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System Functions, Structures and Control Mechanisms in the Human Body.

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Grace Wemyss Section C: System Functions, Structures and Control Mechanisms Homeostasis: Homeostasis is defined as ? ?The ability of the body or a cell to seek and maintain a condition of equilibrium or stability within its internal environment when dealing with external changes.? (16) Homeostasis is the bodies? control mechanisms which are designed to keep the body?s internal environment constant, an example of this will be temperature. Most processes within the human body only work efficiently within a narrow range. Because of this, the body is constantly monitoring the internal environment and makes alterations where necessary. Homeostasis is achieved by a process called negative feedback. Negative Feedback: (17) Negative feedback is when systems respond in an opposite way to stabilise a system as it is able to counterbalance what is affecting the body. Without this the body may, for example, over heat which can be fatal. Negative feedback can reduce abnormally high activity or increase low activity returning the body back to its desired state of equilibrium. Each system that uses negative feedback will have a sensor which constantly monitors the status of that system and changes its status when necessary. Without this constant monitoring the body may get too cold or over heat which without urgent medical attention can result in death. An example of negative feedback is body temperature. The internal body temperature must stay within narrow barriers despite its environmental temperature. If the body goes outside these narrow barriers the body?s state of equilibrium will be unbalanced and the hypothalamus will have to work hard to re-obtain its state of equilibrium. When the body temperature rises above its narrow barriers the body sweats. The body does not sweat out water; sweat is made out of toxins and other waste products. In addition to sweating blood vessels dilate, because of this blood runs close to the skins surface and heat is lost, this causes the body temperature to drop back down to within its normal range. ...read more.


They spread through muscular walls in purkyne tissue. As the wave of excitation spreads upwards from the Apex of the ventricles the muscle starts to contract. This means the ventricles contract from the base upwards pushing the blood up and out to the major arteries located at the top of the heart. This is followed by a short amount of time where there are no impulses passing through the heart muscle, this is the heart relaxing and diastole occurring. (1,2) (4) (5) The function of arteries is to carry blood away from the heart. As the blood is just leaving the heart it is at very high pressure so the arteries need to be able to withstand this. Arteries are adapted to their function in multiple ways; their lumen is relatively small to maintain high pressure in the blood, the wall is relatively thick and contains collagen which is a fibrous protein to give it the strength it will need to with stand the high pressure, elastic fibres in the wall allow it to stretch and recoil when the heart pumps, the recoiling helps maintain high pressure while the heart relaxes, the smooth muscle in the wall can contract and constrict the artery, constriction narrows the lumen and the endothelium can be unfolded when the artery stretches. In the circulatory system there are five different types of vessels, they include; arteries, arterioles, capillaries, venules and veins. Each of the vessels are highly adapted to their function, capillaries are tiny blood vessels which are approximately 7-10 ?m wide. They are the same width as a red blood cell so the cells are able to pass along the capillary but they do have to be squeezed through. This slows the flow of the red blood cells down as they can only pass through one at a time allowing efficient exchange between blood and the tissues. The structure of a capillary is a single layer of flattened endothelium cells. ...read more.


The peripheral system breaks down into two components; these are the somatic nervous system and the autonomic nervous system. Somatic system involves the sensory and the motor neurones which run the skeletal muscles. The somatic nervous system links the parts of the central nervous system and the peripheral nervous system together to help the human body deal with sensation, perception and other cognitive processes the human body may encounter. It also transmits information to and from the sensors and to and from the central nervous system. This system produces voluntary behaviour. The autonomic nervous system only consists of motor neurones which are responsible for carrying impulses to the effectors rather than the skeletal muscles. It transmits information to and from internal organs to sustain life processes. This system meditates involuntary control and responses in the functioning of the body systems which happen automatically. The autonomic nervous system controls processes such as heart rate and digestion. The part of the body that controls the autonomic nervous system is a structure in the brain called the hypothalamus. The actions of the ANS are always involuntary, it is able to adjust our breathing and changes in heart rate when it is necessary e.g. when we participate in exercise and digestion with no contribution. In some cases we are able to control some of these processes ourselves as we can hold our breath or we can raise our heart rate by exercising. Our autonomic nervous system is working every minute of every day of our lives unlike the somatic system which shuts down while we are sleeping. The last division of the nervous system which again consists of two components is the Sympathetic Nervous System and the Parasympathetic Nervous System. These two systems use different neurotransmitters so often have antagonistic effects. The sympathetic nervous system generally increases bodily activity where as parasympathetic nervous system maintains or decreases bodily activities. (13) (14) both these nervous systems have opposite effects on the functioning of the body but balance out. ...read more.

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