Discuss why melanin decreases the synthesis of vitamin D in response to UV radiation. Why is it necessary to maintain normal levels of vitamin D?
What will be an ideal response?
Upon exposure to UV radiation, melanin is produced to protect the skin and to decrease vitamin D production. Too much exposure to sunlight would increase vitamin D levels above normal. Vitamin D levels must be kept within a specific range since excess amounts can lead to calcium imbalance and kidney failure. Recall that Vitamin D is required to absorb calcium ions from the small intestine, which are important for nerve function, muscle contraction, building and maintaining bone tissue, and many other physiological processes.
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At the ________ stage during erythropoiesis the cell has lost all organelles except some ribosomes, but it continues to produce hemoglobin.
Fill in the blank(s) with the appropriate word(s).
Which type of movement in the GI system is primarily responsible for moving chyme back and forth, mixing it with digestive juices and promoting the absorption of nutrients?
A) swallowing B) peristalsis C) defecation D) segmentation
The neuromuscular junction is found between which two structures?
A) Axon terminal of motor axon and T-tubule B) Dendrite of motor neuron and sarcoplasm C) Axon terminal of motor neuron and motor end plate D) Cell body of motor neuron and myofibril
The iron that has been transferred to the liver after the aged erythrocytes were phagocytized is stored by the protein ________.
Fill in the blank(s) with the appropriate word(s).