2. DIGESTION • The process of conversion of complex food substances to simple absorbable forms is called digestion. • Digestion is carried out by our digestive system by mechanical and biochemical methods. 3. PHASES OF DIGESTION • The activities of the digestive system can be grouped under five main headings. • Ingestion :-This is the taking of food into the alimentary tract, i.e. eating and drinking. • Propulsion :-This mixes and moves the contents along the alimentary tract. • Digestion :-This consists of: • Mechanical breakdown of food by mastication(chewing). • Chemical digestion of food into small molecules by enzymes present in secretions produced by glands and accessory organs of the digestive system

1. THE DIGESTIVE SYSTEM
PRESENTER – SHOAIB AKHTAR
MODERATOR – MR.GAURAV PANDEY

2. DIGESTION
• The process of conversion of complex food substances to
simple absorbable forms is called digestion.
• Digestion is carried out by our digestive system by mechanical
and biochemical methods.

3. PHASES OF DIGESTION
• The activities of the digestive system can be grouped under
five main headings.
• Ingestion :-This is the taking of food into the alimentary tract,
i.e. eating and drinking.
• Propulsion :-This mixes and moves the contents along the
alimentary tract.
• Digestion :-This consists of:
• Mechanical breakdown of food by mastication(chewing).
• Chemical digestion of food into small molecules by enzymes
present in secretions produced by glands and accessory organs
of the digestive system

4. CONT…
• Absorption :-This is the process by which digested food
substances pass through the walls of some organs of the
alimentary canal into the blood and lymph capillaries for
circulation and use by body cells.
• Elimination :-Food substances that have been eaten but
cannot be digested and absorbed are excreted from the
alimentary canal as faeces by the process of defaecation.

5. DIGESTIVE SYSTEM
• The human digestive system consists of the alimentary canal
and the associated glands.

6. ALIMENTARY CANAL
• Alimentary Canal
• The alimentary canal begins with an anterior opening
the mouth, and it opens out posteriorly through the
anus.
• The alimentary canal includes the mouth, pharynx,
esophagus, stomach, small intestine, large intestine,
and anus.
• The oral cavity has a number of teeth and a muscular
tongue

7. ACCESSORY DIGESTIVE ORGANS
• Accessory Digestive Organs
• Contains the following organs:
• Teeth, Tongue, Gallbladder, Salivary Glands, Liver, and
Pancreas

8. TEETH
• Teeth are concerned with mastication.
• Depending on the age at which they arise, teeth can be
classified into two types:
1. PERMANENT TEETH: The teeth of adult life.
2. TEMPORARY OR MILK TEETH : The teeth of childhood

9. CONT…
• PERMANENT TEETH:
• They are 32 in number and 16 are present in each jaw.
• Upper and lower half jaw contain 8 teeth.
• They are 2incisor, 1 canine, 2 premolar ,3 molars.
• TEMPORARY TEETH:
• They are 20 in number .
• Each jaw contain 10 teeth.
• Each half of the jaw has 2incisors, 1 canine, and 2 molars.

10. FUNCTION OF TEETH
• Incisors and Canine :- cutting teeth, help in biting off pieces of
food.
• Premolar and molar :- broad and flat surface, help in grinding
or chewing food

11. TONGUE
• Tongue lies in the floor of the mouth and it is attached to hyoid
bone.
• Tongue contain:
1. A root at which blood vessels and nerves pass.
2. A tip which is pointed when the tongue is protruded when
the tongue is in the mouth.
3. Two margins which are in contact with lower teeth.
4. An upper surface which contain a small elevation called
dorsum.
5. A lower surface which contain a soft ligamentous structure
called frenulum.

12. CONT…
• The two important structure of tongue are:-
1. Taste buds which are on the lateral aspects of tongue.
2. Small projections called papillae present on the upper
surface.

13. FUNCTION OF TONGUE
• Chewing(mastication)
• Swallowing(deglutition)
• Speech
• Taste

14. CONT…

15. STRUCTURE OF ALIMENTARY CANAL
• The walls of the alimentary tract are formed by four layers of
tissue:
• adventitia or serosa – outer covering
• muscle layer
• submucosa
• mucosa – lining

16. ADVENTITIA OR SEROSA
• This is the outermost layer.
• In the thorax it consists of loose fibrous tissue and in the
abdomen the organs are covered by a serous membrane
(serosa) called peritoneum
• PERITONEUM
• Peritoneum is the serous membrane lining the abdominopelvic
cavity.
• Visceral peritoneum covers the external surfaces of most
digestive organs and is continuous with the parietal
peritoneum that lines the body wall.

17. PERISTALTIC WAVE
• In much of the digestive tract such as human GIT smooth
muscles tissue contracts in sequence to produce peristaltic
waves.
• This propels a ball of food (called bolus while in oesophagus
and upper GIT and chyme in stomach) along the tract.
1. Contraction of longitudinal muscle ahead of bolus
2. Contraction of circular muscle behind bolus.
3. Contraction in circular muscle layer forces bolus forward.

18. CONT…

19. MUSCLE LAYER
• This smooth muscle layer has inner circular and outer
longitudinal layer of muscle fiber separated by myenteric
plexus.
• Neural innervation control the contraction of these muscle and
hence mechanical breakdown and peristalsis of food within
the lumen .

20. SUBMUCOSA
• This layer consist of loose areolar connective tissue containing
collagen .
• It surrounds muscularis mucosa and consist of flat fibrous
connective tissue and larger vessels and nerves.
• The blood vessels are arterioles ,venules and capillaries.

21. MUCOSA
• It is the innermost layer of digestive tract and has specialized
epithelial cells supported by an underlying connective tissue
layer called lamina propria.
• Lamina propria contain blood vessels, nerves, lymphoid tissue
that support mucosa.
• Beneath the lamina propria is a muscularis mucosa it
comprises layer of smooth muscles which can contract to
change shape of the lumen.

22. SALIVARY GLAND
• There are three pair of salivary gland in the mouth .
• They are paratoid submandibular and sublingual glands.
Parotid glands
• These are situated one on each side of the face below and in
front of each ear . Each gland has a parotid duct opening into
the mouth at the level of the second upper molar tooth.
Submandibular glands
• These lie one on each side of the face under the angle of the
jaw. The two submandibular ducts open on the floor of the
mouth, one on each side of the frenulum of the tongue.

23. CONT…
Sublingual glands
• These glands lie under the mucous membrane of the floor of
the mouth in front of the submandibular glands. They have
numerous small ducts that open into the floor of the mouth

24. SALIVA
• It is a mixed secretion of all the three pairs of salivary gland .it
is an alkaline fluid containing water to the extent of 99%.
• The solid content of saliva are :
1. Mucin which is a glycoprotein.
2. Pytaline ,an enzyme which convert starch into maltose.

25. FUNCTION
1. It convert starch into a soluble sugar called maltose
2. It acts as a solvent for food and helps in its swallowing.
3. It moistens, lubricates and clean the mouth.
4. It excretes organic and inorganic substance and some drugs.

26. PHARYNX
• Pharynx lies between the mouth and oesophagus.
• Pharynx contain three parts :
1. Nasopharynx
2. Oropharynx
3. Laryngopharynx

27. OESOPHAGUS
• Hollow muscular tube.
• It lies between trachea in front and vertebrae column at the
back.
• About 25cm(10 inc.)long and 2cm(0.8 inc.)wide
• Convey solid food and liquid to the stomach.
• It is innervated by fibers from the oesophagal plexus.
• The oesophagus contain sphincter at its upper and lower ends.
These sphincters relax during swallowing

28. DEGLUTITION
• The act of swallowing
• In the mouth food is masticated and mixed well with saliva.
The action of tongue and cheeks convert food into a round
mass called bolus. This bolus is swallowed
• Swallowing occurs in the following three stages.
• Stage 1 : closing of the lips and raising of the tongue against
the palate forces the bolus into Oropharynx . Now the
Nasopharynx is closed by soft palate and larynx is closed by
epiglottis . This prevent the entry of food into respiratory
passage.

29. CONT…
• Stage 2 : By the contraction of the muscle of pharynx, the
bolus is forced into oesophagus.
• Stage 3: In the oesophagus ,contraction of its muscular wall
carries the food down to stomach.
• It must be noted that the first stage is a voluntary act but it is
performed automatically .But the second stage and third
stages are involuntary acts.

30. STOMACH
• The stomach is a J-shaped dilated portion of the alimentary
canal and it receives food from oesophages .
• Temporary storage
• Chemical digestion: pepsin break protein into polypeptides
• Mechanical digestion : three smooth muscle layer are added
and the content are liquefied
• Limited absorption
• Production and secretion of intrinsic factor needed for
absorption of vitamin B12.

31. PARTS OF STOMACH
• Two surfaces : an anterior and a posterior surface
• Two border : an upper border called lesser curvature , a lower
border called greater curvature.
• Two ends : upper end called cardiac end it is guarded by
cardiac sphincter . Lower end called pyloric end, it is guarded
by pyloric sphincter.
• Fundus : a dome shaped upper part lying to the left of cardiac
end.
• Body : the main part of stomach
• Pyloric antrum : the lower part

32. CONT…

33. WALLS OF STOMACH
• It contain four coats:
1. Peritoneal coat(made of serous covering )
2. Muscular coat (made of longitudinal , circular and oblique
fibers)
3. Submucous coat (made of areolar tissue)
4. Mucuous coat (made of mucous membrane)

34. SECRETION OF STOMACH
• The mucous membrane of stomach contain glands which
secrete gastric juice continuously.
• About 2 liters of gastric juice are secreted daily by specialized
secretory glands in the mucosa
• Gastric juice contain
• water
• mineral salts
• hydrochloric acid
• intrinsic factor

35. FUNCTION OF GASTRIC JUICE
• Water further liquefies the food swallowed.
• Hydrochloric acid
• Acidifies the food and stops the action of salivary amylase
• kills ingested microbes
• provides the acid environment needed for the action of
pepsins.
• Pepsinogens are activated to pepsins by hydrochloric acid and
by pepsins already present in the stomach.
• These enzymes begin the digestion of proteins.
• Pepsins act most effectively at a very low Ph.

36. CONT…
• Intrinsic factor (a protein) is necessary for the absorption of
vitamin B12 from the ileum
• Mucus prevents mechanical injury to the stomach wall by
lubricating the contents.
• It also prevents chemical injury by acting as a barrier.

37. SMALL INTESTINE
• The small intestine is continuous with the stomach at the
pyloric sphincter.
• 2.5 cm in diameter, 5 metres long and leads into the large
intestine at the ileocaecal valve .
• In the small intestine the chemical digestion of food is
completed and absorption of most nutrients takes place.
• The small intestine comprises three continuous parts.

38. • Food can be digested by a combination of two methods –
mechanical digestion and chemical digestion
• In mechanical digestion, food is physically broken down into
smaller fragments via the acts of chewing (mouth), churning
(stomach)
• Mechanical Digestion
• Chewing (Mouth)
• Food is initially broken down in the mouth by the grinding
action of teeth (chewing or mastication)
• The tongue pushes the food towards the back of the throat,
where it travels down the esophagus as a bolus

39. • The epiglottis prevents the bolus from entering the trachea,
while the uvula prevents the bolus from entering the nasal
cavity
• Churning (Stomach)
• The stomach lining contains muscles which physically squeeze
and mix the food with strong digestive juices ('churning’)
• Food is digested within the stomach for several hours and is
turned into a creamy paste called chyme
• Eventually the chyme enters the small intestine (duodenum)
where absorption will occur

40. • In chemical digestion, food is broken down by the action of
chemical agents (such as enzymes, acids and bile)
• Stomach Acids
• The stomach contains gastric glands which release digestive
acids to create a low pH environment (pH ~2)
• The pancreas releases alkaline compounds (e.g. bicarbonate
ions), which neutralize the acids as they enter the intestine.

41. • Bile
• The liver produces a fluid called bile which is stored and
concentrated within the gall bladder prior to release into the
intestine
• Bile contains bile salts which emulsify fat.

42. • Enzymes
• Amylase release by salivary glands help in carbohydrate
digestion in mouth.
• Amylase secreted by pancreas help in carbohydrate digestion
in small intestine.
• Proteases digest protein in stomach
• Lipases release from the pancreas help in digestion of smaller
fat droplets.
• Nucleases release by pancreas which digest nucleic acid (DNA,
RNA) into smaller nucleosides.

43. • http://ncert.nic.in/ncerts/l/kebo116.pdf
• https://www.scribd.com/document/341658298/Ross-and-
Wilson-Human-Anatomy-and-Physiology-PDF-12th-Edition