Download Figure 14.4a

Digestion
• Breakdown of ingested food.
• Absorption of nutrients into the blood.
• Alimentary Canal
• A continuous, coiled, hollow, muscular tube
that extends from the mouth to the anus.
• About 9 meters (30 ft) long.
Figure 14.1
Layers of Alimentary Canal Organs
Figure 14.3
Layers of the Alimentary Canal
• 1) Mucosa – innermost layer. In the
esophagus friction-resisting Stratified
Squamous Epithelium is found. Beyond
the esophagus the epithelium is simple
columnar.
• Specialized in different regions to: secrete
mucous, secrete digestive enzymes,
absorb digested materials.
• 2) Submucosa – Found just beneath the
mucosa. Connective tissue containing blood
vessels, nerve endings, lymph nodes.
• 3) Muscular Layer – Smooth muscle.
Inner layer fibers encircle the canal, outer layer
fibers run longitudinally the length of the canal.
Contraction of inner layer narrows the tube.
Wave-like contraction of the outer fibers push
the narrowing and food down tube. (Peristalsis)
• 4) Serous Layer – (outermost) Visceral
Peritoneum. Cells secrete serous fluid that
lubricates the organs.
Mouth (Oral Cavity)
• Entrance to the alimentary canal. Functions to
reduce the size of food and mix it with saliva.
• Cheeks and lips check the size and
temperature of food.
• Tongue aids in mixing food with saliva. Taste
buds determine the suitability of food.
• Palate – Roof of the oral cavity. Anterior
portion is the hard palate. Posterior portion is
the soft palate.
• Uvula – projection at the end of the soft palate.
Causes a reflex that closes the nasal cavity
during swallowing.
Teeth (2 sets)
• Primary or Deciduous Teeth – 20 total.
Appear between 6 months and 2 ½ years of
age. Shed in the same order as they appear.
The roots are reabsorbed and pushed up by the
next set.
• Secondary or Permanent Teeth - 32 total.
Appear between the ages of 6 and 12 years.
All but the 3rd molars. The “wisdom teeth”
appear between 17 and 25 years of age.
Types of Teeth
• Incisors – Front teeth. Chisel shaped.
Used for cutting. 4 in each jaw. (8 total)
• Canines – Cuspids or eye teeth. Used for
tearing. 2 in each jaw. (4 total)
• Premolars – Bicuspids. Flat. Used for
grinding. 4 in each jaw. (8 total)
• Molars – Also flat and used for grinding.
6 in each jaw. (12 total)
Parts of a Tooth
• Crown – Portion above the gum. (gingiva)
• Root – Portion below the gum.
• Enamel – White covering of the crown.
Hardest substance in the body. If lost it is
not replaced.
• Dentin – beneath the enamel. Like bone.
• Pulp Cavity – Contains blood vessels,
nerves and connective tissues.
• Periodontal Ligament – Attaches the
tooth to the jawbone.
Salivary Glands – secrete saliva
• Saliva:
• 1) Moistens food and dissolves food
chemicals so they can be tasted.
• 2) Binds food together. Contains Mucin.
A protein that binds food together.
• 3) Begins carbohydrate digestion.
Contains Salivary Amylase. Splits
starches into disaccharides.
• 4) Saliva also contains lysozyme and
antibodies that inhibit bacterial growth.
3 Pairs of Salivary glands
• Parotid Glands – Largest. Located in front of
and below the ear. Secrete a clear watery fluid
rich in Amylase.
• Submandibular Glands – Located in the floor
of the mouth on the inside surface. Secretion is
mostly mucous.
• Sublingual Glands – Located in the floor of the
mouth under the tongue. Secretion is also
primarily mucous.
Deglutition (Swallowing)
Figure 14.14
Swallowing
• Food, now in the bolus form, is transported
to the stomach via the esophagus.
• Soft Palate prevents food from entering
the nasal cavity.
• Epiglottis covers the entrance to the
Trachea
• A Peristaltic wave moves food down the
esophagus.
Esophagus
• Runs from pharynx to stomach through the
diaphragm. About 25 cm long.
• Conducts food by peristalsis
• Muscles are thickened where they join the
stomach. When they are contracted it
closes the entrance to the stomach.
• When the Peristaltic wave from swallowing
reaches these muscles, they relax and
open the stomach.
Stomach Anatomy
Figure 14.4a
Stomach Anatomy
Capacity of about 1 Liter
Has inner folds called rugae
Regions of the stomach
-Cardiac region – near the esophageal opening
– Fundus – stores food above cardiac region
– Body – main portion
– Pylorus – funnel-shaped terminal end
• Food empties into the small intestine at the
pyloric sphincter
Stomach Functions
• Acts as a storage tank for food
• Site of food breakdown. Mixes food with
Gastric Juice.
• Chemical breakdown of protein begins
• Delivers chyme (processed food) to the
small intestine
• Limited amount of absorption. Alcohol,
glucose, water and some fat-soluble
vitamins.
Structure of the Stomach Mucosa
Figure 14.4b–c
Stomach Secretions
• Mucous lining is thick and made up of several
types of cells
• 1) Mucous Cells – produce a sticky alkaline
mucous
• 2) Parietal Cells – Produce hydrochloric acid
• 3) Chief Cells – Produce protein digesting
enzymes. (pepsinogens) Released in an
inactive form, they become active (Pepsin)
when mixed with HCl.
• 4) Endocrine Cells – Produce Gastrin. A
hormone that increases the protein digesting
enzymes produced by the stomach
• Food in the stomach mixed with gastric
juice eventually forms a semi-fluid paste
called chyme.
• Acidic environment of stomach is very
hostile to microorganisms
• Babies also produce Rennin. An enzyme
that digests milk protein (Caesin)
• Stomach continually churns and empties
into the small intestines about 30 ml at a
time. Takes 4 to 6 hours to empty.
Chemical Digestion in the
Small Intestine
Figure 14.6
Pancreas
• Located near the entrance to the
small intestines.
• Produce pancreatic juice. Contains a
wide spectrum of digestive enzymes
that breakdown all categories of food.
• Pancreatic juice enters the small
intestines (duodenum) through the
Pancreatic Ducts
Pancreatic Enzymes
• 1) Pancreatic Amylase – Splits starches
into disaccharides.
• 2) Pancreatic Lipase – Breaks down fat
molecules into fatty acids and glycerol.
• 3) Proteinases (Trypsin, Chymotrypsin,
Carboxypeptidases) – Break down long
chains of amino acids (Polypeptides) into
small chains of amino acids.
• 4) Nucleases – Breakdown Nucleic acids
into nucleotides..
Liver and Gall Bladder
• Liver is the largest gland in the body
• Only digestive function is the production of Bile
• Bile is a yellow-green solution containing bile
pigments (mainly bilirubin, a breakdown product
of hemoglobin) and bile salts
• Bile does not contain any digestive enzymes.
Bile salts emulsify fats by breaking large fat
globules into smaller ones
• Bile is stored and concentrated in the Gall
Bladder. Bile is released into the duodenum
through the bile duct
Small Intestines
• Longest section of the alimentary canal.
(8-18 ft.) Extends from the Pyloric
Sphincter to the Ileocecal valve.
• 3 subdivisions
•
•
•
•
1) Duodenum – 1st 10 inches.
2) Jejenum – next 40% of the length.
3) Ileum – Last 60% of the length.
Suspended from the abdominal wall by the
a double layered Mesentery which
contains nerves and blood vessels.
Functions of the Small Intestines
• 1) Receive secretions from the liver and
pancreas
• 2) Completes the digestion of chyme
• 3) Site of nutrient absorption into the blood
• 4) Transports residue to the large
intestines
• The inner wall of the small intestines has
innumerable tiny projections called villi that
greatly increases the surface area of the
intestinal wall
Villi of the Small Intestines
Each villus consists of a layer of simple columnar
epithelium surrounding a blood capillary and a lacteal
Each villus consists of a layer of simple
columnar epithelium surrounding a blood
capillary and a lacteal
Absorption in the Small Intestines
• Water is absorbed along the length of the small
intestines
• Enzymes located on the cell membrane of the
absorptive cells of the small intestines breakdown the
food to its final absorbable form
• Carbohydrates – in the form of disaccharides are
broken down into glucose and absorbed by active
transport
• Proteins – in the form of peptides are broken down
into amino acids and absorbed by active transport
• Nucleic Acids are broken down by nucleases into
nucleotides and absorbed by active transport.
• Lipids are absorbed by diffusion
Large Intestine
Figure 14.8
Large Intestines
• Larger in diameter but shorter than the
small intestines (1.5 meters long)
• Attaches to the small intestines at the
ileocecal valve and extends to the anus
• Regions:
– Cecum – Dilated pouch-like structure that
hangs below the ileocecal valve. Veriform
Appendix hangs from the cecum. The
appendix has no digestive function
• Colon – 4 distinct regions
1)
2)
3)
4)
Ascending Colon
Transverse Colon
Descending Colon
Sigmoid Colon
Rectum
Anal Canal
Functions of the Large Intestines
• Absorbs water and electrolytes
• Resident bacteria metabolize remaining
nutrients making vitamins (K and some B
vitamins) and releasing gases (flatus) that
contribute to the odor of feces (methane
and hydrogen sulfide)
• Secretes Mucous that lubricates and holds
feces together