Study Guide: Tissues, Skeletal Tissues, and The Skeleton

Chapter 4: Tissues & Histology

Connective Tissues: Types, Structure, and Function

Connective tissues are a diverse group of tissues that provide support, bind together, and protect tissues and organs of the body. They are classified based on their structure and function.

• Loose Connective Tissue Proper

  • Areolar Connective Tissue: Loose arrangement of fibers (collagen, elastic, reticular) with abundant ground substance; found under epithelia, around organs; functions in support, cushioning, and immune defense.

  • Adipose Connective Tissue: Composed of closely packed adipocytes (fat cells); stores energy, insulates, and cushions organs; found under skin, around kidneys, and in the abdomen.

  • Reticular Connective Tissue: Network of reticular fibers in a loose ground substance; forms the stroma of lymphoid organs (lymph nodes, spleen, bone marrow); supports free blood cells.

• Dense Connective Tissue Proper

  • Dense Regular Connective Tissue: Parallel collagen fibers with few elastic fibers; provides strong attachment (e.g., tendons, ligaments).

  • Dense Irregular Connective Tissue: Irregularly arranged collagen fibers; withstands tension from multiple directions; found in dermis of skin, fibrous capsules of organs and joints.

• Cartilage

  • Hyaline Cartilage: Most common; glassy matrix with fine collagen fibers; supports and reinforces; found in nose, trachea, larynx, costal cartilages, articular surfaces of bones.

  • Elastic Cartilage: Similar to hyaline but with more elastic fibers; maintains shape and flexibility; found in external ear, epiglottis.

  • Fibrocartilage: Thick collagen fibers; strong and compressible; found in intervertebral discs, pubic symphysis, menisci of knee.

Example: The intervertebral discs are composed of fibrocartilage, providing both strength and flexibility to the spine.

Chapter 6: Skeletal Tissues

Types of Cartilage and Growth

• Three Types of Cartilage: Hyaline, elastic, and fibrocartilage (see above for details).

• Appositional Growth: Cartilage-forming cells in the perichondrium secrete new matrix on the surface of cartilage.

• Interstitial Growth: Chondrocytes within cartilage divide and secrete new matrix, expanding cartilage from within.

Perichondrium: Dense irregular connective tissue surrounding cartilage; provides nutrients and resists outward expansion.

Bone Classification and Structure

• Axial Skeleton: Skull, vertebral column, rib cage.

• Appendicular Skeleton: Limbs and girdles (pectoral and pelvic).

• Bone Shapes: Long (e.g., femur), short (e.g., carpals), flat (e.g., sternum), irregular (e.g., vertebrae), sesamoid (e.g., patella).

Bone Structure

• Long Bone Anatomy: Diaphysis (shaft), epiphyses (ends), metaphyses (between diaphysis and epiphyses), compact bone (outer layer), spongy bone (inner layer), periosteum (outer membrane), endosteum (lines internal surfaces), bone marrow (red and yellow).

• Other Bone Types: Flat, irregular, short, and sesamoid bones have thin layers of compact bone surrounding spongy bone; periosteum covers outside, endosteum lines inside.

Bone Tissue Composition

• Organic Components: Osteoid (collagen fibers, ground substance); provides flexibility and tensile strength.

• Inorganic Components: Hydroxyapatite (calcium phosphate crystals); provides hardness and resistance to compression.

Formula for Hydroxyapatite:

$Ca_{10}(PO_4)_6(OH)_2$

Bone Cells

• Osteogenic Cells: Stem cells; differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete osteoid.

• Osteocytes: Mature bone cells; maintain bone matrix.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

Bone Marrow

• Red Marrow: Hematopoietic (blood cell-forming); found in spongy bone of flat bones, epiphyses of long bones (more extensive in children).

• Yellow Marrow: Fat storage; found in medullary cavity of long bones (increases with age).

Bone Development and Growth

• Endochondral Ossification: Bone forms by replacing hyaline cartilage; most bones below the skull (e.g., long bones).

• Intramembranous Ossification: Bone develops from fibrous membrane; forms flat bones (e.g., skull, clavicle).

• Epiphyseal Plate Zones (for long bone growth):

  1. Resting (quiescent) zone

  2. Proliferation (growth) zone

  3. Hypertrophic zone

  4. Calcification zone

  5. Ossification (osteogenic) zone

• Epiphyseal Plate Closure: Occurs at the end of adolescence (approx. 18 years in females, 21 in males); cartilage is replaced by bone, stopping longitudinal growth.

Chapter 7: The Skeleton

Skull Bones and Markings

• 8 Cranial Bones: Frontal, parietal (2), temporal (2), occipital, sphenoid, ethmoid; protect the brain and provide attachment for head and neck muscles.

• 14 Facial Bones: Mandible, vomer, maxilla (2), zygomatic (2), nasal (2), lacrimal (2), palatine (2), inferior nasal concha (2); form the face, cavities for sense organs, and openings for air and food passage.

• Bony Nasal Septum: Formed by the perpendicular plate of the ethmoid bone and the vomer; septal cartilage also contributes.

• Hard Palate: Formed by the palatine processes of the maxillae and the horizontal plates of the palatine bones.

• Zygomatic Arch (Cheekbone): Formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone.

• Bony Orbit: Formed by parts of the frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid bones.

• Paranasal Sinuses: Found in frontal, sphenoid, ethmoid, and maxillary bones; lighten the skull, warm and moisten air, enhance voice resonance.

Vertebral Column and Thorax

• Number of Bones: 26 total (24 vertebrae, 1 sacrum, 1 coccyx).

• Divisions: Cervical (7), thoracic (12), lumbar (5), sacrum, coccyx.

• Spinal Curvatures: Primary (thoracic, sacral; present at birth), secondary (cervical, lumbar; develop after birth).

• Abnormal Curvatures: Scoliosis (lateral), kyphosis (excessive thoracic), lordosis (excessive lumbar).

• Intervertebral Disc: Cushion-like pad; nucleus pulposus (gelatinous center) and annulus fibrosus (collagen and fibrocartilage ring); absorbs shock and allows movement.

Ribs and Girdles

• Rib Articulation: Ribs 2-9 articulate with thoracic vertebrae at two points: the body and the transverse process.

• Rib Classification:

  • True (vertebrosternal) ribs: 1-7; attach directly to sternum.

  • False ribs: 8-12; do not attach directly to sternum.

  • Vertebrochondral ribs: 8-10; attach to sternum via cartilage of rib 7.

  • Floating (vertebral) ribs: 11-12; no anterior attachment.

• Pectoral Girdle: Clavicle and scapula; attaches upper limbs to trunk, allows mobility.

• Pelvic Girdle: Two hip bones (os coxae); attaches lower limbs, supports pelvic organs.

Pelvis Structure and Comparison

• Boundaries:

  • False (greater) pelvis: Above pelvic brim.

  • True (lesser) pelvis: Below pelvic brim.

  • Pelvic inlet (brim): Superior opening of true pelvis.

  • Pelvic outlet: Inferior opening of true pelvis.

• Male vs. Female Pelvis: Female pelvis is wider, shallower, lighter, and has a larger pelvic inlet/outlet for childbirth.

• Bones of the Bony Pelvis: Two hip bones, sacrum, coccyx.

Table: Comparison of Male and Female Pelvis

Feature	Male Pelvis	Female Pelvis
General Structure	Heavier, thicker	Lighter, thinner
Pelvic Inlet	Narrow, heart-shaped	Wide, oval
Pubic Arch Angle	Acute (<90°)	Broad (>90°)
Sacrum	Narrow, longer	Wider, shorter
Acetabula	Large, close together	Small, farther apart

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