The Skeletal System PDF

The Skeletal System Objectives Discuss functions of the skeletal system. Identify types of bones. Describe bone structure. Identify types of bone tissues. Describe bone histology. Explain bone’s role in calcium homeostasis. Understand bone remodeling. Describ...

The Skeletal System Objectives Discuss functions of the skeletal system. Identify types of bones. Describe bone structure. Identify types of bone tissues. Describe bone histology. Explain bone’s role in calcium homeostasis. Understand bone remodeling. Describe factors affecting bone  The Skeletal System Constitutes of the entire framework of bones and their cartilages, along with the joints. ~20% of total body weight. We are born with ~300 bone, but we end up with 206 bones as adults. Why??? Functions of the Skeletal System  Examples: Rib cage protects the lungs and heart. Bones of the spine protect the spinal cord. Bones of the skull protect the brain.  Yellow marrow stores triglycerides which can serve as a source of energy.  Blood cells are produced in the red bone marrow.  Bones store several minerals, especially calcium and phosphorus, which contribute to the strength of bone.  Bones provide a surface for the attachment of skeletal muscles, contributing to the production of movement.  Bones and cartilage of the skeletal system compose Types of Bones Bones are divided into five categories based on their shapes: 1. Long bones 2. Short bones 3. Flat bones 4. Irregular bones 5. Sesamoid bones Each shape of bone has a distinct function. Types of Bones  1. Long Bones + A long bone is one that is cylindrical in shape, being longer than it is wide. + Long bones function as levers; they move when muscles contract. Long bones are found in the arms (humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the fingers (metacarpals, phalanges) and toes (metatarsals, phalanges).  2. Short Bones + A short bone is one that is cube-like in shape (approximately equal in length, width, and thickness). + Short bones provide stability and support as well as some limited motion. The only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles  3. Flat Bones + A flat bone is typically thin and often curved. + Flat bones serve as points of attachment for muscles and often protect internal Examples includeorgans. the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs. 4. Irregular Bones + An irregular bone tend to have a more complex shapes. + Irregular bones protect internal organs. Many facial bones, particularly the ones containing sinuses, are classified as irregular bones.  5. Sesamoid Bones + A sesamoid bone is a small, round bone (shaped like a sesame seed). + Sesamoid bones protect tendons from compressive forces. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and Knee knees. cap The patellae (singular = patella) are (patella ) the only sesamoid bones found in Axial and Appendicular Skeletons Axial and Appendicular Skeletons The appendicular skeleton includes all of the limb bones, plus the bones that unite each limb with the axial skeleton The appendicular skeleton consists of the pectoral and pelvic girdles, the limb bones, and the bones of the hands and feet. The axial skeleton forms the central axis of the body and consists of the skull, vertebral column, and thoracic cage.  The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). The clavicle (collarbone) is an S-shaped bone located on the anterior side of the shoulder. It is attached on its medial end to the sternum of the thoracic cage, which is part of the axial skeleton. The lateral end of the clavicle articulates (joins) with the scapula just above the shoulder joint. You can easily palpate, or feel with your fingers, the entire length of your clavicle. Figure. Pectoral Girdle The pectoral girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial Long Bone Anatomy of a Long Bone  Diagram of Blood and Nerve Supply to Bone Blood vessels and nerves enter the bone through the nutrient foramen.  Proxima l Parts of a Long epiphysi s Metaphy Bone sis + Diaphysis: the long, cylindrical, main portion of the bone. Diaphysi + Epiphyses: the proximal and distal ends of the s bone. + Metaphyses: the regions between the diaphysis and the epiphyses. Metaphysi s + In a growing bone, each metaphysis contains an epiphyseal (growth) plate, a layer of hyaline cartilage Distal epiphysi that allows the diaphysis of the bone to grow in length. s Articula r cartilag Parts of a Long e Bone + Articular cartilage: a thin layer of semi- rigid connective tissue that reduces Medullar y friction and acts as a shock absorber. It cavity lacks blood vessels. + Medullary cavity: hollow region in the diaphysis that contains fatty yellow bone marrow and numerous blood vessels. It minimizes the weight of the bone and Articula r provides maximum strength of the bone cartilag e with minimum weight.  Parts of a Long Bone + Endosteum: a delicate membranous lining of the medullary cavity where bone Endosteu m growth, repair, and remodeling occur. Periosteu m + Periosteum: a tough connective tissue sheath that covers the outer surface of the bone.  Periosteum and Endosteum The periosteum forms the outer surface of bone, and the endosteum lines the medullary cavity.  Cartilage is a strong, A bone is a connective tissue flexible, fibrous tissue (part of where the living cells, tissues, connective tissue) that forms and other components are rubber-like padding at the enclosed within hard non- ends of long bones that help living intercellular material.  Types of Bone Tissues 1. Compact 2. Spongy (cortical)bone (cancellous)bone  1. Compact (cortical) bone The denser, stronger type of bone tissue. It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection. Osteon The microscopic Compact structural bone unit of compact bone (a)This cross-sectional view of compact bone shows the basic structural unit, the osteon. (b) In this micrograph of the osteon, you can clearly see the concentric lamellae and central canals  2. Spongy (cancellous) bone It is lighter than compact bone and found in the interior of some bones and at the end of long bones. It consists of columns of bone called trabeculae. The spaces in some spongy bones contain red marrow, where hematopoiesis occurs. Hematopoiesis (pronounced “heh- ma-tuh-poy-EE- sus”) is blood cell production. Trabecula Space for red e Spongy marrow bone  Diagram of Spongy Bone Spongy bone is composed of trabeculae that contain the osteocytes. Red marrow fills the spaces in some bones  Bone Most bones Tissue contain compact and spongy bone tissue, but their distribution and concentration vary based on the bone’s overall function. Example: a flat bone consists of two layers of compact bone and an interior spongy bone. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer.  Bone Histology Bone tissue Extracellular Cell matrix s ~15% water. 1. Osteogenic ~30% collagen fibers (flexibility). cell ~55% crystallized mineral salts 2. Osteocyte (hardness and strength) (calcium 3. Osteoblast phosphate and calcium carbonate 4. Osteoclast combine to create hydroxyapatite crystals).  Bone Cells Four types of cells are found within bone tissue. Osteogenic cells are undifferentiated and develop into osteoblasts. When osteoblasts get trapped within the calcified matrix, their structure and function changes, and they become osteocytes. Osteoclasts develop from monocytes and macrophages and differ in appearance from other bone cells  Bone Cells: 1. Osteogenic cells: Undifferentiated with high mitotic activity. Located in both the periosteum and the endosteum. Differentiate and develop into osteoblasts. 2. Osteoblasts: Responsible for forming new bone. Found in the growing portions of bone, including the periosteum and endosteum. Synthesize and secrete the collagen matrix Osteoblas Osteogen and calcium salts. t ic cell  Bone Cells: 3. Osteocyte: Form when the secreted matrix surrounding the osteoblast calcifies. The primary cells of mature bone and the most common type of bone cell. Maintain the bone matrix and detect mechanical stress on a bone. 4. Osteoclast: Responsible for bone resorption, or breakdown. Osteoclas Found on bone surfaces. t Essential for calcium (Ca2+) homeostasis. Osteocyt https://www.youtube.com e /watch?v=78RBpWSOl08  Bone Remodeling Osteocl Osteobl ast ast Bone resorption Bone deposition osteoClasts osteoBlasts Carve out Build bone bone  Bone Remodeling Bone continues to renew and reshape itself throughout a person’s lifetime. Bone remodeling: a dynamic process of continual addition of new bone tissue (bone deposition) and removal of old bone tissue (bone resorption). Balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone.  Bone’s Role in Calcium Homeostasis Calcitoni Thyroi d n gland Osteoclasts activity is inhibited/Ca2+ deposited in bone Ca2+ Homeostasis Osteoclasts release Ca2+ from bone Parathyroi Parathyroid d gland hormone  Bone Tissue & Exercise When placed under stress, bone tissue becomes stronger through increased deposition of mineral salts and production of collagen fibers by osteoblasts. Any type of exercise will stimulate the deposition of more bone tissue, but resistance training has a greater effect than cardiovascular activities. Resistance training is especially important  Bone Tissue & Microgravity Astronauts subjected to the microgravity in space lose bone mass. Bone loss can be as much as 1% per week. Astronaut Scott Kelly spent 340 days in space from 2015 to 2016. It took three years before the bones returned to their pre-flight bone mass density, and even when the bones reached that point, they still hadn’t completely recovered the same structure they had as before the astronauts’ flight. The Skeletal System and Homeostasis Homeostasis Osteoporosis: bone resorption (breakdown) is faster than bone deposition (formation). It results from depletion of calcium from the body. Bone mass becomes so depleted that bones fracture, often spontaneously, under the mechanical stresses of everyday living.  Bing Videos Calcium Homeostasis: Regulation & Maintenance Calcium Homeostasis Feedback Loop