The Endocrine System Contributes to: By: To control control of growth, development, reproduction, behaviour, energy metabolism, and water balance By: Secreting hormones To control Organ and tissue functions

Endocrine System A system of ductless secretory organs (glands) located in various parts of the body Include Pineal Anterior/posterior pituitary Thyroid Parathyroid Thymus Adrenal Islets of Langerhans, Ovaries Testes Main function Secrete hormones directly into the blood or extracellular fluid

Hypothalamus Is not a gland but a region of the brain Part of the nervous system Very important for function of endocrine system Produce neurohormones that stimulate or inhibit production of other hormones in the pituitary gland

Hormones of The Hypothalamus Thyrotropin-releasing hormone (TRH) Stimulates release of thyroid-stimulating hormone (TSH) Gonadotropin-releasing hormone (GnRH) Stimulates release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) Growth hormone-releasing hormone (GHRH) Stimulates release of growth hormone (GH) Corticotropin-releasing hormone (CRH) Release of adrenocorticotropic hormone (ACTH) Somatosin Inhibits the release of growth hormone (GH) Dopamine Inhibits the release of thyroid-stimulating hormone (TSH)

Hormones: Maintaining Homeostasis Chemical management system for the body Chemicals produced by cells in one part of the body that regulate the processes of cells in another part of the body Chemical messengers act on cells from another part of the body Local regulators (paracrine) act on nearby cells Self regulators (autocrine) cells that produce chemicals to stimulate their own cellular processes

Tropic vs Non-Tropic Hormones Target endocrine glands Nontropic Hormones Target cells, tissues, and organs

Hormones Produced and secreted by cells, tissues and organs that compose the endocrine system (glands) directly into the blood or extracellular fluid Hormones are circulated throughout the body Only target cells will respond to specific hormones Hormones are broken down by enzymes in target cell, liver or kidneys where they are reused or excreted

Hormones Secreted in an inactive form – prohormones Prohormones are converted by target cells or by enzymes in the blood to an active form Angiotensinogen → angiotensin

Hormones Protein hormones Steroid hormones Consist of AA (3 to 200 in length) Usually hydrophilic (water soluble) Diffuse well through blood Cannot pass through lipid bilayer Steroid hormones Derived from cholesterol Not water soluble Usually encased with protein (protein carrier) to travel through blood Pass easily through lipid bilayer

Hormone Mechanisms Water-Soluble Glucagon Cannot pass membrane Bind to receptor molecules in the cell membrane Signal is activated Secondary messenger is activated (cAMP – cyclic adenosine monophosphate) Change is caused inside cell Acts in the cytosol or the nucleus Regulate protein production, ion channels Activation of protein kinases Glucagon Breakdown of glycogen into glucose

Controlling Blood Glucose Levels

Hormone Mechanisms Lipid-Soluble Aldosterone Can pass membrane (lipid) Bind to receptors inside a cell (cytosol or nucleus) Turn on or off an action of a specific gene Changes amount of protein that is synthesized by cell Aldosterone Increase sodium absorption → increases water retention → increase blood pressure

Major Features of Hormone Mechanisms Only the cells that contain surface or internal receptors for the hormones respond to the hormones Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that are functioning in or produced by the cell Hormones are effective in very small concentrations because of the amplification that occurs in both the surface and internal receptor mechanisms The response to a hormone differs among target organs and among species

Hormones: Negative Feedback Mechanisms Secretion of hormones are regulated by negative feedback mechanisms Hormones inhibit other hormones Multiple hormones can be secreted at a time

The Pituitary Gland The Master Gland Produces hormones that control most of the other glands in the endocrine system Made up of anterior lobe and posterior lobe Links endocrine system to nervous system via portal vein (hypothalamus) Influenced by hypothalamus Releasing hormones/inhibiting hormones

2. portal vein 4. anterior pituitary gland 5. hypophyseal vein 6. posterior pituitary gland 8. pituitary stalk 9. capillary network 10. neurons 11. neurosecretory cells 12. hypothalamus

Anterior Pituitary Gland Major hormones secreted into the bloodstream Tropic Growth hormone (both) thyroid-stimulating hormone adrenocorticotropic hormone follicle-stimulating hormone luteinizing hormone Nontropic Prolactin Melanocyte-stimulating hormone

Prolactin Promote milk production in mammary glands Suckling on nipple causes stimulus Regulated by dopamine Too much Hyperprolactinaemia Too little Hypoprolactinaemia

Growth hormone Cell division, protein synthesis, bone growth Release of growth hormone stimulates release of IGF in liver (insulin growth factor) that stimulates these functions Conversion of glycogen to glucose, fats to fatty acids – regulates levels in blood Stimulates cells to take up FA, AA and limits muscle cells to take up glucose

Growth hormone Underproduction Cause Overproduction Dwarfism Heart disease, increased fat Cause Genetic, benign tumour on pituitary gland Overproduction Acromegaly – body tissues get larger over time Gigantism – excessive production of growth hormone Benign tumour on pituitary gland

Thyroid-stimulating hormone Controls production of the thyroid hormones Underproduction Hyperthyroidism Cause Thyroid is producing too much thyroid hormone Overproduction Hypothyroidism Thyroid if producing too much thyroid hormone

Adrenocorticotropic hormone Controls production of cortisol, adrenaline, noradrenaline Underproduction Cushing’s syndrome Cause Steroid medication, tumour of pituitary gland Overproduction Cushing’s disease Addison’s disease (loss of function of cortex of adrenal gland) Adenoma (non-cancerous tumour) in the pituitary gland Autoimmunity

Follicle-stimulating hormone/luteinising hormone Puberty development/function of the gonads (testes/ovaries) Sex steroid production Germ cell production (sperm/eggs) Underproduction Incomplete development at puberty Infertility Overproduction Turner syndrome (female is missing entire/parts of x chromosome) Kallmann’s syndrome (failure to start/complete puberty) Cause Testicular/ovarian failure,

Melanocyte-stimulating hormone Causes darkening in humans by releasing melanin in the skin and hair and eyes Specialized cells called melanocytes release melanin Protects from UV rays Overproduction Increase production of melanin Cause Prolonged exposure to sun or skin tanning Underproduction Lack of skin pigmentation Loss of natural protection from UV rays and sun Damage to pituitary glands

Posterior pituitary gland Stores and releases 2 major hormones into the bloodstream Antidiuretic hormone (vasopressin) oxytocin These hormones are produced by the hypothalamus and stored here

Antidiuretic Hormone (vasopressin) Causes distal convoluted tubule to become permeable to water Helps maintain water balance Overproduction Kidneys retain too much water Underproduction Kidneys excrete too much water

Oxytocin Contraction of the womb Lactation Overproduction Not clear Underproduction Linked to autism

Thyroid gland Located in the front of the throat and shaped like a bow tie Secretes Thyroxine (T₄) calcitonin

Thyroxine (T₄) Prohormone (inactive) Contains 4 iodine atoms Active form is triiodothyronine Contains 4 iodine atoms Regulates body’s metabolic rate, heart and digestive function, muscle control, brain development, maintenance of bones Overproduction Thyrotoxicosis – too much thyroxine in bloodstream recognized by goitre Causes Hyperthyroidism Graves Disease Underproduction Hypothyroidism Autoimmune diseases, poor iodine diet

Calcitonin Reduces levels of Calcium (Ca²⁺) in the blood stream Opposes the action of parathyroid hormone Overproduction No apparent effect on body Underproduction

Parathyroid gland 4 spherical glands (size of a pea) located on each side of the posterior surface of the thyroid gland Secretes Parathyroid hormone

Parathyroid hormone Stimulates enzymes in kidneys to convert vitamin D into calcitrol increasing absorption of Ca²⁺ and phosphates from food Underproduction Muscle cramps Osteoporosis Overproduction Kidney stones

Pineal gland Located near the centre of the brain Secretes melatonin Secretion of melatonin is controlled by circadian rhythm (biological processes that fluctuate on a 24 hour timetable) Helps to synchronize biological clock (jet lag, sleep disorders) Melatonin also produced in retina of the eye Overproduction Reduced core body temperature Underproduction No apparent effect on the body

Adrenal glands Consist of two regions Adrenal medulla contains highly modified neuro-secretory neurons 2. Adrenal cortex contains non-neural endocrine cells

Adrenal medulla Secretes Epinephrine, nor-epinephrine These chemicals can act as hormones or neurotransmitters (transmit nerve signals to brain) Part of the “fight or flight” response

Epinephrine Released when body encounters stresses Increase heart rate glycogen and fat breakdown Major blood vessels dilate (increase blood flow) Blood vessels in skin constrict (chills and sweating) Increase in blood pressure Reduces water loss Digestive system slows Used to counter anaphylaxis

Adrenal cortex Secretes Aldosterone, cortisol

Glucocorticoids Cortisol – Helps raise blood glucose levels using three mechanisms Stimulate synthesis of glucose from fats and proteins Reduce glucose uptake by the body cells except in the central nervous system Promote breakdown of fats and proteins into fatty acids and amino acids as alternative fuels

Mineralocorticoids Aldosterone Overproduction Causes Underproduction Increase amount of sodium /water reabsorption in bloodstream Increase amount of potassium removal in urine Increase blood pressure Overproduction High blood pressure, low potassium, alkaline blood Causes Adrenal tumour Underproduction Addison’s disease, low blood pressure

Regulating blood sugar Occurs automatically in our body Pancreas – contain both exocrine and endocrine glands Exocrine secretes digestive enzymes into the small intestine Endocrine Islets of Langerhans - Secretes insulin (beta cells) and glucagon (alpha cells)

Insulin/Glucagon Regulate the ability of most tissues in the body to metabolize fuel substances (glucose, fats, proteins)

Insulin Secreted by beta cells Lower blood glucose levels by Acts on skeletal muscles, liver cells, adipose tissue (fat) to uptake glucose In the Liver Lowers fatty acid levels promotes fatty acid uptake and storage in adipose tissue Inhibits breakdown of fats into fatty acids Lowers amino acid levels Promotes protein synthesis Inhibits breakdown of proteins

Glucagon Secreted by alpha cells Increase blood glucose levels by Stimulating breakdown of glycogen into glucose Stimulates breakdown of fats into fatty acids Stimulates breakdown of proteins into amino acids Stimulate cells to use amino acids and non-carbohydrates to synthesize glucose

Glucose levels throughout the day

Unstable levels of glucose Hyperglycemia (above 200mg/dL of blood) Blood glucose levels are too high (norm 115-200mg/dL) Symptoms Frequent urination, sugar in the urine, vision problems, fatigue, weight loss Hypoglycemia (below 70mg/dL of blood) Blood glucose levels are too low (norm 70-115mg/dL) Nervousness, cold sweats, hunger, headaches, weakness

Diabetes High glucose levels in the blood caused by problems with insulin production Classified into 3 different types Type 1 Type 2 Symptoms Gestational Frequent urination, increased thirst/appetite

Type 1 Also called juvenile diabetes or insulin-dependant Beta cells do not produce any insulin Daily administration of insulin is required usually by injection or pump

Type 2 Reduced insulin production or the inability of insulin to bind to its receptors properly Developed in adulthood and is associated with obesity 90% of diabetics have this type Controlling diet and exercise helps restore normal levels of insulin production

Gestational Occurs in about 2 to 10% of pregnant women High blood glucose levels develop during pregnancy Usually a temporary condition but does increase the risk of both mother and child developing later in life

Reproductive Hormones Gonads (sex glands) Males – testes Females – ovaries Sex hormones Androgens, estrogens, progestins Regulate development of male and female reproductive systems, sexual characteristics, mating behaviour

Female Reproductive System Pair of ovaries Located in abdominal cavity Produce female gametes (ova, eggs) Produce estrogen and progesterone FSH and LH from the pituitary gland stimulate the maturation of the follicles in the ovary and trigger ovulation

Estrogen Estradiol Stimulates maturation of the sex organs at puberty Release of egg during ovulation Development of secondary sexual characteristics (breast development, body hair, widening of pelvis) Sex drive

Progestins Progesterone Secreted by the corpus luteum in the ovary Maintains uterus for implantation of a fertilized egg Growth and development of an embryo

Oogenesis Production and release of eggs (ova) by the ovaries Releases oocytes - immature eggs that have undergone 1 meiotic division Polar body is associated with it Disintegrates quickly Females produce up to 1 million Only ~380 are ovulated before menopause

Ovulation Monthly release of one or a few developing oocytes into the oviduct Burst of LH causes follicle to rupture Ova becomes ovum Moves through the oviduct (fallopian tubes) via cilia that line these tubes Fertilization occurs here in the oviduct undergoes second meiotic division only if penetrated by sperm cell producing a zygote If not fertilized egg will degenerate

Ovarian cycle Occurs from puberty to menopause Involves release of a mature egg approx every 28 days Coordinated with the menstrual cycle (month) Prepares the uterus to implant the egg if fertilization occurs

Corpus luteum LH causes ruptured follicle to grow into an enlarged yellowish structure Initiates luteal phase – prepares uterus to receive an egg If egg is fertilized: Acts as an endocrine gland- secretes estrogens, progesterone and inhibin Progesterone – inhibits GnRH – FSH LH Inhibin prevents secretion of FSH If egg is not fertilized Corpus luteum shrinks

Menstrual cycle Begins at day 0 Results from the breakdown of the endometrium Releases blood and tissue breakdown products from the uterus to the outside through the vagina Day 4 or 5 – flow ceases and endometrium begins to grow again Same hormones that control ovarian cycle control this cycle

Menopause High levels of sex hormones stops Late 40’s or early 50’s Menstrual/Ovarian cycle stops Side effects Hot flashes, headaches, mood swings Treated with HRT (hormone replacement therapy)

Male reproductive system Testes Affect the development of male secondary characteristics Secrete androgens (testosterone) Stimulates puberty, facial hair, vocal cords, sex drive Spermatogenesis – production of sperm Release of testosterone in the body is controlled by LH which is controlled by GnRH

Spermatogenesis Sperm development from spermatogonia Takes about 9 to 10 weeks - spermatogonium to sperm Testes produce about 130 million fertile sperm each day

Spermatogenesis Leydig cells - secrete testosterone Sertoli cells – supply nutrients to spermatocytes and seal them off from body’s blood supply Coiled seminiferous tubules located in epididymis store mature sperm Vas deferens – transport sperm upon ejaculation