Chemical Signals in Humans: Regulation and Homeostasis

1. Chemical Signals in Humans SGN 10

2. Regulates growth, development and homeostasis Manages responses to changes in the organism’s environment Linked to nervous system Includes cellular sensors and chemical signals Includes organs called glands The endocrine system – long range signaling

3. Overlap of endocrine and nervous system involves autonomic nervous system Involves relaxation Involves stress (much managed by ganglia of the spinal cord) Versus somatic, or conscious nervous system

4. The chemical signals are called hormones, and can be… polypeptides insulin, glucagon, HGH short peptides oxytocin, ADH glycoproteins FSH, LH biogenic amines, modified amino acids epinephrine, thyroid hormones steroids (modified lipids) sex hormones, aldosterone Students should know differences between the transport, reception and intracellular activity of hydrophilic versushydrophobic signalingmolecules

6. Nervous System The chemical signals are called neurotransmitters, and can be… acetylcholine short peptides opioids biogenic amines norepinephrine, serotonin, dopamine modified amino acids GABA, glutamic acid Endocrine System The chemical signals are called hormones, and can be… polypeptides insulin, glucagon, HGH short peptides oxytocin, ADH glycoproteins FSH, LH biogenic amines, modified amino acids epinephrine, thyroid hormones steroids (modified lipids) sex hormones, aldosterone

7. Biogenic amines Modified amino acids

8. 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.

9. FSH, LH and hCG are utilized during pregnancy

10. 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)

11. Hormones are ligands that bind to cellular receptors, initiating a signal transductionpathway and cellularresponse; only cells with the matching receptors and transduction intermediaries can respond to the hormone

12. Hormones target specific organs or tissues(oxytocin, produced in the posterior pituitary gland, acts on mammary tissue)

13. But hormones also have multiple or widespread effects throughout the body (the sex hormones affect numerous types of tissue; insulin’s effect is body wide) Students should be able to discuss epinephrine’s effects on different types of tissue (epinephrine is produced in the adrenal glands)

14. 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)

15. Some hormones have influence at particular stages of the life cycle (growth hormones) Some hormones regulate more immediate needs (fight or flight, arousal)

16. 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)

17. 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

18. Hormone release stimulated by nervous system Hormone release stimulated by internal condition Hormone release stimulated by other hormones

19. 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)

20. 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) A major role of the endocrine system is to regulate homeostasis Homeostasis is often maintained with antagonistic regulation (involves at least two hormones)

21. Feedback regulation is common in endocrine regulation

22. 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

23. 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

24. 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

25. Control of blood glucose levels- antagonistic with negative feedback

26. 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 glucagon secretion

27. 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)

30. 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

31. 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

32. 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

33. 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 predictable way? Because these phenomena are not always related in the way described above The two physiological conditions (osmolarity and pressure), though very closely related, require alternate but coordinated regulatory systems

34. 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

35. 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

36. Management of these systems is by simply increasing or decreasing the relevant hormones More simple than antagonistic management

37. Dehydration = high osmo, low blood pressure Not enough water; too much sweat Low blood pressure  RAAS system   High Osmo ADH  H2O addition  lowers Osmo  increase bp 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

38. 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)

39. 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 body’s 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 at all prepared Just a typical day!

40. See file for answers to previous

41. 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

43. 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)

44. 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

46. 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

47. 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 slough off but also allow HT hormones to resume, which stimulates a new follicle to mature and the cycle to begin again