Anatomy Ch 6-7

Semirigid Connective Tissue

Weaker than bone, but more flexible and resilient

Chondroblasts

Cells that produce the matrix of cartilage

Chondrocytes

Mature cartilage cells that maintain the matrix and ensure health and viability of cartilage

Occupy small spaces called lacunae

Perichondrium

Dense Irregular connective tissue and stem cells for cartilage growth

Cartilage

* Firm, gel-like extracellular matrix composed of protein and ground substance
* Supporting connective tissue
* Chondrocytes occupy small spaces enclosed by their extracellular matrix called **lacunae**
* Strong and resilient to provide support and withstand deformation
* Usually covered by **perichondrium**

Functions of Cartilage

Supporting soft tissues

Gliding surface at articulations

Precursor model for bone growth

Hyaline Cartilage

* Glassy matrix; chondrocytes in lacunae; usually covered by **perichondrium**
* Most common type of cartilage, but also the weakest
* Smooths joint surfaces, model for bone growth
* Covers articular ends of long

bones; most of the larynx,

trachea, nose

Fibrocartilage

* Parallel collagen fibers in matrix; chondrocytes in lacunae
* Loaded with collagen fibers
* No **perichondrium**
* Absorbs shock; resists compression
* Example: intervertebral discs

Elastic Cartilage

* Contains abundant elastic fibers—forming mesh around lacunae;
* **Perichondrium present**
* Maintains shape while permitting flexibility
* Examples: External ear; epiglottis of the larynx

Bone

* Two-thirds of bone’s weight is inorganic (mostly calcium salts); one-third is organic (collagen and other proteins)

– **Organic parts** provide flexibility

*Cells, collagen fibers*

– **Inorganic parts** provide compressional strength *Hydroxyapatite (“calcium salts”)*

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* **Periosteum**: dense irregular connective tissue covering bone
* Mature bone cells are called **osteocytes**
* Two forms of bone: **compact bone** and **spongy bone**

– Compact bone is arranged in cylindrical osteons of concentric lamellae

– Spaces within spongy bone house hematopoietic cells that generate blood cells

Bones of skeleton are complex organs containing all four tissue types

• Cartilage (connective tissue) \n • Blood (connective tissue) \n • Blood vessels (epithelial tissue)

• Nerves (nervous tissue) \n • Ligaments (connective tissue)

• Tendons (connective tissue)

\-Extracellular matrix is sturdy and rigid due to deposition of minerals (calcification)

Functions of Bone

* Support and protection of more delicate organs
* Movement – attachment site for muscles
* **Hematopoiesis** – blood cell production in red bone marrow
* Storage of mineral and energy reserves

– Calcium and phosphate \n – Lipids stored in yellow marrow

Compact Bone

* The basic unit of compact bone is the **osteon**

*-Also known as a Haversian system*

* Solid and relatively dense
* Contain Circumferential lamellae \n

Spongy Bone (cancellous bone)

* Open lattice of narrow plates called **trabeculae**
* Internal surface of bones
* No osteons


* Trabeculae contains parallel lamellae

Long bones

Greater length than width

Short bones

Nearly equal in length and width, cuboidal

Flat Bones

Thin surfaces

Irregular Bone

Complex shapes

Diaphysis (General Structure of Long Bones)

Elongated, cylindrical shaft

Epiphysis (General Structure of Long Bones)

* Knobby, enlarged regions at each end
* Strengthens joints
* Attachment site for tendons and ligaments

Metaphysis (General Structure of Long Bones)

* Region between diaphysis and epiphysis
* Contains epiphyseal (growth plate)

Articular Cartilage (General Structure of Long Bones)

* Thin layer of hyaline cartilage covering the epiphysis
* Reduces friction and absorbs shock in moveable joints

Medullary Cavity (General Structure of Long Bones)

* Hollow, cylindrical space in diaphysis
* In adults, it contains yellow bone marrow

Endosteum (General Structure of Long Bones)

* Covers most internal surfaces of bones
* Contains osteoprogenitor cells, osteoblasts, and osteoclasts
* Active in bond remodeling, growth, fracture repair

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Periosteum (General Structure of Long Bones)

* Covers external surfaces of bones (except where articular cartilage does)
* Dense irregular connective tissue
* Attached by perforating fibers (collagen fibers) embedded in the bone matrix
* Acts as an anchor for blood vessels and nerves
* Contains osteoprogenitor cells and osteoblasts
* Active in remodeling, growth, fracture repair

Flat Bones Within the Skull

* Two layers of compact bone, with spongy bone (diploë) sandwiched between
* Flat bones (along with short and irregular) __**lack**__ **diaphysis, epiphysis , and marrow cavity**

Osteoprogenitor Cells(Cells of Bone)

Mesenchymal stem cells in endosteum and periosteum; can produce more stem cells or osteoblasts

Osteoblasts (Cells of Bone)

Form bone matrix (secrete as organic osteroid)

Osteocytes (Cells of Bone)

Mature Bone Cells

Reside in lacunae; maintain matrix and detect

mechanical stress on a bone

Osteoclasts

Large, multinuclear cells that dissolve bone matrix (osteolysis), releasing Ca++

– Have ruffled border (specialization of cells to enhance surface area in active space within the cell) \n – Often located in a **resorption lacuna** \n – Secrete hydrochloric acid and enzymes that **dissolve matrix**

Intramembranous Ossification

Develops from mesenchyme

• Produces flat bones of the skull, some facial bones, mandible, and central portion of clavicle

Mesoderm → Mesenchyme → Intramembranous

Endochondral Ossification

* Begins with hyaline cartilage model
* Produces majority of bones in the body

Mesoderm → Mesenchyme → Hyaline Cartilage → Endochondral

Ossification centers form within thickened regions of mesenchyme (beginning in 8th week of development)

\-Some osteoprogenitor cells become osteoblasts

1st Step of Intramembranous Ossification

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Osteoid undergoes calcification

i. Osteoid formation is quickly calcified as calcium salts are deposited onto the osteoid

ii. Calcification entraps osteoblasts and they become osteocytes

2nd Step of Intramembranous Ossification

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Woven bone and surrounding periosteum form

iii. Initially the bone is unorganized and called woven bone (primary bone)

iv. Mesenchyme surrounding woven bone starts to thicken and forms periosteum

v. Newly formed blood vessels start to enter bone

3rd Step of Intramembranous Ossificatiion

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Lamellar Bone **(secondary bone)** replaces woven bone, as compact bone and spongy bone form

iv. Spaces between the trabeculae are filled and becomes compact bone

v. Starts to assume the morphology of flat bone

4th Step of Intramembranous Ossification

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* Produces all other bones of the body
* Begins with a model of fetal hyaline cartilage (8-12weeks)

1st Step Endochondral Ossification

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* Cartilage calcifies, and a periosteal bone collar forms around diaphysis
* Chondrocytes start to hypertrophy (enlarge) and resorb surrounding matrix, producing holes
* Cartilage begins to calcify and nutrients cannot diffuse to the chondrocytes so they die (producing large holes)
* Blood vessels grow toward the cartilage
* Perichondrium forms osteoblasts producing the periosteum
* These osteoblasts secrete osteoid creating the bone collar

2nd Step Endochondral Ossification

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The primary ossification center forms in the diaphysis

* Periosteum bud (capillaries and osteoblasts) extends from the periosteum into the cartilage shaft
* The remaining calcified cartilage acts as a scaffold on which osteoblasts produce osteoid (ossification center)

3rd step of Endochondral Ossification

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Secondary ossification centers form in the epiphyses

* (birth to early childhood)
* Hyaline cartilage in the center of the epiphysis calcifies and begins to degenerate
* Blood vessels and osteoprogenitor cells enter the bone and bone begins to replace the calcified cartilage
* Simultaneously, osteoclasts start to resorb some bone matrix within the diaphysis— creating the medullary cavity

4th Step of Endochondral Ossification

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Bone replaces cartilage, except the articular cartilage and epiphyseal plates

– By late stage of development almost all hyaline cartilage is replaced by bone

– Hyaline cartilage remains as articular cartilage and epiphyseal plate

• Becomes the border between diaphysis and epiphysis

5th Step of Endochondral Ossification

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Epiphyseal plates ossify and form epiphyseal lines

* Bone growth progresses through puberty and ends with ossification of epiphyseal plates
* Epiphyseal line= remnant of epiphyseal plate

6th Step of Endochondral Ossification

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Skull

Hyoid

Located between the mandible and larynx \n Does not articulate with \n another bone \n Contains a midline body \n and two hornlike processes, the greater Cornu and lesser cornu \n The hyoid serves as an attachment site for tongue and muscles of larynx used in swallowing

Vertebral Column

Composed of 26bones

* 24 individual vertebrae
Cervical vertebrae: Seven bones of the neck
Thoracic vertebrae: Twelve bones that help form the superior region of the back and articulate with the ribs
Lumbar vertebrae: Five bones that help form the inferior, concave region of the back
* Two inferior bones are fusions of several vertebrae •
Sacrum: Five fused vertebrae
Coccyx: Four fused vertebrae forming the "tailbone"

Thoracic Cage

Sutures

Linear junctions between skull bones

Fontanelles (soft spots)

Areas between skull bones

Greater Cornu

Lesser Cornu

Sacrum

Five fused vertebrae
S1-S5
triangular bone forming posterior wall of pelvic cavity - Transverse ridges (lines )mark fusion points of the five vertebrae
\-Sacral canal is continuation of vertebral canal
• Sacral hiatus in inferior opening

* Anterior and posterior sacral foramina allow nerves to exit
* Fuses at 26 years

Coccyx

Fusion of four small vertebrae \n -Attachment site for ligaments and muscles \n -Fuses at 26 years \n -May fuse with the sacrum in older individuals

Four fused vertebrae forming the "tailbone" \n Co1-Co4

Cervical vertebrae

Seven bones of the neck \n C1-C7

Lumbar vertebrae:

Five bones that help form the inferior, concave region of the back \n L1-L5

Thoracic vertebrae:

Twelve bones that help form the superior region of the back and articulate with the ribs \n T1-T12 \n Articulate with ribs \n Heart-shaped body \n Demifacets (spots on bones that are articulation-based) \n Vertebral foramen is circular \n Long, inferior-pointing spinous process \n Transverse processes have facets (except T11 and T12)

Facial Bones

Superior orbital fissure

Inferior Orbital fissure

Optic Canal

Nasal Septum

Zygomatic Arch

Mandible

Temporomandibular joint

Temporal Line

Hard Palate

Foramen Magnum

Jugular Foramen

Carotid Canal

Frontal Crest

Frontal Bone

Glabella

Supraorbital margin

Supercilliary arch

Parietal

External Acoustic (auditory) meatus

Mandibular Fossa

Petrous Portion

Internal acoustic (auditory meatus)

Mandibular Fossa

Cranial Vault

Carotid Canal

Malleus

hammer; first of the three auditory ossicles of the middle ear

Incus

anvil; middle of the three auditory ossicles of the middle ear

Stapes

staples; inner of the 3 ossicles of the middle ear

Occipital Condyles

Foramen Magnum

Inferior Nuchal line

Superior nuchal line

Occipital

External Occipital Protuberance

Sagittal Suture

Between parietal bones. Fuse in 40s

Coronal Suture

Between frontal and parietal bones \n Fuse in late 20s

Lamdoid Suture

Between parietal bones and occipital bone \n Fuse in 40s

Squamous Suture

Fuses in late adulthood (60+ years)

Olfactory Foramina

Holes

Superior and middle nasal conchae

Form part of lateral walls of nasal cavity

Perpendicular plate

Sphenoid

Body of sphenoid

Greater wing of sphenoid