Chapter 14. The Digestive System and Body Metabolism

Chapter 14 The Digestive System and Body Metabolism

Textbook and Workbook Assignments Textbook: pg. 463-494 Workbook: 277-281, 283-293, 299 Crash Course Videos: Digestive System part 1 https://www.youtube.com/watch?v=yiotrgfcmqm&t=35s Digestive System part 2 https://www.youtube.com/watch?v=pqgceiaxgme&t=23s Digestive System part 3 https://www.youtube.com/watch?v=jgme7brkpuq&t=27s Metabolism and Nutrition part 1 https://www.youtube.com/watch?v=fr3nxcr9z2u&t=30s Metabolism and Nutrition part 2 https://www.youtube.com/watch?v=kb146y1igtq&t=35s

Functions of the Digestive System 1. Ingestion / Propulsion 2. Digestion Mechanical Chemical 3. Absorption 4. Defecation

Food Goes In & Pushed Through Ingestion placing of food into the mouth Propulsion moving foods from one region of the digestive system to another Peristalsis alternating waves contraction and relaxation squeezes food along the GI tract Segmentation movement of materials back and forth mixing in the small intestine

Digestion Breaking down food Mechanical digestion: makes smaller pieces Chemical digestion: change macromolecules into monomers Ultimate goal:

Anatomy of the Digestive System: Alimentary Canal Accessory Organs Text p. 463-476 WB 277-281, 283-288

Digestive System Structures The alimentary canal Accessory organs

An Overview of Digestion https://www.youtube.com/watch?v=b20vrr9c37q

Membranes of the Digestive Tract Entire alimentary canal has 4 layers: internal mucosa submucosa muscularis external serosa

Mouth Special features: teeth, tongue, saliva Teeth Incisors Canines Premolars Molars Tongue Saliva contains: AMYLASE, water, mucous

Salivary Glands (3) Parotid gland Submandibular gland Sublingual gland Type of secretion (2) Serous Watery fluid containing amylase Mucous Thick fluid binds food Lubricates food to swallow

Pharynx Back of throat Above esophagus

Uvula Flap of skin Prevents food from entering the nasal cavity

Epiglottis Flap of skin Prevents food from entering the trachea

Esophagus Structure Tube between the pharynx and stomach ~ 25 cm long Location Anterior to the vertebrae Posterior to the trachea Passes through the diaphragm

Stomach J-shaped with curvatures Food storage = 1 liter Food becomes chyme Mechanical digestion Churning of food Chemical digestion Digestive enzymes Rugae (expandable folds) Gastric glands in mucosa membrane

Stomach Esophagus Pylorus Lesser curvature Rugae of mucosa Greater curvature Duodenum Pyloric sphincter (valve)

Liver & Gall Bladder LIVER Largest internal organ ~3 pounds Produces bile GALL BLADDER Stores bile Exocrine gland Releases bile into small intestines BILE Substance made of: Cholesterol, dark pigments, salts Helps break up fat molecules (emulsifies fat)

Pancreas Exocrine gland Secretes pancreatic juices Adds digestive enzymes to small intestines

Small Intestine ~20 feet long Duodenum Jejunum Ileum Mesentery Ileocecal junction Contains intestinal gland in submucosa Primary digestion and absorption organ Intestinal enzymes and pancreatic enzymes help complete digestion of all food groups

Small Intestine Circular Folds and Villi Increase surface area for absorption epithelial cells on each villus have ~500 microvilli 600-fold Internal structure capillaries lymph vessel (lacteal)

Large Intestine About 6 feet long Sections: Ascending colon Transverse colon Descending colon Sigmoid colon Home to good / bad bacteria Large % of feces is bacteria

Rectum & Anus Store feces Defecation

Physiology of the Digestive System: Ingestion / Propulsion Mechanical Digestion Chemical Digestion Absorption Mouth through Stomach Text p. 476-482

Ingestion Mechanical Digestion Chemical Digestion Food is placed into the mouth Physically broken down by teeth (chewing) Saliva is released in response to mechanical pressure and psychic stimuli Tongue mixes food with saliva Salivary amylase begins carbohydrate digestion Essentially, no food absorption occurs in the mouth

Salivary Glands Purpose of Saliva Moisten food (water) Bind food together (mucous) Digest carbohydrates (amylase)

Food Movement (Mouth to Stomach) Tongue moves food to pharynx Swallow reflex triggered by food Uvula (soft palate) and epiglottis move Peristalsis of esophagus pushes food to stomach

Swallowing (Pharynx) Two phases of swallowing: 1. Buccal phase 2. Pharyngeal-esophgeal phase

Esophagus No digestion occurs in the pharynx or esophagus! Food bolus is transported to stomach via peristalsis

Stomach Digestion and Absorption Mechanical digestion Chemical digestion Carbohydrates Protein Food becomes chyme Absorbs some materials Water, Aspirin, Alcohol

Stomach Interior Surface Cell Secretions

Components of Gastric Juice Mucus Protects stomach lining against low ph Binds food Hydrochloric acid Lowers stomach ph Acidic ph (ph ~3) Activates pepsinogen pepsin Kills microorganisms Protein digestion enzymes Pepsin active protein-digesting enzyme Rennin begins digesting milk protein (INFANTS ONLY)

Regulation of Gastric Juice Secretion Factors stimulating gastrin hormone release Presence of food (neural) Rising stomach ph (neural) Gastrin hormone causes stomach glands to produce: Protein-digesting enzymes (pepsinogen) Mucus Hydrochloric acid

Food Movement in the Stomach Pyloric valve closed Pyloric valve slightly opened Pyloric valve closed Propulsion Grinding 3 ml of chime moves to pylorus 1 2 3 Retropulsion 2015 Pearson Education, Inc.

Physiology of the Digestive System: Propulsion Chemical Digestion Absorption Defecation Small Intestines through Anus Digestive Illness and Disorders Text p. 482-487 WB 289-292

Work of Enzymes Chemically break down large molecules into their building blocks Each major food group uses different enzymes Carbohydrates monosaccharides Proteins amino acids Fats fatty acids and glycerol

Brush Border Cells Secrete intestinal enzymes: Break double sugars into simple sugars Complete protein digestion

Pancreatic Juices Enzymes = amylase, protease, lipase Alkaline solution neutralizes acidic chyme provides environment for pancreatic enzymes to work Enzymes released when Stimulated by vagus nerve Stimulated by hormones Secretin Cholecystokinin (CCK)

Bile Created in liver, stored in gallbladder Is a fat emulsifier Necessary for absorption of Fat Fat-soluble vitamins (A, D, E, K) Release regulated by Secretin Cholecystokinin (CCK)

Small Intestine Functions Duodenum Bile added Pancreatic enzymes added Disaccharide, protein, fat digestion Jejunum Finalize food digestion Ileum Absorption of nutrients Mesentery Network of connective tissue and blood vessels

Movement of food in Small Intestine Peristalsis Segmental movements Mix chyme with digestive juices Aid in propelling food

Small Intestine Villi Function Absorb nutrients and water Absorb monosaccharides and amino acids (capillaries) Absorb glycerol and fatty acids (lacteal)

Nutrient Absorption

Large Intestine No digestive enzymes are produced Sluggish peristalsis Resident bacteria digest remaining nutrients Ferment cellulose and other carbohydrates Produce some vitamin K and B Release gases Water, electrolytes are absorbed Vitamins K and B are absorbed Forms feces

Intestinal Microflora

How Much Intestinal Microflora?

Functions of the Gut Flora

Stimulus for Mass Movement and Defecation Feces contain: Undigested food residues Mucus Bacteria Water

Mass Movement and Defecation Mass movements are slow, powerful movements that occur 3 to 4 times per day Fiber increases bulk and softens stool Presence of feces in rectum causes defecation reflex Internal anal sphincter relaxes Defecation occurs with relaxation of the voluntary (external) anal sphincter

Defecation Position

Illness and Disorders Heartburn / Acid Reflux / GERD Ulcer Gallstones Crohn s Disease

Heartburn / Acid Reflux / GERD

Ulcer

Gallstones

Crohn s Disease Inflamed regions

Nutrition Metabolism (brief) Text p. 487-490, 490-494 WB 293

Nutrition and Metabolism Most foods are used as metabolic fuel Foods are transformed into ATP ATP is chemical energy that drives cellular activities Energy value of food is measured in kilocalories (kcal) or Calories (C)

Metabolism all of the chemical reactions necessary to maintain life Catabolism substances are broken down to simpler substances; energy is released Anabolism larger molecules are built from smaller ones

Nutrients a substance used for cell growth, maintenance, and repair

Sources of Protein Use: Amino acids make cell proteins, enzymes, cell structures

Sources of Carbohydrates Use: Provide fuel to make ATP

Sources of Fat Use: Make myelin sheaths, cell membranes, adipose tissue, secondary source of cellular energy

Sources of Fat Good: monounsaturated, polyunsaturated Bad: saturated, trans fat

Sources of Minerals

Sources of Vitamins

Water

Healthy Eating Pyramid Red meat, butter: use sparingly Vegetables in abundance Whole-grain foods most meals Daily exercise and weight control White rice, white bread, potatoes, pasta, sweets: use sparingly Dairy or calcium supplement: 1 2 servings Fish, poultry, eggs: 0 2 servings Nuts, legumes: 1 3 servings Fruits: 2 3 servings Plant oils most meals 2015 Pearson Education, Inc.

USDA s MyPlate A diet consisting of foods from the five food groups normally guarantees adequate amounts of all the needed nutrients 2015 Pearson Education, Inc.

Building Block Materials Where does each type come from?

The Central Role of the Liver in Metabolism Liver is the body s key metabolic organ Roles in digestion: Manufactures bile Detoxifies drugs and alcohol Degrades hormones Produces cholesterol Produces blood proteins (albumin, clotting proteins) Plays a central role in metabolism Fun fact: The liver can regenerate if it is damaged or removed

Gluconeogenesis formation of new sugar Amino acids glucose Fat glucose The Liver and Glucose Levels The liver maintains blood glucose levels by: Glycogenesis glycogen formation Glucose molecules glycogen and stored in the liver Glycogenolysis glycogen splitting Glucogen glucose and released from the liver

The Liver and Fat Fats and fatty acids are picked up by the liver Some used to provide energy for liver cells Some are stored Some are broken down into simpler compounds released into the blood Excess fat stored in the liver leads to fatty liver disease

The Liver and Cholesterol Functions of cholesterol: Structural base of steroid hormones and vitamin D Building block of plasma membranes 85% of cholesterol is produced in the liver 15% of cholesterol is obtained from the diet

The Liver and Cholesterol Cholesterol and fatty acids cannot freely circulate in blood and is transported by lipoproteins: HDLs and LDLs Can cause atherosclerosis

The Liver and Cholesterol HDLs help remove cholesterol from the body

Review WB 299 Complete Study Guide Questions

Digestive System

Carbohydrate Digestion Review Foodstuff Enzyme(s) and source Site of action Digestion of carbohydrates Starch and disaccharides Oligosaccharides* and disaccharides Salivary amylase Pancreatic amylase Mouth Small intestine Lactose Maltose Sucrose Brush border enzymes in small intestine Small intestine Galactose Glucose Fructose Absorption of carbohydrates The monosaccharides glucose, galactose, and fructose enter the capillary blood in the villi and are transported to the liver via the hepatic portal vein. *Oligosaccharides consist of a few linked monosaccharides.

Protein Digestion Review Foodstuff Enzyme(s) and source Site of action Digestion of proteins Protein Pepsin in the presence of HCI Stomach Large polypeptides Pancreatic enzymes Small intestine Small polypeptides, small peptides Brush border enzymes Small intestine Amino acids (some dipeptides and tripeptides) Absorption of proteins Amino acids enter the capillary blood in the villi and are transported to the liver via the hepatic portal vein.

Fat Digestion Review Foodstuff Enzyme(s) and source Site of action Digestion of fats Unemulsified fats Emulsified by the detergent action of bile salts from the liver Small intestine Pancreatic lipase Small intestine Monoglycerides and fatty acids Glycerol and fatty acids Absorption of fats Fatty acids and monoglycerides enter the lacteals of the villi and are transported to the systemic circulation via the lymph in the thoracic duct. (Glycerol and short-chain fatty acids are absorbed into the capillary blood in the villi and transported to the liver via the hepatic portal vein.)