Chapter 6 Biology

Main components of blood

• Plasma

• White blood cells

• Red blood cells

• Platelets

Plasma

Transports:

• Blood cells

• Nutrients from the small intestine

• Excretory products from organs

• Hormones from endocrine glands to target organs

Phagocytosis

The process by which a white blood cell engulfs and destroys foreign particles

Phagocytes

Engulf, digest and ingests any foreign particles

Lymphocytes

Produce antibodies:

• Recognise foreign particles

• Destroys disease-causing organisms such as bacteria

• Causes bacteria to clump together for easy ingestion by phagocytes

• Neutralises the toxins produced by bacteria

Platelets

They are fragments of cytoplasm and contain an enzyme that catalyses the conversion of fibrinogen to fibrin threads.

Blood clot

1. Platelets are involved in converting the soluble protein fibrinogen to insoluble threads of fibrin

2. Fibrin threads entangle blood cells to form a whole mass

3. The whole mass forms a clot or a scab

4. This clot seals the wound, preventing the entry of microorganisms and excessive loss of blood

The different blood groups

• A

• B

• AB

• O

Blood group A

Has antigen A and antibody B

Blood group B

Has antigen B and antibody A

Blood group AB

Has antigens A and B and no antibodies

Blood group O

Has no antigens and antibodies A and B

Universal acceptor

Blood group AB

Universal donor

Blood group O

Agglutination

When blood group A blood cells possess antigen A, and antibody A enters the plasma, the red blood cells would clump together and agglutinate

Circulatory system

• Heart

• Arteries

• Arterioles

• Blood capillaries

• Venules

• Veins

Arteries

The blood vessels that carry blood away from the heart. The large artery that leaves the left side of the heart is called the aorta

Heart

Continuously circulates blood throughout the body through pumping it. When the heart relaxes, it fills with blood. When is contracts, the blood is squeezed out with great force

Blood capillaries functions

• Capillary walls are partially permeable to enable substance to quickly diffuse through them.

• The total cross-sectional area of the blood vessels increase which allows for lower blood pressure and a slower flow of blood to give more time for exchange of substances

• Small arteries branch out to form many capillaries which increases the total surface area for exchange of substances

• Walls are one cell thick to reduce diffusion distance

Artery walls

• Thick, elastic wall to withstand the high blood pressure in the artery

• Elasticity also enables the wall to stretch and recoil which helps to push the blood in spurts along the artery and gives rise to the pulse

Artery muscles

When an artery constricts, its lumen becomes narrower and less blood flows through it per unit time. When an artery dilates, its lumen becomes wider and more blood flows in per unit time

Tricuspid valve

Prevents backflow of blood from right ventricle to the right atrium

Bicuspid valve

Prevents backflow of blood from left ventricle to the left atrium

Aortic valve

Prevents backflow of blood from aorta to the left ventricle

Pulmonary valve

Prevents backflow of blood from the pulmonary artery to the right ventricle

Atria

Contains two chambers, right atrium and left atrium

It receives blood from the veins and so has thin walls as they only force blood into the ventricles that lie below them (low pressure)

Ventricles

Contains two chambers, right ventricle and left ventricle

Has thick muscular walls to pump blood around the body (high pressure)

The left ventricle is much thicker than the right as it needs to pump blood throughout the whole body

The right ventricle is thinner as it only needs to pump blood to the lungs so less pressure is required (lungs are also close to the heart)

Median septum

Muscular wall that separates the left and right sides of the heart and runs down the middle of the heart

Prevents mixing of deoxygenated and oxygenated blood

Coronary arteries

They carry blood to the muscles in the walls of the heart

Vena cava

Two large veins.

The upper one transports blood from the head,neck and arms back to the heart

The lower one transports blood from the rest of the body back to the heart

Path of blood through the heart

Deoxygenated blood is returned to the right atrium by the venae cavae.

From the right atrium, the blood passes through the tricuspid valve into the right ventricle

From the right ventricle, the blood leaves the heart by the pulmonary arteries to the lungs

Pulmonary veins transport oxygenated blood from the lungs to the left atrium

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

From the left ventricle, the blood leaves the heart and enters the aorta to be distributed around the body through different arteries

Two small coronary arteries emerge from the aorta and brings oxygen and nutrients to the heart muscles

Systole

When the ventricular or atrial muscles contract

Diastole

When the ventricular or atrial muscles relax

Heartbeat

A ventricular systole and diastole make up one heartbeat (0.8s)

The ventricular and atrial muscles are antagonistic

Cardiac cycle

The atrial muscles contract, forcing blood into the ventricles

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 the backflow of blood into the atria and produces a ‘lub’ sound.

Blood flows from the right ventricle and left ventricle into the pulmonary artery and aorta respectively

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

The ventricular muscles then relaxes. The fall in pressure causes the semi-lunar valves 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

The atrial muscles contract again and the whole cycle repeats

Pressure changes in heart

A slight increase in ventricular pressure is due to the contraction of the left atrial muscles, forcing blood into the ventricle

Ventricular muscles begin to contract and bicuspid valve closes

Ventricular muscles continue to contract without change in volume of blood and pressure rises

Pressure in ventricles becomes higher than that in the aorta. Aortic valve opens from the pressure and volume of blood in ventricle decreases as blood is forced out into the aorta

Ventricular muscles begin to relax and drop in pressure causes aortic valve to close to prevent backflow of blood into the ventricle

Ventricular muscles continue to relax without change in volume of blood and bicuspid valve opens when pressure in ventricle becomes lower than in the atrium

Pressure in ventricle rises as blood continues to enter the ventricle from the atrium

Blood vessels

• Pulmonary artery

• Pulmonary vein

• Vena cava

• Aorta

• Hepatic artery

• Hepatic vein

• Hepatic portal vein

• Renal vein

• Renal artery

Blood returned to the heart path

The pulmonary veins bring blood from the lungs to the left atrium of the heart

The upper vena cava returns blood from the head, neck and arms to the right atrium

The lower vena cava brings blood from the renal vein and hepatic vein to the rest of the body to the right atrium