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Lecture 15

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University of Toronto Scarborough
Biological Sciences
Bebhinn Treanor

Lecture 15—The Endocrine System TOPICS  Types of Cell Signaling  These hormones diffuse through the extracellular fluid and circulate in the blood move  4 different types from the blood to the target tissues & they act on the target tissues by interacting with  Types of Hormones receptors  leads to a series of second messenger activation system or alteration in gene  4 different types transcription  Hormone Receptors  Major Endocrine Glands  Major Hormones  The Hypothalamus and Pituitary  The Thyroid Gland  The Adrenal Gland  2 components: Outer cortex & medulla  Inner medulla releases the major stress hormone (adrenal)  Outer region cortex produces steroid hormones  One of the them cortisol (age more cortisol you have, the more rapidly you age)  The Pancreas, Insulin and Diabetes  The Pineal Gland  Atrial Natriuretic Peptide PHYSIOLOGICAL REGULATORY SYSTEMS  Nervous System: neural networks; rapid signaling  Command, regulatory system  Endocrine System: Endocrine glands secrete hormone that mediate slower, but longer-lasting, responses.  More regulatory than commands  Secretes hormones or other endocrine substances that will circulate through the blood NEUROENDOCRINE SIGNALING  Endocrine responses can be rapid (such as adrenaline) or some can be much slower or  Hormones can also originate from nerves called neurohormones more lasting (such as changes in protein synthesis due to changes in gene)  Rather than a gland producing and secreting hormones, nerves produce & secretes hormones  these hormones are created in extracellular fluid diffuse into the blood and transported through the blood to the target tissue  Similar to hormones secreted from an endocrine cell. In this case, neurohormones are secreted from a neurosecretory neuron.  Example: hormones secreted from neurons in the hypothalamus.  Hypothalamus has neurons which produce 2 hormones 1) Antitoxin 2) ADH  Hormones are released from these nerves directly into the extracellular fluid or blood  Synthesize them in hypothalamus but the axon from the cell are found on the nerve terminals, are found on the posterior pituitary TYPES OF CELL SIGNALING: CIRCULATING HORMONES  Picture: classes endocrine hormonal response  Have a endocrine gland that contain cells which synthesize & secrete a hormone 1 | P a g e CELL SIGNALING REGULATION  4 major methods of signalling 1) Classical endocrine signalling  Endocrine gland releases a hormone transported to the blood into a target tissue 2) Neuroendocrine signalling  Same as endocrine signalling EXCEPT hormone is released from neuron 3) Paracrine regulation  Diffuses through extracellular fluid 4) Autocrine regulation  Diffuses through extracellular fluid PARACRINE AND AUTOCRINE SIGNALING  Autocrine: Hormones act on the cells that produced and released them.  Where a cell would release a particular hormone (this can happen in nerves too) the hormone feeds back on the very cell that released it  Paracrine: Hormones diffuse through the extracellular fluid and act on cells nearby.  An endocrine cell will release a hormone, BUT the hormone diffuses to the extracellular fluid to another cell type where it has its effect by interacting with the receptor for a particular hormone that’s on the target cell  Thus, hormone does not travel through the blood it moves from one cell type to another cell type in extracellular fluid  Picture: cell released acetycholine and dopamine which can act in both paracrine and autocrine signalling  Acetycholine acts as paracrine whereas dopamine acts as autocrine  Often you can get an autocrine substance which has an autocrine effect on the cell which eoether inhibits the release the of paracrine substance or even accelerates the release of paracrine substance 2 | P a g e TYPES OF HORMONES (4 MAJOR TYPES OF HORMONES) capillaries in the lungs (and some degree in the kidney), it is exposed to enzyme 1) Amines: Tyrosine-Based (hydrophilic) called Ace (Ace stands for Angiotensin converting an enzyme)  Ace converts Angiotensin 1 to Angiotensin 2  Angiotensin 2 has a holster of effects  Start off with Phenylalanine  results in Tyrosine series of reaction that end up producing (in this case) 3 hormones which is referred to as catecholamines that is related to blood pressure regulation, osmotic or ion regulation  ** do not need to know the whole biosynthetic scheme  ** Angiotensin 2 triggers the adrenal cortex to release aldosterone  Thus, start off with phenylalanine then Tyrosine, then 3 substances Dopamine,  Have amines and peptides that can be hormones Norepinephrine, Epinephrine  Norepinephrine: is also known as adrenaline  Epinephrine: ‘Epi’ means to surround and ‘nephro’ means kidney  The adrenal gland which synthesizes and releases the hormones is wrapped around the upper portion of kidney (surrounds the kidneys)  These hormones are referred to as catecholamine since they contain both a catechol group (benzene ring with 2 hydroxyl ion) & an amine group  Both dopamine and Norepinephrine can function as neurotransmitters  Epinephrine does not function as neurotransmitters  Epinephrine and Norepinephrine can function as hormones  Dopamine cannot function as hormones  Norepinephrine can either be a neurotransmitter or hormone  Dopamine is just a neurotransmitter (not a hormone)  Epinephrine is just a hormone (not a neurotransmitter) 3) Steroid Hormones  Can be hormones  All steroids are derivative of cholesterol  Examples of Sex steroids: Such as progesterone, testosterone, estradiol, aldosterone  Cortisol: Hormone released from adrenal cortex  All steroid hormones are hydrophobic  they will move through plasma membranes and bind to receptors within cells 2) Peptides  Can also be hormones  Example in picture: peptide called angiotensinogin  which is then converted to peptides called angiotensin  Liver is always producing a protein called angiotensinogin  always circulating in the blood  Upon a stimuli (such as low blood press), the kidneys will produce an enzyme called rennin & release it into the blood rennin acts on angiotensinogin to produce angiotensin 1 Angiotensin 1 circulates through the blood & as it moves through the 3 | P a g e HORMONES RECEPTORS: INTRACELLULAR RECEPTORS 4) Fatty Acids  Hormone receptors inside the cells these receptors can either be in the cytoplasm or in the  A lot of insects use fatty acids in hormones (not found in mammals) nucleus  From a vertebrate, mammalian point of view the 3 major hormone types are amines (such a  Rather than hormone binding to cell surface receptor  it diffuses across the plasma membrane catecholamines), peptides and steroids & binds to the receptor in cytosol  receptor hormone complex moves into the nucleus and affects gene transcription HORMONES RECEPTORS: CELL SURFACE RECEPTORS  Or in the case of receptor in nucleus the hormone moves from blood across plasma  These hormones are going to exert affects either by acting on receptors in cell membrane (cell membrane into the cytosol into the nucles, binds receptor within the nucleus  the receptor surface receptors) OR have an effect by diffusing into cell across plasma membrane and hormone complex binds to the DNA to alter transcription interacting with receptors in the cytosol or nucleus  Picture on left: hormone coming from the blood  diffusing through the extracellular fluid and acting on the plasma membrane to bind to a receptor  Get a series of activation steps  Binding of the hormone to receptor will set in motion one reaction will set in another reaction...  end up with effectors molecules that bring the response within the cell  Picture on right: hormone is released from cell diffused in extracellular fluid into blood circulates in the blood and binds to a receptor in the target cell  In this case, binding of hormone to the receptor causes several pathways to occur Such as production of effector molecule in the cytoplasm or the production of effector molecules which can move into the nucleus and affect transmission  Thus, binding of hormones to cell receptors will trigger the production of effector molecules either in the cytoplasm or nucleus to alter transcription  One of the common types of effector molecules produced in the cytoplasm are kinases and phosphotases  Kinase enzyme which phosphorolates something  Puts a phosphate group onto a molecule  Phosphotase enzyme which dephosphorolates something  Takes off phosphate group  Enzymes are frequently activated or deactivated by phosphorlators or dephosphorolators  Large majority of second messenger signalling which leads to effector molecules is through phosphorolation or dephosphorolation HORMONES RECEPTORS: INTRACELLULAR RECEPTORS (ALDOSTERONE)  Example of intracellular receptor: aldosterone  Kinase and phosphotase are molecules that brings about response by phosphorolating or dephosphorlating proteins & enzymes within cells  Hormone released by the outer regions of adrenal cortex (# of signals that cause the adrenal cortex to release aldosterone which some of them is angiotensin 2, high plasma potassium)  In general: We see aldosterone moving into the cell binding with the receptor receptor hormone complex moves into nucleus alters gene transcription  Result: increase in transcription increase in protein synthesis  Increase synthesis of 3 things: one of which is the Sodium channels (sodium channel can get inserted into a plasma membrane)  occurs in the kidneys (next part...) 4 | P a g e  Occurring in the kidney tubule cell (more to the response than a sodium channel)  Picture: Kidney Tubule  Pre-urine in distil tubule THE MAJOR ENDOCRINE GLANDS AND HORMONES  Kidney Epithelial Cell: separates forming urine on left (in distil tube) from the blood  Summary of the major of endocrine glands and hormones from a mammalian perspective  In response to Angiotensin 2 (high potassium or low sodium in plasma)  Hypothalamus: in brain produces 2 sets of hormones which is referred to as releasing hormones  The cortex release aldosterone aldosterone moves into the cell  interacts with its (RH) & inhibitory hormones (IH) receptors  These hormones are going to move from the hypothalamus into the anterior pituitary  Increases the synthesis of sodium channels and potassium channels and the sodium- potassium Pump/ATPase  also stimulates the channels that are already exist to open  Going to trigger the anterior pituitary to release a # of hormones  Thus, IH & RH signal endocrine cells in the anterior pituitary to release all of those  Effect: sodium moves from pre-urine across the tubular epithelial cell which can be substances pumped across the other side, into the extracellular fluid into the blood  Aldosterone is served to pull sodium back to take it out of the forming urine & bring it back  Hypothalamus also synthesizes and secretes ADH and a hormone called oxytoxin  These are neuro-hormones which are produced in the cell body of hypothalamus into the blood  Released from the nerve terminals of those cells which are found in the posterior  But done the opposite to potassium potassium moved from blood through pituitary extracellular fluid and into the urine  Thus, cell body is in the hypothalamus and the axon moves down into the posterior  Aldosterone is triggering the re-absorption of sodium and the excretion of potassium pituitary  so the hormones are released from the posterior pituitary  Location of Adrenal glands: sitting on top of kidney  Inner medulla produces: catecholamine hormones, ephinephrine, etc  Cortex produces: steroid hormones such as aldosterone  Gonads produce: sex steroids  Pineal gland produces: melatonin (aids in sleep)  Thyroid gland and para-thyroid gland produces: substances involved with metabolism  Within the pancreas, there are endocrine regions called: Islets of Langerhans  They produce: insulin and glucagon (which are involved in blood glucose regulation) 5 | P a g e  Hormones that are released into the capillary bed move through a portal vein to a capillary bed to a anterior pituitary within the anterior pituitary, the RH or IH will trigger endocrine cells within the anterior pituitary to release a # of substances  In general: hypothalamus produce hormones which influence anterior pituitary cells to release other hormones anterior pituitary cells signal other organs to release even more hormones THE HYPOTHALAMUS AND THE ANTERIOR PITUITARY  The hypothalamus produces: 1) Releasing hormones (RH) 2) Inhibiting Hormones (IH)  RHs and IHs move to the anterior pituitary via a portal vein. There they trigger (or inhibit) the THE HYPOTHALAMUS AND THE POSTERIOR PITUITARY release of hormones synthesised by endocrine cells in the anterior pituitary.  There are neurons within the hypothalamus which produce & secrete both oxytocin and  The hypothalamus is also the body’s thermostat – the centre of temperature regulation. Antidiuretic hormone (ADH)  These hormones are produces in the cell bodies within the hypothalamus transported down the axon to the nerve terminals that are found in the posterior pituitary  When the conditions are right, and when the cells are signalled to release their hormones they are released from the posterior pituitary into the blood where they can circulate throughout the body  Effects of oxytocin: has effects on uterus and mammary glands  stimulating uteri contraction & milk production  Effects of ADH: on the kidneys & it causes the kidneys to reclaim water to produce less urine  Prevents the kidney from producing such a large volume of urine  Dieresis: means water flow, thus ANTI-Dieresis prevents large amounts of urine  Receptors of ADH are inhibited by: alcohol (one of the reasons why people need to pee a lot when they drink alcoholkidney is not able to reabsorb water—produce very dilute urine)  Cells within hypothalamus are producing: many RH and IB  They are released from nerve terminals that are in the hypothalamus released into capillary bed 6 | P a g e THE ANTERIOR PITUITARY HORMONES THE ANTERIOR PITUITARY HORMONES  tropic hormones - secreted into blood and transported to other endocrine glands  anterior pituitary releases a # of substances  these hormones are released from the anterior pituitary in response to hormones coming from hypothalamus, and in turn they act on other organs or other glands  Trophic hormone: Hormone that is released form one gland that acts on another glan
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