Chpt_43__DIGESTION_AND_NUTRITION_1_ - Chapter 43: Digestion...

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Chapter 43: Digestion and Nutrition This chapter focuses on digestion and the process by which large molecules of storage products, which we call “food”, are broken down by mechanical and enzymatic means, and small molecules are absorbed into the internal environment, with the unabsorbed food products being eliminated as feces. The Concept Outline (P. 887) and the Concept Review (P. 905) are excellent guides. Nutrition has to do with the quality and amount of food absorbed in relation to one's basal metabolic rate and activity rate. Study the bolded information at the bottom of P. 903. It represents the current state of thinking which is probably incorrect. There are three types of digestive systems: phagocytosis, incomplete, and complete. What is interesting is that nearly all digestion in all the animal kingdom is extracellular. Acellular organisms (Protozoa) digest food intracellularly. Ruminants (Fig.43.16) are animals that ingest much cellulose. Because of their special digestive tract, it is the enzymes that are secreted by the microorganisms that digest the cellulose - not the animal itself. Humans lack this ability. Basic functional aspects of the Complete Digestive System: 1. Motility - muscular contraction - movement to mix and eliminate food - peristalsis or peristaltic action - recall the importance of smooth muscle tissue. 2. Secretion - Introduction of enzymes and other things into lumen (cavity) of the digestive tract. 3. Disassimilation of complex molecules - digestion per se. 4. Absorption - Passage of small molecules into the internal environment 5. Elimination of solid wastes - defecation. Major Food Groups: 1. Carbohydrates: Polysaccharides, Disaccharides, Monosaccharides 2. Fats, fatty acids, triglycerides 3. Proteins, Amino Acids 4. Nucleic Acid, Lipoproteins, and Cholesterol Sites: 1. Oral cavity: Importance of teeth and chewing to begin the disassimilatory process - increases surface area for enzymatic activity. Salivary glands secrete amylase which disassembles starch (polysaccharides) into disaccharides. Mucin also binds food into a bolus . 2. Connecting Tubes: Pharynx to Esophagus to Stomach. Epiglottis must cover trachea; otherwise strangulation occurs. Movement is by wave-like contraction of muscles - peristalsis . 3. Stomach: muscular, stretchable sac with three functions: to store and mix food; dissolves and disassembles complex molecules; regulates movement into small intestine. Stomach is known for acidity - HCl. Acid kills microbes (curtain of death), and initiates the beginning of protein digestion to create "protein fragments." Pepsin is a major enzyme produced by stomach lining. Secretion of HCl stops the action of amylase. Muscular contraction in the stomach's wall produces a product known as
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Chpt_43__DIGESTION_AND_NUTRITION_1_ - Chapter 43: Digestion...

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