AF 1201

Digestive System

Dr. A.M.J.B. AdikariDept. of Animal and Food Sciences

Digestive system

• A tube which extends from mouth to anus

• Comprise of GIT and accessory structures

• Major parts

– Mouth, pharynx, esophagus, stomach, small intestine,

ceacum, large intestine, rectum and anus

• Accessory structures – teeth and tongue

• Related structures – salivary glands, liver, pancreas

• Begins at the mouth and ends at the anus

– Oral cavity

– Esophagus

– Stomach

– Small intestine

– Large intestine

– Rectum and anus

Human Digestive System

• Accessory organs

– Salivary glands

– Liver

– Pancreas

– Gall-bladder

• Functions

– Ingestion

– Grinding

– Digestion

– Absorption

– Elimination

Anatomy of the GIT

• 4 layers

• Mucosa - inner most layer

• Sub mucosa

– loosely arranged connective tissues

– Blood vessels -Absorption

– Extensive neuronal net work

• Muscularis - muscle layer

– 2 layers inner circular & outer longitudinal

• Serosa - outer most layer

Mouth

• Formed by lips, cheeks, hard & soft palates, tongue &

teeth

• Lips

– Facilitate picking of foods

– Clefted upper lips - sheep, goat

– Close mouth - cattle, pig

Grazing vs Browsing????

• Cheeks

– Muscular

– Aid in positioning of food b/w teeth

– Connective tissues, under voluntary control

• Hard palate

– Form the roof of the mouth

– A bone structure, covered by mucous membranes

• Soft palate

– Muscular

– Separate mouth & pharynx

• Tongue

– Striated muscle covered with mucous membrane

– Studded with papillae on dorsal surface

– 4 types of papillae – facilitate taste

All a) Filli form hair like, no taste buds

Domestic b) Fungi form mushroom like, have taste Animals buds

c) Circumvallate large circular projections, contain taste buds

d) Foliate Leaf like, contain taste buds Only in pigs

• Cattle - Use tongue as a prehensive organ

Helps in chewing & bolus formation

Teeth

• Develop from dental lamina

• Two sets

– Temporary (milk teeth)

– Permanent (adult teeth)

– Eruption - approximately determine age at specific

stages

• According to the functions – 4 types

a) Incisors - cutting

b) Canines - tearing

c) Pre molars – grinding

d) Molars - grinding

Dental Formulas

Cattle

Buffalo

Goat

Sheep

Swine

32

32

44

2(DI 0/4, DC 0/0, DP 3/3) 20

2(I 0/4, C 0/0, P 3/3, M 3/3)

2(DI 3/3, DC 1/1, DP 4/4)

2(I 3/3, C 1/1, P 4/4, M 3/3)

Salivary glands

• Chief glands - parotid, mandibular, sub lingual

• Minor glands - labial, buccal, lingual, palantine

• Based on secretions - 3 types of glands

– Serous - secrete water like fluid

- Ex; Parotid, buccal

– Mucous - thick secretions

- Ex; labial, lingual

– Mixed - in between

- Ex; mandibular, sub lingual

Salivary Secretion

• Is a reflex act that stimulated by the presence of food

• Composition of saliva

– Water 99.5%

– Solutes 0.5%

• Inorganic -

• Organic - urea, uric acid, some

Proteins (albumin, globulin)

Polysaccharides, enzymes

• Functions of Saliva

– Mixing

– Lubrication

– Bolus formation

– Swallowing

– Enzymatic digestion

• In ruminants

– Maintain rumen fluid consistency

– Neutralized acids formed by rumen microbes

– Prevent frothing

– Medium for microbial growth

• Functions of mouth

– Prehension

– Chewing

– Insalivation

– Bolus formation

– Offensive

Pharynx

• Common passage for food and air

– Naso pharynx - located dorsally

– Oro pharynx - located ventrally

• Aid in swallowing (deglutition)

Swallowing - mechanism that moves food from

mouth to stomach facilitated by saliva and mucous

• 3 Stages of swallowing

– Oral - pass through mouth - voluntary

– Pharyngeal - pass through pharynx - involuntary

– Esophageal - pass through esophagus - involuntary

Esophagus

• A direct continuation of the pharynx

• Moves bolus from oral cavity to stomach

• Voluntary (upper) and involuntary (lower) muscular

contractions

• Esophageal sphincters controlled by neural and

hormonal mechanisms - Osophageal/ cardiac sphincter

• Functions

– Peristaltic (function of muscularis regulated by

medulla), Lumen - closed when empty

– Aid in swallowing

– Provides passage of food to stomach

Stomach

• Two major kinds of stomach in mammals

– Simple - man, pig, horse, dog

– Complex/compound - ruminants

• In birds, it is composed of a crop, Proventriculus &

Ventriculus

Simple Stomach

• Sub divisions

– Exterior - cardia, fundus, pylorus

– Interior - mucosa is divided into 2 parts

• Esophageal region

• No glands

• White in color

• Glandular region - gastric glands

- can be divided in to 3 regions

Glandular Region

• Cardiac gland region

- mucosa contains simple or compound tubular glands,

- secrete mucous, no enzymes

• Fundic gland region

- true gastric glands, simple tubular glands

(contain three types of cells)

• Mucous neck cells - Mucous

• Chief cells - Pepsin & rennin

• Parietal cells - HCI

• Pyloric region

– No parietal cells

– G-cells - secrete stomach hormone (gastrin) which stimulate

HCI & pepsin

Gastric Juice

– Total secretory products of all 3 types glands

– A colourless,viscous fluid

– Contains HCI ,pepsin, mucous, electrolytes, hormones

• Pepsin

– Inactive form is Pepsinogen synthesized in Chief cells

– Activated by HCI, it hydrolyses proteins

Functions

• Storage

• Digestion

• Absorption

• Endocrine functions (Gastrin)

• Production of intrinsic factor (Vit. B12)