Module 5 Revision: CARE AND PREPARATION OF THE DECEASED
Learning Outcome 1:
Anatomy & Physiology - Cardiovascular System
1. Cardiovascular System
The cardiovascular system is made up of vessels and muscles that help and control the flow of the blood around the body. This process is called circulation. The heart and the body's blood transporting network of arteries, veins and capillaries form the cardiovascular system. As blood is continuously pumped out from the heart around the body it caries oxygen and nutrients to all the cells and removes harmful waste products from tissues.
Blood is pumped around the blood vessel network in two main circuits:
1. Pulmonary circuit
2. Systemic circuit
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Upper - Head and arms
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Lower - GI tract and legs
There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and the tissues; and the veins, which carry blood from the capillaries back toward the heart.
What is a capillary? Capillaries are the smallest blood vessels in the body and convey blood between the arteries and veins. As their walls are only one cell thick they are the site of exchange of many substances between the blood and surrounding tissues.
What is an artery? Arteries are the vessels that carry blood, rich with oxygen and nutrients, away from the heart. As the blood travels round the arteries, it branches off to be able to deliver oxygen and nutrients to specific cells. The blood in your arteries is bright red and is under high pressure as the heart pumps it around the body. Since the pressure within arteries is relatively high, they have thicker structures than the veins.
What is a vein? Veins are the vessels that carry deoxygenated blood and waste products around the body back towards the heart. As cells use the oxygen and nutrients delivered by the arteries they create waste products, such as carbon dioxide. The blood in your veins is under considerably less pressure than in your arteries as it is moving upward back to your heart. Veins have valves in them to stop the blood flowing backwards.
2. The Heart
The heart is a powerful involuntary muscle about the size of a fist and is located just left of centre of the chest between the lungs and above the diaphragm. It is surrounded by the pericardium. It is made up of myocardium, a special spontaneously contracting muscle which is found exclusively in the heart.
The heart chambers
The heart is divided into 4 chambers:
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2 upper atriums
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2 lower ventricles
The ventricles have thicker walls than the atriums - this is because blood is pumped out of the heart at greater pressure from these chambers compared to the atria. A strong muscular wall, the septum, divided the two sides of the heart. Four one way valves control blood flow through the heart chambers and prevent the backflow of blood.
Coverings of the heart
The pericardium is a double-walled sac containing the heart, and comprises the fibrous outer layer and the serous inner layer. The pericardium serves multiple functions:
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Fixes the heart in position
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Gives protection against infection
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Provides the lubrication for the heart
Layers of the pericardium
1. Fibrous pericardium - It is made up of tough connective tissue and acts to protect the heart, anchoring it to the surrounding walls, and preventing it from overfilling with blood.
2. The serous pericardium lines the outer surface of the heart itself.
In between these two layers there is a space called the pericardial cavity, which contains a supply of lubricating fluid known as pericardial fluid – all layers and fluids of the pericardium function in lubricating the heart muscle (myocardium) to prevent friction during heart activity.
The heart wall
The heart wall is made of 3 layers:
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Epicardium
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Myocardium
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Endocardium
Epicardium. The epicardium is the outermost layer of the heart wall and is just another name for the serous pericardium and helps to lubricate and protect the outside of the heart.
Myocardium. The myocardium is the muscular middle layer of the heart wall that contains the cardiac muscle tissue. Myocardium makes up the majority of the thickness and mass of the heart wall and is the part of the heart responsible for pumping blood.
Endocardium. the endocardium is a thin layer of cells that lines the inside of the heart. The endocardium is very smooth and is responsible for keeping blood from sticking to the inside of the heart and forming potentially deadly blood clots.
The thickness of the heart wall varies in different parts of the heart. The upper atria (atriums) of the heart have a very thin myocardium because they do not need to pump blood very far. The lower ventricles, on the other hand, have a very thick myocardium to pump blood throughout the entire body.
3. Major vessels of the circulatory system
The human heart circulatory system is a double system, meaning there are two separate systems of blood flow:
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The left side of the heart deals with systemic circulation
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The right side of the heart deals with pulmonary circulation
A&P Level 3 (part 1)
The Heart and Circulatory System - How They Work
4. Heart - internal
Chambers
The two upper atria are thin-walled chambers that receive blood from the veins.
The two lower ventricles are thick-walled chambers that forcefully pump blood out of the heart.
Differences in thickness of the heart chamber walls are due to variations in the amount of myocardium present, which reflects the amount of force each chamber is required to generate.
Valves
Pumps need a set of valves to keep the fluid flowing in one direction and the heart is no exception. The heart has 4 valves:
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The tricuspid valve and mitral valve, which control blood flow from the upper atria chambers to the lower ventricle chambers.
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The pulmonary valve and aortic valve, which control blood flow out of the ventricles lungs and body.
A normal, healthy heart valve minimizes any obstruction and allows blood to flow smoothly and freely in one direction. It closes completely and quickly, not allowing any blood to flow back through the valve.
Cardiac cycle
The cardiac cycle refers to all the events associated with blood flow through the heart:
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Diastole = relaxation of heart muscle
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Systole = contraction of heart muscle
The atria and ventricles alternately contract in each cardiac cycle. The pressures in the chambers change greatly over the course of the cardiac cycle.
5. Coronary circulation
The coronary circulation consists of the blood vessels that supply blood to, and remove blood from, the heart muscle (myocardium) itself. Coronary arteries supply oxygenated blood to the heart muscle, and cardiac veins drain away the blood once it has been deoxygenated.
Because the rest of the body, and most especially the brain, needs a steady supply of oxygenated blood, the heart works constantly and has many additional and secondary blood supply routes that ensures blood is delivered to the heart even if some of its major vessels are obstructed.
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Self-Assessment Questions - use these for your revision notes
Q. What vessels carry blood away from the heart?
Q. What are the three layers of the heart wall?
Q, What is a vein?
Q. What is an artery?
Q. Deoxygenated blood leaves which ventricle to be carried to the lungs?
Q. The surface of the heart is covered by what?
Q. What are the two different types of heart chamber called?
Q. What are the three functions of the pericardium?
Q. What are the two main circuits that blood is pumped around the blood vessel network?
Q. Why do the ventricles have thicker walls than the atriums?
Q. What is the largest artery in the body called?
Q. What two events takes place during the cardiac cycle?