how diurnal changes, postural changes and temperature affect the heart rate and blood pressure

The heart is the organ that propels blood to all body parts as a result of its rhythmic contractions (systole) and dilations (diastole). The muscles of the human heart are myogenic; they independently initiate and maintain the heart rate even without stimulus. It is, however, subject to control by the autonomic nervous system (Opie 2004). The stimulus for contraction of the heart originates in the sinoatrial (SA) node. It has the innervations connecting it to the autonomic nervous system, and it initiates the heartbeat; thus, it is also called the pacemaker. The cardio-accelerator and inhibitor centers located in the medulla oblongata of the hind brain control the heart rate. Impulses transmitted along the parasympathetic fibers reduce heart rate (Opie 2004). The pumping action of the heart generates the pressure that pushes blood through the arteries. The normal blood pressure in a healthy adult is a systolic pressure of 120mmHg and a diastolic pressure of 80mmHg or slightly lesser. Pulse pressure is the difference between the systolic and diastolic pressure and averages about 40mmHg. Levedahl et al. (2004) explains that the heart rate and blood pressure are affected by hormones and external factors such as diurnal changes, posture and temperature. These exert their influence through a negative feedback mechanism which is effected by the autonomic nervous system. There is a direct correlation between heart rate and these three factors when the body is exposed to these stimuli; they alter the heart rate via regulation through the homeostatic balance mechanism (Rodrigo, Carrera & Jaramillo 2007; Little & Little 1989).

This experiment aims at investigating how diurnal changes, postural changes and temperature affect the heart rate and thus the blood pressure. The heart rate of the subject in this experiment will be measured at different times of the day – morning and evening, while the subject is at various postures and after exposure to various stimuli- heat and cold. These will then be used to determine the effect of these factors on the heart rate.

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