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Introduction to Histology - The Federal University of Agriculture

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INTRODUCTION TO HISTOLOGY
By
Dr. A.K. Akinloye
Department of Veterinary Anatomy
University of Agriculture
Abeokuta
1
What is Histology?
пѓ� The term histology, is derived from the Greek
histos, meaning tissue (web) and logia,
knowledge
пѓ� It is, in the strict sense, the knowledge, or
science, of tissues whether they are of plants or
animals
пѓ� is the study of the microscopic anatomy of cells
and tissues of plants and animals
пѓ� It is performed by examining a thin slice (section)
of tissue under a light or electron microscope
2
What is Veterinary Histology?
пѓ�Is the science that focuses on the detailed
morphology of tissues of domestic animals
with the aid of microscope and correlates
specific structures with function
3
What is Veterinary Microanatomy?
пѓ�Involves the examination and architectural
description of the microscopic anatomy of
normal cells of the body and all their
contents and products
4
HISTORY
пѓ�Robert Hooke was the first person to observe cells in
1665. He looked at thin slices of cork under a very
simple microscope. The cork appeared as little boxes
which he called cells
пѓ�In 1883 Mathias Schleiden and Theodor Schwann
proposed that all plants and animals were composed of
cells which were the basic building blocks of life
пѓ�In 1855 Rudolf Virchow stated that new cells arise
from the division of pre-existing cells and that
chemical reactions needed for life occurred inside the
cell
пѓ�All this work led to the formation of the cell theory
5
LEVELS OF ORGANIZATION
пѓ� Cells
пѓ� Tissues
пѓ� Organs
пѓ� Organ Systems
пѓ� Organism
Tissues
Cells
Organs
Organism
Organ
Systems
6
What is a Cell?
пѓ�Is defined as the smallest basic structure
of
higher
organisms
capable
of
independent existence
7
What is a Tissue?
пѓ�Is a group of cells of similar function and
origin that form functional units
8
What is an Organ?
пѓ�An organ represent an even greater
measure of complexity and is composed of
various tissues
9
What is an Organ System?
пѓ�At an even higher level of organization: An
organ system composed of several
organs (such as the gastrointestinal
system, respiratory system, cardiovascular
system, endocrine system)
10
What is an Organism?
пѓ�An organism can be seen to be formed of
different levels of organization, with
increasing levels of complexity and each
of which plays important roles in the
physiological homeostasis of the body
11
Histological Terms
пѓ� The photographing of stained cells is called
Histography or Photomicrography
пѓ� Histopathology is the microscopic study of
diseased tissue
пѓ� The trained scientists who perform the
preparation of histological sections are
Histotechnicians,
Histology
Technicians
(HT), Histology Technologists (HTL), Medical
Scientists, Medical Laboratory Technicians
or Biomedical scientists
пѓ� Their field of study is called Histotechnology
12
Source of Tissue
пѓ�Histological examination of tissues starts
with surgery, biopsy or autopsy (or
necropsy, in the case of animal tissues).
пѓ�Biopsy is an examination of tissue taken from
a living body
пѓ�Autopsy is an examination of post-mortem
tissue
пѓ�Necropsy is an examination of tissue taken
from dead animal
13
Technical Procedure
пѓ�Fixation
пѓ�The
tissues
are
mechanically
and
biochemically stabilized in a fixative. The most
common fixative is neutral buffered formalin
(10% formaldehyde in phosphate buffered
saline (PBS))
14
Technical Procedure
пѓ�Embedding
пѓ�Sectioning
пѓ�Staining
15
Technical Procedure
пѓ�Processing
пѓ�The most common technique is wax
processing. The samples are immersed in
multiple baths of progressively more
concentrated ethanol to dehydrate the tissue,
followed by a clearing agent such as, xylene
or Histoclear, and finally hot molten paraffin
wax (impregnation). During this 12 to 16 hour
process, paraffin wax will replace the xylene:
16
Staining
пѓ� Routine staining is done to give contrast to the
tissue being examined, as without staining it is
very difficult to see differences in cell
morphology
пѓ� Hematoxylin and eosin (abbreviated H&E) are
the most commonly used stains in histology and
histopathology. Hematoxylin colours nuclei blue,
eosin colours the cytoplasm pink
пѓ� To see the tissue under a microscope, the
sections are stained with one or more pigments
17
Special Staining
пѓ�Other compounds used to colour tissue
sections include:
пѓ� safranin
пѓ�oil red o
пѓ�congo red
пѓ�fast green FCF
пѓ�silver salts
пѓ�numerous natural and artificial dyes
18
Histochemistry
пѓ�refers to the science of using chemical
reactions between laboratory chemicals
and components within tissue. A
commonly
performed
histochemical
technique is the Perls Prussian blue
reaction, used to demonstrate iron
deposits
in
diseases
like
Hemochromatosis
19
Immunohistochemistry
пѓ�Recently, antibodies are used to
specifically
visualize
proteins,
carbohydrates and lipids: this is called
Immunohistochemistry
пѓ�Other advanced techniques include in situ
hybridization to identify specific DNA or
RNA molecules, and confocal microscopy
20
Alternative techniques
пѓ� Cryosection - the tissue is frozen and cut using
a cryostat
пѓ� Tissue staining methods are similar to those of wax
sections
пѓ� Plastic embedding is commonly used in the
preparation of material for electron microscopy.
пѓ� Tissues are embedded in epoxy resin.
пѓ� Very thin sections (less than 0.1 micrometers) are cut
using diamond or glass knives.
пѓ� The sections are stained with electron dense stains
(uranium and lead) so that they can be seen with the
Electron Microscope
21
Histological Classification of Animal Tissues
пѓ�There are four basic types of tissues:
пѓ�Epithelial tissue
пѓ�Muscle tissue
пѓ�Connective tissue
пѓ�Nervous tissue
22
Epithelial tissue
пѓ� A sheet of aggregated cells of a similar type
tightly adhered to each other, constitutes the
external and internal surfaces of the body
пѓ� Epithelium: the lining of glands, bowel, skin and
some organs like the liver, lung, kidney,
пѓ� Endothelium: the lining of blood and lymphatic
vessels,
пѓ� Mesothelium: the lining of pleural, and
pericardial spaces,
23
CONNECTIVE TISSUE
пѓ�Connective tissue is responsible for
providing structural support for the tissues
and organs of the body.
пѓ�This mechanical function is important in
maintaining the form of the body, organs
and tissues.
пѓ�Connective tissue is composed of:
пѓ�cells
пѓ�extracellular matrix.
24
MUSCLE TISSUE
пѓ� Muscle tissue is characterized by its welldeveloped properties of contraction
пѓ� Muscle is responsible for the movements of the
body and the various parts of the body
пѓ� Muscle develops from embryonic mesoderm
Muscle is classified into 3 categories according
to morphology and physiological function:
пѓ� Skeletal Muscle
пѓ� Cardiac Muscle
пѓ� Smooth Muscle
25
NERVOUS TISSUE
пѓ� Nervous tissue consists of two groups of cell
types:
пѓ� Nerve cells (Neurons)
пѓ� Neuroglia.
пѓ� nervous tissue is derived from embryonic
neuroectoderm
пѓ� The nervous system is divided anatomically into:
пѓ� Central Nervous System (CNS), consisting of the
brain and spinal cord.
пѓ� Peripheral Nervous System (PNS), consisting of
nerve fibers, aggregates of nerve cells and glia and
ganglia.
26
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