Chemical Signals in Humans SGN 10 The endocrine system long range signaling Regulates growth, development and homeostasis Manages responses to changes in the organisms environment Linked to nervous system Includes cellular sensors and chemical signals Includes organs called glands Overlap of endocrine and nervous system involves autonomic nervous system
Involves relaxation Versus somatic, or conscious nervous system Involves stress (much managed by
ganglia of the spinal cord) The chemical signals are called hormones, and can be polypeptides insulin, glucagon, HGH short peptides
Oxytocin is a hormone secreted by the posterior lobe of the pituitary gland, a pea-sized structure at the base of the brain. It's
sometimes known as the "cuddle hormone" or the "love hormone," because it is released when people snuggle up or bond
socially. FSH, LH and hCG are utilized during pregnancy Hormones are produced in endocrine glands, which are organs that contain cells that secrete hormones into the bloodstream, which then have their effect on specific target cells in other bodily locations (versus local regulators) Hormones are ligands
that bind to cellular receptors, initiating a signal transduction pathway and cellular response; only cells with the matching receptors and transduction intermediaries can respond to the
hormone Hormones target specific organs or tissues (oxytocin, produced in the posterior pituitary gland, acts on mammary tissue) But hormones also have multiple or widespread effects throughout the body (the sex hormones affect numerous types of tissue; insulins effect is body wide) Students should be able to discuss epinephrines effects on different types of tissue (epinephrine is produced in the adrenal glands)
Many hormones have long term, fluctuating influence during the entire life of the organism, involved in regulating day-to-day metabolism (insulin and glucagon regulate blood glucose levels) Some hormones have influence at particular stages of the life cycle (growth hormones) Some hormones regulate
more immediate needs (fight or flight, arousal) Hormone secreting cells are typically located within organs called glands Numerous endocrine glands and glandular tissues exist throughout the body (other types of glands, exocrine glands, do not produce hormones (secreted into the blood or surrounding tissue) but instead secrete into ducts, that drain the secretion to the digestive tract or to the body surface ducted glands)
Different types of receptors in glands, the brain or other tissue respond to different types of stimuli (can originate externally and internally) Internal sensors respond to temperature, blood solute concentrations, blood pressure, and so on Regulation of body temp (nonhormonal) Regulation of
blood glucose Regulation of blood pressure Hormone release stimulated by internal condition Hormone release stimulated by nervous
system Hormone release stimulated by other hormones The endocrine system is often intricately linked with the nervous system, including external sensors (sight, smell, etc.) Neurons can stimulate glands to secrete hormones
Cells that transmit a nerve signal and in response secrete hormones are called neurosecretory cells Neurotransmitters and hormones have similar modes of action (ligand/receptor cellular response) and some chemicals are used as both (epinephrine is used as hormone and neurotransmitter in slightly different forms) A major role of the endocrine system is to regulate homeostasis Homeostasis is often maintained with antagonistic regulation (involves at least two hormones) Homeostasis involves keeping the
body within a narrow range of conditions (pH, temperature, glucose concentration, etc.); if the value exceeds or falls below this range an endocrine response will ensue; opposite responses operate against extremes of variation (antagonistic responses) Feedback regulation is common in endocrine regulation
A certain body condition will move out of range, setting off cellular sensors, which induce the release of a hormone that has an action that moves the condition back into an acceptable range The initial stimulus (condition out of range) of the sensors is removed so the sensors stop inducing release of the hormone and the action stops This is negative feedback, which is common Positive feedback, where the action creates a condition that instead intensifies the release of the hormone, is more rare, and is used to drive a
process to completion (delivery of baby, suckling stopped) The posterior pituitary produces oxytocin, which induces contractions, which in turn stimulate oxytocin production, until birth Some examples of endocrine control of homeostasis Antagonistic control with negative feedback
Blood glucose Tropic hormones The hypothalamus and pituitary glands Complex coordination of related processes Osmolarity and blood pressure
Multihormone control of a complex system The female reproductive cycle Control of blood glucose levels- antagonistic with negative feedback Blood glucose levels rise after a meal and drop if a person goes for a significant time without eating, yet
levels cannot deviate too far from the norm or serious health risks can result Cells in the pancreas detect high glucose levels and induce other pancreatic cells to secrete insulin; insulin disperses throughout the body where it induces cells to absorb glucose, and induces the liver to absorb glucose and store it
as glycogen Decrease of glucose levels removes stimulus and insulin secretion stops Other cells in the pancreas also detect low blood sugar, inducing the pancreas to release glucagon, which has antagonistic effects in relation to insulin Increase of blood glucose shuts down
Tropic hormones Primary hormones stimulate release of secondary hormones (tropic hormones), which stimulates tissue response or stimulates release of tertiary hormone that in turn induces tissue response The important role of the hypothalamus (HT) and pituitary glands (PG) The HT contains receptors for numerous conditions (temperature, different chemical concentrations, stimulus by the nervous system, osmolarity) and produces numerous types of hormones in response, secreted by neurosecretory cells
HT hormones signal release of other hormones from the anterior and posterior PG, which in turn have many different effects throughout the body Tropic hormones, such as APG hormones, are hormonally stimulated but in turn stimulate another gland, so are intermediate between the original hormone produced in the HT and the eventual response An example of this is the pathway involving thyroid hormones (TH), which are responsible for regulating a wide range of conditions involved in bioenergetics, growth and development, reproduction, etc.
The HT is stimulated by low concentration of a particular TH and is induced to secrete its own hormone, which in turn induces the APG to secrete a hormone that stimulates the thyroid to secrete the needed hormone; negative feedback inhibits pathway Control of osmolarity and blood pressure coordination of related processes Osmolarity refers to blood solute concentration Blood pressure relates to the amount of force required by the heart to push the blood through the vascular system (relates to blood volume, condition of cardiovascular system, etc.) Problems in osmolarity and blood pressure are often due to the same thing and
can be corrected in the same way Often high blood pressure means low osmolarity (dilute blood) = remove water from the blood Often low blood pressure means high osmolarity (concentrated blood) = add water to the blood Osmolarity and blood pressure are regulated by two different systems Why not have the same sensors and response if the two systems are related in a way?
predictable Because these phenomena are not always related in the way described above The two physiological conditions (osmolarity and pressure), though very closely require alternate but coordinated regulatory systems related,
Osmolarity and antidiuretic hormone (vasopressin) Problem = high osmolarity Stimultes ADH (concentrated blood) Solution = add
water to blood Causes increase in blood pressure Problem = low osmolarity Inhibits ADH (dilute blood) Solution = remove water fromblood Causes decrease in
Blood pressure and the renin angiotensin aldosterone system (RAAS) Problem = low blood pressure (low blood volume) Solution = water addition to blood Increase blood pressure Problem = high blood pressure (high
blood volume) Solution = inhibit water addition to blood Management of these systems is by simply increasing or decreasing the relevant
hormones More simple than antagonistic management Dehydration = high osmo, low blood pressure Not enough water; too much sweat High Osmo ADH H2O addition
lowers Osmo increase bp Low blood pressure RAAS system But what about conditions wherein the two states are not correlated?
Heavy salt intake quickly increases Osmo Diarrhea (rapid loss of water and salt) or without decreasing bp wound decreases BP without change to osmolarity Today often heavy salt diet (inducing water uptake) is often coupled with high blood pressure due to coronary disease, smoking, etc. (water uptake bad) so systems are working at cross purposes and under conditions
that they did not evolve for Many high BP medicines suppress angiotensin and RAAS system (inhibit arteriole constriction and water and salt uptake) What does your system do if you have been walking for two days without water you come to a stream; you drink heavily for an extended time you find a salt lick near the stream and lick up a bunch of it, satisfying your bodys salt craving
a sabretooth tiger jumps you and gives you a heavily bleeding gash in your side (but the tiger is in even worse condition because you are a badass) something in the water you drank gives you massive diarrhea you then remember you have a biology test next Friday and are not all prepared Just a typical day! at
See file for answers to previous Multihormone control of a complex system The female reproductive cycle (FRC) The FRC includes two coordinated cycles, the ovarian cycle (OC) and the uterine cycle (UC), which roughly run for 28 days and then repeat throughout sexual maturity The OC involves the maturation of the ovarian follicle, and peaks at ovulation
(release of the egg from the follicle); follicular tissue releases the hormones estradiol and progesterone The OC is itself broken down into two phases - the follicular phase (during which the follicle matures and the egg is released) - the luteal phase (during which the follicle, now known as the corpus luteum slowly disintegrates but continues to produce hormones) The UC involves thickening of the uterine lining and secretion of nutrient fluids, each of which support the embryo; if fertilization does not occur the lining sloughs off The UC is broken down into three phases
- during the proliferative phase the uterine lining thickens in response to estradiol produced by the follicle - during the secretory phase the lining secretes nutrients in response to estradiol and progesterone, produced by the follicle - during the menstrual flow phase (which only proceeds if fertilization has not occurred) the uterine lining sloughs off These cycles are regulated by the hypothalamus At the beginning of the OC the young follicle secretes low levels of estradiol, which induces the HT to stimulate the APG to release follicle stimulating hormone (FSH) and luteinizing
hormone (LH), which are tropic hormones; HT hormone is gonadotropin releasing hormone FSH and LH stimulate follicular growth and estradiol production (positive feedback), eventually leading to ovulation (outside event that terminates positive feedback) Estradiol also stimulates growth of the uterine lining (during the proliferative phase of the uterine cycle Upon ovulation the follicular tissue begins to secrete progesterone along with estradiol, which together
stimulate the uterine secretory phase but also inhibit HT hormones (negative feedback) A lack of HT hormones shuts down APG hormones that stimulate follicular growth and the follicular tissue starts to
disintegrate, decreasing levels of estradiol and progesterone Decreased levels of estradiol and progesterone cause the uterine lining to
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