DIGESTION

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DIGESTION

• Chapter 14

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Functions of the Digestive System

• Breakdown of food (chemical digestion, mechanical
  digestion)
• Ingestion (taking in of nutrients)
• Digestion
• Secretion of enzymes
• Absorption of nutrients
• Excretion of waste
• Motility

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Divisions of the Digestive System

• Alimentary canal (gastro-intestinal tract) Tube
  that extends from mouth to anus
• Over 20ft long
• Parts oral cavity-pharynx-esophagus-stomach-small
  intestine-large intestine-anus

• Accessory organs
• Liver
• Pancreas
• Gall bladder
• Teeth
• Tongue
• Salivary glands

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Anatomy of the Digestive System
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1. ORAL CAVITY

• Functions
• Mechanical digestion
• Chemical digestion
• Structures
• Lips
• Palate
• Tongue
• Salivary Glands

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2. PHARYNX

• Connects oral/nasal pharynx to esophagus and
  larynx
• Structure
• Skeletal Muscle
• 3 regions nasopharynx, oropharynx,
  larynogopharynx
• Function
• Deglutination (swallowing)
• Forces bolus of food into espohagus

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3. ESOPHAGUS

• Connects pharynx to stomach
• Posterior to trachea
• Passes through diaphragm in an opening called the
  esophageal hiatus

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ESOPHAGUS

• Structure
• Mucosa stratified squamous
• Muscularis
• Proximal end skeletal
• Distal end smooth
• Contains 2 sphincters
• Upper esophageal sphincter (UES)
• Lower esophageal sphincter (LES)
• Connective tissue outer layer

• Motility of Esophagus
• Deglutition (proximal end)
• Peristalsis (distal end) wavelike motions

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PERISTALSIS

• An orderly sequence of contractions

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4. STOMACH

• Functions
• Begin digestion of proteins and lipids
• Converts food into a liquid paste called chyme
• Stores food
• Moves chyme into duodenum

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STOMACH STRUCTURES

• J-shaped pouched
• 4 Regions (Cardia, Fundus, Body, Pylorus)
• 2 Borders
• Greater curvature
• Lesser curvature

• Muscularis
• In body there are 3 layers of smooth muscle.
• Inner oblique, middle circular, outer
  longitudinal
• Mucosa
• Gross anatomical folds called Rugae. Rugae
  increase surface area
• Microscopic folds called Gastric Pits.

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RUGAE GASTRIC PITS

• Gastric pits are lined by simple columnar
  epithelium epithelium contains specialized
  cells.
• Surface mucosa cells
• Mucous neck cells
• Parietal cells
• Chief cells
• G-cells

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MOTILITY OF STOMACH

• 1. Peristalsis mixing waves-slower here than
  in esophagus
• 2. Gastric emptying pyloric sphincter
  opens/closes to regulate flow from stomach to
  duodenum

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5. SMALL INTESTINE

• Function Major site of digestion and absorption
  occur here
• Length About 10 ft.
• Supportive Tissue Mesentary
• Location centrally located in abdominal cavity
• Regions
• Duodenum
• Jejunum
• Ileum

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STRUCTURE OF SMALL INTESTINE

• Mucosa
• Gross anatomical folds
• Microscopic folds called villi
• Epithelium Made up of simple columnar cells
  with microvilli. There are a number of
  specialized cells found in this layer

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Motility of Small Intestine

• Peristalsis
• Segmentation adjacent areas of small intestine
  contract simultaneously. This maximizes
  digestion and absorption

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6. LARGE INTESTINE

• Location
• Outlines abdominopelivc cavity surrounds small
  intestine
• Length about 5ft
• Supportive Tissue Mesocolon
• Functions
• Absorption of water, ions, vitamin B K
• Form and excrete feces
• Regions
• Cecum
• Appendix
• Colon (4 regions) ascending, transverse,
  descending, sigmoid (s-shaped)
• Rectum? the last 8 inches of large intestine
• Anus External anal sphincter, Internal anal
  sphincter

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Large Intestine Motility(most diverse forms of
motility)

• Peristalsis
• Gastroileal reflex
• Haustral churning
• Mass peristalsis
• Defecation reflex

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ACCESSORY ORGANS OF THE DIGESTIVE SYSTEM

• Liver
• Gallbladder
• Pancreas

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THE LIVER

• Largest internal organ
• Composed of 4 lobes
• Functions
• Stores vitamins and minerals (iron, vit. D)
• Detoxify/Cleans Blood
• Metabolism of carbohydrates, lipids, and proteins
• Bile production

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THE GALL BLADDER

• Location attached to inferior surface of liver
• Function Stores bile, Concentrates bile

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THE PANCREAS

• Location Posterior to stomach
• Structure
• Gross Head, Body, Tail
• Endocrine portion secrete insulin and glucagon
• Exocrine portion secrete and synthesize
  digestive enzymes that break down proteins,
  carbohydrates and lipids

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Digestion and Absorption of Complex Molecules

• Carbohydrates
• a. Begins in oral cavity with salivary amylase
• b. Remaining digestion occurs in small intestine
  (duodenum) with pancreatic enzymes
• c. Carbohydrates are digested into
  monosaccharides and absorbed across mucosa into
  blood

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• 2. Proteins
• a. Begins in stomach
• b. Remaining occurs in small intestine with
  pancreatic enzymes
• c. Proteins are digested into amino acids and
  absorbed across mucosa into blood
• 3. Lipids
• a. Begins in stomach
• b. Remaining occurs in small intestine