ANS3043 Exam2 - Bone + Tissue

epiblast

the outermost layer of an embryo before it differentiates into ectoderm and mesoderm.

hypoblast

forms the extraembryonic membranes

primitive streak

A groove on the surface of an early embryo along the future long axis of the body
-covers caudal 2/3 of embryo
-establishes bilateral symmetry

Gastrulation

In animal development, a series of cell and tissue movements in which the blastula-stage embryo folds inward, producing a three-layered embryo, the gastrula. (ectoderm, mesoderm, endoderm)

ectoderm

outermost germ layer that forms:
-CNS
-sense organs
-mammary glands
-sweat glands
-skin
-hair
-hooves

Mesoderm

middle germ layer that forms:
-circulatory system
-repro system
-kidneys
-urinary ducts
-muscle
-fat
-connective tissue
-bone

endoderm

inner germ layer that forms:
-digestive system
-liver
-lungs
-pancreas
-thyroid gland
-most other glands

Neurulation

results in formation of precursors of spinal cord, brain, and peripheral nervous system

neurulation process

1. ectodermal tissue thickens and flattens to form neural plate
2. neural folds come together to complete fusion of neural tube
3. neural plate folds to form neural tube, which will become spinal cord and brain
4. neural tube closes; neural crest cells delaminate & migrate to become peripheral nervous system and other cell types
5. closure of neural tube begins in cervical area and extends in both cranial/caudal directions

spinal dysraphism

a group of neural tube defects that describe some manifestation of incomplete closure of the spine

spina bifida

a congenital defect that occurs during early pregnancy when the spinal canal fails to close completely around the spinal cord to protect it

somites

Paired blocks of mesoderm just lateral to the notochord of a vertebrate embryo. form along anterior-posterior axis of developing embryo

somitogenesis

-formation of paired cuboidal masses of mesoderm (somites), one on each side of neural tube
-occurs in a cranial to caudal manner

Dermamyotome

dorsolateral portion of the somite that forms dermatome and myotome (dermis and muscle)

Sclerotome

gives rise to the vertebrae (skeleton)

Embryogenesis

The process by which a single-celled zygote becomes a multicellular embryo. ends once species can be identified and can be called fetus

connective tissue functions

-support, surround and connect other tissues
-structural framework
-protect organs
-store energy reserves (in tissue called adipose)
-transport fluids within body

connective tissue

extensive cellular matrix with relatively few cells (bone, cartilage, loose connective tissue)

connective tissues are classified by

-extracellular matrix
-mixture/arrangement of connective fibers
-type of cells present

connective tissue proper

loose connective tissue and dense connective tissue

supportive connective tissue

-bone and cartilage
-strong protein fibers, thicker ground substance

fluid connective tissue

blood and lymph, no fibers, mostly cells and ground substance

fibroblasts

In connective tissue, cells that
-secrete the proteins for extracellular fibers
-secrete hyaluronic acid which helps make grounding substance
-most abundant fixed cells in connective tissue

macrophages

-immune cells
-can be fixed or wandering

mesenchymal cells

stem cells that respond to injury or infection

Adipocytes

fat cells that make up most of the subcutaneous layer

ground substance

fluid-like or gel-like substance that fills the space between cells and fibers, contains proteoglycans

Proteoglycans

A glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate
-linear core protein with glycosaminoglycans
(chondroitin sulfate and hyaluronic acid are GAGs)

Major types of protein fibers in connective tissue

1. collagenous
2. reticular
3. elastic

Collagen

-main protein in tendons, bone cartilage
-strong, flexible but inelastic
-difference in AA sequence affects strength/functionality

collagen synthesis and maturation

1. alpha chains
- hydroxylation of lysine and proline by enzymes
2. pre-procollagen
- helix formation
3. procollagen
-exported from fibroblast to extracellular matrix
-ends romoved
4. tropocollagen
- tropocollagen molecules align
- lysyl oxidase contributes to cross-link formation (stability and strength)
5. collagen fibril
-maturation of cross-links increase stability (insoluble)
6. collagen fiber (multiple fibrils)

Osteolathyrism

-deficiency in collagen cross-linking caused by reduced lysyl oxidase activity
-caused by eating grass pea or sweet pea
-symptoms: weakness, spinal deformities, joint degeneration

scurvy

-defective collagen formation caused by deficiency in prolyl hydroxylase and lysyl hydroxylase activity
-caused by vitamin c deficiency, needed as co-factor for activity of enzymes
-symptoms: weakness, fatigue, impaired wound healing, osteopenia (weak bones)

reticular fibers

-contains type III collagen
-branching, interwoven network
-small, fine, delicate
-framework in glands, lymphs and connective tissue surrounding soft organs

elastin

-protein
-can be reversibly stretched to nearly 2x length
-cross-links indicate elastin fiber maturation
-high non-polar AA content
-insoluble in water
-in ligaments

loose connective tissue

-fills in space between organs and provides cushioning
-high proportion ground substance
-relatively few collagen and elastin fibers
-can distort and stretch w/o damage
-cushions shock
-vascularized w/ numerous cells
-separates skin from deeper structures
-surrounds/supports blood vessels/nerves
-route for diffusion

dense connective tissue

-structure provides more strength but less flexibility
-numerous fibers, few cells
-dense regular and dense irregular

dense regular connective tissue

-mixture of collagen, elastin and reticular fibers
-fibers align in one direction
-aligned with forces applied to tissue (tendons, aponeuroses, ligaments, elastic tissue)

dense irregular connective tissue

- high amount of collagen
-dense, interwoven randomly arranged fibers
-supports stresses from different directions
-capsules around visceral organs
-dermis of skin
-nerve and muscle sheaths

subcutanous injection

A subcutaneous injection or shot is one into the fatty tissues just beneath the skin.
CT circulatory supply and loose structure provides route for drug diffusion

epidermis

epithelial tissue

dermis (true skin)

dense irregular CT, nerve endings, capillaries, sweat glands, vessels

Scarring occurs when too much ______________ is produced during wound healing.

collagen; collagen fibers become more aligned rather than random

keloids

abnormal response to trauma, fibroblast proliferation, over-production of collagen

compared to bone, cartilage is

-lighter
-half as dense
-more flexible

Ground substance in cartilage is much more _________ than loose or dense connective tissue

rigid

Ground substance in cartilage is made of _________________ __________________

chondroiton sulfates

lacuna

small cavities in bone that contain osteocytes in bone or chondrocytes in cartilage

chondrocyte

mature cartilage cell

types of cartilage

elastic, hyaline, fibrocartilage

elastic cartilage

-mostly elastic fibers
-least tough
-very flexible
-yellowish in color

hyaline cartilage

-mostly densely packed fine collagen fibers
-ends of bones
-tough, resistant to pressure and friction
-somewhat flexible
-bluish-white, glassy
-most abundant cartilage type
-may become bone by ossification

fibrocartilage

-almost all collagen fibers
-little ground substance
-most tough type of cartilage

cartilage characteristics

-highly specialized ECM
-avascular, nutrients supplied by diffusion
-limited healing ability
-limited proliferative capacity of chondrocytes
-chondrocytes are immoble

bone characteristics

-most rigid connective tissue
-made of inorganic matrix & collagen fibers
-few cells
-rich vascular supply
-considerable metabolic activity

Inorganic matrix of bone is composed of _____ and ____. This makes up majority of bone (45%)

calcium and phosphorus

Organic component (30%) of bone is made up of

collagen, proteoglycans and non-collagenous proteins

25% of bone is made up of _____________

water

functions of bone

-protection
-support
-locomotion
-mineral/lipid storage
-hematopoiesis (blood formation)

Matrix of bone is made up of

hydroxyapatite crystals and collagen fibers

hydroxyapatite crystals

-Ca5(PO4)3OH
-fluoride can replace OH to make stronger crystal
-inflexible
-brittle
-resists compression

collagen fibers

-provides flexibility and strength
-gives framework for formation of crystals

flat and irregular bones

-ribs
-skull
-pelvis
-vertebrae
-scapula

long bones

-femur
-tibia
-fibula

long bone structure

diaphysis (shaft) and epiphysis (enlarged ends)

preiosteum

dense, vascularized membrane surrounding bone

growth plate

-the area just below the head of a long bone in which growth in bone length occurs; the epiphyseal plate.
-made up of cartilage, once maturity is reached growth plate closes

medullary cavity

cavity within the shaft of the long bones filled with bone marrow

articular cartilage

covers the surfaces of bones where they come together to form joints

compact bone

-aka cortical bone
-dense structure
-found at periphery of bones
-Ca not readily available

spongy bone

-aka trabecular bone
-network of struts/thick netting
-Ca more readily available
-larger surface area
-vertebrae, flat bones, shafts/ends of long bones

bone tissue

-highly organized
-composed of osteons
-canals surrounded by lamellae
-osteocytes locked within lacunae and linked together through canaculus

osteon

structural unit of compact bone (aka haversian system)

lamellae

Concentric rings made up of groups of hollow tubes of bone matrix

canaculi

passageways forming a branching network for the exchange of materials between blood vessels and osteocytes

osteoblast

cell that will produce new bone (osteo = bone, blast = immature)

osteocyte

mature bone cell within mineralized matrix

osteoclast

-involved in bone resorption and remodeling
-multinucleated, cannot replicate

bone lining cells

inactive cells on bone surface, can be activated if needed for repair

Periosteum

A dense fibrous membrane covering the surface of bones (except at their extremities) and serving as an attachment for tendons and muscles.

cartilage requires relatively ________ amounts of oxygen, while bone requires relatively ________ amounts of oxygen

low, high

osteogenesis

process of bone formation

endochondrial ossification

bone formation from a cartilage template

intramembranous ossification

bone formation as a replacement of connective tissue in the absence of cartilage

During fetal development, most bones have a _________ ____________, which is gradually replaced by bone

cartilage template

endochondrial ossification process

1. mesenchyme condenses during embryogenesis
2. committed mesenchymal cells differentiate into chondrocytes to form model for bone
3. remaining mesenchymal cells surround cartilage core to form perichondrium
4. centrally located chondrocytes undergo hypertrophy, then apoptosis
5. blood vessels fill space left by dead chondrocytes and deliver osteoblasts
6. osteoblasts deposit bone matrix, perichondrium converted to periosteum, bone layer formed around diaphysis
7. primary ossification center established in center of diaphysis, bone formed until diaphysis is filled, osteoclasts hollow out marrow cavity
8. secondary ossification centers from as blood vessels enter near tips of bone
9. osteoblasts produce spongy bone that replace epiphyseal cartilage, articular cartilage and growth plate cartilage left

long bone lengthening

1. growth of cartilage on epiphyseal side of growth plate
2. ossification of cartilage on diaphyseal side of growth plate

zones of growth plate

-reserve (resting) zone
-proliferating zone
-prehypertrophic zone
-hypertrophic zone
-ossification zone

reserve (resting) zone

-chondrocytes closest to epiphysis
-source of chondrocytes forming proliferation zone

proliferating zone

-chondrocytes proliferate and flatten
-chondrocytes lay down a cartilage ECM that later serve as scaffold for bone formation
-pushes epiphysis away from diaphysis

prehypertrophic zone

-chondrocytes enter maturation zone, differentiate and enlarge
-cells produce additional molecules for ECM and collagen fibers, builds cartilage

hypertrophic zone

-chondrocytes and lacuncae become 5-12x bigger
-chondrocytes die and leave behind calcified cartilage matrix that is invaded by capillaries + osteoblasts

ossification zone

-development of new bone
-osteoblasts deposit organic matrix
-connection of adjacent osteocytes by cytoplasmic threads

osteoid + osteoblast differentiation =

ossification

chondrodysplasia

-defective formation of cartilage
-FGF3 involved in arrest of bone growth
-restricts proliferation of cartilage at growth plate, expressed in resting and proliferative chondrocytes
-SNP in FGFR3 gene results in AA substitution and enhanced proliferation of pre-hypertrophic chondrocytes

break joint

denotes the point on a lamb carcass where the foot and pastern are removed at the cartilaginous junction of the front leg (young sheep)

Spool Joint

The joint where the foot and pastern are removed from the front leg of a sheep carcass. A carcass must have two spool joints to be classified as mutton (adult sheep)

long bone growth

-occurs as long as rate of cartilage growth > rate of bone formation within growth plate
-growth finished when cartilage of epiphyseal plate is eliminated and growth plate fused

long bone growth is influenced by

hormones, nutrition, minerals, chronological age

intramembranous bone formation

-direct laying down of bone into primitive connective tissue (mesenchyme)
-mesenchyme ---> osteoblast ---> osteocyte
-skull formed through this process