CIRCULATORY SYSTEM | CLOTTING, VESSELS, ARTERY, VEIN, HEART & ORGANS

PROTECTIVE FUNCTION OF BLOOD

The blood performs two basic functions in mammals and these are: (1) Transportation of various substances and (2) Protection of the body against diseases

The blood defends the body in major ways

Antibody production (Clumping): The lymphocytes produce antibodies which are any of a large variety of proteins normally present in the body or produced in response to an antigen which it neutralizes, thus producing an immune response. This can also be ensured by injecting small dose of the weaker or dead pathogens into the body. This process is known as vaccination or immunization
Neutralization: The whole blood will also produce antitoxins which neutralize the toxins produced by the pathogens.
Phagocyte Action (Engulfing): Phagocytes engulf the pathogens and digest them.
Clotting: The blood platelets clot the blood to prevent germs from entering the body and also prevent loss of blood

MECHANISM OF CLOTTING

When a blood vessel is damaged and exposed to air, platelets in the blood stream release an enzyme thrombokinase. The thrombokinase then converts prothrombin (inactive blood protein) to an enzyme called thrombin. The thrombin then converts thesoluble fibrinogen in the plasma to insoluble fibrin in the presence of calcium ions. The threadlike fibrin then forms a network or mesh on the surface of the wound and blood cells are trapped within the network or mesh to form a clot. The clot dries to scab over the wound.

TYPES OF CIRCULATORY SYSTEM

The circulatory system in animals can be:

Closed or open
Single or double

Closed Circulatory System: This involves the blood vessel called arteries which divides capillaries which later join up with other vessels called veins. Blood is therefore limited to the vessels and the heart it does not have direct contact with the body cells this system is observed in annelids and vertebrates.

Opened Circulatory System: The blood vessels lead out of the heart but end in blood spaces called haemocoels within the body cavity. The blood has direct contact with the cells after which it is returned to the heart. Arthropods and some mollusks have open circulatory system

Single Circulatory System: The blood passes through the heart once in a complete movement round the body e.g. fishes because of their two chambered heart have single circulatory system.

Double Circulatory System: The blood passes twice in the heart every time it makes one complete movement round the body. Each time it passes through a separate path way e.g. mammals. Double circulation gives rise to pulmonary and systematic circulation.

BLOOD VESSELS

Arteries: These are vessels that carry oxygenated blood away from the heart to the body’s organs except for pulmonary artery that carries deoxygenated blood.
Arteriole: A branch of an artery that gives rise to capillaries.
Veins: These are large vessels that carry deoxygenated blood toward the heart except for pulmonary vein which carries oxygenated blood.
Venule: Small vessel that carries blood from the capillaries to the veins.
Capillaries: They link the arteries with the veins around the tissues and organs. They are tiny and thin walled to facilitate easy exchange of gasses nutrients and waste products between the cells and the blood

DIFFERENCES BETWEEN ARTERY AND VEIN

	ARTERY	VEIN
1	It has a thick (muscular walls)	It has thin wall
2	Elastic wall	Non-elastic wall
3	Carries blood away from the heart	Returns blood to the heart
4	Carries oxygenated blood except pulmonary artery	Carries deoxygenated blood except pulmonary vein
5	Blood is pink or bright colour	Blood is dark red in colour
6	Situated deep in muscles	Superficially situated

7	Has small lumen	Large lumen
8	Pressure is high	Pressure is low
9	Pulse is readily detectable	Pulse is not easily detected
10	It has no valve except semi lunar valves	It has valves

THE HEART

The heart is a muscular and powerful organ responsible for pumping blood in the system of mammals. It is located within the chest cavity and protected in the ribs and sternum. The pumping action of the heart is known as heart beat (heart beat). Heart beat per second varies from animal to animal and is often increased at moments of excitement e.g. Humans heart is about 72 beats per minutes.

The special muscles making up the heart is known as cardiac muscles and the heart is enclosed in a two layered tough protective membranes called the pericardium. Pericardial fluid fills the space between the heart and pericardium. It reduces the friction arising from pumping movement of the heart against its surrounding tissues.

STRUCTURE OF THE HEART

The human heart is divided into four chambers, the right and left auricles, the right and left ventricles. The walls of the ventricles are often thicker than those of the auricles. The left ventricles especially have a thick wall because it pumps blood out to all other parts of the body and this requires more pressure.

The heart is divided into two halves by a central barrier called septum. Bicuspid valves separate the left auricle and the left ventricle. This ensures that blood flows only in one direction i.e. from the auricles to the ventricles. Similarly the tricuspid valve exists between the right auricle and the right ventricle. It serves the same function as the former. These bicuspid valves are held in place by special fibers, non-elastic cords known as chordae tendineae.

HEAT BEAT

The heart beat consist of alternate contractions and relaxation of the right and left auricles as well as the right and left ventricle. Human heart beat is about 72 beat per minutes this can be divided into two phases, namely

Diastole: This is the first stage of the heart beat; the two auricles contract forcing blood into the ventricles and oxygenated blood into the left ventricle. As the ventricles gets filled up, the cuspid valves are pushed up and closed.
Systole: This is the second phase of the heart beat. The ventricles contract sending blood out to the two tracks of the main arteries and out of the heart. Deoxygenated blood from the right ventricles passes into the pulmonary artery while oxygenated blood is sent into the aorta. The sequence repeats itself.

BLOOD VESSELS AND ORGANS SUPPLIED

Blood Vessel (Artery) Organ Supplied

Carotid artery ……. Head
Pulmonary artery …….. Lungs
Hepatic artery …….. Liver
Gastric artery …….. Stomach
Mesenteric artery …….. Intestine
Renal artery ……… kidney
Gonadal artery ……… Gonads
Intercostals artery ……… Wall of thorax

Corresponding veins accompany the arteries stated above

GENERAL EVALUATION

Draw a well labeled diagram of the heart
Differentiate between arteries and veins
Explain systole and diastole.
Draw the cross section of the artery
What is pulmonary circulation?