6.2 CIRCULATORY SYSTEM

• Bloodflow through vessels is unidirectional with valves to prevent backflow

• The heart pumps blood out of the arteries and that blood returns to the heart through veins

• Predicted that many fine vessels link arteries to veins these vessels are within the tissues of the body

Single Circulatory System - Fish

Blood passes through the heart once. Oxygenated and deoxygenated blood is mixed

Double Circulatory System - Mammals

Blood passes through the heart twice. Oxygenated and deoxygenated blood is not mixed

Pulmonary Circulation (between heart and lungs)

• Deoxygenated blood from the heart to the lungs
• Oxygated blood from the lungs to the heart

Systemic Circulation (between the heart and body)

• Oxygenated blood from the heart to the body
• Deoxygnated blood from the body to the heart

1. Deoxyganted blood enters the heart by the right atrium

2. Moves from the right atrium to the right ventricle and is pumped to the lungs where CO2 is offloaded and oxygen is picked up

3. Oxygenated blood enters the left atrium 

2. Moves from the left atrium to the left ventricle where it is pumped to the body

3. Oxygen is used for respiration and carbon dioxide is collected as a waste product

4. The blood is now dexygenated and moves to the right atrium and the cycle starts again

4 major blood vessels

• Vena Cava
• Pulmonary Artery
• Pulmonary Vein
• Aorta

4 Valves

• Semilunar valve (Pulmonary Artery)
• Semilunar valve (Aorta)
• Tricuspid valve in right ventricle
• Bicuspid valve in left ventricle

From the lungs oxygenated blood enters the pulmonary vein which enters the heart through the left atrium 

Blood flows from the left atrium to the left ventricle through the bicuspid valve

Blood is pumped to the body via the Aorta

From the body deoxygenated blood enters the Vena Cava which enters the heart through the right atrium

Blood flows from the right atrium to the right ventricle through the tricuspid valve

Blood is pumped to the lungs via the Pulmonary Artery to be oxygenated

• Artery
• Vein 
• Capillary 

Arteries [arterioles]: Carry high pressure blood away from the heart to tissues that need it 

Veins [venules]: Carry the low pressure blood back to the heart using valves to ensure blood flows in the correct direction

Capilliaries: Very small and can penetrate every tissue in the body. Blood moves slowly through them under low pressure providing oppertunities for the exchange of substances

Arteries

• Muscle contracts to decrease the size of the lumen this increases blood pressure
• The small lumen maintains the high blood pressure
• Thick muscular wall and fiburous outerlayer help the artery to withstand high pressure
• Elastic fibres stretch to increase the lumen with each pulse. After the pulse the fibres recoil decreasing lumen size to help maintain high blood pressure

Veins

• Large lumen puts blood under low pressure
• As there is less pressure the walls of veins are are thinner and more elastic and contain less muscle than arteries
• Because of low pressure valves are required to prevent backflow to ensure blood moves toward the heart

Capilliaries

• Smallest blood vessels and help in the exchange of substances to and from blood
• Blood travels slowly and at low pressure to allow for the exchange of substances
• The large number of capilliaries and small lumen sizes the surface provide a large surface area available for the exchange of substances
• The wall is one cell thick to allow for easy diffusion of substances because of short distance
• Basement membrane is permeable to many substances
• The walls and membranes can contain pores for further effcient diffusion

The heart is made of cardiac muscle that beats by myogenic muscle contraction

This is regulated by SA node (pacemaker) controls the rate of the heart beat

SA node is made of myocytes (specialized muscle cells)

Excitation Wave:

1) Starts in the sinoatrial node in the top right concer of wall the right atrium

2) Spreads across to the right and left atrium causing atria to contract

3) Reaches atrioventricular node at the top of the septum (muscle in the middle speparating sides)

4) Carried by nerves down the septum to the ventricles and the base of the heart causing ventricles to contract

Medulla (part of brain stem) which is connected to the spinal cord

Contains the nerve centres for respitory and cardiac systems and vomiting

Medulla montiors the concentration of CO2 in the blood

When CO2 concentrations are too high Medulla sends a nerve impulse down the cardiac nerve

This nerve impulse acts on the SA node making the heart beat faster

When CO2 concentrations are too low Medulla sends a nerve impulse down the vagus nerve

This nerve impulse acts on the SA node making the heat beat slower

Adrenaline: Example of a hormone which are chemical messengers that travel in the blood

Adrenaline causes the SA node to fire more frequently during periods of excitement or stress

This causes the heart to beat faster to get sufficient energy and oxygen to the muscles this is a part of the "fight or flight" response

Systole: A period of contraction

Diastole: A period of relaxation

Diastole is normally longer than Systole

Blood moves through the heart due to differences in pressure

Atria Systole

• Atria walls contract
• Blood pressure is higher in atria than ventricles
• Blood passes from atria to ventricles through the atrio-ventricular valves which are open
• The semilunar valves are closed

Ventricular Systole

• Ventricle walls contract and blood pressure rises within them
• Forces the atrio-ventricular valves to close - to prevent blood backflow into atria
• Semilunar valves open
• Blood pumped out into arteries
• Artia are relaxed (collect blood from veins)

Diastole

• The ventricles relax
• Pressure in the ventricles falls below that of the artia
• Semilunar valves close - prevent backflow [produces dub]
• When ventricle pressure falls below that of atria the atrio-ventricular valves open
• Blood enters from veins into atria and flows to ventricles

The next cardiac cycle begins when the atrial walls contract again

Feed the heart and brings oxygen and nutrients to cardiac cells for aerobic respiration

Coronary Artery Disease

Fatty plaque builds up in the inner lining of coronary ateries - narrowing it (occlusion)

Blood flows is restricted which causes chest pain

Factors likely causing Coronary Artery Disease

• High blood cholesterol levels
• Smoking
• High blood pressure (hypertension)
• High blood sugar level (diabetes)
• Genetic factors

Atherosclerosis: Cholesterol builds up in damaged areas. This eventually forms plaque and the artery will lose its elasticity the lumen narrows restricting blood flow Cornary thrombosis: If the plaque raptures blood clotting is triggered. Blood clots are known as Cornary thrombosis

Athersclerosis can lead to blood clots. If these clots occur in myocardial tissue it is called Coronary Heart Disease

A myocardial infection (heart attack) occurs if the coronary artery becomes completely blocked

Coronary muscle tissue dies as a result of no oxygen and blood

Risk factors of Coronary Heart Disease:

• Genetic: Some people are predisposed for high cholesterol and blood pressure levels
• Age: Older people are more at risk because of less elasticity in arteries
• Sex: Males are at greater risk than females
• Smoking: Constricts blood vessels with increased blood pressure more platelets lead to more clotting
• Exercise: Lack of exercise increases risk because of weakened circulation
• Stress: Linked to increased cholesterol hormones in blood causing increased atherosclerosis

Atheroma is the build up of fatty deposits

Mainly LDL cholesterol "bad cholesterol"

Forms a plaque within the endothelium of an artery

This narrows the lumen of the artery

Explain how an atheroma can lead to dead heart muscle. Suggest how the location of an atheroma can impact the extent of damage to the heart muscle

• The coronary artery supplies heart muscle cells with oxygen and glucose
• If blocked the supply of oxygen and glucose will be reduced or stopped completely
• The muscle cells will die due to lack of aerobic respiration
• Anaerobic respiration leading to a build up of lactic acid
• The reduced pH denatures enzymes and kills the muscle cells
• The area of dead heart muscle is downstream of the atheroma
• If the atheroma is located near the end then the area of an artery - dead muscle will be small, if located near the top - the area of dead muscle will be large