WEEK 10 Endocrine System PDF

Week 10: Endocrine System Objectives Interpret how the hormones of the endocrine system control and restore homoeostasis in the body. List and locate the organs of the endocrine system and explain the functions of each hormone secreted from eac...

Week 10: Endocrine System Objectives Interpret how the hormones of the endocrine system control and restore homoeostasis in the body. List and locate the organs of the endocrine system and explain the functions of each hormone secreted from each organ. Reading Notes Glands are scattered from head to the genitals Major Glands of Endocrine System 1. Pituitary Gland 2. Thyroid Gland 3. Parathyroid Glands 4. Adrenal Gland 5. Pancreas 6. Pineal Gland 7. Thymus Gland 8. Reproductive Gland Week 10: Endocrine System 1  → Other Hormones-secreting cells are found in certain organs of the body, like Liver, heart, Kidneys, & gastrointestinal tract → Endocrine: means “internal secretion” (i.e. Pancreas, liver etc) ▫︎Named endocrine due to cells, tissues, & organs that compose it, ▫︎secrete chemical substances called hormones into internal environment ▫︎Ductless glands and empty hormonal Products directly into blood → Hormones = diffuse from the interstitial fluid into the bloodstream where they act in target cells. → Said, Target cells have specific receptors that are not found on other cells. Composed of proteins or glycoproteins, these receptors have binding sites for a specific hormone. Week 10: Endocrine System 2  → Exocrine Glands: secrete chemicals substance that enter tubes or ducts that leads to body surface. (i.e. stomach (gastric) acid reaching the lumen of the digestive tract & sweat released at the skin’s surface) ⦁ Some cells secrete substance that are not hormones into internal environment but function similar as chemical messenger molecules and are sometimes termed as ‘local hormones’ → Paracrine: secretion enters the interstitial fluid & affect only nearby cells. (i.e. Histamine released from certain white blood cells that causes dilation of nearby blood vessels) → Autocrine: secretions affect only the cell secreting the substance. (i.e liver cells stimulating themselves to release stored iron) ❊ Endocrine system releases hormones into the bloodstream that circulate everywhere in the body. → Hormones secreted by endocrine glands help regulate metabolic processes. These chemical messengers control the rates of certain chemical reactions, aid in transport substances through membranes, & help regulate water balance, electrolyte balance, & blood pressure. Nervous system Vs Endocrine system Nervous system Rapid communication using electrical signals. Releases neurotransmitters into synapses (Fewer targets). Neurotransmitters typically producer shorter-term effects. Short term, localized. Endocrine system Slower communication through blood. Multiple, distant targets. VERY Specific Hormones typically produce longer-term effects on physiology of target. Week 10: Endocrine System 3  Message sent from gland, goes through the blood (Circulating and slowly), getting through its target cell, changing the function of the cell. Shorter longer distance. Hormone = chemical messenger, secreted by endocrine cell/organ that changes the function of another cell. Hormonal Control Receptor specificity → ability for cells to respond to the fit of a hormone (lock and key) Receptor affinity → how tight the fit is, ­affinity = less hormones needed Hormone agonist → allows certain glands to release/inhibit their hormones. Hormone antagonist → oppose or reverse the effects of a hormone. Synergistic effect → two hormones with similar effects produce an amplified response. (i.e., sperm and egg) ◦ Upregulation = ­↑ number of receptors. ◦ Downregulation = ↓ number of receptors on the cell. ̄ sensitivity. ◦ Permissiveness = one hormone being mandatory for other hormones to work. → Chemical structure of hormone determines if its lipid-soluble or water-soluble, which determines how the hormone is transported in the blood & its mechanism of action on its target cells. Action Hormones-Hormones are organic compounds (Two major types) 1. Steroids (or steriodlike substances): steroid are synthesized from cholesterol Week 10: Endocrine System 4  → Steroids are lipids derived from cholesterol that have complex rings of carbon & hydrogen atoms & some oxygen atoms. → Steroids differ by types & numbers of atoms attached to the rings & the way they are joined. → Steroid hormones include, ⦁ Sex hormones, (i.e. testosterone & estrogens) & ⦁ Adrenal Cortex (i.e. out portion of adrenal gland), like aldosterone & cortisol. ⦁ Vitamin D - modified steroid & when converted to active form in kidneys & liver, becomes a hormone. 2. Amino Acid: synthesized from amino acid & including the amines, peptide, proteins & glycoproteins → Hormones called amines (monoamines; biogenic amines) derived from particular amino acids → Norepinephrine & Epinephrine derived from amino acids tyrosine → These hormones synthesized in the adrenal medulla (inner portion of adrenal gland) → Thyroid hormones (thyroxine), synthesized in thyroid gland = another amine composed of tyrosine. → Melatonin = amine thats synthesized from amino acid tryptophan → Nonsteroid hormones combine w/ receptors in the target cell membrane → A hormone- receptor complex stimulates membrane proteins, like Adenylate cyclase, to induce formation of second messenger molecules. → A second messenger, like Cyclic adenosine monophosphate (cAMP), activities protein kinases → The cellular response to a nonsteroid hormone is amplified b/c the enzymes induced by a small number of hormones-receptors complexes can catalyze formation of a large number of second messenger molecules Week 10: Endocrine System 5  Peptide hormones; are short chains amino acids → This group includes - antidiuretic hormones & oxytocin associated w/ posterior pituitary gland, & some hormones produced in hypothalamus, like thyrotropin- releasing hormones Prostaglandins; are paracrine substances, & therefore act on neighbouring cells. → there lipids & synthesized from a type of fatty acid (arachidonic acid) in cell membranes → Produced in liver, kidneys, heart, lungs, thymus, pancreas, brain, & reproductive organs → Prostaglandins modulate hormones that regulate formation of cyclic AMP hormone might change activity of enzyme needed for synthesizing a particular substance or altering the rate at which particular chemicals are transported through cell membrane. Control of Hormonal Secretions → The concentration of each hormone in the body fluids is precisely regulated 1. Some endocrine glands secrete hormones in response to releasing hormones that the hypothalamus secretes 2. Some endocrine glands secrete in response to nervous stimulation 3. Some endocrine glands secrete in response to changes in plasma concentration of a substance 4. In negative feedback system, a gland is sensitive to the physiological effect that its hormone brings about 5. When the physiological effect reaches a certain level, it inhibits the gland 6. As the gland secrete less hormones, the physiological effect is lessened Week 10: Endocrine System 6  Pituitary Gland → attached to the base of brain, posterior lobe part of the nervous system, & an anterior lobe composed of glandular cells. → Releasing hormones from the hypothalamus control anterior pituitary secretions 1. Anterior pituitary hormones (anterior lobe; adenohypophysis) a. The anterior pituitary consists largely of epithelial cells, & it secretes… b. Growth hormones (GH): (1) stimulates body cells to grow & divide (2) Insulin-like growth factor (IGF) is a mediator protein that helps GH function (3) Growth hormone-releasing hormone & somatostatin from the hypothalamus control GH secretion c. Prolactin (PRL): (1) PRL promotes breast development & stimulates milk production (2) A normal function of prolactin in males has not been established (3) Prolactin release-inhibiting hormone from the hypothalamus restrains secretion of prolactin d. Thyroid-stimulating hormones (TSH): (1) TSH controls secretion of hormones from the thyroid gland (2) The hypothalamus, by secreting thyrotropin-releasing hormones, regulates TSH secretion e. Adrenocorticotropic hormone (ACTSH): (1) ACTH controls the secretion of certain hormones from the adrenal cortex (2) The hypothalamus, by secreting corticotropin-releasing hormone, regulates ACTH secretion Week 10: Endocrine System 7  f. Follicle-stimulating hormone (FSH) & luteinizing hormone (LH): (1) Are gonadotropins, hormones that affect the gonads 2. Posterior Pituitary Hormones a. The posterior lobe of the pituitary gland largely consists of neuroglia & the axons of neurons of neurons whose cells are in the hypothalamus b. The two hormones of the posterior pituitary are produced in the hypothalamus c. Antidiuretic Hormones (ADH): (1) ADH causes the kidneys to excrete less water (2) In high concentration, ADH constricts blood vessel walls, raising blood pressure (3) The hypothalamus regulates ADH secretion d. Oxytocin (OT): (1) OT has an antidiuretic effect & can contract smooth muscles in the uterine wall (2) OT also contracts certain cells associated with production & ejection of milk glands of the breasts Thyroid Gland → The thyroid gland is located in the neck & consists of two lateral lobes 1. Structure of the gland a. The thyroid gland consists of many hollow secretory parts called follicles b. The follicles are fluid filled & stored the thyroxine & triiodothyronine the follicular cells secrete c. Extrafollicular cells secrete calcitonin 2. Hormones of the thyroid gland Week 10: Endocrine System 8  a. Thyroxine & triiodothyronine (T3) are collectively called thyroid hormone (1) These hormones increase the rate of metabolism, enhance proteins synthesis & stimulates lipid breakdown (2) These hormones are needed for normal growth & development & for maturation of the nervous system b. Calcitonin (1) Calcitonin lowers blood calcium & phosphate ion concentration (2) This hormones prevents prolonged elevation of calcium after a meal Parathyroid Glands → The Parathyroid glands are on the posterior surface of the thyroid gland. 1. Structure of the glands a. Each gland is small & yellow-brown, within a thin connective tissue capsule b. Each gland consists of secretory cells well supplied w/ capillaries 2. Parathyroid Hormone (PTH) a. PTH increases blood calcium ion concentration & decreases blood phosphate ion concentration b. PTH stimulates resorption of bone tissue, causes the kidneys to conserve calcium ions & excrete phosphate ions, & indirectly stimulates absorption of calcium ions from the intestine c. A negative feedback mechanism operating between the parathyroid glands & the blood regulates these glands Adrenal Glands → The adrenal glands are located atop the kidneys. 1. Structure of the glands a. Each adrenal gland consists of a medulla & a cortex Week 10: Endocrine System 9  b. The adrenal medulla & adrenal cortex are distinct in that they secrete different hormones 2. Hormones of the adrenal medulla a. The adrenal medulla secretes epinephrine & norepinephrine b. These hormones are synthesized from tyrosine & are chemically similar c. These hormones produce effects similar to those of the sympathetic nervous system d. Sympathetic impulses originating from the hypothalamus stimulates secretion of these hormones 3. Hormones of the adrenal cortex a. The cortex produces several types of steroid that includes hormones b. Aldosterone (1) causes the kidney to conserve sodium ions & water & to excrete potassium ions (2) Secreted in response to increased potassium ion concentration (3) By conserving sodium ions & water, it helps maintain blood volume & pressure c. Cortisol (1) inhibits protein synthesis, releases fatty acids, & stimulates glucose formation from non-carbohydrates (2) A negative feedback mechanism involving secretion of CRH from the hypothalamus & ATCH d. Adrenal Sex Hormones (1) These hormones are the male type, w/ the main one being dehydroepiandrosterone(DHEA), although some can be converted into female (2) They supplement the sex hormones produced by the gonads Pancreas Week 10: Endocrine System 10  → The pancreas secretes digestive juices as well as hormones 1. Structure of the gland a. pancreas is posterior to the stomach & attached to the small intestine b. The endocrine portion, called the pancreatic islets (islets of Langerhans), secretes glucagon, insulin, & somatostatin 2. Hormones of the pancreatic islets a. Glucagon stimulates the liver to produce glucose, increasing concentration of blood glucose. it also breaks down fat. b. Insulin activates facilitated diffusion of glucose through certain cell membranes, stimulates its storage, promotes protein synthesis, & stimulates fat storage c. Facilitated diffusion of glucose into nerve cells does not depend on insulin d. Somatostatin inhibits insulin & glucagon release Pineal, Thymus, & Other Glands 1. Pineal Gland a. The pineal gland is attached to the thalamus near the roof of the third ventricle b. Postgangilonic sympathetic nerve fibers innervate it. c. Secretes melatonin, which regulates some circadian rhythms 2. Thymus a. Thymus lies posterior to the sternum & between the lungs b. It shrinks with age. c. it secrete thymosins, which affects the production of certain lymphocytes that, in turn provide immunity 3. Reproductive Organs Week 10: Endocrine System 11  a. The testes secrete testosterone b. The ovaries secrete estrogens & progesterone c. The Placenta secretes estrogen, progesterone & a gonadotropin → The digestive glands like certain glands of stomach & small intestine that secrete hormones → Other hormone-secreting organs include the heart, the kidneys, & the liver, as wells as adipose tissue. Stress & Its Effects → Stress occurs when body responds to stressors that threaten the maintenance of homeostasis. → Stress responses include increased activity of the sympathetic nervous system & increased secretion of adrenal hormones 1. Types of stress a. Physical stress results from environmental factors that are harmful or potentially harmful to tissues b. Psychological stress results from thoughts about real or imagined dangers. Factors that produce this vary w/ the individual the situation 2. Response to Stress a. The hypothalamus controls a general adaptation syndrome (GAS) b. Responses to stress work to maintain homeostasis. c. Persistent stress can lead to an exhaustion phase, which may be fatal Life-Span Changes → W/ age, endocrine glands shrink & accumulate fibrous connective tissue, fat & lipofuscin, but hormonal activities usually remain within the normal range 1. GH levels even out, as muscular strength declines Week 10: Endocrine System 12  2. ADH levels increases due to slowed breakdown 3. The Thyroid shrinks but control of metabolism continues 4. Decreasing levels of calcitonin & increasing levels of parathyroid hormones increase osteoporosis risk 5. The adrenal gland show aging-related changes, but negative feedback maintains functions 6. Muscles, liver, & fat cells may develop insulin resistance. 7. Changes in melatonin secretion affect the body clock 8. Thymosin production declines, hampering resistance to disease. Endocrine Post-Lec SUPP Gastrin and Its Role in Digestion Function: Gastrin is the hormone that promotes the release of several essential digestive components in the stomach: Pepsinogen: A precursor to the enzyme pepsin, aiding in protein digestion. Mucus: Protects the stomach lining from acidic environments. Hydrochloric Acid (HCl): Plays a crucial role in digestion and pathogen defense. Release Trigger: Gastrin is released in response to: The presence of food in the stomach. A rise in stomach pH (indicating a less acidic environment). Week 10: Endocrine System 13  Source: Gastrin is secreted by enteroendocrine cells in the stomach lining. Effects of Gastrin: Hydrochloric Acid (HCl) Production: Parietal cells in the stomach produce HCl, which lowers the stomach pH, creating an acidic environment. This acidic environment facilitates digestion and inhibits harmful microorganisms. Mucus Production: Protects the stomach lining from acidic damage. Protein-Digesting Enzymes: Chief cells secrete pepsinogen, which, when activated, assists in protein breakdown. Acidic pH Impact: Converts pepsinogen to pepsin, initiating protein digestion. Creates a hostile environment for microorganisms. Partial Denaturation of Proteins: HCl unfolds proteins, making them easier for enzymes to break down. Secondary Effects: Stimulates the secretion of bile and pancreatic juice, both important for digestion and absorption of nutrients in the intestines. Hormonal Regulation and Blood Pressure Aldosterone: Function: Promotes sodium (Na+) retention by the kidneys. Effect on Blood Pressure (BP): Sodium retention increases blood volume, which helps raise blood pressure. Antidiuretic Hormone (ADH): Function: Reduces water loss by decreasing urination, helping retain water in the body. Week 10: Endocrine System 14  Trigger: Low blood pressure is detected by the hypothalamus, which signals the release of ADH. Week 10: Endocrine System 15