Digestive System

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Digestive System
Chap 38
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Nutrients

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

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The Digestive System
pg 979
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Accessory Structures of Digestion
pg 981
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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.

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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.

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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.

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Pharyngeal stage
Oral stage
Esophageal stage
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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.

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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.

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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.

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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.

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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-gtjejunum-gtileum
• 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.

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The small intestine
Villus
Small Intestine
pg 983
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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

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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.

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• 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.

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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.

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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.

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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!)

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Digestive Disorders

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

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Digestive Disorders

• 9. Chrohns 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)

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Digestive Disorders

• 17. IBS
• 18. Colon cancer
• 19. Pancreatitis
• 20. Pancreatic cancer

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Hepatitis

• 21. Hepatitis
• A 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

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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

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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.