Digestive

System

Components and Purpose

The digestive system is generally made up of organs that are involved in two main functions:

The mechanical and chemical digestion of food

The absorption of nutrients

The digestive system of animals is used to gain nutrients from an outside source, unlike plants which can generate glucose through photosynthesis

Though mostly similar, digestive systems of different animals do have some unique features

Earthworm Digestive System

An earthworm’s digestive system is basically a

tube that runs through its body. Food is moved

by muscular contractions and most of the

mechanical digestion happens in a

specialized structure called the gizzard

The gizzard is a thick muscular structure that

grinds the food with small grit ingested by the

earthworm

Fish Digestive System

The fish digestive system has a unique structure

called the pyloric caecum. This is located

between the stomach and the intestines.

It aids in the chemical digestion of food

through enzymes. It is also thought to be a

point of absorption of nutrients.

Frog Digestive System

Frogs have a digestive system that consists of

a mouth with unique structures. They have a

sticky tongue that can be used to catch prey

and two sets of teeth to keep prey from

escaping. The eyes of the frog help to push

the prey down to the esophagus when

swallowing

The waste matter

of a frog exits

through an

opening called

the cloaca

Human Digestive System

Similar to other organisms, the human

digestive system is composed of various

organs that form a tract through the body

which function to mechanically and

chemically digest the food for absorption.

Accessory organs (where food does not pass)

are also part of the digestive system.

salivary

glands

esophagus

tongue

pharynx

esophageal

sphincter

stomach

pancreas

pancreatic duct

large intestines

(green)

rectum

anus

gall bladder

bile duct

duodenum

pyloric sphincter

liver

small intestines

Mechanical Digestion

Mechanical digestion involves the physical breakdown of food into smaller pieces which will increase surface area for chemical digestion

Teeth chew and grind food as the initial mechanical breakdown before being moved down through the esophagus through peristalsis

The stomach then churns to aid in further physical breakdown of food

Chemical Digestion

Chemical digestion further breaks food down through chemical means

The stomach releases hydrochloric acid, along with enzymes such as pepsin to help chemically break down food into smaller base components

Accessory organs like the liver and pancreas help to produce liquids that aid breakdown in the small intestines

Absorption and Elimination

Once food has been sufficiently broken down

through mechanical and chemical digestion,

it can be absorbed as nutrients by the body

The majority of absorption happens in the

small intestines through specialized structures

known as villi and microvilli

Villi and microvilli increase surface area for

absorption

Absorption and Elimination

Absorption and Elimination

Water is then

absorbed by the large

intestines before

waste is stored and

then eliminated

through the rectum

and anus