PHS 214

• Endocrine glands


  Glands which synthesize and release the classical hormones into the blood
• Ductless glands


  Endocrine glands that release their hormones directly into the blood without any duct
• Exocrine glands


  Glands that release their secretions through ducts
• The multiple hormone systems play a key role in regulating almost all body functions, including metabolism, growth and development, water and electrolyte balance, reproduction, and behavior
• Importance of hormones


  • Without growth hormone, a person would be a dwarf
  • Without thyroxine and triiodothyronine from the thyroid gland, almost all the chemical reactions of the body would become sluggish, and the person would become sluggish as well
  • Without insulin from the pancreas, the body's cells could use little of the food carbohydrates for energy
  • Without the sex hormones, sexual development and sexual functions would be absent
• Major Endocrine Glands in the Body

  • Pituitary glands (Anterior and Posterior)
  • Thyroid gland
  • Parathyroid gland
  • Pancreas (Islet of Langerhans)
  • Adrenal cortex
  • Adrenal medulla
  • Gonads (Testes and Ovaries)
  • Pineal gland
  • Thymus gland
• Pituitary gland


  A small endocrine gland with a diameter of 1 cm and weight of 0.5 to 1 g, situated in a depression called 'sella turcica' in the sphenoid bone at the base of the skull, connected with the hypothalamus by the pituitary stalk or hypophyseal stalk
• Divisions of the pituitary gland

  • Anterior pituitary or adenohypophysis
  • Posterior pituitary or neurohypophysis
• Between the anterior and posterior pituitary divisions, there is a small and relatively avascular structure called pars intermedia, which actually forms a part of the anterior pituitary
• Hypothalamo-hypophyseal relationship


  The relationship between the hypothalamus and pituitary gland
• Transport of hormones from hypothalamus to pituitary

  1. Hormones from hypothalamus are transported to anterior pituitary through hypothalamo-hypophysial portal blood vessels

  2. Hormones from hypothalamus to posterior pituitary are transported by nerve fibers of hypothalamo-hypophyseal tract
• Neurohormones


  Releasing and inhibitory hormones secreted by the hypothalamus that control anterior pituitary secretion
• Releasing and Inhibitory Hormones Secreted by Hypothalamus

  • Growth hormone-releasing hormone (GHRH): Stimulates the release of growth hormone
  • Growth hormone-releasing polypeptide (GHRP): Stimulates the release of GHRH and growth hormone
  • Growth hormone-inhibitory hormone (GHIH) or somatostatin: Inhibits the growth hormone release
  • Thyrotropic-releasing hormone (TRH): Stimulates the release of thyroid stimulating hormone
  • Corticotropin-releasing hormone (CRH): Stimulates the release of adrenocorticotropin
  • Gonadotropin-releasing hormone (GnRH): Stimulates the release of gonadotropins: FSH and LH
  • Prolactin-inhibitory hormone (PIH): Inhibits prolactin secretion. It is believed that PIH is dopamine
• Hormones Secreted by Anterior Pituitary

  • Growth hormone (GH) or somatotropic hormone (STH): it stimulates growth and division of most body cells, especially in the bones and skeletal muscles
  • Thyroid-stimulating hormone (TSH) or thyrotropic hormone: it stimulates growth and activity of thyroid gland
  • Adrenocorticotropic hormone (ACTH): it increases the concentration of cholesterol and steroids within the adrenal cortex
  • Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH): are involve in the secretion of estrogen and progesterone in female, and testosterone secretion in male. They equally stimulate the production of sperm from testes and maturation of ovarian follicles in female
  • Prolactin: it stimulates lactation and has a direct effect on the breasts immediately after parturition
• Hormones of Posterior Pituitary

  • Antidiuretic hormone (ADH) or vasopressin
  • Oxytocin
• Source of Secretion of Posterior Pituitary Hormones

  ADH and oxytocin are synthesized in the hypothalamus and transported to the posterior pituitary through the nerve fibers of hypothalamo-hypophyseal tract, by means of axonic flow. Proteins involved in transport of these hormones are called neurophysins.
• Functions of ADH and Oxytocin

  • ADH reduces urine output by increasing the reabsorption of water from the glomerular filtrate
  • Oxytocin stimulates two target tissues during and after childbirth: uterine smooth muscle and the muscle cells of the lactating breast
• Thyroid gland


  A butterfly-shaped gland situated at the root of the neck on either side of the trachea, with two lobes connected by an isthmus, weighing 15-20g and larger in females than in males
• Endocrine cell types in the thyroid gland

  • C cells (clear), which secrete a calcium-regulating hormone called calcitonin
  • Follicular cells, which secrete thyroid hormones
• Hormones Secreted by Thyroid Gland

  • Tetraiodothyronine or T4 (thyroxine)
  • Tri-iodothyronine or T3
  • Calcitonin
• T4 and T3


  The major thyroid hormones, with T4 forming about 90% of the total secretion and T3 forming 9% to 10%. They regulate metabolism of carbohydrates, proteins and fats, and increase the basal metabolic rate and heat production.
• Control of Thyroid Gland


  Secretions from thyroid gland are under the control of thyroid stimulating hormones from anterior pituitary gland, which is in turn being controlled by Thyrotropic-releasing hormone (TRH) from the hypothalamus.
• Parathyroid Gland


  Human beings have four parathyroid glands, situated on the posterior surface of upper and lower poles of thyroid gland, which secrete Parathormone essential for the maintenance of blood calcium level within a very narrow critical level.
• Regulation of Parathyroid Hormone Secretion

  Secretion of parathyroid hormone is regulated by blood level of calcium. When it falls, secretion of PTH is increased and vice versa.
• Endocrine function of pancreas

  Performed by the islets of Langerhans, which contain about 1 to 2 million islets in the human pancreas
• Cell types in the islets of Langerhans

  • α-cells, which secrete glucagon
  • β-cells, which secrete insulin
  • δ-cells, which secrete somatostatin
  • PP cells, which secrete pancreatic polypeptide
• Functions of the cell types in the islets of Langerhans

  • Glucagon increases the blood glucose level, peripheral utilization of lipids and the conversion of proteins into glucose
  • Insulin is concerned with the regulation of carbohydrate metabolism and blood glucose level
  • Somatostatin acts within islets of Langerhans and inhibits the secretion of both glucagon and insulin
  • Pancreatic polypeptide is believed to increase the secretion of glucagon from α-cells in islets of Langerhans
• Adrenal glands


  Called the 'life-saving glands' or 'essential endocrine glands', situated on the upper pole of each kidney, made of two distinct parts: adrenal cortex (outer portion, 80% of the gland) and adrenal medulla (central portion, 20% of the gland)
• Hormones secreted by the adrenal cortex

  • Glucocorticoids (cortisol), which are essential for life, regulating metabolism and responses to stress
  • Mineralocorticoids (aldosterone), which is involved in the maintenance of water and electrolyte balance in the body
  • Androgens (male sex hormone), the amount produced are insignificant compared with what is being secreted in the testes
• Hormones secreted by the adrenal medulla


  • Adrenaline (epinephrine)
  • Noradrenaline (norepinephrine)
• Functions of adrenaline and noradrenaline

  Together, they potentiate the fight or flight response by increasing heart rate, blood pressure, metabolic rate, diverting blood to essential organs and dilating pupils
• Testes


  Produce the hormone testosterone under the influence of LH from the anterior pituitary, which regulates male reproductive functions
• Ovaries


  Secrete the hormones estrogen and progesterone during the menstrual cycle, under the influence of LH and FSH from the anterior pituitary, which regulate female reproductive functions
• Pineal gland


  A small body attached to the roof of the third ventricle and connected to it by a short stalk containing nerves, many of which terminate in the hypothalamus, that secretes the hormone melatonin which is controlled by daylight and associated with coordination of circadian and diurnal rhythms, and inhibition of growth and development of sex organs before puberty
• Thymus gland


  Lies in the upper part of the mediastinum behind the sternum and extends upward into the root of the neck, secreting thymosin which is required for the development of T-lymphocytes for cell-mediated immunity
• In humans and most of the higher animals, reproduction occurs sexually, i.e. by mating
• Reproductive system


  Ensures the continuation of species
• Gonads


  The primary reproductive organs which produce the gametes (spermatozoa or ovum)
• Reproductive organs in males

  • External genitalia: scrotum, penis, urethra
  • Internal genitalia: remaining sex organs
• Circadian rhythm


  Biological rhythm that occurs approximately every 24 hours