Circulatory System and Blood Components

Cardiovascular System Cardiovascular system delivers vital nutrients to all cells in the body, and eliminates waste products and carbon dioxide. Transports chemical messengers such as hormones Maintains a constant body temperature Three essential parts: heart, blood, vessels (arteries, veins, capillaries) Average human has 4 to 6L of blood

Blood contains many individual parts that serve many different functions. If blood is placed in a test tube and then spun in a centrifuge, it separates the blood into its parts. Heavier particles can be found at the bottom of the test tube. The liquid (plasma) stays on the top. Plasma makes up about 55% of blood and 90% of the plasma is water, the rest is salt, protein, hormones, nutrients, waste and gases. The other 45% is made up of formed elements such as erythrocytes (red blood cells), leucocytes (white blood cells), and platelets

Red Blood Cells Red blood cells are the most abundant. made in the bone marrow and stored in the spleen. Their primary function is to carry oxygen. They are constantly being destroyed and replaced. Have no nuclei or mitochondria Cytoplasm of the cells contain hemoglobin molecules that bind oxygen and have are made up of four protein chains, each with iron in the centre. Biconcave shape that lets them bend and fit through vessels.

White Blood Cells White blood cells called leucocytes are responsible for helping to defend the body against disease and infection. There are fewer white blood cells than red. Destroy and consume invading bacteria Made in bone marrow Pus sometimes forms on a cut, which is a combination of living and dead white blood cells with the dead bacteria.

Platelets Platelets are important for blood clotting. cell fragments that have broken off from cells in the bone marrow. When they find the damaged blood vessel, they break open and release chemicals called clotting factors into the blood. These factors help platelets to stick together to form a plug. Afterwards a molecule called fibrin is made, which forms a scaffold so that the repair can start. Hemophiliacs do not have a protein to form blood clots.

Blood Flow Can be Divided into Two Circuits

Pulmonary Circuit Lower pressure system Deoxygenated blood enter the heart at the right atrium and flows through the right atrioventricular valve (AV-valve) or the tricuspid valve and into the right ventricle. The AV-valve prevents blood from flowing back into the atrium Next, the blood passes through the pulmonary semilunar valve and enters the pulmonary trunk. From the pulmonary trunk, the blood is pumped to both lungs through the pulmonary arteries where it exchanges gases and then the oxygenated blood then goes from the lungs to the heart through the four pulmonary veins. The blood enters the left atrium and through the bicuspid or mitral valve and into the left ventricle where it is pumped to the rest of the body.

Systemic Circuit high pressure system must propel the blood with enough force for it to travel to all the parts of the body. When the blood leaves the left ventricle, it goes through the aortic semilunar valve and into the aorta (largest artery in the body) The aorta branches into arteries, which branch into arterioles, which turn into capillaries (where the oxygen is released into the cells) Capillaries join to venules which form veins, which bring the deoxygenated blood back to the heart through the superior vena cava (from the upper part of the body) and the inferior vena cava (from the lower part of the body) and into the atrium.

Heart Cycle and Sounds A special region of the heart muscle in the right atrium is where the pacemaker (SA node) is. Heart works in a continuous cycle of relaxation and contraction called the cardiac cycle.

Diastole During diastole, when the heart is relaxed, the blood flows into the 4 chambers. Blood enters the right atrium from the systemic circulation through the vena cavae. Blood enters the left atrium from the pulmonary veins The bicuspid and tricuspid valves are open during diastole, allowing the blood to flow into the chamber. Diastole ends with the contraction of the atria to further fill the ventricles. Lasts for about 0.4 seconds Blood pressure is reduced (diastolic blood pressure)

Systole Systole begins with the contraction of the ventricles and lasts for about 0.3 seconds. blood is expelled from the heart forcefully blood leaves the right ventricle and enters the pulmonary trunk blood leaves the left ventricle and enters the aorta bicuspid and tricuspid valves are closed blood pressure increased (systolic blood pressure)

Blood Pressure Average systolic to diastolic pressure: 120 mm Hg over 80 mm Hg The first heart sound is made at the beginning of systole when the ventricles contract. It creates a force that makes the valves close, and a sound can be heard. At the end of systole, when the pressure falls in the ventricles, the aortic and pulmonary valves close and creates the second sound.

Vessels Arteries = away from heart. Thick walls because they have to withstand the pressure. Three layers: inner epithelial, middle is smooth muscle and outer is connective tissue that allows it to stretch and aids in the process of moving the blood along. Arterioles are smaller than arteries and are less elastic. Capillaries are the narrowest. RBCs have to squeeze through single file and move a lot slower, which enables them to pick up CO2 and unload O2. Venules

Veins have thinner walls, and larger diameters and less muscle and must work against gravity a lot of the time. Have valves so blood can only go one way Skeletal muscles help move the blood Long periods of standing or sitting prevents veins from being squeezed by the skeletal muscle and it stretches the veins If we stretch our veins too often, they lose elasticity and bulges may be visible: varicose veins.