Where is connective tissue typically derived?
- (middle embryonic germ layer)
What type of connective tissue underlies epithelium?
Where is dense regular connective tissue typically found?
What type of connective tissue forms layers in organs?
Dense Irregular CT
- - reticular layer of dermis
- - submucosa of digestive organs
What are the functions of adipose tissue?
- Energy storage
- Provides physical contours that distinguish men and women
What are the components of connective tissue?
- 1) Ground Substance
- 2) Fibers
- 3) Cells
Characteristics & Composition of Ground Substance
amorphous / colorless / homogenous
- synthesized / secreted by resident cells of CT. Protein backbone covalently bound to glycosaminoglycans. Proteoglycans are very hydrophilic
(stain with eosin). Typically surrounded by a thick layer of solvation water.
- Glycoproteins - laminin (major component of basal lamina) & fibronectin
- Tissue fluid - similar to blood plasma (accumulation = edema)
Major types of connective tissue fibers
- Collagen fibers
- Elastic fibers
- Reticular fibers
Most abundant types of collagen
Types I - IV
(90% = Type I)
What forms classically described collagen fibers / collagen bundles?
Type I Collagen
Collagen bundles: acidophilic or basophilic? Why?
- Acidophilic due to charged amino groups
- (stains pink with Eosin in H&E)
Type I Collagen
Connective tissues (skin, bone, tendon, ligaments, fascia, etc...90% of body collagen)
Provides resistance to force, tension, stretch
Type II Collagen
- Cartilage (hyaline, elastic)
- Intervertebral Disks
Type III Collagen
Loose connective tissue (organ tissue, blood vessels, smooth muscle, etc...)
Reticular fibers (forms loose meshwork - i.e. lamina propria, lymphatic organs, etc...)
Type IV Collagen
Basal lamina of epithelia
Type VII Collagen
Secures basal lamina to connective tissue fibers
(Anchoring fibrils of skin, eye, uterus, and esophagus)
Type IX Collagen
Found in cartilage associated with type II collagen fibrils
(stabilize type II fibers by interaction w/ proteoglycan molecules)
Type X Collagen
Produced by chondrocytes in zone of hypertrophy of normal growth plate
Contributes to the mineralization process by forming hex. lattices to arrange types II, IX, XI collagen within the cartilage
Type XI Collagen
- Produced by chondrocytes
- (associated w/ type II collagen fibrils, forms core of type I collagen fibrils)
Regulates size of type II collagen fibrils; it is essential for cohesive properties of cartilage matrix
Composition of elastic fibers
Composed of elastin and fibrillin
Orecin / Resorcin-fuchsin is used to stain _______
Where are elastic fibers found?
Walls of blood vessels (tunica media of aorta)
ligamentum flavum (stretch)
Composition of reticular fibers
Formed by type III collagen
Where are reticular fibers found?
Framework of specialized organs (lymphoid, kidney)
Loose connective tissue
Reticular lamina / lamina propria
Silver salts are used to stain _______
Reticular fibers (argyrophilic)
Most common type of connective tissue resident cell?
Migrating connective tissue cells? Found mainly in which tissue?
- Mast cells
- Plasma cells
(Mainly found in loose CT)
Function of fibroblast
Synthesize ECM (ground substance & fibers)
Types of adipose tissue
- White fat - unilocular
- - mostly in adults
- - energy storage, insulation, cushioning, hormone secretion
- Brown fat - multilocular
- - large amount in newborns (adults = adrenals, aorta, neck, mediastinum)
- - lipid mobilizaiton, heat generation (sympathetic stimulation)
Adipose cells & Fibroblasts are derived from...
Undifferentiated Mesenchymal Cells
Polypeptide from gastric epithelium
- Acts as an appetite stimulant via hypothalamus
- (short term regulation)
- Signals satiety via hypothalamus
(short term regulation)
- Stimulates lipid synthesis and blocks lipolysis
- (long term regulation)
Produced by fat cells
- Acts on hypothalamus to suppress appetite
- (long term regulation)
Obese people are believed to be leptin resistant
Neurogenic Lipid Mobilization Pathway
- Norepinephrine (nerve endings) stimulates cAMP system
- -> activates hormone-sensitive lipase
- -> hydrolyzes stored triglycerides to free fatty acids and glycerol
-> diffuse into capillaries where fatty acids bind to albumin
-> transported for use as energy
Lipid Storage Pathway
Triglycerides transported from intestine and liver by lipoproteins (chylo & vLDL) into blood
-> in adipose tissue capillaries lipoproteins are broken down by lipoprotein lipase
-> free fatty acids and glycerol are released and diffuse from capillary into adipocytes
-> re-esterified into glycerol phosphate -> forming triglycerides (stored until needed)
Large, ovoid cells w/ numerous cytoplasmic granules.
- Originate in bone marrow
- Differentiate in connective tissue
- Granules contain vasoactive and immunoreactive substances.
- - Histamine and slow reacting substance of anaphylaxis (SRS-A)
- - Eosinophil and neutrophil chemotactic factors (ECF and NCF)
- - Heparin (anticoagulant)
- Antibody producing cells derived from B-lymphocytes.
- (Common in loose connective tissue of the gut and glands)
- Basophilic cytoplasm due to RER
- Eccentric nucleus with “clockface” chromatin
- Prominent Golgi apparatus seen as clear, unstained region near nucleus.
Mast Cell - Plasma Cell Interaction
Mast cells have receptors for IgE
Plasma cells make IgE in response to an antigen (i.e. bee venom)
- Upon second exposure, antigen will bind to IgE molecules on the mast cell
- -> This triggers mast cell degranulation
Derived from blood-borne monocytes.
In tissue, best seen if they are actively phagocytic (large vacuolated cytoplasm)
- Part of the Mononuclear Phagocytotic System.
- (Pathologists refer to them as histiocytes)
- Macrophages fuse to for very large, multinucleated cells
- in response to a foreign body (suture material / hair) that has gotten into an incision
Connective tissue immune surveillance system
- B-lymphocytes give rise to plasma cells that synthesize immunoglobulin.
- T-lymphocytes are involved in cell-mediated mmunity.
- Natural Killer (NK) Cells destroy virus infected cells and some tumor cells
Granulocytes with segmented nuclei
First cells to arrive at a site of acute inflammation
(process called diapedesis)
- Active phagocytes (sometimes called microphages)
- Can phagocytose some bacteria. Other foreign substances must be opsinized.
(Pus is an accumulation of dead neutrophils)
Bilobed nucleus & large red granules
- Associated with 3 conditions:
- - Allergic reactions
- - Parasitic infections
- - Chronic inflammatory processes
- Often found in the lamina propria of the gut
- (increase in number with chronic inflammation)
Loose CT vs. Dense CT
Loose CT - lots of cells, fewer fibers
- Dense CT - fewer cells, more fibers
- - Dense irregular (dermis – reticular layer)
- - Dense regular (tendons, ligaments)