Endocrine and Exocrine Glands

The endocrine system consists of a network of glands that secrete hormones directly into the bloodstream to regulate various body functions like growth, metabolism, and reproduction. The nervous system also regulates body functions but does so primarily through electrical impulses rather than chemical hormones from glands.

The skin is the largest organ in the human body, and it belongs to the integumentary system, which also includes hair and nails. This system acts as a protective barrier against environmental damage and pathogens. Other systems like the muscular or endocrine systems do not contain the skin.

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Glands, such as sweat glands, salivary glands, and endocrine glands, are formed by specialized epithelial cells known as glandular epithelium. These cells are highly adapted for synthesizing and secreting substances like hormones, sweat, and enzymes.

The parathyroid glands produce parathyroid hormone, which is the primary regulator of calcium levels in the blood and bones.

Acne is primarily caused by the overactivity of sebaceous glands, which produce oil (sebum). The option provided contains a typo ('celebrations' instead of 'sebaceous').

The pituitary gland is known as the master gland because it secretes hormones that regulate the activity of other endocrine glands.

Brunner's glands are specialized glands located in the submucosa of the duodenum, which is the first part of the small intestine.

• Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood(ductless) rather than through a duct.
•  The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. Hence, Ductless gland is a feature of endocrine glands.

The adrenal glands, specifically through the secretion of hormones like aldosterone and adrenaline, play a critical role in regulating blood pressure. Aldosterone helps regulate blood volume by managing sodium and water retention.

While the pituitary gland is known as the 'master' endocrine gland, both of its lobes are under the control of the hypothalamus; the anterior pituitary receives its signals from the parvocellular neurons and the posterior pituitary receives its signals from magnocellular neurons.

In humans, pheromones are secreted onto our skin through the apocrine glands (sometimes called as human scent glands). These are similar to eccrine glands but the apocrine glands secrete a more oily substance. The apocrine glands are normally associated with hairy areas, such as armpits and the crotch area, and are also usually accompanied by eccrine glands, which help to disperse the pheromone secretions. Apocrine glands are activated at puberty, along with hair growth in the axillary (armpit) regions and crotch, which increase the surface area for pheromone dispersal. 

a) Hypothalamus maintains the constant human body temperature by regulation of the diameter of blood vessels (constriction to conserve heat during body temperature lower than normal or dilation to lose heat by increasing blood flow during body temperature higher than the normal range), shivering and sweating mechanisms.