Introduction to GIT

1. INTRODUCTION TO DIGESTIVE SYSTEM
DR RASHMI

2. INTRODUCTION:
• Digestion is defined as the process by which food is broken down into
simple chemical substances that can be absorbed and used as nutrient by
the body.
• Most of the substances in the diet cannot be utilized as such. These
substances must be broken into smaller particles so that they can be
broken into smaller particles and can be absorbed in to blood and
distributed to various parts of the body for utilization.
• The digestive system is responsible for these functions.

3. FUNCTIONAL ANATOMY OF THE DIGESTIVE
SYSTEM:
• Digestive system is made up of gastrointestinal tract(GI TRACT)
OR alimentary canal and accessory organs, which help in the
process of digestion and absorption.
• GI tract is a tubular structure extending from the mouth up to the
anus with a length of about 30 feet.
• It opens to the external environment on both sides.
• GI tract is formed by two types of organs:
• 1- PRIMARY DIGESTIVE ORGANS.
• 2- ACCESSORY DIGESTIVE ORGANS.

4. 1- PRIMARY DIGESTIVE ORGANS:
• These are the organs where actual digestion takes place.
These organs are:
• 1- Mouth
• 2-Pharynx
• 3-Esophagus
• 4-Stomach
• 5-Small intestine
• 6-Large intestine

5. 2- ACCESSORY DIGESTIVE ORGANS:
• These are the organs which help the primary digestive organs in the process
of digestion.
• These organs are:
• 1- Teeth
• 2-Tongue
• 3- Salivary glands
• 4- Exocrine part of pancreas
• 5- Liver
• 6- Gallbladder

7. ORAL CAVITY

8. HISTOLOGY:
• In general wall of GI tract is formed by four layers which are from
inside out:
• 1- MUCUS LAYER
• 2-SUBMUCUS LAYER
• 3-MUSCULAR LAYER
• 4- SEROUS OR FIBROUS LAYER

10. 1- MUCUS LAYER:
• It is the innermost layer of the wall of GI tract.
• It is also called gastrointestinal mucosa or mucous membrane.
• It faces the cavity of GI tract.
• The mucosa has three layers of structures:
• 1- Epithelial lining which is in contact with content of GI tract.
• 2- Lamina propria formed by connective tissue.
• 3- Muscularis mucosa formed by the smooth muscle fibers.

11. 2- SUBMUCUS LAYER:
• This is present in all part of GI tract except mouth and pharynx.
• This layer contains loose collagen fiber, elastic fiber, reticular fibers
and few cells of connective tissue.
• Blood vessels, lymphatic vessels and nerve plexus are present in this
layer.

12. 3- MUSCULAR LAYER
• This layer in lips, cheeks and wall of pharynx have skeletal muscle
fiber.
• The esophagus have both skeletal and smooth muscle fibers.
• Wall of stomach and intestine is formed by smooth muscle fiber.
• The smooth muscle fiber in stomach are arranged in three layers:
• 1- INNER OBLIQUE LAYER.
• 2-MIDDLE CIRCULAR LAYER
• 3- OUTER LONGITUDINAL LAYER.

13. • The smooth muscle fiber in the intestine are
arranged in two layers:
• 1- INNER CIRCULAR LAYER.
• 2- OUTER LONGITUDINAL LAYER.

14. 4- SEROUS OR FIBROUS LAYER:
• Outermost layer of the wall of GI tract is either serous or fibrous in
nature.
• The serous layer is formed by connective tissue and mesoepithelial
cells.
• It is also called serosa or serous membrane.
• It covers stomach, small intestine and large intestine.
• The fibrous layer is otherwise called fibrosa.
• It is formed by connective tissue.
• It covers pharynx and esophagus.

15. NERVE SUPPLY TO G.I.T
• GIT receive two type of nerve supply
1. Intrinsic
1. extrinsic

16. INTRINSIC NERVE SUPPLY
• It is present within the wall of GI tract from esophagus to anus
• Nerve fibers are interconnected & form 2 major networks
1. Auerbach’s plexus
2. Meissner’s plexus
• These nerve plexus contain cell bodies,processes of nerve cells &
receptors
• Receptors in the G.I.T are stretch receptors & chemoreceptors.
• Intrinsic nerve supply is controlled by the extrinsic nerve supply.

17. AUERBACH’S PLEXUS
• It is also known as myenteric nerve plexus.
• Present b/ inner circular muscle layer & the outer
longitudinal muscle layer
FUNCTION OF MYENTERIC PLEXUS
• It regulate movements of G.I.T
• Some fibers accelerate movement by secreting excitatory
neurotansmitters such as Ach, serotonin, substance P
• Some fiber inhibit by secreting inhibitory neurotransmitters :-
vasoactive intestinal polypeptide(VIP),neurotensin

18. MEISSNER’S NERVE PLEXUS
• Also known as submucus nerve plexus.
• It is present b/w muscular layer & submucosal layer of G.I.T
• The function of these plexus is to regulate secretory function of G.I.T
• These nerve fibers cause constriction of blood vessels of GI tract.

19. EXTRINSIC NERVE SUPPLY
• They control the enteric nervous system
• They are controlled by ANS.
• Both sympathethic & parasympathetic divisions of ANS innervate the
GIT

20. Sympathetic nerve fibers
• Preganglionic sympathetic nerve fibers to GI tract arise from lateral
horns of spinal cord b/w 5th thoracic & second lumbar segments (T5-
L2).
• Funtions of sympathetic nerve fibers
Sympathetic nerve fibers inhibit the movement & decrease the
secretions of GI tract by secreting the neurotransmitter noradrenaline.
It also cause constriction of sphincters.

21. Parasympathetic nerve fibers
• It pass through the cranial & sacral nerves.
• The pre & postganglionic parasympathetic nerve fibers to mouth &
salivary glands pass through facial and glossopharyngeal nerves.
• Nerves from esophagus, stomach, small intestine & upper part of the
large intestine pass through vagus nerve.
• The preganglionic nerve fibers to lower part of L.intestine arise from
2nd,3rd,4th sacral segments (S1,S2 & S3) of spinal cord & pass through
pelvic nerve.
• All preganglionic nerve fiber synapse with postganglionic nerve fibers
in the myenteric & submucus plexus.

22. FUNCTIONS
• Parasympathetic nerve fibers accelerate movements & increase the
secretions of GIT
• The neurotransmitter secreted by the parasympathetic nerve fibers is
Ach.