The Heart and Circulation

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The Heart

The heart is an organ that pumps blood around the body in a double circulatory system.

The right ventricle pumps blood to the lungs where gaseous exchange takes place.

The left ventricle pumps blood around the rest of the body so is made of thicker muscle than the other chambers.

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Arteries and Veins in the Heart

The arteries carry blood away from the heart (aorta, pulmonary arteries and coronary arteries).

The veins bring blood from the body to the heart (vena cava and the pulmonary veins).

The pulmonary arteries move blood to the lungs from the heart.

The aorta moves blood to the upper and lower body from the heart.

The pulmonary veins move blood from the lungs to the heart.

The vena cava move blood from the upper and lower body to the heart.

The coronary arteries branch off the aorta and surround the heart to provide it with its own supply of oxygenated blood.

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Ventricles and Atria

The circulatory system is made of up the heart, blood vessels and blood. Humans have a double circulatory system.

The right ventricle pumps deoxygenated blood to the lungs to take in oxygen. This blood then returns to the heart.

The left ventricle pumps oxygenated blood to the other organs of the body. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped back into the lungs.

The heart's valves prevent backflow of blood.

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How The Heart Contracts To Move Blood

- Blood flows into the 2 atria from the vena cava and pulmonary vein

- The atria contract, pushing blood into the ventricles

- The ventricles contract forcing blood into the pulmonary artery and aorta and out of the heart

- The blood flows to other organs via arteries and returns via veins

- The atria fill again and the whole cycle restarts

The coronary arteries that branch off the aorta and surround the heart provide the heart with its own supply of oxygenated blood.

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Blood Vessels

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Arteries carry oxygenated blood at high pressure away from the heart.

Veins carry deoxygenated blood at low pressure to the heart.

Capillaries are tiny tubes that connect arteries to veins. They are one cell thick and carry the blood close to every body cell to exchange substances. They have permeable walls for diffusion and supply food and oxygen and transport waste. 

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Blood

Blood is a tissue consisting of four main components.

- Red blood cells: disc shaped and biconcave, giving a large surface area to absorb oxygen from the lungs. No nucleus to make more room for haemoglobin, their red pigment. In the lungs, haemoglobin binds to oxygen creating oxyhaemoglobin. This splits into oxygen and haemoglobin in order to release this oxygen to body cells.

- White blood cells: fight communicable disease as part of the immune system. They have large nuclei and can change shape to engulf microogranisms (phagocytosis). Some produce antibodies or antitoxins.

- Platelets: fragments of cells that clot blood at the site of a wound. This blocks the injury preventing excessive blood loss. A lack of platelets can cause excessive bleeding and bruising.

- Plasma: a pale liquid that carries the blood components. It is mostly made of water but with substances such as glucose, amino acids, CO2, urea, hormones, proteins, antibodies and antitoxins. 

Sometimes artificial blood is used when a donor cannot be found with a tissue match. We can use protein from sea worms to make it.

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The Lungs

The thorax is separated from the rest of the body by the diaphragm. The lungs are protected by the ribcage and are surrounded by pleural membranes. Air inhaled enters through the trachea, splitting into two tubes (bronchi). The bronchi split into smaller tubes called bronchioles. These open into small alveoli, where gaseous exchange takes place.

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Alveoli

The lungs contain millions of air sacs called alveoli which are surrounded by a network of capillaries. This is where gas exchange occurs.

The blood in the capillaries next to the alveoli contains lots of CO2 and little oxygen. Oxygen diffuses out of the alveolus into the blood from high to low concentration.

CO2 diffuses out of the blood from high to low concentration into the alveolus to be breathed out.

When the blood reaches body cells oxygen is released from the RBCs and diffuses into body cells.

CO2 diffuses out of the body cells into the blood to be carried back into the lungs.

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Coronary Heart Disease, What Causes It and Risk Fa

CHD reduces blood flow to the heart by blockages in the arteries. It is the most common cardiovascular disease and most commonly causes chest pains, heart attacks and even heart failure.

It is generally caused by a build up of atheroma (fatty deposits) on the walls of coronary arteries. The buildup restricts bloodflow to the heart as it makes narrower arteries (atherosclerosis).

Your risk of developing CHD is higher if you:

- Smoke

- Have high blood pressure

- Have high cholesterol 

- Are unfit

- Have diabetes

- Have family history connected to CHD

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Stents and Statins

CHD effects heart tissue by reducing the amount of oxygen that can reach the heart, causing shortness of breath and angina. This can lead to a heart attack - but there are ways to combat it.

1) Stents - wire mesh tubes that are inserted inside arteries. This mechanical device physically opens them up, allowing for adequate bloodflow to the heart. They work for many years and recovery time is short. However, side effects can include: bleeding, respiratory issues, blood clotting and infection. But these risks are all very unlikely and for the majority of people they combat blocked arteries effectively with no complications.

2) Statins - a group of medicines that lower the body's level of low density lipoprotein (LDL) cholesterol in the bloodstream and reduce production of LDL in the liver. They block the HMG CoA Reductase enzyme, the enzyme needed to make cholesterol. Statins can reduce the risk of heart attack, stroke and death by 25-35%. However, side effects may include: sore throat, non-allergic rhinitis, headache, nausea, digestive issues and joint pains.

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Faulty Heart Valves

A faulty heart valve may not open as wide as it should. This reduces bloodflow to the heart, leading to less blood reaching the body, pressure buildup and fluid collecting in the lungs. Or, they may not close properly, letting blood leak back into the atrium.

Different effects of a faulty valve include fatigue, heart murmur, shortness of breath, swelling of ankles and feet, dizziness, fainting and irregular heartbeat.

An aortic valve replacement is a type of open heart surgery used to treat problems with the aortic valve. It involves removing the faulty valve and replacing it with a new one, made from animal tissue or synthetic materials.

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Artificial Hearts, Pacemakers and Transplants

An artificial heart is a prosthetic device implanted into the body to replace the biological heart.  They last up to 5 years and are often given to patients waiting for a donor. They're less likely to be rejected by the body as they are not living tissue, but the surgery has risks of bleeding and infection. The artificial heart is also not as effective as a biological one, and blood thinners must be taken to prevent clotting and strokes.

An artificial pacemaker is a small electerical device placed inside the right atrium to fulfil the role of a faulty sinus node. It sends out regular adjustable electrical impulses to produce normal contractions of the heart.

A heart transplant places a donated heart inside the body. As a form of open heart surgery, it has risks such as rejection, the heart failing, narrowing of arteries and side effects from immunosuppressants. 

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Cancer and Tumours

A cancer happens when cells divide out of control in the body. They form tumours which can sometimes be felt as lumps in the body. There are two types of tumour:

- Benign: doesn't spread to other cells or tissues but can be dangerous if it presses against vital structures

- Malignant: caused by excessive cell growth, spreading to other cells and tissues. They can cause issues like blockages to the lungs.

When cells move away from the original, primary cancer site through the bloodstream or lymphatic system and spread to other organs and bones where they continue to grow, it is called metastasis. 

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Risk Factors of Cancer

Some factors make you more susceptible to cancer.

-  Smoking

- Poor immune system and chronic infections

- Inheritance

- Air pollution/toxic gas

- Alcohol

- Poor diet or obesity

- Sunlight and radiation

- Reproductive or menstrual factors

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Types of Cancer

Breast Cancer

Can affect anywhere where there is breast tissue and affects both men and women. Divided into invasive (spreads outside the breast) and non-invasive (cannot spread outside the breast) categories. It's the most common cancer in the UK.

Skin Cancer

There are 2 types - melanoma (can spread to other organs) and non-melanoma (can only develop in the upper layers of the skin)

Brain Tumours

A growth of cells in the brain that divides in an abnormal, uncontrollable way. They can be benign or malignant and are graded 1-4 according to their behaviour.

Testicular Cancer

Affects younger men between 15-49 the most.

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Types of Cancer

Lung Cancer

Two main types - small cell lung cancer (caused by smoking or fast growing/quick spreading cells) and non small cell lung cancer (three main types - the cells are larger under a microscope). Around 43 500 people in the UK are diagnosed yearly.

Cervical Cancer

Develops in the cervix. Most cases are caused by HPV, which can cause abnormal change to cervical cells.

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Risk Factors of Specific Cancers

Breast Cancer

Age, gender (women have a higher risk), genes, race, ethnicity (white women have a higher risk)

Skin Cancer

Sun ray exposure, sunbeds, fair skin, red hair, age, family history, other skin conditions, sunburn, moles/freckles

Brain Tumours

Age, medical radiation, previous cancers, genetic history, obesity, smoking, alcohol

Testicular Cancer

Being born with abnormal testicles, middle aged men, race, family history, tall men, smoking, infertility, STIs

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Risk Factors of Specific Cancers

Lung Cancer

Smoking (causes 86% of cases), air pollution, exposure to radon gas, previous lung diseases, family history

Cervical Cancer

HPV, smoking, STIs, obesity, prolonged oral contraceptive use, family history, multiple pregnancies

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Cancer Prevention

Breast Cancer

Breast cancer screenings, regular exercise, healthy diet, breastfeeding

Skin Cancer

Suncream, hats, sunglasses, no sunbed use, avoiding the sun in the peak of its heat in the day

Brain Tumours

No drinking/smoking, healthy diet, exercise, go to GP at first sign of symptoms

Testicular Cancer

Safe sex, no smoking, regular GP checks

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Cancer Prevention

Lung Cancer

No smoking, avoid second hand smoke, healthy diet, regular exercise

Cervical Cancer

Condom use, HPV vaccinations, routine pap smears, no smoking

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