Heart Structures & Circulation PDF

CHAPTER 8 Circulation – The Heart and Blood Vessels  Circulation overview Arteries: blood away from heart Veins: blood towards the heart Capillaries: where most exchange takes place Pulmonary circulation: between the heart and lungs Systemic circulation: between heart and the rest of the bo...

CHAPTER 8 Circulation – The Heart and Blood Vessels  Circulation overview Arteries: blood away from heart Veins: blood towards the heart Capillaries: where most exchange takes place Pulmonary circulation: between the heart and lungs Systemic circulation: between heart and the rest of the body Coronary arteries: supply the heart muscles with blood. Cardiac veins: return blood from heart muscles. Blood flow through blood vessels Heart aorta arteries arterioles capillaries venules veins heart pulmonary arteries lungs pulmonary veins (back to heart, at beginning) red = oxygenated blood blue = deoxygenated blood Specific Blood Vessels (Systemic circulation) Arteries: with highest blood pressure, so they need thick middle and outer layers. Elastic recoil helps move the blood forward. Arterioles: are small arteries. Capillaries: where exchange takes place. Only single layer of endothelium with flattened cells, to facilitate exchange. Venules: are small veins Veins: with low blood pressure, and store lots of blood. Generally with thinner walls, but with high lumen diameter for blood storage. With one way valves.  Blood vessels: arteries Endothelium: smooth epithelial cells, reduces friction of flow Middle layer: smooth muscle can contract and relax for vasoconstriction and vasodilation. Also elastin connective tissue, produces stretching and recoil, which helps move the blood forward. You feel this stretching as your pulse. Outer layer: Connective tissue (collagen) anchors vessels in place and protects them Arteries have the highest blood pressure, so they have thick middle and outer layers. Blood vessels: arterioles Arterioles are basically small arteries. With smooth muscle and endothelium layers. Smooth muscle of arterioles: constricts (vasoconstriction) or widens (vasodilation) to regulate blood flow to capillaries Pre-capillary sphincters contract or relax to regulate blood flow to capillaries When does your blood circulation change? Blood vessels: arterioles and capillaries  Blood Vessels: capillaries Capillaries are where almost all exchange of materials between blood vessels and living tissues takes place. Only endothelium: a single layer of squamous (flat) epithelial cells, which makes exchange easier Gaps and pores allow exchange of nutrients, gases, wastes, hormones, white blood cells between capillaries and tissues Large things stay in capillary: RBC’s, platelets, large proteins like albumin Supply all cells with material needed to survive, remove waste from all cells Capillary structure Capillaries Some blood plasma squeezed out of capillaries by blood pressure Proteins (like albumin) / red blood cells stay in capillary Fluid reuptake by osmotic pressure (water movement from high  low concentration) Albumin plasma protein is important for reuptake of water back into the capillaries by osmosis. Edema in starving children, less albumin protein leads to water staying in tissues  Not all fluid is taken back up by osmosis. The excess fluid: returned to veins near the heart by the lymphatic system (one of its functions) Blood vessels: venules / veins With connective tissue outer layer, smooth muscles middle layer and endothelium inner layer. Carries blood toward the heart. Some exchange of materials occurs at venules Stores blood. 50-60% of all of the blood in your body is in veins. To store this blood, veins tend to have a wide lumen, (interior space) to increase the volume of blood they can store. Blood pressure is low, so veins do not need a thick middle and outer layer like arteries. One-way valves ensure blood flows back to heart  Blood vessels: venules / veins Mechanisms in blood return Gravity (for veins above heart) Contraction of skeletal muscles (movement increases blood flow) Smooth muscles surrounding veins contract One-way valves (works with muscle squeezing) Pressure changes associated with breathing Inhaling produces: low pressure thorax, high pressure abdomen blood flows from high to low pressure (towards heart)  Blood vessels: venules / veins Mechanisms in blood return It is important to exercise on long plane flights: avoid deep vein thrombosis and pulmonary embolisms The heart (what is the path of blood?) Right Left The heart (structure) 4 Chambers: two atria, two ventricles (left ventricle: very muscular, to pump to the whole body) Two atrioventricular (AV) valves, two semilunar valves: (pulmonary and aortic) (blood flows in one direction only, connective tissue prevents valve flaps from opening the wrong way) The heart Cardiac cycle Blood flow follows pressure differences. Valves do not allow back flow. Cardiac cycle “lub-DUB” heart sounds: lub lub: atrioventricular lub (AV) valves close DUB: semilunar valves close DUB DUB Heart Sounds and heart Valves Lub-DUB: sounds of the heart are due to heart valves closing Heart murmurs: unusual heart sounds (swishing noises) indicating backflow through valves. Artificial heart valves can be used to replace faulty valves  Heart muscles contractions Sinoatrial (SA) node: cardiac pacemaker is modified cardiac muscle that generates an electrical signal Gap junctions: carry electrical impulses between cells: many cardiac muscle cells contract at once. Atrioventricular node (AV): receives impulse AV bundle / Purkinje fibers: carry impulse to lower ventricles first, then upper  Controlling the heart rate Heart can beat by itself, at about 100 beats / minute At rest, the medulla oblongata (part of the brain) dampens the sinoatrial node, and your heart beats slower. Stress, exercise: (more oxygen needed) heart stimulated to beat faster by medulla oblongata, and heart rate increases. Heart rate can exceed 100 beats / minute due to nervous stimulation by the medulla oblongata. Maintaining homeostasis of blood pressure Blood pressure: monitored by baroreceptors (stretch receptors) in aorta and carotid arteries, message goes to medulla oblongata. Medulla controls heart rate and width of arterioles: Increased heart rate + vasoconstriction = raised blood pressure Decreased heart rate + vasodilation = decreased blood pressure  Blood Pressure Definitions: Systolic pressure (high) Diastolic pressure (low) Measurement: sphygmomanometer Cardiovascular disorders: high blood pressure Hypertension: (> 140 / 90) You should start to become concerned if blood pressure is (> 120 / 80) Higher pressure leads to stiff, scarred arteries which leads to resistance to blood flow (heart must work harder). Scarred areas inside arteries may have cholesterol plaques deposited (atherosclerosis). Cardiovascular disorders: high blood pressure The silent killer: many don’t know they have it, as there are no obvious signs (except heart attacks and stroke, and then it’s too late). It may cause: Arteriosclerosis Embolism Heart attack Stroke Aneurysm Kidney damage and failure Cardiovascular disorders: high blood pressure Risks: Heredity Race (Africans have a greater risk) Age (blood pressure increases as you age) Sex (males have a greater risk) Arteriosclerosis Obesity Lack of exercise Salt intake Alcohol Smoking (nicotine increases heart rate and hardens arteries) Stress (epinephrine increases heart rate) Diabetes (if not properly controlled) Cardiovascular disorders: atherosclerosis A disease characterized by cholesterol plaque deposits and narrowed arteries. Cardiovascular disorders: embolism Blockage of blood vessels Usually caused by blood clots that have broken off. Can also be formed by tissue fragments, cancer cells, cholesterol clumps, bacterial clumps, air bubbles (SCUBA) Blood flow past the embolism stops or is restricted. Embolisms in coronary arteries can cause heart attacks. Embolisms in arteries that supply the brain can cause strokes. Part of a clot breaks loose, causing an embolism Cardiovascular disorders: angina pectoris These are chest pains and feeling of tightness in the chest, and they are a warning of worse things to come. Atherosclerosis limits blood flow to heart muscles, leads to pain in chest, shortness of breath, sensation of suffocating. If left untreated, a heart attack may follow days, weeks, months or years later. Cardiovascular disorders: heart attack Results in permanent damage to heart muscles. Blocked coronary arteries leads to oxygen cut off from cardiac muscles, which causes heart tissue death. Intense chest pain, pain or numbness in left arm (often for men), jaw and upper back pain (often for women) sweating, nausea, feeling of a heavy weight on chest, making it hard to breath. Get medical help as soon as possible. Aspirin may dissolve a blood clot. Cardiovascular disorders: ventricle fibrillation Most heart attack deaths are due to ventricle fibrillation, irregular heart beats when the sinoatrial node loses control of heart rhythm. Disorganized, “quivering” contractions result, leading to sudden unconsciousness. Defibrillation can hopefully shock the heart back to beating normally CPR can hopefully keep a person alive until professional help arrives. 30 compressions, 2 breaths. Preventing more heart attacks Treat with medications that lower blood pressure and reduce blood cholesterol levels Aspirin once / day helps prevent blood clots Bypass surgery: Veins or arteries grafted onto aorta and coronary arteries to “bypass” blocked areas Balloon angioplasty: flattening plaque so blood can flow. Laser angioplasty: vaporizing plaque Stent: wire / plastic cylinder inserted to keep coronary artery open  Cardiovascular disorders: stroke Stroke: Lack of blood flow to parts of the brain Due to: blocked blood flow to some areas (embolism), or blood vessel rupture (aneurysm) in brain High blood pressure / atherosclerosis = worse risk Brain tissue dies permanently Effects of stroke depend upon area of brain that dies: death, trouble speaking, numbness / paralysation of certain areas of the body, comprehending speech, loss of coordination. Recovery involves “retraining” nerves to take over function from damaged areas Cardiovascular disorders: aneurysm Weakening of arteries and ballooning outward lead to arteries bursting. Can lead to death due to massive internal bleeding Often caused by a combination of atherosclerosis and high blood pressure, weakening of arteries can be caused by genetic factors and injuries too. An aneurysm that has not yet ruptured.  The chart o’ death DEATH!!! Salt Stress Aneurysm Heart attack Stroke Alcohol High blood pressure Atherosclerosis Obesity Smoking High cholesterol Sugar No exercise Diabetes Saturated fats  Reducing risk of cardiovascular disease Smoking: Don’t!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Alcohol: also don’t Exercise and maintain a healthy weight (regular exercise) Reduce stress levels (exercise, back rubs, meditate, bubble baths, yoga, etc.) Cut back on salt, it may cause high blood pressure Diet should be low in saturated fat / cholesterol. Diet should be low in sugar. Sugar causes liver to make more cholesterol Eat soluble fiber (apples, bananas, carrots, barley, oats) they block cholesterol uptake. Fish oil removes cholesterol from blood. Control of diabetes: early diagnosis and treatment is important Monitor blood pressure, treat high blood pressure Benefits of exercise to your heart Reduced blood pressure Lower stress levels Less cholesterol in blood Greater number of red blood cells Greater blood circulation (more blood vessels) supplying the heart itself Stronger heart leads to reduced heart rate (heart does not work as hard over time)  Chiras DD Human biology, health homeostasis and the environment, Jones and Bartlett, Sudbury, Mass, 2002