2.2 Animal tissues, organs and organ systems

2.2.2 (Part 1) Blood Vessels

Keywords: Arteries, Veins, Capillaries
FSL: GCSE Biology Revision "Arteries, Veins and Capillaries"

Arteries: Transport blood away from the heart to the rest of the body. Usually at high pressure.
Veins: Transport blood from the rest of the body back to the heart. They have valves to prevent blood from flowing the wrong way. Usually at low pressure.
Capillaries: The smallest blood vessels, they are responsible for the exchange of oxygen and nutrients between the blood and tissues. They are a single layer of endothelial cells, which minimise the diffusion distance for oxygen and carbon dioxide. They also have pores that allow blood plasma to leak out and form tissue fluid. They link artieries to veins.

Structure of Blood Vessels

- The walls of each type of blood vessel relate to the function of the vessel.
- Blood flows through the lumen of a blood vessel; the artieries have thicker walls and have a smaller lumen, the veins have thinner walls and a larger lumen.
- The walls of the vessels are made of collagen, smooth muscle, and elastic fibres. The fibres allow expansion and recoil which allows the vessels to push blood along, which (in artieries) maintains a high blood pressure.

	Arteries	Veins	Capillaries
Function	Carry oxygenated blood away from the heart	Carry deoxygenated blood back to the heart	Exchange oxygen and nutrients
Pressure	High	Low	Lowest
Lumen Diameter	Small	Large	One Cell Wide
Wall Thickness	Thick	Thin	Thinnest
Muscle & Elastic Fibres	A Lot	Less	None
Valves	Not Present	Present	Not Present

Double Circulatory System

- The double circulatory system is a type of blood circulation system in which blood passes through the heart twice during each complete circuit around the body.
- This system is essential for efficiently transporting oxygen and nutrients to cells and removing waste products.
- It works in two stages:

Pulmonary Circulation: Deoxygenated blood is pumped from the right side of the heart to the lungs. In the lungs, the blood releases carbon dioxide and picks up oxygen. The oxygenated blood then returns to the left side of the heart.
Systemic Circulation: The left side of the heart pumps the oxygenated blood to the rest of the body. As the blood travels through the body, it delivers oxygen and nutrients to tissues and collects carbon dioxide and other waste products. The deoxygenated blood returns to the right side of the heart, completing the circuit.

- It is required because the body needs to maintain a constant supply of oxygen and nutrients; without it our blood would become too acidic.

2.2.3 Blood

Keywords: Red Blood Cells, White Blood Cells, Platelets, Plasma
FSL: GCSE Biology Revision "Blood"

Red Blood Cells

The most common type of blood cell, they are responsible for carrying oxygen from the lungs to the rest of the body, and for transporting carbon dioxide. They contain haemoglobin, which binds to oxygen and carbon dioxide. They have no nucleus (to hold more oxygen), and they are a biconcave shape for a larger surface area so gas diffusion is quicker and easier. They are flexible and so can squeeze through capillaries more easily. As they cannot undergo mitosis (no nucleus), they are made in the bone marrow from adult stem cells.

White Blood Cells

They are made in lymph glands and bone marrow. They have a nucleus, and they fight infection and disease. They can have three different roles:

Engulf and digest microorganisms (phagocytosis)
Produce antibodies (recognition)
Produce antitoxins (neutralisation)

Platelets

These are fragments of cells made from the cytoplasm of large cells. They have no nucleus, and float around in the blood. They recognise damaged blood vessels and bind together to form clots to prevent too much bleeding (via enzyme reactions). They form clotting at the site of a wound forming a scab.

Plasma

A pale, yellow liquid made up of mainly water. It is a transport medium for a wide range of materials including glucose, antibodies, hormones, carbon dioxide, urea and blood cells. It also distributes heat around the body.

2.2.2 (Part 2) The Heart

Keywords: Aorta, valves, pulmonary artery, pulmonary vein, right atrium, left atrium, right ventricle, left ventricle, coronary arteries
FSL: GCSE Biology Revision "The Structure of the Heart"

Deoxygenated blood enters the right atrium through the vena cava.
The right atrium contracts and forces the blood into the right ventricle.
Valves close and stop the blood flowing backwards.
The right ventricle contracts and forces the blood out of the heart through the pulmonary artery to the lungs.
Oxygenated blood returns to the heart in the pulmonary vein and enters the left atrium.
It contracts and forces the blood into the left ventricle.
Valves close and stop the blood flowing backwards.
The left ventricle contracts and forces the oxygenated blood out of the heart through the aorta, to the body.

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- The left side is thicker than the right side because it has to push blood around the entire body rather than just to the lungs and back.
- The sound of your heart is made by the veins closing.
- Cardiac tissues makes up most of the heart.
- This can result in symptoms such as shortness of breath, diziness, rapid heart rate, and cheat pain. This can eventually lead to heart failure.
- Faulty heart valves can be replaced with a biological valve from a human donor or ones made with tissue from a pig or cow, or mechanical valve made from strong, durable materials.
- This operation is usually successful. Mechanical valves last longer but can cause blodo clots, but biological valves are more likely to wear out.

Heart Valves

- Heart valves withstand a lot of pressure.
- Over time they can leak or become stiff and not open fully.
- This makes the heart less efficent.

2.2.4 Coronary Heart Disease

Keywords: Coronary Arteries, Plaque, Stents, Bypass Surgery, Statins

- Coronary artieries: Bring oxygen to heart muscles for aerobic respiration to release energy, allowing the heart to contract.
- Plaque can build up on coronary artieries, causing blockage. This can cause pain, or coronary heart failure (a heart attack).
- From the spec:

In coronary heart disease layers of fatty material build up inside the coronary arteries, narrowing them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle. Stents are used to keep the coronary arteries open. Statins are widely used to reduce blood cholesterol levels which slows down the rate of fatty material deposit. In some people heart valves may become faulty, preventing the valve from opening fully, or the heart valve might develop a leak.
Faulty heart valves can be replaced using biological or mechanical valves. In the case of heart failure a donor heart, or heart and lungs can be transplanted. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery.

Stents

In the case of a stent being used:

Metal mesh holds artery open.
Deflated balloon placed under local anaesthetic.
Balloon is inflated which causes the stent to unfold and open up the artery.

- Stents may only be used for a minor/early blockage.
- They increase blood flow in a coronary artery, there is no need for general anaesthetic, short recovery time, and it's relatively cheap, but it can't open very large blockages.

Bypass Surgery

- Used when blockages are too severe to use a stent.
- Narrowed artieries can be replaced (bypassed) with parts of a vein (comes from other parts of the body).
- They are effective in severe blockages.
- Requires general anaesthetic, and the operation can be risky.

Statins

- Medication given to patients with high cholesterol levels at risk of coronary heart disease or after stent/bypass surgery.
- Reduces the amount of cholesterol in the blood, slowing down the rate of fatty material deposition.

Breathing and Gas Exchange

Keywords: Trachea, Alveoli, Bronchus, Bronchioles, Intercostal muscles, Ribs, Bronchus, Lung, Diaphragm
FSL: GCSE Biology Revision "Gas Exchange in the Lungs"

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yes i hate that its comic sans, no i wont fix it)}

Trachea	The tube that carries air from the lungs to your mouth. Also called the windpipe.
Intercostal muscles	Muscles between the ribs which control movement (the ones that cause inhalation and exhalation).
Ribs	The bones that support and protect the lungs. Moves up and out then down and in when breathing.
Diaphragm	Sheet of connective tissue and muscle at the bottom of the thorax. Changes the thorax's volume to aid in inhalation and exhalation.
Bronchus	Long tubes that come off the trachea (one for each lung). Carry air to the lungs.
Bronchioles	Smaller tubes off the Bronchi that carry air to the alveoli.
Alveoli	Tiny moist air sacs with very thin (one cell thick for a short diffusion distance) walls where gas exchange occurs. There are lots of them to optimise surface area for gas exchange. They also require a good blood supply (for a steep concentration gradient).

Breathing in:

Diaphragm contracts (flattens).
Simultaneously, the intercostal muscles contract (pulls ribs up and out).
Volume of thorax increases.
Pressure decreases (to lower than the air outside).
Air is forced into the lungs.

Breathing out:

Diaphragm relaxes (dome shape).
Simultaneously, intercostal muscles relax (pulls ribs down and in).
Volume of thorax decreases.
Pressure increases (to higher than the air outside).
Air is forced out of the lungs.

Emphysema

- Emphysema is a condition where alveoli rupture and get holes in them.
- It shows itself through shortness of breath, coughing, chest tightness, alveoli rupture, reduced surface area for gas exchange, and it leads to larger holes.