Explore
For Enterprise
Join for Free
Log In

艺术与人文
商务
计算机科学
数据科学
信息技术
健康
数学和逻辑
个人发展
物理科学与工程
社会科学
语言学习
学位
证书

浏览 Coursera 的全部课程

浏览
搜索
企业版
登录
免费加入

02.04 Digestion and Excretion

Loading...

Bugs 101: Insect-Human Interactions

阿尔伯塔大学

4.8（20 个评分） | 5.4K 名学生已注册

Of all the animals on earth, which are the strongest for their size? What about the fastest? Who were the first animals to evolve flight? Insects take all of these titles and more! As the most abundant animals on the planet, insects and other arthropods affect our lives in so many ways. From beneficial interactions like pollination and biological pest control, to the transmission of life threatening diseases; this course will teach you about the big ways that these little arthropods impact our lives. In Bugs 101: Insect-Human Interactions, you will be plunged into the diverse (and sometimes alien) world of arthropods to learn how they work, what they do, and how insects and humans interact every day. After completing this course, you will be able to: Describe the evolutionary relationships between insects and their arthropod relatives Inventory major groups of insects and their diversity Demonstrate evolutionary adaptations that make insects successful Discuss insect biology and human-insect interactions Evaluate positive and negative interactions between insects and humans Propose practical and symbolic roles insects play in human societies

查看授课大纲

您将学习的技能

Biology, Entomology, Science, Ecology

审阅

4.8（20 个评分）

5 stars
18 ratings
3 stars
1 ratings
2 stars
1 ratings

VI

Aug 13, 2019

A study which is highly enjoyable and useful for professionals

CS

Aug 15, 2019

Overall a great course. Would, and have, recommend to others.

从本节课中

Module 02: The Business of Being an Insect Part 1

What makes an insect an insect? How do these strange creatures operate? This module begins to uncover the inner workings of insects, starting with the digestive and circulatory systems.

02.04 Digestion and Excretion10:11

教学方

Dr. Maya Evenden
Professor of Entomology

脚本

In this lesson, we'll switch our attention to

what goes on inside an insect's body,

starting with the digestive and excretory system.

As with many animals,

insects have a complete digestive tract.

This means, that the digestive system consists of

a single complete tube known as the alimentary canal.

The alimentary canal is only a single cell layer thick,

and rests on a thin fibrous

extracellular matrix of tissue,

called the basement membrane,

surrounded by the gut muscles.

The structure of the alimentary canal varies

with the insects diet.

Insects that feed on solid food typically have a wide,

short, and straight alimentary canal.

Strong muscles and specialized membranes

line the inner cavity to protect the gut from abrasions.

Insects that feed on liquid diets

have alimentary canals that are long,

narrow and convoluted, to

maximize the surface area in contact with the liquid.

Liquid diets have a high water content,

so fluid feeding insects have mechanisms to

remove excess water and concentrate the nutrients.

The nutritional properties of an insect's diet

also require modifications to the alimentary canal.

For example, plant feeding insects need to process

large amounts of nutrient poor food

in the form of leaves and stems,

which are typically continuously available.

There is therefore little need for

the alimentary canal to have high storage capacities.

So the digestive tracks of

plant feeding insects are usually short.

Conversely, a diet of animal tissue is nutrient rich,

and its availability is intermittent.

Insects that feed on other animals tend to require

a large food storage capacity in

a long alimentary canal to

sustain themselves when resources are scarce.

The insect digestive system is

divided into three easy to remember

regions: Foregut, midgut and hindgut.

These regions are separated by valves and

sphincter muscles that control the movement of food.

Each region of the alimentary canal

has specialized functions.

The foregut is where food is

ingested and physically broken down,

and may also be the site of food storage.

Most digestion and absorption

of nutrients occurs in the midgut.

While absorption of water,

salts and remaining nutrients occurs in the hindgut.

The function and structure of

the three gut regions differ.

The foregut and hindgut have

a cuticular lining that must be shared with each molt.

While in the midgut,

where nutrient absorption occurs,

there is no cuticular lining.

To see how the insect digestive system works,

we follow the journey of a piece of solid food

through the alimentary canal of a typical insect,

starting at the foregut.

The foregut is the anterior portion

of the alimentary canal,

and is where ingestion, storage,

transport and the physical breakdown of food occurs.

It has a protective cuticular lining

that is shed at each molt.

Food, manipulated or chewed by the mouthparts,

is passed into the mouth,

where digestion begins with

the aid of enzymes in the saliva,

produced by salivary glands.

The food forms of bolus within the muscular pharynx,

after which it moves through

the esophagus and into the crop,

where it can be stored temporarily.

The food then moves into the proventriculus,

where it can be mechanically broken down even

further by rows of cuticular teeth.

This is especially important for insects that feed on

tough or fibrous materials such as leaves.

Not all insects have

a proventriculus lined with tooth-like structures,

especially if the diet consists solely

of liquid food such as nectar or blood.

After being shredded in the proventriculus,

bits of food then pass on into the midgut.

This is the major site of

digestion and nutrient absorption in insects,

where carbohydrate and protein polymers and insect food

are broken down into simple constituents by enzymes.

For optimal enzymatic activities,

conditions in the midgut are usually maintained at

a pH between 6 and 7.5.

Nutrients from digested food are

selectively absorbed by the midgut epithelium,

and transported around the insect's body,

by the insect's blood.

Nutrient absorption is maximized

by an increase in midgut surface area,

caused by out pockets at the anterior end of the midgut,

known as the gastric cecae.

The midgut has no cuticular lining,

but the midgut epithelial cells

secrete a cocktail of digestive enzymes,

and also a structure called the peritrophic membrane.

This structure protects

the delicate midgut epithelium from damage,

and also compartmentalizes the digestive process.

This structure generally moves with

the food bolus and is

excreted with the solid waste material.

Therefore, the midgut epithelial cells need to secrete

the peritrophic membrane continuously

while the insect is actively feeding.

Some liquid feeders, such as

the Hemiptera and Thysanoptera or thrips,

lack a protective peritrophic membrane in the midgut.

Because a liquid diet is less

likely to damage the gut lining.

Nutrient absorption of liquid diets is

facilitated by an extracellular lipoprotein membrane,

called the Perimicrovillar membrane.

The insect body often hosts a number of

beneficial microorganisms, known as symbionts.

They can be found all over the insect,

on the surface of the body,

within specialized cells in the body cavity,

and especially within the alimentary canal.

Symbionts that live in

the alimentary canal help with metabolic processes,

and can include bacteria, fungi,

including yeasts,

and tiny single-celled organisms called protests.

Some symbionts help digest material that

insects are unable to handle alone, such as cellulose.

Whereas others synthesize essential vitamins and

amino acids and can even detoxify poisons.

These beneficial symbionts can be transferred

between individual insects via ingestion,

or from mother to offspring through

vertical or transovarial transmission.

Gastric symbionts are not found in predatory insects.

At the junction between the midgut and the hindgut of

most insects are the malpighian tubules,

tubes that are extensions of the hindgut

that permeate into the insect's body cavity.

The primary function of these tubules is

to remove nitrogenous waste products,

and maintain osmo regulatory balance in the insect.

The distal ends of the malpighian tubules

indiscriminately remove substances dissolved

in the insect's blood.

Any waters, sugars, or salts initially removed,

will then be reabsorbed either at the proximal end of

the malpighian tubules or

in the hindgut before excretion.

Osmoregulation is important in all insects,

as desiccation or drying out is a constant risk.

Terrestrial insects excrete nitrogenous wastes

in a highly concentrated forum called uric acid.

This nitrogenous waste has

low toxicity and can be excreted with very little water.

The last region of the alimentary canal is the hindgut,

which concentrates the waste products and absorbs water,

salts, and essential nutrients

from the remainder of the food bolus.

After resorption, everything left in the hindgut is

excreted from the rectum via the anus as frass.

Like in the foregut,

the hindgut has a cuticular lining that

must be replaced when the insect molts.

Digestion is also aided by a structure

located outside of the alimentary canal,

called the fat body.

The fat body is essentially a network of

fatty tissue located throughout

the insect's abdominal cavity.

It helps to metabolize large macro molecules

like fats, proteins, and carbohydrates,

and is also an essential storage organ

from which the insect

draws nutrients during non-feeding parts

of its life cycle.

Such as when a butterfly is in its cocoon.

The fat body can contribute up to 65 percent of

an insect's entire weight and is often

present in large amounts in reproducing females,

migrating individuals, and die imposing insects.

With that, we have come to the end of the lesson on

the insect digestion and excretory systems.

We hope our journey through the gut has

left you well acquainted with the structures

of the insects alimentary canal

and how they vary in different types of insects.

Up next, the circulatory and gas exchange systems.

探索我们的目录

免费加入并获得个性化推荐、更新和优惠。

Coursera 致力于普及全世界最好的教育，它与全球一流大学和机构合作提供在线课程。

© 2019 Coursera Inc. 保留所有权利。

通过 App Store 下载

通过 Google Play 获取

Coursera
关于
管理团队
工作机会
目录
证书
MasterTrack™ 证书
学位
企业版
政府版

社区
Learners
Partners
Developers
Beta Testers
Translators

连接
博客
Facebook
领英
Twitter
Instagram
YouTube
技术博客

更多
条款
隐私
帮助
内容访问
媒体
联系我们
目录
附属公司