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1. Digestion
Master Traithana
Chaowanapreecha
Master Alfredo V. Garcia III

2. Definition
Digestion – the process of breaking
down food particles (macromolecules)
into smaller, simple molecules that can
be absorbed into cells or the
bloodstream.
Enzymes
Examples: Enzymes
Starch Glucose
Protein Amino acids

3. The digestion of different
organisms

4. The digestion of different
organisms
1. Intracellular digestion – food is taken
into cells by phagocytosis forming a
food vacuole, then lysosome fuses the
vacuole and releases enzymes to
digest food.
Food molecules are absorbed to
cytoplasm. Waste is expelled by
exocytosis.
Examples: Amoeba, paramecium, other

5. Intracellular digestion

6. The digestion of different
organisms
2. Extracellular digestion – organisms
secrete enzymes out of their cells. Food
is digested and absorbed into cells.
Examples: Bacteria, fungi, most animals
including humans

7. The digestion of different
organisms
2 methods to digest:
1. Mechanical digestion – Food is broken
into smaller pieces by chewing,
contracting muscles (peristalsis of
intestines and a stomach). Food can
bind to enzymes better.
2. Chemical digestion – Macromolecules
are broken down into smaller
molecules

8. Digestive systems
of different
organisms

9. Digestive systems of different
organisms
A sponge has
choanocytes engulfing
food into cells and

10. Digestive systems of different
organisms
Coelenterates
have a
gastrovascul
ar cavity,
the
digestion
zone.

11. Digestive systems of different
organisms
A nematode has a complete digestive
system including mouth, esophagus,
intestine, and anus.

12. Digestive systems of different
organisms
An earth worm also has a complete
digestive system including mouth,
esophagus, crop, gizzard, intestine,
and anus.

13. Digestive systems of different
organisms
An insect has a crop storing food
and a gizzard digesting food.

14. Digestive systems of different
organisms
A bird’s digestive system
has beak and mouth
suitable for different
kinds of food,
esophagus, crop,
stomach, gizzard,
intestine, rectum and
cloaca.

15. Digestive systems of different
organisms
Herbivorous mammals likes cows
and buffaloes have 4-chambered
stomach suitable for cellulose
digestion.

18. Digestive systems of different
organisms
Carnivorous animal digestive system

19. Digestive system of a human

20. Human digestive system
Alimentary canal
Mouth pharynx esophagus
stomach
-Teeth
-Tongue
large intestine -Duodenum
-Ascending colon
-Transverse colon -Jejunum
small intestine
-Descending colon -Ileum
rectum anus

22. Human digestive system
Digestive glands
- Salivary glands
- Gastric glands
- Intestinal glands
- Pancreas
- Liver

23. Human digestive system
Digestion in the oral cavity
Oral cavity includes upper jaws, lower
jaws, teeth, gum, cheek lining, hard and
soft palates.
Mechanical digestion
Teeth cut, tear, and grind food into small
pieces, then a tongue mixes food with
saliva secreted from 3 pairs of salivary
glands (sublingual, submandibular, and
parotid).

24. There are 2 sets of human teeth formed
by ectoderm.
- Deciduous teeth, D.T., are firstly formed
at age 6 months and start to fall out at 6
years old. There are totally 20 D.T.
- Permanent teeth, P.T., are completely
formed at age 13.
There are totally 32 P.T.

25. 32 Human permanent teeth include:
1. 4 upper incisors – cut food (well-
developed in rodents)
4 lower incisors
2. 2 upper canines – cut, tear, and separate
food
2 lower canines (well-developed in
carnivores)
3. 4 upper premolars – cut and tear food
4 lower premolars (well-developed in
carnivores)
4. 6 upper molars – chew and grind food

27. Salivation is controlled by
parasympathetic nervous system
(cranial nerve pairs no.7 and 9)
Stimuli: seeing food, smelling, tasting,
toughts amylase
Chemical digestion
amylase
Starch + water dextrin
Dextrin + water maltose

28. How is food transferred from a mouth to a
stomach?
Food travels along esophagus to a stomach
by peristalsis
(muscle contractions: the waves of involuntary muscle
contractions that transport food, waste matter, or other
contents through a tube-shaped organ.)

29. Digestion in a stomach
- Capacity when it’s empty = 50 – 100 mL
- Capacity when it’s full = 1-2 L
Epithelial cells line inner surface of the
stomach and secrete about 2 liters of
gastric juices per day. Gastric juice
contains hydrochloric acid, pepsinogen,
rennin, lipase, potassium chloride, and
mucus; ingredients important in
digestion.

30. Secretions are controlled by nervous
(smells, thoughts, and caffeine) and
endocrine signals.
The stomach secretes hydrochloric acid
and pepsin. Hydrochloric acid (HCl)
lowers pH of the stomach so pepsin is
activated. Pepsin is an enzyme that
pepsin
controls the hydrolysis of proteins into
peptides. The stomach also
mechanically churns the food.
Protein short polypeptides

31. Anatomy of the Stomach
Located on the left side of the body, under the diaphragm, the stomach is a muscular, saclike organ that connects the esophagus and small intestine. Its main function is to bre
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32. Ulcers
Peptic ulcers result when these protective
mechanisms fail. Bleeding ulcers result
when tissue damage is so severe that
bleeding occurs into the stomach.
Perforated ulcers are life-threatening
situations where a hole has formed in
the stomach wall. At least 90% of all
peptic ulcers are caused by
Helicobacter pylori. Other factors,
including stress and aspirin, can also
produce ulcers.

34. Functions of the stomach
- Storing food
- Producing intrinsic factor (IF) important in B12
absorption at the small intestine
- Digesting protein
- Controlling the proper amount of food leaving
the stomach for the small intestine
- Producing hormone gastrin helping in pepsin
and HCl production (in the stomach) and bile
production (in the liver)
- Buffering the food condition if it’s too alkaline.

35. Digestion in the small intestine
-Final digestion and absorption occur.
-The small intestine is a coiled tube over 3 meters long. Coils
and folding plus villi give very large surface area.
-Final digestion of proteins and carbohydrates must occur, and
fats have not yet been digested.
- Food has been broken down into particles small enough to
pass into the small intestine.
-Sugars and amino acids go into the bloodstream via
capillaries in each villus. Glycerol and fatty acids go into the
lymphatic system.
-Absorption is an active transport, requiring cellular energy.

36. Structure of the small intestine

37. Liver, gall
bladder and
pancreas

38. Digestion in the small
intestine
1. CarbohydratesPancreatic amylase
Polysaccharides + water
disaccharides
Disaccharidases from intestine
Disaccharides + water
monosaccharides

39. Digestion in the small
intestine
2. Proteins
Trypsin and chymotrypsin
Polypeptides + water
protein fragments
Carboxypeptidase from pancreas
Fragments + water
Aminopeptidase from intestine
amino acids
Fragments + water
amino acids

40. Aminopeptidase
Carboxypeptidase

41. Digestion in the small
3. Lipids
intestine
Pancreatic lipase + bile (liver)
Triglycerides + water
fatty acids +
monoglycerides
Pancreatic lipase + bile (liver)
What is the function of bile??????

42. 4. Nucleic acids
Pancreatic nuclease
DNA and RNA nucleotides
Intestinal nuclease
Nucleotides nucleotide
bases + monosaccharides
(ribose or deoxyribose)

43. Absorption
- Alcohol and aspirin are absorbed
through the stomach lining into the
blood.

44. Most absorption occurs in the duodenum and
jejeunum. The circular folds and villi covered with
epithelial cells provide a large surface area for
absorption. The epithelial cells are lined with
microvilli that further increase the surface area; a 6
meter long tube has a surface area of 300 square
meters.

45. Glucose, fructose, and galactose are
absorbed by the microvilli by active
transport, then leave the cell and enter
the capillary.
Amino acids cross the epithelial cell
membranes by active transport, then
enter the capillary.
Water, vitamins and minerals are
absorbed by diffusion without digestion.
Absorbed food molecules will be

46. Absorption of lipids by cells in the small
intestine.

47. Any activities happen in
large intestine?
- Water, vitamin,
and mineral
absorption
happens.
- Bacteria E. coli
synthesizes vit.
K.
- Feces
formation

48. Appendectomy
Appendicitis is a painful inflammation of the appendix, a finger-sized tube attached
to the large intestine. To remove an inflamed appendix, surgeons perform a surgical
procedure known as an appendectomy.
The inflammation can be caused by undigested food particles and bacteria.
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49. End.