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Connective Tissue(CT)
Diversity of Connective Tissue
Types and Functions:• Loose Connective Tissue: Areolar and fat
– insulation, protection (padding), loosely connecting structures
• Dense Connective Tissue: Ligaments and tendons– binding and support
• Cartilage – protection, support
• Bone– support
• Blood– transportation
Common Characteristics of all CT
1. Embryonic origin: (mesenchyme)3. Composed of different types of cells within the tissue.
2. Has an extracellular matrix of fibers and ground substance.
Ground substance
4. Variation in amount of blood supply (vascularization)
5. All support epithelium
Loose Connective Tissue
Ex. 1: Areolar – most widely distributed type.– Gelatinous– Loosely packed; lots of liquid held in ground
substance– “packing material” cushioning organs,
subcutaneous, attaches skin to muscle.– Has all three fibers– Cells: fibroblasts, macrophages, mast cells,
and white blood cells– Swells during inflammation (edema)
collagen
Ground substance
Mast cell
Fibroblast
Elastin
Areolar (Prototype)
• Ex. 2: Adipose = Fat!– Loosely packed with sparse matrix– 90% of tissue is mature adipocyte cell– Most of each cell is a fat droplet, so nuclei
is displaced to the side– Richly vascularized– Nutrient storage, cushioning in areas like
abs, hips, around kidneys– High concentrations subcutaneous (under
skin) – shock absorber, insulation– Fat deposits act as local nutrient sources
around active organs (heart, muscles)
Loose Connective Tissue
Adipose
Adipose
• Ex. 3 Reticular– Only contains reticular fibers.– VERY DELICATE – a fine net of fibers
that act as a “soft” skeleton– Supports lympho nodes, bone
marrow, spleen, free blood cells.
Loose Connective Tissue
Dense Connective Tissue• Ex. 1: Dense Regular – Tendons and
Ligaments– Fibers predominate. – Abundant and crowded fibroblasts
make fibers– Little ground substance– Regular, parallel bundles of collagen
fibers– Resist tension: pull and stretching.– Ligaments connect bone to bone– Tendons connect muscle to bone.– Poorly vascularized
Regularly aligned collagen
Fibroblast nuclei
• Ex. 2: Dense Irregular– Thicker, irregularly arranged collagen.– Found where tension is applied in
different directions– Example: Dermis of skin, organs,
joints
Dense Connective Tissue
Dense Regular
Dense Irregular
Cartilage
Characteristics– Resists tension AND compression– Lots of collagen (strong) AND elastic
fibers (flexible)– No nerves or blood vessels– High content of proteoglycans 80%
water– Chondroblasts make matrix until end
of human adolescence– Mature Chondrocytes found in
cavities called lacunae (pit)
Hyaline Cartilage
• Looks glassy (hyalin = glass)• Few chondrocytes, all found in
lacunae• Mostly matrix – lots of collagen• Reduces friction, absorbs pressure• Covers ends of long bones, connects
ribs to sternum, forms rings in trachea and bronchi
Elastic Cartilage
• Looks almost identical to hyaline BUT more elastic fibers more flexible!
• Matrix appears more fibrous• More lacunae, closely spaced.• Found in ear and epiglottis
Hyaline Cartilage
Elastic Cartilage
Fibrocartilage
• Intermediate between dense regular CT and hyaline
• Consists of rows of chondrocytes and collagen fibers
• Compressible AND resists tension• Found in intervertebral discs.
Bone (Osseous Tissue)
• Most supportive tissue in body. • Matrix is similar to cartilage, but with
morer collagen (strong) surrounded by calcium salts
• Osteoblasts make collagen fibers and calcium salts deposited between fibers.
• Well vascularized• Osteocytes stored in lacunae• Bone marrow stores fat and makes blood
cells.
Blood
• Atypical connective tissue• Only classified as such because it
arises from same embryonic tissue• Blood cells are within a matrix of
blood plasma.• Fibers apparent only when blood
clots.
How do damaged tissues repair?
Injured cells release hormones and proteins to signal need for healthy cells to divide and migrate.
Steps to Tissue Repair1) Inflammation• Inflammatory
chemicals released by injured cells, macrophages, mast cells
• Vessels dilate, allowing clotting and plasma proteins and wbc to invade injured site.
• Clotting proteins begin clotting.
2) Restore Blood Supply
• Granulation tissue replaces clot, digested by macrophages
• New capillaries form.• Fibroblast in
granulation tissue make collagen and growth factors.
3) Regeneration or Fibrosis below scab
a) Regeneration: replacement w/ same tissue type
b) Fibrosis: replacement w/ fibrous connective tissue (scar)
Regeneration Capacity
Varies by tissues
High capacity No capacity
•Epithelial
•Bone
•Areolar CT
•Dense I. CT
•Blood forming tissue
•Dense R. CT •Cartilage •Cardiac Muscle
•Nervous Tissue
Fibrosis replaces tissue in non-regenerative tissues
• Mostly collagen• STRONG but lacks flexibility/elasticity• Cannot perform function of tissue that was replaced
Extracellular Matrix• Embeds cells of connective tissue• Medium for nutrients and other dissolved
substances that nourish cells• Made up of ground substance and fibers.• Ground substance
– Texture varies•Can be liquid, gel-like, semi-solid or hard.•depends on amount of cell adhesion proteins
that trap water called proteoglycans –More proteins, more solid ground
substance.
• Fibers provide strength and/or flexibility– Allows for weight bearing, withstanding of
mechanical abuse, tension – protects!!
Dense connective tissue, lots of fibers, little open space.
Loose connective tissue:
Lots of ground substance – fewer fibers
Fibers
• Embedded in ground substance• Adds strength/flexibility.• Created by undifferentiated “blast”
cells of extracellular matrix• 3 Kinds
1. Collagen: Strong2. Elastic: Flexible3. Reticular: Delicate
Collagen (white fibers)
• Rope-like bundles
• Tough, stronger then steel!
• Tension resistant
Return to fibers
Elastic (yellow fibers)
• Long, thin
• Branching networks
• Stretch and recoil ability for elasticity
• Highly concentrated in areas like skin, lungs, vessels where elasticity is needed
Back to common characteristics of CT
Reticular “network” fibers• Short, fine, delicate
• Collagenous, but with more give due to branching network
• Support soft tissue organs, blood vessels
• abundant in boundaries where connective tissue lines other tissues (ex. basement membrane)
Reticular fibers
Collagen
Blood vessel
Cells in Matrix• Cells of CT make and maintain the ground
substance and fibers of extracellular matrix (ECM).
• Each type of CT have immature and mature forms of these cells.
• Immature cells have suffix “-blast” – are actively mitotic and produce ECM.– Fibroblasts – make loose and dense CT proper– Chondroblasts – make cartilage– Osteoblasts – make bone– Hematopoeitic stem cells – make blood
• Mature cells have suffix “-cyte” – maintain health of matrix– Ex. Fibrocyte
• Mature “cyte” cells can reverting to “blasts” to regenerate matrix after injury.
What other cells are in CT?
• Accessory Cells:– White blood cells (macrophages,
plasma cells)– responsible for immune response
– Mast cells – responsible for inflammation following injury or infection.
– Fat cells – store nutrients
Back to common characteristics of CT