Chapter 6 Anatomy Reading Objectives

Describe the effect of too little or too much calcium on the body

- Hypocalcemia, which is abnormally low levels of calcium, can have adverse effects on the body. Without adequate calcium, blood has difficulty coagulating, the heart may skip beats or stop beating, muscles may have difficulty contracting, nerves may have difficulty functioning and bones may become brittle. - Hypercalcemia - Abnormally high levels of calcium, the nervous system is under active, lethargy, sluggish reflexes, constipation and loss of appetite, confusion and in severe cases, coma.

Classify Bones according to their shapes

1 Long Bone - Cylindrical in shape, being longer than it is wide. Found in arms, legs, fingers and toes 2 Short Bone- Cube-like in shape, being approximately equal in length, width and thickness. Found in carpals of wrist and tarsals of ankle. 3 Flat Bone - Thin, also often curved. Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone) and the ribs. 4 Irregular Bone - One that does not have any easily characterized shape and therefore does not fit any other classification. Examples include vertebrae that support the spinal cord and protect it from compressive forces and many facial bones, particularly the ones containing sinuses. 5 Sesamoid Bone - Small, round bone, that is shaped like a sesame seed. These bones form in tendons. Typically found in tendons associated with the feet, hands and knees. EX: Patellae

Define and list examples of bone markings

1. Articulation - Where two bone surfaces come together - tend to conform to one another, such as one being rounded and the other cupped 2. Projection - An area of bone that projects above the surface of the bone - attachment points for tendons and ligaments 3. Hole - An opening or groove in the bone that allows blood vessels and nerves to enter the bone - their shape and size reflect the size of the vessels and nerves that penetrate the bones at these points.

List the nutrients that affect bone health

1. Calcium 2. Vitamin D 3. Vitamin K 4. Magnesium 5. Fluoride 6. Omega - 3 fatty Acids

Discuss the role these nutrients play in bone health

1. Calcium - Needed to make calcium phosphate and calcium carbonate, which form the hydroxyapatite crystals that give bone its hardness 2. Vitamin D - Needed for calcium absorption 3. Vitamin K - Supports bone mineralization; may have synergistic effect with vitamin D 4. Magnesium - Structural component of bone 5. Fluoride - Structural component of bone 6. Omega -3 Fatty Acids - Reduces inflammation that may interfere with osteoblast function

Compare and contrast compact and spongy bone

1. Compact Bone - Dense so that it can withstand compressive forces. Stronger. Can be found under the periosteum and in the diaphysis of long bones. 2. Spongy Bone - Open spaces and supports shifts in weight distribution

Identify the anatomical features of a bone

1. Diaphysis - tubular shaft that runs between the proximal and distal ends of the bone 2. Epiphysis - The wider section at each end of the bone , which is filled with spongy bone 3. Medullary Cavity - The hollow region in the diaphysis, which is filled with yellow marrow 4. Compact Bone- The walls of the diaphysis are composed of this 5. Epiphyseal Plate - Growth plate. Sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length. 6. Endosteum - Delicate membranous lining of the medullary cavity , where bone growth, repair and remodeling occurs. 7. Periosteum - The outer surface covering of the bone - fibrous membrane. Contains blood vessels, nerves and lymphatic vessels that nourish compact bone. 8. Articular Cartilage - A thing layer of cartilage that reduces friction and acts as a shock absorber where the epiphysis meet other bones to form joints.

Describe the effects of hormones on bone tissue

1. Growth Hormone (GH) increases length of long bones, enhances mineralization, and improves bone density. 2. Thyroxine - Stimulates bone growth and promotes synthesis of bone matrix 3. Sex Hormones - Promotes osteoblasts activity and production of bone matrix; responsible for adolescent growth spurt; promote conversion of epiphyseal plate to epiphyseal line 4. Calcitriol - Stimulates absorption of calcium and phosphate from digestive tract 5. Parathyroid hormone - Stimulates osteoclast proliferation and resorption of bone by osteoclasts; promotes reabsorption of calcium by kidney tubules; indirectly increases calcium absorption by small intestine 6. Calcitonin - Inhibits osteoclast activity and stimulates calcium uptake by bones

Describe the function of each category of bones

1. Long Bones- Function as levers; they move when muscles contract 2. Short Bones - Provide stability and support as well as some limited motion 3. Flat Bones - Serve as points of attachment for muscles and often protect internal organs 4. Irregular Bone- Support and protect internal organs 5. Sesamoid Bones - Protect tendons by helping them overcome compressive forces.

Describe the histology of bone tissue

1. Osteoblasts - Bone cell responsible for forming new bone and is found in the growing portions of bone, including the periosteum and endosteum. 2. Osteocytes - The primary cell of mature bone and the most common type of bone cell. Maintain the mineral concentration of the matrix via the secretion of enzymes 3. Lacuna - Space where the osteocyte is located 4. Canaliculi - Channels within the bone matrix 5. Osteogenic Cell - Undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts 6. Osteoclasts - The cell responsible for bone resorption, or breakdown - found on bone surfaces, are multinucleated

List and Describe the functions of the skeletal system

1. Supports the body 2. Facilitates movement - Serve as points of attachment for your muscles 3. Protects internal organs - covers or surrounds them 4. Produces blood cells 5. Stores and releases minerals and fats - Bone matrix acts as a reservoir for a number of minerals important to the body including calcium and potassium, which can be released into the bloodstream to support physiological processes

Describe the steps involved in bone repair

1. When a bone breaks, blood flows from any vessel torn by the fracture. 2. The blood begins to close about 6-8 hours after the fracture, the clotting blood has formed a fracture hematoma. 3. The disruption of blood flow results in the death of bone cells around the fracture. 4. Within about 48 hours, chondrocytes from the endosteum have created an internal callus by secreting a fibrocartilaginous matrix between the two ends of the broken bone, where the periosteal chondrocytes and osteoblasts create an external callus of hyaline cartilage and bone, around the outside of the break, which stabilizes the fracture. 5. Over the next several weeks, osteoclasts resorb the dead bone, osteogenic cells become active, divide and differentiate into osteoblasts and the cartilage in the calli is replaced by trabecular bone via encochondral ossification. 6. Eventually, the internal and external calli unite, compact bone replaces spongy bone at the outer margins of the fracture, and healing is complete.

Define Cartilage

A semirigid form of connective tissue, provides flexibility and smooth surfaces for movement

Define Bone

Also known as osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body

List the steps of endochondral ossification

Bone develops by replacing hyaline cartilage. Cartilage serves as a template to be completely replaced by new bone. 1. Some of the mesenchymal cells differentiate into chondrocytes that form the cartilaginous skeletal precursor of the bones. 2. Soon the perichondrium, a membrane that covers the cartilage, appears 3. The chondrocytes in the center of the cartilaginous model grow in size and as the matrix calcifies, nutrients can no longer reach the chondrocytes. 4. They die and the surrounding cartilage disintegrates. 5. Blood vessels invade the resulting spaces, carrying osteogenic cells with them, many of which will become osteoblasts. 6. Capillaries penetrate the cartilage as it frowns and initiate the transformation of the perichondrium into the bone producing periosteum. 7. The osteoblasts form a periosteal collar of compact bone around the cartilage of the diaphysis. 8. Ossification ramps up and creates the primary ossification center, a region deep in the periosteal collar where ossification begins 9. While these deep changes are occurring, chondrocytes and cartilage continue to grow at the ends of the bones, which increase the bones length at the same time bone is replacing cartilage in the diaphysis. ( Matrix mineralization, death of chondrocytes, invasion of blood vessels from the periosteum, and seeding with osteogenic cells that become osteoblasts)

Explain the function of cartilage

Cartilage serves as a common template for skeletal development. Cartilage serves as a framework, which is laid down during fetal development, which determines where bones will form..

Identify the structures that compose compact and spongy bone

Compact Bone - 1. Osteon - The microscopic structural unit. Each one is composed of concentric rings of calcified matrix called lamellae. 2. Central Canal or Haversian Canal - Running down the center of each osteon - contains blood vessels, nerves and lymphatic vessels. 3. Volkmanns Canal - Allows vessels and nerves to branch off and extend to the periosteum and endosteum. 4. Osteocytes - Located inside spaces called lacunae, found at the borders of adjacent lamellae. Spongy Bone - 1. Trabeculae - Lacunae and osteocytes are found in a lattice-like network of matrix spikes. Each trabecula forms along lines of stress to provide strength to the bone. 2. The spaces contain red marrow in some spongy bone

List the steps of intramembranous ossification

During this, compact and spongy bone develops directly from sheets of mesenchymal (undifferentiated connective tissue) . 1. Mesenchymal cells in the embryonic skeleton gather together and begin to differentiate into specialized cells. Some differentiate into capillaries, while others will become osteogenic cells and then osteoblasts. 2. Early osteoblasts appear in a cluster called an ossification center. 3. The osteoblasts secrete osteoid, uncalcified matrix, which calcifies within a few days as mineral salts are deposited on it. 4. The osteoblasts become entrapped and become osteocytes. 5. As osteoblasts transform into osteocytes, osteogenic cells in the surrounding connective tissue differentiate into new osteoblasts. 6. Osteoid secreted around the capillaries results in the trabecular matrix, while osteoblasts on the surface of the spongy bone become the periosteum. 7. The periosteum then creates a protective layer of compact bone superficial to the trabecular bone. 8. The trabecular bone crows nearby blood vessels, which eventually condense into red marrow

Differentiate among the different types of fractures

Fracture - Broken Bone Types of fracture: 1. Transverse - Occurs straight across the long axis of the bone 2. Oblique - Occurs at an angle that's is not 90 degrees 3. Spiral - Bone segments are pulled apart as a result of a twisting motion 4. Comminuted - Several breaks result in many small pieces between two large segments 5. Impacted- One fragment is driven into the other, usually as a result of compression 6. Green stick - A partial fracture in which only one side of the bone is broken 7. Open (or compound) - A fracture in which at least one end of the broken bone tears through the skin; carries high risk of infection 8. Closed ( or simple) - A fracture in which the skin remains intact

Describe the effect exercise has on bone tissue

Lack of mechanical stress causes bones to lose mineral salts and collagen fibers and thus strength. The internal and external structure of a bone will change as stress increases or decreases so that the bone is an ideal size and weight for the amount of activity it endures. People who exercise more regularly have thicker bones and greater bone density , than people who are more sedentary.

Compare and contract the processes of modeling and remodeling

Modeling - Increases the diameter of the diaphysis and the medullary cavity. Osteoclasts resorb old bone that lines the medullary cavity, while osteoblasts, via intramembranous ossification, produce new bone beneath the periosteum Remodeling - Process by which osteoclasts resorb old or damaged bone at the same time as and on the same surface where osteoblasts form new bone to replace that which is resorbed.

Define Skeletal System

The body system composed of bones and cartilage and performs critical functions for the human body

Explain the process of calcium homeostasis

The bones act as a storage site for calcium : the body deposits calcium in the bones when blood levels get too high, and it releases calcium when blood levels drop too low. This is regulated by PTH, vitamin D, and calcitonin. - When calcium is not binding to receptors, the cells release PTH, which stimulates osteoclast proliferation and resorption of bone by osteoclasts. This releases calcium into the blood and promotes reabsorption of calcium from the urine by the kidneys and stimulates the synthesis of Vitamin D, which in turn stimulates calcium absorption from any digested food in the small intestine. - When blood levels of calcium get too high, the thyroid glad is stimulated to release calcitonin, which inhibits osteoclast activity and stimulates calcium uptake by the bones, but also decreases reabsorption of calcium by the kidneys.

Explain growth activity at the epiphyseal plate

The proliferative zone is the next layer toward the diaphysis and contains stacks of slightly larger chondrocytes. It makes new chondrocytes (via mitosis) to replace those that die at the diaphyseal end of the plate. The longitudinal growth of the bone is a result of cellular division in the proliferative zone and the maturation of cells in the zone of maturation and hypertrophy. The zone of calcifies matrix connects the epiphyseal plate to the diaphysis. A bone grows in length when osseous tissue is added to the diaphysis. When the chondrocytes in the epiphyseal plate cease their proliferation and bone replaces the cartilage, longitudinal growth stops and all that remains is the epiphyseal line.

Describe how bones are nourished and innervated

The spongy bone and medullary cavity receive nourishment from arteries that pass through the compact bone. The Nutrient foramen is small openings in the diaphysis that arteries enter through. - The osteocytes in spongy bone are nourished by blood vessels of the periosteum that penetrate spongy bone and blood that circulates in marrow cavities.