The document outlines the anatomy and functions of the digestive system, detailing the roles of various organs from ingestion to excretion. It describes the digestive tract's structure, including its four layers and essential components like teeth, salivary glands, and the stomach, while emphasizing the significance of each part in processing food. Additionally, it highlights the regions of the small and large intestines, the importance of surface area for absorption, and the histological features that facilitate digestion.

1. Digestive System
Objectives:
Discuss the general functions and anatomy
of the digestive tract
Describe the individual organs of the
system, including a discussion of the gross
and microscopic anatomy.

2. Digestive
System
consists of:
Muscular, hollow tube (= “digestive tract”)
+
Various accessory organs

3. Function
Individual parts
function in:
 ingestion
The function of the system as a
whole is processing food in such a
way that high energy molecules can
be absorbed and residues
 mechanical digestion
eliminated.
 chemical and enzymatic digestion
 secretion
 absorption
 compaction
 excretion and elimination

4. Muscularis
externa
Histological Organization
Tube made up of
four layers.
Modifications
along its
length as
needed.
1
2
3
4

5. The 4 Layers of the Gut
1) Mucosa
Epithelial cells – protection, absorption
2) Submucosa – made up of loose connective tissue
contains submucosal plexus and blood vessels
3) Muscularis externa – smooth muscle, usually two layers -
outer layer: longitudinal
inner layer: circular
4) Serosa
outer layer, functions in protection

6. Ingestion
 Ingestion is the first
step in the process
of digestion.
 Ingestion means
that food is taken
into the mouth,
chewed, and
swallowed.

7. Oral Cavity
 Also called the mouth, the oral
cavity is the place where
ingestion happens.
 Hard and soft palates - form
roof of mouth
 Tongue - skeletal muscle
 Salivary glands - three pairs
 Teeth

8. Oral Cavity
Digestion starts here by two
means:
 Mechanical – teeth tear,
shred, and grind food.
 Chemical – enzymes in
saliva break down food
molecules such as
proteins and complex
sugars.

9. Structure of Teeth
Crown - exposed surface of tooth
Neck - boundary between root and crown
Enamel - outer surface
Dentin – bone-like, but noncellular
Pulp cavity - hollow with blood vessels and
nerves
Root canal - canal length of root

10. Types and Numbers of Teeth
Dental succession:
Deciduous (baby, primary) teeth - 20, replaced by
Permanent teeth - 32 teeth

11. Types and Numbers of Teeth
 All teeth are formed
before milk teeth or
primary teeth are lost.
 It is the action of adult
teeth moving into
place that causes
primary teeth to fall
out.

12. Three pairs of Salivary Glands
Salivary glands help with:
• digestion
• lubrication (swallowing)
• moistening (tasting)
They secrete enzyme-filled
saliva to help break down
food

13. Ingestion
 The tongue is a
muscle that pushes
your food toward
teeth to be
mechanically
processed and
shapes your food into
small rounded pieces
to be swallowed.

14. Swallowing
As you swallow, your
tongue pushes the food to
the back of the mouth.
Since both air and food go
through the pharynx, a flap
of tissue called the
epiglottis covers the larynx
to prevent food from
travelling into the lungs

15. Lesser curvature
Greater curvature
Cardia - end under the heart
Fundus - bulge above the esophageal opening
Body - largest region
Pylorus - J curve, inferior end, terminates in
Cardiac and Pyloric sphincters (importance?)
Rugae – highly extendable interior folds
Figs 25-10/11
Gross Anatomy of the Stomach

16. Histology of Stomach
Type of epithelium lining stomach?
Fig 25.13
Gastric pits – shallow pits, external half rapidly reproduces
for replacement
Gastric glands – deep in lamina propria, 3 types of cells
1. Parietal cells (produce HCl and intrinsic factor)
2. Chief cells (produce pepsinogen)
3. Enteroendocrine cells – G cells (several hormones
including gastrin which stimulates both parietal and chief cells)

17. Regions of Small Intestine
SI is longest part of dig. tube
 Duodenum (short, 12 inches)
– fixed shape & position
 Jejunum (2.5 m long)
– Most of digestion
 Ileum (longest at 3.5 m)
– Most of absorption, ends in
 Ileocecal valve – slit valve into large intestine (colon)

18. Structure of Small Intestinal Wall Fig 25.15
Plicae circulares – circular pleats around the interior of the
small intestine. Slows movement of food, increases surface
area of intestine.
Villi – minute finger-like projections, contain capillaries &
lacteals. Further increase surface area.
Microvilli – sub-microscopic size, projections on single cells.
Aid in absorption of nutrients.
Intestinal glands (crypts)
- intestinal juice production
- Cell regeneration

19. Histology of Small Intestinal Wall

20. Histology of S.I. Wall (cont)

21. Regions of Large Intestine
Cecum – pocket at proximal end with
Appendix
Colon
Ascending colon - on right, between
cecum and right colic flexure
Transverse colon - horizontal portion
Descending colon - left side,
between left colic flexure and
Sigmoid colon - S bend near
terminal end
Fig 25-17
Rectum – terminal end is anal canal - ending at the anus -
which has internal involuntary sphincter and external voluntary
sphincter

22. Structure of the Large Intestine

23. Histology of Large Intestine
1. Mucosa - abundant goblet
cells (produce mucous),
stratified squamous epithelium
near anal canal
2. No villi
3. Longitudinal muscle layer
incomplete, forms three bands
or taenia coli
4. Circular muscle - forms
pockets or haustra between
bands