Endocrine System. Collection of glands that secrete hormones.

Transcription

1 Endocrine System Collection of glands that secrete hormones. Gland- A single cell or a multicellular structure that secretes substances into the blood, a cavity, or onto a surface. Hormones Mediator molecules that are released in one part of the body but regulate the activity of cells in other parts of the body. They are transported by the bloodstream.

2 Arnold A Berthold ( ) In one of the first endocrine experiments ever recorded, Professor Arnold A. Berthold of Gottingen did a series of tests on roosters in 1849 while he was curator of the local zoo.

3 Bethold found that a rooster's comb is an androgen-dependent structure. Following castration, the comb atrophies, aggressive male behavior disappears, and interest in the hens is lost. Importantly, Berthold also found that these castration-induced changes could be reversed by administration of a crude testicular extract (or prevented by transplantation of the testes). Androgen general term for a steroid hormone that is responsible for male characteristics.

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5 Claude Bernard ( ) French physiologist and pioneer of experimental medicine. Worked on function of the pancreas Claude Bernard stated that the endocrine system regulates the internal environment of an animal. The internal secretions were liberated by one part of the body, traveled via the bloodstream to distant targets cells. Circa 1854

6 Charles Edouard Brown-Séquard ( ) Brown took over Bernard s position as professor of experimental medicine in Paris. Was the first to suggest the existence of what we now call hormones that would travel in the bloodstream. On June 1, 1889, before the Sociète de Biologic in Paris, Brown-Sequard reported that he had increased his physical strength, mental abilities and appetite by selfinjection with an extract derived from the testicles of dogs and guinea pigs. Although never substantiated, this claim prompted researchers around the world to pursue the new field of organotherapy (treating illness with medicines prepared from the organs of animals).

7 Charles Edouard Brown-Séquard ( )

8 Functions of the Endocrine System Water Balance controls the amount of solute in the blood. Uterine Contractions & Milk Release Metabolism & Tissue Maturation Ion Regulation Na +, K +, & Ca 2+ Heart Rate & Blood Pressure Regulation Blood Glucose Control Immune System Regulation Reproductive Functions Control

9 Endocrine vs. Nervous System Stimuli from the nervous system can influence the release of certain hormones and vice versa.

10 Hormones Molecules that are produced by endocrine glands: Hypothalamus Gonads (testes & ovaries) Thyroid Gland Parathyroid Glands Pancreas Can also be secreted by other organs such as kidneys, liver, heart, fat, stomach and intestine

11 Endocrine vs. Exocrine Endocrine ductless and secrete into the bloodstream. Secretions change cell metabolism. Exocrine Glands have ducts and secrete into body cavities, into the lumen of an organ (digestive tract) or on to the outer surface of the body (skin). These do not secrete hormones Some glands can be both exocrine and endocrine (liver)

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14 Sensing and signaling Endocrine glands synthesize and store hormones. These glands have a sensing and signaling system which regulate the duration and magnitude of hormone release via feedback from the target cell.

15 Hormones travel via the bloodstream to target cells The endocrine system broadcasts its hormonal messages to essentially all cells by secretion into blood and extracellular fluid. Like a radio broadcast, it requires a receiver to get the message - in the case of endocrine messages, cells must bear a receptor for the hormone being broadcast in order to respond. Generally a target cell has 2,000-10,000 receptors.

16 A cell is a target because is has a specific receptor for the hormone Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptors for the hormone.

17 Hormone Chemistry All hormones are made from either cholesterol or amino acids. Steroid Hormones made from cholesterol & are lipid soluble Ex: estrogens, progesterone, androgens, calcitriol Travel bound to transport proteins Can go into the cell because they are lipid based and receptors are inside the cell or on the nuclear envelope Polypeptide & protein hormones larger molecules Dissolved in plasma Bind to cell membrane Ex: insulin, growth hormone

18 Tyrosine Derivatives (Amino Acid Derivatives) Catecholamines (Monoamines- means 1 amino acid) Receptors on cell membrane Ex: epinephrine, norepinephrine fight or flight Thyroid Hormones Receptors on the nucleus Tyroxine

19 Classification of Hormones

20 Hormone Control Bodily functions are regulated by multiple hormones that regulate each other. Releasing hormones

21 Receptor Control A cell's DNA contains the instructions to create each type of receptor. Receptor proteins are made & embedded in the cell's membrane. This is called expression' of the receptor. The cell is constantly monitoring what's coming in to its receptors and adjusting their quantities accordingly Ex: increase in oxytocin receptors in uterus during third trimester of pregnancy to promote smooth muscle contractions

22 Receptor Control Down Regulation -a decrease in the number of receptors to a message sited on the cell membrane reduces the cell's sensitivity to the message. Ex: downregulation of insulin receptors due to high blood glucose. Up-regulation- if the cell receives a weak signal, it can respond by making more receptors such as to increase the sensitivity to the weak message. An increase in the number of receptors to a message sited on the cell membrane increases the cell's sensitivity to the message.

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25 Synergists & Antagonists Permissiveness a hormone cannot exert its full effects without the presence of another hormone. Synergists two hormones acting together have a greater effect than either of the two alone. Antagonists one hormone opposes the action of another hormone

26 Hypothalamus Located in the dienchephalon of the brain. Hormones actually produced by neurons Influenced by internal and external cues Hormones released into blood vessels that connect to the pituitary gland.

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28 Pituitary Gland Suspended from the floor of the hypothalamus by a stalk called the infundibulum. It sits in a special depression in the sphenoid bone called the sella turcia (turkish saddle)

29 Pituitary Gland About the size of a small marble. Composed of 2 structures with separate functions: Anterior Pituitary (Adenohypophysis) Produces 6 hormones Posterior Pituitary (Neurohypophysis) Extension of the brain Releases 2 hormones produced by the hypothalamus and stored in posterior pituitary

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31 The Hypothalamic Pituitary System The hypothalamus controls the pituitary in two ways: 1. The hypothalamus nerve cells secrete releasing hormones (6). Each releasing hormone either stimulates or inhibits the release of a specific anterior pituitary hormone. These leave the hypothalamus and are transported to the anterior pituitary through blood vessels. 2. The hypothalamus has nerve cells whose axons travel into the posterior pituitary and store hormones produced in the hypothalamus. Action potentials beginning in the hypothalamus cause these hormones to be released into the anterior pituitary.

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33 In the circulatory system, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart.

34 Acromegaly Hypersecretion of growth hormone in adulthood, epiphyseal plates have sealed so long bones no longer lengthen but jaw, browridges, nose, fingers,and toes continue to grow

35 Hyposecretion of growth hormone during childhood, normal proportions but very small Only 1 of about 200 causes for dwarfism Dwarfism

36 Gigantism Hypersecretion of growth hormone in childhood

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38 Adrenal Cortex: Adrenal Glands Glucocorticoids- cortisol is most important Increase fat and protein breakdown, inhibits inflammation Mineralocorticoids - aldosterone is most important which causes kidney s to retain sodium and excrete potassium that makes body retain water. Adrenal Medulla: Adrenalin & Noradrenaline produced during fight or flight response (sympathetic nervous system)

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40 Thyroid Gland

41 Thyroid Hormones Thyroxine (T 4 ) & Triiodothyronine (T 3 ) Both referred to as thyroid hormone Both are derived from tyrosine and have iodine added to them T 4 90% of produced but converted to T3 in liver and kidneys T 3 more active Increases metabolism Calcitonin lowers calcium levels in the blood

42 Goiter Swelling of the thyroid due to lack of iodine because thyroglobulin, a precursor to thyroid hormone builds up in follicles but no thyroxine can be made

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45 Parathyroid hormone (PTH)- Regulates blood calcium levels by stimulating the release of calcium from bone when blood calcium levels are low

46 Pancreas

47 Exocrine Function Pancreas Secretes digestive enzymes Endocrine Function 2 hormones from Islets of Langerhans Secretes glucagon from alpha cells Secretes insulin from beta cells

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