Introduction of gastrointestinal tract

1. Introduction of
Digestive System
RK Goit, Lecturer
Department of Physiology

2. •Digestive system
–performs the mechanical & chemical processes of digestion,
absorption of nutrients, & elimination of wastes
–consists of the mouth, esophagus, stomach, intestine, &
accessory organs
•medical specialty that deals with the structure, function,
diagnosis, & treatment of diseases of the stomach &
intestines is called gastroenterology
•medical specialty that deals with the diagnosis &
treatment of disorders of the rectum & anus is called
proctology

3. •basic chemical unit of our food & our tissue are the same
•our food looks so different from the tissue because the
units are arranged very differently
•in order to achieve rearrangement of the building blocks
of our food, it is first
necessary to break the
food molecules into their
basic constituents

4. •2 groups of organs compose the digestive system:
1.gastrointestinal (GI) tract, or alimentary canal
–a continuous tube that extends from the mouth to the anus
through the thoracic & abdominopelviccavities
–organs include the mouth, most of the pharynx, esophagus,
stomach, small intestine, & large intestine
–length of the GI tract is about 5–7 meters in a living person
(longer in a cadaver-about 7–9 meters)
2.accessory digestive organs
–include the teeth, tongue, salivary glands, liver, gallbladder, &
pancreas
–teeth aid in the physical breakdown of food
–tongue assists in chewing & swallowing
–salivary glands, liver, gallbladder, & pancreas produce or store
secretions that flow into the GI tract through ducts

7. Functions of the digestive system
1.Ingestion
–taking food into mouth
2.Secretion
–release of water, acid, buffers, & enzymes into lumen of GIT
3.Mixing & propulsion
–churning & propulsion of food through GI tract
4.Digestion
–mechanical & chemical breakdown of food
5.Absorption
–passage of digested products from GIT into blood & lymph
6.Defecation
–elimination of feces from GI tract

9. •Mucosa
1.epithelium
–in the mouth, pharynx, esophagus, & anal canal is mainly nonkeratinized
stratified squamous epithelium
–in stomach & intestine is simple columnar epithelium
–several types of endocrine cells (enteroendocrinecells) secrete hormones
2.lamina propria
–is areolar connective tissue containing many blood & lymphatic vessels
–also contains mucosa associated lymphatic tissue (MALT)
3.muscularismucosae
–throws the mucous membrane of the stomach & small intestine into many
small folds, which increase the surface area for digestion & absorption

10. •Submucosa
–consists of areolar connective tissue that binds the mucosa to
the muscularis
–contains many blood & lymphatic vessels that receive absorbed
food molecules
–located in the submucosais an extensive network of neurons
known as the submucosalplexus
–also contain glands & lymphatic tissue

11. •Muscularis
–mouth, pharynx, & superior & middle parts of the esophagus
contains skeletal muscle that produces voluntary swallowing
–skeletal muscle also forms the external anal sphincter, which
permits voluntary control of defecation
–throughout the rest of the tract, the muscularisconsists of
smooth muscle that is generally found in two sheets: an inner
sheet of circular fibers & an outer sheet of longitudinal fibers
–between the layers of the muscularisis a second plexus of
neurons—the myentericplexus

12. •Serosa
–composed of areolar connective tissue & simple squamous
epithelium
–esophagus lacks a serosa; instead only a single layer of areolar
connective tissue called the adventitia forms the superficial
layer of this organ

14. Summary of organs of the digestive system & their functions
ORGAN FUNCTION(S)
Tongue
Maneuvers food for mastication, shapes food into a bolus, maneuvers food
for deglutition, detects sensations for taste, & initiates
digestion of triglycerides.
Salivary glands
Saliva produced by these glands softens, moistens, & dissolves foods;
cleanses mouth & teeth; initiates the digestion of starch.
Teeth
Cut, tear, & pulverize food to reduce solids to smaller particles for
swallowing.
Pancreas
Pancreatic juice buffers acidic gastric juice in chyme, stops the action of
pepsin from the stomach, creates the proper pH for digestion in
the small intestine, & participates in the digestion of carbohydrates,
proteins, triglycerides, & nucleic acids.
Liver
Produces bile, which is required for the emulsification & absorption of
lipids in the small intestine.
GallbladderStores & concentrates bile & releases it into the small intestine.
Mouth
(functions of the tongue, salivary glands, & teeth). Additionally, the lips &
cheeks keep food between the teeth during mastication, & buccalglands
lining the mouth produce saliva.

15. ORGAN FUNCTION(S)
Pharynx Receives a bolus from the oral cavity & passes it into the esophagus.
Esophagus
Receives a bolus from the pharynx & moves it into the stomach; this
requires relaxation of the upper esophageal sphincter & secretion
of mucus.
Stomach
Mixing waves combine saliva, food, & gastric juice, which activates pepsin,
initiates protein digestion, kills microbes in food, helps absorb
vitamin B
12, contracts the lower esophageal sphincter, increases stomach
motility, relaxes the pyloric sphincter, & moves chymeinto the
small intestine.
Small intestine
Segmentation mixes chymewith digestive juices; peristalsis propels chyme
toward the ileocecalsphincter; digestive secretions from the
small intestine, pancreas, & liver complete the digestion of carbohydrates,
proteins, lipids, & nucleic acids; circular folds, villi, & microvilli help absorb
about 90 percent of digested nutrients.
Large intestine
Haustralchurning, peristalsis, and mass peristalsis drive the colonic
contents into the rectum; bacteria produce some B vitamins and
vitamin K; absorption of some water, ions, and vitamins occurs; defecation.

16. Regulation of GI functions
regulated mainly by neural & hormonal influences:
Neural regulation:
•Intrinsic neural regulation
–Enteric nervous system
•Extrinsic neural regulation
–Autonomic nervous system
•Reflex control(gastrointestinal reflexes):
1.Reflexes that are integrated entirely within the gut wall
enteric nervous system
–gastrointestinal secretion,peristalsis

17. 2.Reflexes from the gut to the prevertebralsympathetic
ganglia & then back to the gastrointestinal tract
–gastrocolicreflex-signals from the stomach to cause
evacuation of the colon
–enterogastricreflexes-signals from the colon & small intestine
to inhibit stomach motility & stomach secretion
–colonoilealreflex-reflexes from the colon to inhibit emptying
of ilealcontents into the colon

18. 3.Reflexes from the gut to the spinal cord or brain stem &
then back to the gastrointestinal tract
–reflexes from the stomach & duodenum to the brain stem &
back to the stomach by way of the vagusnerves to control
gastric motor & secretory activity
–pain reflexes that cause general inhibition of the entire
gastrointestinal tract
–defecation reflexes that travel from the colon & rectum to the
spinal cord & back again to produce the powerful colonic,
rectal, & abdominal contractions required for defecation

19. Hormonal regulation:
•Intrinsic hormones
–many hormones are secreted from endocrine cells of GI tract.
•Extrinsic hormones
–GI functions are also influenced by hormones secreted from
other endocrine glands like thyroxine& cortisol.

20. Thank You