THE VASCULAR SYSTEM
This is known as the circulatory system. It consists of the heart, blood vessels, lymphatic vessels and the lymph.
The centre of this system is the heart, which is a muscular organ that rhythmically contracts, forcing the blood through the system of vessels.
The Heart:
The heart weighs approximately 255g in weight in a full grown adult. At birth it beats about 130 times a minute, by the age of six it beats about 100 times a minute and reduces further in adult life to between 65 and 80 per minute the average being around 70 per minute. During 24 hours an adult human heart pumps 36000 litres of blood through 2000 km of blood vessels. The heart is divided into four chambers. These are the right and left atria in the upper part of the heart and the right and left ventricles in the lower part. The right side is divided from the left side by a solid wall called septum, this prevents the venous blood on the right side coming into contact with the arterial blood on the left side of the heart.
Circulation is divided into 2 principle systems. The systemic circulation (around the body) and the pulmonary circulation (to and from the lungs). The general circulation includes two special branches: the portal circulation, which conveys blood from the digestive origins to the liver and the coronary circulation, which supplies the heart.
Blood vessels, which proceed from the heart, are known as arteries. They generally carry oxygenated blood. (The exception is the pulmonary artery) Arteries are the large hollow elastic tubes, which gradually decrease in size, as they spread through the body. The smaller vessels or arteries finally become very fine hair like vessels known as capillaries.
Blood vessels which proceed into the heart, are known as veins. These usually carry de-
Blood:
Is alkaline in reaction and amounts to approximately 5 to 6 litres in the average adult. It is complex in nature but has four principal constitute parts:
Plasma, erythrocytes (red corpuscles) leukocytes (white corpuscles) and platelets.
Plasma: provides the liquid basis of the blood. This is clear straw-coloured liquid, which holds various substances in solution. These include sugar, urea, amino acids, mineral salts, enzymes etc.
Erythrocytes: are inert biconcave discs, they get their colour from haemoglobin, which has the ability to absorb oxygen (when it becomes carbonyl- haemoglobin which becomes dark red.) The average life span of an erythrocyte is 120 days; they are produced mainly in the red bone marrow, their eventual disintegration takes place in the spleen and is finally completed in the liver. These cells are the body’s transporters; they carry oxygen to all the parts of the body and on their return journey pick up waste products, primarily carbon dioxide.
Leukocytes: are larger then erythrocytes and have irregular shape and a nucleus. They are produced in the bone marrow. They are protectors of the body; their chief role is to protect the body from infection by using their power of ingesting.
Platelets: these are derived from large multi nucleated cells in the bone marrow.
They are essential to the blood coagulation (clotting).
The Lymphatic System:
This is the secondary circulation intertwined with blood circulation. The basic material of the lymphatic system is the lymph, which is plasma after it has been exuded from the capillaries. It gives nourishment to the tissue cells and in return takes away the waste products. Tiny lymphatic vessels, which join together to form larger lymph vessels, drain off the liquid and as these lymph vessels convey lymph towards the heart, they are supplied with valves in much the same way as veins. Along their course towards the heart, there are reservoir areas known as lymph nodes. These vary in size from pinhead to a small almond. The purpose of this lymph is to filter the lymph as it passes through and in this way to help prevent infection passing into the blood stream.
Plasma, erythrocytes (red corpuscles) leukocytes (white corpuscles) and platelets.
Plasma: provides the liquid basis of the blood. This is clear straw-
Erythrocytes: are inert biconcave discs, they get their colour from haemoglobin, which has the ability to absorb oxygen (when it becomes carbonyl-
Leukocytes: are larger then erythrocytes and have irregular shape and a nucleus. They are produced in the bone marrow. They are protectors of the body; their chief role is to protect the body from infection by using their power of ingesting.
Platelets: these are derived from large multi nucleated cells in the bone marrow.
They are essential to the blood coagulation (clotting).
The Lymphatic System:
This is the secondary circulation intertwined with blood circulation. The basic material of the lymphatic system is the lymph, which is plasma after it has been exuded from the capillaries. It gives nourishment to the tissue cells and in return takes away the waste products. Tiny lymphatic vessels, which join together to form larger lymph vessels, drain off the liquid and as these lymph vessels convey lymph towards the heart, they are supplied with valves in much the same way as veins. Along their course towards the heart, there are reservoir areas known as lymph nodes. These vary in size from pinhead to a small almond. The purpose of this lymph is to filter the lymph as it passes through and in this way to help prevent infection passing into the blood stream.
The Neurological System:
The neurological system of the body has 2 main diversions:
• The central nervous system
• The automatic (including the sympathetic and parasympathetic) nervous system.
The basis of the nervous system is the nerve cell or neuron. This consists of a nerve cell body with its receiving processes, (the dendrites) it’s transmitting process (the axon) and it’s nerve endings. White nerve fibres are enclosed in a sheaf of myelitis, (are modulated). Grey nerve fibres have no myelitis (are non-modulated).
The Brain:
The brain is at the centre of the nervous system. It is well protected from the outside from the hard bone structure of the skull. Inside, three membranes protect the brain externally. The outer layer is known as arachnoid and the inner layer as the Pia Mater.
The outer layer is anchored to the skull and made of strong fibrous tissue.
The middle tissue is not anchored, which allows the brain to expand and is much more delicate. Under this lies a big reservoir of cerebral spinal liquid, which surrounds the whole brain and on which it rests. Lastly comes the pia mater, which is in contact with grey matter of the brain itself and digs deep down between the brain convolutions. The adult brain weighs rather more than 1360g and it is estimated that it contains 12 million nerve cells.
The brain is made up of three structures: The Corebrum, Corebellum and The Medulla Oblongata.
The Corebrum: This consists of two symmetrical hemispheres. The outer layer of the cerebrum is called the cortex and is arranged in deep irregularly shaped indentations. This is the grey matter of the brain. Underneath the cortex lies nerve fibre (white matter). The cerebrum receives and interprets conscious sensations and controls voluntary movement.
The Corebelluim: This lies behind and below the cerebrum and is much smaller in size. This also has grey matter under which lies white matter. The cerebellum controls muscular co-ordination and balance.
The Medulla Oblongata: This is about 3 cm long, tapering from its greatest width of 2 cm and connecting the rest of the brain with the spinal cord with which it is continuous. It is made up of interspersed white and grey matter. The medulla oblongata acts as the link between the brain and central nervous system, which controls the processes of digestion, heart and lungs etc.
Other parts of the brain include the puns varoli that is a bridge of nerve fibres linking the left and right hemispheres and also the cerebellum with the cerebrum above the medulla oblongata below. This controls all the impulses that pass between the brain and the spinal cord.
The Pituitary Gland: This is a small pea sized gland, which lies on the pituitary fossa in the base of the skull. Its function is dealt with under the endocrine system.
The Hypothalamus: This is situated in the area of the floor of the third ventricle of the brain. It exercises an influence over the autonomic nervous system. It is believed to be involved with the appetite and contains the heat-regulating centre.
The Spinal Cord: Which is continuous with the medulla oblongata, extends downwards through the ventricle of the spinal column. This cord is cylindrical in shape with an outer covering of supporting cells and the blood vessels and an inner egg shaped cord of nerve fibres. There are 12 pairs of cranial nerves given of from the base of the brain. 31 other pairs branch off the spinal cord. These extend to every part of the body. Nerves of the central system fall into 3 categories. Motor or efferent nerves whose primary function is the control of the movement of muscles. Sensory or afferent nerves these carry impulses from the sensory nerve endings to the spinal column and the brain. Mixed nerves these consist of the both motor and sensory fibres.
The autonomic Nervous System: This supplies all the body structure over which we have no control and is divided into two parts. The sympathetic system and the parasympathetic system.
The sympathetic system: Compromises a ganglia Ted cord, which runs on either side of the front of the vertebral column. The principle plexuses of this system are; the cardiac plexus, which supplies all the thoracic viscera and the thoracic hypo gastric plexus, which supplies the pelvic organs.
The parasympathetic nervous system: Consists mainly of the vague nerve, which branches to the organs of the thorax and abdomen but also includes branches from the cranial nerves, mainly the 3rd, seventh and ninth as well as nerves in the sacral reign of the spinal column.
A sympathetic nerve has the effect of increasing body activity and speeds it up.
The parasympathetic slows down body activity. Another function of the autonomic nervous system is related to the reflex nervous action. This is an involuntary reaction to stimulation.
The Brain:
The brain is at the centre of the nervous system. It is well protected from the outside from the hard bone structure of the skull. Inside, three membranes protect the brain externally. The outer layer is known as arachnoid and the inner layer as the Pia Mater.
The outer layer is anchored to the skull and made of strong fibrous tissue.
The middle tissue is not anchored, which allows the brain to expand and is much more delicate. Under this lies a big reservoir of cerebral spinal liquid, which surrounds the whole brain and on which it rests. Lastly comes the pia mater, which is in contact with grey matter of the brain itself and digs deep down between the brain convolutions. The adult brain weighs rather more than 1360g and it is estimated that it contains 12 million nerve cells.
The brain is made up of three structures: The Corebrum, Corebellum and The Medulla Oblongata.
The Corebrum: This consists of two symmetrical hemispheres. The outer layer of the cerebrum is called the cortex and is arranged in deep irregularly shaped indentations. This is the grey matter of the brain. Underneath the cortex lies nerve fibre (white matter). The cerebrum receives and interprets conscious sensations and controls voluntary movement.
The Corebelluim: This lies behind and below the cerebrum and is much smaller in size. This also has grey matter under which lies white matter. The cerebellum controls muscular co-
The Medulla Oblongata: This is about 3 cm long, tapering from its greatest width of 2 cm and connecting the rest of the brain with the spinal cord with which it is continuous. It is made up of interspersed white and grey matter. The medulla oblongata acts as the link between the brain and central nervous system, which controls the processes of digestion, heart and lungs etc.
Other parts of the brain include the puns varoli that is a bridge of nerve fibres linking the left and right hemispheres and also the cerebellum with the cerebrum above the medulla oblongata below. This controls all the impulses that pass between the brain and the spinal cord.
The Pituitary Gland: This is a small pea sized gland, which lies on the pituitary fossa in the base of the skull. Its function is dealt with under the endocrine system.
The Hypothalamus: This is situated in the area of the floor of the third ventricle of the brain. It exercises an influence over the autonomic nervous system. It is believed to be involved with the appetite and contains the heat-
The Spinal Cord: Which is continuous with the medulla oblongata, extends downwards through the ventricle of the spinal column. This cord is cylindrical in shape with an outer covering of supporting cells and the blood vessels and an inner egg shaped cord of nerve fibres. There are 12 pairs of cranial nerves given of from the base of the brain. 31 other pairs branch off the spinal cord. These extend to every part of the body. Nerves of the central system fall into 3 categories. Motor or efferent nerves whose primary function is the control of the movement of muscles. Sensory or afferent nerves these carry impulses from the sensory nerve endings to the spinal column and the brain. Mixed nerves these consist of the both motor and sensory fibres.
The autonomic Nervous System: This supplies all the body structure over which we have no control and is divided into two parts. The sympathetic system and the parasympathetic system.
The sympathetic system: Compromises a ganglia Ted cord, which runs on either side of the front of the vertebral column. The principle plexuses of this system are; the cardiac plexus, which supplies all the thoracic viscera and the thoracic hypo gastric plexus, which supplies the pelvic organs.
The parasympathetic nervous system: Consists mainly of the vague nerve, which branches to the organs of the thorax and abdomen but also includes branches from the cranial nerves, mainly the 3rd, seventh and ninth as well as nerves in the sacral reign of the spinal column.
A sympathetic nerve has the effect of increasing body activity and speeds it up.
The parasympathetic slows down body activity. Another function of the autonomic nervous system is related to the reflex nervous action. This is an involuntary reaction to stimulation.
THE HEART
