Interstitial Fluid Formation and Oedema

By DR QAZI IMTIAZ RASOOL

Objectives

1.Describe the physiological anatomy of capillary circulation.

2.Identify the values for normal capillary blood flow.

3.Discuss the dynamics for interstitial fluid formation.

4.Correlate this knowledge to edema formation.

BODY COMPOSITION

Capillary Exchange Capillary Exchange functionsfunctions

4 important

1. Maintain constant communication between plasma and ISF

2. Speeds the distribution of nutrients, hormones, and dissolved gases throughout tissues

3. Assists the movement of insoluble lipids and tissue proteins that are impermeable

4. Flushes bacterial toxins and other chemical stimuli to lymphoid tissue and organs that provide immunity.

Features of the blood capillaries:

1. 1 mm length.

2. 10 billion capillaries

3. TSA 500-700 sq; mts.

4. Wall is 0.5-1. µ thick

5. 25,000 miles -adult

6. 5 %of blood -flowing

7. Arteriolar ends – precapillary sphincters.

8. Flow slow intermittent,(0.5mm/sec)

9. Alternating periods of closure and opening which occur

6-12 times/ minute.( vasomotion.(O2)

Depending on structure it distinguished three types of capillaries: somatic, visceral and sinusoidal. Capillaries walls are composed from one layer of endothelial cells and basal membrane. Endothelial cells are active elements of capillary bed.

In kidneys glomeruls, intestinal epithelium, capillaries are fenestrated. This specialty permits passing through endothelial cells water, ions and other even rather large molecules as aminoacids or fructose. In red bone marrow, liver and spleen capillaries have interrupted walls, which let passing even blood cells.

Tissue Fluid

small arterysmall vein

lymphatic

cells

arteriole

venule

capillariestissue fluid

Tissue Fluid

- 30 l of plasma pass out of capillaries/ day into the Interstitial Fluid. -27 l resorbed by capillary -3 l left in tissue spaces get resorbed by lymphatics.

Fluid Pressures (Starling’s Law)

Fluid flows only when there is a difference in pressure

1.1st space shifting- normal distribution of fluid in both the ECF compartment and ICF compartment.

2.2nd space shifting- excess accumulation of interstitial fluid (edema)

3.3rd space shifting- fluid accumulation in areas that are normally have no or little amounts of fluids (ascites)

Interstitial Fluid

1.Fluid between cells

2.Derived from capillaries

3.Solutes similar to plasma except for protein content

4.Movement Of Fluid Across Capillaries

5. Starlings factors;-

1.Capillary (hydrostatic) pressure

2.Interstitial fluid (hydrostatic) pressure

3.Plasma oncotic pressure

4.Interstitial fluid oncotic pressure

5. Negative Interstitial fluid pressure

6.Endothelial integrity

7.Lymphatic system

1. Plasma membrane 1. Separates ICF from surrounding interstitial fluid

2. Blood vessel wall 1. Separate interstitial fluid from plasma

Barriers separate ICF, interstitial Barriers separate ICF, interstitial fluid and plasmafluid and plasma

Balance Sheet Arterial/Venous

Net out (Filtration pressure) 13 mmHg// (Reabsorption pressure) 7 mmHg

Outward

1.Cap. pressure 30/10 mmHg

2. Negative interstitial fluid pressure 3/3 mmHg

3. Interstitial oncotic pressure 8/8 mmHg

Total 41/21mmHg

Inward

Plasma oncotic pressure

28/28 mmHg

CONDITION OF THE ARTERIOLES

1.Dilation of the arterioles cap. Blood flow cap. pressure.

2. Constriction of the arterioles cap blood flow cap pressure.

3.Bayliss effect, BP , arterioles are stretched which counteract tendency for pressure to blood flow

4.Venous pressure:

- venous pressure capillary blood pressure

Oedema

An increased volume of interstitial fluid in a tissue or organ

1.Hydrostatic pressure 2.Oncotic pressure3.Endothelial integrity4.Lymphatic integrity

1. Raised Capillary Pressure

Increase of capillary blood pressure (=increase of filtration force):

1.Cardiac edema, there is increase of the venous pressure increase of capillary BP increase of filtration edema.

Cardiac failure1.right ventricular failure - systemic oedema

2.left ventricular failure - pulmonary oedema

3.congestive cardiac failure – both

2.Local venous obstruction1.Pregnancy edema (last months) large uterus --- on the iliac veins

2.Deep vein thrombosis

3.External compression

4.Superior Venous obstruction

.

2. Reduced Oncotic Pressure

Decrease of the colloidal osmotic pressure of the plasma proteins (=decrease of reabsorption force):

-- concentration of plasma proteins decreases to 5gm/dL or less, examples:

a. Malnutrition edema due to decrease of protein intake in diet or decrease of absorption of food proteins from the small intestine.

b. Renal disease due to loss of proteins in urine is called nephrotic syndrome.

3. Lymphatic Obstruction3. Obstruction of lymph vessels (=decrease of lymph drainage):

-Lymphatic obstruction decrease of lymphatic drainage from the affected part lack of drainage of excess tissue fluid which accumulates lymphatic edema, examples:

a. Elephantiasis which is a marked lymphatic edema of the lower limbs due to obstruction of their lymph vessels from inside by filarial worms (parasites).

b. Obstruction of the lymph vessels by malignant cells (tumour). Edema occurs in the part drained by the obstructed lymph vessels.

c. Tumours

d. Fibrosis

e.Inflammation

4. Increase of capillary permeability (= increase of filtration):

◦ capillary dilatation due to release of vasodilator substances such as histamine & kinins, e.g. Allergic edema, Inflammatory

5.Surgery

6.Congenital abnormality

HYPERVOLUMIA

NA+ and water retention (=increase of plasma volume):

plasma volume increase of filtration through the capillary wall edema

◦Excessive secretion of Aldosterone and glucocorticoids i.e, Cushing’s syndrome.

◦Prolonged use of (cortisol) as a drug.

◦ In pregnancy due to high level of estrogen and progesterone.

1..

TYPES OF EDEMA:

1. Soft “pitting” edema i.e it pits on pressure. Most types of edema are pitting e.g. cardiac edema, nutritional edema… etc.

2. Hard “non-pitting” edema which occurs in some conditions e.g. in hypothyroidism (myxedema) due to presence of excess mucoproteins and fluids in the interstitial spaces.

According to its location or distribution, edema may be

1. Local edema e.g.

Edema of the triple response. Inflammatory edema

Edema in one limb (due to deep vein thrombosis in one lower limb).

2. Generalized edema e.g. Cardiac edema. Nutritional edema Renal edema