Review of histology

1. Histology

2. Introduction
 Definition of Histology : to study the fine structure
associated with its function in the human body.
Contents: cells (basic units of structure) and intercellular
substance

 Tissues (epithelial, connective, muscle and nervous)
 more than 2 kinds of tissues
 Organs
  organs with related functions
 Systems

4. Epithelial Tissue (ET)
 Characteristics:
1. Membrane-like structure: crowded cells with very scanty
intercellular substance.
2. Polarity : basal end rests on the basement membrane (BM),
 the distal end associates with functions, e.g. absorption
(microvilli by EM, striated boarder by LM), secretion (gland:
goblet cell, acinus) and etc.
3. Avascular: in general ET has no blood vessels, may be rich
in nerve endings.

5. Classification of Epithelia
 1. The simple epithelium (each cell rests on BM) mainly
associated with lubrication, transport, absorption or
secretion function. It can be divided into:
 (1). Simple squamous epithelium (e.g.endothelium)
 (2). Simple cuboidal epithelium ( renal tubules)
 (3). Simple columnar epithelium (intestinal inner-surface)
 (4). Pseudostratifird (cilliated) columnar epithelium
 ( trachea inner-surface)

8.  2. The stratified epithelium ( multi-layers contain deep,
middle and superficial layers, only the basal cells rest on
BM), mainly associated with protection function. Based on
the shape of the suface cells, it can be divided into:
 (1)Stratified squamous epithelium : non-keratinized
(esophageal inner-surface), keratinized (skin epidermis)
 (2) Stratified cuboid epithelium
 (3) Stratified columnar epithelium
 (4) transitional epithelium (urothelium): relaxed 
stretched, may be pseudostratified.

11. Contacts between adjoining epithelial cells on the
lateral side
 From free end towards basal there are 4 types of contacts between
adjoining cells on lateral side of the simple columnar epithelium:
 1. Tight junctions (belt type): some fusions of cell membrane prevent
large molecules from passing through intercellular space.
 2.Intermediate junction (belt type): the cytoplasmic filaments are
anchored to the dense material on cytoplasmic faces of the cell
membrane to form terminal web, functioning as support.
 3. Desmosome (plague type): it is a spot-weld type in cell to cell
attachment. Some filaments connect the desmosome plaques across
the intercellular space and intermediate line (fusion of the cell coats,
glycocalyx ).

12.  4.Gap junction (spot type ) : a series of microwholes pass through the
narrow intercellular space, about 3nm. It is an area of low electrical
resistance to ionic flow, involved in cell to cell communication.
 The combined above tight, intermediate and gap junctions may
constitute a junctional complex, although the tight junction, desmosome
and gap junction may exist independently.
 Notice: these junctions also exist in each kind of primary tissues, not
limited in the epithelial tissue.

14. Key points
 1. How to distinguish/identify the following epithelial tissues,
e.g. the simple squamous epithelium, simple columnar
epithelium, pseudostratified cilliated columnar epithelium,
stratified squamous epithelium and trasitional epithelium.
 2. The structure and function of the tight junction, gap
junction and desmosome.

15. Connective tissue (CT)
 Characteristics:
 1.The cells are scattered with no polarity.
 2. A great amount of intercellular substance (IS) may
differentiate into fibers and ground substance (GS,
amorphous).
 3. Always accompanied by blood vessels.
 4. Associated with connection, support, nutrition and
defense functions.

16. Classification: based on the character of IS in CT
General CT Support CT Embryonic CT
Fluid GS with fibers Solid GS with fibers Fluid GS with few fibers
Fibrous (loose /dense) Cartilage Mesenchyme
Adipose Bone
Reticular

17. The structure of mesenchyme
Mesenchymal cells: stallate-shaped, undifferentiated type (with
differentiation capacity) with pale stained nucleus, distinct nucleuolus
and weak basophilia cytoplasm.
In the adult the mysenchyme still retained in some regions, e.g.around the
small blood vessels
The mesenchymal cells can differentiate into the blood vessel
endothelium, smooth muscle and each kind of CT, if required.

19. Structure of loose connective tissue
There are 6 kinds of cells and 3 kinds of fibers.
Cells:
1. Fibroblast (fibrocyte, inactive type ) and 2. Plasma cell are both of
protein-secreting type, with developed mitochondria, Golgi complex,
especially the granular endoplasmic reticulum, resulting in cytoplasm
basophilia. The protein products of the fibroblast are fibers (collagen,
elastic and reticular) and ground substance; the protein products of
plasma cell are antibodies/ immunoglobulins, such as IgG, IgE and etc.
3. Macrophage: function as scavenger by the lysosome and involve
immune response by direct way, e.g. process antigen as the antigen
presenting cell (APC) and by indirect way through mediators secreted
from the macrophage, e.g. IL1and CSF respectively stimulate T cell
and neutrophils to proliferate.

20.  4. Mast cell: there are lots of heterochromatic granules (the staining
color of granules is different from the color of the dye used ) in
cytoplasm. The granules contain heparin, histamine, etc.
The histamine can enhance permeability of the capillary. During the
receptor, IgE of the mast cell combined with its specific sensitive
antigen may result in anaphylaxis, such as asthma, urticaria, hay fever,
and etc
5. Wandering leucocytes: e.g. the lymphocyt, eosinophil, and etc.
increase in number during inflammation.
The plasma cell, macrophage, mast cell and wandering leukocyte
function as immune cells.
6. Fat cell (adipose cell) : synthesis and store of lipid (nutrition).

22. Fibers: function mainly as support
1. Collagen fiber (white fiber): with tensile strength
The collagen fiber consists of collagen synthesized by the fibroblast. The
fibril is made up of pre-collagen molecules arranged in stepwise way,
appeared as striated with EM. The striation with periodicity of 64 nm can
be identified as collagen fiber.
The wavy bundle of collagen fiber can be stained with eosin in red color.
2. Elastc fiber (yellow fiber): with elasticity decreased with aging
The elastic fiber consists of elastin synthesized by the fibroblast. The
thicker elastic fiber also can be stained with eosin.
3. Reticular fiber (argyrophilia fiber): The reticular fiber is a premature type
of the collagen fiber coated by a layer of glycoprotein. The reticular fiber
can be demonstrated by silver staining.

23. Ground substance (GS): also secreted from the fibroblast, homogenous
(amorphous) under LM and involved in barrier and nutrition function.
The GS consists of proteoglycans (polysaccharide) and glycoprotin.
1. Proteoglycans: the major component of proteoglycans is the large
molecule of hyaluronic acid (bottle brush type) with negative charge to
combine Na+ and H + OH- , besides a small amount of tissue fluid.
The ultrastructure of GS functions as a molecular sieve to prevent
from dispersion of deleterious materials/ bacteria.
2. Glycoprotein: only a small amount
The glycoprotein contains fibronectin, laminin,etc, providing substantial
base for cell recognition, adhesion and migration.

25. Key points
 1.The fine structure associated with function of the fibroblast, plasma
cell, macrophage and mast cell.
 2. How to identify fibrocyte, plasma cell, macrophage and mast cell
respectively.
 3. How to distinguish collagen fibers from elastic fibers.