Connective tissue histology

Year 1 - Semester 1

types of ordinary connective tissue

loose and dense

types of loose connective tissue

aerolar, adipose, reticular

features of aerolar tissue

empty spaces between sections of tissue, loose open framework of collagen, elastic and reticular fibres, lots of ground substance

ground substance

a hydrated, gel-like material that fills the spaces between cells and fibers

function of aerolar tissue

supports epithelial linings of GI, respiratory and urinary tracts, loose packing between cells of other organs

features of white loose adipose tissue

‘chicken wire’ appearance, each adipocyte is supported by delicate network of collagen and reticular fibres, fibrocytes, mast cells, sparse amorphous ground substance, rapid turnover of lipid

features of brown adipose tissue

large, rounded nuclei, vacuolar-looking tissues inside cell instead of large cytoplasm space

function of adipose tissue

energy storage, insulation, supports and protects organs

function of brown adipose tissue

thermoregulation in young and small mammals by dissipating stored energy as heat

features of loose reticular tissue

3D mesh of collagen reticular fibres and reticular cells, loose ground substance

function of loose reticular tissue

provides framework for lymphoid and hematopoietic organs, acts as a filter for migrating immune cells, allows exchange of nutrients and waste between blood and parenchymal cells

features of dense irregular tissue

little ground substance, dense network of randomly interwoven collagen fibres and extracellular proteins, few fibroblasts

function of dense irregular tissue

provides strength, stability and protection by withstanding forces from multiple directions so prevents tearing in skin dermis, organ capsules and joint capsules

features of dense elastic tissue

high concentration of elastic and collagen fibres

function of dense elastic tissue

allows recoil of tissue following stretching, maintains pulsatile flow of blood through arteries, aids passive recoil of lungs following inspiration

liquid support tissue

specialised connective tissue with a fluid extracellular matrix, can be blood or lymph

function of liquid support tissue

to transport substances, homeostasis, defence

function of basement membrane

cell adhesion, diffusion barrier, regulation of cell growth

types of cartilage tissue

hyaline, fibrocartilage, elastic

features of hyaline cartilage

chondrocytes in lacunae often clumped together, glassy matrix, no visible fibres

function of hyaline cartilage

to provide a smooth, low-friction surface for joints, protect bones, supportive framework for structures

features of fibrocartilage

chondrocytes in lacunae, collagen fibres in ground substance, fewer chondrocytes, chondrocytes aligned in rows

function of fibrocartilage

to provide shock absorption, structural support and stabilisation to intervertebral discs

annulus fibrosis of intervertebral disc

compact outer ring of fibrocartilage surrounding gelatinous core (nucleus pulposus)

features of elastic cartilage

large, clear cytoplasm, large nuclei, elastic and collagen fibres in ground substance

what is the most common type of cell in adult connective tissue?

fibroblast

what is the most common type of fibre produced by fibroblasts?

collagen

functions of bone

support soft tissue and attachment for skeletal muscles, protection of internal organs, assists movement, mineral homeostasis, blood cell production from red bone marrow, triglyceride storage as yellow bone marrow

osteogenic cell

cell capable of forming new bone tissue

osteoprogenitor

specific mesenchymal stem cell found in periosteum and endosteum that differentiates into osteoblasts, found just beneath the connective tissue layer

process of bone formation

1. osteoprogenitors differentiate into osteoblasts which secrete osteoid (organic matrix)

2. mineral crystals are added to the osteoid which causes the matrix to calcify, cells die leaving cavities, calcium ions and other electrolytes are released from osteoblasts by exocytosis

3. osteoblasts deposit bone on cartilage template and become entombed in the bone matrix, causing them to become osteocytes

bone resorption

osteoclasts attach to bone surface and release weak acid and enzymes into bone matrix to dissolve it, causing calcium and phosphate ions to be released which diffuse into capillaries

Howship’s lacuna

a depression resorbed from bone surface, into which acid and proteolytic enzymes are released from osteoclasts

Haversian system

the structural and functional unit of compact bone, consists of a central Haversian canal containing blood vessels and nerves, surrounded by concentric rings of bone matrix called lamellae

histological features of compact bone

osteons with Haversian canal, concentric lamellae, lacunae with osteocytes (elongated brown specks arranged in concentric layers around Haversian canals), canaliculi visible as fine lines, periosteum, Haversian systems visible in transverse sections, interstitial systems

periosteum

a double-layered membrane that covers the outer surface of compact bone, protecting it and providing it with blood vessels and nerves

method of flat bone development

intramembranous ossification

flat bone development process

1. mesenchymal cells differentiate into osteoblasts and blood vessels

2. osteoblasts gather in clusters to form ossification centres and secrete osteoid

3. calcium salts deposit on the osteoid, causing it to calcify

4. osteoblasts become trapped in the matrix and mature into osteocytes

5. this process continues and the outer layer of tissue becomes compact bone while the inner portion becomes spongy bone

method of long bone development

endochondral ossification

long bone development process

1. mesenchymal cells are induced to become chondrocytes which secrete a cartilage matrix

2. chondrocytes near the centre of the model enlarge and the surrounding matrix begins to calcify

3. calcified cartilage matrix is invaded by blood vessels and specialised cells

4. osteoblasts and other cells enter the matrix through blood vessels

5. osteoblasts deposit bone on calcified cartialge, replacing it with bone

tissues found within the marrow cavity

adipose and haemotopoietic tissue

where is fibrocartialge most commonly found?

tendon insertions