Chapter 7 Skeletal System Skeletal System Functions: Give shape to structures-Ex. Face Support and protection of tissues: Ex: Lower limbs, pelvis, and vertebrae support the body’s weight Ex: Skull protects the eyes, ear, and brain Blood cell formation Mineral storage Ex: Calcium

Bone Classification Long Bones (a) Short Bones (b) Flat Bones (c) Irregular Bones (d) Sesamoid (Round) Bones (e)

Parts of a Long Bone distal proximal red yellow epiphysis diaphysis compact bone spongy bone articular cartilage periosteum endosteum medullary cavity trabeculae marrow red yellow

2 Parts of a Long Bone Epiphysis- Proximal- Distal- Diaphysis- Medularry cavity- Compact bone- Spongy bone- Red bone marrow- Yellow bone marrow-

Compact and Spongy Bone

Microscopic Structure of Compact Bone Osteon- Central canal- perforating canal osteocyte lacuna bone matrix

Bone Development (osteogenesis or ossification) 1. Intramembranous Ossification bones originate within sheetlike layers of connective tissues broad, flat bones skull bones (except mandible) intramembranous bones 2. Endochondral Ossification bones begin as hyaline cartilage form models for future bones most bones of the skeleton endochondral bones

Endochondral Ossification (hylaine cartilage model) A/B. Bones start as cartilage in fetus covered with a layer of bone matrix (periosteum) C. Bone matrix made by osteoblasts (bone-forming cells) D/F. As the fetus develops the cartilage model is digested away opening up the medullary cavity E. By birth most of the cartilage has been converted to bone except articular cartilage (cover ends of bone) and epiphyseal plates (line of cartilage through the epiphysis) E. As child gets older, bones become longer along the epiphyseal plates

Ossification How bones grow longer New cartilage is formed on the epiphyseal plate facing the bone ends and along the external end of the articular cartilage. As new cartilage is added the old cartilage is replaced with bony matrix. This process lengthens the bone.

Ossification How bones grow wider Osteoblasts add bone tissue to the periosteum on the external face of the diaphysis Osteoclasts (bone destroying cells) remove bone tissue from the endosteum on the internal face of the diaphysis These processes happen at the same rate which causes the bone to widen.

What controls bone growth? Parathyroid (PTH) Hormone The parathyroid gland in the neck reads the calcium levels in the blood. When calcium levels are low the parathyroid releases PTH hormone to activate osteoclasts. Osteoclasts “eat away” bone tissue from the human skeleton to release calcium into the bloodstream. This process brings up the calcium levels in the blood. The opposite occurs when calcium levels are too high in the blood.

Factors Affecting Bone Development, Growth, and Repair Deficiency of Vitamin A – retards bone development Deficiency of Vitamin C – results in fragile bones Deficiency of Vitamin D – rickets, osteomalacia Insufficient Growth Hormone – dwarfism Excessive Growth Hormone – gigantism, acromegaly Insufficient Thyroid Hormone – delays bone growth Sex Hormones – promote bone formation; stimulate ossification of epiphyseal plates Physical Stress – stimulates bone growth

Bones of the Skull Human skull consist of 26 bones 8 bones make up the cranium 14 bones make up the face

Cranium forehead roof of nasal cavity roofs of orbits frontal sinuses supraorbital foramen coronal suture

Cranium side walls of cranium roof of cranium sagittal suture 2. Parietal (2) side walls of cranium roof of cranium sagittal suture

Cranium back of skull base of cranium foramen magnum 3. Occipital (1) back of skull base of cranium foramen magnum occipital condyles

Cranium side walls of cranium floor of cranium 4. Temporal (2) side walls of cranium floor of cranium floors and sides of orbits squamous suture mandibular fossae external acoustic meatus styloid process zygomatic process (makes zygomatic arch)

Cranium base of cranium sides of skull floors and sides of orbits 5. Sphenoid (1) base of cranium sides of skull floors and sides of orbits sphenoidal sinuses

Cranium 6. Ethmoid (1) roof and walls of nasal cavity floor of cranium Makes nasal cavity

Facial Skeleton upper jaw anterior roof of mouth floors of orbits 1. Maxillary (2) upper jaw anterior roof of mouth floors of orbits sides of nasal cavity floors of nasal cavity

Facial Skeleton L shaped bones located behind the maxillae 2. Palatine (2) L shaped bones located behind the maxillae posterior section of hard palate floor of nasal cavity lateral walls of nasal cavity

Facial Skeleton prominences of cheeks lateral walls of orbits 3. Zygomatic (2) prominences of cheeks lateral walls of orbits floors of orbits temporal process (articulates with zygomatic process)

Facial Skeleton medial walls of orbits 4. Lacrimal (2) medial walls of orbits groove from orbit to nasal cavity, providing a pathway for tears. 5. Nasal (2) bridge of nose

Facial Skeleton 6. Vomer (1) inferior portion of nasal septum

Facial Skeleton extend from lateral walls of nasal cavity 7. Inferior Nasal Conchae (2) extend from lateral walls of nasal cavity Support mucous membranes within nasal cavity

Facial Skeleton lower jaw mandibular condyle coronoid process 8. Mandible (1) lower jaw mandibular condyle coronoid process mandibular foramen mental foramen

Infantile Skull Fontanels – fibrous membranes

Infant Skull