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Lecture Outline
The Digestive System
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Anatomy of the Digestive System
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Alimentary canal (gastrointestinal
tract)
Digestion includes both physical
and chemical processes that
reduce food into soluble molecules
Functions of the digestive system:
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Ingest food
Break food down into small molecules
Absorb nutrient molecules
Eliminate nondigestible wastes
Anatomy of the Digestive System
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The Mouth (Oral Cavity)
•
Tongue is composed of skeletal muscle
Papillae
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Frenulum attaches it to the floor of the mouth
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Help it handle food
Contain taste buds
Roof separates it from the nasal cavities
Hard palate
Soft palate
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Salivary glands
Parotid
Sublingual
Submandibular
Saliva
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Salivary amylase – begins the process of digesting starch
Moistens food and prepares it for swallowing
Antibacterial lysozyme and secretory antibodies
17.3: Mouth
• The mouth:
• Ingests food
• Mechanically breaks up
solid particles, mixing
them with saliva
(mastication)
• Functions as an organ of
speech and sensory
reception
• Is surrounded by lips,
cheeks, tongue, palate
• Includes oral cavity and
vestibule
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or display.
Lip
Hard palate
Soft palate
Uvula
Palatine
tonsils
Tongue
Lingual frenulum
Vestibule
Lip
5
Major Salivary Glands
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Parotid
gland
Tongue
Masseter
muscle
Submandibular
gland
Mandible (cut)
Sublingual gland
Submandibular
duct
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Serous cell
Serous Mucous
Duct
cell
cell
Serous cell
Duct Mucous cell
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(a)
Duct
(b)
(c)
a: © The McGraw-Hill Companies, Inc./Al Telser, photographer; figure b: © Biophoto Associates/Photo Researchers, Inc.; figure c: © The McGraw-Hill Companies, Inc./Al
Anatomy of the Digestive System
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The Pharynx
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Three parts
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Nasopharynx
Oropharynx
Laryngopharynx
Palatine tonsils
Lingual tonsils
Pharyngeal tonsil (adenoids)
Swallowing
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Voluntary phase
Reflex action – once food or drink is pushed
back to the oropharynx
Palate
• The palate forms the
roof of the oral cavity
and consists of a hard
anterior part and a soft
posterior part
• The uvula extends
from the soft palate
• Palatine tonsils
• Pharyngeal tonsils
(adenoids)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Frontal sinus
Sphenoidal sinus
Nasal cavity
Hard palate
Vestibule
Tongue
Tooth
Lip
Pharyngeal tonsil
Opening of auditory tube
Soft palate
Nasopharynx
Oral cavity
Uvula
Palatine tonsil
Oropharynx
Lingual tonsil
Hyoid bone
Epiglottis
Laryngopharynx
Larynx
Esophagus
Trachea
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Anatomy of the Digestive System
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The Wall of the Digestive Tract
Mucosa (mucous membrane layer)
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Layer of epithelium
Lines the lumen
Glandular epithelial cells secrete digestive enzymes
Goblet cells secrete mucus
Submucosa (submucosal layer)
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Loose connective tissue
Contains blood vessels, lymphatic vessels, and nerves
Peyer’s patches are scattered throughout the
submucosa
Muscularis (smooth muscle layer)
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Inner, circular layer
Outer, longitudinal layer
Serosa (serous membrane layer)
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Thin, outermost layer of squamous epithelium
Secretes serous fluid
Adventitia – outer layer of the esophagus
Anatomy of the Digestive System
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The Esophagus
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Muscular tube
Peristalsis pushes food along the
alimentary canal
Function is to transport food to the
stomach
Esophageal sphincter marks the
entrance to the stomach
Heartburn occurs when some of the
stomach contents escapes into the
esophagus
Anatomy of the Digestive System
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The Stomach
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Thick-walled, J-shaped organ
Continuous with the esophagus and
duodenum of the small intestine
Rugae – deep folds in its wall
Stores and liquefies food
Starts the digestion of proteins
Regions of the Stomach
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Cardiac
Fundic
Body
Pyloric
Anatomy of the Digestive System
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Digestive Functions of the Stomach
Acts on food both chemically and physically
Muscular wall churns and mixes food with gastric
juice
Gastric glands produce gastric juice:
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Chief cells
Secrete pepsinogen
Pepsinogen becomes the protein-digesting
enzyme pepsin
Parietal cells
Produce hydrochloric acid – kills bacteria and
activates pepsin
Produces intrinsic factor – binds to vitamin B12
and prevents it from being destroyed in the
acidic environment
Enteroendocrine cells produce gastrin
Mucous cells secrete protective mucus
Structure of the Wall
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Artery
Vein
Mesentery
Serosa
Circular fold
Mucosa
Microvilli
Submucosa
Goblet cell
Nucleus
Longitudinal muscle
Circular muscle
Epithelium
Simple columnar
epithelium
Lacteal
Villi
Capillaries
Mucosa
Lacteal
Lymph nodule
Intestinal gland
Mucous gland in submucosa
Nerve
plexuses
Serosa
Circular muscle
Longitudinal muscle
Muscular
layer
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Anatomy of the Digestive System
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Peritoneum
serous membrane
Parietal peritoneum lines the abdominal
wall
Visceral peritoneum covers the organs
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Lesser omentum – mesentery that runs
between the stomach and liver
Greater omentum – mesentery that hangs
down in front of the intestines
Cushions and insulates the abdominal cavity
Contains macrophages
Can wall off portions of the alimentary wall
that may be infected
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display.
Liver
Stomach
Gallbladder
Transverse colon
underneath
Greater
omentum
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Anatomy of the Digestive System
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The Small Intestine
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Extends from the pyloric valve of the
stomach to the ileocecal valve where
it joins the large intestine
Regions of the Small Intestine
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Duodenum
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Glands secrete mucus
Receives pancreatic secretions and bile
Jejunum
Ileum contains Peyer’s patches
Anatomy of the Digestive System
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Wall of the Small Intestine
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Circular folds
Villi
Microvilli
Anatomy of the Digestive System
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Functions of the Small Intestine
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Digestion of fats, proteins, and
carbohydrates into soluble molecules
Absorption of nutrients
Movement of nondigested remains to
the large intestine
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Segmentation-ring-like contraction
Peristalsis –pushing movements
Anatomy of the Digestive System
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Regulation of Contraction and Secretion in the
Digestive Tract
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Hormones
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Gastrin - causes gastric contraction and secretion
by gastric glands
Secretin – causes bicarbonate release from
pancreas
Gastric inhibitory peptide – inhibits gastric action
Cholecystokinin – causes enzyme release from
pancreas
Leptin – from adipocytes, causes full feeling
Ghrelin – from stomach, triggers hunger
Anatomy of the Digestive System
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The Large Intestine
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Absorbs water, salts, and some vitamins
Stores indigestible material until it is eliminated
Cecum
Blind end
Vermiform appendix
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Colon
Four portions
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Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Haustra
Taenia coli
Rectum
Anal canal
Anatomy of the Digestive System
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Feces
75% water
25% solids
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Bacteria
Fiber and other indigestible remains
Diarrhea and Constipation
Constipation
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Feces is dry and hard
Chronic constipation is associated with
hemorrhoids
Major causes of diarrhea
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Infection of the lower intestinal tract
Nervous stimulation
Anatomy of the Digestive System
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Other Disorders of the Large Intestine
Polyps
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Small growths arising from the epithelial lining
of the colon
Can be benign or cancerous (colon cancer)
Diverticulosis
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Presence of saclike pouches
Diverticulitis – when inflammation occurs
Cramps or steady pain
Fever
Loss of appetite, nausea, and vomiting
Accessory Organs of Digestion
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Salivary glands
Teeth
Pancreas
Endocrine function – pancreatic islets
secrete insulin and glucagon
Exocrine function acinar cells produce
pancreatic juice
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Sodium bicarbonate
Digestive enzymes for all types of foods
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Amylase digests starch
Three protein-digesting enzymes – inactive forms –
activated by enterokinase
Trypsin
Chymotrypsin
Carboxypeptidase
Lipase digests fat
Nucleases break down nucleic acids
Accessory Organs of Digestion
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The Liver
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Liver Structure
Two main lobes
Each lobe is divided into many hepatic lobules
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Portal triads are located between the lobules
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Hepatic cells
Hepatic sinusoids
Kupffer cells – phagocytic macrophages
bile duct
A branch of the hepatic artery
A branch of the hepatic portal vein
Bile ducts merge to form the common hepatic duct
Accessory Organs of Digestion
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Liver Functions
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Detoxifies blood
Stores iron and vitamins A, D, E, and K
Makes plasma proteins
Maintains blood glucose concentrations
Produces urea after breaking down amino
acids
Forms and secretes bile
Helps regulate the blood cholesterol level
Accessory Organs of Digestion
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Liver Disorders
Jaundice
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Hemolytic jaundice
Obstructive jaundice
Hepatitis
Cirrhosis – liver becomes fatty and then
liver tissue is replaced by fibrous scar
tissue
Accessory Organs of Digestion
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The Gallbladder
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Stores excess bile
When needed, bile leaves the
gallbladder via the cystic duct
Function of bile salts
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Emulsification of fats
Enhance absorption of fatty acids,
cholesterol, and fat soluble vitamins
Chemical Digestion
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Digestive enzymes are hydrolytic enzymes
Break down substances
Introduce water at specific bonds
Starch
Salivary amylase
Pancreatic amylase
Disaccharases (brush border enzymes) complete digestion
to monosaccharides in the small intestine
Proteins
Pepsin
Three pancreatic proteinases
Trypsin
Chymotrypsin
Carboxypeptidase
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Peptidases (brush border enzymes) complete the digestion
of proteins into amino acids in the small intestine
Fats
Emulsified by bile
Digested by pancreatic lipase
Effects of Aging
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Incidence of gastrointestinal disorders
increases
Periodontitis
Esophageal hiatal hernia
Heartburn
Peristalsis slows
Peptic ulcers may occur more frequently
Diverticulosis and constipation
The liver shrinks
Gallbladder difficulties occur
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Gallstones
Cancer
Homeostasis
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Alimentary canal is also part of the
endocrine system
Nutrients absorbed by the alimentary
canal are used for energy
Nutrition
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Nutrient – substance the body
uses to maintain health
A balanced diet contains all the
essential nutrients
Nutrients enter the blood and is
distributed to the tissues
Essential molecules must be
present in food because the body
is unable to produce them
Nutrition
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Glucose is the body’s immediate
energy source
Fats are a long-term energy
source
Amino acids
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Used by the cells to construct
proteins
Nine essential amino acids
Nutrition
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Vitamins
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Vital to life
Play essential roles in cellular
metabolism
Fat-soluble - vitamins A, D, E, and K
Water-soluble
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B-complex vitamins and vitamin C
Most are coenzymes
Nutrition
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Minerals
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Inorganic elements
Macronutrients
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Sodium
Magnesium
Phosphorus
Chlorine
Potassium
Calcium
Micronutrients
Nutrition
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Eating Disorders
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Obesity
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Body weight 20% or more above the ideal weight
for a person’s height
28% of women and 10% of men in the U.S. are
overweight
Caused by a combination of factors
Bulimia Nervosa
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Can coexist with either obesity or anorexia
nervosa
Bingeing then purging
Alters blood composition
Stomach acids can cause teeth to erode
Nutrition
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Anorexia Nervosa
Morbid fear of gaining weight
Individuals have a distorted self-image
Individuals have all the symptoms of
starvation
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Low blood pressure
Irregular heartbeat
Constipation
Constant chilliness
Bone density decreases
Menstruation stops in females
Internal organs do not function well
Skin dries up