Download 8.2 The Digestive System - Father Michael McGivney

10.2 The Human Digestive
Tract
Hierarchical Organization of the
Body
Atom  molecules  organelles  cells 
tissues  organs  organ system 
organism
* Four main types of tissues: connective,
epithelial, nervous & muscle.
Digestive System Overview
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Known as gastrointestinal (GI) tract or alimentary
canal.
Open at both ends to the outside world.
Consists of long convoluted tube with accessory
organs.
Components: mouth, pharynx, esophagus,
stomach, small intestine, large intestine & anus.
Accessory organs include: salivary glands,
pancreas, liver & gallbladder.
Animation: Organs of
Digestion
Steps in Digestion
1.
2.
3.
4.
Ingestion
Digestion
Absorption
Elimination
Types of Digestion
Mechanical: physical breakdown of food
 Food mass is shredded, torn & churned.
 Occurs in mouth & stomach.
Chemical
 Chemicals and enzymes break down food.
 Occurs in mouth (saliva amylase),
stomach & small intestine.
Structure of the Digestive Tract

Lumen (hollow interior) surrounded by
several layers of tissue:
 Mucosa
 Submucosa
 Circular
smooth muscle
 Longitudinal smooth muscle
 Serosa
Structure of the Digestive Tract
Mucosa

Highly folded; contains
mucus/enzyme/hormone
secreting cells &
absorptive cells.
Submucosa

Connective tissue;
contains blood vessels &
nerves.
Structure of the Digestive Tract
Circular Smooth Muscle

Responsible for peristaltic contractions; constricts
lumen.
Longitudinal Smooth Muscle

Responsible for peristaltic contractions; shortens
tract.
Serosa

Connective tissue; separates digestive tract from
other abdominal organs.
Organs of the Digestive System
Oral Cavity
 Esophagus
 Stomach
 Small Intestine
 Large Intestine

Oral Cavity
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Lips, tongue, teeth & jaw muscles
break food down into smaller pieces.
Food mixes with saliva and amylase, which
begins the chemical digestion of carbohydrates.
A bolus (moistened ball-like mass) forms and is
swallowed.
The bolus passes through the pharynx, past the
epiglottis & through the esophagus.
Structures of the Mouth
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Gums: part of the jaw that holds the teeth
Frenulum: the layer of pink tissue that attaches the lip
to the gum
Hard Palate: front part of the roof of your mouth, made
of bone and skin, also used in the breakdown of food
Soft palate: back part of the roof of your mouth, made
of muscle, expands for swallowing
Uvula: a pinkish-red pointed structure hanging from
the soft palate, direct food down the esophagus
Lingual tonsil: a rough and bumpy covering near the
back of the tongue
Palatine Tonsil: an area found on each side of the
throat, used to help prevent bacteria from getting into
the body.
Salivary Glands
Parotid glands: lie just below the skin in front of
each ear, secrete a watery fluid that contains
salivary amylase.
 Sublingual glands: below the tongue in the
floor of the mouth
 Submandibular glands:
located below the roof of
the tongue in the throat.

N.B. Saliva contains an enzyme
called amylase, which begins the
chemical digestion of starch into sugar

Esophagus
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Muscular tube that connects pharynx
& stomach.
The cardiac or lower esophageal
sphincter connects the esophagus
to the stomach.
Constriction of this ring of smooth
muscle prevents reflux (ensures
one-way flow of food).


Pressure exerted by food on the
sphincter causes it to open, and food
enters the stomach
Peristalsis is a series of coordinated
muscular contractions that propels
food along the digestive tract into the
stomach.
Stomach
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J-shaped stretchable organ.
Acts as a reservoir for food (1.5 L).
Two sphincters control the movement of food
coming into and out of the stomach.
 Cardiac
sphincter: Between the stomach & the
esophagus.
 Pyloric sphincter: Between the stomach & the small
intestine (the duodenum).
Specialized cells of the stomach
1.
2.
3.
Mucous secreting cells: lubricate
stomach’s walls and protects stomach
lining
Parietal cells: secrete hydrochloric acid
Chief cells: secrete pepsinogen
HCl + pepsinogen  pepsin (enzyme)
HCl breaks
up
connective
tissue that
holds food
together
The hormone
gastrin regulates
the amount of HCl
produced
Pepsin breaks protein
molecules up into short
polypeptides
Animation:
carbohydrate digestion
- myDr.com.au
Stomach
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Smooth muscle forms folds (rugae)
that allow the stomach to expand.
Mechanical digestion: Walls churn
& squeeze bolus.
Chemical digestion: Bolus mixes
with gastric juices.

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Hydrochloric acid secreted by
gastric glands.
Pepsinogen released & converts to
pepsin (enzyme that breaks down
proteins).
Bolus becomes a liquefied paste
(chyme).
http://www.mcgrawhill.ca/
school/applets/abbio/ch06
/gastric_three_phases_of.
swf
Stomach
Mucus cells secrete mucus to line &
protect stomach from HCl (aq).
 Ulcers: HCl (aq) burns a hole through the
mucus, irritating the stomach cells below

 Usually
the result of a
particular type of
bacteria (antibiotics
required).
Small Intestine
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Major site of digestion &
absorption (80% occurs).
About 6 m long & has a
SMALLER diameter than
the large intestine.
Lined with tiny finger-like
projections called villi,
which project into the
lumen.
Microvilli line the villi.
Villi & microvilli increase
the surface area for
absorption.
Small Intestine

Consists of three sections:
Duodenum
2. Jejunum
3. Ileum.
1.
Absorption
Chemical digestion
Chemical
digestion &
absorption
Small Intestine

Functions:
http://www.mcgrawhill.
ca/school/applets/abbi
o/quiz/ch06/enzyme_a
ction_and_the_h.swf
 Break
down of carbs. By amylases, proteins by
peptidases, and fats by lipases
 Absorption of monosaccharides, amino acids, fatty
acids and glycerol (by microvilli)
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Mechanical digestion: Alternating contraction &
relaxation of the smooth muscle mixes chyme
with intestinal juices & secretions from the
pancreas & liver.
Nutrients absorbed into capillaries in the villi.
Nutrients transported to the liver & then to all
Tutorial 50.1 The Digestion and
body cells.
Absorption of Fats
Products from fat digestion are absorbed into
lacteals, which connect to the lymphatic system.
Large Intestine
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Reabsorbs water, salt & some vitamins (no
digestion).
Holds & compacts unabsorbed material (cellulose/
bacterial fragments).
About 1.5 m long & has a LARGER diameter than
the small intestine.
Consists of four sections:
1.
2.
3.
4.
Caecum
Colon
Rectum
Anus.
Large Intestine
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Chyme passes from the small intestine into the
caecum, through the ileocaecal valve.
Waste products accumulate & are compacted
into feces (3/4 water, 1/4 solid matter)
Feces pass through the rectum & exit the body
through the anus.
Appendix attached to caecum, exact function is
unknown.
Large Intestine

Defecation controlled
by two sphincters:
 Rectal
sphincter:
Between the large
intestine & the rectum.
 Anal sphincter:
Between the rectum &
the anus.
The
Digestive
System
Pancreas
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Finger-shaped organ
approximately 15 cm in
length.
Located below the
stomach.
Contains a duct that
empties into the small
intestine
Specialized for secreting
hormones & enzymes
necessary for proper
digestion.
Pancreas
The acidity of chyme triggers cells in the
duodenum to release a hormone called
secretin.
 Secretin enters the bloodstream, signaling
the release of bicarbonate ions (a base)
from the pancreas.
 Bicarbonate ions neutralize the HCl in the
duodenum, raising the pH so that pepsin
becomes inactive and allows digestion of
nutrients.
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Pancreas
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Other pancreatic enzymes:
 Lipases:
digests lipids.
 Carbohydrases/pancreatic amylase: digests
sugars & starches.
 Proteases: digests proteins.
 Trypsinogen: released & activated (trypsin) in
the small intestine to digest proteins.
Liver
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Functions:
 Regulates
metabolism.
 Produces and secretes bile into the small
intestine
 Removes any toxins (e.g., hydrogen peroxide,
alcohol & drugs) via catalase.
 Excessive alcohol &
drug use will lead to liver
damage &/or death.
Liver
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After skin, the liver is the second largest organ in
the body (1.5 kg).
The liver synthesizes & secretes 1 L of bile per
day.
Bile acts as detergent to breakdown or emulsify
fat.
 Contains
bile salts, bile
acids, cholesterol, water,
phospholipids, fatty acids
water.
&
Liver & Gallbladder
The liver has a left and right lobe.
 The gallbladder is under the right lobe &
stores and concentrates bile.
 When fat enters the duodenum, CCK (a
hormone) is released, signaling the
gallbladder to release bile through the bile
duct & into the duodenum.

http://www.
ahealthyme.
com/Imageb
ank/digestiv
e.swf
Liver & Gallbladder
Tutorial 50.2 Insulin and
Glucose Regulation
Digestive system
animation illustrating
digestion Constipation Advice
Digestive System
/ Drag & Drop
Quiz (Organs of
the Digestive
System)