The Skeletal System

Functions Framework for support Transmits movement Maintains shape Protects internal organs from mechanical injury Contains and protects the red bone marrow, one of the hemopoietic (blood-forming) tissues Mineral reservoir - storage site for excess calcium and phosphorus Storage of fats – yellow marrow

Types of skeletons Fluid-filled body cavity (hydrostatic) Fluid-filled closed chambers Internal pressure generated by muscle contraction E.g. sea anemone and worms

Types of skeletons Exoskeleton Arthropods Hard segments covering muscles and visceral organs Muscles are attached to the exoskeleton Restricts growth and size of animal  molting

Types of skeletons Endoskeleton Internal, often mineralized, connective tissue Muscles on the outside Cartilage – sharks and rays Other vertebrates – cartilage is replaced by bone as embryo matures and develops

Bone Tissue Compact bone Spongy bone Periosteum series of Haversian canals concentric layers of bone cells (osteocytes) new bone formed by osteocytes Spongy bone ends of long bones less dense than compact bone spongy bone of femur, humerus, and sternum contains red marrow yellow marrow at center is used to store fats Periosteum outer layer of bone rich in nerve endings, blood, and lymphatic vessels inner portion forms new bone or modifies existing bone to meet new conditions

Appendicular and axial skeleton Axial skeleton (80 bones) axis of the body support and protect the organs of the head, neck, and trunk Skull Sternum Ribs Vertebral Column + sacrum and coccyx Appendicular skeleton (126 bones) anchors appendages to the axial skeleton Upper Extremities Lower Extremities Pectoral Girdle Pelvic Girdle

Joints or articulations Meeting of two bones Types of joints Immovable Slightly movable Freely movable

Types of bone cells Osteoblasts Osteocytes Osteoclasts immature bone cells manufacture hormones and enzymes that aid in bone mineralization Osteocytes mature osteoblasts that have migrated into lacunae (spaces) form bone, maintain matrix, and act for calcium homeostasis Osteoclasts cells responsible for bone reabsorption and shaping located on bone surfaces

Types of bones Long bones Short bones Flat bones Irregular bones Long shaft (diaphysis) Two joint surfaces (epiphyses) Mostly compact bone e.g. femur, tibia, fibula, radius, ulna, Short bones Cube-shaped, mostly spongy bone e.g. bones of wrist and ankle, patella Flat bones Thin and curved e.g. skull and sternum Irregular bones Irregular and complicated shapes e.g. spine and hips

Bone formation Intramembranous ossification  formation of the flat bones of the skull Endochondral ossification  formation of long bones

Bone remodeling Resorption of bone (by osteoclasts) followed by replacement of bones (by osteocytes) Functions to regulate calcium levels, repair damaged bones, and shape and sculpt the skeleton during growth Rate is regulated by parathyroid hormones (PTH) and Vitamin D

Disorders of the skeletal system Osteoporosis Reduced bone density leading to fractures Rickets and osteomalacia Softening of bones leading to deformations and fractures Arthritis Inflammation of joints Bone fractures Scoliosis

Muscular system Name 3 characteristics of muscle tissue. Describe 3 types of muscle tissue according to location, structure, and nervous control. Define the following terms: muscle fiber, myofibril, myofilament, sarcomere, actin, and myosin. Describe the sliding-filament theory. References?