Chapter 47: Endocrine System and Cellular Signaling

1. Chapter 47: Endocrine System and Cellular Signaling AP BIOLOGY

2. I) Hormones • Hormones are chemical messengers that affect cellular metabolism • Metabolism includes: • Protein synthesis • Enzyme activation • Changes in membrane permeability • Mitotic division • Release of enzymes, hormones, or other secretions • Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body. • Hormones that target other glands are known as tropins (topic hormones)

3. II) Hormones and Signal transduction • Signal transduction pathways link signal reception with cellular response • Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein. • Different receptors recognize different chemical messengers, which can be peptides, small chemicals or proteins, in a specific one-to-one relationship. • In multicellular organisms, signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole. • Hormones are involved in signal transduction pathways

4. C) A receptor protein recognizes signal molecules, causing the receptor protein’s shape to change, which initiates transduction of the signal. • Protein hormones interact with receptors to initiate second messengers • Second messengers permit signals to reach targets inside cells • Signal transduction is the process by which a signal is converted to a cellular response. • Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals, with the result of appropriate responses • Second messengers are often essential to the function of the cascade. • Many signal transduction pathways include: • i. Protein modifications • ii. Phosphorylation cascades in which a series of protein kinases add • a phosphate group to the next protein in the cascade sequence

5. III) Types of Hormones Protein Steroid (lipid) Enter cells directly Bind to a nuclear hormone receptor (NHR) NHR carries protein into nucleus and binds to DNA Regulates gene expression Control RNA synthesis Function as repressors or activators • Can not enter cell • Not lipid soluble • Proteins are large and charged • Hydrophilic, ionic • Bind to receptors • Trigger second messenger activity • Second messengers: • Cyclic AMP (cAMP) • Inositol TriPhosphate (IP3)

6. Steroid (Lipid) hormone activity

7. III) Protein Hormones and Second messengers • Second messengers are molecules that relay signals from receptors on the cell surface to target molecules inside the cell, in the cytoplasm, or nucleus. • Since protein hormones cannot enter the cell they must utilize these complex second messenger molecules. • Cyclic AMP (cAMP) • When a protein hormone binds to a receptor it activates a G-protein, such as Ras. • G-proteins are Guanosine Nucleotide Proteins (GTPase) that interact with GTP, forming GDP and phosphate • The G-protein will then bind to and activate the membrane-bound enzyme adenylyl cyclase • Adenylyl cyclasereactswith ATP to form cyclicAMP. • The cyclic AMP then goes on the activate specific proteins. • Some ion channels, for example, are gated by cyclic AMP. • An important protein activated by cyclic AMP is protein kinase A, which goes on the phosphorylate certain cellular proteins. • Hormones that use cAMP: Adrenalin, glucagon ANIMATION

8. Protein hormones and second messengersCyclic AMP

9. Protein hormones and second messengersInositol Triphosphate (ip3)

11. III) Protein Hormones and Second messengers • Inositol Tri-phosphate • When a protein hormone binds to a receptor it activates a G-protein, such as Ras. • G-proteins are Guanosine Nucleotide Proteins (GTPase) that interact with GTP, forming GDP and phosphate • The G-protein will then bind to and activate the membrane-bound enzyme phospholipase-C • Phospholipase-C produces inositol tri-phosphate (IP3) • Inositol Tri-Phosphate diffuses through the cytoplasm to the endoplasmic reticulum • The ER releases calcium ions in response to the IP3 binding. • The calcium ions activate calcium-sensitive proteins in the cytoplasm Animation

13. IV) Human glands and hormones • Pituitary Gland • Located at the bottom of the brain under the hypothalamus • Contains two lobes • Anterior (front) Lobe • Secretes the following hormones • TSH (Thyroid Stimulating Hormone): stimulates thyroid gland • ACTH (AdrenoCorticotropic Hormone): stimulates the cortex of adrenal glands • HGH (Human Growth Hormone): stimulates bone/muscle growth • LH (Luteinizing Hormone): stimulates ovulation/sperm maturation • FSH (Follicle Stimulating Hormone): stimulates egg/sperm development • Prolactin: stimulates milk ejection • Posterior Lobe • Secretes the following hormones: • Oxytocin : labor contractions • ADH (Anti-diuretic hormone): stimulates kidney tubules to retain water in the body

15. B) Hypothalamus • 1. Located just above the pituitary gland • 2. Secretes releasing factors to regulate pituitary • 3. Integrates nervous and endocrine systems • C) Thyroid • 1. Located in neck • 2. Secretes three hormones: • a) Thyroxine (T4): increases metabolism and cellular respiration, cell growth, differentiation • b) Triiodothyronine (T3): increases metabolism,cellular respiration, cell growth, differentiation • c) Calcitonin: lowers blood calcium levels (absorbs calcium into bones) • 3. Thyroxine and triiodothyronine contain iodine • Iodine is essential for proper thyroid functioning. • D) Parathyroid • 1. Located next to thyroid gland • 2. Secretes Parathormone: Raises blood calcium levels; releases calcium from bone and absorbs • from kidneys and intestines

16. E) Pancreas • 1. Located under stomach • 2. Endocrine and exocrine gland • a ) exocrine: secretes into ducts • 3. Contains two sets of cells that secrete hormones • A) Islets of Langerhans • 1. alpha cells: secrete glucagon to hydrolyze glycogen into glucose • 2. beta cells : secrete insulin to lower blood glucose levels

17. F) Adrenal Gland • 1. Located on top of each kidney • 2. Two parts to each gland • a) Adrenal Cortex – outer part of the gland • 1) Secretes: • a. Cortisol: reduce inflammation; increase glucose metabolism • b. Aldosterone: increase sodium absorption from kidney tubules • c. Androgens: testosterone • b) Adrenal Medulla – inner part of the gland • 1) Secretes hormones involved in the fight-or-flight response • a. Epinephrine • b. Norepinephrine • 2) Functions: increase heart rate, blood pressure, muscle contraction

18. G) Gonads • 1. Testes: secrete testosterone • 2. Ovaries: secrete estrogen and progesterone • Estrogen: Female secondary sex characteristics • Regulates menstrual cycle • > Occurs at high concentrations near the end of the follicular phase, estrogen • becomes a positive inducer of the anterior pituitary • > Positive feedback triggers the anterior pituitary to release more FSH and LH • more FSH and LH cause the ovary to produce more estrogen • > The ensuing LH surge is responsible for ovulation • Progesterone: • > Stimulates secretory and vascular activity of the endometrium, (thickens uterine lining) • preparing for implantation of an embryo • > Secreted by the corpus luteum (empty follicle) after ovulation

19. IV) Other regulatory mechanisms • Circadian Rhythms “biological clocks” • Biological processes that oscillate within a 24 hour period • One dark and one light period • Regulated by the Pineal Gland (secretes melatonin) which controls sleep patterns B) Other Hormone-related Compounds • Prostaglandins • Compounds that exert an effect on a small group of cells in one area • No widespread effects • Blood clotting; dilation of cervix • Pheromones • Compounds used to attract mates; for recognition of resources • Ex: trailing of terminates

20. Feedback inhibition

21. Insulin and Glucagon Negative feedback

22. REGULATION OF BLOOD CALCIUM LEVELS BY PTH

23. Menstrual Cycle – Hormones & Feed Back A) 28 day cycle of Pituitary and Ovarian hormones 1. Hypothalamus – secretes GnRH (Gonadotropin Releasing Hormone) 2. Pituitary secretes FSH and LH - follicle begins to form in ovary 3. Ovary secretes estrogen in response to FSH - estrogen stimulates more FSH- - - - - more FSH stimulates more estrogen 4. Follicle grows, and LH causes follicle to rupture, releasing egg (ovulation) 5. LH causes cells in the ruptured follicle to produce progesterone (cells turn yellow in response to progesterone – this is the corpus luteum) - progesterone thickens endometrium - progesterone inhibits LH - as LH levels drop, progesterone production decreases - as progesterone decreases, endometrium begins to degrade 6. Progesterone secretion stops 7. Hypothalamus – secretes GnRHand LH and FSH begin to increase 8. Ovary secretes estrogen in response to FSH

24. Pituitary Hormones

25. VII) Changes in signal transduction pathways can alter cellular response. • Conditions where signal transduction is blocked or defective can be deleterious, preventative or prophylactic (using medicines to prevent disease). • 1. Diabetes • Islets cells malfunction • Type I: Insulin production stops • Treatment: insulin injections to lower blood glucose levels • Type II: insulin produced is not effective - cell receptors do not bind insulin • Treatment: medications that make cells more responsive • 2. Hypothyroidism • Abnormally low thyroxine levels • Symptoms: extreme fatigue, weight gain, cold intolerance, muscle cramps, feeling of not enough sleep