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UNCW BIO 241 - Small and Large Intestine

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BIO 241 1st Edition Lecture 22 Outline of Last Lecture I. Accessory organs – liverII. Liver histologyIII. Bile and its regulationIV. Other liver functionsV. Accessory organs – gallbladderVI. Small intestine gross anatomyVII. Small intestine histologyVIII. Mechanical digestion in small intestineIX. Chemical digestion in small intestineOutline of Current Lecture I. Chemical digestion of carbohydratesII. Chemical digestion of proteinsIII. Chemical digestion of fatsIV. Regulation of the small intestineV. Absorption in the small intestineVI. Large intestine gross anatomyVII. Large intestine histologyVIII. Mechanical digestion in large intestineIX. Chemical digestion in large intestineX. Absorption in the large intestineXI. Defecation reflexCurrent LectureI.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II.III.IV.V. Monosaccharides, amino acids, chylomicrons (fats), and waterare all absorbed in the small intestine. According to Dr. Ballard,about 90% of total absorption takes place in the small intestine.Amino acids travel in the following direction: hepatic portal blood liver  inferior vena cava  general circulation. Fats flow inthe following direction: lymph  lacteals  intestinal trunk thoracic duct  general circulation. Chylomicrons are too largeto travel to the blood first which is why they enter the lymphaticsystem.VI. In a cadaver, the large intestine is 5 ft x 2.5 inches, but smaller inliving humans. The entrance is called the cecum which attachesto the appendix. It is broken into four sections known as thecolon which is shown to the right. After the sigmoid colon, thereis the rectum, anal canal, anus, internal anal sphincter, andexternal anal sphincter. These sphincters consist of smoothmuscle and are therefore involuntary. Similar to sausage links,the colon is separated into sac-like segments called haustras. This translation is “little house.” VII. The large intestine’s histology is similar but different from the small intestine. It still has simple columnar epithelium and intestinal glands, but no plicae circulares, no villi, no microvilli, rich in goblet cells, and taenia coli (what separates the haustras). VIII. Mechanical digestion in the large intestine consists of peristalsis, haustral churning (contraction of separate haustras), and mass peristalsis aka gastrocolic reflex (begins as soon as food enters the stomach. IX. As mentioned earlier, the small intestine does most of the aborption and digestion. Chemicaldigestion in the large intestine consists of bacterial fermentation in which some simple molecules are released. Bacteria also secrete vitamin K and some B complex vitamins. X. The large intestine is responsible for absorbing simple molecules and vitamins and most of the remaining water (~900 ml/day). Feces consists of water (100 – 150 ml/day), undigested foodstuffs (plant fibers = cellulose), bacteria, products of bacterial decomposition, and sloughed epithelial cells. XI. The defecation reflex can be described by the distention of the rectum which stimulates stretch receptors. They send inputs to the sacral spinal cord area + sensory input to cerebral cortex. The sacral parasympathetic output causes contraction of descending colon, sigmoid colon, and rectum and reflex relaxation of internal anal sphincter. Voluntary relaxation of external anal sphincter occurs next (in the infant this is also reflexive) which increases pressure in the rectum. This finally leads to expulsion of


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UNCW BIO 241 - Small and Large Intestine

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