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Essentials of Human Anatomy & Physiology
Chapter 38-2
The Digestive System
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Digestive Functions
• Ingestion - active process, conscious choice
• Mechanical processing - physical manipulation/distortion
• Digestion - chemical breakdown of food into organic
fragments
• Secretion - release of water, acids, enzymes, buffers and
salts
• Absorption - movement of organic substrates,
electrolytes, vitamins and water across the epithelium into
the interstital fluid of the digestive tract
• Excretion - elimination of waste products
– defecation - eliminates feces
– Urination - eliminates urine
Alimentary Canal &
Accessory Organs
Gastrointestinal System
• Function:physical and
chemical breakdown of food
• Includes alimentary canal:
path of material flow
• Accessory organs: salivary
glands, tongue, teeth, liver,
gallbladder, and pancreas
Alimentary Canal &
Accessory Organs
Alimentary Canal
Food Movement
• Peristalsis
• Segmentation - occurs in most areas of small
intestine , some areas of large intestine
– churning of contents to mix with secretions
Alimentary Canal
Oral Cavity
• AKA – Buccal Cavity
• Functions –
–
–
–
mechanical processing
lubrication
analysis
limited digestion of carbohydrates & lipids
Alimentary Canal
• Mouth: physical and
chemical breakdown.
• Mastication-the act of
chewing
• Saliva contains enzyme
amylase to break down
carbohydrates
Alimentary Canal
Oral Cavity
• Hard palate - palatine process of maxillary bone
• Soft palate - posterior to hard palate
– uvula-
• Tongue - skeletal muscle
• Salivary glands - 3 pair - each produces a slightly
different type of saliva
– Salivary amylase - parotid salivary glands
breakdown complex carbohydrates into maltose
Alimentary Canal
Alimentary Canal
Teeth
• Deciduous teeth - baby teeth, milk teeth, primary
teeth
• Secondary dentition - permanent teeth
–
–
–
–
Incisors
Cuspids
Bicuspids
Molars
Alimentary Canal
Accessory Organs
Alimentary Canal
Pharynx and Esophagus
• Pharynx - common passageway for food , liquids,
and air
• Esophagus - muscular tube to carry food and
liquids to the stomach
– Swallowing - deglutition
• Bolus - oval shaped ball of food
• Hiatal hernia - abdominal organs are pushed
through the esophageal hiatus
Alimentary Canal
Alimentary Canal
• Pharynx- contains
opening to trachea as
well. Epiglottis covers
opening of trachea.
• Esophagus:muscular
tube dorsal to trachea
• Relies on a rhythmic
wave-like motion called
peristalsis
Alimentary Canal
Alimentary Canal
Esophagus- transverse view
Alimentary Canal
• Sphincter-a circular
muscle that constricts a
passage or closes a
natural orifice (opening)
• Cardiac sphincter
• Pyloric sphincter
• Food sits in stomach for
1-4 hours. Gastric juices
contain hydrochloric
acid- activates pepsin,
kills bacteria.
Alimentary Canal
Stomach
• Lined with simple columnar epithelium
• Major functions–
–
–
–
Bulk storage
Mechanical breakdown
Use of acids and enzymes to break chemical bonds
Production of the intrinsic factor - glycoprotein
necessary for the absorption of vitamin B12
• Chyme - injested materials mixed with gastric
juices
Alimentary Canal
Alimentary Canal
Stomach
• 4 Regions of the Stomach
–
–
–
–
Cardia
Fundus
Body
Pylorus
• Pyloric sphincter
• Rugae - ridges and folds
• Muscles of the Stomach
– Circular, longitudinal, oblique
Digestive Enzymes
• When chyme enters the duodenum, proteins & carbohydrates are
only partly digested, & fat digestion needs to be carried out
• Enzymes aid in digestive breakdown & absorption of chyme
_____________________________________________________________
Bile Salts (Liver & Gallbladder)
Pancreatic & Salivary Amylase (Pancreas & Mouth)
Fat  Fat Droplets
Starch + H2O  Maltose
Bile is a thick digestive
fluid secreted by the
liver and stored in
gallbladder.
Facilitates digestion by
emulsifying fats into
fatty acids, which can
be absorbed by the
digestive tract
Trypsin & Pepsin (Pancreas)
Protein + H2O  Peptides
Lipase (Pancreas)
Fat Droplets + H2O  Glycerol + Fatty Acids
Peptidases (Intestinal Juice)
Peptides + H2O  Amino Acids
Maltase (Intestinal Juice)
Maltose + H2O  Glucose
Alimentary Canal
Alimentary Canal
Small Intestine
• 80%-90% of absorption
• Duodenum - closest to the stomach
• Jejunum - most of chemical digestion and nutrient
absorption occurs here
• Ileum
– Ileocecal valve - controls flow into large intestine
Alimentary Canal
• Small intestine: not so
small! 20 feet x 1 inch
• Duodenum- 1st 10 inches.
bile and pancreatic juice
enter
• Jejunum- next 8 ft.
• Ileum- final 12 ft. When
food leaves small
intestine, digestion is
complete
Alimentary Canal
Alimentary Canal
Alimentary Canal
Small Intestine Wall
•
•
•
•
Picae - transverse folds
Villi - finger like projections
Microvilli - cover each villi
Lacteal - terminal lymph - located in each villi
– Chylomicrons - protein-lipid packages
• to large to enter blood capillaries
• travel through lymph system
• Intestinal juice- moistens chyme, buffers acids
Alimentary Canal
Alimentary Canal
Accessory Organs
• Liver- largest gland in
your body
• Secretes bile- emulsifies
fat, makes them water
soluble.
• Stores glucose in the
form of glycogen
• Makes clotting proteins
• Detoxifies blood
Accessory Organs
Liver
• Metabolic regulation
– Extract absorbed nutrients or toxins
– Monitor and adjust circulating levels of organic
nutrients
– Fat soluble vitamins A,D,E,K are absorbed and stored
• Hematological regulation – one of the largest
blood reservoir in the body
– Synthesize plasma proteins
• Bile production - synthesized from cholesterol
– Normal digestion and absorption of fats
Accessory Organs
Liver
• Double Blood Supply
– Hepatic artery - oxygenated blood
– Hepatic portal vein - deoxygenated blood
• carries newly absorbed nutrients
Accessory Organs
Accessory Organs
Gall Bladder
• Gallbladder– Storage area for bile
– Modification of bile
• Emulsification - bile salts (assortment of lipids)
break apart, large droplets of lipids, then coat them
to make it easier for enzymes to attack
• Gallstones - stored bile becomes concentrated
Gall Stones
Accessory Organs
• Gall bladder- stores and
concentrates bile
• Pancreas- produces
insulin, pancreatic juices
amylase and lipase.
Insulin regulates the
uptake of glucose by the
cells
Accessory Organs
Pancreas
• The Pancreas- endocrine/exocrine organ
– Pancreatic islets
• Alpha cells
• Beta cells
– Acinar cells - secrete pancreatic proenzymes
Accessory Organs
Alimentary Canal
Large Intestine
• Large Intestine Functions:
– Reabsorption of water
– Compaction of feces
– Absorption of vitamins
– Storing of fecal material
Alimentary Canal
• Large intestine5 feet
x 2 inches. Separated from
small intestine by ileocecal
valve
• Final absorption of water,
storage of indigestible
material, absorption of
vitamins B and K by
bacteria.
• Colon connects to rectumanal canal opens to the anus
Fecal material is expelled.
Alimentary Canal
Large Intestine
• Haustra – pouches, giving bubbled appearance
• Cecum- from small intestine
– Ileocecal valve
– Vermiform appendix
• Colon
–
–
–
–
Ascending - up
Transverse- across
Descending –down
Sigmoid-end
• Rectum
• Anus
Alimentary Canal
Alimentary Canal
Alimentary Canal &
Accessory Organs