L24 Microcirculation and lymphatic system.pdf

Microcirculation and lymphatic system Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe characteristics of the capillary blood flow. List types of the capillaries and Identify the capillary function. Define vasomotion and describe its regulatio...

Microcirculation and lymphatic system Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Describe characteristics of the capillary blood flow. List types of the capillaries and Identify the capillary function. Define vasomotion and describe its regulation. Describe mechanisms of capillary exchange and Explain forces of Starling & describe Starling equation. Describe lymphatic system and list its function. Define oedema & describe its pathophysiological causes. Functional Parts of the Circulation 1- Arteries: transport blood under high pressure to the tissues because it contain strong vascular walls. 2- Arterioles: they are small branches of the arteries. they act as control conduits as they have strong muscular walls that can close the arterioles completely or, by relaxing, can dilate the vessels severalfold. So, arterioles alter blood flow. 3- Capillaries: Exchange fluid, nutrients, electrolytes, hormones between the blood and interstitial fluid. It contain thin wall. Functional Parts of the Circulation 4- Venules: collect blood from the capillaries then to veins. 5- Veins: Conduct blood from venules to the heart. They serve as a major reservoir of extra blood (Capacitance vessels). Because the pressure in the venous system is low, and the venous walls are thin. Blood volume 84% of the blood volume is in the systemic circulation 16% is in the heart and lungs. 9% Pulmonary 64% veins 13% arteries 7% heart 7% arterioles & capillaries Capillary circulation Adult body contains 40 billion capillaries with surface area = 6300m². Only 25% of capillaries (1 billion) are open with surface area = 3000 m². Diameter of the capillaries is 5μm at arterial end and 9μm at venous end. Capillaries formed of single layer of endothelial cell and contains precapillary sphincters. Velocity of blood flow in the capillaries = 0.2-0.3 mm/sec. RBC transverses the capillary in 2 seconds. 0.5-1 μm thickness 0.7mm long Types of capillaries Continuous capillaries Site: Muscle and brain. Structure: protein ridge that hold the cells together, small pores between the cells allow molecules up to 10nm. Strainer Fenestrated capillaries Site: Kidney, intestinal villi, and endocrine glands. Structure: it contains fenestration (large pores) , 20100nm in diameter → permit passage of large molecules. Types of capillaries Sinusoidal capallaries Site: liver , spleen and bone marrow Structure: it has very wide lumen, intracellular large gaps (600-3000nm in diameter) Capillary Vasomotion and Function Vasomotion: Capillary blood flows intermittently, turning on and off every few seconds or minutes. Causes of vasomotion: intermittent contraction of the metarterioles and precapillary sphincters. Regulation of Vasomotion by:  O2 concentration: ↓ O2 concentration → the intermittent periods of capillary blood flow occur more often, and the duration lasts longer → ↑ O2 concentration. Capillary Vasomotion and Function Function of the capillary circulation: Exchange of water, nutrients, and other substances between the blood and interstitial fluid Lipid-soluble substances diffuse directly through the cell membranes of the capillary endothelium. Like, O2 & CO2 Water-soluble, non–lipid-soluble substances diffuse through intercellular pores in the capillary membrane, like water, Na+, Cl-, and glucose Capillary fluid exchange The capillary hydrostatic pressure tends to force fluid and its dissolved substances through the capillary pores into the interstitial spaces. Conversely, osmotic pressure caused by the plasma proteins (called colloid osmotic pressure) tends to cause fluid movement by osmosis from the interstitial spaces into the blood. Interstitial space Starling forces that determine Fluid Movement Through the Capillary Membrane 1. The capillary hydrostatic pressure (Pc), which tends to force fluid outward through the capillary membrane 2. The interstitial fluid hydrostatic pressure (Pif), which tends to force fluid inward through the capillary membrane when Pif is positive but outward when Pif is negative. 3. The capillary plasma colloid osmotic pressure (Πp), which tends to cause osmosis of fluid inward through the capillary membrane 4. The interstitial fluid colloid osmotic pressure (Πif), which tends to cause osmosis of fluid outward through the capillary membrane Net Filtration Pressure(NFP) = Pc − Pif −Πp + Π if Starling forces that determine fluid movement through the capillary membrane At the arterial end =The capillary hydrostatic pressure = 30 to 40 mm Hg At venous end = 10 to 15 mm Hg in the middle = 25 mm Hg. in the kidney = 60 mm Hg. Pc = 10 Pc = 30 Pc = 25 Starling forces that determine fluid movement through the capillary membrane Pc = 30 Πp= 28 Πif = 8 Pif = -3 At the arterial end: The capillary hydrostatic pressure Pc= 30 mmHg The interstitial hydrostatic pressure Pif= - 3 mmHg Plasma oncotic pressure Πp = 28 mmHg Interstitial oncotic pressure Πif = 8 mmHg So, Net filtration pressure = [30 – (-3)] – [28 – 8] = 13mmHg 20 L is filtered /day Starling forces that determine fluid movement through the capillary membrane Pc = 10 Pc = 30 Πp= 28 Pif = -3 Πif = 8 At the venous end: The capillary hydrostatic pressure = 10 mmHg The interstitial hydrostatic pressure = -3 mmHg Plasma oncotic pressure = 28mmHg Interstitial oncotic pressure = 8 mmHg So, Net fitration pressure = [10 − (-3)] − [28−8]= -7mmHg (Net reabsorption) 18 L is reabsorped/ day 18 L reabsorbed 20 L filtered 2 L drained by lymphatic N.B: Net Filtration pressure (13mmHg) > Net reabsorption pressure (7 mmHg) → excess fluid in the tissue , 20L is filtered /day while 18L is reabsorbed/ day = 2 liter is drained by lymphatics. Lymphatic system Lymphatic system An accessory route through which fluid can flow from the interstitial spaces into the blood. Content: contain isotonic transparent fluid, similar to plasma but with less protein (3 gm%) and rich in lymphocytes Lymphatic capillary is highly permeable blind vessel lined by single layer of endothelial cells drain into → lymphatic vessels → thoracic and right lymphatic duct → open in superior vena cava. Factors that maintain Lymph Flow 1. Rhythmic contraction of smooth muscle of the wall of the lymphatic. 2. Skeletal muscle contraction. 3. Negative intrathoracic pressure 4. The hydrostatic pressure of the interstitial fluid. 5. Arterial pulsation 6. Gravity (only for lymph from upper body) Function of Lymphatic system 1. Return of excess tissue fluid that is not reabsorped by the capillaries Lymphatics can carry proteins and large particulate matter away from the tissue spaces. 2. Removal of bacteria from the tissue by the lymph node. 3. Drainage of lymphocyte from the lymph node into the blood. 4. Absorption of long chain fatty acid making the lymph of the thoracic duct has milky appearance. Edema Definition: excess fluid accumulates in the extracellular or in tissues space of body tissues. Types of edema Extracellular edema Intracellular edema  Excess intracellular fluid.  It is non pitting edema  Excess fluid in the interstitial space.  It is pitting edema. Causes: Causes: 1- depression of Na+-K+ pump → excess Na+ inside the cell → osmosis of water. 2- Inflammation. 1. 2. 3. 4. 5. Increase capillary hydrostatic pressure. Decrease colloid osmotic pressure. Increase capillary permeability Excessive salt retention Inadequate lymph drainage. Causes of Extracellular edema 1. Increase capillary hydrostatic pressure: due to increase venous pressure (heart failure, venous obstruction, and varicose veins). 2. Decrease colloid osmotic pressure → decrease tissue fluid reabsorption due to decrease albumin (hypoproteinemia) Causes of hypoproteinemia: 1- Lack of protein intake (nutritional edema, Kwashiorkor). 2- Decrease albumin production in liver disease. 3- Loss of albumin in kidney disease. Puffy eye kidney disease liver disease. Kwashiorkor Causes of Extracellular edema 3. Increase capillary permeability: due to inflammation, allergy, prolonged ischemia, and vitamin C deficiency 4. Excessive salt retention: due to renal and cardiac edema 5. Inadequate lymph drainage: due to blockage of the lymph vessels → accumulation of fluid and proteins in the tissue spaces → Non pitting edema Lymphedema Review Questions Which of the following components of the Starling equation is altered in a patient with kwashiorkor? A. B. C. D. Decreased capillary colloid oncotic pressure Decreased interstitial capillary pressure Increased capillary hydrostatic pressure Increased interstitial colloid oncotic pressure Summary Describe characteristics of the capillary blood flow. List types of the capillaries and Identify the capillary function. Define vasomotion and describe its regulation. Describe mechanisms of capillary exchange and Explain forces of Starling & describe Starling equation. Describe lymphatic system and list its function. Define oedema & describe its pathophysiological causes.