HHP3115 Unit 1 Notes Chapter 6 PDF

Chapter 6 – Bones and Skeletal Tissues Cartilage: - Found throughout adult body o Ear and nose o Articular cartilage (found in joints) and costal cartilage (attaches ribs to sternum) o Larynx and epiglottis o Intervertebral discs and pubic symphysis - Primari...

Chapter 6 – Bones and Skeletal Tissues Cartilage: - Found throughout adult body o Ear and nose o Articular cartilage (found in joints) and costal cartilage (attaches ribs to sternum) o Larynx and epiglottis o Intervertebral discs and pubic symphysis - Primarily water - Flexible Types of cartilage: 1. Hyaline cartilage: most abundant type a. Provides support through flexibility b. Found at ends of bones (articular & costal cartilage) c. Make up the cartilage that makes up embryonic long bones (before ossification occurs) d. Nose 2. Elastic cartilage: contains many elastic fibers a. Able to tolerate repeated bending b. Ear 3. Fibrocartilage: resists strong compression and strong tension (opposite forces) a. Unique b. Intervertebral discs c. Pubic symphysis d. Actually some is found in the knee Bones are organs because they contain multiple tissues - Mostly connective tissue - Also nervous and blood tissue, epithelial tissue lining blood vessels o They’re living! So they need this blood supply - Also cartilage down at the end of bones (articular cartilage) - Functions: o Support o Movement (muscle have to pull on something rigid in order to contract) o Protection (think: skull, ribs) o Mineral storage (calcium and phosphate) o Blood-cell formation (red bone marrow) o Energy metabolism (some effect on insulin release from pancreas) Chemical composition of bone: - ~35% organic components o Cells, fibers, organic substances o Collagen is very abundant (useful for resisting tension forces) o Allows the bone to be flexible - ~65% inorganic mineral salts o Primarily calcium phosphate o Resist compression forces o Keeps it stiffer Most fractures are a result of TWISTING forces - Because compression forces are resisted by mineral, and tension forces are resisted by collagen Example of forces: - Just standing causes both compression (due to body pushing down on it), and tension (due to the bending that results from the first force) on the femur o If they weren’t flexible enough to bend, they’d be brittle - Heating of the bone makes it become brittle o Loses its flexibility of organic materials - Adding acid to bones make it way too flexible o Loses its mineral components that give strength Types of cells in bone: - Osteogenic cells: stem cells that differentiate into osteoblasts - Osteoblasts: actively produce and secrete bone matrix o Bone matrix is called osteoid - Osteocytes: keep the osteoid healthy o The living cells that you find within bones - Osteoclasts: responsible for resorption of bone (removing the mineral calcium and phosphate) o Derived from a line of white blood cells o Secrete HCl and lysosomal enzymes Bone is a constantly evolving/remodeling tissue - That’s why it needs cells to both break down and build up different areas of the bone - This is in response to the forces upon different bones Types of bones: Long bones: longer than they are wide Irregular bones: miscellaneous category (vertebrae, pelvis) Flat bones: thin and flat Short bones: generally cube-shaped (carpals and tarsals) Structure of a long bone: Compact bone: very few pores, outer layer Spongy/cancellous bone: porous, inner portion Proximal epiphysis/ Diaphysis/ Distal epiphysis Epiphyseal line: border between diaphysis/epiphysis - In childhood, this is the epiphyseal growth plate Medullary cavity: hollow inside of diaphysis - Helps us lighten up the bone - Leaves space for the bone marrow Periosteum: outer covering (connective tissue) Endosteum: lines medullary cavity (connective tissue) In both these layers, there’s osteoblast/clast activity Nutrient arteries: provide nutrition to the bone Vessels penetrate throughout the bone and supply nutrition to the osteocytes Microscopic structure of compact bone: - Repeated cylindrical units called osteons - Center of each osteon is a central canal o Holds artery, vein, and nerve - There are several concentric rings surrounding the central canal o Each ring is called a lamella o Lacunae: the gaps between each of these rings  Osteocytes reside in here o Canaliculi: gaps that travel through the lamella to get to successive rings, aiding in delivery of nutrition to the living cells o Collagen fibers line up parallel to each other within each lamella, but every consecutive lamella has collagen fibers that run PERPENDICULAR its adjacent lamellae  This is what helps us resist twisting forces  It also helps stop crack propagation Ossification/osteogenesis: bone tissue formation - Membrane bones – formed directly from mesenchyme o Process is called intramembranous ossification o Only a few bones (particularly skull/clavicles) use this process - Other bones (majority) – develop initially from hyaline cartilage o Process is called endochondral ossification Endochondral ossification: - All bones (except some of bones of skull/clavicle) use this process - Bones are modeled in hyaline cartilage o Begins forming late in 2nd month of human development (around beginning of fetal period) o Not entirely gone until early adulthood (particularly the clavicles) - Cartilage is gradually replaced by mineral bone Stages in endochondral ossification: - Early on, the entire bone model is hyaline cartilage - Bone collar: outer “diaphysis” – the first site of bone formation - Hollowing of the medullary cavity (primary ossification center) - Hollowing in both ends of the epiphyses (secondary ossification centers) - Bone growth: o Length: epiphyses get further apart from each other  Chondroblasts in the cartilaginous growth plate are replicating on the epiphyseal side  Lengthening the bone  Chondroblasts are disintegrating on the diaphyseal side, as they are replaced with bone  Epiphyseal plates remain the same thickness for most of childhood/adolescence, since replication and disintegration are occurring at similar rates   As adolescence comes to an end, disintegration occurs at a faster rate  The growth plate gets thinner and thinner, till it’s eventually gone  At that point, the diaphysis and epiphysis bone fuse together, and growth is done o Width:  Osteoblasts add bone tissue to the EXTERNAL surface of the diaphysis  Osteoclasts remove bone form the INTERNAL surface of the diaphysis  Expands the medullary cavity  This is called appositional growth because it bone tissue is added to the surface Some things to think about – bone growth in length: - You can take an X-ray (usually of wrist) to judge how much more a child will grow by looking at growth plate thickness - You have more joints as a kid than you do as an adult; growth plates are technically joints because cartilage separates the two portions of bone Bone remodeling: - Bone is a dynamic living tissue - 500 mg of calcium may enter or leave the adult skeleton each day - Cancellous bone of the skeleton is replaced every 3-4 years - Compact bone is replaced every 10 years Within limits, the bone has the ability to alter its strength in response to mechanical stress - Increased mechanical stress -> deposition of mineral salts, production of collagen fibers - Decreased mechanical stress -> demineralization and collagen reduction -> weakening of bone Mechanical stress comes from weight-bearing activities, walking, running, etc. - Helps build and retain bone mass Why might someone lose bone mass? - Bedridden persons - Reduced activity while in a cast - Astronauts in a weightless environment As mechanical forces change, the microscopic anatomy of the bone changes - Example: switching from running to swimming - Compression and tension lines are actually moving - Osteoblasts build up bone matrix where it’s needed, an osteoclasts break down bone matrix where it’s not needed Stages in healing a fracture: 1. Hematoma formation: collection of blood at the site of injury a. The blood vessels that were broken during fracture release this blood 2. Fibrocartilaginous callus formation: fibrous tissue and cartilage fill the break a. New blood vessels are also forming 3. Bony callus formation: cartilage is replaced with bone a. Basically this is just like embryonic bone development 4. Bone remodeling: bony callus -> normal bone that’s specialized to whatever forces it normally incurs Bone Diseases: Osteoporosis: characterized by low bone mass (due to pores and thinning) - Bone reabsorption outpaces bone deposition - Occurs in most women after menopause (largely due to decreased estrogen levels) Osteomalacia: bones are inadequately mineralized, in adults Rickets: essentially the same thing as osteomalacia, but occurs in children - Consequences: bow-legged o Occurs because bones aren’t strong enough to withstand body weight - Cause: vitamin D deficiency (you need vitamin D to be able to use calcium) o Vitamin D comes from diet, and sunlight (skin produces it) o Smog in industrial societies -> kids getting lots of rickets. We solved this by  fortifying milk with vitamin D, and introducing child labor laws Paget’s disease: excessive rate of bone deposition (and remodeling as a whole) - This leads to the bone tissue never really maturing - Fairly common in elderly people - Potential cause: virus? - Consequence: bones get really thick, potentially creating pain Osteosarcoma: a type of bone cancer - Usually affects kids/teens - Usually happens at the knee - Generally caused by osteoblasts replicating out of control The skeleton throughout life: - In kids and teens: formation exceeds reabsorption - In young adults: formation equals reabsorption - In old age: reabsorption exceeds formation o Everyone loses bone mass as they get older, osteoporotic or not o We can help minimize this by weight-bearing activities and walking (within limits – try not to cause more damage than good!