Explain the electrical of the heart during a heart beat

The cardiac cycle regulation is myogenic (self stimulated). The sympathetic part of the nervous system accelerates the heart beat, this system meets the demands of the body, the parasympathetic system stops and slows things down, this part of the nervous system think that the body is fine and not in any urgent need of anything.

Electrical activity within the heart happens as follows;

As the SA nodes contract, they send electrical impulses the SA nodes are located in the upper wall of the right atrium these are responsible for electrical stimulation, these impulses travel to the right and left atrium. These impulses cause the the upper two chambers in the heart to contract. The electrical impulses then move to the AV (atrio- ventricular) node. Once the impulses reach here, they are held for a short period, the reason for this is so that the right and left atrium can continue to empty it's blood into the ventricles.

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The structure of the heart and the cardiac cycle

The walls of the heart are made from cardiac muscle, it is made of three layers, epicardium, myocardium and the endocardium. The left side of the heart deals with oxygenated blood and the right side with deoxygenated blood. The heart has 4 chambers pumping blood around the body, the left and right side each have an upper chamber called the atrium and a lower chamber called a ventricle, blood flows from an atrium into a ventricle through a valve called a cuspid valve.

Veins bring the blood to the arteries and take blood away from the ventricles, the valves that are in the beginning of the arteries leaving the ventricles are called semi-lunar valves. The semi-lunar valves and the cuspid valve make sure that the blood only flows through the heart in one direction.
When the heart has been filled up and emptied this is called the cardiac cycle. During this cycle each chamber goes through two phases. Diastole and systole.
Diastole is when the wall relaxes and the chamber gets bigger and fills with blood.
Systole is when the it contracts getting smaller and forcing the blood out.


Cardiac cycle
Deoxygentated blood enters the right atrium thorough the vena cava, it is then pumped down the tri-cuspid valve and enters the right ventricle, the blood is then pumped up through the pulmonary valve towards the lungs in the pulmonary artery. The blood is now oxygenated, it now gets transported back to the heart, it does this by entering the pulmonary vein and into the left atrium, from here it goes through the bicuspid valve into the left ventricle. It then gets pumped through the Aortic (semi-lunar) valve and exits the heart out of the aorta and goes to the cells that require oxygen, the process then starts over again.

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The structure of arteries, veins and capillaries

Blood flows through the body through, veins, arteries and capillaries.

Arteries take oxygenated blood away from the heart to the tissue. Arteries have thick muscular and elastic walls, the reason for this is because they have to flow blood through at a high pressure. When the heart forces blood into the artery it slightly expands as the muscles and fibres are stretched. These fibres then contract pushing the blood towards the capillaries . When you press an artery against something solid, there is a slight expansion and contraction. This happens once every heartbeat, this is what is known as a pulse. As the arteries get nearer to the tissue they get narrower, these narrow arteries are known as arterioles.

Capillaries are one cell thick so gaseous exchange can take place. Lots of capillaries are called capillary beds. with the being one cell thick this speeds up the diffusion of substances e.g glucose and oxygen.
Capillaries are found at the ends of arterioles and they take the blood a tissue. When the blood enters the capillaries, the pressure of this forces some of the plasma through the capillary walls.

Veins have a large lumen, have a smooth lining and are only one cell thick, they also have a tough fibrous outer layer.

Before leaving the tissue the blood from the capillaries flows into a slightly larger vessel called venules, the venules join up to form veins.
Veins take deoxygenated blood from the tissue back to the heart. The walls of the vein contain muscle and elastic fibres but they are much thinner than the walls of arteries, as they do not have the ability to cope with as much pressure. The pressure within the veins is sometimes so low it cannot keep the blood moving. To ensure movement in one direction, veins contain one way valves called pocket valves.

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The transportation of oxygen and carbon dioxide in the blood

Oxygen is transported in the blood by RBC. Oxygen is picked up in the lungs by haemoglobin which transports the oxygen to the cells that need it and when they release oxygen they pick up carbon dioxide. Carbon dioxide is then carried back to the lungs where most of it is exhaled. The whole process is mediated by chemical triggers in the body.
This binding of oxygen is a reversible reaction. When haemoglobin and oxygen bind together this is called oxyhaemoglobin. CO2 Diffuses from the tissues into the RBC, this combines with the water to form carbonic acid.
This is normally a slow reaction, but the RBC is greatly accelerated by an enzyme called carbonic hydrase.

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The structure of a red blood cell and how it relates to it's function

RBC are biconcave in shape, they are very flexible and have the ability to twist, bend and bounce back to their original shape when they are squeezing through blood vessels and through minute capillary alleyways. The red colour of blood is due to oxygenated blood cells.
RBC are the most numerous type of cell in the blood. RBC are packed with haemoglobin involved in the carriage of oxygen.

RBC mature in the bone marrow, which is closely attached to a macrophage. The RBC manufacture haemoglobin until it accounts for 90% of the dry weight of the cell. The nucleus is squeezed out of the cell and is then ingested by the macrophage. RBC lives for120 days and are then ingested by phagocytic cells in the liver and spleen.

Adults have a limited number of cytes produced in the thoracic bones, vertebrae, cranial bones and the ends of the femur and the humerus. Our blood contains 25 trillion red cells, these cells are replaced by 3 million per second.

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Components of plasma and their functions

Blood is a highly specialised tissue , composed of many different kinds of components, red cells, white cells, platelets and plasma.

The blood plasma in needed because without it nothing would flow. Plasma is the liquid part of the blood and is about 90% water in which the RBC, WBC and platelets are suspended. The rest of it consists of dissolved food and waste substances, mineral ions. The major protein in plasma is Albumin. Albumin helps keep the blood from flowing out of the blood vessels and into tissues. Albumin binds to and carries substances like hormones. Albumin is made in the liver serum it helps it transport round the body together. The serum Albumin helps maintain the osmotic pressure of the blood.

Red blood cells specialist name is erthocytes and the white blood cells specialist name is leukocytes.

RBC transport oxygen from the lungs to the where it is needed and carry away carbon dioxide.
WBC identify and bind to bacteria, viruses and fungi so they can be removed. WBC are larger than red cells and there aren't as many white cells as red.
Platelets are produced by cells which break up into small fragments, these fragments do not contain a nucleus but are capable of producing enzymes involved in blood clotting.

Plasma carries RBC, WBC, platelets around, they contain sugar fat and protein. 55% of blood volume is made up of plasma. Plasma allows blood to navigate fast moving substances in solution, and slow moving thicker substances in suspension. Solution(dissolves) suspension (sits on the water).
As the heart pumps blood to the cells the plasma brings nourishment to them and removes any waste products.

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The role of the nervous system in generating breathing rhythm

The nervous system is responsible for sending, receiving and processing nerve impulses throughout the body. Nerves are connected throughout the whole body to the brain. The nerves carry information throughout the body in the form of electrochemical signals called impulses.The nervous system has two parts , the central nervous system and the peripheral nervous system.The CNS is the control centre for all body systems, it receives sensory information,processes it and sends out a response. The PNS, the nerves carry messages from sensory receptors to the CNS and from the CNS to the effectors.

The brain acts as a device that makes sure that your body is functioning correctly and efficiently and making any adjustments necessary, it does this by sending out messages to the effectors.

Parts of the brain involved in generating the breathing rhythm are the medulla oblongata and the pons. The medulla oblongata is located at the the base of the brain. this parts manages automatic processes that take place inside your body, e.g heart rate, blood pressure and breathing adjustments.

Breathing is automatic and is controlled by your brain, the rate of breathing is set to meet the oxygen demands of your cells. The autonomic nervous system has two parts the sympathetic and parasympathetic. The sympathetic is mostly active in times of stress. and the parasympathetic controls maintenance and helps conserve the body's energy.

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www.becomehealthynow.com/article/bodynervousadvance
Parsons, R. GCSE Physiology and health. The Revision Guide: Revisions guide pt.1&2 (paperback)