Inspiration (inhalation) occurs when the intra-pulmonary pressure is less than the atmospheric pressure. This is achieved by the contraction of the diaphragm, which flattens and moves downwards, and the contraction of external intercostal muscles, which lift the ribs and sternum. This increases the thoracic volume and lung capacity, drawing air in. Expiration involves relaxation of these muscles.
Explanation:
Vitamin A (Retinol) is essential for the formation of rhodopsin (visual purple), a pigment in the rod cells of the retina necessary for vision in low light conditions. Deficiency of Vitamin A leads to night blindness (nyctalopia), where a person has difficulty seeing in dim light. Severe deficiency can also cause xerophthalmia and complete blindness.
Explanation:
Diabetes insipidus results from insufficient ADH or kidney response, causing polyuria and polydipsia with dilute urine. Diabetes mellitus is hyperglycemia.
Explanation:
Chief (peptic) cells secrete pepsinogen, which is activated to pepsin by HCl. Parietal cells secrete HCl and intrinsic factor. Goblet cells secrete mucus.
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