EXAM 3 Study Guide A&P PDF

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BSC2085 Visual Anatomy & Physiology Exam 3 Study Guide Chapters 6, 8, 9 Chapter 6: Bone, or Osseous tissue is a type of connective tissue. Just like other connective tissues, it is made up of cells and matrix. A rounded hole through a bone is termed a foramen. The shaft of a long bone is called the diaphysis. The head is called the epiphysis. Spongy bone reduces the weight of the skeleton and reduces the load on muscles. During appositional growth bones grow wider. Appositional growth is an increase in bone diameter due to the addition of bone matrix at the bone's outer surface. As a bone increases in diameter, the medullary cavity increases in diameter because bone matrix is removed by osteoclasts. Epiphyseal cartilages allows a bone to grow in length. When the epiphyseal plate is replaced by bone, long bones have reached their adult length. Externally, a bone is covered with a sheath called the periosteum. This has a tough, outer fibrous layer of collagen and an inner osteogenic layer . The internal surface of a bone is lined with endosteum, a thin layer of reticular connective tissue. The four types of cells found in osseous tissue are the osteogenic cells, osteoblasts, osteocytes, and osteoclasts. Osteogenic cells are the stem cells that undergo mitosis and differentiate into osteoblasts. Osteoblasts are the bone-forming cells that secrete the organic components of the bone matrix. Osteocytes are mature osteoblasts that have become stuck in their own matrix. They reside in cavities called lacunae (lacuna, singular). Osteoclasts are bone-dissolving cells. They develop from the same stem cells that give rise to the blood cells. Each stem cell contributes a nucleus, so the mature osteoclast is a large and multinucleated. The side of the cell facing the bone surface has a ruffled border which increases the cell surface area, and thus enhances the efficiency of bone resorption. Osteoclasts free calcium from bone to maintain blood calcium levels. The matrix of osseous tissue consists of one-third organic matter and two-thirds inorganic matter. The organic matter is synthesized by the osteoblasts and includes collagen, glycosaminoglycans, proteoglycans, and glycoproteins. The inorganic matter consists mainly of hydroxyapatite, a crystallized calcium phosphate salt. The medullary cavity contains the red bone marrow and the yellow bone marrow. There are two kinds of bone marrow, red and yellow. Red bone marrow is hemopoietic (blood producing). Yellow marrow consists mainly of adipose tissue and is not hemopoietic. In adults, red marrow is limited to the skull, vertebrae, ribs, sternum, part of the pelvic girdle, and the proximal heads of the humerus and femur. The formation of bone is called ossification or osteogenesis. Bone develops by two methods, intramembranous and endochondral ossification. Intramembranous ossification produces the flat bones of the skull and most of the clavicle. Intramembranous ossification is bone formation within connective tissue without the prior development of a cartilage model. All of our other bones are formed by endochondral ossification in which a bone develops from a preexisting model composed of hyaline cartilage. Resorption is the process of dissolving bone and returning its minerals to the bloodstream. Bone resorption is carried out the osteoclasts. Mineralization is a crystallization process in which calcium, phosphate, and other are ions taken from the blood plasma and deposited into the skeleton. Mineralization is carried out by the osteoblasts. Denaturing collagen from the bone matrix would cause a bone to become more brittle. Bone plays a central role in the regulation of blood levels of calcium. A calcium deficiency in the blood is called hypocalcemia. Hypocalcemia causes excessive excitability of the nervous system and leads to muscle tremors, spasms, or tetany. Tetany is the inability of a muscle to relax. An excess of calcium in the blood is called hypercalcemia. Hypercalcemia is rare but has the opposite effect of hypocalcemia. Hypercalcemia causes depression of the nervous system, muscle weakness, sluggish reflexes, and sometimes cardiac arrest. Calcium homeostasis is regulated by three hormones: calcitriol, calcitonin, and parathyroid hormone. Calcitriol and parathyroid hormone both increase the blood calcium concentration, and calcitonin lowers the blood calcium concentration. These hormones use different methods to raise or lower the blood calcium levels such as increasing or decreasing osteoblast or osteoclast activity, increasing calcium absorption by the small intestine, and promoting the reabsorption of calcium ions by the kidneys so less calcium is lost in the urine. Given a scenario you should be able to predict whether blood calcium levels will increase or decrease. For example, if a hormone increases osteoblast activity blood calcium levels will decrease. Why? Because osteoblasts are bone forming cells. They take calcium ions(and other minerals) from the blood and deposit them into the skeleton. Since they are taking the calcium ions from the blood there

is now less calcium in the blood because some of it has been deposited into the skeleton. Decreasing osteoblast activity would have the opposite effect and cause blood calcium levels to increase. Why? Because less calcium is being taken from the blood and deposited into the skeleton, and therefore calcium levels in the blood increase. What happens to blood calcium levels when we increase or decrease osteoclast activity? Remember, osteoclasts are bone-dissolving cells and release the calcium ions (and other minerals) from the skeleton into the blood. Increasing calcium absorption by the small intestine causes blood calcium levels to increase. Promoting or increasing the reabsorption of calcium ions by the kidneys cause blood calcium levels to increase because less calcium is lost in the urine. Chapter 8: Any point where two bones meet is called a joint, or articulation. The study of joint structure, function, and dysfunction is called arthrology. There are four kinds of joints; bony, fibrous, cartilaginous, and synovial. In a fibrous joint the adjacent bones are bound by collagen fibers that emerge from one bone, cross the space between them, and penetrate into the other. There are three kinds of fibrous joints; sutures, gomphoses, and syndesmoses. Sutures bind the bones of the skull together. The attachment of a tooth to its socket is a gomphosis. In a syndesmosis the two bones are bound by longer collagenous fibers. For example, the interosseous membrane between the radius and ulna is a syndesmosis. The most familiar type of joint is the synovial joint. In synovial joints, the facing surfaces of the two bones are covered with articular cartilage. These surfaces are separated by a narrow space, the joint cavity. Within the joint cavity is a slippery lubricant called synovial fluid. A connective tissue joint (articular) capsule encloses the cavity and retains the fluid. It has an outer fibrous capsule continuous with the periosteum of the adjoining bones, and an inner, cellular synovial membrane. Articular cartilage is found covering both epiphyseal portions of articulating bone and nutrients diffuse from synovial fluid within the joint. The synovial fluid is secreted by fibroblast-like cells of the synovial membrane. Synovial fluid nourishes the articular cartilages, removes waste from the articular cartilages, and lubricates the joint for almost friction-free movement. Synovial joints allow for the greatest range of motion. A bursa is a fibrous sac filled with synovial fluid, located between adjacent muscles, where a tendon passes over a bone, or between bone and skin. Chapter 9: Muscle tissue, one of the four basic tissue groups, consists chiefly of cells that are highly specialized for contraction. The plasma membrane of a muscle fiber is called the sarcolemma, and its cytoplasm is called the sarcoplasm. Within the sarcoplasm are myofibrils, glycogen, and myoglobin. Individual muscle cells are surrounded by endomysium. At each end of the muscle, the collagen fibers of the epimysium, and each perimysium and endomysium, come together to form a tendon. The smooth endoplasmic reticulum of a muscle fiber is called the sarcoplasmic reticulum. The sarcoplasmic reticulum is a reservoir of calcium ions. It forms a network around each myofibril and has dilated end-sacs called terminal cisternae. The sarcolemma has tubular infoldings called transverse (T) tubules, which penetrate through the cell and emerge on the other side. A T tubule and the two terminal cisternae associated with it constitute a triad. Each myofibril is a bundle of protein microfilaments called myofilaments. There are three kinds of myofilaments; thick, thin, and elastic. Thick filaments are made of several hundred molecules of a protein called myosin. Thin filaments are composed mainly of two intertwined strands of a protein called fibrous (F) actin. Each fibrous (F) actin is made up of monomers of globular (G) actin. A thin filament also has 40 to 60 molecules of another protein called tropomyosin. Tropomyosin blocks the active sites of actin in a relaxed muscle fiber. Each tropomyosin molecule has a small calcium-binding protein called troponin bound to it. Elastic filaments are made of a huge springy protein called titin (connectin). Myosin and actin are called contractile proteins. Tropomyosin and troponin are called regulatory proteins. Each segment of a myofibril from one Z disc to the next is called a sarcomere. A sarcomere is the functional contractile unit of the muscle fiber. The structural explanation of how a muscle fiber contracts is called the sliding filament theory. Thick filaments and thin filaments become connected by myosin cross-bridges during muscle contraction. One nerve fiber and all the muscle fibers innervated by it are called a motor unit. The narrow space between the synaptic terminal and the muscle fiber is the synaptic cleft. The increase in muscle tension that is produced by increasing the number of active motor units is called recruitment.

Acetylcholine is the neurotransmitter responsible for stimulating the muscle fiber. Acetylcholine is released from the synaptic knob, diffuses across the synaptic cleft and binds to acetylcholine receptors on the sarcolemma. When Acetylcholine is done stimulating a muscle fiber it is broken down by the enzyme Acetylcholinesterase. Synaptic vesicles containing neurotransmitters are released by exocytosis when the action potential arrives. In an unstimulated (resting) cell, there are more anions on the inside of the plasma membrane than on the outside. Thus the plasma membrane is electrically polarized. This is referred to as the Resting Membrane Potential (RMP). There are more potassium ions inside the cell than outside, and more sodium ions outside the cell than inside. When a muscle fiber is stimulated ion gates in the plasma membrane open and Na+ diffuses down its concentration gradient into the cell. This causes the inside of the plasma membrane to briefly become positive. This change is called depolarization of the membrane. Depolarization is the when the inside of the cell becomes positive due to sodium ions rushing in. After depolarization, repolarization occurs when potassium ions rush out of the cell causing the inside of the cell to become negative again. The refractory period prevents it from propagating back in the direction from which it began. Na+ gates eventually close and K+ gates open. K+ diffuses out of the cell down its concentration gradient. The loss of positive potassium ions from the cell turns the inside of the membrane negative again. This is called repolarization. In response to action potentials arriving along the transverse tubules, the sarcoplasmic reticulum releases calcium ions. The calcium ion gates on the synaptic knob are voltage-regulated. They open and close in response to changes in voltage (action potentials). The acetylcholine receptor ion gates of the sarcolemma are ligand-regulated. They open and close in response to neurotransmitters or chemical messengers. Acetylcholine is acting as the ligand, in this case. Muscle contraction or tension without a change in length is called isometric contraction. Muscle contraction with a change in length but no change in tension is called isotonic contraction. In isotonic concentric contraction a muscle shortens as it maintains tension. In isotonic eccentric contraction a muscle lengthens as it maintains tension. A weightlifter uses concentric contraction when lifting a dumbbell and eccentric contraction when lowering it. There are two pathways for ATP synthesis, aerobic respiration and anaerobic fermentation. Aerobic respiration requires a continual supply of oxygen, produces carbon dioxide and water as its end products (these do not lead to muscle fatigue), and is the primary metabolic pathway for ATP synthesis in slow-twitch muscle fibers. Anaerobic fermentation produces lactic acid as an end product. Lactic acid is a major contributor to muscle fatigue. In the absence of oxygen a cell must get it’s ATP by this pathway. Creatine phosphate acts as an energy reserve in muscle tissue. ATP supplies the energy for a muscle fiber contraction. In a short, intense exercise such as 6 seconds of sprinting the phosphagen system supplies most of the ATP. There are two physiological classes of muscle fibers, slow oxidative (slow) and fast glycolytic (fast). Slow oxidative fibers are also called slow-twitch, red, or type I. These fibers have relatively abundant mitochondria, myoglobin, and blood capillaries. These fibers are well adapted to aerobic respiration and therefore do not fatigue easily. Fast glycolytic fibers are also called fast-twitch, white, or type II fibers. These fibers are well adapted for quick responses but not for fatigue resistance. They are rich in enzymes of the phosphagen and glycogen-lactic acid systems. These fibers produce their ATP primarily by anaerobic fermentation which is why they are quick to fatigue. Muscular strength depends on a variety of anatomical and physiological factors including muscle size, fascicle arrangement, and size of active motor units. Skeletal muscle cells, cardiac muscle cells, and smooth muscle cells may also be called myocytes. Skeletal muscle cells are also called muscle fibers because they are long and thread-like. However, it is not appropriate to refer to cardiac and smooth muscle cells as fibers. Skeletal muscle is voluntary, and cardiac and smooth muscles are involuntary....