Connective Tissue

Question 1

Connective tissue cellular components

Answer 1

fibroblasts, fibrocytes, adipocytes, mast cells, macrophages, plasma cells, eosinophil, and lymphocytes

Question 2

Fibroblasts
(s, f, l)

Answer 2

Structure :dendritic to fusiform cells with oval, euchromatic nuclei

Function: produce fibers

Location: throughout connective tissue, close to fibers

Question 3

Fibrocytes
(s, f, l)

Answer 3

Structure: flat, fusiform cells with thin, heterochromatic nuclei

Function: maintain fibers

Location: throughout the connective tissue, close to mature fibers

Question 4

Adipocytes (unilocular and multilocular)
(s, f, l)

Answer 4

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

Question 5

Mast cells
(s, f, l)

Answer 5

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

Question 6

Macrophages
(s, f, l)

Answer 6

Structure: various sizes and shapes, often difficult to identify

Function: phagocytose pathogens and debris

Location: throughout connective tissue

Question 7

Plasma cells
(s, f, l)

Answer 7

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

Question 8

Eosinophil
(s, f, l)

Answer 8

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

Question 9

Lymphocytes
(s, f, l)

Answer 9

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

Question 10

Neutrophils
(s, f, l)

Answer 10

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

Question 11

Fibers in connective tissue

Answer 11

Collagen fibers (Type I), Elastic and fibrillin fibers, Reticular fibers (Type III collagen)

Question 12

Collagen fibers
(s, f, l)

Answer 12

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

Question 13

Elastic fibers
(s, f, l)

Answer 13

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

Question 14

Reticular fibers
(s, f, l)

Answer 14

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”

Question 15

Ground substance
(s, f, l)

Answer 15

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

Question 16

Loose connective tissue
(s, f, l)

Answer 16

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

Question 17

Dense irregular connective tissue
(s, f, l)

Answer 17

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

Question 18

Dense regular connective tissue
(s, f, l)

Answer 18

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

Question 19

Elastic connective tissue
(s, f, l)

Answer 19

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

Question 20

Reticular connective tissue
(s, f, l)

Answer 20

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

Question 21

Unilocular adipose connective tissue
(s, f, l)

Answer 21

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

Question 22

Multilocular adipose connective tissue
(s, f, l)

Answer 22

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

Question 23

Hyaline cartilage
(s, f, l)

Answer 23

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

Question 24

Elastic cartilage
(s, f, l)

Answer 24

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

Question 25

Fibrocartilage (Fibrous cartilage)
(s, f, l)

Answer 25

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

Question 26

How does cartilage get its nutrients? What does this result in?

Answer 26

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.

Question 27

How does cartilage grow? (Types of growth)

Answer 27

Occurs mainly before adulthood, slowly decreasing through adolescence.
Appositional growth and interstitial growth

Question 28

Appositional growth

Answer 28

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.

Question 29

Interstitial growth

Answer 29

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.

Question 30

Isogenous groups

Answer 30

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.

Question 31

Osteoprogenitor cells
(s, f, l)

Answer 31

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

Question 32

Osteoblasts
(s, f, l)

Answer 32

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

Question 33

Osteocytes
(s, f, l)

Answer 33

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

Question 34

Osteoclasts
(s, f, l)

Answer 34

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

Question 35

Periosteum
(s, f, l)

Answer 35

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

Question 36

Endosteum
(s, f, l)

Answer 36

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

Question 37

Compact bone
(s, f, l)

Answer 37

Structure: highly organized into osteons

Function: mechanical support, protection, weight transfer, mineral storage

Location: outer surfaces of the bone

Question 38

Spongy bone
(s, f, l)

Answer 38

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

Question 39

Marrow spaces
(s, f, l)

Answer 39

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

Question 40

Haversian system (Osteon)
(s, f, l)

Answer 40

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

Question 41

Central/Haversian canal

Answer 41

Structure: central channel for vessels and nerves

Function: conduct vessels and nerves throughout the length of the osteon

Location: center of each osteon

Question 42

Perforating/Volkman’s Canal
(s, f, l)

Answer 42

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

Question 43

Concentric lamellae
(s, f, l)

Answer 43

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

Question 44

Cement line
(s, f, l)

Answer 44

Structure: darker staining line

Function: demarks the outer limit of each osteon

Location: outer boundary of each osteon

Question 45

Canaliculi
(s, f, l)

Answer 45

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

Question 46

Interstitial lamellae
(s, f, l)

Answer 46

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

Question 47

Outer circumferential lamellae
(s, f, l)

Answer 47

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

Question 48

Sharpey fibers
(s, f, l)

Answer 48

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

Question 49

Inner circumferential lamellae
(s, f, l)

Answer 49

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

Question 50

Trabeculae
(s, f, l)

Answer 50

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

Question 51

Red Marrow
(s, f, l)

Answer 51

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

Question 52

Yellow marrow
(s, f, l)

Answer 52

Structure: unilocular adipose tissue

Function: lipid storage

Location: most marrow cavities of long bones in adults

Question 53

Woven/Primary/Immature bone

Answer 53

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.

Question 54

Lamellar/Secondary/Mature bone

Answer 54

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.

Question 55

Parathyroid Hormone vs. Calcitonin

Answer 55

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

Question 56

Membranous ossification

Answer 56

bone formation within the mesenchyme. Osteoprogenitor cells –> osteoblasts — produce bony matrix —-> become osteocytes. Matrices interconnect and remodel to form compact bone and spongy bone

Question 57

Endochondral ossification

Answer 57

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.