The Gastrointestinal System By Jennifer Turley and Joan Thompson © 2013 Cengage

Presentation Overview The Process The Organs Enzymes & Hormones After digestion: absorption transportation utilization excretion

What is Digestion? The breaking down of food Big food parts into smaller ones (mechanical) Involves muscles and nerves Big nutrients into smaller ones (chemical) Involves acid, enzymes, and hormones

What is an Enzyme? Protein that catalyze metabolic reactions, and are necessary for most biochemical reactions to occur. Digestive enzymes specifically break down food substances. Examples include: amylase for carbohydrate, protease for protein, and lipase for Lipids/Fat.

What is a Hormone? Chemicals produced by cells (typically in an endocrine gland), and are secreted, then affect the behavior of cells at distal sites in the body. Examples of hormones in digestion include: cholecystokinin and secretin.

The journey begins in the mouth with Mechanical digestion: chewing (mastication) Chemical digestion: saliva (lubrication) and amylase (breaks down digestible carbohydrate) food becomes bolus

The Esophagus Peristalsis begins. Peristalsis is: a muscular wave action that occurs throughout the intestinal tract. It is controlled by the central nervous system and facilitates excretion by propelling food stuff through the body.

The Stomach Is a muscular organ & storage reservoir. Mechanically digests food by mixing & churning. Chemically digests food with acid and some enzymes (pepsin). Here, the bolus becomes chyme.

The Small Intestine Duodenum Jejunum Ileum Villi & Microvilli

Signaling the accessory organs Why? For assistance in digesting the food stuff. How? By hormones. The cells of the intestinal wall produce the hormones cholecystokinin and secretin which enter the blood stream and signal the accessory organs.

The Accessory Organs The Liver The Gallbladder The Pancreas Makes bile Stores bile The Pancreas Makes enzymes for the chemical digestion of carbohydrates, proteins, and fats Makes sodium bicarbonate to neutralize stomach acid

The Function of Bile Emulsifier

Mechanisms of Absorption Passive (Simple) Diffusion (Transport): Nutrients like water & lipid byproducts pass freely across membranes via a concentration gradient. Facilitated Diffusion (Transport): Nutrients like water soluble vitamins diffuse across membranes using a specific/selective transport proteins. Active Transport: Nutrients like glucose & amino acids move across membranes against a concentration gradient using a specific/selective transport protein & energy/ATP.

Absorption

Sites of Absorption Duodenum: many nutrients Jejunum: many nutrients Ileum: only selected nutrients Colon (large Intestine): water

Transportation of Nutrients Blood vessels: water soluble nutrients Lymphatic vessels: fat soluble nutrients

Cellular Storage Short term Intermediate Long term

Metabolic Usage Catabolic reactions: Breaking down (things get smaller). Involve hydrolysis reactions. Are degrading or destructive in nature. Anabolic reactions: Building up (things get bigger). Involve condensation reactions. Are synthesizing or constructive in nature. Homeostasis: The balance of catabolic and anabolic reactions in a person so a relatively stable internal environment or equilibrium is achieved.

Metabolic Examples What action does the enzyme lipase have on triglycerides: Anabolic, catabolic or neither? What action does bile have on triglycerides: Anabolic, catabolic or neither? What action does the hormone secretin have on the liver: Anabolic, catabolic or neither?

Excretion The Kidney: water & water soluble waste. The Skin: water & water soluble waste. The Lung: carbon dioxide & water. The Colon (Large Intestine): Water is removed & waste (bacteria, fiber, sloughed cells, & undigested food) is compacted.

Summary Chemical & mechanical digestion. Enzymes vs hormones. The gastrointestinal tract, organs, and accessory organs. Nutrient absorption & transportation. Assimilation of nutrients, storage, & metabolic usage. Excretion of waste. References for this presentation are the same as those for this topic found in module 3 of the textbook