The Physiology of the alimentary canal

1. Introduction to Gastrointestinal
Physiology
Ms. Chanda Chisunka
Physiology Lecturer

2. Functions of the GIT
• Obtain resources from the external environment
• Water
• Minerals
• Nutrients (Lipids, Carbohydrates, Proteins, vitamins)
• Break down large particles into smaller ones
• Transfer materials from external environment  blood  cells

3. Physiological Anatomy
Digestive tract
• oral cavity
• pharynx
• esophagus
• stomach
• small intestine
• large intestine
• anus

4. Accessory Organs of the GIT
Accessory organs include;
• salivary glands
• pancreas
• liver
• gall bladder

5. Cross section anatomy of the GIT
There are four main layers from the lumen outward; the
mucosa, the submucosa, the muscularis and the serosa.

6. Cross section of the GUT

7. Cross section of the GUT

8. Mucosa
• The innermost layer of the digestive tract and has specialised
epithelial cells supported by an underlying connective tissue layer
called the lamina propria.
• The lamina propria contains blood vessels, nerves, lymphoid tissue
and glands to support the mucosa.
• Maybe simple or stratified

9. Mucosa cont...
• Muscularis mucosa. This comprises layers of smooth muscle
which can contract to change the shape of the lumen.
• Mucosa has folds. And projects into lumen in small fingerlike
extensions called villi. Individual cells have microvilli.
• Tubular invaginations also present, these invaginations are
gastric glands in stomach and crypts in intestine.

10. Submucosa
• This layer surrounds the muscularis mucosa. It consists of fat,
fibrous connective tissue, larger blood vessels and nerves.
• At its outer margin, there is a specialised nerve plexus called
the submucosal plexus or meissner plexus.
• This supplies the mucosa and submucosa.

11. Muscularis Layer
• This is a layer of smooth muscle.
• This layer has an inner circular layer and outer longitudinal layers of
muscle fibers seperated by Myenteric plexus or Auerbachs plexus.
• Neural innervations control the contraction of these muscles and
hence the mechanical breakdown and peristalsis of the food within
the lumen.

12. Function of th muscles
• Contraction of the circular layer decreases the diameter of
the lumen while contraction of the longitudinal layer
shortens the length of the gut.

13. Serosa / Mesentery
• Outer layer of the GIT
• Formed by fat and another layer of epithelial cells called
mesothelium

14. Digestive System Processes
• Motility
• movement of food through the digestive system
• Secretion
• release of substances to enhance breakdown of food
• Digestion
• physical and chemical breakdown of food
• Absorption
• transfer of materials to internal environment

15. Salivary secretion
• The principal glands of salivation are the parotid, submandibular, and sublingual glands;
in addition, there are many very small buccal glands.
• Daily secretion of saliva normally ranges between 800 and 1500 mls.
• The parotid glands secrete almost entirely the serous type of secretion.
• The submandibular and sublingual glands secrete both serous secretion and mucus.
.

17. Other Salivary Glands
• MINOR SALIVARY GLANDS (diffusely scattered in oral cavity):
• BUCCAL (cheek)
• PALATINE (palate)
• LABIAL (lip)
• LINGUAL (tongue)
• Secrete 10% of total volume of saliva
• Account for about 70% of mucus secreted

18. Serous secretion
• Their watery secretion contains enzymes (amylase, lysozyme),
Immunoglobulins e.g IgA
• The parotid glands are composed entirely of serous glands

19. Parotid gland
• Connective tissue contains many lymphocytes and plasma cells.
• Plasma cells secrete IgA
• Complex released in saliva is resistant to enzymatic digestion and
constitutes an immunologic defense within the oral cavity

20. Mucinous secretion
• Larger than serous acini
• Abundant cytoplasm filled with clear mucus
• Only the palatine and lateral lingual glands are entirely mucus-secreting
• Parotid – purely serous
• Submandibular – mixed
• Sublingual - mostly mucous

21. Duct system
• Transport saliva and modify its electrolyte composition
• INTERCALATED DUCT: 1st segment, lined by squamous or low cuboidal epithelium.
• In serous and mixed glands
• Secrete bicarbonate ion into the acinar product
• Absorb chloride ion from the acinar product
• STRIATED DUCT: Involved in transport of water and electrolytes; reabsorbs sodium from
secretion and adds K into secretion

22. Ducts
PAROTID
• STENSEN’S DUCT
SUBMANDIBULAR (floor of mouth)
• WHARTON’S DUCT
SUBLINGUAL (very short ducts)
• empties into floor of mouth

23. Functions of saliva
• Saliva contains two major types of protein secretion:
• (1) a serous secretion that contains ptyalin (an alpha-amylase), which
is an enzyme for digesting starches,
• (2) mucus secretion that contains mucin for lubricating
and for surface protective purposes.
Saliva has a pH between 6.0 and 7.0, a favourable range for the
digestive action of ptyalin

24. Functions of saliva cont...
• Wets and lubricates oral cavity and ingested food
• Initiates digestion of carbohydrates (amylase) and lipids (lingual lipase)
• Secretes germicidal protective substances:
• Immunoglobulin IgA
• Lysozyme
• Buffering function
• Forms protective secretion on teeth

25. Organic composition
• water
• electrolytes
• lubricants
• antimicrobial compounds
• enzymes
• These components of saliva facilitate speech, mastication and swallowing, and
initiate food digestion. In addition, it protects the oral mucosa and the teeth.

26. Secretion of ions in saliva
• Saliva contains especially large quantities of potassium and
bicarbonate ions because these ions are secreted into the saliva
• Conversely, the concentrations of both sodium and chloride ions are
several times less in saliva than in plasma.
• Saliva is thus hypotonic to blood plasma.

27. Secretion and absorption of ions in saliva

28. • Happy Studying!