The Digestive System and Nutrition Chapter 14 Canale MVCC

Digestive System Figure 14.1 ACCESSORY ORGANS: Salivary glands • Saliva moistens food • Bicarbonate maintains pH • Amylase digests starch • Lysozyme inhibits bacteria Liver • Produces bile • Performs various functions associated with processing and storing nutrients Pancreas • Secretes digestive enzymes into small intestine • Secretes bicarbonate into small intestine to neutralize stomach acid Gallbladder • Stores and concentrates bile Appendix • No known digestive function Pharynx • Passageway for food and air • Participates in swallowing Esophagus • Moves food from pharynx to stomach Mouth • Teeth chew food • Tongue positions and tastes food ORGANS: Stomach • Stores and mixes food • Begins chemical digestion of protein by enzymes and acid • Regulates delivery to the small intestine Anus • Expels undigested material Rectum • Passageway for feces Sigmoid colon • Stores feces Large intestine • Absorbs the last of the water and nutrients • Stores waste material Small intestine • Digests proteins, fats, and carbohydrates • Absorbs most of the water and nutrients • Secretes digestive hormones and enzymes Figure 14.1

Gastrointestinal (GI) Tract Layers Structure Common layers throughout the system Mucosa - Mucous membrane layer. Lines the digestive tract. Submucosa - Connective tissue layer. Contains blood vessels, lymph vessels, and nerves Muscularis - Two layers of smooth muscle. Responsible for motility of the digestive tract Serosa - Connective tissue outer covering . Protects and anchors the digestive tract Animation—The Digestive System

Gastrointestinal (GI) Tract Wall Lymph vessel Vein Lumen Circular layer Longitudinal layer Serosa • Connective tissue outer covering • Protects and anchors the digestive tract Mucosa • Mucous membrane layer • Lines the digestive tract Submucosa • Connective tissue layer • Contains blood vessels, lymph vessels, and nerves Muscularis • Two layers of smooth muscle • Responsible for motility of the digestive tract Artery Nerve Gastrointestinal (GI) Tract Wall Figure 14.2

Digestive System Processes Five processes Mechanical processing and movement chewing and mixing Secretion Fluid Digestive enzymes and hormones Bile, acid, alkali, mucus

Digestive System Processes Five processes (continued) Digestion Breaking down food to smallest absorbable units Absorption Through mucosa Into blood or lymph vessels for transport via circulation. Elimination Undigested material eliminated

Motility: Peristalsis – smooth muscle contractions Figure 14.3a

Motility: Segmentation Figure 14.3b

The Mouth: Teeth Figure 14.4a–b

The Mouth: mechanical and chemical digestion The mouth begins digestion Teeth Types: incisors, canines, premolars, molars Structure: crown, root Mechanical digestion – increases surface area of food Tongue Skeletal muscle Moves food in mouth Taste – sweet, bitter, hot/spicey

The Mouth Saliva – chemical digestion Salivary glands located: Parotid – side of face Submandibular – lower jaw Sublingual - under tongue Composition Mucin, salivary amylase, bicarbonate, lysozyme Begins the break down of carbohydrates from polysaccharides to disaccharides

Salivary Glands Figure 14.5

Swallowing: Voluntary phase: Tongue pushes bolus of food into pharynx Figure 14.6a

Swallowing: Delivers Food to Stomach Involuntary phase/swallowing reflex Receptors in pharynx stimulated by presence of food Soft palate rises Larynx rises slightly Epiglottis closes opening to trachea Tongue pushes food further Food enters esophagus

Swallowing Figure 14.6b

Pharynx and Esophagus Pharynx Esophagus Common passageway for air and food Participates in swallowing Esophagus Connects pharynx to stomach A mix of skeletal and smooth muscle Mucus-secreting cells assist passage of food Food motility Gravity and peristalsis

Structure of the Stomach Wall Figure 14.7a–b

Stomach Function Food storage Digestion Regulation of delivery Held and digested and then slowly released into the small intestine. Digestion Mechanical and chemical digestion Digestion of carbohydrates, proteins and fats Regulation of delivery Slowly releases food into small intestines (allows for optimal absorption).

Stomach Function Specific cells secrete gastric juice Intrinsic factor Hydrochloric acid Produces a pH of about 2; breaks down large bits of food Intrinsic factor Made by same cells that make acid; needed to absorb vitamin B12 Mucus Secreted by cells that line the stomach Protects stomach lining from acid Pepsin - enzyme HCL activates pepsin – to begin breakdown of proteins.

The Stomach Figure 14.7

Stomach Contraction: blends food – mechanical digestion Movement = propels forward into small intestine Direction: from lower esophageal sphincter to pyloric sphincter Chyme: result of mixing; affects hormone secretions, regulating peristalsis and emptying of stomach

Peristalsis Figure 14.8

Small Intestine Functions Digestion Absorption!!! Neutralizes acid from stomach Adds digestive enzymes and bile Breaks proteins, carbohydrates, and lipids to absorbable materials (simple molecules – so they can enter cells). Absorption!!! 95% of food absorbed in small intestine

Small Intestine Structure Regions Mucosa adaptations Duodenum – portion after stomach Jejunum – middle small intestines Ileum – part before the Mucosa adaptations Villi containing blood and lacteal capillaries Increase surface area – maximum absorption!!

The Wall of the Small Intestine Figure 14.9a–b

The Wall of the Small Intestine Figure 14.9c

Major Digestive Enzymes Table 14.1

Accessory Organs: Aid Digestion and Absorption - (food does not enter Pancreas Exocrine functions – released through ducts Secretes digestive enzymes Amylase – carbohydrates Trypsin – proteins Secretes sodium bicarbonate – neutralize acid

Accessory Organs: Aid Digestion and Absorption Liver Produces bile Bile stored in gull bladder and secreted into small intestine Digests lipids – gives feces a brown color Hepatic portal system Drains blood from the digestive tract to the liver Metabolic functions Storage, synthesis, and chemical processing

• Stores and concentrates bile Liver • Produces bile (water and electrolytes, cholesterol, bile salts, lecithin, and pigments) Esophagus Stomach Common bile duct Pancreatic duct Gallbladder • Stores and concentrates bile • Delivers bile to the duodenum via the common bile duct Pancreas • Secretes enzymes (proteases, amylase, lipase) • Produces sodium bicarbonate • Delivers these products to the duodenum via ducts Duodenum Figure 14.10

Accessory Organs: Aid Digestion and Absorption Figure 14.11

Large Intestine: Structure and Function Functions Absorbs nutrients and water Eliminates waste Structure Cecum - receives chyme from small intestines appendix – evolutionary function Colon Ascending, transverse, descending, sigmoid

Rectum - when food enters and is stretched a neural reflext causes the internal sphincter to relax and the rectum to contract. Potty training is learning conscious control of this sphincter. Anus - exit

Large Intestine Transverse colon Ascending colon Descending colon Small intestine Ileocecal valve Cecum Appendix Sigmoid colon Rectum External anal sphincter (skeletal muscle) Internal anal sphincter (smooth muscle) Anus Anal canal Figure 14.12

Absorption of Nutrients Proteins and carbohydrates Active transport – requires ATP! Lipids Broken down and reassembled Water Osmosis - disruption can lead to constipation or diarrhea Vitamins and minerals Assorted means

Absorption of Proteins and Carbohydrates Figure 14.13

Endocrine and Nervous Systems Regulation of Digestion Regulation dependent on volume and content of food Nervous system Stretch receptors in stomach – send signal to hypothalamus telling our body whether we are hungry or not. (hunger is different than appetite) Hormones Gastrin Secretin Cholecystokinin (CCK)

Absorption of Fats Figure 14.14

Endocrine and Nervous Systems Regulation of Digestion Gastrin Stimulates release of gastric juice – Excreted when the NS gets a signal from stretch receptors in stomach that food is present. Stimulates large intestine motility Secretin Stimulates pancreas to secrete water and bicarbonate (neutralizes acide) Occurs when duodenum is stretched Slows peristalsis in stomach Cholecystokinin (CCK) Signals pancreas to secrete digestive enzymes Signals gall bladder to release bile

Nutrients: Utilized or Stored Until Needed Figure 14.15

Food Guide Pyramid Figure 14.16

Nutrition Carbohydrates Major energy source Simple or complex Lipids Cell components and energy sources Saturated, unsaturated, and trans fats Proteins 20 amino acids (8 essential ) Vitamins Fat soluble and water soluble Minerals Recommended daily allowance Fiber Benefits colon

Weight Control: Energy Consumed Versus Energy Spent Basic Metabolic Rate (BMR) Number of calories needed at rest Influencing factors Gender, body composition, age, health, stress, food intake, genetics

Weight Control: Energy Consumed Versus Energy Spent Energy balance and body weight Caloric content Fat = 9 calories Proteins and sugars = 4 calories Excess intake leads to increased storage (weight) Physical activity Uses calories Healthy weight improves health

Disorders of the Digestive System Disorders of the GI tract Lactose intolerance Diverticulosis Colon polyps Disorders of accessory organs Hepatitis Gallstones Malnutrition Obesity Pandemic Eating disorders Anorexia nervosa Bulimia