The heart is a hollow muscular organ, which acts as a pump circulating blood through the blood vessels by the contraction of heart muscles. The contraction of the heart beat takes place about 70 to 80 times a minute, but the rate is increased by exercise and excitement.
The heart is divided into left and right sides by a central partition. There is no connection between the two sides and each halt acts as a separate pump. The right side contains de-oxygenated blood and the left side oxygenated blood. Each side is divided into cavities, thin walled upper cavities called (AURICLES) and thick walled lower cavities called VENTRICLES. Each atrium opens into the ventricle below it, the opening containing a valve which allows blood to flow in one direction only from atrium to ventricle. The two atriums contract together forcing blood into the ventricles. Contraction of the ventricles then forces blood into the large arteries through which it leaves the heart. Pocket-like semilunar valves in the inner walls of the arteries prevent the flow of blood back into the heart. THE CIRCULATION OF BLOOD De-oxygenated blood from all parts of the body flows through the Veins into the right atrium. This blood Contains Carbon-dioxide and also digested food which has entered the blood from the small intestine.
The contraction of the right atrium forces the blood through the valve into the right ventricle, which in turn contracts, driving the blood through the pulmonary artery into the lungs. There carbon dioxide leaves the blood and oxygen enters. The oxygenated blood still containing digested food returns to the left atrium, forces blood into the left ventricle, from here it is pumped into the main artery. The AORTA, which has branches to all parts of the body including the skin and hair follicles. In the capillary network of the body tissues oxygen and food are transformed to the cells and waste carbon dioxide enters the blood to be returned to the heart.
THERE IS DOUBLE CIRCULATION
1 ) The pulmonary Circulation, from right ventricle to lungs and back to the left atrium.
Heart-Lungs-Heart.
2) The systemic circulation, from left ventricle to the body tissues eg. hair papilla and back to the right atrium.
Heart-Body Tissues-Heart.
THE BLOOD SUPPLY TO THE HEAD
Soon after leaving the heart, the aorta branches to supply the arms and head. The two common carotid arteries, which supply the head run up through the neck, one along each side of the windpipe. At about the level of the adams apple they divide into an internal and an external branch. The internal carotid arteries pass through openings in the temporal bones of the skull, to take blood to the brain.
The external carotid arteries remain outside the skull and continue one along each side of the head. Branching to supply the muscles and skin of the face and scalp.
The temporal branch takes blood to the scalp. It divides into capillaries in the skin of the scalp and supplies blood to the hair follicles. These capillaries join to form the temporal branch of the jugular vein, which takes de-oxygenated blood from the head to the heart.
The blood supply to the face and scalp is largely provided by the branches of the external carotid artery, however, branches of the ophthalmic branch of the internal carotid artery supply the scalp, forehead, upper lip and nose.
The facial artery, a branch of the external carotid artery, enters the race by curling round the body of the lower jawbone, just anterior to the cheek muscles. From this point it makes a tortuous course past the angle of the mouth to the medial angle of the palpebral fissure of the eye. Near the angle of the mouth it gives off a superior and inferior labial branch which communicates directly with those of the opposite side across the midline.
The superficial temporal artery, a terminal branch of the external carotid artery, supplies the temple and the scalp and by the transverse facial artery the cheek. The forehead and front part of the scalp are supplied by the supraorbital and the supratrochlear arteries, both branches of the ophthalmic artery which is itself a branch of the internal carotid artery. The posterior part of the scalp is supplied by two further branches of the external carotid artery these are the posterior auricular f and occipital arteries. The course and distribution of these vessels are illustrated. These vessels supplying the face and scalp communicate freely with each other across the midline and are thus able to establish an effective collateral circulation following obstruction or ligation before the external carotid artery.
The heart is divided into left and right sides by a central partition. There is no connection between the two sides and each halt acts as a separate pump. The right side contains de-oxygenated blood and the left side oxygenated blood. Each side is divided into cavities, thin walled upper cavities called (AURICLES) and thick walled lower cavities called VENTRICLES. Each atrium opens into the ventricle below it, the opening containing a valve which allows blood to flow in one direction only from atrium to ventricle. The two atriums contract together forcing blood into the ventricles. Contraction of the ventricles then forces blood into the large arteries through which it leaves the heart. Pocket-like semilunar valves in the inner walls of the arteries prevent the flow of blood back into the heart. THE CIRCULATION OF BLOOD De-oxygenated blood from all parts of the body flows through the Veins into the right atrium. This blood Contains Carbon-dioxide and also digested food which has entered the blood from the small intestine.
The contraction of the right atrium forces the blood through the valve into the right ventricle, which in turn contracts, driving the blood through the pulmonary artery into the lungs. There carbon dioxide leaves the blood and oxygen enters. The oxygenated blood still containing digested food returns to the left atrium, forces blood into the left ventricle, from here it is pumped into the main artery. The AORTA, which has branches to all parts of the body including the skin and hair follicles. In the capillary network of the body tissues oxygen and food are transformed to the cells and waste carbon dioxide enters the blood to be returned to the heart.
THERE IS DOUBLE CIRCULATION
1 ) The pulmonary Circulation, from right ventricle to lungs and back to the left atrium.
Heart-Lungs-Heart.
2) The systemic circulation, from left ventricle to the body tissues eg. hair papilla and back to the right atrium.
Heart-Body Tissues-Heart.
THE BLOOD SUPPLY TO THE HEAD
Soon after leaving the heart, the aorta branches to supply the arms and head. The two common carotid arteries, which supply the head run up through the neck, one along each side of the windpipe. At about the level of the adams apple they divide into an internal and an external branch. The internal carotid arteries pass through openings in the temporal bones of the skull, to take blood to the brain.The external carotid arteries remain outside the skull and continue one along each side of the head. Branching to supply the muscles and skin of the face and scalp.
The temporal branch takes blood to the scalp. It divides into capillaries in the skin of the scalp and supplies blood to the hair follicles. These capillaries join to form the temporal branch of the jugular vein, which takes de-oxygenated blood from the head to the heart.
The blood supply to the face and scalp is largely provided by the branches of the external carotid artery, however, branches of the ophthalmic branch of the internal carotid artery supply the scalp, forehead, upper lip and nose.
The facial artery, a branch of the external carotid artery, enters the race by curling round the body of the lower jawbone, just anterior to the cheek muscles. From this point it makes a tortuous course past the angle of the mouth to the medial angle of the palpebral fissure of the eye. Near the angle of the mouth it gives off a superior and inferior labial branch which communicates directly with those of the opposite side across the midline.
The superficial temporal artery, a terminal branch of the external carotid artery, supplies the temple and the scalp and by the transverse facial artery the cheek. The forehead and front part of the scalp are supplied by the supraorbital and the supratrochlear arteries, both branches of the ophthalmic artery which is itself a branch of the internal carotid artery. The posterior part of the scalp is supplied by two further branches of the external carotid artery these are the posterior auricular f and occipital arteries. The course and distribution of these vessels are illustrated. These vessels supplying the face and scalp communicate freely with each other across the midline and are thus able to establish an effective collateral circulation following obstruction or ligation before the external carotid artery.
