Regulation of the cardiovascular system by
examining changes in heart rate
Prepared for Dr. Isabelle Lys
Lecturer of SBI171 Anatomy &Physiology
Charles Darwin University
Summer Semester 2012-2013
Every day the human body is involved in various tasks which can alter a person’s heart rate. Some internal and external factors that contribute to changes in HR are thermo-regulatory changes, diurnal changes and sudden postural changes, which are among others such as the Autonomic Nervous system, circulating chemicals, position, exercise, emotional state, gender, age and baroreceptor reflex (Waugh & Grant 2010).
During a recent research Armstrong, Kenny, Green and Seely (2011) discovered slight diurnal changes in heart rate in the healthy young adult participants. Twenty four adults were monitored over a period of 48 hours to assess their heart rates during morning, afternoon and evening. They recorded minimal increase during the evening hours of 0.5%.
In addition to diurnal changes, postural changes also have a large impact on heart rate as Koyama, Asahina, Honma, Arai and Hattori (2008) found in a research about the 'Altered Heart Rate Control in Response to Postural Change in Patients with Machado–Joseph Disease' (a common type of autosomal dominant hereditary spinocerebellar degeneration), that there were changes in MJD patients as well as those not affected by MJD. Furthermore a study into how postural changes influence heart rate variability showed that there was a significant difference in HR in sudden postural changes such as sitting to standing and lying to standing (Chen et al. 2011).
Another point that will have an impact on HR, according to Robertson (2012), is thermo-regulatory changes. Waugh and Grant (2010) also support this stating that the heart rate will rise and fall with body temperature changes. Body temperature is regulated by the hypothalamus which is alerted to changes in temperature by thermo-receptors that are located throughout the body. Robertson (2012) explains that the hypothalamus is essential in maintaining homoeostasis; when the thermo-receptors alert the hypothalamus the temperature is above equilibrium it will then use different systems to restore the body to a homoeostatic state. Some methods that are used to restore homeostasis are sweating, vasodilation, vasoconstriction and shivering (Liu, Lian & Liu 2008).
Hypertension, a common cardiovascular disorder that removes the body from a homoeostatic point, affects one in five people and becomes more prevalent with age (Thakker 2009). High blood pressure (hypertension) is described as an increase in blood flow which may occur during fever, physical exertion, emotional stress, obesity, diabeties, smoking and a sedentary lifestyle (Marieb & Hoehn 2010). According to Waugh and Grant blood pressure above 140/90 mmHg is considered higher than normal. Thakker (2009) also supports this theory stating that according to NICE, hypertension is a BP persistently above 140/90 mmHg.
An increase in blood pressure is triggered by rising levels of carbon dioxide, falling levels of oxygen and falling levels of PH (Marieb & Hoehn 2010). These all indicate failing tissue perfusion and these changes are detected by chemoreceptors which sends signals to the cardiovascular system. The cardiovascular system then increases blood pressure to supply adequate oxygen to the tissues and by doing so causes the body to return to homoeostasis (Waugh & Grant 2010).
During Prolonged high blood pressure the force that is placed on the arteries is so high that degeneration of the arteries occurs; this is known as arteriosclerosis (Waugh & Grant 2010). High blood pressure also increases the speed of the arteries hardening and causes the heart work too hard (Ahmad & Tabassum 2011). Constant Hypertension, as noted by Marieb and Hoehn (2010), is the main cause of heart failure, vascular disease, renal failure, and...
References: Waugh, A & Grant, A, 2010, 'Ross and Wilson Anatomy and physiology in health and Illness 11th Edition ', Elsevier Limited, Sydney, Australia
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