AP Chapter 23 Digestive System

Digestive Disorders Are Common

"Excluding childbirth, digestive disorders such as heartburn, hermorrhoids, IBS, and duodenal stomach ulcers are the leading cause of hospitalization among US and Canadian adults ages 20-44 years. They account for over 70 million medical visits yearly in the US alone." (degestive.niddk.nih.gov)

Appetite Vs. Hunger

1. Appetite: desire to consume specific foods triggered by external cues. (sights, smell) independent of hunger. 2. Hunger: Desire to consume food that is triggered by internal physiological signals. (hypoglycemia; fatigue, lightheadedness, weakness, the shakes, or irritability).

Ghrelin

Released by the stomach to stimulate the desire to eat at usual mealtimes.

Large Intestine Anatomy

1. Cecum-- saclike first part of the large intestine. 2. Appendix- accumulation of lymphoid tissue that sometimes becomes inflamed (appendicitis). Hangs from the cecum 3. Colon- Ascending - travels up right side of abdomen. Transverse- travels across the abdominal cavity. Descending- travels down the left side. Sigmoid- S-shaped region; enter the pelvis. Sigmoid colon, rectum, and anal canal are located in the pelvis. 4. Anal Canal- Ends at the anus. 5. Anus- opening of the large intestine. External anal sphincter- formed by skeletal muscle and under voluntary control. Internal anal sphincter- formed by smooth muscle and involuntarily controlled. These sphincters are normally closed except during defecation. The large intestine delivers undigestible food residues to the body's exterior.

Regions of a Tooth

1. Crown 2. Root

Large Intestine Contains:

1. Goblet cells produce alkaline mucus to lubricate the passage of feces. Muscularis externa layer is reduced to three bands of muscle called teniae coli. These bands of muscle cause the wall to pucker into haustra (pocketlike sacs).

Digestive Distress Signals

1. Hiccup 2. Indigestion 3. heartburn 4. colic 5. flatulence 6. diarrhea 7. nausea 8. vomiting 9. loss of appetite 10. constipation 11. fecal incontinence.

Classification of Teeth

1. Incisors - cutting 2. Canines (eyeteeth) - tearing or piercing. 3. Premolars (bicuspids) - grinding 4. Molars- grinding.

Processing of Food Involves Six Essential Activities

1. Ingestion: eating. 2. Propulsion: movement of food through the alimentary canal which includes: swallowing. Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation. 3. Mechanical breakdown: includes chewing, mixing food with saliva, churning food in stomach and segmentation. Segmentation: local constriction of intestine that mixes food with digestive juices. 4. Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks. 5. Absorption: passage of digested fragments from lumen of GI tract into blood or lymph. 6. Defecation: elimination of indigestible substances via anus in form of feces.

Small Intestine (3 structural modifications that increase surface area for food absorption)

1. Microvilli-- tiny projections of the plasma membrane (create a brush border appearance) 2. Villi-- fingerlike projections formed by the mucosa. House capillary bed and lacteal. 3. Circular folds (plicae circulares) -- deep folds of mucosa and submucosa.

Food Propulsion

1. Peristalsis occur from the fundus to the pylorus, forcing food past the pyloric sphincter. 2. Grinding: The pylorus meters out chyme into the small intestine (3 ml at a time). 3. Retropulsion: peristaltic waves close the pyloric sphincter, forcing content back into the stomach. The stomach empties in 4-6 hours.

Functions of the Stomach

1. Temporary storage tank for food. 2. site of food breakdown 3. chemical breakdown of protein begins 4. delivers chyme (processed food) to the small intestine.

Energy

1. The capacity for work. 2. The ability to do work, or produce change.

Organs of the Digestive System Fall into Two Groups

1. alimentary canal (gastrointestinal or GI tract or gut) 2. Accessory digestive organs

Functions of the Digestive System

1. ingestion- placing of food into the mouth. 2. propulsion- movement of foods from one region of the digestive system to another. 3. Food breakdown- mechanical breakdown. Mechanical digestion prepares food for further degradation by enzymes. 4. Food breakdown: digestion. Occurs when enzymes chemically break down large molecules into their building blocks. Each major food group uses different enzymes. 5. Absorption: end products of digestion are absorbed in the blood or lymph. Food must enter mucosal cells and then into blood or lymph capillaries. 6. defecation: elimination of indigestible substances from the GI tract in the form of feces.

Main Functions of the Digestive System

1.Take in food 2. break it down into nutrient molecules 3. absorb molecules into the bloodstream 4. rid body of any indigestible remains.

Peristalsis

Adjacent segments of the alimentary canal organs alternately contract and relax. Food is moved distally along the tract. Primarily propulsive; some mixing may occur.

Layers of the GI Tract

All digestive organs have the same four basic layers, or tunics. 1. mucosa 2. submucosa 3. muscularis externa 4. serosa

Treatment of Ulcers

Antibiotics for Helicobacter pylori. Antisecretory agents -- stop excessive secretions. Mucosal protectant-- form barriers to ulcers.

Submucosa (the brains of the gut)

Areolar connective tissue with many blood vessels & lymphatic vessels. Highly innervated with millions of nerve fibers (enteric nervous system). Meissner's Plexus- innervate mucosa to regulate secretions. Parasympathetic/sympathetic rxns. Sensory neurons- also present in smooth muscle to detect stretching & motor neurons to regulate blood vessel diameter.

Childhood Obesity Has Both Immediate and Long-Term Effects on Health and Well-Being (Long-Term Effects)

At risk for adult health problems such as: heart disease, type 2 diabetes, stroke, several types of cancer, osteoarthritis. Overweight and obesity are associated with increased risk for many types of cancer, including cancer of the breast, colon, endometrium, esophagus, kidney, pancreas, gallbladder, thyroid, ovary, cervix, and prostate, as well as multiple myeloma and Hodgkin's lymphoma.

The Gut: Our Second Brain?

Autonomous organized microcircuits. 500 million nerve cells. 100 million neurons-- the size of a cat brain. It has 20 different neuron types. It senses the food; it knows exactly what to do. It senses by chemical and mechanical means. It has to move the food-- it has to mix all the various elements which we need for digestion. It controls also the secretion, which actually digests food.

Root

Cement- covers outer surface and attaches the tooth to the peridontal membrane (ligament). Periodontal membrane holds tooth in place in the bony jaw.

Alimentary Canal

Continuous muscular tube that runs from the mouth to anus. Digests food: breaks down into smaller fragments. Absorbs fragments through lining into blood. Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus.

Function of Bile

Emulsify fats by physically breaking large fat globules into smaller ones.

Another Component of Digestive Health is...

Energy Production.

Chemical Digestion Begins in the Small Intestine

Enzymes are produced by: intestinal cells, pancreas. Pancreatic ducts carry enzymes to the duodenum. Bile, formed by the liver, enters the duodenum via the bile duct.

Crown

Exposed part of tooth above the gingiva (gum). 1. Enamel- covers the crown. 2. dentin- found deep to the enamel and forms the bulk of the tooth, surrounds the pulp cavity. 3. Pulp cavity- contains connective tissue, blood vessels, and nerve fibers (pulp). 4. Root canal- where the pulp cavity extends into the root. The neck is a connector between the crown and the root. Region in contact with the gum.

Pancreas

Found posterior to the parietal peritoneum. Mostly retroperitoneal. Extends across the abdomen from spleen to duodenum. Produces a wide spectrum of digestive enzymes that break down all categories of food. Secretes enzymes into duodenum. Alkaline fluid introduced with enzymes neutralizes acidic chyme coming from stomach. Hormones produced by the pancreas: insulin, glucagon.

Mucosa

Functions: different layers perform one or all three. Secretes mucus, digestive enzymes, and hormones. Absorbs end products of digestion. Protects against infectious disease. Made up of three sublayers: 1. epithelium 2. lamina propria 3. muscularis mucosae.

Food Breakdown

Gastric juice is regulated by neural and hormonal factors. Presence of food or rising pH causes the release of the hormone gastrin. Gastrin causes stomach glands to produce: protein-digesting enzymes, mucus, hydrochloric acid. Hydrochloric acid makes the stomach contents very acidic. Acidic pH activated pepsinogen to pepsin for protein digestion. Provides a hostile environment for microorganisms. Protein digestion enzymes: 1.pepsin - an active protein-digesting enzyme 2. Rennin- works on digesting milk protein in infants, not adults. Alcohol and aspirin are virtually the only items absorbed in the stomach.

Prevention of Obesity

Healthy lifestyle habits, healthy eating, physical activity. Children are influenced by families, faith-based institutions, government agencies, media, food and beverage industries and entertainment industries. Schools play a critical role in establishing a safe and supportive environment with policies and practices that suppose healthy behaviors. Schools provide opportunities for students to learn about practice healthy eating and physical activity behaviors.

Childhood Obesity Has Both Immediate and Long-Term Effects on Health and Well-Being (Immediate Health Effects)

High risk factors for cardiovascular disease; 1. high cholesterol 2. high blood pressure 3. in a population-based sample of 5- to 17-year olds, 70% of obese youth had at least one risk factor for cardiovascular disease. 4. Prediabetes 5. bone and joint problems 6. sleep apnea 7. social and psychological problems such as stigmatization and poor self-esteem.

Our Body Is In A Constant State of Change

It is the raw material we put in us that are used for this renewal. Raw material = food we eat. 5% replacement/5% body weigh is replaced each day by new tissue. Fluids recycled, RBC die every 120 days, epithelial cells of our epidermis replaced every 30 days. Taste buds on tongue every 7 days. Ciliated epithelial of the GI tract every 1-3 days. Components of food make useful body parts.

Large Intestine

Larger in diameter, but shorter in length at 1.5 m, than the small intestine. Extends from the ileocecal valve to the anus. Subdivisions: 1. cecum 2. appendix 3. colon 4. rectum 5. anal canal.

Liver

Largest gland in the body. Consists of four lobes suspended from the diaphragm and abdominal wall by the falciform ligament. Connected to the gallbladder via the common hepatic duct. Bile is produced by cells in the liver. Bile leaves the liver through the common hepatic duct and enters duodenum through the bile duct. Bile is a yellow-green, watery solution containing: bile salts and bile pigments, cholesterol, phospholipids, and electrolytes.

Saliva

Mixture of mucus and serous fluids. Helps to moisten and bind food together into a mass called a bolus. Contains salivary amylase to begin starch digestion. Dissolves chemicals so they can be tasted.

Muscularis Externa

Muscle layer responsible for segmentation and peristalsis. Contains inner circular muscle layer and outer longitudinal layers. Circular layer thickens in some areas to form sphincters.

Segmentation

Nonadjacent segments of the alimentary canal organs contract and relax. Food is moved forward, then backward. Primarily mixes food and breaks it down mechanically; some propulsion may occur.

Cellular Respiration

O2+glucose-->CO2+H2O+ATP+heat

Serosa

Outermost layer, which is made up of the visceral peritoneum. Formed from areolar connective tissue covered with mesothelium (single layer of squamous epithelium) in most organs. Replaced by fibrous adventitia in esophagus. Dense connective tissue that holds esophagus to surrounding structures. Retroperitoneal organs have both an adventitia and a serosa.

Peptide YY

Released by the gastrointestinal tract after a meal in proportion to the number of calories consumed to reduce appetite.

How Do We Get From Food to ATP?

Respiration and fermentation are two of the fundamental chemical reactions that power metabolism. Metabolism is the process by which the cells break down (or build up) glucose and produce ATP in order to provide the cell with a constant source of energy. Glucose is a key intermediary in cell metabolism. Cells use glucose to build fats, carbohydrates, and other compounds; and cells recover glucose by breaking down these molecules. Glucose is a monosaccharide (carbohydrate) that is oxidized through either cellular respiration (under aerobic conditions) or fermentation (under anaerobic conditions) to produce ATP.

Gallbladder

Sac found in shallow fossa of liver. When no digestion is occurring, bile backs up the cystic duct for storage in the gallbladder. During digestion of fatty food, bile is introduced into the duodenum from the gallbladder. Gallstones are crystallized cholesterol, which can cause blockages.

Leptin

Secreted from adipocytes in proportion to their size to regulate energy intake and expenditure.

Peritoneum

Serous membranes of abdominal cavity that consists of: 1. Visceral peritoneum: membrane on external surface of most digestive organs. 2. Parietal peritoneum : membrane that lines body wall. 3. Peritoneal cavity: fluid-filled space between two peritoneums. Fluid lubricates mobile organs. 4. Mesentery: double layer of peritoneum; layers are fused back to back. Extends from body wall to digestive organs. Provides routes for blood vessels, lymphatics, and nerves. Holds organs in place and also stores fat. 5. Intraperitoneal (peritoneal) organs: organs that are located within peritoneum.

Structure of the Stomach Mucosa

Simple columnar epithelium dotted by gastric pits that lead to gastric glands. Gastric glands-- situated in gastric pits and secrete gastric juice, including: intrinsic factor, which is needed for vitamin B12 absorption in the small intestine. Types of gland cells: Mucous Neck Cells produce bicarbonate-rich alkaline mucus and thin acid mucus. Chief Cells produce protein-digesting enzymes (pepsinogens). Parietal Cells produce hydrochloric acid. Enteroendocrine Cells produce a hormone called gastrin.

Peptide Ulcers

Sores or lesions in the mucous membrane of the stomach or upper intestinal tract.

Small Intestine

Subdivisions: 1. duodenum: attached to the stomach. Curves around the head of the pancreas. 2. jejunum- attaches anteriorly to the duodenum. 3. ileum- extends from jejunum to large intestine. Meets the large intestine at the ileocecal valve.

Teeth

Teeth masticate (chew) food into smaller fragments. Humans have two sets of teeth during a lifetime: 1. Deciduous (baby or "milk") teeth. A baby has 20 teeth by age 2. First teeth to appear are the lower central incisors. 2. permanent teeth. Replace deciduous teeth between the ages of 6 and 12. A full set is 32 teeth, but some people do not have wisdom teeth (third molars). If they do emerge, the wisdom teeth appear between ages of 17 and 25.

Accessory Digestive Organs

Teeth, tongue, gallbladder, digestive glands: produce secretions that help break down foodstuffs. Salivary glands, liver, pancreas.

Nutrients

The chemicals in food that cells use for growth, maintenance and repair. They include: water, carbohydrates, lipids, proteins, minerals, vitamins.

Stomach

The stomach is a C-shaped organ located on the left side of the abdominal cavity. Food enters at the cardioesophageal sphincter from the esophagus (also called LES). Food empties into the small intestine at the pyloric sphincter (valve).

Salivary Glands

Three pairs of salivary glands empty secretions into the mouth. 1. Parotid glands: found anterior to the ears. 2. Submandibular glands 3. Sublingual glands. Both submandibular and sublingual glands empty saliva into the floor of the mouth through small ducts.

Duodenal Ulcers

Ulcers of the first part of the small intestine.