BIOLOGY: the study of life
CYTOLOGY: the study of cells emphasizes structure of cells
CELL BIOLOGY: the study of cells emphasizes function, chemistry and molecular aspects
HISTOLOGY: the study of the body’s tissues how tissues are organized into organs
HISTO-PATHOLOGY: the study of abnormal or diseased tissue
ANATOMY: the study of structure
UNIT 2801 – LECTURE 1 – HISTOLOGY (Cell Structure and Function I)
THE CELL
smallest unit of living structure
independent existence
protein, carbohydrate, fat, nucleic acids & inorganic material
2 MAJOR CLASSES OF CELLS
PROKARYOTES
true nucleus – nucleoid is not membrane-delimited
EUKARYOTES
-membrane-bound nucleus
-cytoplasm contains organelles
- only erythrocytes do not have this appearance
UNITS OF MEASUREMENT IN HISTOLOGY
micrometre = 10-6 metres = micron = m
nanometre = 10-9 metres = 1/1000m = nm
most cells = 5m - 20m diameter
red blood cells = 7m
magnification – enlarges something = decrease quality in image
resolving power- ability to tell two close objects apart
HOW WE STUDY CELLS AND TISSUES
FIX to preserve tissue structure
EMBED to stiffen the tissue for cutting
SECTION so that details can be resolved
STAIN to produce contrast within tissue and cells
TISSUE
= an orderly arrangement & distinctive pattern of cells which co-operatively perform a particular function
BASIC TISSUE TYPES
morphology- classification by appearance
e.g.
Skin epithelial tissue – described as flat and numerous layers of cells – stratified squamous epithelium
Muscle – cardiac smooth visceral tissue muscle (location and function)
EPITHELIAL TISSUE
Introduction:
- Epithelium is a tissue that:
o covers the body surfaces  forms a continuous layer – no breaks
o lines internal body cavities (e.g. peritoneal, pleural) - it is termed mesothelium
o Lines tubules (e.g. gastrointestinal tract, blood vessels, kidney tubules) – blood and
lymph vessels - called endothelium.
o forms glands (e.g. exocrine, endocrine)
- Any substance that enters or leaves the internal env. of body must cross and epithelium.
- Epithelia are avascular (lacking blood vessels), but all epithelia "grow" on an underlying layer
of vascular connective tissue.
- It has a high regeneration capacity ranging from a few days (e.g. small intestine lining) to 1
month (e.g. epidermis of skin)
- Able to repair & renew – along base- tiny little cells - stem cells – go through mitosis- dividing
to replace epithelial cells above them.
Structure:
-
Consist of closely apposed cells without intervening intercellular substances.
Cells closely apposed (closely packed) – because mainly their function (protection,
absorption, secretion) relates to their appearance, absorption, – don’t want cells getting
between cells need things to get thru cells or a complete barrier
Function:
Owing to the strategic location of epithelium at the border between the internal and external
environments, the functions of epithelium are many and varied
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protect the internal environment of the body against :
o
mechanical damage
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loss of fluids (desiccation) - waterproofing
o
invasion of foreign bodies
Regulate the movement of material between external and the extracellular fluid of body e.g.
epithelium lining kidney and intestinal tract.  Typically described as ion-transport. All the
substances entering or leaving the body must pass through epithelium and are under its control.
The ion-transporting epithelium may become highly specialized for absorption or excretion.
Secretion of chemicals e.g. sweat, saliva, hormones -- The glandular secretions of the body by
glands (exocrine and endocrine) are mainly a function of specialized epithelium.
Facilitate rapid exchange of materials esp. gases. – Exchange epithelia – usually thin, flattened
cells.
Some epithelia are modified for sensory reception including recognition of sensory stimuli such as
pain or as chemoreceptors (such as taste buds)
Cilia
Goblet
cells
Basal
cells
Basement
membrane
Connective
tissue
Capillaries
Morphological classification:
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no of cell layers – simple (one layer), stratified (lots of layers)
shape of the cells
o squamous (flattened , elongated cells – found in mouth, skin, anus – places of abrasion
and slotthing- off and mechanical damage occurring)
o cuboidal (height and width the same)
o columnar cells (tall columns) the taller the cell is more likely to be involved in absorption
or secretion function (respiratory tract and gastro-intestinal tract/ gut) – shorter more
likely to be involved in mechanical protection
Never get layers of columnar cells – never find stratified columnar epithelium.
Type
Simple squamous epithelium
Histology
layer of flattened, scale- or plate-like cells.
Where found?
large body cavities and heart, blood vessels
and lymph vessels
The nuclei of the epithelial cells are often
flattened or ovoid, i.e. egg-shaped, and they
are located close to the centre of the cells.
Simple cuboidal epithelium
Simple columnar epithelium
Cells appear cuboidal in sections
in small excretory ducts of many glands, the
perpendicular to the surface of the epithelium.
follicles of the thyroid gland, the tubules of
Viewed from the surface of the epithelium they
the kidney and on the surface of the
look like small polygons.
cells are taller than they are wide
ovaries.
The nuclei of cells within the epithelium are
(GIT) from the cardia of the stomach to the
usually located at the same height within the
rectum.
internal surface of the gastrointestinal tract
cells - often close to the base of the cells.
Stratified squamous epithelium
deepest cells – basal cell layer are cuboidal or
columnar in shape- in contact with the
basement membrane
The basal cell layer is followed by layers of
cells with polyhedral outlines.
Close to the surface of the epithelium, cells
become more flattened.
At the surface of the epithelium, cells appear
like flat scales - similar to the epithelial cells of
simple squamous epithelia.
Stratified cuboidal and
columnar epithelia
not common
A two-layered cuboidal epithelium is, for
example, seen in the ducts of the sweat
glands
CONNECTIVE TISSUE
Introduction:

Are animal tissue that supports, connects, and surrounds organs and other body parts e.g lamina
propria, dermis, tendons, adipose, cartilage & bone
- Consists mainly of collagen, elastic and reticular fibres, fatty tissue, cartilage, or bone
- Common features are –
o ground substance - substance (empty space in between full of proteins and enzymes)
o fibers - (thin fibres- elastin, thick- collagen fibers and reticular fibres) – fibres made up of
smaller components fibrils and microfilaments made by fibrobalsts
o cells.  resident cells (Fibrocytes/fibroblasts, Adipocytes (fat cells), macrophages &
mast cells) and immigrant cells (cells that move in and out – from blood usually during
inflammation e.g. neutrophils, eoisnophils, basophils, moncytes, B lymphocytes, plasama
cells and T-lymphocytes)
-
Generally – fibroblast, collagen, amorphous (shapeless) material underneath an epithelium in the
wall of organs.
great diversity in appearance of a connective tissue - morphological diversity
major cell type present - fibroblast – secretes collagen and elastic fibres  long/ large flat cells
Function:

Structural support
o maintenance of the anatomical form of organs and organ systems.
o e.g.
 The connective tissue capsules surrounding organs (such as the kidney, lymph
nodes).
 The loose connective tissue acts to fill the spaces between organs.
 The tendons (connecting muscles to bone)
 elastic ligaments (connecting bones to bones)
 The skeletal tissues (cartilage and bone) are special forms of connective tissue.

Metabolic functions
o serves a nutritive role.
o All the metabolites from the blood pass from capillary beds and diffuse through the
adjacent connective tissue to cells and tissues.
o Similarly waste metabolites from the cells and tissues diffuse through the loose
connective tissue before returning to the blood capillaries.
The adipose tissue (especially that of the hypodermis) serves as an energy store and also provides
thermal insulation. Surplus calories can be converted into lipid and stored in adipocytes.
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Blood components and blood vessels
The hematopoietic tissues (blood-forming tissues) are a further specialized form of connective
tissue. e..g myeloid tissue (bone marrow) and the lymphoid (lymphatic) tissue.
The lining of the blood and lymphatic vessels (endothelial cells) as well as the peripheral blood,
are also specialized forms of connective tissue.
Defensive functions
Various components of the connective tissue play roles in the defense or protection of the body
including many of the components of the vascular and immune systems (plasma cells,
lymphocytes, neutrophils, eosinophils, basophils, mast cells).
-
The various macrophages of the body are also categorized as connective tissue cells.- important
in tissue repair as well as defense against bacterial invasion.
The fibroblasts of connective tissue proliferate in response to injury of organs and migrate to and
deposit abundant new collagen fibers, resulting in the formation of fibrous scar tissue.
Erythrocytes
long extension processcytoplasmic processes- long
flat cells (fibroblasts)produce the fibres of
connective tissue
.
Morphological Classification:
-
loose connective tissue – more cells than fibres  looks pale – can see individual cells e.g.
lamina propria  connective tissue underneath an epithelium
dense connective tissue - lots of cells and lots of fibres
ordered/regular arrangement (tendon or ligament) or irregularly arranged (dermis of skin)
NERVOUS TISSUE
-
The nervous system consists of all nervous tissue in the body.
Functions of Nerve Tissue
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Nervous tissue allows an organism to sense stimuli in both the internal and external environment.
The stimuli are analysed and integrated to provide appropriate, co-ordinated responses in various
organs.
The afferent or sensory neurons conduct nerve impulses from the sense organs and receptors to
the central nervous system.
Internuncial or connector neurons supply the connection between the afferent and efferent
neurons as well as different parts of the central nervous system.
Efferent or somatic motor neurons transmit the impulse from the central nervous system to a
muscle (the effector organ) which then react to the initial stimulus.
Autonomic motor or efferent neurons transmit impulses to the involuntary muscles and glands.
Neurones have long processes, which extend from the part of the cell body around the nucleus,
the perikaryon or soma.
The processes can be divided into two functionally and morphologically different groups,
dendrites and axons.
o Dendrites - darker stained projection – carries impulses to the cell body - Can be multiple.
o Dendrites are part of the receptive surface of the neurone- emerge from the perikaryon
(cell body)
o Dendrites can be smooth, or they can be studded with small, mushroom-shaped
appendages, which are called spines.
o
o
o
axon - clearer projection, carries impulses away from cell body
The axon is the "transmitting" process of the neurone
The axon forms small, bulb-shaped swellings called boutons at the ends (terminal
boutons) or along the course (boutons en passant) of its branches.
CNS
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Nervous tissue of the CNS does not contain connective tissue other than that in the meninges
and in the walls of large blood vessels.
Collagenous fibers or fibrocytes/blasts are consequently not observed
absence of connective tissue- CNS tissue has a very soft, somewhat jelly-like consistency.
CNS tissue contains several types of non-neuronal, supporting cells, neuroglia
PNS
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The PNS comprises all nervous tissue outside the brain and spinal cord.
It consists of groups of neurones (ganglion cells) called ganglia + supporting cells  schwann &
satellite cell, feltworks of nerve fibres, called plexuses, and bundles of parallel nerve fibres that
form the nerves and nerve roots.
Nerve fibres, which originate from neurones within the CNS and pass out of the CNS in cranial
and spinal nerves, are called efferent or motor fibers.
Nerve fibres which originate from nerve cells outside the CNS but enter the CNS by way of the
cranial or spinal nerves are called afferent or sensory nerve fibres.
nerve (neural processes) or ganglion (nerve cell bodies)
nerve cells = neurons
supporting cells in the CNS = neuroglia
supporting cells in the PNS = schwann & satellite cells
MUSCLE TISSUE
- defined by its function – because structurally looks similar

junctions hold muscle cells apposed each other
Dark stained
nucleus
pink stain –
cytoplasmic
extensions
Faint horizontal bars –
delineating the end of the
muscle cell
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easily recognized
muscle cells  in muscle cells are called fibres
cells are elongated (long cytoplasmic extensions) and orientated (lined up in the same direction)
arranged in bundles – all covered in connective tissue
Smooth Muscle Tissue.
- made up of thin-elongated muscle cells, fibres- pointed at their ends
- Has a single, large, oval nucleus.
- Filled with a specialised cytoplasm, the sarcoplasm
- Surrounded by a thin cell membrane, the sarcolemma.
- Each cell has many myofibrils which lie parallel to one another in the
direction of the long axis of the cell.  not arranged in a definite striped
(striated) pattern, as in skeletal muscles - hence the name smooth muscle
- Smooth muscle fibres interlace to form sheets or layers of muscle tissue
rather than bundles.
- location: of hollow organs such as the digestive tract (lower part of the
oesophagus, stomach and intestines), the walls of the bladder, the uterus,
various ducts of glands and the walls of blood vessels .
Functions:
Smooth muscle controls slow, involuntary movements such as the
contraction of the smooth muscle tissue in the walls of the stomach and
intestines.
The muscle of the arteries contracts and relaxes to regulate the blood
pressure and the flow of blood.
Smooth Muscle Tissue
Skeletal Muscle Tissue.
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Most abundant tissue
Attached to and bring about the movement of the
various bones of the skeleton
The whole muscle- enclosed in a sheath of connective
tissue, the epimysium  Sheath folds inwards into the
substance of the muscle to surround a large number of
smaller bundles, the fasciculi.
These fasciculi - consist of still smaller bundles of
elongated, cylindrical muscle cells, the fibres.
Each fibre is a syncytium, i.e. a cell that have many
nuclei.
The nuclei are oval in shaped and are found at the
periphery of the cell, just beneath the thin, elastic
membrane (sarcolemma).
The sarcoplasm also has many alternating light and
dark bands, giving the fibre a striped or striated
appearance (hence striated muscle).
each muscle fibre is made up of many smaller units,
Skeletal Muscle Tissue
the myofibrils.
Each myofibril consists of small protein filaments,
known as actin and myosin filaments.
The myosin filaments are slightly thicker and make up the dark band (or A-band).
The actin filaments make up the light bands (I-bands) which are situated on either side of the dark
band.
The actin filaments are attached to the Z-line. This arrangement of actin and myosin filaments is
known as a sacromere.
Functions :
o
o
Skeletal muscles function in pairs to bring about the co-ordinated movements of the
limbs, trunk, jaws, eyeballs, etc.
Skeletal muscles are directly involved in the breathing process.
Cardiac (Heart) Muscle Tissue.
- Found only in the walls of the heart.
Its fibres , like those of skeletal muscle, have cross-striations and contain
numerous nuclei.
- However, like smooth muscle tissue, it is involuntary.
- Cardiac muscle differ from striated muscle in the following aspects:
o they are shorter,
o the striations are not so obvious,
o the sarcolemma is thinner and not clearly discernible,
o there is only one nucleus present in the centre of each cardiac fibre
o and adjacent fibres branch but are linked to each other by so-called
muscle bridges.
- The spaces between different fibres are filled with areolar connective tissue
which contains blood capillaries to supply the tissue with the oxygen and
nutrients.
Functions of Cardiac (Heart) Muscle Tissue
o
Cardiac muscle tissue plays the most important role in the contraction
of the atria and ventricles of the heart.
Cardiac Muscle tissue
o
It causes the rhythmical beating of the heart, circulating the blood and its contents
throughout the body as a consequence.
ORGANS
= various forms & combinations of the basic tissue types joined together as a functional and anatomical
unit
 Organs have their own blood and neural supply
 epithelial tissue = parenchyma
 connective tissue = stroma
THE PLASMA MEMBRANE (UNIT MEMBRANE)
= selectively permeable sheet like structure encasing the cell
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structural
- It encompasses the cytoplasm – responsible for much of the cells interaction with the outside
world.
- selectively permeable – allows ions and molecules to pass thru and prevents movement of others
= prevent loss of essential components.
- membrane – has transport systems that allow substances that cannot cross the plasma
membrane to pass thru
- also has special receptor molecules that help [prokaryotes detect and respond to chemicals in
their surroundings.
EM reveals the Plasma Membrane as a trilaminar structure (9-11nm wide)
FLUID MOSAIC MODEL
- most widely accepted mode of the membrane structure
= describes the organization of the plasma membrane at the molecular level
= proposes that membranes are lipid bilayers within which proteins float.
FREEZE-FRACTURE ETCHING techniques reveal the molecular structure of the Plasma Membrane
CYTOPLASM
WHAT IS THE FUNCTION OF THE CYTOPLASM?
Provides order for reactions occurring within ground substance
- cytoplasm contains
o enzymes for glycolysis, fatty acid synthesis, reactions of urea cycle, glycogen synthesis
and degradation and protein synthesis
o intermediates of metabolism
o cofactors
CYTOPLASMIC COMPONENTS
ORGANELLES
 membrane-bound (mitochondria & ER)
 non-membranous (ribosomes & centrioles)
INCLUSIONS
 secretory vesicles
 pigment granules
 lipid droplets
 glycogen
CYTOPLASMIC MATRIX
 amorphous, no structure
 soluble electrolytes & molecules
 3-D network thin trabeculae (electron microscope)