blood vessels.pdf

BLOOD VESSELS Dr. S. Ngubane  The Structure of Blood Vessels Venous Circuit Arterial Circuit Types of blood Tunica externa Large vein...

BLOOD VESSELS Dr. S. Ngubane  The Structure of Blood Vessels Venous Circuit Arterial Circuit Types of blood Tunica externa Large vein Large artery vessels Tunica externa Tunica Tunica media a.Arteries media Tunica b.Arterioles interna Endothelium c.Capillaries Endothelium Lumen Elastic layer Tunica interna d.Venules Inferior vena cava e.Veins Aorta Medium-sized vein Medium-sized artery Tunica externa Tunica externa Tunica media Tunica media Tunica interna Tunica interna Valve Venule Arteriole Tunica externa Endothelium Endothelium Lumen Valve Precapillary sphincter Endothelial cells Fenestrated Continuous capillary capillary Capillary pores Basement membrane 2  Tunics of blood vessels Tunica interna - inner layer; composed of simple squamous endothelium on a basement membrane and elastic fibers Tunica media - middle layer; composed of smooth muscle tissue Tunica externa - outer layer; composed of connective tissue 3  Arteries Elastic arteries: closer to the heart; allow stretch as blood is pumped into them and recoil when ventricles relax Muscular arteries: further from the heart; have more smooth muscle in proportion to diameter; also have more resistance due to smaller lumina Arterioles: 20−30 µm in diameter; provide the greatest resistance; control blood flow through the capillaries 4  Microcirculation Blood Blood Precapillary Metarteriole (forming flow flow Arteriole Venule sphincter arteriovenous shunt) Artery Vein Capillaries Smallest blood vessel: 7−10 µm in diameter Single layer of simple squamous epithelium tissue in wall Where gases and nutrients are exchanged between the blood and tissues Blood flow to capillaries is regulated by: a. Vasoconstriction and vasodilation of arterioles b. Precapillary sphincters: a band of smooth muscle that adjusts blood flow into 5 capillaries mainly in the mesenteric microcirculation.  Types of Capillaries a.Continuous capillaries: Adjacent cells are close together; found in muscles, adipose tissue, and central nervous system (add to blood-brain barrier) b.Fenestrated capillaries: have pores in vessel wall; found in kidneys, intestines, and endocrine glands c.Discontinuous: have gaps between cells; found in bone marrow, liver, and spleen; allow the passage of proteins 6  1. Different capillaries are distributed across the different tissues according to metabolic needs 2. Blood flow regulatory mechanism Precapillary sphincters and vasoconstriction and vasodilation as informed by the smooth muscle relaxation and contraction, respectfully regulate blood flow 3. During an adrenalin rush Blood is distributed according to the needs of various tissues during the surge. There would be increased blood flow towards some tissues eg CNS and inhibition of blood towards some eg GIT 7  + + - 8  Veins Most of the total blood volume is in veins Lower pressure (2 mmHg compared to 100 mmHg average arterial pressure) Thinner walls than arteries, larger lumen; collapse when cut 9  Veins cont: 4.Need help to return blood to the heart: a.Skeletal muscle pumps: Muscles surrounding the veins help pump blood. b.Venous valves: Ensure one-directional flow of blood c.Breathing: Flattening of the diaphragm at inhalation increases abdominal cavity pressure in relation to thoracic pressure and moves blood toward heart. 10 The action of one-way venous valves CVS 2015 11 ATHEROSCLEROSIS 9  Atherosclerosis Most common form of arteriosclerosis (hardening of the arteries) a.Contributes to 50% of the deaths due to heart attack and stroke b.Plaques protrude into the lumen and reduce blood flow. a.Plaques form in response to damage done to the endothelium of a blood vessel. b.Caused by smoking, high blood pressure, diabetes, high cholesterol 13 14  Atherosclerosis c. LDL+VLDL oxidised d. Immune system monocytes= h. rupture- forming a clot a.Caused by smoking, high blood pressure, diabetes, e. Inflammatory cytokines high cholesterol CRP f. Cell proliferation- smooth b.Damage the endothelial lining= Nitric oxide muscle cells start to migrate deacreased Out to the foam cells- release collagen Protein cap- to protect from blood 15 g. Ca+ --hardens the foam cells  Inflammation in Atherosclerosis a.Atherosclerosis is now believed to be an inflammatory disease. b.C-reactive protein (a measure of inflammation) is a better predictor for atherosclerosis than LDL levels. c.When endothelial cells engulf LDLs, they become oxidized LDLs that damage the endothelium d.Antioxidants may be future treatments for this condition. 16  Cholesterol and Lipoproteins a.Low-density lipoproteins (LDLs) carry cholesterol to arteries. 1) People who consume or produce a lot of cholesterol have more LDLs. 2) This high LDL level is associated with increased development of atherosclerosis b.High-density lipoproteins (HDLs) carry cholesterol away from the arteries to the liver for metabolism. 1)This takes cholesterol away from the macrophages in developing plaques (foam cells). 2)Statin drugs (e.g., Lipitor), fibrates, and niacin increase HDL levels. 3) Monitoring ones diet. Saturated fats increase LDL and unsaturated fats increase HDL 17 a.Ischemia is a condition characterized by inadequate oxygen due to reduced blood flow. 18  Ischemic Heart Disease a.Ischemia is a condition characterized by inadequate oxygen due to reduced blood flow. 1)Atherosclerosis is the most common cause. 2)Associated with increased production of lactic acid and resulting pain, called angina pectoris (referred pain). 3)Eventually, necrosis of some areas of the heart occurs, leading to a myocardial infarction (heart attack). 19  Ischemic Heart Disease cont: 4)Nitroglycerin produces vasodilation a)Improves blood flow b)Reperfusion injury may cause death of neighboring cells to enlarge the infarct 20  Detecting Ischemia 1)Depression of the S-T segment of an electrocardiogram 2) Plasma concentration of blood enzymes a) Creatine phosphokinase – 3-6 hours, return to normal in 3 days b) Lactate dehydrogenase – 48-72 hours, elevated about 11 days c) Troponin I – today’s most sensitive test d) Troponin T 21 Self directed learning 22  The heart during exercise Heart rate (or pulse rate) is the number of times your heart beats every minute. It is expressed in beats per minute (bpm). Normal resting heart rate varies from individual to individual and is affected by fitness. The fitter you are, the lower your resting heart rate will be. The average resting heart rate is about 60–75 bpm. You can measure how fast your heart is beating by taking your pulse. This can be done at the wrist or the neck. Count how many times your heart beats in 6 seconds and then multiply by 10. CVS 2015 23  The heart during exercise Each individual has a maximum heart rate – the fastest that their heart is able to beat. Testing it properly is difficult and unpleasant, as it involves pushing your body to its absolute limit. However, maximum heart rate can be estimated using a simple formula: Maximum Heart Rate (MHR) = 220 – age So, a healthy 25 year-old would have a maximum heart rate of 220 – 25 = 195 bpm CVS 2015 24  Heart rate, stroke volume and cardiac output The pulse rate is not the only way of measuring the heart. Stroke volume is the amount of blood pumped out of the left ventricle per beat. Cardiac output is the amount of blood pumped out of the left ventricle of the heart per minute Cardiac output can be calculated by multiplying the stroke volume by the heart rate: cardiac output = stroke volume x heart rate CVS 2015 25  The heart during exercise During exercise, the body uses up oxygen and nutrients at a much faster rate. To keep the body supplied with what it needs, the heart beats faster and with greater force. This means that the heart rate and stroke volume increase Regular exercise causes changes to the heart.  The heart gets larger  The muscular wall become thicker and stronger  Stroke volume at rest increases, leading to a lower resting heart rate CVS 2015 26  Blood pressure An individual’s blood pressure is affected by a number of factors.  Age – it increases as you get older.  Gender – men tend to have higher blood pressure than women.  Stress can cause increased blood pressure.  Diet – salt and saturated fats can increase blood pressure.  Exercise – the fitter you are the lower your blood pressure is likely to be. Having high blood pressure puts stress on the heart. It can lead to angina, heart attacks and strokes. CVS 2015 27