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Skin and tissue
Terms in this set (18)
What is the effect of sunlight on skin color? Why?
Darkens skin. Exposure to sunlight causes keratinocytes to secrete chemicals that stimulate melanocytes. Prolonged exposure causes melanin buildup to help protect the DNA (nucleus) of skin cells from UV radiation by absorbing rays and dissipating as heat.
Briefly explain why sunburned skin peels rather than being shed as a powder.
Sunburned skin accelerates production of protein Fas, which causes genetically damaged cells to commit suicide to reduce risk of mutation which could cause cancer. So many cells dying together causes skin to peel.
In a condition known as sunstroke, the victim appears flushed, the skin is warm and dry, and the body temperature rises dramatically. Explain these observations based on what you know concerning the role of the skin in thermoregulation.
The body is dehydrated so sweat is no longer being produced. Flushed skin would be due to blood being pumped to surface and dilation of blood vessels in an attempt to release heat. Body temp rises because sweat is not evaporating and carrying away heat.
Many medications can be administered transdermally by applying patches that contain the medication to the surface of the skin. These patches can be attached anywhere on the skin except the palms of the hands and the soles of the feet. Why?
The palms and soles have more eccrine sweat glands, which would cause the patch to not stick there well, and would also make absorption more difficult.
Why is a subcutaneous injection with a hypodermic needle a useful method of administering drugs?
Subcutaneous tissue is vascular tissue. Drugs can enter bloodstream to be distributed throughout the body.
Explain why warm, dry climates feel cooler than warm, humid climates, even though the temperatures may be the same.
Sweat evaporation is more difficult, meaning that less heat is dissipated from the body (vapor pressure inhibits evaporation).
Why is regional infection or inflammation of the skin usually very painful?
Because the Merkel (tactile) cells are present at the epidermal/dermal junction, and each has a nerve ending associated with it; i.e. there are many cells to function as pain receptors.
An 80-year-old grandmother sets her thermostat at 26ºC (80ºF) and wears a sweater on balmy spring days. When asked why, the grandmother says she is cold. Can you give one possible cause for her feeling cold?
The subcutaneous fat layer of the hypodermisis gone in an 80-year-old, which makes it more difficult for her body to retain heat.
Why are you advised to avoid exercise in a steam room, particularly if you have a heart condition?
When external temperature is lower than body temperature, skin's surface looses heat and cools body. Skin's blood vessels constrict in cool weather and when exercising to allow more blood to reach other areas. A steam room is humid, meaning that sweat will not have a cooling effect, so overhearing may occur. Every degree increase means the heart beats faster, which causes the heart to need more blood. A steam room is also hot, compounding the potential for overheating by not constricting blood vessels, decreasing blood flow to the heart and making the heart pump blood to the skin to be cooled by evaporation as well. These things combined means that the heart is working extra hard compared to regular working out.
What is the function of red marrow in the bones and how does it differ in adults and infants?
Red marrow makes blood cells. It is found mainly in trabecular cavities of spongy part of long bones and in the diploe of flat bones. In newborns, medullary cavity and all areas of spongy bone contain red marrow. In adults, yellow marrow fills medullar cavity and blood cell production occurs mainly in the heads of the humerus and femur.
Summarize the process of endochondral ossification (two paragraphs).
Starts with a hyaline cartilage model of the bone. Primary ossification center is in the middle of shaft. Bone collar forms around the diaphysis from primary ossification center. Cartilage in the center of diaphysis calcifies and then develops cavities. The periosteal bud invades the internal cavities and spongy bone forms. The diaphysis elongates and a medullary cavity forms. Secondary ossification centers appear in the epiphyses. The epiphyses ossify (no medullary cavity forms; spongy bone remains). When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.
Describe the growth of a long bone; indicate what occurs in the 5 layers of the growth area.
Depends on presence of epiphyseal cartilage. Resting or quiescent zone (the side of the epiphyseal plate facing the epiphysis): cartilage relatively inactive. Proliferation or growth zone (cells at the epiphysis-facing side of the stack abutting the resting zone; these cells form stacks): cells divide quickly, pushing the epiphysis away from the diaphysis and lengthening the entire long bone. Hypertrophic zone (older chondrocytes in stack): older cells hypertrophy and their lacumar erode and enlarge, leaving large interconnecting spaces. Calcification zone: surrounding cartilage matrix calcifies and chondrocytes die and deteriorate. Ossification or osteogenic zone: long slender spicules of calcified cartilage at the epiphysis-diaphysis junction are invaded by blood vessels from medullary cavity, osteoclasts partly erode spicules, then osteoblasts quickly cover then with new bone and ultimately spongy bone replaces them.
How do bones respond to mechanical stress?
A bone grows or remodels in response to the demands placed upon it. A bone is loaded whenever weight bears down on it or muscles pull on it. Loading is off center and bends the bone. Bending compresses the bone of one side and subjects it to tension on the other; so long bones are thickest midway along the diaphysis, where bending stresses are greatest. When bones are not stressed they are featureless.
What are the effects of thyroid and parathyroid hormones on blood calcium levels?
Parathyroid hormone- when blood levels of ionic calcium decline, PTH is released; the increased PTH level stimulates osteoclasts to resorb bone, releasing calcium into blood; as blood concentrations of calcium rise, the stimulus for PTH release ends; the decline of PTH reverses its effects and causes blood calcium ion levels to fall. Thyroid- calcitonin lowers blood calcium levels temporarily when administered at abnormally high doses.
Which is likely to heal faster, a bone injury or a cartilage injury? Why?
A bone injury is likely to heal faster. Bone has blood supply (marrow, medullary cavity) which allows nutrients to reach the injury quickly. Also, bone is already constantly remodeling itself, whereas chondrocytes are relatively inactive once bone formation is complete.
What are the main differences between a male and female pelvis?
Female pelvis is tilted forward, adapted for childbearing, true pelvis defines birth canal, cavity of true pelvis is broad, shallow and has greater capacity. Female pelvis bones are less thick, lighter, thinner and smoother. Female acetabula are smaller and farther apart. Pubic angle/arch is broader and more rounded. Female sacrum is wider, shorter and curvature is accentuated. Female coccyx is more moveable and projects inferiorly (compared to anteriorly in males). Greater sciatic notch is wide and shallow in females (narrow and deep in males). Pelvic inlet is wider and oval from side to side in females (narrow and heart shaped in males). Pelvic outlet is wider and ischial tuberosities are shorter, farther apart and everted in females (outlet narrower and ischial tuberosities are longer, shaper and point more medially in males).
What structural feature allows more mobility in the shoulder (relative to the hip)?
In the shoulder, only the clavicle attached to the axial skeleton, so scapula can move across the thorax, whereas the pelvic girdle is securely attached to axial skeleton with some of the strongest ligaments in the body. The shoulder socket is shallow and pporly reinforced, so the humerus' movement is not restricted, whereas the pelvic socket is deep and cuplike and the femur head is securely in place (more stability, less mobility).
Why do shoulder separations occur so easily?
Head of humerus sits in very shallow socket, so stability is dependent on tendons and muscles.
The weakest reinforcement of the shoulder is anteriorly and inferiorly, so most dislocations occur in those directions. The main anterior ligaments are the glenohumeral, and they are weak. Joint capsule is loose and weak. These factors increase mobility, at the expense of stability, causing dislocations to occur more easily.
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