Nota Digestion

8/3/2019 Nota Digestion

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Learning objectives

By the end of this chapter, students should be ableto:

Describe the mechanism of feeding

State and explain four stages of food processingincluding hormonal control.

Differentiate thevariation in vertebratedigestive system.


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Main feeding mechanismsSuspension feeders

Substrate feeders

Fluid feeders

Bulk feeders


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Main feeding mechanisms Suspension feeder/ filter feeders

Sieve small food particles from water

E.g :whales, clams and flamingos
http://upload.wikimedia.org/wikipedia/commons/b/b2/Lightmatter_flamingo.jpghttp://en.wikipedia.org/wiki/Image:Humpback_stellwagen_edit.jpg


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Main feeding mechanisms Substrate feeders

Animals that live in/on their food sourceEat their way through the food

E.g : earthworms and termites
http://en.wikipedia.org/wiki/File:Coptotermes_formosanus_shiraki_USGov_k8204-7.jpghttp://en.wikipedia.org/wiki/File:Regenwurm1.jpg


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Main feeding mechanisms Fluid feeders

Suck nutrient-rich fluid from a living host

E.g : mosquito, aphids
http://en.wikipedia.org/wiki/File:Aphids_feeding_on_fennel.jpg


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Main feeding mechanisms Bulk feeders

Eat relatively large pieces of food (swallow altogether)

Spend a long time to digest their food

E.g : snake


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Mouth

Esophagus

Stomach

Large intestine

Rectum

Anus

Tongue

Glands in mouth that make saliva

Pancreas

Liver

Gallbladder


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The mammalian digestive system consists of analimentary canal and accessory glands thatsecrete digestive juices through ducts

Mammalian accessory glands are the salivaryglands, the pancreas, the liver, and thegallbladder


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Stages of Food Processing

Ingestion is the act of eating

Digestionis the process of breaking food downinto molecules small enough to absorb In chemical digestion, the process ofenzymatic hydrolysis

splits bonds in molecules with the addition of water

Absorption is uptake of nutrients by body cells

Eliminationis the passage of undigested materialout of the digestive compartment

Fi


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Fig. 41-7

Ingestion Digestion Absorption Elimination

Undigestedmaterial

Chemical digestion

(enzymatic hydrolysis) Nutrientmoleculesenter bodycells

Smallmolecules

Mechanicaldigestion

Food

Piecesof food

1 2 3 4


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Digestion:

Mechanical

&

Chemical


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Animals with simple body plans have agastrovascular cavitythat functions in both

digestion and distribution of nutrients.

More complex animals have a digestive tube

with two openings, a mouth and an anus -called a complete digestive tract or analimentary canal

Digestive Compartments


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Gastrovascular Cavity

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Fig 41

-10a


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Fig. 41-10a

Cecum

Anus

Ascendingportion oflarge intestine

Gall-bladder

Small

intestineLargeintestine

Smallintestine

Rectum

Pancreas

Liver

Salivary glands

Tongue

Oral cavity

PharynxEsophagus

Sphincter

Stomach

Sphincter

Duodenum ofsmall intestine

Appendix


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Variation of alimentary canal

related organ Crop is a pouch like organ in which food is usually

softened, moistened and stored temporarily

Gizzards Actively churn and grind the food (physicalfragmentation)

Fig 41-9a


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Fig. 41 9a

Esophagus

Mouth

Pharynx

Crop Gizzard

Typhlosole

Intestine

Lumen of intestine

Anus

(a) Earthworm

Fig. 41-9b


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Fig. 41 9b

(b) Grasshopper

Foregut

Mouth

Crop

Gastric cecae

Esophagus Rectum

Anus

Midgut Hindgut

Fig. 41-9c


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Fig. 41 9c

(c) Bird

Stomach

GizzardIntestine

Esophagus

Anus

Crop

Mouth

Fig. 41-10b


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g 4

Anus

Liver

Pancreas

Smallintestine

Large

intestine

Rectum

Stomach

Gall-bladder

A schematic diagram of thehuman digestive system

Esophagus

Salivaryglands

Mouth


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The first stage of digestion is mechanical and

takes place in the oral cavity- Human teeth suit their omnivorous lifestyle.

- They are simple carnivorous at their mouth front by having

cuspids and incisors.

- Behind the cuspids are two premolars and three molars usedfor grinding and crushing food.


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Fig. 41-18


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g

Incisors

(c) Omnivore

Molars

(b) Herbivore

(a) Carnivore

CaninesPremolars


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The palate, the bone-reinforced section of the mouthprovides a hard surface for the tongue to press the food

in order to mix with the saliva.


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As for the tongue, besides equipped with taste buds to

help us taste the food, the tongue helps shaped it intoa bolus.


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Salivary gland produce and secrete saliva that

* Cleanses the mouth* Moistens and dissolves food chemicals

* Aids in bolus formation

* Contains salivary amilase which initiates thechemical digestion (breaking down) of starch into

sugar.

Three types salivary glands

(parotid, sublingual and submandibular)


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The esophagus is a muscular tube that conveysboluses from the pharynx to the stomach byperistalsis.

The region we call our throat is the pharynx, ajunction that opens to both the esophagus andthe trachea (windpipe)

The trachea leads to the lungs

Esophagus


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Esophagus From esophagus to the anal canal of the walls of the GI

(gastrointestinal tract) have the same four tunics:

- mucosa, submucosa, mascularis externa and serosa.


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During swallowing, the esophageal sphincter muscle is relaxed

allowing bolus to enter the esophagus

epiglottis is down

glottis is closed

- Coughing occurs when the swallowing reflexfails and food or liquids reach the windpipe

Fig. 41-11-2


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Larynx

Trachea

Epiglottis

upPharynxTongue

Glottis

Esophagus

Esophagealsphinctercontracted

Food

Tostomach

Tolungs

Epiglottisdown

Esophageal

sphincterrelaxedGlottis upand closed

Fig. 41-11-3


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Larynx

Trachea

Epiglottis

upPharynxTongue

Glottis

Esophagus


Food

Tostomach

Tolungs

Epiglottisdown

Esophageal

sphincterrelaxedGlottis upand closed

Epiglottisup


Sphincterrelaxed

Relaxedmuscles

Contractedmuscles

Relaxedmuscles

Stomach

Glottisdownand open


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In the esophagus, peristalsis happens

A wavelike contraction that squeezes a bolusdownwards to the stomach

The movement of food is controlled by a sphincter.


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Both layers of muscularis externa

contract involuntarily, meaning

that whenever one muscle layer

contract the other one relax.

This causes the peristalsis

process to happen and brings the

bolus to the stomach.


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Stomach The stomach is

convulated, enablingto fold up when empty

and open out like anexpanding balloonwhenever it is full offood


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STOMACH

A bolus is moved down through the

esophagus through peristaltic contractions

When the sphincter at the entrance ofthe

stomach opens, food enters the stomach

Pyloric sphincter causes the chyme

to enter the small intestine one

squirt at a time (2 6 hours)


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Small Intestine

The small intestine is about 4.5 m long where thefirst 25 cm is the duodenum; the remainder isdivided into jejunum and ileum.

The small intestine is the longest section of thealimentary canal

It is the major organ of digestion and absorption


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Small Intestine


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Small intestines

The epithelial wall of the small intestine is coveredwith tiny, fingerlike projection calledvilli.

The epithelial cells lining the villi have manycytoplasmic extensions called the microvilli.

This greatly increases the surface area of the smallintestine that helps in the absorption process.


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Small intestines


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Large Intestine The large intestine (colon) is much shorter than the small

intestine but it possesses a larger diameter.

No digestion takes place within the large intestine and onlyabout 4% of fluid absorption happens here.

Undigested material is compacted and stored.

Bacterial fermentation happens at the colon and produces

gases.

Compacted feces will be driven by peristalsis from the largeintestine into a short tube called rectum.


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Large intestine


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Large intestineTwo sphincters control passage to the anus;i) composed of smooth muscles that open involuntarily

in response to pressure inside the rectum.

ii) composed of striated muscle that can be voluntarilycontrolled by the brain.


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Accessory organ

Consists of :

pancreas

gallbladderliver


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Pancreas

The pancreas is an exocrine organ pancreatic fluid issecreted through the pancreatic duct

The pancreatic fluid contains hydrolytic enzymes:

1. Trypsin & chymotrypsin (protein digestion)

2. Pancreatic amylase (carbohydrate digestion)

3. Lipase (fat digestion)
http://upload.wikimedia.org/wikipedia/commons/1/15/Gray1100.png


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Pancreas The enzymes are released as inactive enzymes called

zymogens which will then be activated by the brushborder enzymes of the small intestine.

Pancreatic fluid also contains bicarbonate thatfunction in neutralizing the HCl from the stomach.

The pancreas also plays a role as an endocrine gland.


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Liver The main exocrine secretion of the liver is bile which is

a mixture ofbile pigments and bile salts.

The bile pigments (by-products of red blood celldestruction) did not participate in the digestionprocess. It is eliminated with feces.

Bile saltswill play an important role in fat digestion(emulsification process).


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Gallbladder Gallbladder functions in storage and

concentration of bile salts.

The arrival of fatty food to the

duodenum triggers a reflex, causingcontraction and injection of

gallbladder to the duodenum.


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Human Digestive System

Chemical Digestion

Accomplished through the use of chemicals known asdigestive enzymes

These complex molecules, such as fats, proteins, andcarbohydrates, are digested (broken down) intosmaller molecules.

These smaller molecules can then be absorbed for use

by cells.


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Chemical digestion MOUTH

The salivary amylase enzyme begins hydrolyzingstarch in the food

Salivary amylase will turn starch to oligosaccharide

and dissaccharides (maltose).salivary amilase

polysaccharides ------------------ > maltose


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Chemical digestion STOMACH

The stomach secretes gastric juice from gastric glands

Gastric juice contain mucus, enzymes (pepsin &renin) and strong acid (HCL pH 1.5 2).

Mucus functions in lubricating and protecting the cell

lining in the stomach from the acidity of the gastricjuice


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Chemical digestion - STOMACH

The enzyme secreted is pepsinogen, an inactive formof the digestive enzyme pepsin.

Acids converts pepsinogen to active pepsin byremoving a small portion of the molecule andexposing the active sites

HCL

Pepsinogen------- > Pepsin

Fig. 41-12

Esophagus


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Interior surfaceof stomach

p g

Chief cells

Smallintestine

Epithelium

Stomach

Sphincter

Parietal cell

Pepsinogen and HClare secreted.

HCl convertspepsinogen to pepsin.

Pepsin activatesmore pepsinogen.

Chief cell

Folds ofepithelialtissue

Pepsin

Sphincter

Pepsinogen

HCl

H+Cl

Parietal cells

Mucus cells

Gastric gland

1

2

2

3

3

1

5m


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Chemical digestion - STOMACH

Pepsin will digest protein into short polypeptides tomake easier for the protein to undergo furtherdigestion in the small intestine.

pepsin

Protein ------------ > short polypeptides

Contraction of the muscles in stomach will aids inchemical digestion.

The stomach will mix the food boluses with the gastricjuice , forming a mixture called chyme.


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Chemical digestion SMALL INTESTINE

The first portion of the small intestine is the duodenum,

where acid chyme from the stomach mixes with digestivejuices from the pancreas, liver, gallbladder, and the smallintestine itself.

The epithelial lining of the small intestine is called thebrush border that released enzymes.

Chyme entering the duodenum will trigger the release of

pancreatic juice.

The enzymes in the pancreatic juice break downcarbohydrates, proteins, fats and nucleic acids


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1. Protein digestion

Trypsin

Chymotrypsin

Protein ----------------------- > smaller polypeptides

Carboxypeptidase

Aminopeptidase Brush border enzyme

Dipeptidase

Small polypetides ------------------------- > Amino acids


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2. Carbohydrate digestion

Pancreatic amylase

Polysaccharides -------------------- > di/mono saccharides

Disaccharides brush border

Disaccharides ---------------------- > monosaccharides


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3. Nucleic acid digestion

Pancreatic nucleases

DNA & RNA-------------------- > nucleotides

IntestinalnucleasesNucleotides ---------------------- > bases / sugar


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4. Fat digestion

Bile saltsFat globules ------------------- > Fat droplets (Emulsified)

PancreaticlipaseFat droplets ------------------- >fatty acids + glycerol


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For fat digestion, a process called emulsificationhappens in the smallintestine. This process functionsin accelerating fat digestion.

Fats are triglycerides (not water-soluble). In thechyme, they will clump to form fat globules

As the fat globules move in the intestinal wall, themovement of the muscle layers breaks apart the fatglobules into small droplets that get coated with bilesalts.


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Bile salts are negatively charged, making the dropletsrepel each other (separated with each other) and forman emulsion.

Emulsion droplets, which are separated, give fatdigesting enzyme lipase a greater surface area to acton.

By the time peristalsis has moved the chyme mixturethrough the duodenum, chemical digestion of ourmeal is just about to complete.

Fig

. 41-13

Oral cavity,

Carbohydrate digestion

P l h id Di h id

Protein digestion Nucleic acid digestion Fat digestion


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Oral cavity,pharynx,esophagus

Stomach

Lumen ofsmall intes-tine

Epitheliumof smallintestine(brushborder)

Polysaccharides

Smaller polysaccharides,maltose

Polysaccharides

Maltose and other

disaccharides

Disaccharides

Proteins

Small polypeptides

Pepsin

Pancreatic amylases

Salivary amylase

Disaccharidases

Monosaccharides

Small peptides

Amino acids

Amino acids

Polypeptides

Smallerpolypeptides

Pancreatic trypsin andchymotrypsin

Pancreatic carboxypeptidase

Dipeptidases, carboxypeptidase,and aminopeptidase

DNA, RNA

Pancreaticnucleases

Fat globules

NucleotidesFat droplets

Nucleosides

Nitrogenous bases,sugars, phosphates

Nucleotidases

Nucleosidasesandphosphatases

Glycerol, fattyacids, monoglycerides

Bile salts

Pancreatic lipase

(starch, glycogen) (sucrose, lactose)

Fig. 41-13a


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Oral cavity,pharynx,

esophagus

Stomach

Lumen ofsmallintestine


Carbohydrate digestion

Polysaccharides

Smaller polysaccharides,maltose

Polysaccharides

Maltose and otherdisaccharides

Disaccharides

Pancreatic amylases

Salivary amylase

Disaccharidases

Monosaccharides

(starch, glycogen) (sucrose, lactose)

Protein digestion


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Stomach



Proteins

Polypeptides

Smallerpolypeptides

Pancreatic trypsin andchymotrypsin

Pepsin

Dipeptidases, carboxypeptidase,and aminopeptidase

Monosaccharides

Small polypeptides

Amino acids

Pancreatic carboxypeptidase

Amino acids

Small peptides

Fig. 41-13c


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Nucleic acid digestion

DNA, RNA

Nucleotides

Pancreaticnucleases

Nucleosidasesandphosphatases

Nucleosides

Nucleotidases

Nitrogenous bases,sugars, phosphates

Fig. 41-13d


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Fat digestion

Fat globules

Fat droplets

Pancreatic lipase

Bile salts

Glycerol, fatty

acids, monoglycerides


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Absorption in the Small Intestine

The small intestine has a huge surface area, due to

villiand microvillithat are exposed to theintestinal lumen

The enormous microvillar surface greatlyincreasesthe rate of nutrient absorption

Fig. 41-15


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Muscle layers

Microvilli (brushborder) at apical(lumenal) surface

Vein carrying blood

to hepatic portal vein

Villi

Intestinal wall

Key

Nutrientabsorption

Largecircularfolds

Bloodcapillaries

Epithelialcells

Villi

Lymph

vessel

Basalsurface

Lacteal

Epithelial cells

Lumen

Fig. 41-15b Microvilli (brushborder) at apical


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) p(lumenal) surface

Key

Nutrientabsorption

Bloodcapillaries

Epithelialcells

Villi

Lymphvessel

Basal

surface

Lacteal

Epithelial cells

Lumen


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Each villus contains a network of blood vessels and a

small lymphatic vessel called a lacteal

After glycerol and fatty acids are absorbed by

epithelial cells, they are recombined into fats withinthese cells

These fats are mixed with cholesterol and coatedwith protein, forming molecules calledchylomicrons, which are transported into lacteals

Fig. 41-16Lumenof smalli i

Triglycerides


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intestine

Lacteal

Chylomicron

Phospholipids,cholesterol,and proteins

Triglycerides

MonoglyceridesFatty acids

Epithelialcell


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Amino acids and sugars pass through the epithelium

of the small intestine and enter the bloodstream

Capillaries and veins from the lacteals converge in

the hepatic portal vein and deliver blood to theliver and then on to the heart


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Hormonal ControlFour hormones altogetheri. Gastrin

ii. Cholecytoskinin (CCK)

iii. Secretin

iv. Enterogastrone

Fig. 41-14

Gallbladder

Liver

Bile


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Secretinand CCK

Stomach

+

Duodenum of

small intestine

Gastrin

Secretin

Pancreas

CCK

CCK

Key

Stimulation

Inhibition

+

+

++


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Hormonal control

Gastrin (from stomach) stimulates the production ofgastric juice.

CCK (from duodenum) stimulates the release ofdigestive enzymes from the pancreas and bile saltsfrom the bladder

Secretin (from duodenum) stimulates the release ofbicarbonate from the pancreas

Enterogastrone (from duodenum) inhibits peristalsisand acid secretion from the stomach slowingdigestion of fat


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Vertebrate digestive system Most herbivores lack enzyme that digest cellulose in

the vegetation cell wall, so they depend onmicroorganisms role to aid in their digestion.

Ruminants such as cows and other herbivores, theyhave multiple stomach chambers in which cellulose isslowly broken down.


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Ruminant digestive system-cow The first chamber contains of a rumen and a smaller

chamber called reticulum and the second portionconsists of two additional chambers called the

omasum and abomasum.

The breakdown of cellulose in tough plant materialshappens in the first and second stomach chamberwhere bacterial symbionts release digestive enzymes todigest the nutrients in cellulose.


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Ruminant digestive system-cow The cow will then regurgitates and rechews the

contents of the first sac before swallowing again.

This process is called rumination. This action exposes

more surface area for the enzymes to react, resulting inmore nutrients to be released for the hosts benefit.

In the omasum water is absorbed

In the abomasum, digestion is carried out by the cow'sown enzyme. Absorption completed here.


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Cow digestive system


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Vertebrate digestive system In animals like rodents, horses, deer and rabbits, thedigestion of cellulose is carried out by microorganismsin the enlarged cecum.

Because it is located beyond the stomach,regurgitation is impossible.

Therefore, they swallowed their feces in order for theabsorption process to happen.


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Rabit digestive system The ingested litter is called cecotropes and rabbitsneed to ingest it to avoid malnutrition.

The fecal pellets are dry, consist of undigested fibercompared to the mucus-coated cecotropes.


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Rabit digestive system


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Carnivore & Herbivore digestive system Carnivores usually have large expandable stomach

because it is harder for them to catch prey.

Shorter alimentary canal because it is easier todigest meat as compared to vegetation.

Herbivores generally have longer alimentary canalsthan carnivores, reflecting the longer time neededto digest vegetation

Fig. 41-19


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Cecum

Small intestine

HerbivoreCarnivore

Colon(largeintestine)

StomachSmallintestine


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Tutorial Divide yourself into four groups. Each group will have to answer one

question only and topic will be given as listed below. Discuss andpresent.

Q1: Trace a bite of food through the human digestive tract, listing eachstructure to which it passes.

Q2 : Summarize step-by-step digestion of a

a) carbohydrates b) fat c) proteins

Q3 : How does absorption of fat differ from the absorption of glucose?

Q4 : Give the functions of three types of accessory glands that secretedigestive juices in vertebrate Identify their secretions

Nota Digestion

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