A. ACTIVITY
Briefly explain the main cause or mechanism of increase in respiratory rate or depth and/or respiratory difficulties in the following cases: (one to two sentences only)
1. Initiation of exercise
At the onset of exercise, the abrupt increase in breathing at the start of exercise is due to neural changes that send excitatory impulses to the dorsal respiratory group (DRG) of the medullary respiratory center in the medulla. These changes include (1) anticipation of the activity, which stimulates the limbic system; (2) sensory impulses from proprioceptors in muscles, tendons, and joints; and (3) motor impulses from the primary motor cortex (precentral gyrus).
2. Moderate exercise
With moderate exercise, the increase is due mostly to an increase in the depth of breathing rather than to increased breathing rate. The more gradual increase in breathing during moderate exercise is due to chemical and physical changes in the bloodstream including (1) slightly decreased PO2, due to increased O2 consumption; (2) slightly increased PCO2, due to increased CO2 production by contracting muscle fibers; and (3) increased temperature, due to liberation of more heat as more O2 is utilized.
3. Abrupt ascent into high altitudes
Abrupt ascent to high altitude leads to a decrease in partial pressure of oxygen (PO2) in the inspired air, resulting in hypoxia (insufficient oxygen levels in the body). This triggers the peripheral chemoreceptors in the carotid bodies and aortic arch to detect the low oxygen levels, stimulating an increase in respiratory rate and depth as a compensatory mechanism to enhance oxygen uptake and alleviate hypoxia.
4. Paralysis of phrenic nerve
The phrenic nerves (arising from cervical plexus: C3, C4, & C5) supply motor fibers to the diaphragm that stimulate its contraction, hence, an injury/paralysis to these nerves cause breathing to stop because they can’t send nerve impulses anymore to the diaphragm. Without this impulse, the lungs wouldn't be able to expand its room to take in air which impairs the ability to inhale effectively leading to compensatory increased respiratory efforts.
5. Severe anemia
Severe anemia, a condition in which the body lacks sufficient amounts of hemoglobin or healthy red blood cells to transport oxygen to the tissues, triggers compensatory mechanisms to improve oxygen delivery. Chemoreceptors detect oxygen drop, thus send signals to the brain's respiratory center which then prompts an increase in respiratory rate and depth while kidneys release erythropoietin, stimulating red blood cell production to address anemia's underlying cause and improve oxygen-carrying capacity.
6. Advanced pregnancy
In advanced pregnancy, the increase in respiratory rate is primarily attributed to hormonal changes and the growing uterus. Elevated levels of progesterone lead to increased sensitivity of the respiratory centers in the brainstem, resulting in a higher drive to breathe. Additionally, the expanding uterus puts pressure on the diaphragm, necessitating deeper breaths to meet the body's oxygen demands and maintain optimal oxygen levels for both the mother and the developing fetus.
REFERENCES:
Prabhakar & Peng. (2004, Jan 1). Peripheral chemoreceptors in health and disease . https://journals.physiology.org/doi/full/10.1152/japplphysiol.00809.2003
Juber. (2022, Sept 29). Phrenic Nerve: What to Know. https://www.webmd.com/lung/phrenic-nerve-what-to-know
Mayo Clinic. (2023, May 11). Anemia. https://www.mayoclinic.org/diseases-conditions/anemia/symptoms-causes/syc-20351360
LoMauro & Aliverti. (2015, Dec). Respiratory physiology of pregnancy. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4818213/
Tortora, G. J., & Derrickson, B. H. (2017). Principles of Anatomy and Physiology. (15th Ed.). John Wiley & Sons Inc.