lecture24nth - How is peristalsis able to push the...

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Unformatted text preview: How is peristalsis able to push the food/chyme along in one direction? Why don't the contractions squirt food in both directions? What is a bolus? Figure 21-5 Secretion Figure 21-1 Figure 20-2 Secretion first ions, then water follows different transporters in apical vs. basolateral membranes active transport - ATPases Na+ ATP symporters and antiporters H+ Na+ HCO3ClNa+ 2 ClK+ K+ H+ ATP K+ channels (gated, not gated) Na+ K+ Figure 21-6 Cl- Why is it so important to increase the pH of the chyme in the small intestine (from the acidic conditions in the stomach)? enzymes are pH specific Figure 4-7 Pancreas - endocrine AND exocrine gland Figure 21-7 Secretions • saliva (salivary glands) • HCl solution (stomach cells) • digestive enzymes (saliva, stomach, small intestine) • NaHCO3 solution (pancreas, duodenum) • NaCl solution (crypt cells of small intestine, colon) • mucus (salivary glands, stomach, intestine) • bile (liver cells, stored in gall bladder) - bile salts, bilirubin, cholesterol, some drugs Bile – secreted by liver and stored in gallbladder Figure 21-10 Review carbohydrates and simple sugars Where are enzymes? Amylase - in saliva Disaccharidases - brush border enzymes (anchored) Figure 21-15 Absorption of peptides (amino acids, dipeptides, tripeptides) cotransporters Na+, H+ larger peptides/ proteins? Figure 21-17 What about prions? Figure 3. Small intestine; mouse, 1 hour after inoculation with homogenized sheep brain with scrapie. Okamoto, et al. (2003) Experimental Transmission of Abnormal Prion Protein (PrPsc) in the Small Intestinal Epithelial Cells of Neonatal Mice. Vet Pathol 40:723–727. Review! Figure 2-8 Figure 21-19 Fake foods The fake foods (fat and sugar "substitutes") are legal and regulated by the FDA Fake fat – Olestra use in food new use in paint Fake sugar – Saccharin (300x; 1879; toluene derivative) Aspartame (200x; 1965; two amino acids, metabolized; NutraSweet) Neotame (8000x; modified aspartame; NutraSweet; 2002) Sucralose (600x as sweet as sucrose, Cl- replace OHgroups in sucrose, Splenda, passes through body) Remember Fig. 11-5 (autonomic sympathetic and parasympathetic pathways)? vagus nerve – important parasympathetic neurons to digestive system (and heart and lungs) Peptide hormones of GI tract • >30 described (only some are "accepted" as hormones, e.g. see six listed in Table 21-1) • affect secretion of enzymes (stimulate or inhibit) • affects satiety/hunger • motility, emptying (increases, decreases) • let's pick one to learn: gastrin A lot is going on in the stomach Figure 21-25 Why would large amounts of non-absorbed synthetic foods (e.g. Olestra) cause diarrhea? A. because it will stick to the walls of the intestine, making it waterproof (and blocking the absorption of water) B. because it will increase the osmolarity of the lumen contents C. because it blocks aquaporin (water pores) Large intestine absorbs water Figure 21-31 How about defense? saliva contains lysozyme (antibacterial enzyme) and immunoglobulins HCl in stomach helps kill ingested organisms (microbes, bacteria) and denatures proteins Figure 21-22 Communication between different parts of digestive system Implications for oral drug delivery (with meal, without meal, with water, etc.) Figure 21-28 ...
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