Connective Tissue Flashcards
Connective tissue cellular components
fibroblasts, fibrocytes, adipocytes, mast cells, macrophages, plasma cells, eosinophil, and lymphocytes
Fibroblasts
(s, f, l)
Structure :dendritic to fusiform cells with oval, euchromatic nuclei
Function: produce fibers
Location: throughout connective tissue, close to fibers
Fibrocytes
(s, f, l)
Structure: flat, fusiform cells with thin, heterochromatic nuclei
Function: maintain fibers
Location: throughout the connective tissue, close to mature fibers
Adipocytes (unilocular and multilocular)
(s, f, l)
Structure: spherical cells with large lipid droplets (multiple in multilocular) and peripherally, displaced flattened nuclei
Function: store lipids, cushion and insulate nearby structures
Location: throughout connective tissue, abundant in adipose connective tissue
Mast cells
(s, f, l)
Structure: large, ovoid cells with spherical nuclei and abundant dark-brown granules
Function: produce and secrete inflammatory mediators such as histamine
Location: throughout connective tissue, abundant in dermis and mucosal lamina propria
Macrophages
(s, f, l)
Structure: various sizes and shapes, often difficult to identify
Function: phagocytose pathogens and debris
Location: throughout connective tissue
Plasma cells
(s, f, l)
Structure: oval cells with eccentric “clock face” nuclei, perinuclear clearing due to Golgi complex, basophilic cytoplasm
Function: produce antibodies
Location: throughout connective tissue, abundant in mucosal lamina propria
Eosinophil
(s, f, l)
Structure: bilobed nuclei, eosinophilic (almost hot pink) granule-filled cytoplasm
Function: immune function, mediators of allergic response and parasitic infection response
Location: throughout connective tissue, circulate in blood
Lymphocytes
(s, f, l)
Structure: relatively small, oval cells, clear cytoplasm and dense nuclei
Function: immune function, major role in adaptive response
Location: throughout connective tissue, abundant at the site of chronic inflammation, circulate in blood
Neutrophils
(s, f, l)
Structure: nuclei with three to four lobes, granular cytoplasm
Function: immune function, acute inflammatory response
Location: throughout connective tissue, abundant at the site of acute inflammation, circulate in blood
Fibers in connective tissue
Collagen fibers (Type I), Elastic and fibrillin fibers, Reticular fibers (Type III collagen)
Collagen fibers
(s, f, l)
Structure: thick, eosinophilic, long, rope-like strands mostly composed of type I collagen
Function: provide flexibility, structural support, and strength to the tissue
Location: scattered throughout connective tissues, abundant in bones, tendons and ligaments
Elastic fibers
(s, f, l)
Structure: Thin, dark, long, branched hair-like strands composed of elastin and fibrillin
Function: provide elasticity, give the tissue ability to distend and recoil
Location: scattered throughout connective tissues, abundant in large arteries and the dermis
Reticular fibers
(s, f, l)
Structure: very thin, short, type III fibrillar strands. Not visible without silver stain (agryophyllic)
Function: provide a delicate meshwork and supporting scaffolding or cells and other fibers in a tissue
Location: scattered throughout connective tissues, abundant in lymph nodes, spleen, liver, and other “soft organs”
Ground substance
(s, f, l)
Structure: viscous, gel-like substance with high water content; appears as clear non-staining areas.
Major components: proteoglycans, multiadhesive glycoproteins, and glycosaminoglycans
Function: contribute to mechanical and structural support, anchor fibers and cells in respective areas of the tissue, allow for diffusion of nutrients and chemicals throughout the tissue
Location: throughout connective tissue; in between cells and fibers
Loose connective tissue
(s, f, l)
Structure: relatively cellular connective tissue with all three types of loosely arranged fibers, and abundant ground substance; well vascularized; fibers are sparse and irregularly arranged
Function: support, cushion, and deliver vascular supply to the near by epithelia. Immediately respond to epithelial injury or contact with antigens
Location: commonly under epithelia; throughout dermis, lamina propria, layers surrounding glands and ducts
Dense irregular connective tissue
(s, f, l)
Structure: composed of densely packed mostly collagen fibers in diverse orientations with much less ground substance and sparse fibrocytes
Function: provide structural support and strength to withstand force applied from multiple directions
Location: deeper layer of dermis (reticular dermis) and sub-mucosa
Dense regular connective tissue
(s, f, l)
Structure: composed of densely packed collagen fibers arranged in parallel with sparse ground substance and fibrocytes wedged between fibers; not vascular
Function: provide structural support and strength to withstand force applied in one direction (the direction of fiber orientation)
Location: tendons, ligaments, aponeuroses
Elastic connective tissue
(s, f, l)
Structure: composed of parallel layers of elastic fibers, interspersed with fibrocytes, other fibers, and smooth muscle cells
Function: provide structural support while allowing certain level of distension and recoil
Location: large arteries, certain vertebral ligaments
Reticular connective tissue
(s, f, l)
Structure: composed of meshwork of predominantly reticular fibers, fair amount of ground substance and reticulocytes (reticular cells, fibroblasts) and parenchymal cells
Function: provide structural scaffold for relatively soft organs that functionally require a large capillary/lymph network or organs composed mostly of secretory cells
Location: liver, spleen, lymph nodes, pancreas, bone marrow, salivary glands, and endocrine glands
Unilocular adipose connective tissue
(s, f, l)
Structure: composed of mostly unilocular adipocytes (large spherical cells with a large single lipid-filled globule taking up most of the cytoplasmic space with a perinuclear, flattened nucleus
Function: lipid storage, insulation, and protection
Location: throughout the adult body, hypodermis, mesentery, omentum, and other visceral fat pads
Multilocular adipose connective tissue
(s, f, l)
Structure: composed mostly of multilocular adipocytes (large, spherical cells with abundant small lipid filled vesicles in cytoplasm, central nuclei and abundant mitochondria)
Function: heat generation
Location: throughout the body of the embryo and infants
Hyaline cartilage
(s, f, l)
Structure: firm, solid and rigid tissue with limited pliability; chondrocytes located in lacunae; ECM of mostly type II collagen and glycoaminoglycans giving it at a glassy appearance; surrounded by perichondrium (dense connective tissue) containing chondroblasts (similar to fibroblasts), fibroblasts/fibrocytes, and blood vessels
Function: provide structural support, rigidity and protection to soft tissues in the vicinity; provide low friction joint surfaces and distribute force
Location: costal cartilages, articular surfaces, epiphyseal plates, and nose
Elastic cartilage
(s, f, l)
Structure: firm, solid tissue with flexibility and elasticity; chondrocytes in lacunae; ECM of abundant elastic fibers and hair-like branching strands in various orientations; perichondrium surrounding with dense connective tissue
Function: provides structural support and rigidity but also a range of flexibility and elasticity to change shape and return to the original form and position
Location: Pinna of the external ear, external auditory meatus, auditory tube, epiglottis
Fibrocartilage (Fibrous cartilage)
(s, f, l)
Structure: firm, solid tissue that resembles dense connective tissue but has chondrocytes in lacunae; ECM of abundant collage fibers and thick, long strands often in one orientation; No distinct perichondrium
Function: provide structural support and rigidity to resist compression and shear forces and absorb shock
Location: pubic symphysis, annulus fibrosus of intervertebral disks, menisci
How does cartilage get its nutrients? What does this result in?
Cartilage is avascular. Thus, it relies on the blood vessels in the perichondrium (and other surrounding tissues) for diffusion of nutrients. Results in slow and limited ability to heal and repair itself when injury occurs.
How does cartilage grow? (Types of growth)
Occurs mainly before adulthood, slowly decreasing through adolescence.
Appositional growth and interstitial growth
Appositional growth
Chondroblasts in the perichondrium produce cartilaginous matrix and thicken the cartilage from the periphery. Chondroblasts become encased in the matrix they produced and are then called chondrocytes.
Interstitial growth
Chondrocytes in the middle of the cartilage divide (become isogenous groups) and then each daughter cells starts secreting its own matrix around itself eventually becoming separated from each other.
Isogenous groups
a group of chondrocytes that arose from a single chondrocyte during interstitial growth. In the early stage, isogenous groups of chondrocytes can be identified by their close proximity to each other or by a number of chondrocytes in the same lacuna.
Osteoprogenitor cells
(s, f, l)
Structure: pool of meschymal stem cells, stellate to squamous morpholog, difficult to identify on regular stain
Function: give rise to osteoblasts with appropriate stimuli, may differentiate into other types of connective tissue cells
Location: mesenchyme, inner most layer of periosteum; endosteum; bone marrow
Osteoblasts
(s, f, l)
Structure: active - cuboidal to columnar with basophilic cytoplasm and euchromatic nuclei and distinct nucleoli; inactive - squamous, difficult to identify
Function: secrete osteoid (type I collagen and bony matrix proteins) that calcifies
Location: innermost layer of the periosteum, endosteum; usually in contact with newly forming bone
Osteocytes
(s, f, l)
Structure: osteoblasts encased in calcified matrix mature and become osteocytes; dendritic morphology
Function: maintain bony matrix; mechanotransduction
Location: main cell body in lacunae, cell processes in canaliculi
Osteoclasts
(s, f, l)
Structure: large, multinucleated macrophage derivative
Function: resorb bone tissue
Location: resorption bay (Howship lacunae); a concave depression on the bone surface, scattered throughout endosteum and periosteum
Periosteum
(s, f, l)
Structure: dense connective tissue covering bone
Function: deliver neurovascular supply to the bone, allow tight attachment of the muscles and other structures to the bone
Location: Outer surfaces of most compact bone
Endosteum
(s, f, l)
Structure: resembles simple squamous epithelium composed of inactive osteoblasts, Osteoprogenitor cells, and osteoclasts
Function: source of new osteoblasts and osteocytes
Location: inner surfaces of compact bones, canals; outer surfaces of all spongy bone
Compact bone
(s, f, l)
Structure: highly organized into osteons
Function: mechanical support, protection, weight transfer, mineral storage
Location: outer surfaces of the bone
Spongy bone
(s, f, l)
Structure: network of thin plates or branches of bony tissues with spaces in between
Function: weight transfer, quick mineral turnover, reduce the weight of the bones, provide large surface area for bone resorption/formation
Location: inner portions of the bone; center of diaphysis and epiphysis of long bones and centers of most bones
Marrow spaces
(s, f, l)
Structure: spaces filled with erythrocytes and adipocytes
Function: site of blood formation and fat storage, lighten the weight of the bone
Location: spaces between the sponge bone trabeculae
Haversian system (Osteon)
(s, f, l)
Structure: cylindrical units within compact bone
Function: bear and transfer weight in the long axis
Location: throughout compact bone, oriented parallel to the long axis of the bone or in the direction of the force applied
Central/Haversian canal
Structure: central channel for vessels and nerves
Function: conduct vessels and nerves throughout the length of the osteon
Location: center of each osteon
Perforating/Volkman’s Canal
(s, f, l)
Structure: channel that runs perpendicular to the long axis of the osteon
Function: deliver vessels and nerves throughout the thickness of the compact bone
Location: varies, run perpendicular to the long axis of the osteon
Concentric lamellae
(s, f, l)
Structure: concentric layers of bony matrix with collagen fibers in each layer running in opposite direction
Function: layered arrangements and fiber orientation allow optimal weight bearing and even weight transfer
Location: rings of bony matrix in each osteon
Cement line
(s, f, l)
Structure: darker staining line
Function: demarks the outer limit of each osteon
Location: outer boundary of each osteon
Canaliculi
(s, f, l)
Structure: short, narrow, hair-like channels
Function: conduct osteocyte process, allow them to make physical contact and chemical contact via adhesions and gap junctions
Location: radiate from each lacuna and often run the width of each lamella
Interstitial lamellae
(s, f, l)
Structure: non-cylindrical layers of bony matrix
Function: fill the gap between osteons; weight bearing and transferring; remnant of remodeled osteon
Location: in between osteons
Outer circumferential lamellae
(s, f, l)
Structure: several layers of bony matrix on the outer most side of the compact bone
Function: bind the osteons from the outside, site of attachment for periosteum
Location: outermost layer of compact bone
Sharpey fibers
(s, f, l)
Structure: thick, ropy bundles of collagen type I fibers extending from periosteum into the compact bone
Function: tightly anchor periosteum to the compact bone
Location: extend from periosteum into the outer concentric lamellae and often deeper into the peripheral osteons
Inner circumferential lamellae
(s, f, l)
Structure: several layers of bony matrix on the inside of the compact bone
Function: bind the osteons from the inside site of attachment for endosteum
Location: innermost layer of the compact bone
Trabeculae
(s, f, l)
Structure: bony spicule, small think, short bony tissues. In adults, bony matrix is lamellar (layered). No osteons
Function: collectively allow weight transfer, source of quick bone absorption and formation
Location: throughout the central portion of most bones
Red Marrow
(s, f, l)
Structure: hematopoietic tissue
Function: blood cell production
Location: most marrow cavities in infants and young children. Marrow cavities of flat bones and vertebrae in adults
Yellow marrow
(s, f, l)
Structure: unilocular adipose tissue
Function: lipid storage
Location: most marrow cavities of long bones in adults
Woven/Primary/Immature bone
First bone that forms during ossification process. Collagen fibers are unorganized and osteocytes in lacunae are randomly scattered throughout bony matrix. Usually found in embryo and fetus or in adults at healing sites and the alveolar processes of the maxilla and mandible.
Lamellar/Secondary/Mature bone
Bone tissue that forms through remodeling of woven bone. Collagen fibers are well organized. Osteocytes in lacunae are regularly arranged and spaced throughout matrix. Found in most adult compact and spongy bones.
Parathyroid Hormone vs. Calcitonin
PTH - released by parathyroid glands, inhibits osteoblasts from producing bony matrix which stimulates osteoclast stimulating factor (OSF) secretion, which increases bone reabsorption by the osteoclasts, ultimately increasing the blood calcium level
Calcitonin - released by parafollicular cells (C-cells) of the thyroid and inhibits osteoclasts, thus reducing bone reabsorption and ultimately decreasing blood calcium level
Membranous ossification
bone formation within the mesenchyme. Osteoprogenitor cells –> osteoblasts — produce bony matrix —-> become osteocytes. Matrices interconnect and remodel to form compact bone and spongy bone
Endochondral ossification
Bone formation in the cartilage mold. Hyaline cartilage forms from mesenchyme –> hyaline cartilage forms isogenous groups –> and then osteoblasts and eventually osteocytes;
zone of rest, zone of proliferation, zone of hypertrophy, zone of calcification, zone of ossification.
Occurs in long bones that need to lengthen rapidly without requiring direct blood supply. Occurs at the epiphyseal plate.
