The human body is a complex system that is made up of types of cells which combine to make tissues and organ systems, which are affected by internal and external environments.
“It is common knowledge that the internal temperature of the body is 37?C and that it varies very little, despite wide variations in the external environmental temperature. Many other physiological parameters show a similar degree of consistency, for example plasma glucose, blood pressure, plasma concentrations and so on. This maintenance of a stable internal environment is essential for the normal healthy function of the body’s cells, tissues and organs. It is called homeostasis (literally ‘staying the same’ or ‘standing still’).”
The Human Body, Gillian Pocock and Christopher Richards, page 7
The factors the body must control, within specific ranges, to achieve homeostasis are things such as blood pressure, pH, temperature, blood sugar and oxygen levels. Disease can occur when one of these systems start to function outside their normal ranges. There are numerous homeostatic systems in the body, but for this assignment I will be primarily focussing on the regulation of blood pressure. It is essential for biological health that blood pressure is kept within a normal range. Blood is pumped around the body and supplies our cells and tissues with a vital supply of nutrients and removes any waste products. This process has to occur at a specific rate otherwise disease will occur due to a build up of toxic waste products. A receptor will detect an internal stimulus which will send a signal through an afferent pathway to a control centre. The control centre will then compare these to a set point. After this an efferent signal is sent out to an effecter (for blood pressure) and the effecter will produce a controlled response that should oppose the stimulus and return the variable to within its normal range, known as negative feedback.

Consistently high blood pressure (diastolic blood pressure greater than 100mmHg) is known as hypertension and is very common. (Pollock and Richards 2008).

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Maintaining equilibrium within the internal environment of the body is essential for the body to be in a state of normal homeostasis. Important factors such as blood pressure are controlled and maintained within acceptable ranges through hormonal responses and natural reflexes from the control centres that are situated in the brain. The response from the control centres in the brain is brought about by effectors. The resulting response is checked and leads to negative feedback bringing the blood pressure levels back into acceptable parameters, bringing the body back into equilibrium. Keeping blood pressure at an adequate level is essential for the body; it ensures that all tissues and organs of the body are supplied with rich supply of blood which brings with oxygen and essential nutrients. This rich supply of blood is pumped around the body by the heart. The heart is the engine room that drives the blood around the body. The control centres in the brain send messages to heart and blood vessels to bring about changes in blood pressure which go against the detected changes bringing about negative feedback. Homeostasis starts to be lost when these mechanisms in the body start to breakdown or are overloaded bringing about disease, hypotension and hypertension.