In humans, electrolyte homeostasis is regulated by hormones such as the antidiuretic, aldosterone, and parathyroid hormones. Serious electrolyte disturbances, such as dehydration and over-hydration, may lead to cardiac and neurological complications that, unless they are rapidly resolved, will result in a medical emergency.
Water and minerals are reabsorbed back into the blood in the colon large intestine where the pH is slightly acidic—about 5. Privacy Policy. Skip to main content.
Digestive System. Search for:. Absorption in the Small Intestine The absorption of nutrients occurs partially by diffusion through the wall of the small intestine. Learning Objectives Describe the role played by the small intestine in the absorption of nutrients. Key Takeaways Key Points Digested food is able to pass into the blood vessels in the wall of the small intestine through the process of diffusion.
The inner wall, or mucosa, of the small intestine is covered in wrinkles or folds called plicae circulares that project microscopic finger-like pieces of tissue called villi, which in turn have finger-like projections known as microvilli. Each villus transports nutrients to a network of capillaries and fine lymphatic vessels called lacteals close to its surface.
Key Terms villi : Tiny, finger-like projections that protrude from the epithelial lining of the intestinal wall. Examples Examples of nutrients absorbed by the small intestine include carbohydrates, lipids, proteins, iron, vitamins, and water. Absorption of Monosaccharides, Amino Acids, Dipeptides, Tripeptides, Lipids, Electrolytes, Vitamins, and Water Glucose, amino acids, fats, and vitamins are absorbed in the small intestine via the action of hormones and electrolytes.
Learning Objectives Describe the process of absorption of nutrients in the small intestine. This dehydration, combined with peristaltic waves, helps compact the chyme. The solid waste formed is called feces. It continues to move through the descending and sigmoid colons. The large intestine temporarily stores the feces prior to elimination.
The body expels waste products from digestion through the rectum and anus. This process, called defecation, involves contraction of rectal muscles, relaxation of the internal anal sphincter, and an initial contraction of the skeletal muscle of the external anal sphincter. The defecation reflex is mostly involuntary, under the command of the autonomic nervous system. But the somatic nervous system also plays a role to control the timing of elimination. Download Digestive System Lab Manual.
Passive, paracellular absorption occurs in the jejunum and ileum, and, to a much lesser extent, in the colon when dietary calcium levels are moderate or high.
In this case, ionized calcium diffuses through tight junctions into the basolateral spaces around enterocytes, and hence into blood. When calcium availability is high, this pathway responsible for the bulk of calcium absorption, due to the very short time available for active transport in the duodenum. Phosphorus is predominantly absorbed as inorganic phosphate in the upper small intestine.
Phosphate is transported into the epithelial cells by contransport with sodium, and expression of this or these transporters is enhanced by vitamin D. Iron homeostasis is regulated at the level of intestinal absorption, and it is important that adequate but not excessive quantities of iron be absorbed from the diet.
Inadequate absorption can lead to iron-deficiency disorders such as anemia. On the other hand, excessive iron is toxic because mammals do not have a physiologic pathway for its elimination. Iron is absorbed by villus enterocytes in the proximal duodenum.
Efficient absorption requires an acidic environment, and antacids or other conditions that interfere with gastric acid secretion can interfere with iron absorption. Barrett, et al. Ganong's Review of Medical Physiology, 26e. McGraw Hill; Accessed November 11, McGraw Hill. Download citation file: RIS Zotero. Reference Manager. Autosuggest Results. Identify the source and functions of short-chain fatty acids in the colon. Delineate the requirements for, and mechanisms of uptake for vitamins and minerals.
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