Heart and Blood Vessels.docx

Heart and Blood Vessels- - Deoxygenated blood from the head and arms enters the heart through the superior vena cava. Deoxygenated blood from the rest of the body enters the heart through the inferior vena cava. - Both vessels empty into the right atrium. The contraction of the atrium causes this bl...

Heart and Blood Vessels- - Deoxygenated blood from the head and arms enters the heart through the superior vena cava. Deoxygenated blood from the rest of the body enters the heart through the inferior vena cava. - Both vessels empty into the right atrium. The contraction of the atrium causes this blood to flow through the tricuspid valve into the right ventricle. When the ventricle contracts, it forces the blood out through the semilunar valve into the pulmonary artery, which goes into the lungs, where the blood loses CO2 and collects oxygen - Oxygenated blood leaves the lungs through the pulmonary veins and enters the heart at the left atrium. The contraction of the atrium causes this blood to flow through the bicuspid valve into the left ventricle. When the left ventricle contracts, it forces the oxygenated blood into the aorta, through the semilunar valve. Blood from the aorta travels around the whole body Hepatic Portal System Veins that do not return to the heart but go to a second capillary bed are called portal veins. The vein leading from the intestines to the liver is called the hepatic portal vein. The hepatic portal vein brings blood rich in digested food, but lacking in oxygen, from the intestine directly to the liver. The blood is modified in the liver and then transported back to the heart. (6) Heartbeat The heart muscle is a specialised tissue. It is strong, branched, and never tires. The normal rate of the human heart when resting is about 75 beats per minute. CO2 levels in the blood are monitored by the Medulla Oblongata in the brain and this information is used to control the heartbeat. Each beat of the heart sends a pulse of pressure along the artery. This is most easily detected at the wrist or neck and is normally taken at the wrist using the first two fingers of the left hand. The heartbeat is the sound made by the valves of the heart closing. It is often described as a ‘lub-dub’ sound. The ‘lub’ is made when the bicuspid and tricuspid valves shut under the backpressure from the blood in the contracting ventricles. The ‘dub’ sound is made when the semilunar valves of the aorta and pulmonary artery slam shut at the backpressure from the arteries. Heart-muscle tissue is auto-rhythmic and will beat on its own. However, there is a pacemaker in place to coordinate the contraction of cells in sequence. It consists of a group of cells in the wall of the right atrium, called the sino-atrial (SA) node which initiates the actual contraction, and a relay station in the wall between the left and right atria near the ventricles, called the atrioventricular (AV) node. The Cardiac Cycle The Cardiac cycle is one complete sequence of blood filling and emptying the heart. - Diastole is the period of relaxation during which the heart fills - Systole is the period of contraction during which the heart empties - Both sides of the heart beat in unison During diastole, the muscles of the atria and ventricles relax, allowing blood to flood from the vena cava and pulmonary veins into the atria and ventricles. - Once the chambers are full, the SA node initiates contraction, which forces the last of the blood from the atria into the ventricles. Once the atria is completely empty, the AV node initiates systole. - This contraction slams the cuspid valves shut, preventing blood being forced back into the atria and forcing blood out of the heart through the semilunar valves into the aorta and pulmonary arteries - Both atria and ventricles relax, and diastole starts again. The semilunar valves prevent backflow of blood under pressure from the arteries Blood pressure - Blood pressure is the force exerted by the blood on the walls of the arteries due to the contracting of the heart. It depends on the volume of blood within the system and the space available within the blood vessels - Blood pressure is measured in an artery of the upper arm using a sphygmomanometer. - An inflatable cuff is used to measure the pressure required to stop the blood flow at this point. Two pressures are measured: systolic and diastolic pressures of the ventricles (120/80 mm Hg – for a healthy adult). - These values normally rise with age. If the lower of the two is above 95 the person is suffering from high blood pressure (hypertension). High blood pressure is often caused by blockages in arterioles or small arteries. A healthy circulatory system - Smoking: Smoking can cause cancer, emphysema, atherosclerosis, and high blood pressure which can lead to heart attacks and strokes - Diet: A diet rich in saturated fats can lead to obesity which can cause high blood pressure and a blockage of coronary arteries, leading to heart disease - Exercise: Regular exercise improves the efficiency of the circulatory system and reduces the risk of heart disease Blood Composition Plasma Plasma makes up 55% of blood. Plasma is a straw-coloured liquid matrix composing of 90% water and 10% dissolved proteins, salts, foodstuffs and waste materials. Functions of Plasma Proteins - A series of proteins prevent blood loss and the entry of pathogens by clotting - Antibodies mark pathogens and infected or damaged cells for attack by phagocytic white blood cells - Albumen maintains the osmotic balance within the organism Functions of Dissolved Salts - Maintain osmotic balance - Essential for the proper functioning of cells Red Blood Cells -Red blood cells are the most abundant cells and are produced in the red bone marrow of long bones. - Red blood cells do not contain a nucleus or mitochondria when they are mature, which allows them to carry out their role of transporting oxygen around the body with maximum efficiency - Biconcave discs - Filled with the red respiratory pigment haemoglobin - Survive for approximately 120 days before being broken down and recycled by the spleen and liver to make bile pigments White Blood Cells White blood cells are made in the bone marrow. Their numbers can increase when an infection is present. White blood cells defend the body from attack. There are many different types of white blood cells including: - Monocytes: The largest white blood cell and account for about 7% of all white blood cells. They form part of the innate immune system, attacking and engulfing anything they consider not to be part of the body itself. Monocytes have a large bean shaped nucleus; they move by amoeboid motion and engulf cells by phagocytosis. After engulfing the cells, they present antigens from the destroyed cell to T-Cells. - Lymphocytes: Have a large spherical nucleus and they make up 20-40% of all white blood cells. They are stored in the lymphatic system. Most are short lived, surviving for only a few weeks. There are many types of lymphocytes including T Cells (attack invaders), and B-Cells (make antibodies). Platelets - Cellular fragments that play a major role in blood clotting - They gather at the site of a wound and start a series of chemical reactions that result in the production of fibrin - Fibrin forms a network of strands across the wound, trapping blood cells and forming a scab. This prevents blood loss and the entry of pathogens Blood Groups - Blood groupings are based on antigens that occur on the outer surface of blood cells. An antigen is a substance that produces an immune response, which is essentially the production of a protein called an antibody. - Blood groups determine which blood groups can be safely received in blood transfusions. - If someone is given the wrong blood group in a transfusion there may be a sever allergic reaction, which can kill. Blood Group O A B AB Antigens Neither A B A and B Antibodies A and B B A Neither Population 55% 31% 11% 3% Rhesus Factor - The Rhesus protein was first discovered in Rhesus Monkeys - Blood with the rhesus antigen on the surface is said to be Rhesus positive (RhD+), and blood without it is said to be Rhesus negative (RhD-) Importance in pregnancy - If the mother is Rhesus negative, and the unborn child is Rhesus positive, then some of the baby’s Red blood cells with Rhesus antigens may cross into the mother’s bloodstream at the end of pregnancy. - The mother will recognise these rhesus antigens as ‘foreign’ and produce antibodies against them. Usually there is no danger to the baby during the first pregnancy, though the mother is now sensitised to the rhesus antigen. - The antibodies produced by the mother will destroy the baby’s red blood cells in subsequent Rhesus positive babies because antibodies pass into baby. - This may cause the baby to be anaemic, brain damaged or stillborn - To prevent this happening, the mother may be injected with Rhesus antibodies immediately after the birth of her first child. These will destroy the baby’s red blood cells before they cause a natural build-up of anti-Rhesus antibodies in her blood Mandatory Practical – Dissect, Display and identify a sheep’s or ox’s heart - Place the heart on a dissecting board with the front facing upwards - Identify the blood vessels: aorta, pulmonary artery, vena cava and pulmonary vein. - Make a shallow cut in the left ventricle and the left atrium. - Push open the chambers and examine the internal structure. - Locate the bicuspid valve and note the chordae tendinae – anchoring the cusps of the valve - Repeat the previous steps for the right side of the heart. - Locate the tricuspid valve and note the chordae tendinae anchoring the cusps - Note the difference between the walls of the left ventricle and the right ventricle - Locate the septum separating the left from the right side of the heart. - Insert a forceps under the moderator band in the right ventricle - Identify the opening at the base of the aorta, above the semi-lunar valves, leading to the coronary arteries - To highlight the coronary arteries: Using a dropper, pump air into the opening at the base of the aorta Mandatory Practical – Investigate the effect of exercise on the pulse rate of a human - Measure your resting pulse rate at the wrist, using your second finger. Count the number of beats in 15 seconds and multiply this figure by 4. Repeat twice more and take an average - Take some gentle exercise, like walking, for three minutes and then sit down -Record your new pulse rate three times and take an average Note the time taken for the pulse to return to its resting rate - Take some strenuous exercise, like running, for three minutes and sit down - Record the new pulse rate three times and take an average - Once again, note the time it takes for your pulse to return to its resting rate - Document the results as follows Activity Pulse Rate 1 Pulse Rate 2 Pulse Rate 3 Average Pulse Rate Time taken to return to resting rate Resting Running Walking - Heart rate increases with level of exercise - The faster the heart rate is after exercise, the longer it takes to return to normal - A fit person’s heartbeat is slower at rest, and returns to resting rate faster than that of an unfit person