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Large intestine

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**Anatomy and Structure of the Large Intestine:**
– The large intestine consists of the cecum, colon, rectum, and anal canal.
– It is approximately 5 feet long in adults.
– The colon has a segmented appearance due to haustra.
– Specific sections of the colon include ascending, transverse, descending, and sigmoid.
– The cecum is the first section and is wider than the transverse colon.
– The large intestine absorbs water and electrolytes but does not play a major role in food absorption.
– Blood supply to the large intestine comes from the superior mesenteric artery and inferior mesenteric artery.
– Lymphatic drainage is specific to different parts of the colon.
– Nerve supply includes sympathetic and parasympathetic components.
– Development of the gastrointestinal tract involves multiple germ layers.

**Physiology and Function of the Large Intestine:**
– Water absorption at the colon occurs against an osmotic pressure gradient.
– The large intestine houses over 700 species of bacteria, aiding in digestion and vitamin synthesis.
– Gut flora in the large intestine metabolize undigested polysaccharides to short-chain fatty acids.
– Bacteria in the large intestine produce vitamins like K and biotin for absorption.
– The large intestine secretes bicarbonate to neutralize acidity produced by fatty acids.
– Functions of the large intestine include absorption of water and electrolytes, fermentation of carbohydrates, and synthesis of vitamins.

**Colonoscopy and Medical Interventions:**
– Colonoscopy is an endoscopic examination used for visual diagnosis, biopsy, and removal of lesions.
– Polyps as small as one millimeter can be removed during colonoscopy for further examination.
– Virtual colonoscopy reconstructs imagery from scans but does not allow therapeutic maneuvers like polyp removal.
– Colonoscopy is vital for colorectal cancer screening and detection of other colon issues.
– Surgical interventions like resection for hepatic metastases and flexible sigmoidoscopy are used for prevention and treatment.

**Variations in Intestinal Anatomy in Different Species:**
– The large intestine in various species differs in structure and function.
– Colon anatomy varies among animals, with some lacking a true large intestine.
– Rectal glands in sharks aid in osmotic balance but are not homologous to the caecum.
– Cloaca-derived rectum is present in mammals, except monotremes.
– The large intestine in animals serves similar diagnostic purposes as in humans.

**Diseases, Conditions, and Gut Microbiota:**
– Diseases affecting the large intestine include inflammatory bowel disease, colorectal cancer, diverticulitis, and irritable bowel syndrome.
Gut microbiota in the large intestine affect host metabolism, immune system development, and digestion.
– The microbiota produce short-chain fatty acids and impact various health conditions.
– Population-based studies focus on the role of gut microbiota in protecting against neoplasms.

Large intestine (Wikipedia)

The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being removed by defecation. The colon is the longest portion of the large intestine, and the terms are often used interchangeably but most sources define the large intestine as the combination of the cecum, colon, rectum, and anal canal. Some other sources exclude the anal canal.

Large intestine
Front of abdomen, showing the large intestine, with the stomach and small intestine in gray.
Part ofGastrointestinal tract
SystemDigestive system
ArterySuperior mesenteric, inferior mesenteric and iliac arteries
VeinSuperior and inferior mesenteric vein
LymphInferior mesenteric lymph nodes
Latincolon or intestinum crassum
Anatomical terminology

In humans, the large intestine begins in the right iliac region of the pelvis, just at or below the waist, where it is joined to the end of the small intestine at the cecum, via the ileocecal valve. It then continues as the colon ascending the abdomen, across the width of the abdominal cavity as the transverse colon, and then descending to the rectum and its endpoint at the anal canal. Overall, in humans, the large intestine is about 1.5 metres (5 ft) long, which is about one-fifth of the whole length of the human gastrointestinal tract.

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