Lake Michigan College Biological Science 101

Digestive System System Outline with multimedia links

Introduction

• Type of digestive system based on diet. [heterotrophic]
  • Carnivore - eat animals [short digestive tract and cutting teeth]
  • Herbivore - eat plants [long digestive tract and grinding teeth]
  • Omnivore - eat everything [intermediate length and dentition]
• Type of digestive tract
  • Incomplete digestive tract [mouth but no anus] found only in Cndaria and flatworms
  • Complete [mouth + anus]
• Function of digestion is to break down large food molecules to suitable size for absorption into cells
• Type of digestion
  • Intracellular - within the cell [endocytosis, food vacuole and lysosome]
  • Extracellular - within a digestive tract
• Functional Terms: ingestion, mastication, swallowing, digestion, absorption, peristalsis, defecation.
• Site of digestion of three food types
  1. Digestion of Carbohydrates [oral cavity & small intestine]
  2. Digestion of fats [small intestine]
  3. Digestion of proteins [stomach & small intestine]

Vertebrate Digestive System

• Tongue with papillae on dorsum
• Palate [hard palate & soft with uvula] is the roof of the oral cavity
• Salivary Glands secrete saliva for lubrication [contains amylase that digests starch]
• Dentition
  • 4 types of teeth [incisors, canines. premolars, molars] [see torso skull, lateral view]
  • Tooth regions are crown, neck and root
  • Tissues or layers of tooth [dentin] [enamel] [cementum] [pulp cavity]

• Functions in swallowing

• Mucosa [epithelium] is inner lining
• Submucosa [connective tissue]
• Muscularis [circular and longitudinal] functions in peristalsis
• Serosa is outermost epithelial covering
• See 4 layers of esophagus also see duodenum with villi

• Located between pharynx and stomach
• Starts peristalsis (wave of muscular contraction that moves food)

  Stomach(22) stores food and initiates digestion of proteins Gastric rugae are ridges on internal surface of stomach Cells of the stomach mucosa provide secretions for protein digestion Parietal Cells secrete HCl Chief Cells secretes protein enzyme Mucus or goblet cells secrete protective mucus Physiology of stomach [See story of William Beaumont & Alexis St. Martin]

  Small Intestine(35) [functions in digestion and absorption]
  • Projections from the mucosa are villi, and cellular projections from the columnar epithelial cells of the mucosa are microvilli, which function in absorption.
    • See human mucosa with villi
    • See cross section of microvilli]
  • Three regions of small intestine
    1. duodenum is 25 cm portion from pylorus to jejunum
    2. jejunum is 1 m portion from duodenum to ileum
    3. ileum is 2 m portion from jejunum to ascending colon
  • See model of of jejunum and ileum]
  • Pancreas is dual organ [digestive enzymes] [glucose regulating hormones - insulin & glucagon]
  • Pancreatic digestive enzymes are transported to duodenum by pancreatic duct
  • see pancreas & duodenum on LMC Lab Torso
  Liver
  • Lobes [LMC liver model - posterior view]
  • Nutrients absorbed from intestine immediately go to liver.
  • Liver maintains heomeostasis of nutrients [i.e. glucose at constant level]
  • Liver produces bile and bile is collected in hepatic ducts
    • Many of the body's waste products are secreted into the bile
    • From hepatic duct bile enters gall bladder
    • Bile enters duodenum through common bile duct
    • Bile ducts and gall bladder. See Gall Bladder Disease
    • Bile is critical for the digestion and absorption of fats. The physiological term is emulsification of fats
  Large Intestine(52) (Colon) LMC labeled model
  • Regions of colon are ascending colon, transverse colon, descending colon, sigmoid colon
  • Colon reabsorbs water to convert liquid to solid feces
  • Cecum and Vermiform Appendix on portion of ascending colon.
  • Rectum(54) is a muscular organ that stores and eliminates feces.
  • Rectum ends at anus

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  Nutrition

  Organisms classified by type of nutrition

  • Autotroph versus heterotroph
  • Heterotrophs subdivided by diet type into carnivores, herbivores and omnivores
  • Pigs are omnivores (eat both plant and animal materials)
  • What evidence suggests humans are omnivores?

  Macronutrients [nutrients required in grams]

  1. Carbohydrates [more than 50% of diet]
     • Simple vs complex carbohydrates
     • Fiber is a complex carbohydrate you don't digest
     • Starch is complex carbohydrate you digest into glucose, a simple carbohydrate.
     • Glucose is in blood as primary source for ATP energy
     • glucose stored in liver as glycogen (complex carbohydrate)
  2. Proteins
     • 20 amino acids required to synthesize protein
     • Eight Essential amino acids cannot be synthesized by human cells
     • Complete proteins contain essential amino acids
     • Incomplete proteins lack essential amino acids
  3. Lipids [less than 30% of diet]
     • Review saturated (hydrogenated) vs unsaturated fatty acids
     • Health problems associated with diet high is saturated fats
  4. Water [solvent for digestive reactions and metabolism]

  Micronutrients [nutrients required in milligrams or micrograms]

  • USDA guidlines for micronutrients are RDA.
  • Deficiencies lead to adverse effects.
    • Beriberi due to lack of B1 (thiamine)
    • Scurvy due to lack of C
  • Vitamins [13 essential small organic nutrients required in diet]
    • Fat Soluble [A, D, E, K]
      • Stored in liver
      • Tend to be toxic in excess
    • Water Soluble [B-complex and C]
      • Not stored in body
      • Tend to not be toxic in excess
    • Antioxidants [Vitamin C, E, and Beta-carotene a precursor to vitamin A]
  • Minerals [essential elements required in diet]
    • Deficiencies cause health problems.
    • Excess of most minerals have adverse effects.
    • Trace minerals are reqired in very small amounts [iodine, cobalt, selenium]

  Nutritional Calorie

  • Fats contain twice the calories as carbohydrates or proteins.
  • Daily caloric intake should = caloric expenditure.
  • Caloric expenditure dependent on BMR, age, sex, health + activity level.
  • Unused food calories are stored as fat.
  • BMI value over 25 is considered overweight

  Reccomendations

  • Food pyramid

  
  

  Top!

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  Etymology of Medical Terms

  
  http://www.lakemichigancollege.edu/liberal/bio/bio101/diges_nutr.html -- Revised Becember 4, 2002
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