THE GROUND TISSUES

EPITHELIAL TISSUES

CONNECTIVE AND SUPPORTIVE TISSUES

MUSCLE TISSUES NERVOUS TISSUE

HISTOLOGY 1.5.: CONNECTIVE AND SUPPORTIVE TISSUES

A diverse group of tissues that share a common origin from the mesenchyme of the embryo.

They provide structural and metabolic support for other tissues and organs throughout the body, bind the tissues to form organs, and the organs to form organ systems and organism. They contain blood vessels and mediate the exchange of nutrients, metabolites and waste products between tissues and the circulatory system.

THUS:

•

Origin: from the mesoderm

•

Blood supply: densely vascularized

•

Nerve supply: densely innervated

Tissue components of the connective and supportive tissues:

• •

Cells of great variety (fixed and free cell types, see later) Extracellular matrix (ECM) - ground substance - fibers (collagen, elastic, reticular)

Extracellular matrix (ECM) I. THE GROUND SUBSTANCE

A highly hydrated gel in which the cells and fibers are embedded Molecular components: Proteoglycan consisting of dimeric glycosaminoglycans (GAGs) bound to a protein core: chondroitin sulphate

(cartilage, arteries, skin, cornea)

keratane sulphate

(cartilage, bone, cornea)

heparane sulphate

(arteries, lung)

dermatan sulphate

(skin, tendon,ligaments, sclera, lung)

hyaluronic acid

(vitreous humor of eye, synovial fluid, loose CT, skin, cartilage, umbilical cord)

Hydrophilic side chains of GAGs bind a considerable amount of extracellular fluid – water reservoir of the organism.

It is a part of the connective and supportive tissues not visible in

• • •

histological preparates, unless special staining methods are applied: Toluidine-blue PAS staining Alcian-blue staining

Extracellular matrix (ECM) II. CONNECTIVE TISSUE FIBERS

1. COLLAGEN fibers

The most abundant protein in the body.

H.E-stained light micrograph Scanning electron micrograph Two isolated fibers artificially coloured in the computer (SEM) Cross-striation observed in the transmission electron micro scope

Synthesis of collagen fibers

: • • •

Takes place in the rER of fibroblasts: pro-

a

-chains form triple helices These procollagen molecules are transferred to the Golgi complex Tropocollagen molecules are released via exocytosis from Golgi-vesicles

•

Tropocollagen molecules are assembled to form collagen fibers in ECM Properties of collagen fibers

• • • •

Non-branching bundles of changing thickness High tensile strength Poor sheer strength They can be stretched to approximately 5 % of their initial length

SYNTHESIS OF COLLAGEN FIBERS BY FIBROBLASTS

Specific staining for the visualization of collagen fibers: Azan staining stains the collagen fibers selectively in blue colour other tissue componenst are stained red

TYPES OF COLLAGEN FIBERS

Type I.: 2

a

1 chains + 1

a

2 chain the most common (bone, skin,tendon, ligaments) Type II.: 3

a

1 chains predominates in cartilage Type III.: 3

a

1 chains in embryonic CT and skin Type IV.: still unknown composition in the basal laminae of adults Type V.: still unknown composition mainly in the embryo

2. ELASTIC FIBERS

They are present in organs whose normal function requires elasticity in addition to tensile strength Wall of the aorta stained with H.E.

and resorcin fuchsin, specific staining for elastic fibres

SYNTHESIS OF ELASTIC FIBERS:

• • •

Takes place in the rER of fibroblasts (and smooth muscle cells): tropoelastin molecules Transformed to elastin, cross-linked and assembled in the extracellular space Microfibrils secreted prior to elastin provide scaffolding on which elastin forms fibers and sheets PROPERTIES OF ELASTIC FIBERS

•

Occur in the form of individual, branching and anastomosing fibers

•

They can be stretched 2.5 times of their original length to which they return when released

SYNTHESIS OF ELASTIC FIBRES BY FIBROBLASTS

3. RETICULAR FIBERS

Individual collagen fibers coated by proteoglycans and glycoproteins.

This coating causes their affinity for silver salts.

They form delicate flexible networks around capillaries, muscle fibers, nerves, adipose cells and hepatocytes.

Serve as scaffolding in endocrine, lymphatic and blood cell-forming organs.

Reticular fibers around hepatocytes and around kidney tubules (as part of basement membrane)

SYNTHESIS OF RETICULAR FIBRES BY FIBROBLASTS

CELL TYPES OF THE CONNECTIVE TISSUES I.

Fixed cells: fibrocytes fibroblasts

mesenchymal cells adipose cells II. Free cells: macrophages mast cells

plasma cells melanocytes blood-derived cells (

lymphocytes, monocytes, eosinophils,neutrophils)

I.

FIXED CELLS

I.1. Fibrocytes, fibroblasts:

The most common fixed cell types.

Fibroblast:

metabolically more active (see before: synthesis of ECM components) (purple arrows).

Fibrocyte:

metabolically less active, more slender cell and nucleus, less cell organelles (green arrows)

I.

FIXED CELLS

I.2. Mesenchymal cells Pluripotent undifferentiated cells around blood vessels: Serve as a reservoir of cells that can differentiate into other connective tissue cell types.

I. FIXED CELLS:

I.3. Adipose cells: LM TEM SEM

Adipose cells, single or in groups are normal components of the connective tissue (they may form a separate tissue: adipose tissue).

Spherical or polyhedral cells with a large lipid droplet surrounded by a thin cytoplasmic rim.

II. FREE CELLS:

II.1. MACROPHAGES (histiocytes): in non-reactive CT are fixed, upon stimulation they become motile. Phagocytotic cell type, rich in hydrolytic enzymes.

LM SEM TEM

THE MONONUCLEAR PHAGOCYTE SYSTEM

Connective tissue: Liver: Lung: Lymph nodes: Spleen: Bone marrow: Serous cavities: Bone: Central nervous system: Skin: Synovia: histiocytes Kupffer-cell alveolar macrophage free and fixed macrophages free and fixed macrophages fixed macrophages pleural and peritoneal macrophages osteoclasts microglial cells histiocytes type A cells

II.FREE CELLS: II.2. Mast cells: around blood vessels in skin and intestine.

TEM LM LM

Large metachromatic granules: histamine, heparin, serotonin

II. FREE CELLS:

II.3. Plasma cells: In the loose CT of gastrointestinal tract, respiratory system and female reproductive system, in the lymphatic tissue.

They develop from B-lymphocytes, produce antibodies.

LM TEM

II. FREE CELLS

II.4. Melanocytes Large pigmented cells of neural crest-origin. They occur in the dermis of skin, meninges, choroid and iris.

II. FREE CELLS:

II.5. Other free cells temporarily occurring in the CT Lymphocytes, monocytes, granulocytes (in details see the chapter „Blood” later)