Transport in Humans (chapter 6)

Plasma

Plasma transports:

• blood cells around the body

• nutrients from the small intestines to other parts of the body

• excretory products from organs where they are produced to excretory organs for removal

• hormones from endocrine glands to target organs

Red blood cells

• circular, biconcave in shape

• no nucleus

• contain a red pigment called haemoglobin

• flexible

Main function is to transport oxygen from the lungs to other parts of the body.

White blood cells

Phagocytes:

• Phagocytosis is the process by which a white blood cells engulfs and destroy a foreign particles such as bacteria.

Lymphocytes:

• recognise foreign particles

• destroy diseases-causing organisms such as bacteria and viruses

• cause bacteria to clump together for easy ingestion by phagocytes

• neutralise the toxins made by the bacteria.

Platelets

Platelets are fragments of cytoplasm. They contain an enzyme that catalyses the conversion of fibrinogen to fibrin threads. These threads form a network that entangles red blood cells to form a clot.

How does blood clot work?

The clot seals wound, preventing excessive loss of the blood, preventing foreign particles from entering bloodstream.

• Platelets are involved in converting the soluble protein fibrinogen to insoluble of fibrin which involves enzyme.

• Fibrin threads entangle blood cells and the whole mass forms a clot pr a scab. The clots seals the wound, preventing microorganisms and excessive blood lost.

Arteries

• Blood that flows in the arteries is fast-moving

• arteries walls are thick, muscular and elastic. the elastic layer is much thicker in the arteries nearest to the heart.

• the thick elastic heart helps to withstand the high blood pressure which enables the artery wall to stretch and recoil or spring back

• When an artery constricts, the lumen becomes narrower and les blood flow through

• When an artery dilates, the lumen becomes wider and more blood flows through it

Veins

• Blood pressure in the veins is much lower than the blood pressure in the arteries.

• veins need not be as thick and muscular as those in arteries

• most veins have internal valves

How are substances transferred between capillaries and tissue fluids

• tiny spaces between tissue cells contain a colourless liquid, tissue fluid which transport dissolved substances between tissue cells and blood capillaries

• dissolved food substances and oxygen diffuse from the blood in the blood capillaries into tissue fluids.

Cardiac Cycle

1. the atrial muscles contract, forcing blood into the ventricles

2. After a short pause, the ventricular muscles contract, causing a rise in pressure inside the ventricle . the rise in pressure causes the bicuspid and tricuspid valves to close to prevent backflow of blood into the atria. This produces ‘lub’ sound. The semi-valve opens. Blood flows from the right ventricle and left ventricle into pulmonary artery and aorta respectively.

3. As the ventricular muscles contract, the atrial muscles relax. The right atrium receives blood from the vena cavae while the left atrium receive blood from the pulmonary veins

4. The ventricular muscles then relax. the fall in pressure causes the semi-lunar valves to close to prevent backflow of blood from the pulmonary artery and aorta into the ventricles. This produces a softer ‘dub’ sound. The bicuspid and tricuspid valves also open and blood flows from the atria into the ventricles .

5. The atrial muscles contract again and the whole cycle repeats itself.

Heart attack

• Blood flow to a particular part of the heart may be completely blocked. Due to the blocked blood flow, that part of the heart does not receive sufficient oxygen and nutrients causing that region of the heart to die.

• Extensive heart muscle damage is often fatal

Causes of Coronary Heart disease

• Fatty substances such as cholesterol and saturated fats may be deposited on the inner surface of the coronary arteries.

• This narrows the lumen of these arteries and increases blood pressure, which develops a rough inner surface

• This increases the risk of a blood clot forming in the artery.

• The supply of blood and oxygen to the heart muscles may be cut off, where heart muscles may be damaged, causing a heart attack.

Risk Factors of Heart Diseases

• Smoking

• Unhealthy diet

• Genetic factors

• Age

• Sedentary lifestyle (lack of exercising)