chemical control

• Endocrine glands lack ducts and are called ductless glands
• Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts
• Organised endocrine bodies in the human body include: pituitary, pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads
• The hypothalamus contains neurosecretory cells called nuclei that produce two types of hormones: releasing hormones and inhibiting hormones
• Gonadotrophin releasing hormone stimulates the pituitary synthesis and release of gonadotrophins
• Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary
• Pituitary gland is anatomically divided into an adenohypophysis and a neurohypophysis
• Adenohypophysis consists of two portions: pars distalis (anterior pituitary) and pars intermedia
• Pars distalis produces growth hormone (GH), prolactin (PRL), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), luteinizing hormone (LH), and follicle stimulating hormone (FSH)
• Pars intermedia secretes melanocyte stimulating hormone (MSH)
• Neurohypophysis (posterior pituitary) stores and releases oxytocin and vasopressin
• Over-secretion of GH leads to gigantism, while low secretion results in pituitary dwarfism
• Excess GH secretion in adults can lead to Acromegaly
• Prolactin regulates the growth of mammary glands
• TSH stimulates the synthesis and secretion of thyroid hormones
• ACTH stimulates the synthesis and secretion of glucocorticoids from the adrenal cortex
• LH and FSH stimulate gonadal activity and are called gonadotrophins
• In males, LH stimulates the synthesis and secretion of androgens from the testis
• In males, FSH and androgens regulate spermatogenesis
• In females, LH induces ovulation and maintains the corpus luteum
• FSH stimulates growth and development of ovarian follicles in females
• Vasopressin stimulates water and electrolyte resorption by the kidney, reducing water loss through urine
• Pineal gland secretes melatonin, which regulates the body's 24-hour rhythm
• The thyroid gland is composed of two lobes located on either side of the trachea, interconnected by a thin flap of connective tissue called isthmus
• Each thyroid follicle is composed of follicular cells that synthesize two hormones: tetraiodothyronine or thyroxine (T4) and triiodothyronine (T3)
• Iodine is essential for the normal rate of hormone synthesis in the thyroid; iodine deficiency in the diet leads to hypothyroidism and enlargement of the thyroid gland, known as goitre
• Thyroid hormones regulate the basal metabolic rate, support red blood cell formation, control the metabolism of carbohydrates, proteins, and fats, and influence the maintenance of water and electrolyte balance
• The thyroid gland also secretes a protein hormone called thyrocalcitonin (TCT) which regulates blood calcium levels
• The parathyroid glands secrete parathyroid hormone (PTH), which increases blood Ca2+ levels by stimulating bone resorption, reabsorption of Ca2+ by renal tubules, and Ca2+ absorption from digested food
• The thymus gland, located between the lungs behind the sternum on the ventral side of the aorta, secretes thymosins that play a major role in the differentiation of T-lymphocytes for cell-mediated immunity and promote antibody production for humoral immunity