PPT MICROCIRCULATION OF VASCULAR SYSTEM

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DR HAROON RASHID ASSOCIATE PROFFESSOR DEPARTMENT OF PHYSIOLOGY COLLEGE OF MEDICINE ALMAJMAAH SAUDIA ARABIA

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MICROCIRCULATION – (CAPILLARY CIRCULATION):

MICROCIRCULATION – (CAPILLARY CIRCULATION) Dr.Haroon Rashid.

OBJECTIVES.:

OBJECTIVES.   Describe the physiological anatomy of capillary circulation. Identify the values for normal capillary blood flow. Discuss the dynamics for interstitial fluid formation. Correlate this knowledge to edema formation.  

Slide4:

The term Microcirculation refers to the functions of the capillaries and the neighboring lymphatic vessels. 5 % of circulating blood volume is present in the capillaries at any given time. This takes part into the exchange of nutrients, gases and waste products between the blood & tissues.

Lymphatic circulation :

Lymphatic circulation The interstitial fluid enter lymphatic capillaries through loose junctions between endothelial cells . Lymph flow back to the thoracic duct is promoted by contraction of smooth muscle in wall of lymphatic vessels & contraction of surrounding skeletal muscle . Failure of lymphatic drainage can lead to Edema .

The Microcirculation:

The Microcirculation Important in the transport of nutrients to tissues Site of waste product removal Over 10 billion capillaries with surface area of 500-700 square meters Solute and fluid exchange

Types of capillaries:

Types of capillaries Classified according to the size of the pores Brain – the pores are very tight and allow only very small molecules to pass thru. Kidney & Intestine - the pores are wider – fenestrations Liver - the endothelium is discontinuous with wide gaps between the cells.

EXCHANGE OF SUBSTANCES ACROSS THE CAPILLARY WALL:

EXCHANGE OF SUBSTANCES ACROSS THE CAPILLARY WALL This occurs by. Simple diffusion Lipid soluble gases such as O2 & CO2 readily diffuse through the endothelial cells. Bulk Flow - the most important mechanism for fluid transfer driven by Starlings forces.

Slide10:

Fluid movement = Kf [ (Pc – Pi) – ( Π c - Π i ) Kf = filtration coefficient

FLUID COMPARTMENT.:

FLUID COMPARTMENT. Total Body Water-60% of Body Weight.(42liters) in a 70kg person. Classification:-Intracellular fluid- 40%(28 liters) Extracellular fluid-20%(14liters) / \ Plasma-5% Intercellular-15%

PERCENTAGE OF FLUID.:

Average 70 kg person total body weight 42 litres total H 2 O 60% 28 l. Intracellular fluid (ICF ) 40% 14 l. Extracellular fluid (ECF ) 20% % is important in fluid therapy divided into ¾ ISF and ¼ plasma water 10.5 l. Interstitial fluid (ISF) 15% 3.5 l. Plasma water 5% PERCENTAGE OF FLUID.

Interstitial fluid:

Interstitial fluid Interstitial fluid; also known as intercellular fluid and tissue fluid is fluid between the cells of multicellular organisms bathes and surrounds the cells of the body, and provides a means of delivering materials to the cells, intercellular communication, and removal of metabolic waste.

Slide14:

- It represents the largest portion of the ECF compartment . The plasma and the interstitial fluid intermingle through pores in the blood capillaries which allow water and most dissolved substances except protein to diffuse . The exchange of material across the capillaries occurs at high rate by diffusion in both direction.

Slide15:

Formation of the IF ;The high content of proteins in the plasma accounts for its higher osmotic pressure compared to that of the IF which will attract fluid and dissolved substances into the circulation from the tissue spaces . Opposing this force is the hydrostatic pressure of the blood which tends to force fluids out of the circulation and into the tissue spaces, thus equilibrium is always maintained.

Slide17:

Edema; Is the term used to describe an unusual accumulation of interstitial fluid which occurs when an alteration in the balance mentioned earlier occurs . It could happen due to decrease in plasma albumin concentration leading to a decrease in blood osmolarity thus allowing fluid to escape from the circulation to the interstitial space.

Slide18:

The rate of filtration at any point along the capillary depends on a balance of forces – STARLINGS FORCES. 1. Capillary hydrostatic pressure Arterial end = 37 mmHg Venous end = 17 mmHg 2. Plasma colloid osmotic pressure = 25 mmHg 3. Interstitial hydrostatic pressure = 0 -1 4. Interstitial colloid osmotic pressure = 0 mmHg

Slide19:

Arteriolar end  fluid moves out into tissue spaces Venous end  fluid enters into capillaries. Any decrease in plasma proteins (hypoproteinemia) or increase in capillary hydrostatic pressure (cardiac failure) causes edema. (abnormal increase in interstitial fluid volume ) Histamines, bradykinin increases capillary permeability  edema.

Starling’s forces across capillary wall:

Starling’s forces across capillary wall 5/22/2016 20 Filtration Absorption

What is Edema?:

What is Edema? Accumulation of fluid beneath the skin or in a body cavity Palpable swelling produced by expansion of the interstitial fluid volume

Causes of Edema:

Causes of Edema Increase capillary pressure Increase vascular volume Heart failure Kidney disease Pregnancy Environmental heat stress Venous obstruction Thrombosis Liver disease Decrease colloidal osmotic pressure Increase loss of proteins Nephrotic syndrome Burns Decrease production Starvation, Malnutrition Liver disease

Edema::

Edema: The abnormal accumulation of fluid in a specific organ vs generalized. In capillary: Balance between hydrostatic pressure and oncotic (colloid osmotic) pressure.

Interstitial hydrostatic pressure::

Interstitial hydrostatic pressure: Varies from one organ to another: Subcutaneous tissue: Subatmospheric (-2 mmHg) Liver, kidney: + Brain: As high as 6 mmHg

Organ specific::

Organ specific: Brain: Cerebral edema Lung: Intra-alveolar=pulmonary edema, intra-pleural=pleural effusion Peritoneum=ascites Severe generalized edema=anasarca

Reduced oncotic pressure::

Reduced oncotic pressure: Reduction in production of colloids--- plasma proteins. Liver failure Malnutrition

Slide27:

Increase in loss of colloids--- plasma proteins. Nephrotic syndrome Catabolic states

Increase capillary hydrostatic pressure::

Increase capillary hydrostatic pressure: Venous end: Heart failure, deep venous thrombosis, superior vena cava obstruction etc. Arterial end: Pre-capillary dilatation. Calcium channel blockers.

Capillary leaks::

Capillary leaks: Result of capillary damage: Pleura: Infections, tumors Alveoli: Inhalation of noxious substance, eg chlorine gas etc

Diverse causes of edema::

Diverse causes of edema: Anaemia Hypothyroidism

Hormones involved in edema::

Hormones involved in edema: Renin angiotensin aldosterone system: secondary hyperaldosteronism ADH (Vasopressin) ANP

Jugular venous pressure::

Jugular venous pressure: Elevated and pulsating: =hypervolemia Then edema: Due to increased capillary hydrostatic pressure: Cardiac failure, or isolated RV (pulmonary Hypertension.) Hypervolemia caused by transfusion

Generalized edema without hypervolemia::

Generalized edema without hypervolemia: Decreased capillary colloid oncotic pressure: liver, kidney, catabolic states, malnutrition. Increased interstitial colloid oncotic pressure: lymphatic. Increase in capillary permeability: Inflammation, toxins, severe anaemia

Slide34:

Capillary Circulation. Define interstitial fluid with normal values. Define edema,& causes of it.

Slide35:

References:- Guyton & Hall,12 th edition. Ganong-24 th edition. Internet.

Slide36:

THANK YOU.

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