HIstology M4

Specialized connective tissue

Bone

a specialized dense connective tissue in which the intracellular substance or matrix is filtered with calcium salts

Bone

consists of cells, fibers, and ground matrix, but unlike others its extracellular components are calcified, making it hard, unyielding substance ideally suited for its supportive and protective function in the skeleton.

Bone

• serves for attachment of muscles, tendons and ligaments

• It contributes shape to the body.

• It acts as levers by which movement of the body is performed

Osteoprogenitor cells

relatively undifferentiated cells having the capacity for mitosis. They are active during normal growth of bones and undergo division

osteoblasts

osteoprogenitor cells transform into

Osteoblasts

“bone forming cells”, they are responsible for the synthesis of the organic components of bone matri

Osteoblasts

• premature

• located at the surface of the bone tissue, when engaged in matrix synthesis.

• have cuboidal shape and a basophilic cytoplasm

Organic and Inorganic component

components of bone matrix

collagen, ground substance

Organic component consists of?

Calcium, phosphorous, minor components

Inorganic component consist of?

Organic component

consists of collagenous fibers embedded in a ground substance. It compromises about 50% of its dry weight

Collagen

• constitutes about 90% of the organic substance and synthesizes from vesicles of the rough endoplasmic reticulum

• Occurs in form of cross striated fibers; predominantly Type I collagen.

Ground substance

also known as mucopolysaccharide/glycosaminoglycans

Ground substance

• serves as cement substance, in which the collagenous fibers are embedded.

• synthesized from the vesicle of Golgi apparatus

Chondroitin, keratin, and hyaluronic acid

Ground substances contains:

Inorganic Component

Constitute about 50% of its dry weight of the bone matrix

Calcium hydroxyapatite, phosphorous, minor

Essentially abundant inorganic substance:

Calcium hydroxyapatite

most abundant inorganic substance

phosphorous

Forms the hydroxyapatite crystals of calcium phosphate, which contributes to the hardness of bone

Minor

Bicarbonate, citrate, magnesium, potassium and sodium

periosteum, endosteum

2 fibrous covering of bone

periosteum

a layer of dense connective tissue that is very fibrous externally but more cellular and vascular near the surface of the bone matrix

Endosteum

a thin layer of flattened or squamous cells lining the central cavities of bone including narrow spaces of haversian canals

woven bone, lamellar bone, compact bone

types of bone

Woven bone (newly calcified)

• irregular and random arrangement of cells and collagen; lightly calcified

• Developing and growing bones; hard callus or bone fractures

• Known as immature bone; primary bone; bundle bone

Lamellar bone (remodeled)

• parallel bundles of collagen in thin layers (lamellae), with regularly spaced cells between; heavily calcified.

• All normal regions of adult bone

• Known as mature bone; secondary bone

Compact bone (cortical)

• parallel lamellae or densely packed osteons, with interstitial lamellae

• Thick, outer region (beneath periosteum) of bones.

• Found mostly in the diaphysis of long bones and plates of flat bones.

Haversian system or osteon

unit of structure of a compact bone is called

Haversian canal

also known as osteon canal; a longitudinal, vascular at the central axis of the Haversian system

Concentric lamellae

a bony plate of lamellae arranged concentrically around the haversian canal

Osteocytes

mature bone cells lodged in cavities found along the connective lamellae

lacunae

lenticular cavities uniformly spaced throughout the mineralized interstitial substance of bone, each completely filled with osteocyte

Bone canaliculi

• slender, branching, tubular passages that extend in all directions from the lacunae.

• It is thru these canals that the nutritive substance from the blood vessel of periosteum reach the more distant osteocytes.

Concentric

bone structure that enclosed the haversian system.

Interstitial

found between osteon

Outer circumferential

adjacent to periosteum

Inner circumferential

adjacent to endosteum

Cancellous bone

• Found in the epiphysis, metaphysis, diploe of fat bones, and medullary cavities.

• Interconnected thin spicules or trabeculae covered by endosteum.

• Located in inner region of bones, adjacent to marrow cavities

Trabeculae, lamellae, osteocytes

Cancellous bones consists of:

Trabeculae

bony processes give porous appearance to the bone

Lamellae

– arranged in scaffolding or lattice work of spicules, which form irregular small marrow cavities

Osteocytes

haphazardly arranged within a lamellae

osteogenesis

also called as bone formation

Intramembranous ossification

• occurs in the development of flat bones of the skull, the maxilla and mandible.

• Bone develops within a layer of connective tissue and it does not involve the removal or replacement of cartilage

Intracartilagenous ossification

• also called endochondral ossification

• occurs in the formation of bones of base of the skull, in the vertebral column, in the pelvis and in the extremities.

• Most bones of the body are derived from a hyaline cartilage model.

Appositional growth, interstitial growth

2 types of growth of bone

appositional growth

it is the growth in the circumference of bones

interstitial (longitudinal) growth

it is the growth of length of bones

Cartilage

• a firm, pliable type of specialized connective tissue

• Intercellular substance has a rigid consistency.

• Less resistant to pressure than bone.

Fibers, ground substance (cartilage martrix)

In general, cartilage consists of:

Cartilage

• Provide a sliding area for joints to facilitate bone movements.

• Essential for growth of long bones both before and after birth

• support the soft tissue

Chondrocytes

• cell of cartilage

• Flattened to oval or spherical shape, lodged in lacunae and arranged singly or in isogenous group

Nucleus

– round or oval and pale staining, containing nucleol

Cytoplasm

basophilic containing mitochondria, occasional lipid droplets, and variable amounts of glycogen.

Perichondrium

• Sheet of dense connective tissue that surrounds cartilage in most places, forming an interface between the cartilage and the tissues supported by the cartilage

• Contains blood supply and nerve supply of cartilage

Hyaline, elastic, fibrous cartilage

types of cartilage

Hyaline cartilage

most common in which the matrix contains a moderate amount of collagenous fibrils

Elastic cartilage

the matrix contains collagenous plus large number of elastic fibers

Fibrous cartilage

matrix contains abundance of collagenous fibers.

Hyaline cartilage

• Most common and widely distributed type of cartilage in the body.

• characterized by chondrocytes that have elliptical or flattened shaped at the periphery.

• Ground substance or cartilage matrix is abundant and embedded in it is a moderate amount of collagenous fibers

Hyaline cartilage

• e small and evenly dispersed in the matrix, making the matrix appear transparent

• allows growth of long bones; provides rigidity with some flexibility in the trachea, bronchi, ribs and nose; forms strong, smooth, yet somewhat flexible articulating surfaces; forms the embryonic skeleton.

Elastic cartilage

• More flexible type of cartilage

• Gross: yellowish color due to the presence of elastin in elastic fibers.

• contains abundance of elastic fibers. The ground substance is less abundant. The ground substance is less basophilic or slightly acidophilic

• Provides rigidity with even more flexibility than hyaline cartilage because of elastic fibers

Fibrous cartilage

• A type of tissue with a characteristic intermediate between dense connective tissue and hyaline cartilage

• Characterized by chondrocyte that are smaller and tend to be flattened but still lodged in lacunae, arranged in rows, in between thick bundle of collagenous fibers so that the amorphous ground substance is extremely rare and appears as acidophilic.

Fibrous cartilage

• There is no identifiable perichondrium in fibrocartilage.

• Somewhat flexible and capable of withstanding considerable pressure; connects structures subjected to great pressure

upper respiratory tract, articular ends, epiphyseal plates of long bones, fetal skeleton

location of hyaline cartilage

chondrocytes, chondroblasts

Major cells of hyaline cartilage

Hyaline cartilage

homogenous, with Type II collagen and aggrecan

Hyaline cartilage

provides smooth, low-friction surfaces in joints; structural support for respiratory tract

chondrocytes, chondroblasts

Major cells of elastic cartilage

Elastic cartilage

Type II collagen, aggrecan and darker elastic fibers

external ear, external acoustic meatus, auditory tube, epiglottis, and certain other laryngeal cartilages

location of elastic cartilage

Elastic cartilage

provides flexible shape and support of soft tissues.

Fibrocartilage

Type II collagen and large areas of dense connective tissue with type I collagen

Chondrocytes, fibroblasts

Major cells of Fibrocartilage

intervertebral discs, pubic symphysis, meniscus, and certain other joints, insertions of tendons

Locations of Fibrocartilage

Fibrocartilage

provides cushioning, tensile strength, and resistance to tearing and compression

Blood

• Transport nutrients, oxygen, wastes and carbon dioxide to and from tissues

• To convey hormones, cytokines, chemokines and other soluble regulatory molecules

• To transport leukocytes and antibodies through the tissues

• To maintain homeostasis.

Osteoporosis

brittle bone disease; mostly found in elderly and leads to high risk for accidents and injuries involving bones

Hematopoiesis

formation and development of blood cells; A continuous, regulated process of blood production

cell renewal, proliferation, differentiation, maturation

Hematopoiesis includes

Prenatal, adult hematopoiesis

2 stages of hematopoiesis

Prenatal hematopoiesis

• Mesoblastic/megaloblastic stage — fetal yolk sac.

• Hepatic stage – liver.

• Medullary/myeloid – red bone marrow.

Adult hematopoiesis

Long bones, flat bones and bone marrow

Multipotent HSC, committed progenitor

types of hematopoietic stem cell

Multipotent/pluripotent HSC

undifferentiated cell producing cells of multiple lineages limited, limited self renewal (e.g. myeloid sc and lymphoid sc)

Committed progenitor

undifferentiated cell capable of producing cells of one lineage, colony forming units (CFUs) (e.g. erythroid CFU and granulocyte-macrophage CFU)

Erythropoietin (EPO), Thrombopoietin (TPO), Granulocyte CSF (G-CSF), Granulocyte-macrophage CSF (GM-CSF), Interleukins

regulators of hematopoiesis

Erythropoietin (EPO)

major regulator of erythropoiesis, stimulates erythroid CFU cells and proerythroblasts

Thrombopoietin (TPO)

increases platelet production, stimulates megakaryocyte CFU cells

Granulocyte CSF (G-CSF)

increases production of neutrophils, stimulates granulocyte-macrophage CFU cells.

Granulocyte-macrophage CSF (GM-CSF)

increases macrophage production, stimulates granulocyte macrophage and CFU cells.

Interleukins

stimulate B and T cell formation, function together with G-CSF and GM-CSF

Erythropoiesis

• no visible granules

Erythropoiesis

• cell become smaller

• basophilic to eosinophilic

• nucleus condenses and ultimately disappears

Erythrocyte

• size: 7.5 μm in diameter

• pink cytoplasm

• rbc are non-nucleated

• Life span is 120 days

Granulopoiesis

Formation of the granular leukocyte: neutrophil, eosinophil and basophils.

Neutrophil

• 2-5 lobe nucleus

• have pink and grey-blue granule

• 10 hours lifespan

myeloblast < 4%, promyelocyte, myelocyte, metamyelocyte, band form

precursors of neutrophil

eosinophil

• Coarser and more deeply red staining granules.

• Usually has two lobes of nucleus; rarely seen with more than two lobes.

• Special role in allergy, inflammation and parasite infection.

Basophil

• Occasionally seen

• Dark cytoplasmic granules

• Role in immediate hypersensitivity response.

• Gives rise to mast cells.