# Anatomy and Physiology of Animals/Body Organisation

!original image by
grrphoto cc
by{width="400"}

In this chapter, the way the cells of the body are organised into
different tissues is described. You will find out how these tissues are
arranged into organs, and how the organs form systems such as the
digestive system and the reproductive system. Also in this chapter, the
important concept of homeostasis is defined. You are also introduced to
those pesky things---directional terms.

## Objectives

After completing this section, you should know:

-   the "Mrs Gren" characteristics of living organisms
-   what a tissue is
-   four basic types of tissues, their general function and where they
    are found in the body
-   the basic organisation of the body of vertebrates including the main
    body cavities and the location of the following major organs:
    thorax, heart, lungs, thymus, abdomen, liver, stomach, spleen,
    intestines, kidneys, sperm ducts, ovaries, uterus, cervix, vagina,
    urinary bladder
-   the 11 body systems
-   what homeostasis is
-   directional terms including dorsal, ventral, caudal, cranial,
    medial, lateral, proximal, distal, rostral, palmar and plantar. Plus
    transverse and longitudinal sections

## The Organisation Of Animal Bodies

Living organisms move, feed, respire (burn food to make energy), grow,
sense their environment, excrete and reproduce. These seven
characteristics are sometimes summarized by the words "MRS GREN".
functions of:

**M**ovement

**R**espiration

**S**ensitivity

**G**rowth

**R**eproduction

**E**xcretion

**N**utrition

Living organisms are made from cells which are organised into tissues
and these are themselves combined to form organs and systems.

Skin cells, muscle cells, skeleton cells and nerve cells, for example.
These different types of cells are not just scattered around randomly
but similar cells that perform the same function are arranged in groups.
These collections of similar cells are known as **tissues**.

There are four main types of tissues in animals. These are:

-   **Epithelial** tissues that form linings, coverings and glands,
-   **Connective** tissues for transport and support
-   **Muscle** tissues for movement and
-   **Nervous** tissues for carrying messages.

### Epithelial Tissues

Epithelium (plural epithelia) is tissue that covers and lines. It covers
an organ or lines a tube or space in the body. There are several
different types of epithelium, distinguished by the different shapes of
the cells and whether they consist of only a single layer of cells or
several layers of cells.

#### Simple Epithelia - with a single layer of cells

!**Diagram 4.1**: Squamous
epithelium

##### Squamous epithelium

Squamous epithelium consists of a single layer of flattened cells that
are shaped rather like 'crazy paving'. It is found lining the heart,
blood vessels, lung alveoli and body cavities (see diagram 4.1). Its
thinness allows molecules to diffuse across readily.
 !**Diagram 4.2**: Cuboidal
epithelium

##### Cuboidal epithelium

Cuboidal epithelium consists of a single layer of cube shaped cells. It
is rare in the body but is found lining kidney tubules (see diagram
4.2). Molecules pass across it by diffusion, osmosis and active
transport.  !**Diagram 4.3**: Columnar
epithelium

##### Columnar epithelium

Columnar epithelium consists of column shaped cells. It is found lining
the gut from the stomach to the anus (see diagram 4.3). Digested food
products move across it into the blood stream. 
!**Diagram 4.4**: Columnar epithelium with
cilia

##### Columnar epithelium with cilia

Columnar epithelium with cilia on the free surface (also known as the
apical side of the cell) lines the respiratory tract, fallopian tubes
and uterus (see diagram 4.4). The cilia beat rhythmically to transport
particles.  !**Diagram 4.5**: Transitional
epithelium

#### Transitional epithelium - with a variable number of layers

The cells in transitional epithelium can move over one another allowing
it to stretch. It is found in the wall of the bladder (see diagram 4.5).


#### Stratified epithelia - with several layers of cells

!**Diagram 4.6**: Stratified squamous
epithelium
Epithelia with several layers of cells are found where toughness and
resistance to abrasion are needed.

##### Stratified squamous epithelium

Stratified squamous epithelium has many layers of flattened cells. It is
found lining the mouth, cervix and vagina. Cells at the base divide and
push up the cells above them and cells at the top are worn or pushed off
the surface (see diagram 4.6). This type of epithelium protects
underlying layers and repairs itself rapidly if damaged.

##### Keratinised stratified squamous epithelium

Keratinised stratified squamous epithelium has a tough waterproof
protein called **keratin** deposited in the cells. It forms the skin
found covering the outer surface of mammals. (Skin will be described in
more detail in Chapter 5). 

### Connective Tissues

Blood, bone, tendons, cartilage, fibrous connective tissue and fat
(adipose) tissue are all classed as connective tissues. They are tissues
that are used for supporting the body or transporting substances around
the body. They also consist of three parts: they all have cells
suspended in a ground substance or **matrix** and most have **fibres**
running through it.

#### Blood

Blood consists of a matrix - plasma, with several types of cells and
cell fragments suspended in it. The fibres are only evident in blood
that has clotted. Blood will be described in detail in chapter 8.

#### Lymph

Lymph is similar in composition to blood plasma with various types of
white blood cell floating in it. It flows in lymphatic vessels.

#### Connective tissue 'proper'

!**Diagram 4.7**: Loose connective
tissue
Connective tissue \'proper\' consists of a jelly-like matrix with a
dense network of collagen and elastic fibres and various cells embedded
in it. There are various different forms of 'proper' connective tissue
(see 1, 2 and 3 below).

##### Loose connective tissue

Loose connective tissue is a sticky whitish substance that fills the
spaces between organs. It is found in the dermis of the skin (see
diagram 4.7).

##### Dense connective tissue

Dense connective tissue contains lots of thick fibres and is very
strong. It forms tendons, ligaments and heart valves and covers bones
and organs like the kidney and liver. 

#### Adipose tissue

Adipose tissue consists of cells filled with fat. It forms the fatty
layer under the dermis of the skin, around the kidneys and heart and the
yellow marrow of the bones.

!**Diagram 4.8**:
Cartilage

#### Cartilage

Cartilage is the 'gristle' of the meat. It consists of a tough
jelly-like matrix with cells suspended in it. It may contain collagen
and elastic fibres. It is a flexible but tough tissue and is found at
the ends of bones, in the nose, ear and trachea and between the
vertebrae (see diagram 4.8). 

#### Bone

Bone consists of a solid matrix made of calcium salts that give it its
hardness. **Collagen** fibres running through it give it its strength.
Bone cells are found in spaces in the matrix. Two types of bone are
found in the skeleton namely **spongy** and **compact bone**. They
differ in the way the cells and matrix are arranged. (See Chapter 6 for
more details of bone).

### Muscle Tissues

Muscle tissue is composed of cells that contract and move the body.
There are three types of muscle tissue:

!**Diagram 4.9**: Smooth muscle
fibres

#### Smooth muscle

Smooth muscle consists of long and slender cells with a central nucleus
(see diagram 4.9). It is found in the walls of blood vessels, airways to
the lungs and the gut. It changes the size of the blood vessels and
helps move food and fluid along. Contraction of smooth muscle fibres
occurs without the conscious control of the animal.
 !**Diagram 4.10**: Skeletal muscle
fibres

#### Skeletal muscle

Skeletal muscle (sometimes called **striated**, **striped** or
**voluntary muscle**) has striped fibres with alternating light and dark
bands. It is attached to bones and is under the voluntary control of the
animal (see diagram 4.10).  !**Diagram 4.11**:
Cardiac muscle
fibres

#### Cardiac muscle

Cardiac muscle is found only in the walls of the heart where it produces
the 'heart beat'. Cardiac muscle cells are branched cylinders with
central nuclei and faint stripes (see diagram 4.11). Each fibre
contracts automatically but the heart beat as a whole is controlled by
the **pacemaker** and the involuntary **autonomic nervous system**.
 !**Diagram 4.12**: A motor
neuron

### Nervous Tissues

Nervous tissue forms the nerves, spinal cord and brain. Nerve cells or
**neurons** consist of a cell body and a long thread or axon that
carries the nerve impulse. An insulating sheath of fatty material
(**myelin**) usually surrounds the axon. Diagram 4.12 shows a typical
motor neuron that sends messages to muscles to contract.


## Vertebrate Bodies

We are so familiar with animals with backbones (i.e. vertebrates) that
it seems rather unnecessary to point out that the body is divided into
three sections. There is a well-defined **head** that contains the
brain, the major sense organs and the mouth, a **trunk** that contains
the other organs and a well-developed **tail**. Other features of
vertebrates may be less apparent. For instance, vertebrates that live on
the land have developed a flexible neck that is absent in fish where it
would be in the way of the gills and interfere with streamlining.
Mammals but not other vertebrates have a sheet of muscle called the
**diaphragm** that divides the trunk into the chest region or **thorax**
and the **abdomen**.

## Body Cavities

!**Diagram 4.13**: The body
cavities

In contrast to many primitive animals, vertebrates have spaces or **body
cavities** that contain the body organs. Most vertebrates have a single
body cavity but in mammals the diaphragm divides the main cavity into a
**thoracic** and an **abdominal cavity**. In the thoracic cavity the
heart and lungs are surrounded by their own membranes so that cavities
are created around the heart - the **pericardial cavity**, and around
the lungs -- the **pleural cavity** (see diagram 4.13).


## Organs

!**Diagram 4.14**: Cells, tissues and organs forming the digestive
system

Just as the various parts of the cell work together to perform the
cell's functions and a large number of similar cells make up a tissue,
so many different tissues can "cooperate" to form an organ that performs
a particular function. For example, connective tissues, epithelial
tissues, muscle tissue and nervous tissue combine to make the organ that
we call the stomach. In turn the stomach combines with other organs like
the intestines, liver and pancreas to form the digestive system (see
diagram 4.14). 

## Generalised Plan Of The Mammalian Body

!**Diagram 4.15**: The main organs of the vertebrate
body

At this point it would be a good idea to make yourself familiar with the
major organs and their positions in the body of a mammal like the
rabbit. Diagram 4.15 shows the main body organs. 

## Body Systems

Organs do not work in isolation but function in cooperation with other
organs and body structures to bring about the MRS GREN functions
necessary to keep an animal alive. For example the stomach can only work
in conjunction with the mouth and oesophagus (gullet). These provide it
with the food it breaks down and digests. It then needs to pass the food
on to the intestines etc. for further digestion and absorption. The
organs involved with the taking of food into the body, the digestion and
absorption of the food and elimination of waste products are
collectively known as the digestive system.

### The 11 body systems

1.  Skin

    :   The skin covering the body consists of two layers, the
        **epidermis** and **dermis**. Associated with these layers are
        hairs, feathers, claws, hoofs, glands and sense organs of the
        skin.
2.  Skeletal System

    :   This can be divided into the bones of the skeleton and the
        joints where the bones move over each other.
3.  Muscular System

    :   The muscles, in conjunction with the skeleton and joints, give
        the body the ability to move.
4.  Cardiovascular System

    :   This is also known as the circulatory system. It consists of the
        heart, the blood vessels and the blood. It transports substances
        around the body.
5.  Lymphatic System

    :   This system is responsible for collecting and "cleaning" the
        fluid that leaks out of the blood vessels. This fluid is then
        returned to the blood system. The lymphatic system also makes
        antibodies that protect the body from invasion by bacteria etc.
        It consists of lymphatic vessels, lymph nodes, the spleen and
        thymus glands.
6.  Respiratory System

    :   This is the system involved with bringing oxygen in the air into
        the body and getting rid of carbon dioxide, which is a waste
        product of processes that occur in the cell. It is made up of
        the trachea, bronchi, bronchioles, lungs, diaphragm, ribs and
        muscles that move the ribs in breathing.
7.  Digestive System

    :   This is also known as the **gastrointestinal system**,
        **alimentary system** or **gut**. It consists of the digestive
        tube and glands like the liver and pancreas that produce
        digestive secretions. It is concerned with breaking down the
        large molecules in foods into smaller ones that can be absorbed
        into the blood and lymph. Waste material is also eliminated by
        the digestive system.
8.  Urinary System

    :   This is also known as the **renal system**. It removes waste
        products from the blood and is made up of the kidneys, ureters
        and bladder.
9.  Reproductive System

    :   This is the system that keeps the species going by making new
        individuals. It is made up of the ovaries, uterus, vagina and
        fallopian tubes in the female and the testes with associated
        glands and ducts in the male.
10. Nervous System

    :   This system coordinates the activities of the body and responses
        to the environment. It consists of the sense organs (eye, ear,
        semicircular canals, and organs of taste and smell), the nerves,
        brain and spinal cord.
11. Endocrine System

    :   This is the system that produces chemical messengers or
        hormones. It consists of various **endocrine glands** (ductless
        glands) that include the pituitary, adrenal, thyroid and pineal
        glands as well as the testes and ovary.

## Homeostasis

All the body systems, except the reproductive system, are involved with
keeping the conditions inside the animal more or less stable. This is
called **homeostasis**. These constant conditions are essential for the
survival and proper functioning of the cells, tissues and organs of the
body. The skin, for example, has an important role in keeping the
temperature of the body constant. The kidneys keep the concentration of
salts in the blood within limits and the islets of Langerhans in the
pancreas maintain the correct level of glucose in the blood through the
hormone insulin. As long as the various body processes remain within
normal limits, the body functions properly and is healthy. Once
homeostasis is disturbed disease or death may result. (See Chapters 12
and16 for more on homeostasis).

## Directional Terms

!**Diagram 4.16**: The directional terms used with
animals{width="522"}
!**Diagram 4.17**: Transverse and longitudinal sections of a
mouse
In the following chapters the systems of the body in the list above will
be covered one by one. For each one the structure of the organs involved
will be described and the way they function will be explained.

In order to describe structures in the body of an animal it is necessary
to have a system for describing the position of parts of the body in
relation to other parts. For example it may be necessary to describe the
position of the liver in relation to the diaphragm, or the heart in
relation to the lungs. Certainly if you work further with animals, in a
veterinary clinic for example, it will be necessary to be able to
accurately describe the position of an injury. The terms used for this
are called **directional terms**.

The most common directional terms are **right** and **left**. However,
even these are not completely straightforward especially when looking at
diagrams of animals. The convention is to show the left side of the
animal or organ on the right side of the page. This is the view you
would get looking down on an animal lying on its back during surgery or
in a post-mortem. Sometimes it is useful to imagine 'getting inside' the
animal (so to speak) to check which side is which. The other common and
useful directional terms are listed below and shown in diagram 4.16.

  Term                    Definition                                                       Example
  ----------------------- ---------------------------------------------------------------- -----------------------------------------------------------
  Dorsal                  Nearer the back of the animal than                               The backbone is dorsal to the belly
  Ventral                 Nearer the belly of the animal than                              The breastbone is ventral to the heart
  Cranial (or anterior)   Nearer to the skull than                                         The diaphragm is cranial to the stomach
  Caudal (or posterior)   Nearer to the tail than                                          The ribs are caudal to the neck
  Proximal                Closer to the body than (only used for structures on limbs)      The shoulder is proximal to the elbow
  Distal                  Further from the body than (only used for structures on limbs)   The ankle is distal to the knee
  Medial                  Nearer to the midline than                                       The bladder is medial to the hips
  Lateral                 Further from the midline than                                    The ribs are lateral to the lungs
  Rostral                 Towards the muzzle                                               There are more grey hairs in the rostral part of the head
  Palmar                  The \"walking\" surface of the front paw                         There is a small cut on the left palmar surface
  Plantar                 The \"walking\" surface of the hind paw                          The pads are on the plantar side of the foot

Note that we don't use the terms **superior** and **inferior** for
animals. They are only used to describe the position of structures in
the human body (and possibly apes) where the upright posture means some
structures are above or superior to others.

In order to look at the structure of some of the parts or organs of the
body it may be necessary to cut them open or even make thin slices of
them that they can be examined under the microscope. The direction and
position of slices or sections through an animal's body have their own
terminology.

If an animal or organ is sliced lengthwise this section is called a
**longitudinal** or **sagittal section**. This is sometimes abbreviated
to LS.

If the section is sliced crosswise it is called a **transverse** or
**cross section**. This is sometimes abbreviated to TS or XS (see
diagram 4.17). 

## Summary

-   The characteristics of living organisms can be summarised by the
    words "**MRS GREN**."
-   There are 4 main types of tissue namely: **epithelial, connective,
    muscle** and **nervous tissues**.
-   **Epithelial tissues** form the skin and line the gut, respiratory
    tract, bladder etc.
-   **Connective tissues** form tendons, ligaments, adipose tissue,
    blood, cartilage and bone, and are found in the dermis of the skin.
-   **Muscular tissues** contract and consist of 3 types: **smooth,
    skeletal and cardiac**.
-   Vertebrate bodies have a **head, trunk** and **tail**. Body organs
    are located in **body cavities**. 11 body systems perform essential
    body functions most of which maintain a stable environment or
    **homeostasis** within the animal.
-   **Directional terms** describe the location of parts of the body in
    relation to other parts.

## Worksheets

Students often find it hard learning how to use directional terms
correctly. There are two worksheets to help you with these and another
on tissues.

Directional Terms Worksheet
1

Directional Terms Worksheet
2

Tissues Worksheet

## Test Yourself

1\. Living organisms can be distinguished from non-living matter because
they usually move and grow. Name 5 other functions of living organisms:

:   1\.
:   2\.
:   3\.
:   4\.
:   5\.

2\. What tissue types would you find\...

:   a\) lining the intestine:
:   b\) covering the body:
:   c\) moving bones:
:   d\) flowing through blood vessels:
:   e\) linking the eye to the brain:
:   f\) lining the bladder:

3\. Name the body cavity in which the following organs are found:

:   a\) heart:
:   b\) bladder:
:   c\) stomach:
:   d\) lungs:

4\. Name the body system that\...

:   a\) includes the bones and joints:
:   b\) includes the ovaries and testes:
:   c\) produces hormones:
:   d\) includes the heart, blood vessels and blood:

5\. What is homeostasis?

6\. Circle which is correct:

:   a\) The head is cranial \| caudal to the neck
:   b\) The heart is medial \| lateral to the ribs
:   c\) The elbow is proximal \| distal to the fingers
:   d\) The spine is dorsal \| ventral to the heart

7\. Indicate whether or not these statements are true.

:   a\) The stomach is cranial to the diaphragm - true \| false
:   b\) The heart lies in the pelvic cavity - true \| false
:   c\) The spleen is roughly the same size as the stomach and lies near
    it - true \| false
:   d\) The small intestine is proximal to the kidneys - true \| false
:   e\) The bladder is medial to the hips - true \| false
:   f\) The liver is cranial to the heart - true \| false

/Test Yourself Answers/

## Websites

-   Animal organ systems and homeostasis

Overview of the different organ systems (in humans) and their functions
in maintaining homeostasis in the body.

<http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookANIMORGSYS.html>

-   Wikipedia

Directional terms for animals. A little more detail than required but
still great.

<http://en.wikipedia.org/wiki/Anatomical_terms_of_location>

## Glossary

-   Link to
    Glossary

