Colon Mucosa
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Colon Mucosa
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DNA Methylation
Short-Chain Fatty Acid
Apoptosis
Nested Gene
Methylation
Bacterium
Secretion (Process)
Mucosa
Lamina Propria
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The Assessment of Gastrointestinal Function
M.H.Z. Labib, B.J.M. Jones, in Scientific Foundations of Biochemistry in Clinical Practice (Second Edition), 1994
Salt and Water Absorption
The colonic mucosa has tight intercellular junctions, which facilitate efficient extraction of sodium from small-bowel effluent and stools. The small-bowel effluent of 1500 mL that enters the colon every day contains 200 mmol Na+, 100 mmol Cl− and 10 mmol K+. Normal stools contain 1–5 mmol Na+, 1–2 mmol Cl− and 5–15 mmol K+ in 100–150 mL of water and a mass of 200 g. The colon is not physiologically homogeneous.69 The proximal colon absorbs Na+better than the distal and Cl− absorption is best in the transverse and sigmoid colon. The principal mechanisms of Na+ absorption have been identified in man but they do not account for 100% of Na+absorbed:
(i)
electrogenic Na+ absorption not linked with another solute occurs more in the distal colon;
(ii)
electroneutral Na+ absorption, which appears to be indirectly linked with Cl−- absorption via parallel exchange mechanisms, Na+–H+ and Cl−–HCO3−.
At equal concentrations of Na+ and Cl−, chloride absorption is greater than Na+ and the difference is accounted for by HCO3− secretion. Failure of Cl−-HCO3− exchange results in severe infantile diarrhoea in congenital chloridorrhoea. Unlike the small bowel, colonic NaCl absorption is not stimulated by glucose or amino acids.69
Water absorption occurs against a gradient of up to 50 mmol/L, unlike the isotonic absorption in the small bowel. The colon receives up to 1500 mL of fluid from the small bowel every day with peak flows of up to 5 mL/min, 2 h after a meal. Stool water is approximately 100–150 mL a day. Water absorption is stimulated by net NaCl absorption. The tight intercellular junctions prevent leakage back to the lumen. An increase in colonic water load by 4 L may lead to diarrhoea, but up to 80% of the total load may be absorbed and values of up to 7 L absorbed a day have been observed. The bolus size appears to be more critical; a 250-mL bolus does not alter faecal water output but 500 mL produces a liquid stool.69 The control mechanisms for delivery of small-bowel effluent via the intact ileocaecal valve are therefore as important to colonic function as those that control gastric emptying via an intact pylorus.
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Normal Physiology of the Gastrointestinal Tract and Gender Differences
ROBYN G. KARLSTADT MD, FACG, ... AMY FOXX-ORENSTEIN DO, FACG, in Principles of Gender-Specific Medicine, 2004
A. Anatomy
The colonic mucosa of normal women contains more endogenous prostacyclin (PG-I2) than that of normal men, especially in the ascending and transverse colon [124]. Of note, men's highest values were seen in the cecum and rectum, whereas women's highest values were seen in the ascending and transverse colon. Menstrual cycle phase was not assessed in this small study and the clinical significance is unclear.
Cytosolic and nuclear androgen receptors have been identified in normal colonic mucosa but men have higher amounts of nuclear androgen receptors than women [125]. The significance of this finding is not fully understood but some studies have shown that colonic adenomas have reduced numbers of receptors compared to mucosa of normal individuals, suggesting a possible protective effect of androgen receptors. Normal individuals also have mRNA receptors for estrogen and progesterone in normal colonic tissue and though men have slightly higher values for both, the differences are minimal. The amounts are comparable with those found in breast and endometrium. In one study, the levels for these receptors increased with increasing grade of colorectal cancer [126].
The anal canal is shorter in women as is the length of the sphincter and the length of the area of highest pressure, located anteriorly [127,128]. Although the puborectalis was the same length in men and women, it actually represented a greater proportion of the anal canal in women, and in one study, the area of overlap of the puborectalis and external anal sphincter was the area of highest squeeze pressure [129]. This high pressure area is located more distal in women and presents a potential foci of sphincter disruption if patients have a long episiotomy or perineal tear during childbirth [127]. Men have higher internal and external anal sphincter pressures than women [128]. Additionally, men tolerate more volume in the rectal vault and have shorter pudendal nerve latency time, indicating better neuromuscular integrity of the pelvic floor [130,131]. Women have greater perineal descent and a greater external sphincter muscle fiber density than men [131]. These latter findings are enhanced with age. Older men demonstrated a longer time to expel a balloon, suggesting that aging may be associated with some pelvic floor dysfunction [130].
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Systems Toxicologic Pathology
Timothy A. Bertram, ... Sureshkumar Muthupalani, in Haschek and Rousseaux's Handbook of Toxicologic Pathology (Third Edition), 2013
Intestines
The colonic mucosa is covered by relatively flat mucus-secreting cells and crypts. Several substances serve as growth factors that can positively stimulate epithelial growth. These include gastrin, TGF-α, and TGF-β. The influence of these growth factors is exerted on the stem cell. The ingestion and digestion of food appear to be important in maintaining growth of the intestinal mucosa. Mucosal toxicity can be exhibited by decreased cell production or increased cell loss, which can lead to atrophy or ulceration. Increased cell production can lead to hyperplasia.
In the colon, epithelial restitution is associated with migration of cells at a speed of approximately 2 μm/min. Rapid epithelial restitution is now considered one of the primary defense mechanisms of the stomach, small intestine, and colon, but occurs only under conditions in which damage is confined to the superficial mucosa. Regions of the mucosa with gross hemorrhagic lesions heal by a lengthy process of tissue replacement involving cell mitosis. It is thought that maintenance of regional blood flow in the area of damage is important for prevention or repair of lesions. Indirect damage may occur when blood flow to the area of damage is compromised.
Three mechanisms influence restitution of the mucosal barrier after toxic damage: (1) increased epithelial cell production rate; (2) reduced cell cycle time (the period between two successive divisions of proliferating cells); and (3) an increased proliferative compartment via an increase in the proportion of cells in the proliferative cycle or an increase in the absolute number of cells that are replicating at any given time. In contrast, under adaptive conditions (intestinal resection or dietary change) only one mechanism is operative: increased cell production rates via increased numbers of cells that are proliferating. The intestinal mucosa can also be induced to proliferate as a healing response near areas of cellular toxicity and ulceration. Prostaglandin E2 and fermentable fibers (e.g., guar) are examples of inducers of mucosal proliferation in the intestinal tract. Mechanisms of restitution after proliferative unit ablation are not well established.
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Hematopoietic Stem Cell Transplantation for Malignant Diseases
Pashna N. Munshi, ... Robert Korngold, in Clinical Immunology (Fifth Edition), 2019
Solid Tumors
Skin and colonic mucosa are primary targets of both acute and cGvHD, and this would suggest that allo-HSCT would be effective therapy in the treatment of cancers of these organs. Yet allo-HSCT is not effective in the control of these cancers, illustrating the discrimination between target antigens of normal tissues of GvH, such as the colonic crypt cells, compared with antigens expressed by tumors derived from these tissues targeted by GvT. With the exception of allo-HSCT in the treatment of renal cell cancer, in which a GvT effect was seen to be clinically evident in some but not all studies, transplantation in the treatment of solid tumors, such as neuroblastoma, Wilm tumor, and germ cell tumors, is limited to auto-HSCT with one or more cycles of dose-intensive chemotherapy.
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Hazards and Diseases
G.L. Nichols, in Encyclopedia of Food Safety, 2014
Health Effects
Entamoeba histolytica invades the colonic mucosa producing ulcerative lesions and profuse bloody diarrhea (amebic dysentery). Acute amebic colitis has a gradual onset, with a 1–2 week history of mild-to-moderate abdominal pain and tenderness, tenesmus (feeling the need to defecate). There are frequent watery diarrheic stools (e.g., five or more episodes per day) usually with abundant mucus and blood, and contain motile amebic trophozoites. During the chronic stages of the infection these symptoms disappear, and only cysts are found in the feces. Most patients experience abdominal pain, whereas some have intermittent diarrhea alternating with constipation. Fever is less unusual, whereas other associated symptoms include weight loss and anorexia.
Feces are almost always positive for occult blood if frank blood is not present. The dysenteric symptoms usually resolve within a few days following appropriate treatment. Severe cases of amebic colitis are characterized by bloody dysenteric stools, diffuse abdominal pain, high fever, and severe dehydration, and patients usually appear quite ill. Other presentations of acute intestinal amebiasis include extensive fulminant necrotizing colitis, toxic megacolon, and perianal ulceration.
Systemic infection can lead to abscess formation, particularly in the liver and lungs. Clinical complications, such as fulminating necrotic colitis and intestinal perforations, are the main cause of death in cases of invasive intestinal amebiasis.
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CARRIER-MEDIATED UPTAKE OF SUGARS THROUGH THE BASOLATERAL MEMBRANE OF COLON EPITHELIUM
E. Scharrer, B. Amann, in Nutrition, Digestion, Metabolism, 1981
METHODS
The experiments were performed with lamb colon mucosa stripped completely of serosa and muscle layers (Scharrer 1978). The age of the lambs was 1 to 3 weeks. The colon mucosa (colon ascendens) was mounted on a plastic stopper so that only the antiluminal surface was in contact with the incubation medium (Scharrer 1978). The preparations were incubated in 100 ml centrifuge tubes containing 20 ml Krebs Henseleit bicarbonate buffer. Substrate uptake into the colon cells was related to 1 cm2 tissue. In order to correct for radioactivity present in the extracellular fluid of the colon mucosa, the Krebs Henseleit bicarbonate buffer contained in addition to the 14C– or 3H–labelled substrate 3H– or 14C–labelled PEG (mole wt.: 4000). Details of the procedure are described elsewhere (Scharrer 1978, Scharrer and Amann 1980).
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Infections of the Gastrointestinal Tract
Gregory Y. Lauwers, ... Richard L. Kradin, in Diagnostic Pathology of Infectious Disease (Second Edition), 2018
Common Histologic Features of Bacterial (Invasive) Colitis
In response to infection the colonic mucosa shows remarkable histologic variability. In practice, the dilemma is to distinguish between infectious colitis and the early manifestations of chronic inflammatory bowel disease. Early in the course of infectious colitis, edema of the lamina propria with clusters of neutrophils and ectatic capillaries are the dominant findings. Established crypt abscesses are rare. The changes are commonly patchy, and the overall mucosal architecture is preserved. Minimal degenerative changes, limited to the upper half of the mucosa, can be seen. These include mucin depletion and epithelial damage with flattened cytoplasm associated with cryptic dilatation. Concurrently, the inflammatory infiltrate of the lamina propria is mixed, characteristically with more neutrophils than lymphocytes and plasma cells. Microthrombi can plug dilated capillaries and can account for the focal hemorrhage of the lamina propria.
Later in the course of the infection, biopsies may show scattered neutrophils, inflammation with slightly decreased goblet cells, mucin depletion, and cellular degeneration, sometimes with vacuolization. A mild increase in plasma cells is commonly noted in the lamina propria, sometimes in association with lymphoid aggregates. However, a well-established dense basal lymphoplasmacytic infiltrate is uncommon. These changes habitually resolve in 2 to 3 weeks or certainly within a trimester.273-275
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