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01:119:116 (653)
Lecture 23

01:119:116 Lecture 23: Lecture 23 - Digestion
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Department
Biological Sciences
Course
01:119:116
Professor
Dr.Christy Beal
Semester
Spring

Description
Lecture 23 - Digestion I. Introduction to Digestion A. Heterotrophy ➢ All animals are heterotrophs ○ Fig 41.5 B. Four Stages 1. Ingestion ○ Types ■ Fig 41.6 2. Digestion ○ Process of breaking down complex organics ■ Mechanical - chewing → increases surface area for enzymes ■ Chemical - enzymes → hydrolysis 3. Absorption - cells take up molecules 4. Elimination - undigested passes out of system ➢ Enzymes hydrolyze biological molecules in animals ➢ How do you avoid digesting yourself? C. Digestive Compartments 1. Intracellular digestion ○ Food vacuoles ○ Lysosomes 2. Extracellular digestion - breakdown in compartments ○ Can eat big things ○ Gastrovascular cavity ■ Mouth = anus, hydra ○ Alimentary canal - two openings, one-way, you! ■ Fig 41.7 Alimentary canal ➢ Accessory glands ○ 3 pairs of salivary glands ○ Pancreas ○ Liver & Gallbladder ➢ Peristalsis - smooth muscle, waves of contraction ➢ Sphincters - ring-like muscular valves, doors II. Human Digestive System A. Components ➢ Let’s follow a meal from mouth to all the structures ○ Fig 41.9 B. Food Processing Prior to Stomach 1. Prior to ingestion ○ Digestive processes triggered ○ Saliva 2. Oral cavity - ingestion ○ Teeth → mechanical digestion ○ Salivary glands → amylase chemical ○ Mucus → mucins (glycoproteins) ○ Tongue - forms food into a bolus 3. Pharynx throat ○ Swallowing ○ Epiglottis - covers glottis ■ Prevents food from entering airway ● Fig 41.10 4. Esophagus ○ Tube between pharynx & stomach ○ Cardiac sphincter ■ Peristalsis ● Bolus to stomach & moves food in intestines ○ Fig 41.9 5. Stomach - very elastic - 2 Liters! ○ Stomach linings - puts to gastric glands ○ Gastric glands ■ Gastric juice ○ Mucus cells ■ Mucus, protect from acid ○ Fig 41.11 C. Food Processing in Stomach ➢ Chief cells ○ Makes pepsinogen ➢ Parietal cells - ATP driven pump H+ into lumen and diffuse into Cl- into lumen ➢ Now in stomach lumen ○ H+ & Cl- → HCl ➢ Lows pH in Stomach ➢ HCl - antimicrobial & activates pepsinogen ○ Pepsinogen → pepsin ■ Endopeptidase ■ Breaks internal peptide bonds at specific sites ■ Makes smaller peptide chains ➢ Stomach churns → Chyme ➢ Includes: ○ pH 2, small polypeptides ○ Mucus, smaller carbs ○ Some undigested material ➢ Exits through pyloric sphincter ○ Fig 41.9 D. Food Processing in Small Intestines 1. Small intestines (SI) ○ ~6 meters - th
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