Physiology and Function in Human Digestion

Hormonal Regulation: Parathyroid, Vitamin D3, Liver, and Kidney

Parathyroid hormone, vitamin D3, liver, and kidney. Parathyroid hormone is important for the intestinal absorption of calcium through the synthesis of vitamin D. Specifically, it regulates the enzyme necessary for converting vitamin D to its active form in the kidneys, which in turn increases calcium absorption in the intestine. The liver is responsible for selective extraction of parathyroid hormone, while the kidney is exclusively responsible for its fragmentary removal.

The two major types of adrenocortical hormones. The two main types of adrenocortical hormones are glucocorticoids and mineralocorticoids. Glucocorticoids play numerous roles in the human endocrine system, including the regulation of sodium and potassium, which are crucial for normal fluid balance, blood pressure, and proper circulation. Cortisol in particular regulates the metabolism of nutrients and glucose production by the liver. Mineralocorticoids such as aldosterone, progesterone, and deoxycorticosterone play an important role in the retention of minerals in the kidneys (especially sodium) and in maintaining the potassium–sodium balance.

Adrenocortical Hormones and Islets of Langerhans

The cells of the islets of Langerhans. The islets of Langerhans contain five different cell types: alpha cells, which produce glucagon; beta cells, which produce insulin; delta cells, which produce somatostatin; and two other types of cells (PP and D1 cells), both of which produce human pancreatic polypeptide hormone, though their precise functions are less well understood than those of alpha, beta, and delta cells. Alpha cell functions increase glucose production, while delta cell functions are inhibitory and regulate the production of other hormones.

Five methods for diagnosis and monitoring of diabetes mellitus. Diabetes mellitus is typically diagnosed and monitored through fasting plasma glucose levels, non-fasting plasma glucose levels, the presence of hyperglycemia, glycosylated hemoglobin (HbA1C), and diabetic ketoacidosis. Generally, fasting plasma glucose levels of 100–125 mg/dL, non-fasting glucose levels above 140 mg/dL, and glycosylated hemoglobin levels above 6% are considered indicative of glucose intolerance. Additionally, numerous cardiac, circulatory, immune system, ocular, and wound-healing issues are associated with diabetes mellitus and often precipitate its diagnosis.

Functional syncytium in the intestine. Peristaltic contractions of consecutive intestinal segments create and maintain forward movement of the bolus through the intestine. Segmental contractions also occur, which do not result in forward movement but are necessary to ensure thorough mixing of the bolus and maximal contact with the intestinal walls, facilitating optimal nutrient absorption.

Diabetes Mellitus: Diagnosis and Monitoring

The Law of the Gut. According to the Law of the Gut, gastrointestinal motility (peristalsis) consists of a rhythmic wave of contractions of smooth muscle fibers throughout the entire length of the digestive system. This wave begins in the oral cavity and continues all the way to the anal sphincter.

The ileocecal valve. The ileocecal valve is a sphincter that separates the small and large intestines. Its primary function is to prevent the reflux of colon contents back into the small intestine.