• The main transport system of humans is the circulatory system, a system tubes (blood vessels) with a pump (the heart) and valves to ensure one-way flow of blood
• Its functions:
  • To provide nutrients and oxygen to the cells
  • To remove waste and carbon-dioxide from the cells
  • To provide efficient gas exchange

Single Circulation in Fish

• Fish have the simplest circulatory system of all the vertebrates.
• A heart consisting of :
  • one blood collecting chamber (the atrium), and
  • one blood ejection chamber (the ventricle)
• They send blood to the gills where it is oxygenated
• The blood then flows to all the parts of the body before returning to the heart. This is known as a single circulation because the blood goes through the heart once for each complete circulation of the body
• However, as the blood passes through capillaries in the gills, blood pressure is lost, but the blood still needs to circulate through other organs of the body before returning to the heart to increase blood pressure. This makes the fish circulatory system inefficient

The Double Circulation of Mammals

• Beginning at the lungs, blood flows into the left-hand side of the heart, and then out to the rest of the body.
• It is brought back to the right-side of the heart, before going back to the lungs again
• This is called a double circulation system, because the blood travels through the heart twice on one complete journey around the body:
  • one circuit links the heart and lungs (low pressure circulation),
  • the other circuit links the heart with the rest of the body (high pressure circulation)

The Importance of a Double Circulation

• Oxygenated blood is kept separate from deoxygenated blood.
  • The septum in the heart ensures this compete separation
  • Oxygenated blood flows through the left-side of the heart while deoxygenated blood flows through the right
• The blood pressure in the systemic circulation is kept higher than that in the pulmonary circulation.
  • The left ventricle, with a thicker wall, pumps blood under higher pressure o the body and delivers oxygenated blood effectively to all parts of the body.
  • The right ventricle has a thinner wall and pumps blood to the lungs under lower pressure, thereby avoiding any lung damage

The Heart

• The function of the heart is to pump blood around the body.
• The right side pumps blood to the lungs and the left side pumps blood to the rest of the body
• Right Atrium: Collects deoxygenated blood and pumps it to the right ventricle
• Right Ventricle: Pumps deoxygenated blood to the lungs
• Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs
• Septum: Separates the left and right sides of the heart
• Pulmonary Vein: Carry oxygenated blood from the lungs to the left atrium
• Left Atrium: Collect oxygenated blood and pumps it to the left ventricle
• Left Ventricle: Pumps oxygenated blood to the body via the aorta
• Aorta: Carries oxygenated blood from the left ventricle to the rest of the body
• Tricuspid and Bicuspid Valves: Prevent back-flow of blood into the atria from the ventricles
• Pulmonary and Aortic Valves: Prevent back-flow of blood from the arteries into the ventricles

Functioning of the Heart

• The heart beats as the walls of the cardiac muscles contract and relax
• When it contracts, the heart becomes smaller, making blood flow out, this is called systole
• When they relax, the heart becomes larger allowing blood to flow into the atria and ventricles. This is called diastole
• The rate at which the heart beats is controlled by a patch of muscle in the right atrium called pacemaker which send electrical signals through the walls of the heart causing the muscle to contract
• Between the atria and ventricles are atrio-ventricular valves (bicuspid on the left and tricuspid on the right). When the ventricles contract, these valves stop blood flowing back into the atria

Effect of Exercise on Heartbeat

• A heartbeat is a contraction
• Each contraction squeezes blood to the lungs and body
• The heart beats about 70 times a minute, more if you are younger, and the rate becomes lower the fitter you are
• During exercise, the heart rate increases to supply the muscles with more oxygen and glucose, allowing the muscles to respire aerobically and they have sufficient energy to contract

Risk Factors of Coronary Heart Disease (CHD)

• Coronary arteries help supply blood to the heart muscles and if the artery gets blocked by a blood clot, for example, the coronary artery can no longer supply oxygen and nutrients to the heart muscles
• This blockage is termed coronary heart disease
• When there is no oxygen supply, the heart cannot contract and the heart stops beating, leading to a heart attach or cardiac arrest

Risk Factors

• Age: The risk of getting CHD increases as a person gets older
• Stress: Long term stress increase the chances of getting CHD
• Gender: Males are affected more by CHD than females
• Diet: A diet that contains high amounts of salt, saturated fat, and cholesterol increases the chances of getting CHD
• Smoking: Nicotine contained in cigarettes cause damage to the circulatory system
• Genetics

Roles of Diet and Exercise in the Prevention of Coronary Heart Disease

• Having a healthy diet and exercising helps reduce the risk of coronary heart disease
• A diet that has low saturated fats is best to prevent this disease
• Exercising helps to reduce weight gain and blood pressure

Treatment of CHD

• The simplest treatment for a patient who suffers from coronary heart disease is to be given a regular dose of aspirin (salicylic acid)
• Angioplasty and stent: involves the insertion of a long, thin tube called a catheter into the blocked or narrowed blood vessel
  • A wire attached to a deflated balloon is then fed through the catheter to the damaged artery
  • Once in place, the balloon is inflated to widen the artery wall, effectively freeing the blockage
  • In some cases, a stent is also applied
• By-pass Surgery: The surgeon removes a section of blood vessels from a different part of the body, such as the leg
  • The blood vessel is then attached around the blocked region of artery to by-pass it, allowing blood to pass freely.

Blood and the Lymphatic System

Main Blood Vessels to and from the Heart, Lungs, and Kidneys

LYMPHATIC SYSTEM

• The lymphatic system is made up of lymph nodes and lymph vessels
• Lymph nodes contain many lymphocytes which filter lymph.
• Lymph vessels collect lymph and return it to the blood

Function of the Lymphatic System

• The lymphatic system is involved in the circulation of body fluids
• The fluid that surrounds the cells of a tissue is called tissue fluid
  • This fluid is plasma leaked from the blood capillaries
  • Tissue fluid plays a major role in the exchange of substances between cells and blood
  • It supplies cells with oxygen and nutrients and takes away waste products including carbon-dioxide
  • At the end of the capillary bed, the tissue fluid leaks back into the blood, and becomes plasma again, but not all of it.
  • A little of it is absorbed by the lymphatic vessel and becomes lymph
  • The lymphatic vessel takes the lymph to the blood stream by secreting them in a vein near the heart, called the subclavian vein
  • The lymph in the lymphatic vessels is moved along by the squeeze of muscles against the vessel, just like some veins
  • The return of tissue fluid to the blood in the form of lymph fluid prevents fluid build up in the tissue
• Protection

• The lymphatic system is a major component of the immune system, which fights against infection.
• One group of white blood cells (lymphocytes) is made in the lymph glands, such as tonsils, spleen, adenoids
• The glands becomes much more active during an infection because they are producing and releasing a large number of lymphocytes

BLOOD

Components of Blood

• Red Blood Cells: it is red due to the presence of hemoglobin and carries oxygen and transports it into the tissues
• White Blood Cells: Fight against infections by phagocytosis and antibody formation.
  • The two most important white blood cells are phagocytes and lymphocytes
  • Phagocytes: They collect at the site of an infection, engulfing (ingesting) and digesting harmful bacteria and cell debris – a process called phagocytosis
  • Lymphocytes: Produce antibodies
• Platelets: Cause blood clotting
• Plasma: Transport of blood cells, ions, soluble nutrients, hormones, carbon-dioxide, urea, and plasma proteins

Blood Clotting

• When an injury causes a blood vessel wall to break, platelets are activated
• They change shape, from round to spiny, stick to the broken vessel wall and each other, and begin to plug the break
• The platelets also interact with fibrinogen, a soluble plasma protein, to form insoluble fibrin. Calcium is required for that.

Necessity for Blood Clotting

• To prevent excessive blood loss from the body when there is a damage of the blood vessel
• To maintain the blood pressure
• To prevent the entry of microorganisms and foreign particles into the body
• To promote wound healing