Homeostasis Of Blood Pressure

Homeostasis defines a self-regulating system within the body that maintains a steady balance while adjusting to conditions that are crucial for the body to keep functioning efficiently (The Editors of Encyclopedia Britannica). This essay will discuss homeostasis, the homeostatic mechanism controlling blood pressure and the consequences of the homeostatic imbalance.

Blood pressure measures the amount of pressure your blood is having on the wall of your arteries throughout your body. Blood pressure plays a crucial part in how your heart and circulation works within your body. If it is not controlled within the ideal ranges (also known as the set point) and homeostasis is not achieved it can result in either hypertension (high blood pressure) or hypotension (low blood pressure). Both of which can result in severe consequences such as heart attacks, stroke, kidney disease, and even fatality (Marieb & Hoehn, 2019).

The homeostasis of blood pressure works by using a negative feedback loop (Figure, 1) that is made up of three components: the sensor, control centre and the effector. The sensor, which is also known as the baroreceptor, monitors the physical values. The control centre constantly compares the ideal range. If the range moves too far away from the set point the control centre will then activate an effector (Marieb & Hoehn, 2019; Top Hat, 2019).Figure 1 (TopHat, 2019)

Baroreceptors, which are located in the carotid sinus and the aortic arch are the sensors that are constantly measuring blood pressure within the body. It is made up of nerve fibres that extend within the walls of the arterial vessels. (Physiology Illustrated, 2005) When changes outside of the ideal range are detected it stimulates the nerve endings within in the arterial walls, sending electrical signals firing in the baroceptor neurons. These signals travel to the cardiovascular control centre in the brain to initiate the baroreflex to regulate the blood pressure (Huang, Y., Jiang, L., Lau, O-C., Lo, Y-C., Mak, F-T,A., Yao, X. & Yao, Y.; Figure 2, Marieb & Hoehn, 2019; Rabinovitch, A., Friedman, M., Braunstein, D., Biton, Y., & Aviram, I.).

In hypertension the effectors, the heart and blood vessels will aim to restore the balance with the use of two mechanisms, vasodilation and decreased cardiac output. With the use of these two mechanisms the heart rate will decrease and the vessels will expand in diameter, causing the blood pressure to drop back within the ideal range (Marieb & Hoehn, 2019; Scogna, 2014; Top Hat, 2019).

In hypotension the effector will aim to restore the balance via vasoconstriction and increased output. The use of these mechanisms will increase the heart rate and decrease the diameter of the blood vessels returning the value back to the set point to avoid homeostatic imbalance (Marieb & Hoehn, 2019; Scogna, 2014; Top Hat, 2019). Figure 2 (Marieb & Hoehn, 2019)

Sometimes the set point can be reset under particular conditions such as exercise, when the blood pressure usually increases with exertion. This particular increase is not considered abnormal, it is the body’s response to the heightened need for oxygen within the muscle tissues. When the muscles require more oxygen, the body reacts by increasing the blood flow to muscle tissues, which increases blood pressure. This resetting of the normal homeostatic set point is needed to meet the heightened need for oxygen by muscles (Scogna, 2014).

The homeostatic imbalance of blood pressure can have several consequences to other body systems, such as the renal and cardiovascular systems. For example; hypertension can lead to renal failure. When hypertension is apparent for a long period of time it damages the blood vessels causing obstruction of blood flow to the kidneys, which then causes the filtration process to slow down or in some cases, completely stop (Marieb & Hoehn, 2019).

Hypotension will result from increased strain on the heart, impairing its ability to maintain normal cardiac output, resulting in shock. Low cardiac output results in poor blood flow to organs which leads to organ failure as there is not enough blood flow to meet the needs of body tissues. Inadequate supply of blood to the organ cells causes oxygen starvation which results in cell death (Bidani & Griffen, 2014; Marieb & Hoehn, 2019).

The homeostasis of blood pressure includes both short and long term controls. With the short term control being the hormonal control and the baroreflex (neural control). The renal mechanisms act as the body’s long term regulator of blood pressure. All these controls work together to maintain blood pressure within the normal range. I have highlighted the action of the neural control which only makes up a component of the homeostasis of blood pressure (Marieb & Hoehn, 2019).

References

1. Bidani, A. K. , & Griffin, K. A. (2004). Pathophysiology of hypertensive renal damage: Implications for therapy. Hypertension, 44(5), 595-601. doi:10.1161/01.HYP.0000145180.38707.84
2. [bookmark: _Hlk18602868]Huang, Y., Jiang, L., Lau, O-C., Lo, Y-C., Mak, F-T,A., Yao, X. & Yao, Y., Frontiers in Physiology. (2016). Vol 7:384, Aortic baroreceptors display higher mechanosensitivity than carotid baroreceptors. doi:10.3389/fphys.2016.00384/full
3. Marieb, E.N, & Hoehn K. (2019). Human anatomy & physiology (11th ed). Essex, England: Pearson Education
4. [bookmark: _Hlk18574717]Rabinovitch, A., Friedman, M., Braunstein, D., Biton, Y., & Aviram, I. (2015). The baroreflex mechanism revisited. Bulletin of Mathematical Biology, 77(8), 1521-1538. doi:10.1007/s11538-015-0094-
5. Scogna, K. (2014) Homeostasis. In K. L.Lerner & B.W.Lerner (Eds). The gale encyclopedia of science, (5th ed), 2014, Retrieved from https://link-gale-com.elibrary.jcu.edu.au/apps/doc/CX3727801229/ITOF?u=james_cook&sid=ITOF&xid=5c5bd8b9
6. The Editors of Encyclopedia Britannica. (n.d). Homeostasis biology. retrieved from https://www.britannica.com/science/homeostasis
7. Top Hat. (2019). Introduction to health science: A top hat interactive text. Toronto, Canada: Top Hat Monocle.