Chapter 5: The Skeletal System PDF

CHAPTER 5 The Skeletal System  Skeletal System: Connective Tissue Bones: mostly calcium crystals, also phosphate crystals, collagen and elastin protein fibers Cartilage: with collagen and elastin fibers Ligaments: Connects bone to bone. Tendons: Connects muscle to bones. Both: Dens...

CHAPTER 5 The Skeletal System  Skeletal System: Connective Tissue Bones: mostly calcium crystals, also phosphate crystals, collagen and elastin protein fibers Cartilage: with collagen and elastin fibers Ligaments: Connects bone to bone. Tendons: Connects muscle to bones. Both: Dense, regular connective tissue. Parallel collagen fibers, torn if stress is applied perpendicular to fiber’s orientation. Sprain: torn tendon or ligaments. Ice pack in first day to reduce swelling, heat pad after that to increase blood flow à faster healing. Cartilage and tendons/ligaments: low blood supply = slow healing. Ligaments  Bone functions Muscles attach to bones. Contracting muscles interacting with bones enables movement. Supports entire body, gives body its shape Protects internal organs (ribcage, skull, vertebrae) Forms blood cells (femur, humerus, sternum, coxal, vertebrae, etc. with red bone marrow) Stores calcium and maintains homeostasis of blood calcium levels Smallest bones transmit sound vibrations in the middle ear Long bone parts Hyaline cartilage Spongy bone  Bone cells Cells: Chondroblasts: forms cartilage, including hyaline cartilage of early fetal skeleton, and cartilage of cartilage growth plates Osteoblasts form solid bone, become trapped in bone spaces and become osteocytes to maintain the bone. Osteoclasts break down solid bone for remodeling the skeleton and releasing calcium.  Structure of Bone Osteocytes within solid bone to maintain it. Nutrients and wastes diffuse between cells, and some cells are in contact with blood vessels. Note: spongy bone with calcium crystal lattice: lighter than compact bone, but also not as strong. Figure 5.1 Slide 5.2  Bone Remodeling Changes in shape, size, strength Osteoclasts dissolve bone, osteoblasts deposit bone. Women’s coxal bones (pelvis) remodelled during puberty. Exercise remodels and builds bones! Overall, pressure on bones can make them change shape and get stronger. Osteoporosis: lower bone density / easy to break An imbalance in the activity of osteoblasts / osteoclasts leads to osteoporosis. Preventing osteoporosis especially important for women! Estrogen à increased osteoblast activity. Menopause (40-50) = reduced estrogen = less osteoblast activity. Osteoclasts are still active, and decrease bone mass Osteoporosis: lower bone density / easy to break Prevention: Exercise early in life builds up bone mass. You also need vitamin D and calcium. Don’t smoke Treatment: Hormone therapy for older women (slightly increased breast cancer risk). Medications alter activity of osteoclasts / osteoblasts. Osteoporosis  Long Bone Development Early fetus: hyaline cartilage model. Cartilage formed by chondroblasts Fetus: blood vessels à some conversion of cartilage to bone. Cartilage dissolves and osteoblasts move in, forming bone. Childhood: primary and secondary ossification sites formed and grow Adolescence: Growth hormone causes lengthening of bone. Puberty: estrogen, testosterone stimulate growth, but also cause uniting of diaphysis and epiphysis. Cartilage growth plate disappears and growth stops. Long Bone Development Long Bone Development Chondroblasts Osteoblasts  Hormones and long bone growth Growth hormone during adolescence. Testosterone / estrogen during puberty. These stimulate growth, but also stimulate merger of the primary and secondary ossification sites (no more growth plate means no more growth) So why are men, on average, taller than women? Estrogen stimulates merger of ossification sites sooner than testosterone does in men, so women’s growth stops sooner. Rate of bone growth is faster for men as well. Girls: growth during puberty starts a little earlier, but stops at around age 18 Boys: growth during puberty starts a little later, but stops at around age 21 Bone helps maintain homeostasis of blood Ca2+ Bone cells influenced by hormones Parathyroid hormone: removes calcium from bone, (stimulates osteoclasts) Calcitonin: adds calcium to bone, (stimulates osteoblasts) Depends on calcium concentration in blood Calcium is necessary for muscle contraction and nervous transmission: Low blood calcium à more parathyroid hormone released by parathyroid glands High blood calcium à more calcitonin released by thyroid gland Skeletal System Axial, (midline) bones in blue text Appendicular (appendages) in black text  Axial Skeleton: The Skull Tears allowed out Protects brain Vertebrae attach, Connects to cartilage, Middle and inner ears spinal cord allowed in which forms the rest embedded in temporal bone of the nose  Axial Skeleton: The Skull Sinuses are spaces within the skull. This makes the skull lighter These sinuses are lined with mucus membranes, and are connected with the nasal passages. This mucus can contribute to a runny nose associated with a cold or allergies  Axial Skeleton: Vertebral Column Vertebral column Vertebrae can be: cervical (neck), thoracic (with ribs), lumbar (lower back), sacral (fused bones at the hip), coccyx (fused vestigial bones that were once part of a tail) 33 total vertebrae (some fused) Spinal cord through a tube formed by vertebrae. Intervertebral disks: fibrocartilage, cushion vertebrae; assist in movement, flexibility. Damaged disks may pinch nerves Herniated / ruptured disks = extreme pain Center of disk is softer, and gel-like. Sudden movements or too much strain: soft center squeezed out at a weak spot. Herniated disk: pressure squeezes nerve Ruptured disk: center squeezed out entirely! Recovery with physiotherapy Surgery trims disk, or removes it entirely. Lift with your legs!  Axial Skeleton: Vertebral Column Spinal injuries may cause paralysis / loss of feeling. Do not move injured people if they might have spinal injuries.  Axial Skeleton: Ribs / sternum Ribs Twelve pairs Bottom two pair floating (not attached to sternum) Important for breathing: ribs pulled outwards and upwards Sternum: Breastbone Three bones fused, attached to diaphragm muscle for breathing  Appendicular Skeleton Pectoral girdle: shoulder Clavicle (most frequently broken bone), scapulas Pelvic girdles: hip Coxal bones, sacrum (pubic symphysis stretches in women for child birth, enabling baby’s head to pass) A woman’s pelvis is wider than a man’s, with a wider pelvic opening. Male versus female pelvises Female: wider pelvis, sacrum does not tilt in, ischial spines do not point in.  Appendicular Skeleton Limbs Arms: humerus, radius, ulna, carpals, metacarpals and phalanges Legs: femur, patella, tibia, fibula, tarsals, metatarsals and phalanges  Joints Classified by degree of movement Fibrous joint: immovable (like skull); Fontanels “soft spots” during birth and early childhood, some flexibility allows easier birth and brain growth in childhood Cartilaginous joint: slightly movable, cartilage connection; (lower ribs to sternum, between vertebrae) Synovial joint: freely movable bone ends covered with smooth, hyaline cartilage, attached by ligaments, bones are surrounded by dense connective tissue that forms a capsule, synovial membrane produces synovial fluids for lubrication Hinge and ball-and-socket synovial joints, as examples Synovial Joints  Skeletal system problems Dislocations: Bones forced out of joints. Dislocations are often accompanied by sprains (damaged tendons and ligaments) and inflammation. Examples include fingers, shoulders and knees A dislocated ankle (from one of my ex-students)  Broken bones: 1) Blood flows into broken area forming a blood clot (hematoma) 2) Chondroblasts create a mass of fibrocartilage called a callus (felt as a ring joining bones together) 3) Osteoclasts remove dead bone and blood cells of the blood clot 4) Osteoblasts convert the cartilage callus into bone 5) The broken region is actually stronger after healing! Broken bone held together by a callus, that solidifies  Torn cartilage: cartilage may tear when twisted or if excessive pressure occurs. Repairs slowly because of little blood flow. Arthroscopic surgery can repair ligaments / cartilage in joints. Slide 5.13  Arthritis: joint inflammation Osteoarthritis: cartilage lining ends of bones wears out, increasing friction between bones, inflaming joints. Controlling weight = less stress on joints (especially knees and ankles). Rheumatoid arthritis: auto-immune disease, immune system attacks synovial membrane in joints. Scar tissue forms, and joints may fuse. Hands with rheumatoid arthritis, some joints have become fused  Chiras, DD, Human Biology, Health, Homeostasis, and the Environment, Jones and Bartlett, Sudbury, Mass, 2002