Digestive tract (GI) of monogastric animals

Created by rockztar 

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Prehension

taking in of feed or water

Digestion

breakdown large food molecules (CHO, proteins, lipids) into suitable products (sugars, amino acids, fatty acids) for absorption.
i. Mechanical action (chewing, grinding)
ii. Chemical action (HCL)
ii. Enzymatic action (by animal or microbes in animals)

Absorption

transfer of small molecules from the lumen of GI-tract to the circulating blood

Digestive System-Monogastric animals

Have single compartment stomach
eg. human, pigs, horses, dogs, cats or avian
Have limited ability to digest and utilize fiber (NDF) (except horses)

Digestive System-Ruminant animals

- multi-compartment stomach
eg. cows, sheep, goats, deer,..etc

- high ability to digest/utilize fibrous feeds

Monogastric digestive tract

Consist of 6-main parts:
1. Mouth
2. Esophagus
3. Stomach
4. Small Intestine (SI)
5. Large Intestine (LI)
6. Supportive organs
a. Liver
b. Pancreas
c. gall bladder

Mouth

Functions:
1. Receive feed
Lips, teeth and tongue help in prehension

2. Saliva secretion
3-paired saliva glands in the mouth
i. Parotids gland
ii. Submandibular (submaxillary) gland
iii. Sublingual gland
3. Digestion
- Mechanical (chewing)
- Enzymatic (α-amylase → starch digestion)

4. Food taste
- tasted buds
- #'s &distributions vary between animals

Composition of saliva(mouth)

99% water
-Mucus → lubrication aid for swallowing
-Bicarbonate salts (Na) → buffer to regulate pH of stomach
-Amylase enzyme in some species
Human-strong activity
Pigs- limited
Horses- not exist

Saliva Functions

1. Lubricant
2. Protection of membranes in mouth
3. Digestion (amylase)
4. Thermoregulations (dogs-panting; cats-grooming

Factors affecting saliva production

1. Feed intake
as intake increase → saliva flow ↑

2. Feed moisture content
wet feed → ↓saliva

3. Diet composition (fiber)
fiber increase chewing → saliva flow ↑

4. Health

Esophagus

Hollow muscular tube lined with mucosal cells that transport ingesta from the mouth to stomach

Peristaltic muscular contractions

Cardiac valve (sphincter) at the end of esophagus prevent ingesta from moving back.

Stomach

Size vary between species
human: 1.5 L (20% of human GI relative capacity)
Pigs: 7.9 L (30% of pigs GI relative capacity)
horses: 18.2 L (9% of horses GI relative capacity)

Functions:Stomach

1. Storage of ingested feed (control flow)
2. Reduce feed particle size through its muscular movements
3. Initiate protein digestion
4. Secretions of gastirc juices

Secretions in the stomach (gastric Juices)

1.Hydrochloric acid (HCL)
2. Pepsinogen
3. Mucus

Hydrochloric acid (HCL)

- Lowers stomach pH = 1-3

Low pH cause:
a. Initiate protein digestion (denaturation)
b. Activate a protein digestive enzyme (pepsin)
c. Kill pathogenic bacteria in ingested feeds

Pepsinogen

- inactive proteolytic enzyme
- conversion to pepsin (active proteolytic enzyme) requires HCL (low pH condition)

Mucus

- Protecting stomach wall from acid and pepsin
- Malfunction → Ulcer

No absorption of nutrients in the stomach


- Materials leaving the stomach called Chyme

Liver Functions

1.Bile synthesis
2. Site for urea formation
3. Detoxification of harmful compounds
4. Storage of CHO (glycogen) and vitamins
5. Synthesis of glucose
6. Synthesis of cholesterol and triglycerides
7. Synthesis and degradation of amino acids

Bile Synthesis(Liver Function)

- Made in the liver
- Stored in gallbladder
- Secreted bile enters duodenum (small intestine) via duct (bile duct).

Bile Function(Liver Function)

a. Emulsification of fats to facilitate lipids digestion and absorption in small intestine
b. Activate pancreatic lipase enzyme

Pancreas

Assist in CHO, proteins and lipids digestion in small intestine
Pancreatic secretions enter duodenum (small intestine) via duct

Pancreatic secretions:

1. Digestive enzymes:
2. Bicarbonate (buffer)
3. Hormones

Digestive enzymes

a. Amylase → digest starch
b. Trypsin
c. Chymotrypsin
d. Carboxypeptidase
e. Neuclease
b - e → involve in proteins digestion
f. Lipase → digest lipids
g. cholesterol esterase → digest cholesterol

Bicarbonate (buffer)

- Neutralize small intestine pH
- Enzymes require pH > 6.5 to function in small intestine (duodenum)

- Pancreatic enzymes and bicarbonate are made in pancreas → released into duodenum (small intestine) via duct.

Hormones

a. Insulin
b. Glucagon

- Released into blood
- Regulate (maintain) blood glucose level

High blood glucose → insulin release →↑ glucose uptake by cells and also increase glycogen synthesis

Low blood glucose → ↑ glucagon release →
a. breakdown glycogen to glucose
b. increase synthesis of glucose from AA

Small Intestine (SI)

The part between stomach and large intestine
-Length vary between animals
- Main site for CHO, protein and lipid digestion and nutrients absorption in monogastric animals

3 sections
of Small Intestine (SI)

1. Duodenum
2. Jejunum
3. ileum

Duodenum

- First section of SI
- Shortest section
- Main site for CHO, protein and lipid digestion
- pH = 6.0-6.5

- Digestion accomplished by secretions from:
a. Pancreas (enzymes and buffer)
b. Duodenal wall (enzymes)
c. Liver (bile)

duodenal wall secretions

-Enzymes
1. Maltase
2. Sucrase help in CHO digestion
3. Lactase

4. Aminopeptidase
5. Dipeptidase help in protein digestion

Jejunum and ileum

Jejunum = Middle section
Ileum = Last section

Jejunum & ileum are the main site for nutrients absorption (AA, glucose, FA, vit & minerals)

Walls of lower intestine are folded and lined with villi (fingerlike projections) → help in ↑ing surface area

Each villi has minute projections called microvilli → more ↑ in surface area

Absorption in SI

1. Passive diffusion
2. Facilitated diffusion
3. Active absorption

. Passive diffusion

from high to low concentration
eg. minerals, water

. Facilitated diffusion

- from high to low concentration but use carrier proteins in intestinal surface
- eg. vitamins

Active absorption:

- from low to high concentration
- requires energy and specific carrier proteins
eg. Glucose and amino acids

Large Intestine (LI)

Shorter but wider than SI.
Size vary between species

3 Sections of LI

1.Cecum
2. Colon:
3. Rectum

Cecum

- first section of LI
- Contain active bacteria similar to rumen bacteria
- Fermentation site
Monogastric animals however, don't benefit from these vitamins and bacterial protein

Colon:

Storage site
water absorption (also some minerals absorption)
No absorption of amino acids and sugars

Rectum

last section

LI functions

1. Fiber digestion
- Digestion by bacteria inhabiting the cecum
(very limited in monogastric animals except in horses)
- End-products of fermentation (VFA, B-vits, bactereial protein) have little use.

2. Absorption
- water (mainly)
- very limited absorption of nutrients (feedstuff or microbial origin)
- No AA or glucose absorption

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