Animal Physiology: Functions and Processes

Animal Physiology

ZLY 306

•

Animal physiology

 is the study of animal

functions and bodily processes.

Course Outline

•

Feeding Mechanisms

-

Filter feeders, Deposit feeders, Fluid feeders,

Carnivores and Herbivores.

-

Digestion in Mollusc, herbivores, insects and

mammals

-

Cellulose digestion in herbivores and wood

eating animals

Text books

•

Basic Animal Physiology by William Ose Odiete

•

Integrated Principles of Zoology by Hickman

Roberts, Keen Larson,L’Anson Eisenhour

Introduction

•

All organisms require energy in order to maintain

their complex structure, development and daily

activities.

•

The sun is the ultimate source of energy for all

life on the earth’s surface.

•

However you  will agree that not all organisms

are able to utilise the energy from the sun

directly

•

Hence we require a medium which will allow

us to utilise the energy from the sun.

•

How?

•

AUTOTROPHIC ORGANISM 

– require only

inorganic compounds absorbed from their

surroundings to provide raw materials for

synthesis and growth.

Table of Contents

•

Nutritional Requirements

•

Food Types

•

Feeding Mechanisms

•

Overview of Food

Processing

(Click on topics to access slides)

Animals are heterotrophs that require food for

fuel, carbon skeletons, and essential

nutrients.

By definition a 

heterotroph

 is an organism that

obtains organic food molecules by eating

other organisms or their by-products.

A nutritionally adequate diet

satisfies three needs:

1.

Fuel

 , chemical energy; for the cellular work of the

body.

2.

Organic Raw Materials

 in the form of carbon

skeletons used in biosynthesis

3.

Essential Nutrients

 which are substances that the

animal cannot make for itself from any raw material

and must be obtained from food in a prefabricated

form

Food Types

Animals fit into one of three dietary categories:

1.

Herbivores

, animals that eat mainly

autotrophs (plant and algae)

2.

Carnivores

, animals that eat other animals

3.

Omnivores

, animals that regularly consume

animals as well as plant or algal matter

However, most animals are 

opportunistic feeders

; eating

foods that are outside their main dietary category

when these foods are available.

(Click on highlighted words for links to web resources)

Diverse feeding adaptations have evolved among animals.

Four main groups of mechanisms by which animals ingest

food:

•

Suspension-feeders

: (filter feeders) many

aquatic animals that sift small food particles

from the water.

•

Substrate-feeders

 (deposit-feeders): animals

that live in or on their feed source, eating their

way through the food

•

Fluid-feeders

: animals that survive by sucking

nutrient-rich fluids from a living host

•

Bulk-feeders

: animals that eat relatively large

pieces of food

The four stages of food processing:

1.

Ingestion

: the act of eating

2.

Digestion

: enzymatic breakdown of the

macromolecules of food into their monomers

3.

Absorption

: body cells take up nutrients such as

amino acids and simple sugars from the digestive

system

4.

Elimination

: occurs as undigested material passes

out of the digestive system as feces

WHO EATS WHAT?

•

 Dogs eat bones

•

 Goats eat leaves

•

Cat eat rats

•

Rat eats fish

•

Fowls eat grains

•

Hawks eat chicken

•

Animal foods are often so bulky to be

absorbed directly. Hence different food habits

have been developed by different animals in

order to transform it into a form at which it

can be utilised

•

All food categories are based on dietary habits

Categories of feeding

•

HERBIVORES – Feed  mainly on plant life

•

CARNIVOROUS - feed mainly on herbivores

and other carnivores

•

OMNIVOROUS – eats both plants and animals

•

SAPROPHAGOUS – animals feed on decaying

organic matter

Suspension/Filter feeder

•

A filter feeder is any animal that obtains food by filtering

water for nutritious particles.

•

A filter feeder is also known as a suspension feeder, Examples

of a filter feeder include, flamingos, clams,  sponges and blue

whales.

•

A filter feeder uses some mechanism, like a filter basket, or

baleen (as in baleen and blue whales) to gather aquatic prey

•

 usually plankton

•

These are siphoned it to their mouths for consumption and

digestion.

•

Sharks that eat plankton have

specialized feeding mechanisms. The

basking shark eats plankton by

swimming at the surface with its

mouth open.

•

The water rushes through the mouth

and out the gills. Gill rakers at the

entrance to the gill catch and filter

out all of the plankton (small

organisms that float in the water).

•

Gill rakers,  are numerous in the

basking shark, but are shed in the

winter when the food supply of

plankton is scarce

Gill raker

Filter feeding

•

Many bivalve molluscs, for example the mussel

Mytilus edulis

, feed on particles suspended in the

surrounding water.

•

They do this by 

filter feeding

.

The mussel lives in the intertidal zone, attached

to a solid surface by threads secreted by the

muscular foot, so it is not able to move around

like some related molluscs.

•

Filter feeding in bivalves

•

When it is covered by seawater, the two shells

open slightly, allowing water to enter the body

of the mollusc, which is protected by the shell

when the tide is out. From this extend a pair

of short tubes, also called siphons.

•

 A current of water is drawn in through one

opening, then across the gills and out through

another opening. This movement is powered

by the combined effect of 

many cilia: hair-like

projections

 from cells lining the spaces inside

the mussel's shell.

•

The gills hang down like net curtains, trapping small particles

•

as well as extracting dissolved oxygen from the water.

•

 Cilia on the filaments send a current of mucus down each strand

and then onward towards the mouth. Any particles of a suitable

size which are trapped are then digested.

•

Incidentally, this is not unlike the means by which foreign

particles including bacteria are trapped in mucus in the human

respiratory system, and then taken into the stomach and

digested

Feeding structures in Amphioxus

Deposit/Substrate feeders

•

Deposit feeders obtain food particles by sifting through soil,

vaguely analogous to the way that filter feeders get food by

filtering water.

•

Prominent examples are earthworms, other annelids such as

polychaete worms, and fiddler crabs

•

Deposit feeding is a feeding strategy that only works in fertile

areas with a lot of pre-existing life.

•

The top layer of soil is targeted, typically within six inches of the

surface, as this is the soil most likely to contain food particles that

haven't been completely broken down yet.

•

Biologists call these food particles 

detritus

. After detritus has been

broken down to a chemically neutral state, it becomes known as

humus

.

.

Fluid feeders

•

Animals that obtain their nutrients by consuming

fluids from another organisms  are called fluid

feeders.

•

 Animals which practice fluid feeding include

hummingbirds spiders, aphids,  ticks, mosquitos,

leeches. bees and butterflies.

•

Fluid feeding is defined as getting your nutrients

by consuming the fluids of another organism

Fluid Feeders

•

 Fluid feeding is obviously a successful mode,

and has probably been around since insects

first crawled onto land about 428 million years

ago, during the Devonian period

•

The most despised fluid feeders

are those that feed on human

blood, spreading infections and

some of the worst diseases .

•

 Mosquitos  spread malaria,

which afflicts half a billion people

every year and kills between one

and three million

•

Fluid feeders need some way

to pierce the protective wall

(skin or plant walls) getting in

the way of the fluid,

•

 then some proboscis-like

appendage for sucking out all

the fluids.

•

 Aphids are specialized in

doing this with plants, which is

why they can be found in such

numbers on certain plants,

especially those that produce

an abundance of sweet fluid

.

Bulk feeders

•

Bulk feeding is one of the feeding strategies used

by animals to obtain food. Bulk feeding is

exhibited by animals that eat pieces of other

organisms or swallow them whole.

•

Bulk feeding is one of the most common feeding

strategies among animals, especially among

macroscopic animals, with which we are most

familiar. Many herbivores, carnivores, and

omnivores employ bulk feeding

Bulk feeders

•

Some bulk feeders, such as cows, are

specialized for consuming plants, and have

large barrel-like stomachs to break down

difficult-to-digest grass.

•

Others, such as felines and canids are

specialized carnivores, evolved to hunt down

living  organisms, kill them, and consume the

fresh kill.

I. Mechanisms for dealing with small

particles.

–

A

. Pseudopodial 

(e.g., many protozoans). Pseudopods

consist of fingerlike projections of the cell membrane

and its contents (cytoplasm) that surround and engulf

food.

–

B. 

Ciliary

 (e.g., sponges, bivalve mollusks). Cilia are

minute hairlike projections of cell membranes that, by

concerted beating in wave rhythm, set up water

currents or physically move food particles.

–

C. 

Tentacular

 (e.g., certain sea cucumbers). Tentacles

are slender, flexible organs on the head. They may

function in sensory perception and in actually

securing food.

–

D. 

Mucoid

 (e.g., many snails, such as 

Vermetus

). In this

case, the food particles become attached to a sticky

mucous sheet secreted by special cells.

–

E. 

Muscula

r (e.g., certain coelenterates). In the

jellyfish 

Rhizostoma

, pulsations of the bell-shaped

body draw water and food in through perforations in

the arms, then expel the water after the food is

removed.

–

F. 

Setous

 (e.g., many small crustaceans, such as

copepods). Setae are bristle like projections of the

cuticle and are found on the appendages of many

invertebrates.

II. Mechanisms for dealing with large

particles or masses.

–

A. For swallowing inactive food, such as bottom

deposits (e.g., many polychaete worms, some

fishes).

–

B. For scraping and boring (e.g., some gastropod

and bivalve mollusks).

–

C. For seizing prey.

•

1. For seizing and swallowing only (e.g., 

Hydra

,

many polychaete worms, many lower

vertebrates).

•

2. For seizing and masticating (e.g., Crustacea,

mammals).

•

3

. For seizing followed by external digestion (e.g., some

starfishes, spiders). (In such cases, the secretory and

absorptive surfaces of the digestive system may be

applied to the food by everting [i.e., turning inside out]

the stomach, a method employed by starfish.

•

4. Alternatively, digestive enzymes may be injected into

the prey, liquefying the tissues, which may then be

ingested by the predator. This mechanism is found in

spiders.)

III. Mechanisms for taking in fluid or

soft tissues.

–

A. For piercing and sucking (e.g., leeches, mosquitoes).

–

B. For sucking only (e.g., many flies, butterflies).

–

C. For absorption through surface of body (e.g., various

invertebrates feeding on decaying organic matter, internal

parasites such as tapeworms, which lack a digestive tract).

•

A different classification, often used, rests on the

nature of the behaviour for procuring food:

•

A. 

Filter

 feeders strain food from the surrounding

medium more or less indiscriminately.

•

B. Selective feeders analyze the environment with their

sense organs before aiming feeding responses at

chosen items.

•

Some feeding patterns, however, cannot be easily

fitted into either of these classes alone; spiders,

for example, sieve prey from the air with webs

but perform directed responses to the insects

trapped.

•

Selective feeding requires good sensory and

nervous equipment and, in most cases,

considerable mobility. It is therefore found mainly

among higher animals.

•

The 

primitive

 sea anemones are selective feeders in that,

capable of paralyzing relatively large prey with their

stinging cells, they do not discharge them until informed by

chemical and tactile senses that prey is present.

•

At the other extreme, whalebone whales are filter feeders,

even though they are 

highly evolved 

mammals. Swimming

at the surface with mouth open, they filter off large

plankton (krill) using several hundred horny plates with

hairlike fringes hanging down from the roof of the mouth;

availability of a rich food source has caused the evolution of

their feeding patterns to diverge widely from that of most

other mammals.

Feeding patterns adopted by species are the

result of evolutionary interplay between

•

 (1) structural properties inherent in their

phylogenetic line

•

(2) the ecological situations to which they

have been exposed.

•

These interactions are too complex to make

generalizations profitable.

•

The best approach is to study each species as

a separate case in the light of its entire biology

Herbivores

•

There are 3 groups of animals that have

sucessfully adopted herbivores feeding habit.

•

These are

•

Gastropod mollusca

•

Insects

•

Herbivorous mammals

•

Hebivores have chewing , biting rasping or

grazing mouthparts for dealing with plant

materials

•

As different as the methods of nutrition may be among snails (there

are herbivores, omnivores and carnivores),

•

These methods can be retraced to common organs. To feed, snails

use an organ, that is present in most molluscs and unique in the

animal kingdom: The radula or a rasp tongue.

•

 The radula is a chitinous ribbon used for scraping or cutting food.

•

 Basically, it consists of an elastic band  and armed numerous

transverse and longitudinal rows of chisel – like teeth (with a large

number of chitin teeth.) for cutting plant parts.

•

To feed, this rasping band is used like the transportation band of a

bucket excavator, food particles rasped of are transported back into

the gullet. The bow-shaped jaw is used to cut off food particles.

•

•

A snail feeding on leaf of green food pulls the leaf into

its mouth using the radula and then cuts it off with the

jaw.

•

Similar to other animals' teeth, the radula as well is

adapted strongly to the respective methods of

nutrition.

•

While plant-eating species, have broad and blunt

radula teeth, predatory snails usually have dagger or

lance shaped radula teeth, enabling them to hold the

prey and also to rip flesh from it.

•

The African giant  land snail Archachatina achatina

have about 200 longitudinal  rows with about 100

teeth per transverse row in the radula.

•

The radula is constantly worn out as the gastropod

grazes on plant materials hence they are replaced from

the posterior long coiled part.

•

Marine gastropods feed on algae on rock surfaces

•

Terrestrial snails  feeds on leaves and succulent fruits

Assignment 2

•

What are the adaptations for herbivore life in

i). a gastropod mollusc ?

•

ii). a grasshopper?

•

Radula Types

.

•

Two salivary gland open into the gullet, which are used to digest

food for the first time. A snail's stomach is a simple blind sac, in

which the digestion by saliva  continues.

•

The main part of digestion takes place in the main digestive gland, a

specialised gland taking most of the place in the visceral sac. It is

also called a hepatopancreas, being both liver and pancreas.

•

While usually the liver only produces digestive fluids and stores

nutrients, in a snail's hepatopancreas also digestion takes place.

Also, lime is gained from the food, later transported via the blood

stream to the shell-building cells of the mantle.

Grazing snails

 a. After material is scraped off the substrate

      it is passed into the digestive tract going

      first down the esophagus into the stomach

       then into the intestine.  The intestine is

       very long.

This not only facilitates the breakdown of

cellulose, but also the up- take materials.

   b.  Because cellulose is rather indigestible,

this

 process requires a long processing

. time

Buccal mass

•

The buccal mass is the first part of the digestive system, and

consists of the mouth and pharynx. The mouth includes a 

radula

,

and in most cases, also a pair of jaws.

•

The pharynx can be very large, especially in carnivorous species.

•

Ducts from large 

salivary glands

 lead into the mouth, and the

oesophagus also supplies the digestive enzymes that help to break

down the food.

•

Many carnivorous species have developed a 

proboscis

, containing

the oral cavity, radula, and part of the oesophagus. At rest, the

proboscis is enclosed within a sac-like sheath, with an opening at

the front of the animal that resembles a true mouth. When the

animal feeds, it pumps blood into the proboscis, inflating it and

pushing it out through the opening to grasp the gastropod's prey. A

set of retractor muscles help pull the proboscis back inside the

sheath once feeding is completed.

•

Several herbivorous species, as well as carnivores that

prey on sessile animals, have also developed simple

jaws, which help to hold the food steady while the

radula works on it.

•

 The jaw is opposite to the radula and reinforces part of

the foregut

•

The purely carnivorous the diet, the more the jaw is

reduced.

Herbivores (insects)

Insects that are herbivores : Grasshoppers,

Crickets, Termites and ants

•

The mandibles and maxilla have a strongly

toothed and heavily chitinized edges bearing

pointed cusps for cutting  and flat cusps for

crushing vegetable matter

•

Prescence of muscular  gizzard or

proventriculus for crushing ingested plant

materials

Strong mandibles in Grasshopper

mandibles

Herbivorous mammals

These include

•

      Elephants (Proboscidae)

•

       Horses and Zebra (perissodactyl)

•

       Sheeps, goats, pigs deer, cattle (artiodactyls)

•

       Grasscutters and rabbits (rodents)

•

Cows lack the upper incisor

teeth; a position replacedby a

horny pad acting as a

template for cutting grass and

any other vegetable matter

•

Cannies are absent and a long

space (diastema) before the

premolars and molars

•

These have flat surfaces with

cutting ridges or cusps for

thorough chewing and

grinding to break cellulose ,

cell wall of plants

•

In rodentsthe incisors

are very large, curved

and chisel like for

gnawing food

•

The remaining incisors

canine and some

anterior premolars are

missing thus leaving a

large gap in front of

the cheek teeth.

•

Teeth: 

The dentition of herbivores is quite varied depending

on the kind of vegetation a particular species is adapted to

eat.

•

Many herbivore's incisors are not pointed, but flat edged.

The molars, in general, are squared and flattened on top to

provide a grinding surface.

•

The molars cannot vertically slide past one another in a

shearing/slicing motion, but they do horizontally slide across

one another to crush and grind.

•

These are useful tools for biting, crushing and grinding.

•

Jaws: 

Herbivore's jaws, as well as the jaws of human beings

cannot shear.

•

The angle of the mandible has expanded to provide a broad

area of attachment for the well-developed masseter and

pterygoid muscles (these are the major muscles of chewing in

plant-eating animals).

•

The 

masseter and pterygoid muscles 

hold the mandible in a

sling-like arrangement and swing the jaw from side-to-side.

•

 Accordingly, the lower jaw of plant-eating mammals has a

pronounced sideways motion when eating. This lateral

movement is necessary for the grinding motion of chewing.

Digestion

•

An herbivore's saliva (as well as man's) is alkaline,

containing carbohydrate digestive enzymes.

•

Because plant foods are difficult to break down

due to lots of indigestible fiber, herbivores have

significantly longer and in some cases, more

elaborate guts than carnivores.

•

For herbivores as well as humans, The stomach

volume represents about 21-27% of the total

volume of the human GI tract. the pH of the

stomach ranges from 4 to 5 with food in the

stomach.

•

Man's, as well as other herbivore's small intestines are

10 to 12 times the length of their body, and winds itself

back and forth in random directions.

•

This is a tool designed for keeping food in it for long

enough periods of time so that all the valuable

nutrients and minerals can be extracted from it before

it enters the large intestine.

•

Herbivores large intestines, or colons, are puckered

and pouched, and run in three directions (ascending,

traversing and descending), designed to hold wastes

that originally were foods high in water content. This is

so that the fluids can be extracted from these wastes

Carnivores

•

Carnivores capture and ingest other animals

(bulk feeders).

•

 Scavengers among them feed on dead

animals and do not normally pursue to

capture prey.

•

Arnivores ingest over large prey hence feeding

is Intermittent (irregular)

•

Carnivore must posses  means to  capture and

 seize

•

This requires speed consider crocodile and

Lion

•

Saltwater 

crocodiles

 are capable of explosive

bursts of 

speed

 when launching an attack

from the 

water

•

Distensible wide mouth and foregut

•

Vertebrate carnivores  use strong, sharp and

pointed teeth and claws for prehension

•

Suitable teeth for crushing and dismembring

prey

•

Teeth:

•

The teeth of a carnivore are discretely spaced

so as not to trap stringy debris.

•

 The incisors are short, pointed and prong-like

and are used for grasping and shredding. The

canines are greatly elongated and dagger-like

for stabbing, tearing and killing prey.

•

The molars (carnassials) are flattened and triangular

with jagged edges such that they function like serrated-

edged blades.

•

Because of the hinge-type joint, when a carnivore

closes its jaw, the cheek teeth come together in a back-

to-front fashion giving a smooth cutting motion like the

blades on a pair of shears.

•

These are tools that are useful for the task of piercing

into flesh

•

Jaws:

. carnivore's jaws move up and down with

minimal sideways motion. The jaw joint is a simple

hinge joint lying in the same plane as the teeth.

•

The "angle" of the mandible (lower jaw) in carnivores is

small. This is because the muscles (masseter and

pterygoids) that attach there are of minor importance

in these animals.

•

The lower jaw of carnivores cannot move forward, and

has very limited side-to-side motion.

•

These are tools that are useful for the tasks of

shearing, ripping and tearing flesh and swallowing it

whole.

•

Digestion: 

A carnivore  saliva does not contain

digestive enzymes.

•

Carnivores have a simple (single-chambered) stomach.

The stomach volume of a carnivore represents 60-70%

of the total capacity of the digestive system.

•

Since most carnivores average a kill only about once a

week, a large stomach volume is advantageous

because it allows the animals to quickly gorge

themselves when eating, taking in as much meat as

possible at one time which can then be digested later

while resting.

•

 A carnivore's stomach also secretes powerful digestive

enzymes with about 10 times the amount of

hydrochloric acid than a human or herbivore.

•

The pH is less than or equal to "1" with food in the

stomach, for a carnivore. E. Coli bacteria, salmonella,

campylobacter, trichina worms [parasites] or other

pathogens would not survive in the stomach of a lion

or other carnivore due to such high stomach acidity.

•

A carnivore's or omnivore's small intestine is three to

six times the length of its trunk. This is a tool designed

for rapid elimination of food that rots quickly.

•

Man's, as well as other herbivore's small intestines are

10 to 12 times the length of their body, and winds itself

back and forth in random directions. This is a tool

designed for keeping food in it for long enough periods

of time so that all the valuable nutrients and minerals

can be extracted from it before it enters the large

intestine.

Assignment 3

•

What are the tools found in other smaller

animals for capturing ingesting digesting and

assimilating food during feeding?

•

Crabs

•

Cray fish

•

Catfishes

•

Toads and frogs