Pulmonary, Cutaneous, and Cerebral Circulations PDF

Pulmonary, cutaneous and cerebral circulations Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Trace the pulmonary blood flow from the right ventricle to the left atrium. Describe the function of the pulmonary vessels Identify the relationship between...

Pulmonary, cutaneous and cerebral circulations Dr. Ghada Elgarawany Assistant professor of Medical Physiology www.gmu.ac.ae COLLEGE OF MEDICINE Trace the pulmonary blood flow from the right ventricle to the left atrium. Describe the function of the pulmonary vessels Identify the relationship between pressure, volume, flow , resistance in the pulmonary circulation. Describe the cutaneous circulation and the cutaneous vascular reactions. Describe the characteristics of cerebral circulation, CSF and blood brain barrier. Characteristics of Pulmonary circulation 1. It lies between right and left side of the heart. It receives all cardiac output. 2. Thin vessels, Thickness of pulmonary artery is 30% of the aorta. Small pulmonary arteries has little muscles in the wall. 3. Pulmonary capillaries are large and have many anastomosis, each alveolus is surrounded by many anastomosis. 4. It exposed all the time to negative intrathoracic pressure. 5. It is Low pressure system (Blood pressure is 1/6 systemic circulation). 6. Pulmonary artery contains deoxygenated blood while the pulmonary veins contain oxygenated blood. Function of pulmonary circulation 1- Exchange of respiratory gases (O2 and CO2). 2- Blood reservoir: volume of blood in the pulmonary circulation is 1 liter. In Hemorrhage: vasoconstriction of the pulmonary circulation → shift of blood to the systemic circulation. 3- Blood filters: pulmonary capillaries filter the venous blood from minute blood clots and tissue debris before they reach the circulation. Relationship between pressure, volume, flow , resistance in the pulmonary circulation Pulmonary artery pressure 1. Systolic blood pressure = 25mmHg. 2. Diastolic blood pressure = 10 mmHg F= ∆𝑷 𝑹 PBP= 𝟐𝟓 𝟏𝟎 3. Mean pulmonary pressure = 15 mmHg Pulmonary blood flow = 5 liters/min Pulmonary resistance Pulmonary resistance = 0.13- 0.15 PRU It is 1/7 resistance of the systemic circulation What is the difference between Pulmonary and systemic blood pressure Regulation of pulmonary circulation Central Peripheral Nervous: Sympathetic system supplies the pulmonary blood vessel → pulmonary vasoconstriction (shift of blood to systemic circulation) Decrease O2 tension (Hypoxia), increase CO2 tension and increase H+ concentration Hormonal: Norepinephrine, epinephrine and angiotensin II → pulmonary vasoconstriction Peripheral regulation Decrease O2 tension (Hypoxia), increase CO2 tension and increase H+ concentration in certain alveoli → vasoconstriction of pulmonary blood vessel in these alveoli → shift of the blood to other healthy alveoli. Effect of gravity on pulmonary circulation Gravity has marked effect on pulmonary circulation. In standing position→ little blood flow to the top of the lung and the flow is increased in the lower lung. There is linear increase in the pulmonary blood flow from the apex to the base of the lung. Intermittent So the Blood Flow is 1- Intermittent at the apex : blood flow only in systole because the Pulmonary pressure is more than the alveolar pressure only in systole 2- Continuous at the base: blood flow in systole and diastole because the Pulmonary pressure is more than the alveolar pressure both in systole and diastole. Cutaneous Circulation (skin) Cutaneous blood flow = 500ml/min. The arterioles are responsible for body temperature regulation , while capillaries are responsible for the color of the skin. Function 1. Body temperature regulation. 2. Reservoir of the blood. 3. Skin nutrition. Continuous Cutaneous Circulation Cutaneous vascular reactions 1. White line reaction: A light stroke on the skin by a blunt object produce a white line. It is due to constriction of precapillary sphincter. 2. Triple response of Lewis: 1. Red line stage: due to capillary vasodilation 2. The spreading flare: due to local axon relfex that causes arteriolar vasodilation 3. The wheal (oedema) : due to increase capillary permeability that causes fluid to move to interstitial spaces Cerebral Circulation Cerebral blood flow = 750ml/min. Blood flow to the gray matter is 6 times the blood flow to the white matter. It is very sensitive to ischemia and hypoxia because 1. It has a very high metabolic rate. 2. Brain metabolism is aerobic (need O2). 3. Brain uses only glucose as a source of nutrition. Cerebrospinal fluid (CSF) A clear fluid surrounding the brain that cushions and protects it within skull. Formed by choroid plexus, it is about 150 ml. Function: Protection, Nourishment and Drainage of waste material of the brain. Cerebral Circulation Blood Brain Barrier It is histological and functional barrier that separate the blood inside the cerebral capillaries from the surrounding interstitium. Formed of 1. Endothelial tight junctions. 2. pericytes in the Basement membrane. 3. Astrocyte foot processes. Function: 1. Keep the internal environment of CNS in a homeostatic situation. 2. Prevent entry of toxin to the brain. 3. Keep brain antigens inside it. Summary Trace the pulmonary blood flow from the right ventricle to the left atrium. Describe the function of the pulmonary vessels Identify the relationship between pressure, volume, flow , resistance in the pulmonary circulation. Describe the cutaneous circulation and the cutaneous vascular reactions. Describe the characteristics of cerebral circulation, CSF and blood brain barrier.