2. • The digestive system is the collective name
• Describe the alimentary canal, accessory organs and variety
of process
• Prepare food for absorption
• The alimentary canal begins at mouth
• Passes through the thorax, abdomen and pelvis
• End at anus
• The complex of digestive processes gradually breaks down the
foods
• Chemical substances or enzymes effect these
3. Process of Digestion
• The activities in the digestive system can be grouped as
• Ingestion
• This is the process of taking food into the alimentary tract
• Propulsion
• This moves the contents along the alimentary tract
• Digestion consists of
• Mechanical breakdown of food by, e.g. mastication (chewing)
• Chemical digestion of food by enzymes produced by glands
• Absorption
• This is the process by which digested food enter into the blood and lymph
capillaries
• Elimination
• Undigested substances are excreted by the bowel as faeces
4. ORGANS OF THE DIGESTIVE SYSTEM
• Alimentary tract
• Long tube through which food passes
• Start at mouth and terminates at the anus
• Various Part Include
• Mouth Pharynx
• Oesophagus Stomach
• Small intestine Large intestine
• Rectum Anal canal
• The length of the GI tract is about
5–7 meters
5. Accessory organs
• Various secretions poured by glands in the lining membrane
• Gastric juice by stomach
• Glands situated outside their secretions carry by ducts to
• Include
• 3 Pairs of salivary glands
• Pancreas
• Liver and the biliary tract
• These organs and glands are linked physiologically as well
as anatomically
6. Basic Structure Of The Alimentary Canal
• Alimentary canal follow consistent pattern from the oesophagus
onwards
• Not apply so obviously to mouth and the pharynx
• Modification in structure found for special functions
• The walls of the alimentary tract are formed by four layers of tissue
• Adventitia or Outer covering
• Muscle layer
• Submucosal layer
• Mucosa(Inner lining)
7. • Adventitia (outer covering)
• In thorax it consists of loose fibrous
tissue
• In abdomen it covered to peritoneum
• Peritoneum is the largest serous
membrane
• A closed sac containing a small amount of
serous fluid
• Physical barrier to local spread of
infection
• Consist of two layers
• Parietal layer: Lines the abdominal wall
• Visceral layer: Covers the organs within
the abdominal and pelvic cavities
8. Muscle layer
• Consists of two layers of smooth muscle
• The outer layer arranged longitudinally
• Inner layer encircle the wall of the tube
• Contain blood vessels lymph vessels
• Plexus of sympathetic and parasympathetic
nerves
• Involve in contraction and relaxation
• A waves like pattern of contraction Peristalsis
• Contraction mixes food with the digestive
juices
• Onward movement of the content
• Form valves preventing backflow
10. • Submucosa
• Consists of loose connective tissue with some elastic fibers
• It contain plexuses of
• Blood vessels
• Nerve
• Arterioles
• Venules
• Capillaries
• Nerve plexus
• Sympathetic and parasympathetic
11. Mucosa
Consists of three layers of tissue:
• Mucous membrane
The innermost
Formed by columnar epithelium
Three main functions:
Protection, secretion and absorption
• Lamina propria
Consisting of loose connective tissue
Provide supports contain blood vessel
• Muscularis mucosa
Thin outer layer of smooth muscle
12. Mouth
• Referred to as oral or buccal cavity
• It is a space extends from
• Gums and teeth to the fauces (throat)
• Formed by the
• Cheeks
• Hard and soft palates
• Tongue
• Covered externally by skin
• Internally by a mucous membrane
• Composed of nonkeratinized stratified squamous epithelium
• Buccinator muscles & connective tissue
13. • Labia surrounding the opening of the mouth
• Orbicularis oris
• labial frenulum
• The oral vestibule is a space b/w cheeks and lips
• Internally by gums and teeth
• Palate separates the oral cavity from the nasal cavity
• Hard palate form the anterior portion
• Soft palate forms the posterior portion
14. Salivary Glands
• Secrete saliva into the oral cavity
• Keep the mucous membranes pharynx moist
• Cleanse the mouth and teeth
• When food enters the mouth its secretion increases
• Lubricates dissolves and begins the chemical breakdown of the food
• The mucous membrane of the mouth and tongue contains
• many small salivary glands that open directly, or indirectly via
• There are three pairs of major salivary glands
• Parotid
• Submandibular
• Sublingual glands
15. Composition of Saliva
• Chemically, saliva is 99.5% water and 0.5% solutes
• Immunoglobulin A, the lysozyme and salivary amylase
• Chloride ions in the saliva activate salivary amylase
• Bicarbonate and phosphate ions buffer acidic foods
• Immunoglobulin A (IgA) prevents attachment of microbes
• Enzyme lysozyme kills bacteria
16. • Salivation
• The secretion of saliva
• Controlled by the autonomic nervous system
• Amounts of saliva secreted daily 1000–1500 ml
• Sympathetic stimulation during stress resulting in dryness of the
mouth
• Impulses from the taste buds to salivary nuclei in the brain stem
• Return to parasympathetic stimulation of facial glossopharyngeal
Functions of saliva
Chemical digestion of polysaccharides
Lubrication of food
Cleansing and lubricating
Non-specific defence
Taste
17. Esophagus
• The esophagus is a collapsible muscular tube
• About 25 cm long
• Lies posterior to the trachea
• Begins at laryngopharynx reach
to stomach
• Esophageal hiatus
• Hiatus hernia
• Having nonkeratinized stratified
squamous epithelium
18. • Near the stomach the mucosa contains mucous glands
• Muscularis of the superior one third skeletal muscle
• Middle portion is mixed
• Lower one third is smooth muscle
Nasopharynx
Hard palate
Soft palate
Uvula
Oropharynx
Epiglottis
Laryngopharynx
Larynx
Esophagus
19. • Forms two sphincters
• Upper esophageal sphincter consists of skeletal muscle
• Lower esophageal sphincter of Smooth muscle
• The esophagus secretes mucus and transports food into
stomach
• It does not produce digestive enzymes
• It does not carry on absorption
Lower esophageal
sphincter
20. Stomach
• The stomach is a J-shaped enlargement of the GI tract
• Inferior to the diaphragm
• The stomach connects the esophagus to the duodenum
• Stomach is to serve as a mixing chamber and holding reservoir
• Stomach forces a small quantity of material into the first portion of the
small intestine
• In the stomach, digestion of starch continues, digestion of proteins and
triglycerides begins
• Semisolid bolus is converted to a liquid
• Certain substances are absorbed
• The stomach has four main regions
• Cardia
• Fundus
• Body
• Pylorus
CARDIA
FUNDUS
BODY
PYLORUS
21. • The stomach composed of the same basic layers as the rest of the GI tract
• Mucosa is a layer of simple columnar epithelial cells
• Gastric glands contain three types of exocrine gland cells
• Secrete their products into the stomach lumen:
• Mucous neck cells
• Chief cells
• Parietal cell
• Mucous neck cells secrete mucus
• Parietal cells produce intrinsic factor and hydrochloric acid
• Chief cells secrete pepsinogen and gastric lipase
22. • Gastric juice is secretions of mucous, parietal, and chief cells
• 2000–3000 mL of gastric juice is secreted per day
• Gastric glands include G cell, in the pyloric antrum secretes the hormone
gastrin into the bloodstream
• Muscularis has three layers of smooth muscle
• Outer longitudinal layer
• Middle circular layer
• Inner oblique layer
23. Mechanical and Chemical Digestion in the
Stomach
• Food is converted into chyme
• Foods remain in the fundus for a hour without mixed with gastric juice
• Strongly acidic fluid kills many microbes in food
• Denature protein and its enzymatic digestion of proteins also begins in the
stomach
• Gastric lipase digest lipid
• Small amount of nutrients are absorbed here
24. Small Intestine
• Continuous with the stomach at the pyloric sphincter
• Leads into the large intestine at the ileocaecal valve
• About 5 meters long and lies in the abdominal cavity
• Comprises of three main sections
• Duodenum
• About 25 cm long and curves around the head of the pancreas
Receive secretions from the gall bladder and pancreas
• Jejunum
• The middle section
• About 2 meters long
• Ileum
• Terminal section about 3 meters long
• Ends at the ileocaecal valve
25. • The walls of the small intestine are composed of the four layers
• Peritoneum
• Mesentery
• Double layer of peritoneum
• Attaches the jejunum and ileum to the posterior abdominal wall
• Mucosa
• The surface area of mucosa increased by villi and microvilli
• They promote mixing of chyme as it passes along
26. Chemical digestion in the small intestine
• When chyme passes to small intestine
• Mixed with pancreatic juice, bile and intestinal juice,
• In the small intestine the digestion of all the nutrients is completed
• Carbohydrates are broken down to monosaccharides
• Proteins are broken down to amino acids
• Fats are broken down to fatty acids and glycerol
• Pancreatic juice
• Pancreatic juice enters the duodenum and consists of
• Water
• Mineral salts
• Enzymes:
• Amylase
• Lipase
• Inactive enzyme precursors:
• Trypsinogen
• Chymotrypsinogen
• Procarboxypeptidase
• Pancreatic juice is alkaline (pH 8)
27. LARGE INTESTINE (COLON)
• Terminal portion of the GI tract
• Overall functions of the large intestine
• Completion of absorption
• Production of certain vitamins
• Formation of feces
• Expulsion of feces from the body
28. • It is about 1.5 m (5 ft) long and 6.5 cm (2.5 in) in diameter
• Extends from the ileum to the anus
• Four major regions of
• Cecum
• Colon
• Rectum
• Anal canal
• Opening from the ileum
guarded by ileocaecal sphincter
• Allows materials from the small
intestine to large intestine
29. • Cecum
• Inferior to the ileocaecal valve
• Small pouch about 6 cm (2.4 in.) long
• Appendix attach to it
• Colon
• Long tube in which the cecum merge
• Divided into
• Ascending
• Transverse
• Descendin
30. • Ascending colon
• Ascends on the right side of the abdomen
• Reaches the inferior surface of the liver
• Transverse colon
• Continuation of the colon across the
abdomen to the left side as
• Curves beneath the inferior end of the
spleen
• Descending colon
• Inferiorly to the level of the iliac crest
• The sigmoid colon
• Near the left iliac crest,
• Projects medially to the midline and
terminates as the rectum
Ileocaecal
sphincter
Cecum
Appendix
Ascending
colon
Descending
colon
Transerve colon
Sigmoid
colon
31. • Rectum
• The last portion
• 20 cm (8 in.) of the GI tract
• Anterior to the sacrum and coccyx
• Anal canal
• The terminal 2–3 cm (1 in.) of the rectum
• The mucous membrane arranged in
longitudinal folds called anal columns
• Anus
• Opening of the anal canal to the exterior
• Guarded by an internal anal sphincter of
smooth muscle and an external anal
sphincter of skeletal muscle
32. Functions of the large intestine, rectum and
anal canal
• Absorption
• Absorption of water continues
• Absorption of mineral salts, vitamins and some drugs
• Microbial activity
• Heavily colonized by certain types of bacteria
• Synthesize vitamin K and folic acid
• Mass movement
• Does not exhibit peristaltic movement
• A strong wave along the transerve colon forcing content to
descending and sigmoid colon known as mass movement
• Often precipitated by the entry of food into the stomach
• This combination of stimulus and response is called the gastrocolic
reflex
33. Defaecation
• When contents of the sigmoid colon enter into the rectum
• Stimulation of nerve endings in its walls by stretch
• Defaecation occurs by reflex
• Pudendal nerve to the external anal sphincter
• is under conscious control
• Defaecation involves
• Involuntary contraction of the muscle of the rectum
• Relaxation of the internal anal sphincter
• Contraction of the abdominal muscles
• Lowering of the diaphragm increase
intra-abdominal pressure
