The Endocrine System

1. The Endocrine System Part 3: Integration & Control

2. The Endocrine System • Endocrinology: The study of the endocrine system. • Endocrine System: Communicates with & helps control body systems via hormones. • Communication is slower than in the nervous system & has longer-lasting effects. • Hormones: Chemicals secreted directly into the bloodstream to affect target cells or organs.

3. Glands • Exocrine Glands: Secrete hormones into ducts, which then drain the hormones into another structure. • E.g., salivary and sweat glands.

4. Glands • Endocrine Glands: Secrete the hormones directly into the bloodstream. Typically rely on… • Negative Feedback Systems: Releases hormones to counteract the effects of other hormones with the goal of maintaining homeostasis.

5. Hormones • Three Chemical Classes of Hormones: • Steroid Hormones • Amines • Peptide (Protein) Hormones • Local Hormones: • Eicosanoids

6. Hormones • Steroid Hormones: • Lipid-soluble • Hydrophobic (NOT water-soluble) • Must bind to transport proteins to effect target cells. • Examples: • Aldosterone • Estrogen • Calcitriol • Testosterone

7. Hormones • Amines aka Biogenic Amines: • Require tyrosine (an amino acid) for synthesis. • Hydrophilic (water-soluble) • Examples: • Epinephrine • Dopamine • Thyroid hormones

8. Hormones • Peptide Hormones aka Protein Hormones: • Amino acid polymers • Hydrophilic (water-soluble) • Examples: • Oxytocin • ADH • hGH

9. Hormones • Eicosanoids aka Local Hormones: • Considered paracrine secretions • Have very brief effect on many cells f the body. • Eicosanoids Include… • Prostoglandins: Secreted by organs to serve various functions. • Leukotrienes: Control allergic & inflammatory reactions. • Examples: • Prostadcyclin: Inhibits blood clotting & vasoconstriction • Thromboxanes: Override the effects of prostacyclin when injured.

10. Hormone Effects • Hormone Receptors: Protein or glycoprotein molecules on target cells. • Site of binding for hydrophobic hormones on the cell nucleus. • Binding allows alterations in the gene expression of the cell, which triggers the receptor cell’s response. • Second-Messenger Systems: System for hormone binding for hydrophilic hormones. • Causes the activation of enzyme molecules to catalyze the desired reaction.

12. Hormone Effects • Up-Regulation: Hormones increase the number of receptors & therefore sensitivity. • Down-Regulation: Hormones decrease the number of receptors & therefore sensitivity. • Synergistic Effects: Hormones work together to produce a combined greater effect. • Permissive Effects: One hormone enhances the target cell’s response to another hormone. • Antagonistic Effects: Hormones oppose each other’s effects.

13. Feedback Systems • Negative Feedback Mechanisms: Maintains the body condition in question within a small “normal range” of its set point. • MOST hormones work using negative feedback! • Examples: • Blood sugar range (80-120mg/ml) • Body Temperature (36.5-38*C) • Blood pH • Your thermostat!

15. Endocrine Glands: Hypothalamus • Hypothalamus: Controls primary functions, including water balance, sleep & sex drive, & acts as a main controller for the ANS. • Produces 9 Major hormones: • 7 control the Pituitary gland • Oxytocin (OT): Stored in Posterior Pituitary Gland. • Antidiuretic Hormone (ADH): Stored in Posterior Pituitary Gland. • Infundibulum: Stalk that connects the hypothalamus & pituitary glands. • Sella Turcica: Bony saddle-shaped structure on the superior surface of the sphenoid.

17. Endocrine Glands: Pituitary • Pituitary Gland aka Hypophysis: The “master gland: of the endocrine system, controlled by the hypothalamus. Two parts: • Anterior Pituitary Gland: aka Adenohypophysis: • Posterior Pituitary Gland: aka Neurohypophysis

19. Endocrine Glands: Pituitary • Anterior Pituitary Gland: • Made up of.. • Anterior Lobe • Pars Tuberalis • Hypothalamo-Hypophyseal Portal System: Allows blood to flow from capillaries in the hypothalamus into the portal veins of the anterior pituitary. • Transports the inhibitory & releasing hormones from the hypothalamus to control the APG.

20. Endocrine Glands: Pituitary • Anterior Pituitary Hormones: 7 Major Hormones • Gonadotrophs: Hormones that target sex hormones. • Follicle-Stimulating Hormone (FSH): Stimulates follicle & egg development in females & sperm production in males, stimulates estrogen secretion. • Luteinizing Hormone (LH): Stimulates ovulation in females & testosterone secretion in males.

21. Endocrine Glands: Pituitary • Trophic Hormone Gonadotrophin: • Thyrotrophs: Stimulates the seceretion of thyroid hormones. • Thyroid-Stimulating Hormone (TSH) aka Thyrotropin. • Somatotrophs: Stimulates Human Growth Hormone (HGH) for body growth & development & metabolism regulation. • HGH also controls Insulinlike Growth Factors, important in regulating hypoglycemic & hyperglycemic reactions.

22. Endocrine Glands: Pituitary • Lactotrophs: Trigger mammary glands to produce milk via prolactin (PRL). • Can indirectly stimulate testosterone secretion in males. • Corticotrophs: Hormones that stimulate the adrenal cortex to secrete glucocorticoids. • Adrenocorticotropic Hormone (HCTH) aka Corticotropin: Stimulates adrenal cortex. • Melanocyte-Stimulating Hormone (MSH): Can darken skin when levels are too high.

23. Endocrine Glands: Pituitary • Posterior Pituitary Gland: Doesn’t synthesize hormones, but stores hypothalamus-produced hormones. • Oxytocin (OT): Important in enabling positive-feedback mechanism of labor & in the ejection of milk from mammary glands. • Antidiuretic Hormone (ADH): Decreases the production of urine from the kidneys to prevent dehydration. • Increases blood volume &U pressure due to water retention in kidneys, sweat glands, & blood vessels.

24. Endocrine Glands: Pineal • Pineal Gland: Mass of neural and secretory (pinealocytes) cells siitting on the roof of the brain’s 3rd ventricle. • Melatonin: Only hormone produced – acts as an antioxidant, regulates internal biological clock, circadian rhythms. • Production is INCREASED in darkness and DECREASED in bright light. • Seasonal Affective Disorder (SAD): Depression triggered by overproduction of melatonin during the winter’s lack of natural light.

26. Endocrine Glands: Thyroid • Thyroid Glands: Largest & most vascular endocrine gland; inferior to larynx with lobes on either side of the trachea. • Thyroid Follicles: Sacs that make up the majority of the thyroid gland and store the hormones produced. • 3 Specialized Thyroid Hormones: • Triiodothyronine • Thyroxine • Calcitonin

27. Endocrine Glands: Thyroid • 3 Specialized Thyroid Hormones: • Triiodothyronine aka T3: Increases Basal Metabolic Rate (BMR) to increase the rate of oxygen consumption; increases ATP production, accelerates growth, & stimulates protein synthesis. • Contains 3 iodine atoms; produced by follicles & diffused into blood stream. • Released during cold, pregnancy, low metabolic rates, or low thyroid hormone levels. • Release is regulated by the hypothalamus.

28. Endocrine Glands: Thyroid • 3 Specialized Thyroid Hormones: • Thyroxine aka Tetraiodothyronine aka T4: Produces the same basic effects as T3, but is less potent & released in much larger quantities. • Contains 4 iodine atoms; produced by the follicles & diffuses into the bloodstream. • Target cells may concert T3 to T4 • Calcitonin: Lowers the level of calcium in the blood by inhibiting osteoclasts. • Produced by the parafollicular cells in between the follicles of the thyroid & triggered by high Ca2+ levels in the bloodstream.

30. Thyroid Disorders • Hypothyroidism: Lowered production of thyroid hormones. Can be passed down by the mother and result in stunted growth, low body temperature, and possible mental retardation. • Myxedema: Low metabolism, increased weight gain, & high blood pressure due to low levels of thyroid hormones.

32. Thyroid Disorders • Goiter: Pathological enlargement of the thyroid gland, typically caused by iodine deficiency. • Graves Disease: An autoimmune disease where antibodies cause the thyroid to grow abnormally. • Can lead to lead to elevated heart rates and metabolism. • Triggered by a goiter becoming toxic.

34. Endocrine Glands: Parathyroid • Parathyroid Glands: Regulates calcium, magnesium, & phosphate ion levels in the blood via parathyroid hormone (PTH). • Found behind the thyroid, attached to the thyroid. • PTH & Calcitonin work together to regulate homeostasis of calcium in the bloodstream. • Stimulates Calcitriol to aid in calcium absorption from food.

36. Parathyroid Disorders • Hyperparathyroidism: Too much parathyroid hormone is produced, causing elevated levels of calcium in the bloodstream. • Leads to softening of the bones & a risk for kidney stone formation. • Hypoparathyroidism: Too little parathyroid hormone is produced, causing the spontaneous creation of action potentials. • Leads to muscle twitches, spasms, & tetany.

37. Endocrine Glands: Thymus • Thymus Gland: Assists the immune system. • Produces hormones responsible for developing & regulating T-cells crucial to the autoimmune responses. • Thymosin • Thymic Humoral Factor (THF) • Thymic Factor (TF) • Thymopoietin

39. Endocrine Glands: Adrenals • Adrenal Glands: Located on top of the kidneys. • Adrenal Cortex: Outer layer • Zona Glomerulosa: Secrete mineralcorticoids to maintain homeostasis. • The enzyme renin to stimulate aldosterone (regulates sodium & potassium levels & controls blood pressure by increasing blood volume.) • Zona Fasciculata: Secretes glucorticoids to increase energy supplies, regulate metabolism, break down protein & tryglycerides, & help resist stress. • Cortisol (90% of glucorticosteroid activity) is released in response to stress. Release controlled by the hypothalamus; increases metabolism, lowers inglammation, depresses immune response.

40. Endocrine Glands: Adrenals • Zona Reticularis: Responsible for the synthesis & secretion of androgens (masculinizing hormones). • Dehydroepiandrosterone (DHEA) is important for female sex drive & can be converted to estrogen. • Adrenal Medulla: Inner Layer composed of autonomic nervous system ganglia. • Chromaffin cells: Ganglia that release stress hormones instead of neurochemicals that increase heart rate, blood pressure, blood flow, oxygen intake, & glucose production. • Epinephrine aka Adrenaline • Norepinephrine aka Noradrenaline

42. The Pancreas • Pancreas: Functions as both an endocrine & exocrine gland. • Pancreatic Islets aka Islets of Langerhans: Function as endocrine glands; series of 4 different cells. • Alpha Cells (A Cells): Secrete glucagon to raise the blood sugar level by triggering glycoeogenesis in the liver. • Beta Cells (B Cells): Secrete insulin to lower the blood sugar level by increasing the synthesis of glycogen, protein, & fat.

43. The Pancreas • Delta Cells (D Cells): Secrete somatostatin to inhibit growth hormone & regulate the secretion of insulun & glucagon. • F Cells: Secrete Pancreatic Polypeptide to inhibit somatostatin secretion & the secretion of enzymes from the gallbladder & pancreas.

45. Gonads • Gonads: The ovaries (females) and testes (males). • Ovaries: Produces estrogen, progesterone, inhibin, & relaxin. • Mammary gland production, the menstrual cycle, and pregnancy are maintained by progesterone, estrogen, FSH, & LH. • Inhibin inhibits the secretion of FSH. • Relaxin is important for delivery. • Testes: Produce testosterone, which regulates the production of sperm & helps develop masculine features (facial hair, deep voice, etc.)

46. Other Hormones • Atrial Natriuretic Factor (ANF): Produced by the heart when blood pressure is too high, causing the kidneys to increase urine output & lower the blood pressure. • Calcitriol: Produced by the kidneys and used to regulate calcium levels and works with FPO to stimulate red blood cell production. • Humon Chorionic Gonadotropin (HCG): Produced by the placenta to support pregnancy. • Stomach & small intestine secrete hormones that help regulate digestion.

47. General Adaptation Syndrome • General Adaptation Syndrome: The three stages the body goes through in “fight or flight” mode or during times of stress. • Alarm (Fight or Flight) Reaction: Norepinephrine and epinephrine are released to arouse the body. • Blood glucose, aldosterone, and angiotension levels increase. • Resistance Reaction: If stress continues, cortisol is increased to break down fats & proteins to glucose for instant energy. • Exhaustion: If the stress still continues, cortisol levels become too high and cause headache, ulcers, & immune compromise.