CIRCULATION OF THE BLOOD.
The blood maintains a suitable environment for the individual cells of the body by transporting the necessary substance to and from that environment. The mechanism that ensure an adequate flow of blood to the tissues are therefore vital parts of the homeostatic process. since the need of any cell fro blood -borne substances varies with its metabolic activity and active muscle uses more oxygen than a resting muscle there must be a way to increase its blood supply when necessary. the amount of blood available, however, is limited and any increase in the blood flow and distribution of blood requires changes in those factors that are responsible for moving the blood. the flow of blood and the factors that control it constitute what we know as HEMODYNAMIC.
There are three basic elements in the movement of blood: flow, pressure, and resistance. they are so closely interrelated that one cannot consider one without the others. flow blood is caused by pressure generated by the ventricle and is directly proportion to the pressure. flow is impeded by any resistance along the way , and is inversely proportional to that resistance.
The blood flow is the volume of blood passing a point in a given period of time, usually a minute, and is expressed in milliliters or liters per minute. it may be the blood flow to a particular organ,or the blood flow in the entire circulatory system. the total blood flow is the volume of blood leaving the left ventricle each minute, and is the same cardiac output. and five liters per minute, this distributed among the organs of the body according to their needs. the organs in the adbominal cavity receive nearly half the total cardiac output.
PRESSURE AND RESISTANCE
The force imparted to the blood by the heart is opposed by various types of resistance to it flow, and if the pressure developed by the resistance, there is little or no blood flow and the circulation virtually ceases.
It is not the pressure itself that causes blood to flow, but the pressure gradient. this can be illustrated with a mechanical system in which a reservoir provides the head of pressure for a fluid filled system. when the outlet is closed, the pressure is the same throughout, as indicated by the identical fluid heights in the vertical tubes; there is pressure , but no pressure gradient and no flow.
Not all of the energy expended by the heart to develop the pressure is used to cause blood to flow. because the blood in arteries is under pressure, it pushes outward against the artery wall. the artery resists this force by pushing in to balance the outward force of the blood.
ESSENTIAL HUMAN ANATOMY AND PHYSIOLOGY. BY BARBARA R LANDAU.
Tuesday, July 3, 2007
Sunday, July 1, 2007
BOOK REPORT 1
INTRODUCTION TO THE NERVOUS SYSTEM.
the nervous system is communication system based on the conduction of impulses that provide information and give directions. structures called receptors are sensitive to certain changes in their immediate environment. receptors in the skin, for example, generate impulse when stimulated by touch or pressure.receptors are located on the ends of nerve fiber, which transmit the impulse to the spinal cord or brain to effectors such as skeletal ,smooth, and cardiac muscle, and glands, which cay out the direction sent from the spinal cord or brain. still other nerve fibers transmit information to other nerve fiber.
the operation of the nervous system involves receiving and processing information generated by many receptors in many parts to the body, and directing the response of many effectors to bring about appropriate response.
the nervous system can be and has been divided into many different fragments, each one of which is often refereed to as a"nervous system." there is, however, only one nervous system, though it does have several parts. structurally, the nervous system may be divided into the central nervous system and the peripheral nervous system. the central nervous system consists of the Brian and the spinal cord. it contains the centers where connection are made between nerve fibers bringing information from receptors and nerve fibers carrying in formation to effectors.the brain , which is the highly specialized superior end of the spinal cord it is capable of the sophisticated activities including consciousness, which in turn is necessary for perception and awareness, willed movements and complex movement patterns, learning, and memory. the brain exerts control over many spinal cord activities and even over certain endocrine glands.
the peripheral nervous system is made up of the nerves connecting the peripheral parts of the body with the central nervous system. twelve pairs of nerves arise from the brain and are called the cranial nerves. thirty-one pairs of spinal nerves arise from the spinal cord. there are eight cervical, twelve thoracic.five lumbar, five sacral and one coccygeal nerve, named on the basis of the level at which they emerge from the vertebral canal. the somatic component is what is usually meant by "the nervous system," since it innervates supplies the general body structures(soma= body).
CELL OF THE NERVOUS SYSTEM.
what is commonly known as a "nerve," such as one might find in an extremity, is made up of many nerve cell processes held together by connective tissue in much the same way that muscle cells are held together. the outermost layer is the epineurium, which ensheaths the whole nerve and is continuous with the deep fascia. group of nerve fiber are surrounded by perineurum, and individual nerve fiber are enclosed by endoneurium. small blood vessels also run in the connective tissue. as large nerve trunks approach the periphery they divide into progressively smaller branches, until finally only a single fiber remains.
the nervous system is communication system based on the conduction of impulses that provide information and give directions. structures called receptors are sensitive to certain changes in their immediate environment. receptors in the skin, for example, generate impulse when stimulated by touch or pressure.receptors are located on the ends of nerve fiber, which transmit the impulse to the spinal cord or brain to effectors such as skeletal ,smooth, and cardiac muscle, and glands, which cay out the direction sent from the spinal cord or brain. still other nerve fibers transmit information to other nerve fiber.
the operation of the nervous system involves receiving and processing information generated by many receptors in many parts to the body, and directing the response of many effectors to bring about appropriate response.
the nervous system can be and has been divided into many different fragments, each one of which is often refereed to as a"nervous system." there is, however, only one nervous system, though it does have several parts. structurally, the nervous system may be divided into the central nervous system and the peripheral nervous system. the central nervous system consists of the Brian and the spinal cord. it contains the centers where connection are made between nerve fibers bringing information from receptors and nerve fibers carrying in formation to effectors.the brain , which is the highly specialized superior end of the spinal cord it is capable of the sophisticated activities including consciousness, which in turn is necessary for perception and awareness, willed movements and complex movement patterns, learning, and memory. the brain exerts control over many spinal cord activities and even over certain endocrine glands.
the peripheral nervous system is made up of the nerves connecting the peripheral parts of the body with the central nervous system. twelve pairs of nerves arise from the brain and are called the cranial nerves. thirty-one pairs of spinal nerves arise from the spinal cord. there are eight cervical, twelve thoracic.five lumbar, five sacral and one coccygeal nerve, named on the basis of the level at which they emerge from the vertebral canal. the somatic component is what is usually meant by "the nervous system," since it innervates supplies the general body structures(soma= body).
CELL OF THE NERVOUS SYSTEM.
what is commonly known as a "nerve," such as one might find in an extremity, is made up of many nerve cell processes held together by connective tissue in much the same way that muscle cells are held together. the outermost layer is the epineurium, which ensheaths the whole nerve and is continuous with the deep fascia. group of nerve fiber are surrounded by perineurum, and individual nerve fiber are enclosed by endoneurium. small blood vessels also run in the connective tissue. as large nerve trunks approach the periphery they divide into progressively smaller branches, until finally only a single fiber remains.
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