Endocrine System and Hormones

GDC Learning Outcomes

• 1.1.5 Discuss dental, oral, and craniofacial anatomy and relate it to patient care.
• 1.1.6 Discuss relevant physiology and relate it to patient care.

Learning Outcomes

• Understand the endocrine system's role.
• Label a diagram of the endocrine system.
• Name the major glands.
• List the hormones they secrete.
• Describe the different hormone functions.

The Endocrine System

• The main role is homeostasis.
• It helps maintain the normal balance of the body's internal environment.
• It helps maintain homeostasis of the body's internal environment.
• The endocrine system comprises of ductless glands.
• These glands secrete hormones directly into the blood.
• Hormones are chemical messengers.
• Hormones influence many processes including growth, development, stress response, nutrition, and reproduction.
• Disorders are due to having too much (hyper) or too little (hypo) of a hormone.
• Hypoglycaemia or low blood sugar is an example of an endocrine disorder.
• Hyperthyroidism or too much thyroxine is an example of an endocrine disorder.
• Studying the endocrines system helps us to understand clinical presentations, oral manifestations of endocrine disease, behaviour, and medical emergencies.

Endocrine Glands

• Pituitary gland
• Pineal gland
• Thyroid gland
• Parathyroid glands: there are four.
• Adrenal glands: there are two.
• Pancreatic islets
• Thymus
• Ovaries: there are two.
• Testes: there are two.

Pituitary Gland & Hypothalamus

• The pituitary gland is situated in the hypophyseal fossa of the sphenoid bone below the hypothalamus.
• It is attached to the hypothalamus by a stalk.
• Together, the hypothalamus and pituitary gland, work a system called negative feedback regulation.

Hypothalamus Hormones

• Growth hormone releasing hormone
• Growth hormone release inhibiting hormone
• Thyrotrophin releasing hormone
• Corticotrophin releasing hormone
• Prolactin releasing hormone
• Prolactin inhibiting hormone (dopamine, PIH)
• Luteinising releasing hormone (LHRH)
• Gonadotrophin releasing hormone (GnRH)

Hormones Secreted by the Pituitary Gland - Anterior Pituitary

• Growth Hormone
• Prolactin
• Thyroid Stimulating Hormone
• Corticotrophin Releasing Hormone
• Gonadotrophins

Hormones Secreted by the Pituitary Gland - Posterior Pituitary

• Oxytocin
• Antidiuretic Hormone

Functions of Growth Hormone (GH)

• GH promotes growth of the skeleton, muscles, connective tissue, kidneys, liver, Intestines, pancreas, and adrenal glands.
• In children, GH is concerned with general growth.
• In adults, GH is concerned with maintenance and repair.

Other Pituitary Gland Hormones

• Thyroid stimulating hormone (TSH) stimulates growth and activity of the thyroid glands.
• Adrenocorticotrophic hormone (ACTH) stimulates activity of the adrenal cortex.
• ACTH increases the output of steroid hormones especially cortisol.
• Prolactin stimulates lactation (milk production) after childbirth.
• Gonadotrophin hormones are released in response to luteinising hormone releasing hormone (LHRH) from the hypothalamus.

Other Pituitary Gland Hormones

• After puberty the Anterior Pituitary secretes Gonadotrophin (sex hormones) in males and females.
• Follicle stimulating hormone (FSH) stimulates production of gametes.
• Luteinising hormone (LH) stimulates the ovaries to produce oestrogen / progesterone and the testes to secrete testosterone.

Posterior Pituitary Hormones

• Oxytocin promotes contraction of the uterus and produces breast milk along with prolactin.
• Antidiuretic hormone (Vasopressin) influences resorption of water by the kidney tubules resulting in concentration of urine.
• Antidiuretic hormone stimulates contraction of the muscular tissues of capillaries and arterioles, raising blood pressure.

Thyroid Gland

• It is situated in the neck.
• It's in front of the larynx and trachea.
• It secretes 3 hormones: thyroxine, triiodothyronine, and calcitonin.
• Iodine is essential for production of the thyroid hormones.
• Thyroxin and T3 regulate basal metabolic rate, carbohydrate, protein, lipid metabolism (weight), nervous & cardiovascular systems, motility of GI tract (peristalsis), and female reproductive cycle & lactation.
• Calcitonin regulates blood calcium by reduction of blood calcium.
• It stores calcium in bones.
• Excretes calcium by kidneys.
• It opposes the action of parathormone.
• Release is stimulated by an increase in ionised calcium in the blood after a meal.

Parathyroid Glands

• Four glands are embedded in the thyroid gland, two per lobe.
• Produce the hormone parathormone AKA parathyroid hormone.
• Important in the maintenance of plasma calcium levels.
• Parathormone works with calcitonin to regulate blood calcium.
• Parathormone raises blood calcium by influencing the uptake by the small intestine and the amount of calcium resorbed by kidneys.
• Parathormone can stimulate calcium to be withdrawn from the skeletal system if there is not enough calcium in the diet.
• To maintain blood calcium levels, the parathormone and calcitonin aid in muscle contraction, blood clotting, and nerve impulse transmission.

Adrenal Glands

• They are situated atop each kidney.
• They are 4cm long, 3cm wide.
• They consist of two parts: the outer cortex and the inner medullar.
• The cortex is essential to life.
• Glucocorticoids (e.g. cortisol) is concerned with glucose metabolism produced in response to stress.
• Under stress, the hypothalamus induces the anterior pituitary to release ACTH (adrenocorticotrophic hormone).
• ACTH causes the adrenal cortex to release glucocorticoids.
• Glucocorticoids combat stress by increasing blood sugar, formation of new sugar, conversion of amino acids to glucose by the liver.
• It increases lipolysis (fatty acids & glycerol converted to glucose for energy production), breakdown of proteins to amino acids, and promotion of sodium & water reabsorption from renal tubules.
• Large quantities of glucocorticoids have an anti-inflammatory action, suppress the immune system and the response of tissues to injury and delay wound healing.
• Aldosterone (a mineralocorticoid) is concerned with electrolyte balance in the body.
• Electrolyte regulates blood volume and levels of sodium and potassium.
• Electrolyte stimulates reabsorption of sodium and water and the amount of potassium which is excreted.
• Aldosterone is secreted when there are low blood sodium levels or when blood potassium increases.
• The adrenal medulla produces two hormones: adrenaline (epinephrine) and noradrenaline (norepinephrine).
• Adrenaline is concerned with the fight or flight response.
• Increasing metabolic rate, heart rate & blood pressure.
• Dilates blood vessels of muscles, heart and brain, pupils, and bronchioles.
• Converts glycogen to glucose.
• Constricts blood vessels in the skin.
• Noradrenaline is responsible for the maintenance of blood pressure and vasoconstriction (except coronary arteries).

Pancreatic Islets

• Insulin and glucagon are concerned with homeostasis of blood glucose levels.
• Somatostatin inhibits the secretion of insulin and glucagon.
• Regulation of blood glucose and other absorbed nutrients.
• Insulin lowers blood glucose levels by stimulating uptake and use of glucose by muscle and connective tissue cells.
• It promotes the storage of glucose by increasing conversion of glucose to glycogen especially in the liver and skeletal muscles.
• Glucagon increases blood glucose levels by converting glycogen to glucose and gluconeogenesis (formation of new sugars from e.g. protein).
• Glucagon is secreted in response to a low blood glucose level.

Hormones Secreted by the Ovaries

• The ovaries secrete Oestrogen & progesterone.
• Regulation of the menstrual cycle
• Sexual maturity occurs due to these hormones.

Testes

• The Testes produce Spermatozoa & the hormone Testosterone.
• Testosterone & luteinising hormone (from antpituitary).
• Sexual maturity in men is driven by this.
• Secondary sexual characteristics are controlled here.

Thymus Gland

• It is situated in the chest behind the sternum.
• It secretes the hormone Thymosin.
• Thymosin is needed for the development of T-lymphocytes for cell- mediated immunity.
• Thymosin supports the growth and maturation of the thymus and other lymph tissue.
• As adulthood is reached thymosin production and the effectiveness of T-lymphocytes declines.

Pineal Gland

• It is about 10 mm long and produces the hormone Melatonin.
• Melatonin secretion is suppressed by daylight.
• Melatonin co-ordinates Circadian & daily rhythms (24 hour cycles) and possibly influences the hypothalamus.
• It inhibits the development of ovaries and testes before puberty.
• It prevents the production /release of gonadotrophins before puberty.
• After puberty it begins to shrink and is often calcified by later life.

Test your knowledge of the endocrine system and the hormones it produces. This quiz covers hormone deficiencies, hormone functions, and the role of the endocrine system in maintaining homeostasis. It also explores the relationship between specific hormones and their target glands.