Consider statements about human physiology: 1. The sinoatrial node is the pacemaker of the heart. 2. The atrioventricular node delays the impulse before it reaches the ventricles. 3. The Purkinje fibers distribute the impulse to the ventricular muscle. Which are correct? MCQ with Answer and Explanation

Explanation:
Growth hormone (somatotropin) stimulates protein synthesis, cell division, and growth of bones and muscles, especially during childhood. Thyroxine regulates metabolism, cortisol is a stress hormone from the adrenal cortex, adrenaline is from the adrenal medulla. GH deficiency leads to dwarfism; excess causes gigantism or acromegaly.

Explanation:
Thyroid Stimulating Hormone (TSH), also known as thyrotropin, is a glycoprotein hormone secreted by the thyrotroph cells of the anterior pituitary gland. Its primary and specific target is the thyroid gland. TSH binds to receptors on the thyroid follicular cells, stimulating all aspects of their function: the uptake of iodine, the synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), and the release of these hormones into the bloodstream. TSH secretion is regulated by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus and by negative feedback from T3 and T4.

Explanation:
The periderm is the outer protective covering of stems and roots that have undergone secondary growth (thickening), replacing the primary epidermis. It is composed of three distinct layers: 1) Phellem (cork): The outermost layer, consisting of dead, compactly arranged cells with suberized (waterproof) walls that provide protection and prevent water loss. 2) Phellogen (cork cambium): The middle, meristematic layer that produces phellem outwards and phelloderm inwards. 3) Phelloderm (secondary cortex): The innermost layer, consisting of living, parenchymatous cells.