Chapter 11
Biology 25: Human
Biology
Prof. Gonsalves
Los Angeles City College
Loosely Based on Mader’s
Human Biology,7th edition
Skeletal System
Components: Bones, ligaments, and cartilage.
Functions:
Along with muscular system:
 Movement and locomotion.
 Mechanical work: Lifting, pulling,
pushing objects.
 Body support.
 Protection of delicate internal organs (brain,
heart, lungs, etc.)
 Calcium storage

Homeostatic Role:

Helps maintain constant blood calcium
levels.
Skeletal System: Protection, Movement, & Support
Connective Tissue
Large amounts of extracellular (ECF)
material in the spaces between connective
tissue cells.
 4 Types of Connective Tissue:
 Connective tissue proper
 Cartilage
 Bone
 Blood

Connective Tissue Proper
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Loose connective tissue:
 Scattered collagen and tissue fluid.
 Dermis of skin
Dense fibrous connective tissue:
 Regular arranged.
 Collagen oriented in same direction.
• Tendons
 Irregularly arranged.
 Resists forces applied in many directions.
• Capsules and sheaths
Cartilage
 Chondrocytes.
 Supportive
and protective tissue.
 Elastic properties to tissues.
 Precursor to many bones.
 Articular surfaces on joints.
Bone
 Hydroxyapatite
crystals
 Osteoblasts:
Bone-forming cells
 Osteocytes:
Trapped osteoblasts: less active
 Osteoclasts:
Bone resorbing cells

General Anatomy of a Long Bone
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Diaphysis - main shaft of the bone
Epiphysis - large end of the bone
Metaphysis - where above meet during bone growth
Articular Cartilage - covers epiphysis, reduce friction
Periosteum - dense, white covering around the bone
 fibrous layer - blood, lymph, nerves pass through
 osteogenic layer - where bone cells originate
Medullary (marrow) Cavity - adults, yellow marrow
Endosteum - lines medullary cavity, houses bone cells
Microanatomy of Compact (Dense) Bone
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General Features
 few empty spaces (dense)
 thicker in diaphysis than epiphysis
 concentric ring-like structure
Osteon (Haversian System) - Components of Compact Bone
 central (Haversian) canal - vessels and nerves
 osteocytes - mature bone cells (from osteoblasts)
 lacunae - spaces where osteocytes reside
 lamellae - rings around canal, house lacunae
 canaliculi - projections from lacunae + osteocytes
Supporting Structures
 perforating (Volkmann) canals - run perpendicular
 interstitial lamellae - between osteons
Ossification: The Formation of Bone During Development

Endochondral Ossification (replacing hyaline
cartilage)
 cartilage "bone model" formed in the embryo
 perichondrium - membrane around the cartilage
 vessel penetrates cartilage, brings osteoblasts
 cartilage converted into compact bone
 perichondrium --> periosteum
 chondrocytes gradually hypertrophy and die
 vessels move into space and convert to bone
 primary ossification center - in diaphysis
 secondary ossification center - in epiphysis
 epiphyseal plate - between the two, still cartilage
Bone Remodeling - Spongy Bone Converted to Compact Bone
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osteoclasts - resorption of old bone tissue
 lysosome release of digestive enzymes
 cell "phagocytoses" (engulfs) particles
osteoblasts - lay down new bone in its place
bone constantly undergoes remodeling throughout life
 Ca needed in muscle, nerve, blood clotting
 fractures repaired immediately
Factors essential for proper bone growth
 Ca and P in proper amount in diet
 trace amounts of Boron and Manganese
 Vitamin D - regulates Ca metabolism
 Vitamin C - maintenance of bone matrix
 Vitamin A - osteoclast/blast function
 Vitamin B12 - osteoblast function
 Human Growth Hormone (HGH) - pituitary
 Calcitonin - thyroid, Ca absorption to bone
 Parathormone - parathyroid, Ca release to blood
 Sex Hormones - Testosterone + Estrogen
Classification of
Bones
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Long Bones – considerably longer than wide; shaft with 2 ends
(most limb bones, finger bones, etc.)
Short Bones – roughly cube shaped (wrist bones)
Sesamoid bone – short bone within a tendon (patella)
Flat bones – Flattened, thin, and usually curved (most cranial
bones, ribs, sternum, and scapula)
Irregular bones – irregularly shaped (vertebrae, hip bones)
Bone Classification

There are two divisions of the adult skeleton with
a total of 206 bones
 Axial Skeleton includes 80 bones
 Skull (22), middle ear ossicles (6), hyoid (1),
vertebral column (26), and thorax (25)
 Appendicular Skeleton includes 126 bones
 Pectoral girdle (4), upper extremities (60),
pelvic girdle (2), and lower extremities (60)
Synovial Joints

Structure
 any joint where there is a space between bones
 synovial cavity - space between the bones
 freely moveable joints (diarthrotic)
 articular cartilage - covers articular surface
 articular capsule - encloses the cavity itself
 fibrous capsule - attached to periosteum
• ligaments - clearly defined connections
 synovial membrane - inner layer of capsule
• produces synovial fluid
• reduces friction in the joint
 accessory ligaments - additional support
 extracapsular - outside capsule
 intracapsular - within capsule
 articular discs (menisci) - pads between bones
 bursae - sac-like structures that reduce friction
 between tendons, muscle, ligaments: and bone