SLE132 BIOLOGY: FORM AND FUNCTION
PRACTICAL TWO
Vertebrate tissue structures
Purpose
To examine some of the common tissue types found in animals.
Pre-practical quiz on Moodle
A quiz will be posted on the SLE132 page of Moodle, in the Resources and Assessments
section, ONE WEEK before the first practical, and will close the day before the practical
class. This quiz will test your knowledge of practical 2 and ensure you have prepared
yourself for the class. You will have two opportunities to complete this quiz so please
ensure you have thoroughly read the practical notes before you attempt the quiz. Your
result from this quiz will contribute 1% of your overall SLE132 mark.
Introduction
As a building is constructed of certain basic structural components such as brick walls,
insulation, electrical wiring, plasterboard and wallpaper, so, too, is an organism made up
of different components. The basic structural components of multicellular organisms are
called tissues. A tissue is a functional collection of cells and associated intercellular
material that is specialised to carry out a specific role. And just as a building may be
divided into a number of different rooms, each of which serves a different function, so
too is a multicellular organism usually composed of a number of different organs, each
of which carries out a specific function.
Four, basic categories of tissue may be recognised in animals:
•
epithelial tissue: e.g., tissue that lines the boundary of the body.
•
connective tissue: e.g., cartilage of the knee.
•
muscular tissue: e.g., bicep muscle.
•
nervous tissue: e.g., neurons of the brain.
Organs may be composed of different arrangements of one or more of these tissues. For
example, the intestine has an inner and an outer layer of epithelial tissue, a very thin layer
of muscle, connective tissue and two other quite thick layers of muscle tissue.
In this practical class, you will examine some of these basic tissues in more detail. You will
look at the gross structure of the tissues (40-100x), as well as the microscopic structure
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SLE132 BIOLOGY: FORM AND FUNCTION
(400x). You will also be able to compare the microscopic structure of a variety of different
forms of the one tissue type.
NOTE: if you have not use a compound microscope before, see Appendix 3.
The tissues that you will examine in this class are taken from vertebrate animals. The same
basic tissue types can be found in invertebrate animals, but some particular features may
vary, (e.g. some forms of muscle tissue are found in earthworms that are not found in
vertebrate animals).
You should remember that cells, tissues, and organs are all three-dimensional structures.
When you look at a slide under a microscope, you are looking at a thin cross-section of
the whole specimen. You must be careful about the way in which you interpret the
sections which you examine before making inferences about the three-dimensional
structure of the original specimens.
Most of the sections you will be looking at are stained with eosin and haematoxylin.
Haematoxylin stains the nuclei purple, eosin stains the rest of the cell pink. Knowing this,
it is easier to find a cell once you have found the nucleus, although not all cells are
sectioned through the nucleus.
Classification of types of vertebrate tissue
Epithelial tissue:
• simple or stratified
• ciliated or non-ciliated
• squamous, cuboidal, columnar, stratified or pseudostratified
Connective tissue:
• loose connective tissue
– may be either reticular and areolar (mainly fibrous), or adipose (fat)
• dense connective tissue
– e.g. ligaments, tendons, (fibrous dense connective tissue) cartilage,
bone (solid matrix connective tissue)
• vascular connective tissue
– e.g. blood and lymph (fluid matrix)
Muscle tissue:
• skeletal muscle
– striated, voluntary muscle
• cardiac muscle
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SLE132 BIOLOGY: FORM AND FUNCTION
– striated, involuntary muscle
• smooth muscle
– non-striated, involuntary muscle
Nervous tissue:
• neurons
• glial cells
Epithelial tissue
Epithelial tissue has the following important features:
 It covers and lines the surfaces of the body;
 It is comprised of closely packed cells and so forms an effective barrier between
the external medium and underlying tissues;
 It possesses little intercellular material;
 It nearly always active, with material passing across or through the epithelial layer
either from underlying tissue (secretion) or from the environment (absorption);
 It is avascular, having no blood vessels within it. Nutrients and waste are
transported to and from epithelia by blood vessels located close to the epithelium,
but within the underlying tissue. Movement of nutrient and waste occurs by
diffusion from the blood vessel to the tissue and vice versa;
 It possesses a basement membrane, usually only seen with the aid of an electron
microscope, between it and the underlying tissue; and,
 It displays a remarkable capacity for regeneration.
Epithelial tissue can be classified hierarchically in the following way:
i.
It may be divided into different types according to the number of layers of cells:
 simple epithelium - consists of one layer of cells. This often lines a lumen (the
inside space of a tubular structure).
 stratified epithelium - consists of multiple layers of cells. Only the bottom layer
touches the basement membrane; the apical surface often faces the lumen.
 (pseudostratified epithelium consists of what appears to be two or more layers
of epithelium, but all cells reach the basement membrane).
ii.
It may be further divided into two groups according to whether or not the cells in
the outer layer of the tissue are ciliated or not.
iii.
It can also be classified according to the shape of the cells. These groups are:
 Squamous (scale-like) - flattened plate-like cells. The nuclei are flattened and
oriented parallel to the cell surface. These cells are well suited to fluid,
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SLE132 BIOLOGY: FORM AND FUNCTION


metabolite or gas exchange between the external medium and the internal
tissues, which lie below the epithelium.
Cuboidal - cells are approximately equal in height, length and width. Nuclei
are normally spherical and found near the cell centre. These cells may be
adapted to play a role in secretion, or may serve for protection.
Columnar - cells are taller than they are wide and usually possess an ovoid,
basally located nucleus. They may be adapted for secretion or absorption and
are well suited to protecting the underlying tissue.
Connective tissue
Connective tissue is a term applied to a basic type of tissue of mesodermal origin which
provides structural and metabolic support for other tissues and organs throughout the
body. All connective tissues have two major constituents: cells and extracellular material
(commonly called the extracellular matrix).
Three basic types of cells are found in connective tissues:
 Fibroblasts - which are responsible for the secretion and maintenance of the
extracellular matrix;
 Adipocytes - which are responsible for the storage and metabolism of fat; and,
 Various cells with defense and immune functions.
The physical properties of each type of connective tissue are mainly determined by the
nature of the extracellular material. This consists of a matrix of organic material called
ground substance within which are embedded a variety of fibres (which are also
secreted by fibroblasts). The components of the ground substance and the nature of the
fibres embedded within it vary between the different types of connective tissue.
The fibres occur in three forms:
 Dense bundles of collagen fibres;
 Reticular fibres which are made of thin collagen but are arranged in networks
instead of bundles; and,
 Elastin fibres.
These fibres are present in all forms of connective tissue but in varying amounts and
proportions. Classification of the basic connective tissues depends on the predominant
type of fibre. Collagenous connective tissues are most common; the density of collagen
fibres and their regularity and arrangement varies according to the function of the tissue.
Reticular connective tissue forms a delicate supporting framework for highly cellular
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organs such as liver, lymph nodes and endocrine glands. Elastic connective tissues
contain large amounts of elastin, which is highly elastic protein that may be arranged
into fibres or continuous sheets.
The general structure of connective tissue is well illustrated by the two forms of (solid)
dense, collagenous connective tissue found in the skeleton of vertebrate animals:
cartilage and bone.
Cartilage
Cartilage is a connective tissue which combines strength with flexibility. It is more flexible
than bone because its extracellular material lacks the mineral salts present in bone.
Cartilage grows from the inside and does not disrupt surface relationships with
surrounding tissues as it grows. This property makes it an important tissue in the rapid
growth phases of an animal. Such a growth phase occurs in the embryonic stage and
thus cartilage serves as the skeletal base for the developing embryo. In the adult human,
cartilage is found in areas where its flexibility is more appropriate than the rigidity of bone.
Bone
Bone is a rigid, dense connective tissue in which the matrix is strengthened by the
deposition of salts such as calcium carbonate and calcium phosphate. Bone gives rigid
support and is the main tissue of the skeleton of adult vertebrates.
Preparation of bone sections has a characteristic difficulty brought about by the hard
mineral components. These parts of the bone make cutting thin sections very difficult,
hence in this practical we use decalcified bone preparations. Because the
decalcification occurs after fixation we are able to retain the original shape and
orientation of the tissue without the supporting calcium matrix. Soft tissues, such as those
you have looked at today, undergo the same fixation process to fix their structural
components in one place, but do not have the added difficulty of the hard mineral
component of bone.
Muscle tissue
Muscle tissue is responsible for movement via contraction of the filamentous proteins,
actin and myosin. Muscles provide support and can also effect other types of movement:
for example, they can propel blood through blood vessels, food or other bodily secretions
through tracts, and also contribute to thermoregulation by the heat caused by the
contractions.
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SLE132 BIOLOGY: FORM AND FUNCTION
Muscle cells are long and narrow, hence the term ‘muscle fibre’ but there are three
different types of muscle tissues that vary in appearance and histology:
 Skeletal muscle - or striated muscle, is attached to bones by tendons (bundles of
collagen fibres). This type of muscle tissue contains multi-nucleated cells and is
controlled voluntarily by the somatic nervous system.
 Cardiac muscle – found in the heart, is also striated. Cardiac muscle is involuntary
and adjoining cells are connected by intercalated disks.
 Smooth muscle - is involuntary and lacks striations. This type of muscle is responsible
for contracting hollow internal organs such as those found in the digestive tract.
Procedure
Biological drawing 1: Epithelial tissue
You are provided with slides showing examples of simple epithelium and stratified
epithelium. Examine these specimens under both low- (10 x objective) and high-power
(40 x objective) magnifications, ensuring that you can identify the major diagnostic
features of each type of epithelium that are evident with light microscopy.
Make simple, high-power drawings of a region of simple epithelium and a region of
stratified epithelium - showing how the cells form layers/structures.
Where possible, label the nucleus, cell membrane, lumen, apical surface, basal
membrane.
Biological drawing 2: A section through cartilage
Examine the slide showing a specimen of cartilage. Make a high-power drawing of a full
region of cartilage; identify and label the following features:
•
The Matrix, which consists of a complex protein called chondrin with a network of
collagen fibres embedded in it;
•
Lacunae are spaces scattered throughout the matrix that in life are filled with fluid;
•
Chondrocytes or cartilage cells found in small groups in the lacunae. These secrete
the matrix of chondrin (chondroitin sulphate) and have dark-staining nuclei;
•
The perichondrium is a thin, fibrous membrane that surrounds the cartilage. The
perichondrium bears numerous blood vessels from which nutritive substances diffuse into
the cartilage; and
•
Adipose tissue is loose connective tissue composed of adipocytes (fat cells).
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SLE132 BIOLOGY: FORM AND FUNCTION
Biological drawing 3: Longitudinal section (LS) of skeletal muscle
Make a high-power drawing of a region of muscle. Label the following features:
•
Parallel arrangement of muscle fibres. Each fibre is a multinucleate cell, formed by
the fusion of many uninucleate cells early in the development of the muscle tissue;
•
The peripherally located nuclei in each fibre;
•
The striations (bands) which run across each fibre. These can be difficult to see in
conventionally stained preparations. Try closing the iris diaphragm as far as possible and
focusing up and down carefully with both the objective lens and the condenser; and
•
The sarcomeres, which are the repeated units along the length of the muscle.
Biological drawing 4: Transverse section ( TS) of an organ
Make a low-power drawing of the section. Identify and label all the different tissues in this
organ. Think about the function of each layer of cells within the tissue. You should be able
to find examples of:
•
Muscle tissue
•
Connective tissue
•
Epithelial tissue
Label the areas of the organ interior and exterior to the body on your tissue map.
Question 1: What type of muscle tissue is associated with the whole organ (from drawing
4)? List three features that distinguish this muscle from skeletal muscle. (3 marks)
Question 2: List similarities and differences between simple and stratified epithelium that
are evident from your drawing 1. (2 marks)
Assessment (8%)
Pre-prac quiz on Moodle: Resources and Assessment section 1% final assessment.
Hand in the following at the end of class: 7% final assessment (31 marks).
1. A biological drawing of simple and stratified epithelial tissue with statements about
the similarities and differences between the two (10 marks).
2. Clearly labelled drawings of cartilage and skeletal muscle with full legends (2 x 6
marks).
3. Clearly labelled tissue map of the organ with full legend (6 marks).
4. Answers to the written question 1 (3 marks).
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