Cytology, embryology, General histology презентация

Definition
Tissues -- groups of cells organised to perform one or more functions.

Please, note and write down:
4 basic types of tissues:
Epithelial (Epithelium)
Connective
Muscular
Nervous

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There are two main types of Epithelial Tissue:
1. Covering and lining
2. Glandular

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Covering and lining epithelia lie on the free surface:
- cover outer body surfaces (i.e. skin) and
- line inner body surfaces:
-- lumen of hollow organs (i.e. intestine)
-- cavities (i.e. peritoneal cavity),
-- blood vessels,
-- ducts (in glands),
-- tubules (in kidneys).

Characteristics
Consists of cells only (there is no matrix).
Cells tightly appose in sheets.
Cells rest on the basement membrane.
Note: connective tissue lie under the basement membrane

Importance :
Epithelium create a selective barrier between the organism and its external environment:
any substances must pass through the epithelial cell, not between them.

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Two types of surface epithelia:
epithelium is simple, when it is one cell layer thick
and stratified when it is two or more cell layer.

Maine functions
protection
diffusion or absorption or excretion = exchange

Another functions
transport (along free surface)
secretion
sensation.

Characteristics.
3. polarity - cells have 2 surfaces :
the apical or free surface - towards the lumen or outside world
the basal surface, closest to the basement membrane
4. Epithelia are avascular, do not contain blood vessels, but are nourished by diffusion of substances from capillaries in underlying connective tissue.
5. It is frequently mitotically active

Shape of cells:
Squamous.
Cuboidal.
Columnar.

!!! In case of stratified epithelia the second name describes the shape of the top layer of cells.

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The morphology of the epithelium
correlates with its function:
- Epithelia involved in secretion or absorption are typically simple.
-- Stratified epithelia usually impermeable and protective

Simple Squamous Epithelium
lines blood vessels (endothelium), closed body cavities (mesothelium), alveoli in the lungs
Function: controls diffusion, osmosis and filtration

Simple Cuboidal Epithelium
lines tubules and ducts

Simple Columnar
Lines stomach, intestine.
Usuallly has microvilli = finger-like projections of cell membrane
Function – absorption.

Pseudostratified
Single cell layer
All cells attach to basement membrane but not all reach free surface
Nuclei at varying depths

Stratified squamous Epithelium
Several cell layers thick,
Surface cells flat
2 types:
Keratinized = surface cells dead and filled with keratin
Example - Skin
Nonkeratinized = no keratin in moist, living cells at apical surface
Example - Cornea

Stratified Cuboidal Epithelium
Surface cells cuboidal
Lie in sweat gland ducts, male urethra

Stratified Columnar Epithelium
Surface cells columnar
Line very large ducts of gland, male urethra

Multilayered
Surface cells varying in shape from round to flat if stretched
Lines hollow organs of the urinary tract that expand from within
Transitional Epithelium

Please, note and write down:
!! The morphology of an epithelium often correlates with its function:
- Epithelia involved in secretion or absorption are typically simple.
The height of the cell often reflects the level of secretory or absorptive activity.
-- Stratification of the epithelium usually correlates with impermeability and protection

GLANDULAR EPITHELIA
- form glands.
Function – secretion = synthesis and releasing of substances.

GLANDULAR EPITHELIA
- Secretion – cyclic process.
4 phases:
1. diffusion of metabolites into the cell
2. synthesis proper
3. releasing of substances from the cell
4. cell restoration

There are two types of gland in the body: exocrine and endocrine.
Exocrine glands secrete through ducts or directly onto an surface (skin or cavity of inner organs).
Endocrine secrete hormones into the bloodstream.

By cell number
Unicellular
Ex.: Goblet cell
secrete mucus and lubricate small and large intestine, respiratory tract
Multicellular

2 portions of gland: Parenchyma and Stroma
Parenchyma - the epithelial, secreting cells of the gland which perform the gland's essential function.
Stroma - supporting cellular framework of connective tissue which contains blood vessels and nerves and gives structure to the gland.

Two type of secretion
of Exocrine Glands
Mucous - viscous, slimy
(mucus lines and lubricates cavities of all inner hollow organs)
Serous - watery
Ex.: exocrine pancreas (enzymes), sweet gland,
Fluid in serous cavities, joints.

Classification of Exocrine Glands by type of secretion
3. Mixed (Seromucous)
Ex.: Submandibular and sublingual salivary glands; trachea and bronchi.

3 types of secretion mechanism:
Merocrine (= eccrine)
Apocrine
Holocrine

Merocrine (most common):
Secretory granules fuse with the apical plasma membrane and are secreted into the lumen of the gland.

Apocrine
(ex.: lactating mammary gland (fat droplet))
small portion of apical cytoplasm with secretory granules is pinched off

Holocrine - ex: Sebaceous glands of skin
the cell fills with its secretory product (lipids),
dies and disintegrates, releasing its product.

Mechanisms of Glandular Secretion

A Structural Classification of Exocrine Glands