Endocrine system and nutrition; Nutrition and endocrine system

1. Endocrine system and nutrition;Nutrition and endocrine system

2. Let’s define some more - Define Hormone • The term hormone is derived from a Greek verb meaning – to excite or arouse • Hormone is a chemical messenger that is released in one tissue (endocrine tissue/gland) and transported in the bloodstream to reach specific cells in other tissues • Regulate the metabolic function of other cells • Have lag times ranging from seconds to hours • Tend to have prolonged effects • Hormone actions must be terminated – how?

3. Intercellular communication types • Autocrine - the cell signals itself through a chemical that it synthesizes and then responds to. Autocrine signaling can occur: • solely within the cytoplasm of the cell or • by a secreted chemical interacting with receptors on the surface of the same cell • Paracrine - chemical signals that diffuse into the area and interact with receptors on nearby cells (cells within the same tissue). • Endocrine - the chemicals are secreted into the blood and carried by blood and tissue fluids to the cells they act upon. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/H/Hormones.html

4. Bloodstream

5. Endocrine versus Nervous system • Both use chemical communication • Both are being regulated primarily by negative feedback • Released in synapse • Close to target cells • Signal to release by action potential • Short live effect • Crisis management Neurotransmitters Hormones • Released to bloodstream • Can be distant from target cells • Different types of signal • Long term effect • Ongoing processes

6. Control of Hormone Release • Blood levels of hormones: • Are controlled by negative feedback systems • Vary only within a narrow desirable range • Hormones are synthesized and released in response to: • Humoral stimuli • Neural stimuli • Hormonal stimuli

7. Humoral Stimuli • Secretion of hormones in direct response to changing blood levels of ions and nutrients • Example: concentration of calcium ions in the blood • Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone) • PTH causes Ca2+ concentrations to rise and the stimulus is removed

8. Neural Stimuli • Neural stimuli – nerve fibers stimulate hormone release • Preganglionic sympathetic nervous system (SNS) fibers stimulate the adrenal medulla to secrete catecholamines Figure 16.5b

9. Hormonal Stimuli • Hormonal stimuli – release of hormones in response to hormones produced by other endocrine organs • The hypothalamic hormones stimulate the anterior pituitary • In turn, pituitary hormones stimulate targets to secrete still more hormones

10. Let’s define some more - Define nutrients • Nutrientsare chemicals in foods that our bodies use for growth and function • Organic nutrientscontain carbon, an essential component of all living organisms • Carbohydrates, lipids, proteins, vitamins • Inorganic nutrients: nutrients that do not contain carbon • Minerals and water • Macronutrientsare nutrients required in relatively large amounts • Provide energy to our bodies • Carbohydrates, lipids, proteins

11. Hormone structure - based on chemical structure • Two main classes 1. Amino acid-based hormones Amino acid derivatives • Structurally similar to amino acids • Derivative of tyrosine : thyroid hormones catecholamines (Epinephrine, norepinephrin, dopamine), • Derivative of tryptophan - melatonine.

12. Hormone structure • Peptide hormones – 2 groups • Short polypeptides and small proteins – hormones secreted by heart, thymus, digestive tract, pancreas, hypothalamus (ADH and OT) and anterior pituitary (ACTH, GH, MSH, PRL) • Glycoproteins– consist more than 200 amino acids and have carbohydrate side chains. • anterior pituitary (TSH, LH and FSH), kidneys (erythropoietin), reproductive organs (inhibin)

13. Hormone structure 2. Steroids (Lipid derivatives) • Synthesized from cholesterol • Gonadal and adrenocortical hormones

14. A Structural Classification of Hormones

15. Distribution of Hormones in bloodstream • Hormones that are released into the blood are being transported in one of 2 ways: • Freely circulating • Bound to transport protein

16. Distribution of Hormones in bloodstream • Freely circulating (most hormones) • Hormones that are freely circulating remain functional for less than one hour and some as little as 2 minutes • Freely circulating hormones are inactivated when: * bind to receptors on target cells * being broken down by cells of the liver or kidneys * being broken down by enzymes in the plasma or interstitial fluid • Bound to transport proteins – thyroid and steroid hormones (>1% circulate freely) • Remain in circulation longer

17. Target Cell Specificity • Hormones circulate to all tissues but only activate cells referred to as target cells • Target cells must have specific receptors to which the hormone binds • These receptors may be intracellular or located on the plasma membrane

18. Interaction of Hormones at Target Cells • Three types of hormone interaction • Permissiveness – one hormone cannot exert its effects without another hormone being present • For example, thyroid hormone increases the number of receptors available for epinephrine at the latter's target cell, thereby increasing epinephrine's effect at that cell. Without the thyroid hormone, epinephrine would only have a weak effect • Synergism – more than one hormone produces the same effects on a target cell • Antagonism – one or more hormones opposes the action of another hormone

19. Target Cell Activation • Hormone exert their effects on target cells at very low bloodconcentrations (ng-10-9 gr; pg-10-12 gr) • Target cell activation depends on three factors • Blood levels of the hormone • Relative number of receptors on the target cell • The affinity of those receptors for the hormone • The time required to effect target cells depends on the hormone - some influence immediately and some (steroids; why?) require hours or days • Hormone effect duration also varies and can range between seconds to hours

20. Receptors number on target cell • down regulation – the presence of the hormone induces a decrease in the receptors concentration; • high levels of hormone – cell less sensitive • Up regulation – absence of the hormone induces the increase in receptors concentration; • Low levels of hormone – cell more sensitive • In most systems the maximum biological response is achieved at concentrations of hormone lower than required to occupy all of the receptors on the cell (spare receptors). • Examples: • insulin stimulates maximum glucose oxidation in adipocytes with only 2-3% of receptors bound • LH stimulates maximum testosterone production in Leydig cells when only 1% of receptors are bound

21. Receptors for hormones are located: • The hormone must interact with a specific receptor in order to affect the target cell • In the cell membranes of target cells • In the cytoplasm or nucleus

22. Mechanisms of Hormone Action • Two mechanisms, depending on their chemical nature • Water-soluble hormones (all amino acid–based hormones except thyroid hormone) • Cannot enter the target cells • Act on plasma membrane receptors • Coupled by G proteins to intracellular second messengers that mediate the target cell’s response • Lipid-soluble hormones (steroid and thyroid hormones) • Act on intracellular receptors that directly activate genes

23. Indirect effect – through G-protein and 2nd messenger

24. Links the first messenger (hormone) and the second messenger Hormone Protein receptor G protein (inactive) G protein activated The actions of second messengers for hormones that bind to receptors in the plasma membrane Effects on Ca2+ Levels Effects on cAMP Levels Some G proteins use Ca2+ as a second messenger. Many G proteins, once activated, exert their effects by changing the concentration of cyclic-AMP, which acts as the second messenger within the cell. Ca2+ Hormone Hormone Hormone Protein receptor Protein receptor Protein receptor Enhanced breakdown of cAMP Increased production of cAMP G protein activated G protein activated G protein activated Opening of Ca2+ channels Release of stored Ca2+ from ER or SER Acts as second messenger cAMP cAMP ATP AMP Ca2+ Ca2+ Ca2+ acts as second messenger Ca2+ Reduced enzyme activity Calmodulin Opens ion channels Activates enzymes Activates enzymes If levels of cAMP increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell. In some instances, G protein activation results in decreased levels of cAMP in the cytoplasm. This decrease has an inhibitory effect on the cell. The calcium ions themselves serve as messengers, generally in combination with an intracellular protein called calmodulin. Figure 16.2 1

25. Receptors on the cell membrane • Hormones do not induces changes in cell activity directly but via the induction of the appearance and action of other agents • Hormones are referred to as first messengers and the agents that are activated by the hormones are called second messengers. • All amino-acid hormones (with exception of the thyroid hormone) exert their signals through a second messenger system: • cAMP • PIP

26. Receptors on the cell membrane • Second messengers function as enzyme activator, inhibitor or cofactor • A small number of hormone molecules induce the appearance and activity of many 2nd messenger molecules – amplification • one single hormone can induce the activation of more than one 2nd messenger • Activation of a 2nd messenger can start a chain of reactions – receptor cascade

27. Amino Acid-Based Hormone Action: cAMP Second Messenger • Hormone (first messenger) binds to its receptor, which then binds to a G protein • The G protein is then activated • Activated G protein activates the effector enzyme adenylate cyclase • Adenylate cyclase generates cAMP (second messenger) from ATP • cAMP activates protein kinases, which then cause cellular effects

28. Amino Acid-Based Hormone Action: PIP-Calcium • Hormone binds to the receptor and activates G protein • G protein binds and activates phospholipase • Phospholipase splits the phospholipid PIP2 into diacylglycerol (DAG) and IP3 (both act as second messengers) • DAG activates protein kinases; IP3 triggers release of Ca2+ stores • Ca2+ (third messenger) alters cellular responses

29. Intracellular Receptors and Direct Gene Activation • Steroid hormones and thyroid hormone • Diffuse into their target cells and bind with intracellular receptors • Receptor-hormone complex enters the nucleus • Receptor-hormone complex binds to a specific region of DNA • This prompts DNA transcription to produce mRNA • The mRNA directs protein synthesis

30. http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/moaction/change.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/moaction/change.html

31. What Are Carbohydrates? One of the three macronutrients Important source of energy for all cells Preferred energy source for nerve cells Composed of carbon, hydrogen, oxygen Good sources: fruits, vegetables, grains Important component of the glycoprotein hormones (gondotrophins, Thyroid-stimulating hormone, erythropoietin to name few)

32. Different types of carbohydrates Simple carbohydrates Contain one or two molecules Commonly referred to as sugars Monosaccharides contain one molecule Glucose, fructose, and galactose Disaccharides contain two molecules Lactose, maltose, and sucrose

33. What Are Carbohydrates? Glucose The most abundant carbohydrate Produced by plants through photosynthesis

34. Different types of carbohydrates - Complex carbohydrates Oligosaccharides contain 3 to 10 monosaccharides Most polysaccharides consist of hundreds to thousands of glucose molecules (Starch, glycogen, most fibers)

35. Complex Carbohydrates - Starch Plants store carbohydrates as starch Amylose—straight chain of glucose Amylopectin—branched chain of glucose Resistant starch (fiber)—glucose molecules linked by beta bonds are largely indigestible Sources: grains, legumes, fruits, vegetables

36. Complex Carbohydrates - glycogen Storage form of glucose for animals (humans) Not found in food and therefore not a source of dietary carbohydrate Stored in the liver and muscles

37. Complex Carbohydrates - fiber Composed of long polysaccharide chains Dietary fibers are non-digestible parts of plants Functional fibers are non-digestible forms of carbohydrates extracted from plants or manufactured in a laboratory and have known health benefits Total fiber = Dietary fiber + Functional fiber

38. Complex Carbohydrates - Soluble fibers Dissolve in water; viscous and gel-forming Fermentable, digested by intestinal bacteria Associated with risk reduction of cardiovascular disease and type 2 diabetes Examples: pectin, gum, mucilage Found in citrus fruits, berries, oats, beans

39. Complex Carbohydrates – insoluble fibers Do not dissolve in water, nonviscous Cannot be fermented by bacteria in the colon Promote regular bowel movements, alleviate constipation, and reduce diverticulosis Examples: lignins, cellulose, hemicelluloses Good sources: whole grains, seeds, legumes, fruits, and vegetables ABC Video Whole Grains

40. The Role of Carbohydrates – Energy Each gram of carbohydrate: 4 kcal Red blood cells use only glucose for energy Both carbohydrates and fats supply energy for daily activities Glucose is especially important for energy during exercise

41. The Role of Carbohydrates – prevent ketosis Fat breakdown during fasting forms ketones Excess ketones increase blood acidity and cause ketoacidosis Sufficient energy from carbohydrates prevents ketone production as alternate energy source (will be discussed later in the course) Fad Diets

42. The Role of Carbohydrates - Spare Protein Gluconeogenesisoccurs when a diet is deficient in carbohydrate The body will make its own glucose from protein Amino acids from these proteins cannot be used to make new cells, repair tissue damage, support the immune system, or perform any of their other functions

43. Complex Carbohydrates Have Health Benefits Fiber May reduce the risk of colon cancer Helps prevent hemorrhoids, constipation, and other intestinal problems May reduce the risk of diverticulosis May reduce the risk of heart disease May enhance weight loss May lower the risk of type 2 diabetes Diverticulosis and Fiber

44. How Much Carbohydrate? Recommended Dietary Allowance (RDA) is 130 grams/day to supply adequate glucose to the brain Acceptable Macronutrient Distribution Range (AMDR) is 45% to 65% of daily calories Focus on fiber-rich carbohydrate foods

46. Simple Carbohydrates Diets high in simple sugars: Can cause tooth decay May increase “bad cholesterol” May decrease “good cholesterol” May contribute to obesity ABC Video Sugar and Processed Food

47. Complex Carbohydrates Most Americans eat too little complex carbohydrates Enriched foods are foods in which nutrients that were lost during processing have been added back so the food meets a specified standard Fortified foods have nutrients added that did not originally exist in the food (or existed in insignificant amounts)

48. Complex Carbohydrates Adequate Intake (AI) for fiber 25 g per day for women 38 g per day for men, or 14 g of fiber for every 1,000 kcal per day It is best to get fiber from food (also a source of vitamins and minerals) An adequate fluid intake (at least 8 oz/day) with high-fiber diets is recommended

49. http://www.medbio.info/Horn/Time%203-4/homeostasis_2.htm

50. Endocrine organs: Pancreas Pancreas structure Exocrine pancreas (99% of volume) Cells (pancreatic acini) forming glands and ducts that secrete pancreatic fluid and enzymes with digestive function Endocrine pancreas (1%) Small groups of cells scattered in clusters (pancreatic islets) that secrete hormones