Blood & Circulatory System

• • The septum is a muscular wall that runs through the middle of the heart and divides it into two halves.
  • The left-hand side of the heart contains oxygenated blood.
  • The right-hand side contains deoxygenated blood.
• • The atria are the two upper chambers of the heart.
  • The right atrium collects blood from the venae cavae.
  • The left atrium collects blood from the pulmonary vein.
  • The atria then contract and pump the blood into the two ventricles simultaneously.
• • The ventricles are the lower chambers of the heart.
  • The right ventricle pumps blood up through the pulmonary artery.
  • The left ventricle pumps blood up through the aorta.
• The left ventricle has to pump blood up to the head, against the force of gravity, and also to all tissues in the body as part of the systemic circuit. This means more pressure is needed on the left side and the walls need to be thicker to withstand this pressure.
• The aorta is the major artery on the left-hand side of the heart. It pumps oxygenated blood to all the cells in the body.
• The pulmonary artery is the major artery on the right-hand side of the body. It pumps deoxygenated blood to the lungs. This is the only artery in the body that pumps deoxygenated blood.
• The pulmonary veins are the major veins on the left-hand side of the heart. They bring oxygenated blood from the lungs back into the heart. They are the only veins in the body that carry oxygenated blood.
• The venae cavae are the major veins on the right-hand side of the heart. They bring deoxygenated blood from the cells back to the heart. The superior vena cava brings blood from the head and chest back to the heart. Blood from the legs and lower region of the body is brought back to the heart through the inferior vena cava
• The semilunar valves separate the ventricles from the great vessels (the aorta and pulmonary arteries).
• Functions of the Circulatory System

  • It carries nutrients and oxygen to all cells.
  • It removes waste from cells to prevent the waste from becoming toxic.
• • An open circulatory system is when blood is pumped to open-ended blood vessels.
  • Blood leaves the open-ended blood vessels, and materials are exchanged between the blood and the cells through diffusion. Blood then returns to the heart.
  • Open systems are usually found in invertebrates such as insects and crabs.
  • Blood flows under very low pressure in open circulatory systems.
• • A closed circulatory system is one where blood remains in a continuous system of blood vessels, i.e. it does not leave the blood vessels.
  • Materials are exchanged between the blood and the cells through the walls of the capillaries, which are only one cell thick.
  • Humans and most mammals have a closed circulatory system, as we are too big of an organism to rely on diffusion for the exchange of materials.
  • Blood flows under high pressure in a closed circulatory system.
• Benefits of a Closed Circulatory System

  • Blood can be pumped faster
  • Blood flow to different organs can be controlled
• The Pulmonary Circuit

  This circuit starts on the right-hand side of the heart.

  • Deoxygenated blood is pumped from the pulmonary artery upwards to the lungs, where gas exchange occurs in the alveoli.
  • Oxygenated blood is then returned to the heart through the pulmonary vein on the left-hand side.
• The Systemic Circuit

  This circuit starts on the left-hand side of the heart.

  • Oxygenated blood gets pumped to all the cells in the body through the aorta.
  • Deoxygenated blood is then returned to the heart through the vena cava on the right-hand side.
• Benefits of a Two-Circuit Circulatory System

  • Oxygenated blood can be separated from deoxygenated blood.
  • Blood pressure can remain high, which helps pump blood to all the tissues.  
• Portal system

  A portal system is a blood pathway that starts and ends in capillaries.

  Example: Hepatic portal vein, which connects the duodenum of the small intestine to the liver.
• Cardiac Muscle

  • The heart is composed of cardiac muscle, a special type of muscle that doesn’t fatigue. 
  • This means that it performs involuntary contractions which keep the heart pumping blood all around our circulatory system. 
  • Cardiac muscle cells are found in the middle layer of the heart: the myocardium.
• Smooth Muscle Tissue

  • Blood vessels like arteries and veins have a layer of smooth muscle cells.
  • This smooth muscle can expand which will allow increased blood flow through vessels.
• Skeletal Muscle Tissue

  • Contractions of skeletal muscle in the circulatory system help with the movement of blood in veins.
  • When a muscle contracts, the veins within that muscle get compressed, resulting in an increase in blood pressure. This increase in blood pressure pushes the blood back towards the heart.
• The Pericardium

  • The pericardium is a layer of tissue on the outside of the heart.
  • It protects the overall heart structure. 
  • It is filled with a fluid that prevents against friction when the heart beats.
• Function of Valves

  The function of valves is to prevent the backflow of blood in veins when skeletal muscles are not contracting.
• Chordae Tendineae and Papillary Muscles

  • The heartstrings or chordae tendineae connect the papillary muscles to the tricuspid and bicuspid valves. 
  • These papillary muscles contract when the ventricles contract, preventing the valves from slipping out of place.
• Arteries

  • Arteries are blood vessels that carry blood away from the heart. 
  • They usually carry oxygenated blood under high pressure except for the pulmonary artery which carries deoxygenated blood.
• Organ

  Two or more different tissues working together to carry out a function.
• Veins

  • Veins carry blood toward the heart. 
  • They usually carry deoxygenated blood, except for the pulmonary vein.
  • Veins also contain valves to prevent the backflow of blood. They are needed because the blood is under low pressure.
  • Contraction of skeletal muscle moves blood along in veins since the pressure is low.
• Capillaries

  • Capillaries are much smaller blood vessels than veins and arteries. 
  • They are composed of only one layer of endothelial cells and spaces between these endothelial cells allow for easy exchange of materials between the blood and tissue cells through diffusion.
  • Capillaries receive blood from arterioles (small arteries) and blood exits capillaries from venules (small veins). Therefore we say capillaries form the link between arteries and veins.
• Coronary Veins

  • Coronary veins return deoxygenated blood to the right atrium.
  • Unlike the blood that is pumped from the heart, it does not enter through the vena cava.
  • Instead, it is returned directly to the right atrium
• Coronary Arteries

  • The heart receives oxygenated blood from the coronary arteries.
  • These arteries originate from the aorta and are located just above the aortic valve on the left-hand side of the heart. 
• Heartbeat

  Your heartbeat is the rhythmic expansion and contraction of the cardiac muscle.
• • Your heartbeat is controlled by a pacemaker (SA node) that is located at the top of the right atrium. 
  • The heartbeat sound, “lub-dub”, is caused by the closing of the valves.
  • The lub sound is created when the tricuspid and bicuspid valves close.
  • The dub sound is created when the semilunar valves close.
• Pulse

  The rhythmic expansion and contraction of the arteries.

  • Your pulse is often felt at the wrist or neck as the artery is very close to the surface of the skin, and therefore you can feel the expansion and contraction easily.
  • The average pulse rate is 72 bpm.
• Blood pressure

  Blood pressure is the force of the blood pushing against the artery wall.

  • Blood pressure is usually written as a fraction.
  • The top number represents systolic pressure, or the pressure in arteries when the ventricles contract.
  • The bottom number represents diastolic pressure, or the pressure in the arteries when the ventricles are not contracting.
  • Blood pressure is measured using a sphygmomanometer or a blood pressure monitor.
• Smoking

  • Nicotine increases your blood pressure and heart rate, and can cause arteries to narrow. 
  • Carbon monoxide binds to the haemoglobin in our red blood cells which reduces the amount of oxygen red blood cells can carry. As a result, there is not enough oxygen for respiration, so energy levels decrease and the heart has to work harder. 
  • There are numerous chemical substances which can cause plaque to build up in blood vessels and cause blood to thicken and to clot.
• Exercise

  • Exercise helps to maintain a healthy weight and prevent obesity. Since your heart is a muscle, exercise can greatly improve the strength and efficacy of the heart.
  • Your resting heart rate can determine your fitness levels. 72 beats per minute (bpm) is said to be an average adult’s resting heart rate. The more you exercise, the lower your resting heart rate should be.
• Diet

  • Saturated Fat Intake

  High consumption of saturated fat can cause cholesterol to build up and block your arteries. This can lead to a stroke or a heart attack, particularly if the coronary arteries get blocked.

  • Salt Intake

  High salt consumption increases your blood pressure which can cause heart attacks.

  • Obesity can cause high blood pressure and increase the risk of heart attacks and strokes.
• Factors that slow down our heartbeat:

  • Alcohol can slow down your heartbeat as the medulla oblongata's control of your breathing is being slowed down. 
  • Sleep also slows down your heartbeat as your body does not require energy.
• Factors that speed up our heartbeat:

  • Exercise increases our heartbeat so that more oxygenated blood can reach our muscles.
  • Stress increases our heartbeat because the hormone adrenaline gets released.
• Heartbeat Control

  1. The SA node sends an electrical signal down the wall of the atrium, which makes the atria contract.
  2. This electrical signal is picked up by the AV node (atrioventricular), which is located between the right atrium and the ventricle.
  3. There is a bundle of cardiac muscle fibres called Bundle of His that are located between the two ventricles and these fibres transmit the signal from the AV node to the ventricles which causes them to contract.
• Diastole

   The relaxation of the heart muscle.