Connective and Adipose Tissue

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Functions of Connective Tissue:

• Framework.

• Packing.

• Bricks.

• Mechanical protection.

• Nutrition.

• Defense.

• Repair.

Major Components of Connective Tissue:

A. Ground substance.

B. Fibers.

C. Cells.

Embryology of Connective Tissue:

Develops from mesoderm but some in the head derives from neural crest.

Contents of Ground Substance in Connective Tissue:

• Interstitial fluid with GAGs.

• Structural glycoproteins like fibronectin and laminin.

• Fibers including collagen, reticular and elastic.

• Cells Glycosaminoglycans (acid mucopolysaccahrides).

• Polysaccharide molecules made of repeating disaccharides.

• Very hydrophilic and diffusion occurs in this space Proteoglycans have a protein core with sulfated GAGs.

Fibronectin:

Fibronectin, a structural glycoprotein, occurs as:

• A plasma component synthesized by the liver and endothelium.

• A secreted product for cell attachment.

• A fibrous component of the ECM.

Laminin:

• Laminin is a major ECM linker molecule with multiple binding sites for epithelial and muscle cells, type IV collagen and heparan sulfate proteoglycans.

Collagen:

• Most abundant protein in the body.

• 30% dry weight of body.

• Inelastic.

• High tensile strength.

• Can occur as fine fibrils or bundles.

• Found in: aponeuroses, tendons, etc.

Types of Collagen:

More than 12 kinds.

Type I Collagen:

Most abundant.

• Fibers.

• In bones, tendons, organ capsules, dermis.

• Produced by fibroblasts, osteoblasts (bone), chondroblasts (cartilage), and odontoblasts (teeth).

Type II Collagen:

• No fibers, thin fibrils.

• In hyaline cartilage.

• Produced by chondroblasts.

Type III Collagen:

• A major collagenous component of reticular fibers.

• Produced by fibroblasts, smooth muscle, Schwann cells, hepatocytes.

Type IV Collagen:

• Does not form fibrils.

• In basal lamina.

• Produced by epithelial cells.

Collagen assembly:

Polypeptide alpha chains assembled in RER 3 alpha chains assemble into procollagen and is exocytosed procollagen is transformed to tropocollagen tropocollagen aggregates into fibrils fibrils form fibers fibers aggregate to form dense bundles.

Reticular fibers:

• Stain by silver methods.

• Argyrophilic, silver loving, stains black.

• Supports like a delicate basket.

• Finely branched network joined at right angles.

• A typical collagen type III but with a polysaccharide coat.

• Abundant in lymphatic tissue and hematopoietic tissue.

Elastic Fibers:

• Consist of fibers or fenestrated sheets.

• Free ends form Y's.

• Protein elastin is deposited initially as elaunin between oxytalan microfibrils.

• Contain 2 unique amino acids, desmosine and isodesmosine.

• Produced by fibroblasts in skin and smooth muscle in large blood vessels with an elastic component.

• Elastin can stretch 150% of its original length.

Cells that maintain the extracellular membrane:

Cell types responsible for the synthesis and maintenance of ECM -blast, capable of mitosis -cyte, mature, no longer divide.

Fibroblasts:

Fibroblast Synthesizes collagen, reticular and elastic fibers, GAGs and glycoproteins of ground substance (reticular cells are fibroblasts specialized for the production of reticular fibers) Most common fixed cell in Connective Tissue Oval nucleus.

White Adipose Tissue:

Unilocular adipose All fat in humans this type.

Brown Fat:

Multilocular adipose In hibernating animals, newborns and fetuses In adult found along aorta and in interscapular fat of mediastinum.

Blood-Tissue gas exchange:

Continuous (somatic) Fenestrated (visceral) with diaphragms, where rapid exchange gas between tissues and blood is required, as in endocrine glands and intestine Fenestrated without diaphragms, very thick basal lamina in kidney glomerulus Sinusoidal large diameter to slow blood flow in spleen, bone marrow and liver.

Mast Cells:

• Mediate allergic reactions.

• Long lived and can proliferate.

• Found only in tissues.

• Life span of weeks or months.

• Common along blood vessels in GI and respiratory tracts.

• Sensitive sentinels for immune system.

• Compound exocytosis.

• Specific granules.

Anaphylactic Shock:

The first exposure to allergen triggers plasma cells to produce immunoglobulin IgE that attaches to mast cell receptors. During the second exposure, antigens bind to IgE receptors and cause degranulation of specific granules and release of plasma membrane leukotrienes; Histamine causes vasodilation, smooth muscle contraction in bronchial tree and leakiness in blood vessels that can lead to drop in blood volume and low blood pressure Leukotrienes (slow reacting substance of anaphylaxis) are similar to histamine but slower Eosinophil chemotactic factor for anaphylaxis smooths out histamine response.

Plasma Cells:

• Plasma cell originates from B lymphocytes.

• Plasma cells produce antibodies.

• Common at sites of potential entry of foreign bodies, GI, resp.

• Cartwheel chromatinPlasma Cell.

Neutrophils:

• Highly mobile and phagocytic.

• Central role in acute inflammatory reaction.

• Major constituent of pus Neutrophil.

Eosinophils:

Eosinophils are involved with "damage control," neutralizes histamine, inhibits mast cell degranulation and inhibits vasoactive substances produced by mast cells and basophils *Enter bloodstream and circulate 6-10 hours before entering tissue where they remain for their 8-12 day life span *1-3% of blood leukocytes Eosinophil.

Basophils:

• Basophil, similar to mast cell.

• 0.5% of white blood cells.

• Found only in blood.

• Life span of only a few days.

• Incapable of division Basophil.

Lymphocytes:

Lymphocyte T lymphocytes initiate cell mediated immune responses B lymphocyte generate plasma cells Lymphocyte.

Monocytes:

Monocytes (histiocytes) are produced in bone marrow, circulate a day or two and migrate to the Connective Tissue and differentiate into macrophages that live 2 about months.

Macrophages:

• Resident macrophages: present in a given site in the absence of an exogenous stimulus.

• Elicited macrophages: mobilized at a site in response to a stimulus.

• Activated macrophages: have acquired enhanced phagocytic and antigen presenting activity in response to a local stimulus.

Reticuloendothelial System:

Mononuclear phagocyte system = macrophage system = reticuloendothelial system. Includes all highly phagocytic cells and their monocyte precursor.

Types of Connective Tissues:

A. Embryonic connective tissue.

B. Mesenchyme.

C. Mucoid.

Lose Connective Tissue Proper:

A. Areolar.

B. Reticular.

C. Adipose.

Dense Connective Tissue Proper:

A. Dense irregular connective tissue.

B. Dense regular connective tissue.

C. Elastic.

Supportive Connective Tissue:

A. Cartilage - hyaline, elastic, fibrocartilage.

B. Bone.

Open Histology Questions:

How may pancreatic cancers cause ascites and jaundice?

How may abnormal pancreatic anatomy cause vomiting?

Additional Reading:

Basic Histology

1. Introduction to Histology
2. Basic Cell Physiology
3. Actin, Microtubules, and Intermediate Filaments
4. Mitochondria, Nucleus, Endoplasmic Reticulum, Golgi
5. Epithelium (Epithelial Tissue)
6. Connective and Adipose Tissue
7. Types of Cartilage
8. Osteogenesis
9. Nervous Tissue
10. Muscle Tissue
11. Cardiovascular System
12. Blood and Hematopoiesis
13. Lymphoid Tissue
14. Digestive Tract I: Oral Cavity
15. Digestive Tract II: Esophagus through Intestines
16. Liver, Pancreas, and Gall Bladder
17. Respiratory System
18. Integument
19. Urinary System
20. Endocrine System
21. Male Reproductive System
22. Female Reproductive System
23. Eye and Ear

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

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