The human body is a complex assembly of multiple systems that perform complementary functions. Even so, the body has a system that ensures that the many body functions, beginning at the cellular level, operate in a manner that does not deviate from the narrow range of internal balance, irrespective of the changes in the external environment. In this case, homeostasis acts as a self-regulating process, allowing the body to maintain internal stability while adjusting to changing external conditions (Billman, 2020). Homeostatic regulation is not merely a product of a single feedback cycle; instead, it is a complex interaction of multiple feedback systems that occurs at local, neural, and hormonal levels. Multiple-level regulation allows for specific responses and more specific and rapid responses to changes in the body’s ecosystem. Also, multi-level regulation provides a backup if one level fails to maintain body functions essential for life.
Gastric activity
The response to food begins before the food enters the mouth via the so-called cephalic bas. Cephalic bas is the first phase of ingestion, usually controlled by the neural response to the stimulus provided by food via aspects such as sight, sense, and smell, which trigger the neural response, resulting in salivation and the secretion of digestive juices such as gastric and salivary secretions (Lasschuijt et al., 2020). This response prepares the stomach to receive food. Once the food arrives in the stomach, the gastric phase begins, and the gastric juices and enzymes process the food ingested. This phase builds on the cephalic basal stimulation. The gastric phase is stimulated by stomach distention, decreases in the gastric content (PH), and food in the stomach, which promote local, hormonal, and neural responses. The endocrine system helps regulate the acidic environment of the stomach. During the gastric phase, the G cells in the stomach secrete gastrin hormone in response to protein in the stomach. Gastrin hormone stimulates the release of hydrochloric acid, which aids in protein digestion. However, when the stomach is empty, somatostatin stops the production of HCL since the acidic environment needed for digestion is no longer required in a process controlled by a negative feedback mechanism.
The muscular contractions of the stomach walls mix food and digestive substances, forming chyme, which passes at regular intervals to the small intestine. The arrival of chyme into the small intestine marks the beginning of the intestinal phase. This process triggers the production of digestive secretions, which control the gastric emptying rate. Moreover, chyme entry into the small intestines triggers hormonal and neural events that coordinate the activities of digestive system components such as the pancreas, liver, and gall bladder. The secretions from the liver, pancreas, and gallbladder play an essential role in the digestion of chyme. The hormone secretin stimulates the pancreas to secrete an alkaline bicarbonate solution that neutralizes the acidic chyme and delivers it to the duodenum. The hormone acts in tandem with cholecystokinin, which, besides stimulating the production of the requisite pancreatic juices, stimulates the release of bile into the duodenum.
Respiratory system
Variance in levels of respiratory gases outside of the physiologic phase threatens cell, tissue, and organism survival; therefore, these levels are kept in appropriate concentrations to achieve homeostasis (Guyenet & Bayliss, 2022). Peripheral chemoreceptors can detect changes in oxygen and carbon dioxide partial pressure and rapidly initiate and transduce signals into neuronal activity, which in turn alters respiration through the regulation of pulmonary gas exchange. When arterial PCo2 slightly varies, central chemoreception responds to regulate regular gas exchange and to significant changes to reduce acid-base changes. The rise in alveolar CO2 levels is detected by chemoreceptors located in the medulla oblongata, which relay signals to the respiratory centers in the brainstem to initiate changes to restore normal PCO2. When detected, an increase in PCO2 increases ventilation, where more carbon dioxide is exhaled. Changes influence this mechanism in CSF pH. A slight rise in Pco2 increases the PH of CSF, which in turn stimulates the respiratory center to increase ventilation. However, If the levels remain high abnormally long, the choroid plexus cells within the brain allow HCO3- infiltration into the CSF, which helps regulate PCO2.
References
Billman, G. E. (2020). Homeostasis: The Underappreciated and Far Too Often Ignored Central Organizing Principle of Physiology. Frontiers in Physiology, 11, 200. https://doi.org/10.3389/fphys.2020.00200
Guyenet, P. G., & Bayliss, D. A. (2022). Central respiratory chemoreception. Handbook of Clinical Neurology, 188, 37–72. https://doi.org/10.1016/B978-0-323-91534-2.00007-2
Lasschuijt, M. P., Mars, M., de Graaf, C., & Smeets, P. A. M. (2020). Endocrine Cephalic Phase Responses to Food Cues: A Systematic Review. Advances in nutrition (Bethesda, Md.), 11(5), 1364–1383. https://doi.org/10.1093/advances/nmaa059
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