School of Nursing, Midwifery and Interprofessional Studies.
With reference to acid-base balance explore the role of the respiratory system in maintaining blood pH?
‘We live and die at the cellular level’ (Reid, 2011). Homeostasis is crucial for normal cellular function. Acid-base homeostasis is the part of human homeostasis and refers to the balance between the production and elimination of H+ hydrogen ions (pH) within the body fluids (William, Simpkins, 2001, p.236). Metabolic reactions within the cells often produce a huge excess of H+. Lack of any mechanism for its excretion would lead H+ levels in body fluids rise quickly to the lethal levels (Tortora, Grabowski 2006, p.1001); therefore the homeostasis of the right H+ levels is crucial for our survival. In a healthy person several systems work interdependently on maintaining blood’s pH (Sheldon, 2001, p.23): buffer, renal and respiratory systems. In this essay I will concentrate on the pH of the blood in relation to the acid-base balance and the role that respiratory system has in maintaining it.
Blood pH is a measure of its acidity or alkalinity. A pH of 7.4 is considered neutral in the systemic arterial blood within its narrow range of around 7.35 and 7.45. When the pH is greater than 7.45 the blood is considered to be alkalotic and when the pH is lower than 7.35 then the blood is considered acidotic (Sheldon, 2001, p.23).
Fig. 1: Diagram of blood pH scale:
The acidity or alkalinity of blood is a result of H+ concentration within it, and this on the other hand results from the carbon dioxide concentration in the blood. Carbon dioxide is a toxic waste product generated in the oxidation of fats, carbohydrates and proteins within the cells. The gas itself is not an acid, but it reacts with water to form carbonic acid which then dissociates to form a hydrogen ion and a bicarbonate ion: CO2+H2O↔ H2CO3↔H++ HCO3-
The respiratory system helps to control the acidity of blood by regulating the elimination of CO2 and H2O through ventilation and on the other hand, blood pH (H+ concentration) plays a major role in respiratory control.
Respiratory muscles belong to the voluntary breathing system and are controlled by the respiratory centre located in the medulla oblongata and the pons of the brain stem (Hinchliff, Montague, Watson, 2005, p.605). Gregoire and Gallagher (2004, p.224) suggest, that the breathing centre controls a number of inseparable parts, which work together to ensure that any inspiration is harmoniously followed by an appropriate expiration. Also, the frequency and the volume of air per inspiration are regulated. In order to regulate the breathing in an efficient manner, the respiratory centre must be informed of the need for the ventilation in the body mainly by chemoreceptors which are sensitive to the PCO2 (carbon dioxide pressure) or the pH of the blood. Those chemoreceptors can be found in the aortic arch and in the carotid artery (Thomson, Adams, Cowan, 1997, p.51).
According to Tortora and Derrickson (1006, p. 1002), the pH of bodily fluids and breathing rate react via the negative feedback loop. When the aforementioned chemoreceptors detect any changes in blood pH, they will stimulate the respiratory centre to alter the ventilation rate in order to bring the acid-base balance to its homeostatic level. When the blood acidity increases, the pH decreases and causes the chemoreceptors to stimulate the inspiratory area in the brain. This results in diaphragm and other respiratory muscles to contract more frequently and forcefully (resulting in increased CO2 excretion). This will cause less H2CO3 to form, therefore less H+ will be present in the blood, resulting in increase of blood’s pH. When this response will bring blood pH back to normal, its acid-base balance will be back to its homeostatic level (Tortora, Derrickson, 2006, p.1002). The same negative feedback will respond, when the blood CO2 level will...
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