Ca

- Contains large amounts of K and P but moderate amounts of Mg and S

- Also contains large amounts of proteins (4 times as much as of the plasma)

Regulation of fluid distribution

The distribution of ECF between the plasma and interstitial spaces is determined by the balance between the hydrostatic and colloid osmotic forces across the capillary membrane. The distribution of fluid between IC and EC fluids is determined by osmotic effect of smaller solutes across the cell membrane (Why?)

Principle of fluid exchange

Since water is the major component of IC and EC compartments we will focus on its exchange:

Osmosis : the net diffusion of water across a selectively permeable membrane from a region with high water concentration to a region with low water concentration. -The rate of water diffusion is the rate of osmosisOsmole: the total number of particles in a solution if it’s measured by Osmole/Kg of water called Osmolality and if measured in Osmole/L of solution called Osmolarity

Osmotic Equilibrium OE is maintained between IC and ECFsWe can divide fluids according to tonicity into 3 classes:

1- isotonic: IC=EC and solutes can’t leave the cell it doesn’t cause the cell to shrink or swell2- hypotonic: has lower concentration of impearment solutes. Water will diffuse into the cell causing its swelling3- hypertonic: has higher concentration of impearment solutes. Water will diffuse out of the cell causing its shrinkage

Basic principles of exchange across the cell

membrane

1- water moves across the cell membrane freely 2- the cell membrane is almost completely impermeable to solutes

Physiology: EdemaEdema: presence of excessive fluid in the tissuesEdema can be divided into:

1- IC edema: excessive fluid inside the cells occurs in 3 conditions:A- hypornatremia (what?). B- depression of the metabolic system of the tissue. C- lack of adequate nutrients to the cell 2- EC edema: occur because of 2 reasons:A- abnormal leakage of fluidB- failure of lymphatic system to return fluid

How IC edema occurs?Blood flow delivery of oxygen and nutrients If blood flow becomes to slow to maintain normal tissue metabolism depression of cell membrane ionic pump Na that leaked into the cell can’t be pumped out IC Na concentration osmosis of water into the cell

EC edema The most important clinical cause of EC edema is extensive capillary filtration

What are the determinants of capillary filtration?1- filtration coefficient 2- capillary hydrostatic pressure. 3- plasma colloid osmotic pressure

Major types of EC edema

1-Lymphedema: when lymphatic function is impaired because of blockage or loss of lymphatic vesselsWhy it causes edema?

Blockage of lymphatic vessel is associated with infections of lymphatic nodes ( filaria nematodes) Lymphedema can occur with certain types of cancer or after surgery

2- Edema caused by heart failure:-fails to pump blood from arteries to veins venous and capillary pressure capillary filtration- AP excretion of salts by the kidneys blood volume capillary hydrostatic pressure- Blood flow to the kidneys renin secretion aldosterone secretion angiotensin IISalts and water retention

3- Edema caused by left-sided heart failure:(How?)

4- edema caused by the Kidneys:

Less excretion of salts and water by the kidneys cause:ECF volume to increase some of it leak to interstitial fluid and the other remains in the blood leading:1- increase of interstitial volume2- hypertension because of increased blood volumeLeading ultimately to generalized body edema.

5- edema caused by plasma proteins:

Low plasma protein concentration is due to

1- failure to produce plasma proteins by the liver2- leakage of plasma proteins from the plasmaLeading to decreased plasma colloid osmotic pressure and increased capillary filtration and consequently to edema

Categories of Edema1- Pitting Edema: when interstitial fluid pressure rises to +ive range leading to free fluid accumulation. It pushes the brush pile of proteoglycans filament apart. The fluid is not in Gel sate. 2- Nonpitting Edema: when tissue cells are swelled not the intersitium or when the interstitium becomes clotted with fibrinogen so that it can’t move freely

Why normal people don’t have edema?

Because of the safety factors:1- low compliance of interstitial fluid when its pressure is –ive. (providing 3 mmHg)2- the ability of lymph flow to increase 10 to 20-fold. (providing 7 mmHg) 3- wash-down of interstitial fluid protein concentration. (providing 7 mmHg)As a result there is 17 mmHg safety factor against edema

Pathology: OEDEMA Edema is observable swelling from fluid accumulation in body tissues. Edema most commonly occurs in the feet and legs, where it is referred to as peripheral edema. The swelling is the result of the accumulation of excess fluid under the skin in the spaces within the tissue

Approx. 60% of lean body weight is water;Two thirds of which is intracellular Most of the remaining water is found in extracellular compartments in the form of interstitial fluid ; only 5% of the body’s water is in plasma .

Body Cavities

Pathophysiological causes

Increased Hydrostatic pressure Impaired venous return

Congestive heart failureConstrictive pericarditisAscites (liver cirrhosis)Venous obstruction or compression  Thrombosis  External pressure (e.g., mass)  Lower extremity inactivity with prolonged dependency

..Arteriolar Dilation

HeatNeurohumoral dysregulation

Reduced Plasma Osmotic Pressure (Hypoproteinemia)

Protein-losing glomerulopathies (nephrotic syndrome)Liver cirrhosis (ascites)MalnutritionProtein-losing gastroenteropathy

Lymphatic ObstructionInflammatoryNeoplasticPostsurgicalPost-irradiation

Sodium RetentionExcessive salt intake with renal insufficiencyIncreased tubular reabsorption of sodium  Renal hypoperfusion  Increased renin-angiotensin-aldosterone secretion

InflammationAcute inflammationChronic inflammationAngiogenesis

PhysiologyFluid movement between the vascular and interstitial spaces is governed mainly by two opposing forces-

the vascular hydrostatic pressure and the colloid osmotic pressure produced by plasma proteins.

Pathophysiology Incremented Hydrostatic Pressure

Decremented Plasma Osmotic Pressure

Increased Vascular Permeability

Lymphatic Obstruction

Sodium & Water Retention

MORPHOLOGY

Edema is easily recognized on gross inspection; microscopic examination shows clearing and separation of the extracellular matrix elements. Although any tissue can be involved, edema most commonly is encountered in subcutaneous tissues, lungs, and brain.

The Lymphatic SystemAnatomy

Summary

Edema is the result of the movement of fluid from the vasculature into the interstitial spaces; the fluid may be protein-poor (transudate) or protein-rich (exudate).

SummaryEdema may be caused by:

increased hydrostatic pressure (e.g., heart failure) increased vascular permeability (e.g., inflammation) decreased colloid osmotic pressure, due to reduced plasma albumin

decreased synthesis (e.g., liver disease, protein malnutrition)increased loss (e.g., nephrotic syndrome)

lymphatic obstruction (e.g., inflammation or neoplasia). sodium retention (e.g., renal failure)

REFRENCE1-ROBBIN’S BASIC PATHOLOGY –CH32-GUYTON & HALL 12E –CH253-MEDICINENET