The Endocrine System:

1. The Endocrine System: the human body system that is responsible for our raging teenage hormones and homeostasis Jasmine Han, Inam Sakinah, & Kirstin Nygaard

2. The Endocrine System: Overview The overall goal of this body system is to maintain homeostasis. • Hormones are chemicals released by one or more cells that affects cells in other parts of the organism.They assist by carrying messages through the bloodstream to target cells throughout the bloodstream. • These hormones have different jobs, such as: growth & development, reproduction; they also regulate things like metabolism, biological clock, extracellular fluids , and glandular secretion.  • Although this system is slower than the nervous system's communication systems, hormones have a powerful influence on the body.

3. Where is the Endocrine System?  The Pituitary Gland is considered the MASTER GLAND since it controls the other glands.

4. GLANDS & Hormones 

5. Pineal Gland • Stimulated by nerves in the eyes • Produces melatonin at night • Melatonin – involved in circadian rhythm. Levels rise at night (makes you sleepy) and drop in the morning (wakes you up) • Affects reproductive functions in the gonads • Affects thyroid and adrenal cortex functions

6. Hypothalamic-pituitary axis • Forms two distinct systems – the hypothalamus and the pituitary gland • The axis is the functional interaction between these two systems

7. Hypothalamus • Maintains the body’s internal environment by regulating the autonomic nervous system, endocrine system, body temperature, water balance, and appetite • The neurons in the hypothalamus influence the two sections of the pituitary gland • Neurosecretory cells produce and release hormones into the bloodstream

8. Hypothalamus hormones • Growth-hormone-releasing hormone • Stimulates the synthesis and release of growth hormone (GH) • Corticotropin-releasing hormone (CRH) • Secreted in response to stress • Thyroid-releasing hormone • Stimulates the release of thyrotropin (TSH) • Gonadotropin-releasing hormone (GnRH) • Stimulates the release of  Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) • Antidiuretic hormone (ADH) • Oxytocin

9. Pituitary Gland • Located below the hypothalamus • Secretes growth hormones • 1930 experiment • Biologists removed the pituitary gland from rats • The rats stopped growing, couldn’t maintain a normal body temperature, and their genitals, thyroid glands, and adrenal cortexes shrunk • Suggests that the pituitary gland secretes hormones that regulates the production of other hormones • Two types – posterior and anterior

10. Posterior pituitary • Extension of the brain • Stores antidiuretic hormones (ADH) and oxytocin which are produced from the neurosecretory cells in the hypothalamus

11. Antidiuretic Hormone • Released when someone is dehydrated (prevents you from peeing) • Helps the kidneys reabsorb water • Triggers the insertion of aquaporins into the apical membrane -> cells become more permeable to water -> large amounts of water are reabsorbed • Increases permeability to urea -> increases osmolarity of surrounding fluid -> water loss from the filtrate • Defective forms of ADH produces an abundance of urine. May suffer from diabetes insipidus • Negative feedback –Maintains stable conditions and homeostasis • The effect of the hormone causes the hormone to not be released

12. Oxytocin • Causes uterine contractions during childbirth and milk release when a baby is being nursed • More contractions -> more nerve impulses to the hypothalamus -> release of oxytocin • Positive feedback – the stimulus brings about an effect • Stimulates affiliative behaviors in both sexes

14. Anterior pituitary • Develops from cells in an embryo’s mouth and throat lining (not directly connected to the hypothalamus) • Neurosecretory cells secrete stimulatory or inhibitory signals into blood vessels. The signals are carried to the anterior pituitary -> the anterior pituitary alters the secretion of hormones that enter the bloodstream and act on target tissues or glands • Hormones produced stimulate the production of other hormones

15. Anterior Pituitary Hormones Affecting Other Glands • Adrenocorticotropic hormone (ACTH) • When injected into humans, cortisol levels in their blood rises • Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) • Involved in producing sex hormones and regulating the menstrual cycle • Thyroid-stimulating hormone (TSH) • Triggers the production of thyroid hormones • Gonadotropic hormones • Stimulates the testes and ovaries to produce gametes and sex hormones

16. Anterior Pituitary HormonesNot Affecting Other Glands • Growth hormone (GH) • Promotes lengthening of the long bones in children and muscle growth, tissue repair, and lactation in adults • Prolactin • Stimulates mammary gland growth and milk production • Melanocyte-stimulating hormone (MSH) • Skin-color changes in fish, amphibians, and reptiles

18. Parathyroid Glands • Embedded in the thyroid gland • Can be as small as a grain of rice or as big as a pea • Control how much calcium there is in our bones and blood • Releases the parathyroid hormone (PTH) to increase the calcium levels in the blood

19. Thyroid Gland • Located in the neck • Releases thyroid hormone and calcitonin • Thyroid hormone – increases metabolic rate • Calcitonin – lowers blood calcium • Two distinct lobes • Follicles filled with triiodothyronine (T3) and thyroxine (T4)

20. T3 and T4 • Increases cellular metabolism • In mammals, T3 has a stronger effect than T4 • In mammals, T4 is converted to T3 in the liver • T4 increases metabolic rate and heart rate. It also promotes growth • In amphibians, T3 is responsible for most of the changes that occur in metamorphosis

22. Adrenal Glands • Two small glands that sit on top of the kidneys. The cortex (outer portion) secretes steroid hormones. The medulla (inner portion) secretes epinephrine and norepinephrine.

23. Catecholamines • Small compounds derived from tyrosine (an amino acid) that are used as hormones or neurotransmitters • Includes epinephrine, norepinephrine, and dopamine

24. Epinephrine (Adrenaline) • Released when the adrenal medulla is stimulated by action potentials from your sympathetic nerves • Released during the fight-or-flight response (short term response to stress) • When humans are injected with epinephrine, there is an increase in the concentration of free fatty acids and glucose in the blood, pulse rate, blood pressure, and oxygen consumption by the brain and they feel anxiety and excitement • Redirects blood away from the skin and digestive system and toward the heart, muscles, and brain • Relaxes smooth muscles -> opens blood vessels -> increases blood delivery to target tissues

25. Norepinephrine • Stress hormone • Produced in the adrenal medulla • Released directly onto target cells • Affects the brain (parts where attention and responding actions are controlled) • Fight-or-flight • Increases heart rate -> triggers the release of glucose -> more blood to skeletal muscles

27. Pancreas • Thin organ that is located in the abdomen • Two types of tissue – exocrine and endocrine • Exocrine tissue produces digestive juices which are sent to the small intestines • Endocrine tissue (pancreatic islets) produces and secrete insulin and glucagon directly into the blood • Pancreatic islets – groups of pancreatic cells (3 types) • Alpha cells secrete glucagon • Beta cells secrete insulin • Delta cells secrete somatostatin • Insulin – secreted when there is too much glucose in the blood. Insulin tells the liver to take the extra glucose out of circulation. Regulates blood sugar • Glucagon – secreted in response to low blood sugar. Forces cells to produce or release glucose. Regulates blood sugar • Somatostatin – inhibits the release of glucagon and insulin. Helps with carb metabolism

28. Glands • Endocrine • Secrete products into the bloodstream (instead of ducts) -> delivered to the rest of the body • Only target cells can respond to certain hormones • Exocrine • Secretes substances through a duct into a space

31. Gonads • Primary function is to produce gametes (a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote) • Gender specific • Females have ovaries • Males have testes

32. Ovaries • Located on both sides of the uterus below the openings of the fallopian tubes • Secrete sex hormones • Produce estrogen and progesterone • Estrogen – helps maintain sexual organs and secondary sex characteristics. Necessary for egg maturation • Progesterone – secreted after ovulation. Causes the uterine lining to thicken

33. Testes • Secrete sex hormones • Located outside of the body in the scrotum • Produce androgens (e.g. testosterone) • Testosterone – stimulates sperm production and reproductive behaviors • Causes the development of male characteristics such as facial hair, deepening of the voice, and the growth spurt that takes place during puberty

34. Communication in Endocrine System

35. Secreted Signaling Molecules • Stimulate responses by binding to receptors on target cells • Endocrine Cells secrete hormones into extracellular fluids • Reach target cells through bloodstream (hemolymph) • Can exist within organs from organ systems or in endocrine glands (ductless organs) • Travel to all parts of the body • Local Regulators act over short distances and reach target cells by diffusion • Paracrine signaling – target cells are close to secreting cell • Autocrine signaling – regulators act on secreting cell

36. Secreted Signaling Molecules • Neurohormones are secreted by neurosecretory cells through diffusion from nerve cells into bloodstream • Called neuroendocrine signaling • Example: ADH involved in water balance and kidney function • Pheromones NOT classified as hormones • Communication that occurs in external environment between other animals

37. Secreted Signaling Molecules • Hormones classified into 4 categories or chemical groups • Peptide and Proteins (Polypeptide) • Derived from long protein chains • Steroids • Derived from cholesterol • Amines • Derived from single amino acid • Eicosanoids • Derived from fatty acids • Divided based on structure and synthesis process • Thus, vary in solubility and therefore, cellular response pathways

38. Refers to how binding of hormones to certain receptors causes changes in cytoplasmic molecules , amplifies signaling, and can sometimes alter gene transcription Cellular Response Pathways

39. Water-Soluble Hormones • Water-Soluble Hormones secreted by exocytosis • Bind to receptors on cell surface • Travel solo in blood stream • Pathway • Binding stimulates cellular response through signal transduction • Converts extracellular chemical signal to an intracellular response • Occurs through a series of molecular interactions

40. Example Triggers cascade of molecular interactions resulting in synthesis of cyclic AMP (second messenger) Stress triggers Adrenal gland to secrete epinephrine Epinephrine arrives at liver cell and binds to G protein-coupled receptor cAMP activates protein kinase A kinase A activates an enzyme that stimulates glycogen breakdown and an enzyme that inhibits glycogen synthesis

41. Lipid-Soluble Hormones • Lipid-soluble hormones are secreted through diffusion • Bind to receptors within cell (intracellular) • Travel in blood stream connected to transport protein • Pathway • Receptor transduces signal within cell • No intermediate molecular interactions like signal transduction

42. Steroid hormone receptors exist in cytosol before binding • Hormone-receptor complex forms • Receptor interacts with DNA directly or via DNA binding protein • Allows for gene expression by activating specific genes • Non-Steroid hormone receptors present in nucleus • Receptor binds to specific locations on DNA to stimulate gene transcription

43. Hormone Effects • Type of receptor and cell location = integral to chemical responses produced by a single hormone • Different effects allow body to have more effective and intense reactions during emergencies. • Specialized based on species • Ex: frog

44. Local Regulators • Act on target cells (neighboring cells or secreting cells) quicker than hormones despite following similar pathways • Prostaglandins • Produced by many cell types • Have different effects • Control of blood pressure • Dilation and constriction of blood vessels • Contraction and relaxation of smooth muscles • Other Examples: cytokines, growth factors, and nitric oxide

45. Types of Feedback Positive Feedback Negative Feedback Negative feedback occurs when the rate of the process decreases as the concentration of the product increases. It controls the rate of a process to avoid accumulation of a product.  Example: Insulin • Positive feedback occurs when the rate of a process increases as the concentration of the product increases. It is not a way to maintain stable conditions and homeostasis.  Example: Oxytocin

46. Negative Feedback • Process of response limiting the initial stimulus • Results in turning off hormone pathway • Final and essential step in simple hormone pathways • Prevents excessive pathway activity • MAINTAINS HOMEOSTASIS

47. Negative Feedback Example • Oxytocin regulation of milk during nursing • Nuerohormone pathway: • 1) Baby suckling stimulates sensory neurons in nipples to send signals to hypothalamus • 2) Triggers neurosecretory cell (posterior pituitary gland) to secrete neurohormone (oxytocin) • 3) Oxytocin diffuses and travels to smooth muscles in breasts prompting milk release • 4) Leads to more suckling increasing release • Response increasing stimulus = positive feedback • Baby stops suckling and pathway shuts off = negative feedback • Example of animal responding to environmental changes

48. Biorhythms and Melatonin • Melatonin secretion by pineal gland allows for regulation of functions connected to seasons or light • Main target for melatonin = suprchiasmatic nucleus (biological clock) • Decreases SCN activity • Amount of secretion depends on length of night • Demonstrates influence of external environment on hormone behavior

49. ADH • ADH pathway responds to changes in internal environment • Osmoreceptors help regulate water balance in body

50. Insulin and Glucagon • Example of a twin hormone pathway • Pathways counterbalance each other • Optimal blood glucose concentration = 90 mg/100 mL • When glucose concentration rises above this set point, insulin is released • Stimulates all body cells outside brain to uptake of glucose • Slows glycogen breakdown in liver • Prevents conversion of amino acids and glycerol to glucose • Decreases glucose concentration