Introduction to the Human Body Chapter 6 Skeletal System Introduction to the Human Body Chapter 6

Functions Functions Support Protection Assisting in movement Mineral homeostasis Hemopoiesis Triglyceride storage

Bone Types Types of Bones Long bones Short bones Flat bones Irregular bones Sesamoid bones Long bones: Longer than they are wide Usually have medullary cavity (yellow marrow) All in the limbs (appendicular only) Short bones: Same length in all directions (approximately cuboidal) Carpals and Tarsals Flat Ribs Skull Ilium Irregular What might be irregular? Vetebrae Grab bag Zygomatic Mandible Sesamoid Bonus bones Grow within the

Macroscopic (long bone) Diaphysis-- Epiphysis (proximal & distal) Metaphysis (proximal & distal) Articular cartilage Periosteum – dense irregular CT Medullary cavity Endosteum

Review Name the 4 types of bones. Name the ends of a long bone. Name the shaft of a long bone. Name the part between the ends and shaft of a long bone. the 3 types of bone cells.

Structure Microscopic 25% water, 25% collagen, 50% mineral salts Cell types Osteoblasts Osteocytes Osteoclasts Mineral salts: what minerals? Cell types: do prefix/suffix analysis “clast” is new

Structure: Compact Bone Compact bone is made up of round units called osteons Central (Haversian) canals Perforating (Volkmann’s) canals Concentric lamellae Lacunae Canaliculi Intro: There are several kinds of bone. We’re going to focus on two: compact bone and spongy bone Where found?

Compact Bone Compact bone is made up of round units called osteons Central (Haversian) canals – run longways through bone; center of osteons. Concentric lamellae- concentric circles Perforating (Volkmann’s) canals – carry nerves, blood & lymph vessels from the periostium. Perpendicular to the long axis (aka, perpendicular to the central canal) Concentric lamellae – rings of matrix Lacunae – spaces containing osteocytes Canaliculi – channels connecting lacunae *Both central and perforating canals have blood vessels Direct flow of nutrients from vessels through cell processes of osteoblasts and from one cell to the next

Structure: Spongy Bone Made up of trabeculae Lighter than compact bone. Supports red marrow in spaces – makes blood Trabeculae contain lacunae & osteocytes.

Figure 6.02b-c Histology of Bone

Review How are compact and spongy bone different? How are osteocytes arranged within compact bone? How are Volkman’s and Haversian canals similar? How are they different?

Ossification Ossification 2 types Intramembranous ossification Endochondral ossification

Ossification Intramembranous Ossification - Flat bones Development of center of ossification Center of ossification – site where the bone develops Mesenchymal cells (stem cells) cluster together and differentiate into osteoblasts Calcification The osteoblasts secrete matrix until they are completely surrounded by it. Secretion stops and the osteoblasts become osteocytes

Ossification Formation of trabeculae As the bone matrix forms it develops into trabeculae that fuse together to form spongy bone Blood vessels grow into the spaces between the trabeculae and the mesenchyme along the surface Connective tissue develops into red bone marrow

Ossification Development of periosteum At the periphery of the bone, the mesenchyme condenses and develops into periosteum The spongy bone eventually grows together into compact bone Spongy bone remains in the center

Intramembranous Ossification

Ossification Endochondral Ossification Replacement of cartilage by bone Most bones are formed in this way 5 Steps Development of the cartilage model Growth of the cartilage model Development of the primary ossification center – region where bone tissue will replace most of the cartilage

Ossification Development of the secondary ossification center – similar to primary ossification center only spongy bone remains in the center Formation of articular cartilage and the epiphyseal plate – responsible for the lengthwise growth of long bones

Figure 6.03 Endochondral Ossification of the Tibia

Endochondral Ossification

Review How are endochondral and intramembranous ossification different? Describe how are the skeletons of the following different: fetus, young child, adolescent, adult.

Homeostasis Homeostasis Minerals (Ca, P, Mg) Vitamins A, C, and D Growth & maintenance Bone remodeling replaces old bone with new bone. 4 factors: Minerals (Ca, P, Mg) Vitamins A, C, and D Hormones: human growth hormone (hGH), estrogens, & androgens Weight-bearing exercise

Homeostasis Calcium homeostasis – 99% stored in bone Parathyroid hormone (PTH) – stimulates osteoclasts, raises blood Ca2+ levels. Calcitonin (CT) – inhibits osteoclasts, decreases blood Ca2+ levels.

Figure 6.04 Negative Feedback System for the Regulation of Blood Calcium

Review What are the effects of PTH and Calcitonin on bones? What 4 factors affect bone growth and maintenance?