The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver, and gallbladder).In this system, the process of digestion has many stages, the first of which starts in the mouth. Digestion involves the breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. Chewing, in which food is mixed with saliva begins the process of digestion. This produces a bolus which can be swallowed down the esophagus and into the stomach. Here it is mixed with gastric juice until it passes into the duodenum, where it is mixed with a number of enzymes produced by the pancreas. Saliva also contains a catalytic enzyme called amylase which starts to act on food in the mouth. Another digestive enzyme called lingual lipase is secreted by some of the lingual papillae on the tongue and also from serous glands in the main salivary glands. Digestion is helped by the mastication of food by the teeth and also by the muscular actions of peristalsis and segmentation contractions. Gastric juice in the stomach is essential for the continuation of digestion as is the production of mucus in the stomach. Peristalsis is the rhythmic contraction of muscles that begins in the esophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract. This initially results in the production of chyme which when fully broken down in the small intestine is absorbed as chyle into the lymphatic system. Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood in the colon of the large intestine. The waste products of digestion (faeces) are defecated from the anus via the rectum.

1. Comparative anatomy
( Chordates)
Digestive system
1-Human
2-Ruminant
3-Avian
4-Horse
5-Fish
Dr.Omer

2. Digestive System

3. Introduction
• Three (3) basic types of digestive systems according
to their stomachs :
►Monogastric – simple stomach.
►Ruminant (cranial fermentor) – multi-compartmented
stomachs.
►Hind gut (caudal) fermentor – simple stomach, but very
large and complex large intestine

4. Types of Digestive Systems
Cats
Chickens Pigs
DogsTurkeys
Monogastrics Ruminants
Hind Gut
Fermentors
Beef Cattle Dairy Cattle
Deer
SheepGoats
Horses
Rabbits
Ostrich

5. Types of Digestive Systems
• Are divided into three groups based on their
food sources
1. Herbivores are animals that eat plants
exclusively
2. Carnivores are animals that eat other animals
3. Omnivores are animals that eat both plants and
other animals
5

6. Carnivore
• Eat primarily
other animals.
Herbivore
• Eat primarily
plant materials.
omnivore
• Eat combination
of plant and
animal material.

7. The Human Digestive System

8. Human
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Primates
Family Hominidae
Genus Homo
Species sapiens

9. Introduction
• The digestive system is used for breaking down food
into nutrients which then pass into the circulatory
system and are taken to where they are needed in the
body.

10. Main Functions of Digestive Tract
• The major activities of GI tract
• 1-Ingestion: taking in food
2.Motility
• Propel ingested food from mouth toward rectum
3.Secretion of juices e.g. saliva
• Aid in digestion and absorption
4.Digestion
• Food broken down into absorbable molecules
5.Absorption
• Nutrients, electrolytes, and water are absorbed or transported
from lumen of GIT to blood stream
6.. Egestion (Elimination) : removing any leftover wastes

12. Digestion
• Types
– Mechanical (physical)
• Chew
• Tear
• Grind
• Mash
• Mix
– Chemical
• Enzymatic reactions to improve digestion of
– Carbohydrates
– Proteins
– Lipids

13. Anatomy of the Digestive Tract
GIT consists of;
– Oral cavity or mouth
– Pharynx
– Esophagus
– Stomach
– Small intestine
– Large intestine
– Rectum
– Anus

14. Mouth or oral cavity
• Ingestion - bringing food into the body
– tongue - taste buds detect chemical composition of food
• Mastication - chewing (physical digestion)
– teeth and tongue
• Chemical digestion - saliva
– moistens food
– amylase - breaks down starch
– lysozyme - antibacterial agent

15. Mouth and Teeth

16. Esophagus
• Muscular tube connecting the pharynx to the stomach.
• Functions include:
1. Secretes mucus
2. Moves food from the throat to the stomach using
muscle movement called peristalsis
 Cardiac Sphincter – connects esophagus and stomach
• If acid from the stomach gets in here that’s heartburn.

17. 17

18. Stomach
• Muscular sac-like organ
• Chemical and physical digestion
– forms chyme
• goblet cells – mucus
– forms a protective barrier against the high acidity of the
stomach content.
– parietal cells – HCl
– kills bacteria, denatures proteins
• chief cells - pepsinogen
– pepsinogen activated by HCl  pepsin
– pepsin breaks down proteins

19. 19
The Stomach

20. Small intestine
Functions
Digestion
Digest carbohydrates : amylase from pancreas
Digest proteins : trypsin & chymotrypsin from pancreas
Digest lipids (fats) bile from liver & lipase from pancreas
Absorption
VILLI – small finger-like projections that increase the surface area
MICROVILLI – even smaller finger-like projections on the VILLI
LACTEAL – large lymph vessel found on each villus (Absorbs FAT)
Capillaries – small blood vessels found on each villus (Absorbs all
nutrients EXCEPT Fat)

21. The Parts of Small intestine
1. Duodenum - most digestion occurs here
2. Jejunum - some digestion and some
absorption occur
3. Ileum - mostly absorption

22. SMALL INTESTINE
• The small
intestine is divided
• duodenum
• jejunum
• ileum.

23. • Pancreas has 2 functions:
a) Endocrine functions: secretes insulin and glucagon from islets of
Langerhans
b) Exocrine function: secretion of pancreatic juice
• It has 2 components: aqueous and enzymatic components.
• Aqueous component (contains HCO3) is important for neutralizing
stomach acid in the duodenum so pancreatic enzymes can function
properly
• Enzymatic component is essential for the proper digestion and
absorption of carbohydrates, fats, and proteins
• Pancreatic enzymes include trypsin, chemotrypsin, lipase, and
amylase
Functions of the Pancreas

24. 24

25. Liver
Functions of the Liver:
1) Metabolic regulation
• Store absorbed nutrients, vitamins
• Release nutrients as needed
2) Hematological regulation
• Plasma protein production
• Remove old RBCs
3) Production of bile
• Required for fat digestion and absorption

26. Liver

27. Liver

28. The Large Intestine (colon)
• Much shorter than small intestine, but has larger
diameter
Functions
1. Goblet cells: create mucus that lubricates colon and
protects mucosa.
2. Absortive cells: Maintain water balance, solidify
feces, absorb vitamins and some ions
• Prepare waste for expulsion
28

29. 29

31. Digestive System
– Ruminants –
Mouth, esophagus, liver, pancreas, gall bladder,
small intestine, and large intestine have functions
similar to monogastrics.

32. Cow
•
• Kingdom Animal
• Phylum Chordata
• Class Mammalia
• Order Artiodactyla
• Family Bovidae
• Genus Bos
• Species indicus Asian humped cattle
taurus European non-humped cattle

34. Reticulum
• Holding area for feed after it passes down esophagus.
• Provides additional area for fermentation.
• Contains microorganisms, like rumen
• Collection compartment for foreign objects.
• Helps open and close rumen.
• Minimal separation with rumen.
“honeycomb”

35. Rumen
• Largest of the four components.
• On the left side of the animal.
• Storage site and fermentation .
• Houses millions of microorganisms.
• Lined with millions of finger-like projections (papillae) that are
needed for absorption.
“paunch”

36. Omasum
• A heavy, hard organ that has many folds or leaves.
• Little, if any digestive activity.
• Grinds feed particles.
• Removes moisture.
“many piles”

37. Abomasum
• True, glandular stomach
• Functions similarly to monogastric stomach
• Secretes gastric juices which aid in digestion.
Infected with barber pole worms

38. Organs of the Digestive System
– Hind Gut Fermentors –
Mouth, esophagus, stomach, liver, pancreas,,
and small intestine have similar functions as
compared to monogastrics.
Horse doesn’t have gall bladder

41. Digestive Tract
- Horse-
Esophagus
Stomach
Duodenum
Small
intestineCecum
Large
colon
Small colon
Rectum

42. Organs of the Digestive System
– Hind Gut Fermentors –
• Large Intestine
► Major difference between monogastrics and hind gut fermentors is the
large intestine.
► Large intestine is exceptionally large and complex compared to
monogastrics and ruminants.
The large intestine of hind gut fermentors is analogous to the rumen in
ruminants.
► Microbes digest structural carbohydrates (cellulose, hemicellulose) and
soluble carbohydrates that escape digestion in small intestine to VFA’s.
 VFA’s absorbed from large intestine and utilized by the animal.
► Microbial protein produced in large intestine is wasted (only very limited
absorption from large intestine).

43. Avian Digestive System

45. Avian Digestive Systems
• Mouth
– no teeth
– Salivation excretion moistens food
• Esophagus
– has a modification called the “crop” which stores
and moistens food
– connects mouth and stomach

46. Avian Digestive Systems
• Stomach
– Contains two parts
• Proventriculus: same as monogastric stomach and
provides digestive excretions
• Gizzard: located after proventriculus, very muscular,
used to grind food

47. Avian Digestive Systems
• Small Intestine
– similar functions as in ruminants and monogastric
systems
• Large Intestine
– similar functions as in ruminants and monogastric
systems
– “cloaca”: chamber into which urinary and genital
canals open
– “ceca”: aids in fiber digestion and absorption

49. Digestive System Comparisons
Function Monogastric Ruminants
Hind Gut
Fermentors
Digest and extract
energy from cellulose
Very limited
(large intestine)
Yes
(rumen/reticulum)
Yes
(large intestine)
Utilize dietary sugar
sources directly
Yes
(absorbed as glucose)
No
(fermented to VFA’s)
Yes
(absorbed as glucose)
Utilize protein from
feeds directly
Yes Limited
(most converted to microbial
protein)
Yes
Utilize fat from feeds
directly
Yes Some
(most fermented to VFA’s)
Yes
Utilize microbial
protein
No Yes
(60-80% of AA from microbes)
No

51. Human Cattle Bird Horses
Teeth 32 32 0 40-42

52. Organs of digestive system Comparisons
Ruminant
• Mouth
• Esophagus
• Stomach
– Reticulum
– Rumen
– Omasum
– Abomasum
• Small intestines
• Large intestines
Monogastric
• Mouth
• Esophagus
• Stomach
• Small intestines
• Large intestines
Liver
Pancreas
Liver
Pancreas

53. Thank you