Connective Tissue and ECM ✅ Flashcards by C F

Examples of connective tissues

Fat and other soft padding tissue

Bone

Tendon

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What are the main components of connective tissue?

Cells

Extracellular matrix (ECM)
-protein fibers- collagen, elastic, reticular
-ground molecules- amorphous component with specialized molecules

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How does the dispersal of cells of connective tissues in the ECM compared to epithelial cells?

More widely dispersed in the ECM for cells of connective tissues

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ECM overview in connective tissue

Mixture of fibers and ground substance

Determines physical properties of the tissue
->major role in function of tissue (amount and structure of each component correlates to tissue function)

Gives structural and biochemical support to surrounding cells

Produced and assembled under control of support cells
-mostly fibroblasts

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What are the classifications of connective tissue?

Embryonic connective tissue

Connective tissue proper

Specialized connective tissue

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Embryonic connective tissue

Mesenchyme

-mucus connective tissue

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Connective tissue proper

Loose connective tissue

Dense connective tissue
-regular
-irregular

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Specialized connective tissue

Cartilage

Bone

Adipose tissue

Blood

Hemopoietic tissue

Lymphatic tissue

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What are the general functional features of connective tissue?

Support and connect tissues
-connective sheath (surrounds a muscle)
-tendons (attach muscles to bones)
-skeleton (supports positions of body)

Protection
-fibrous capsules and bones, protect fragile organs

Defense
-specialized cells in blood, defend from microorganisms that enter body

Nutrition
-transport gases, nutrients, waste & chemical messengers by blood and lymph

Insulation
-store energy as fat, contribute to thermal insulation by adipose cells

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What form can cells in connective tissue be found in?

Active form
- ‘-blast’, dividing and secreting components of ground substance

Inactive form
- ‘-cyte’

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Where do connective tissue cells derive from?

Mesenchyme (fetal supporting tissues)

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Common function of connective tissue cells

Synthesis

Maintenance

Recycling of ECM material

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Types of connective cell tissues

Fibroblasts
-secrete, maintain and recycle matrix in most tissues

Adipocytes
-modified support cells, specialized in storage and metabolism of fat
-together form adipose tissue

Chondrocytes, osteoblasts, osteocytes
-secrete and maintain matrix in cartilage and bone

Mast cells, tissue macrophages
-cells of innate immune system
-activated by chemicals of antigen

Lymphocytes
-cells of adaptive immune system
-activated by antigen

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Fibroblast

Principal cell of connective tissue

Synthesizes
-collagen
-elastic fibers
-reticular fibers

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Mast cells

Have many cytoplasmic granules
-contain chemical signals, histamine and heparin

When irritated or damaged, initiate a chemical response
-release histamine

Come from hematopoietic stem cells
-part of immune system

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Macrophages

Large cells

Derive from a monocyte
-essential components of immune system

When stimulated, release cytokines
-small proteins, act as chemical messengers
-cytokines recruit other immune system cells to infected sites and stimulate their activities

Permanent residents of their tissues
-aside from blood

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What types of fibers do fibroblasts produce?

Collagen fibers

Elastin fibers

Reticular fibers

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Collagen fiber

Most abundant structural component of connective tissues

Most abundant protein in mammals (25-35%)

One fiber is mad of collagen fibrils

Secreted into ECM by fibroblasts
-in form of collagen molecule

Flexible, great tensile strength
-resist stretching
-gives ligaments and tendons their characteristic resilience

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Components of collagen fiber

Alpha-chain

Chains assemble->

Procollagen peptidase
-triple helix with loose ends

Assembly

Collagen fibril
-10-500nm

Assembly

Collagen fibre
-1-500 microm

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How many types of collagen?

At least 28

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Elastic fiber

Contains the protein elastin, with lesser amounts of other proteins (fibrillin) and glycoproteins
-returns to its original shape after being stretched or compressed
-allows tissues to respond to stretching/ distension

Synthesized by fibroblasts and vascular smooth muscle cells

Prominent in elastic tissues found in
-skin
-walls of large blood vessels
-some ligaments that support spine

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What is reticular fiber mostly made of?

Type III collagen

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Reticular fiber

Synthesized by
-fibroblasts, some exceptions
-reticular cells, hemopoietic and lymphatic tissues

Found throughout
-most abundant in reticular tissue of soft organs eg liver, spleen
-anchor and give structural support to parenchyma (functional cells, blood vessels, nerves of organs)

In embryonic tissue and during wound healing
-indicator of tissue maturation

Ground substance

Amorphous, gel-like substance
-in extracellular space that contains all components of ECM, except the fibers
-occupies the spaces between cells and fibers

High water content

Provides lube for collagen fibers

Secreted by fibroblasts

What does ground substance consist predominantly of?

Proteoglycans Glycosaminoglycan molecules (GAGs) Multi adhesive glycoproteins

Structural elements of connective tissue: flow chart

Cells ⬇️ Fibroblast Macrophage Mast cell Plasma cell Plasma cell Lymphocytes Leukocytes Adipose cell ECM ⬇️ Fibers ⬇️ Collagen Elastic Reticular ECM ⬇️ Ground substance ⬇️ Proteoglycans GAGs Multi adhesive glycoproteins

General features of loose connective tissue

Loosely arranged fibers and abundant cells of various types Primarily located under epithelia that cover body surfaces and line internal surfaces of the body Most cells types are transient (respond to stimuli) Site of inflammatory and immune reactions

Areolar tissue

Loose connective tissue Holds organs in place Attaches epithelial tissue to other underlying tissue

Reticular tissue

Loose connective tissue Dominant in locations with high cellular content

Adipose tissue

Loose connective tissue Most common type of connective tissue in humans

Dense connective tissue

Fibers are the main matrix element -fewer cells -fibers mainly composed of type I collagen , between the collagen fibres are rows of fibroblasts ->forms strong, rope-like structures such as tendons and ligaments Make up lower layers of dermis -arranged in sheets

Cartilage

Composed of chondrocytes -make ECM, abundant in ground matrix -embedded in cartilage matrix -space they occupy= lacunae Avascular -nutrients need to diffuse through matrix to reach chondrocytes -this is a factor of why cartilaginous tissue healing is very slow

Cartilage types

Hyaline cartilage Fibrocartilage Elastic cartilage

Hyaline cartilage

Most common Short, dispersed collagen fibres Large amount of proteoglycans In: -rib cage -nose -covers bones where they meet moveable joints

Fibrocartilage

Tough -due to thick bundles of collagen fibres dispersed through matrix Eg- intervertebral disks

Elastic cartilage

Contains elastic fibres, collagen, proteoglycans Gives support and elasticity -eg external ear

Bone

Hardest connective tissue ECM is mostly collagen fibres, embedded in a minéralisée ground substance (calcium phosphate) Osteoblasts and osteocytes Highly vascularized -can recover from injury fairly quick

Osteoblasts

Active bone forming cells Produce organic part of ECM

Osteocytes

Mature bone cells Located in lacunae

Fluid connective tissues

Cells circulate in a liquid ECM, the plasma Blood and lymph

Blood contains

Erythrocytes Leukocytes Platelets

Erythrocytes

Transport oxygen and CO2 In blood

Leukocytes

In blood Defense against potentially harmful microorganisms/molecules

Platelets

In blood Cell fragments Involved in blood clotting

Lymph contains

Liquid matrix -similar to plasma White blood cells

Adipose tissue: tissue type, role, composed of..

Specialized connective tissue Plays role in energy homeostasis Made of adipocytes -fat cells Energy stored in liquid droplets of adipocytes -in form of triglycerides Regulates energy homeostasis -by secreting paracrine and endocrine substances

Types of adipose tissue

White Brown

Brown fat adipocytes

Store lipids -in many droplets High metabolic activity

White fat adipocytes

Store lipids as single large droplet Metabolically less active

Large number of adipocytes

Adipose tissue

Adipose tissue-derived stem cells

Capable of self-renewal and multi potential differentiation Adult stem cells

Primary type of adipose tissue in adults

White adipose tissue

Where is white adipose tissue located?

Subcutaneously -mammary glands -mesenteries -retroperitoneal spaces -visceral pericardium -orbits -bone marrow cavity

White adipose tissue function

Insulation Energy storage Hormone production -eg leptin, adiponectin, resistin

Where is the nucleus in white adipose tissue?

Flattened nucleus In periphery of cell

Brown adipose tissue

Present during fetal life, in infants -diminishes after 1st decade Smaller cells, nucleus in eccentric position, not flat Cytoplasm full of empty vacuoles -lipid is lost during tissue preparation Brown due to high levels of iron-containing mitochondria Differentiate from mesenchymal stem cells Metabolism generates heat -thermogenesis (hibernating animals have a lot of brown adipose tissue)