Digestive SystemDigestive System

Chap 38

NutrientsNutrients• Water – most important nutrient!!!!most important nutrient!!!!• Carbohydrates – main energy source for the

body• Fats – essential fatty acids, energy stores• Proteins – growth, structure, transport,

regulation, metabolism, essential amino acids• Vitamins – organic molecules that work with

enzymes, water soluble, fat soluble, essential• Minerals – inorganic, Ca, K, Fe

• Eat a balanced Diet!!!pp 972 - 975

Food PyramidFood Pyramid

Fats, Oils, and Sweets (use sparingly)Soft drinks, candy, ice cream, mayonnaise, and other foods in this group have relatively few valuable nutrients.

Milk, Yogurt, and Cheese Group(2-3 Servings)Milk and other dairy products are rich in proteins, carbohydrates, vitamins, and minerals.

Meat, Poultry, Fish, Dry Beans, Eggs, and Nut Group(2-3 servings)These foods are high in protein. They also supply vitamins and minerals.Vegetable Group

(3-5 servings)Vegetables are a low-fat source of carbohydrates,fiber, vitamins, and minerals.

Fruit Group(2-4 servings)Fruits are good sources of carbohydrates, fiber, vitaminsand water.

Bread, Cereal, Riceand Pasta Group(6-11 servings)The foods at the base of the pyramid are rich in complex carbohydrates and also provide proteins, fiber, vitamins, and some minerals.

Fats

Sugars

pg 976

The Digestive System• Mouth – mechanical and chemical –

breaking down food

• Esophagus – mechanical

• Stomach – mechanical*, chemical, chyme

• Small intestine – mechanical, chemical*, digest, absorb

• Large intestine – mechanical, H2O absorption

The Digestive SystemThe Digestive System

Mouth

Salivary glands

Stomach

Pancreas (behind stomach)Large intestine

Small intestine

Rectum

Gallbladder (behind liver)

Liver

Esophagus

Pharynx

pg 979

Accessory Structures of Accessory Structures of DigestionDigestion

Liver

Gallbladder

Duodenum

Bile duct

Pancreas

Pancreatic duct

To rest of small intestine

pg 981

Four Main Stages of Food Processing

• Ingestion- act of eating.

• Digestion – process of breaking food down into molecules that can be absorbed by the body.

• Absorption – absorbing the nutrients into the blood.

• Elimination – ridding the body of waste.

The Mammalian Digestive System

• Peristalsis is the rhythmic contractions of smooth muscle along the digestive tract that keep food moving along.

• Sphincters close off various parts of the tube for regulation of the passage of food between chambers.

The Oral Cavity• Chewing physically breaking the food into

smaller pieces and exposing more surface area for enzymes to act on.

• Salivary amylase breaks down starch. Saliva also contains mucin with makes food slippery.

• Salivary lysozyme

• Bolus is the ball of food that gets pushed into the esophagus.

Oral stage Pharyngeal stage

Esophageal stage

The Stomach

• Can accommodate about 2 liters of food. • Chyme is what the bolus becomes in the

stomach after digestive juices are added.• Ridges in the stomach called ruggae help churn

food.• Pepsin in stomach breaks down proteins.

– Pepsinogen is the inactive form of pepsin and is activated by HCl.

– HCl also helps denature proteins in the chyme.

Digestion in the Stomach A Closer Look

• Gastric Pits in the stomach lining are composed of specialized epithelial cells.

• Gastric pits create the gastric juices.– Parietal Cells secrete HCl.– Chief Cells secrete pepsinogen.– Mucus Cells secrete mucus that protects the

stomach lining.

Digestive Feedback Systems

• Pepsin activates more pepsinogen.

• The sight of food creates a nervous response that causes gastric juices to be secreted.

• A drop in pH and distention of the stomach creates a negative feedback response that signals a need for secretion of gastric juices.

Stomach “Problems”

• Gastric ulcers are lesions in the stomach lining.• Can occur when the lining is eroded faster that it

is replaced (from excess HCL alone)• Helibacter pylori can cause ulcers but can be

treated with antibiotics (bacteria based)• Heartburn occurs when acidic chyme seeps

back through the cardiac sphincter between the esophagus and stomach.

Enter the Small Intestine!

• The pyloric sphincter is between the small intestine and the stomach.

• It takes 2 to 6 hours after a meal for the stomach to empty.

• duodenum->jejunum->ileum• The small intestine secretes bicarbonate to

neutralize the acid chyme coming from the stomach.

• Bile is secreted by the gallbladder to emulsify fats which are broken down by an enzyme called lipase which is secreted by the small intestine.

The small intestineThe small intestine

Small Intestine Villus

Circular folds

Villi

Epithelial cells

Capillaries

Lacteal

Vein

Artery

pg 983

Small Intestine Enzymes • Carbohydrates

– Pancreatic amylase secreted by the pancreas breaks down starch.

– Maltase, Sucrase, Lactase break down disaccharides and are built into the intestinal epithelium.

• Protein Digestion– Chymotrypsin, Trypsin,Carboxypeptidase,

Aminopeptidase, enteropeptidase.

• Nucleic Acids – Nucleases• Lipids - Lipases

Absorption of Nutrients

• Villi and microvilli increase surface area(300m2) for maximum absorption.

• Intestinal epithelium absorb nutrients either by diffusion or active transport.

• Nutrients are carried away from the intestine by capillaries at the core of the villi.

• Lacteals are lymphatic vessels that are surrounded by capillaries in the core of the villi that absorb fats which are combined with proteins.– These lipid proteins are called chylomicrons.– They travel from through the lymphatic system and eventually

drain back into the blood and travel to the heart.

• Capillaries and veins drain blood into the hepatic portal vessel which carries blood to the liver.– Ensures that the liver has first access to the

nutrients in the blood.– The nutrient balance of the blood leaving the

liver may be very different than it was when it entered.

– One of the many functions the liver include regulating glucose levels in the blood and converting amino acids into carbohydrates.

– From the liver the blood travels to the heart to be pumped to the rest of the body.

Hormonal Regulation of Digestion

Hormones released by the stomach and duodenal wall ensure that digestive juices are only around when they are needed.

The sight of food will stimulate the brain to tell the stomach wall to release gastrin which in turn stimulates gastric juices to be secreted.

Gastric juices cause more gastric juices to be released.

A drop in pH inhibits gastrin.

Reabsorbing Water

• Most of the water from waste is absorbed in the colon.

• The junction between the duodenum and the colon is called the Cecum (first 2-3 inches).

• A fingerlike projection that extends from the cecum is called the appendix. Function is uncertain, but it may help with production of flora (good bacteria) for the colon.

Colon Bacteria

• Flora are bacteria that live within the body that are beneficial.

• E. coli live in the colon and produce vitamins, K, B, biotin and folic acid as they metabolize the remaining food waste.

• Also generate gases such as methane and hydrogen sulfide as by-products of microbial metabolism (flatus!)

Digestive Disorders

• 1. Diseases of salivary glands• 2. Mumps• 3. Tooth decay (dental caries)• 4. Gingivitis• 5. Periodontitis• 6. Malocclusion• 7. GERD• 8. Ulcers

Digestive Disorders

• 9. Chrohn’s Disease (IBS of end of ileum and beginning of colon, but can be anywhere in GI tract.)

• 10. Pylorospasm• 11. Pyloric stenosis• 12. Appendicitis• 13. Hemorrhoids• 14. Stomach cancer• 15. Diverticulitis• 16. Ulcerative Colitis (IBS of colon)

Digestive Disorders

• 17. IBS

• 18. Colon cancer

• 19. Pancreatitis

• 20. Pancreatic cancer

Hepatitis

• 21. HepatitisA: viral and spread by contact with infected stool

(restaurant, day care centers, infected water in developing countries, etc.)

- Symptoms: (2-7 weeks after exposure) tired, nausea, weight loss, liver pain, fever, sore

muscles, jaundice (increased levels of yellowish pigment bilirubin found in bile increased in blood), dark urine, clay-colored stools

- Diagnose with blood test for antibodies and/or liver biopsy

Hepatitis

• B: viral (acute hepatitis) spread through contact with blood and other body fluids (unprotected sex, drug use, tattoos and piercings, razors, toothbrushes, etc.), but not kissing, sharing food or drink, etc. CAN be passed on during childbirth.

• Symptoms: most people may be asymptomatic or feel like the flu

• Diagnose with blood test and/or liver biopsy

Hepatitis

• C: virus that can lead to permanent liver damage, cirrhosis, liver cancer or liver failure, it is also blood-borne and most people are asymptomatic until liver damage occurs

• Same symptoms and diagnosis as A and B, but much more serious. Often diagnosed by accident when donating blood or as part of a routine check-up.

• More common if had blood transfusion or organ transplant before 1992

- Not as likely to go away on own as A or B. Can become chronic.