The cardiac cycle

We all know that the main purpose of the heart is to pump blood around the body so that our vital organs and our muscles can receive the oxygen that they require!!

In this part I will be looking at the cardiac cycle of the heart and how this process works!

The heart is a cardiac muscle it has four chambers these are left ventricle, left atrium, right ventricle and right atrium.(The atrium's are at the top of the heart and the ventricles are at the bottom of the heart)
Oxygenated blood passes through the pulmonary vein in the left atrium, when the atrium is full the atrioventricular valves open allowing the blood to be pushed into the ventricles. As the blood enters the ventricles the atrioventricular valves stop the blood from flowing back into the atrium. The ventricles contract pushing the blood through the semi-lunar valves into the aorta. This is where the blood leaves the heart and travels around the body via the arteries, arterioles and capillaries. Deoxygenated blood enters the heart through the superior vena cava and the inferior vena cava into the right atrium, as the pressure builds up in the atrium the semi-lunar valves are pushed open allowing the blood to enter the right ventricles. When the heart contracts the deoxygenated blood is forced into the pulmonary artery so that the blood can enter the lungs and become oxygenated.

Did you know that your heart beats 70 times a minute! and that each heartbeat lasts around 0.8seconds!

Within each heart beat the heart relaxes and contracts this is known as systole(contract) and diastole (relax). The heart is relaxed longer then it is contracted. This is because the nervous system which is in a part of the brain called the medulla oblongata sends electrical impulses to the heart in order to stimulate the sinoatrial node (SAN), This is know as the hearts natural pacemaker. These electrical impulses allow the cardiac muscle to contract the right and left atrium allowing the blood to pass through the atrioventricular valves into the relaxed ventricles. There is a slight delay here so that the atria can empty fully. The electrical impulses spread into tissues called Bundle of His. These tissues connect the atrioventricular node to the septum. The bundle of his has branches leading into the ventricle walls known as purkinje fibres. The purkinje fibres allow the impulse to travel through them so that they can get to the ventricle walls. as this happens it the impulses cause the ventricles to contract (also known as ventricular systole). The impulses are stronger at the ventricles because the blood has further to travel than the atria.
This process is repeated every time the heart beats and it is known as THE CARDIAC CYCLE.

Cardiac output is the volume of blood pumped by each ventricle in one minute.
It is calculated by a simple sum Q = SV x HR (this means Q(cardiac output) = SV(stroke volume) x HR(heart rate)
Measuring Cardiac output is extremely important as it allows us to know how healthy a heart is. This allows us to know if the heart is under strain i.e. heart failure. In a healthy human being the average cardiac output is around 5 litres of blood per minute.

The heart has its own system called a pacemaker which is connected to the SA node located at the top of the heart. It contains sympathetic and parasympathetic nerve fibres. These fibres release hormones which can either slow the heart rate down or speed the heart rate up. These hormones are delivered under conditions of rest(parasympathetic nerve fibres) or emotional and physical activity (sympathetic nerve fibres).

Blood plasma

Plasma is the liquid part of the blood, it transports dissolved substances around the body. Also it fights against disease and removes unwanted waste materials from cells.
the blood plasma helps to maintain body temperature and control the pH of blood. Another function of plasma is that it contains clotting agents so when blood is exposed to air it will clot. this is to prevent anymore bacteria entering the body.
Plasma contains 90% water and the other 10% consists of glucose, amino acids, vitamins, mineral salts, hormones, antibodies and antitoxins. all of the different substances in the plasma have a job to do. for example; amino acids and glucose travel in the blood so that they can be diffused into areas that need it i.e. if there is muscle tissue damage then the amino acids help to repair it and they help with growth. if there is no damage that needs repairing then the substances will be stored and used later when they are need for anaerobic respiration. the glucose will travel to muscles for storage or they will travel to the liver where the hormones which travel in the plasma will help to turn glucose into glycogen.
Antibodies and antitoxins travel in the blood plasma as this is the most efficient way for them to get to areas of infection quickly.


http://www.ivy-rose.co.uk/HumanBody/Blood/Blood_StructureandFunctions.php

The structure and function of Red Blood Cells
Red blood cells (RBC) are produced in our bones. our bones reproduce them constantly because red blood cells only have a life span of 120days. The cells become worn out and die. They are the primary cells in our body as their function is too deliver oxygen to our cells and remove carbon dioxide and other waste materials.
RBC have biconcave discs this means that the centre of both sides of the cell is depressed. The depressed centre allows the cells to have more cell membrane surface to allow the diffusing of oxygen and carbon dioxide to take place. This shape also allows for the RBC to have a large surface area for oxygen. Due to the structure of the RBC they are more flexible than other cells and they can squeeze through tight passages such as capillaries between cells in tissues. They can also bend and return to their original shape.
RBC contain a protein chemical called hemoglobin. This protein gives the cells their 'red' colour. Hemoglobin also contains iron. When a red blood cell is first produced it has a nuclei. As it matures it loses the nuclei, this is to allow more space for the haemoglobin so that it can carry as much oxygen as possible. As the RBC passes through the lungs oxygen molecules attach themselves to the hemoglobin. The blood travels around the body and allows the hemoglobin to release the oxygen into cells . once releasing the oxygen the hemoglobin has a large surface area that it needs to fill so it bonds with carbon dioxide and other waste products and transports them back to the lugs so that they can be eliminated from the body. This cycle continues constantly.

Heart Anatomy

video on the anatomy of the heart!

Blood

Blood has two components, plasma and cells. Plasma is the liquid part of the blood. it is made up of 90% water and the other 10% are materials that are essential for life. i.e. nutrients and vitamins - these are dissolved in the blood plasma.
The cell part of the blood contains RBC (Red blood cells), WBC (White blood cells) and platelets. The RBC consists of a protein called Hemoglobin which carries oxygen from the lungs around the body, they also help with the removal of carbon dioxide. When RBC are produced they contain a nucleus as the RBC matures the nucleus leaves the cell. The WBC fight infections, they are often referred to as Leukocytes. The WBC are part of the immune system and they circulate in the blood stream so that they can be transported to infected areas in the body. The platelets are used by the body for clotting.
as the blood circulates the body the materials that are in the plasma diffuse into cells and tissues. they diffuse from high concentrated areas too low concentrated areas (in other words the higher the difference in concentration the higher the amount of materials diffused.)


This is a picture to show what the platelets do when they begin to clot.

structure of arteries, veins and capillaries

An artery is a vessell that carries blood away from the heart. All arteries except for the pulmonary artery and its branches carry oxygenated blood. small arteries are called arterioles. Arteries have elastic tissue in their wall and they have a thick muscle layer in the walls aswell. This structure allows the arteries to cope with the high pressure of blood flow caused by the heart beat. The endothelium is folded allowing the artery to expand.














A vein carries blood towards the heart. All veins except for the pulmonary veins contain deoxygenated blood small veins are called venules. the main veins of the body have valves to prevent blood flowing in the wrong direction. Contraction of body muscles help the blood flow through the veins. Veins are wider than arteries and they have very little elastic or muscle tissue. The space in the centre of the vein is much larger than the arteies.










Capillaries are vessells which transport the blood from arterioles to venules. they are microscopic vessells which are in most of our ogans and tissues in the body. The structure of the capillaeies are very important because it helps with the function of what it does. They are only one cell thick so that they can allow the exchange of oxygen, carbon dioxide, minerals, salts and water to occur between the capillary and the surrounding tissues.

Structure of the respiratory system

The organs of the respiratory system consists of the nose, pharynx, larynx, oesophagus, trachea, bronchi and the lungs.
The nose consists of three nasal cavities in order to supply the lungs with as mush oxygen as possible. the nose filters the air of impurities as well as warming and moistening the air before it enters the lungs.

The pharynx is a tube like structure which allows both air and food too pass through before they reach the appropriate tubes.
The larynx is situated below the pharynx and just above the opening of the trachea, it is part of the vital airway to the lungs.
the epiglottis is one of the main cartilages in the larynx it is small and is attached to the thyroid cartilage along one edge. the epiglottis protects the airway against solids and liquids entering during swallowing.
the trachea is a long tube which holds open the passage way so that air can reach the lungs from the outside. if this airway becomes obstructed for even a few minutes then it Will result in loss of consciousness because of the lack of oxygen supplied.
At the end of the trachea the tube divides into two parts known as the bronchi, each bronchi enter the lungs and branch of into bronchioles. Each bronchiole has little air sacs at the end known as alveoli so that gaseous exchange can take place. Gaseous exchange is when oxygen is diffused into the blood capillaries from the alveoli and carbon dioxide is diffused into the alveoli from the blood capillaries.


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