Endocrine System Quiz

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• November 21, 3:00 PM - 6:00 PM
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Today's Learning Objectives

• Describe chemical classification of hormones
• Compare and contrast mechanisms of action of hydrophilic vs. hydrophobic hormones
• Compare and contrast different types of second messenger systems
• Describe hormonal actions and interactions from: pituitary gland, thyroid gland, adrenal gland, islets of Langerhans
• Describe action of miscellaneous endocrine glands and hormones

Hormones: What are some hormones that you can think of?

• The text provides a cartoon image and caption discussing hormones

Comparison of Nervous & Endocrine

• Nervous System:
  • Quick response (milliseconds)
  • Short duration effect
  • Works via electrical impulses and direct release of chemicals (neurotransmitters)
  • Affects specific cells (neurons, muscle, gland) resulting in specific responses (e.g., muscle contraction)
• Endocrine System:
  • Slower response (minutes to hours)
  • Potentially long duration effect (hours to days)
  • Works via chemical signals (hormones) released into blood capillaries
  • Affects multiple cells throughout the body with specific hormone receptors ("target cells")
  • Results in changes in metabolic activities of cells (e.g., protein synthesis, ATP production)

Endocrine Glands

• Ductless glands that secrete hormones
• Chemicals secreted into blood to communicate (slow)
• Each hormone binds to a specific receptor on a target cell
• Affects the metabolism of target cells

Check in with a neighbor

• Table comparing peptide, steroid, and amino acid-derived hormones (synthesis, storage, release from parent cell, transport in blood, half-life, receptor location, response to receptor-ligand binding, general target response, examples)

Chemical Classification of Hormones

• Amine: Derived from tyrosine or tryptophan
  • Examples: norepinephrine, epinephrine, thyroxine, triiodothyronine
  • Hydrophobic
• Polypeptide/protein: Chains of amino acids
  • Examples: ADH, growth hormone, insulin, glucagon
• Glycoproteins: Carbohydrate attached to protein
  • Examples: LH, FSH, TSH
• Steroids: Lipids derived from cholesterol
  • Examples: testosterone, estrogen, progesterone, cortisol
  • Hydrophobic

Hormone Function

• Hormones affect only certain tissues/organs (target cells/organs)
• Target cells must have specific protein receptors
• Hormone binding alters cellular activity

Steroid Hormone: Mechanism of Action

• Steroid hormone passes through plasma membrane (non-polar)
• Binds to receptor in the cytoplasm forming a complex
• Complex moves into the nucleus

Steroid Hormone Receptor

• 2 Complexes (dimerize)
• Bind to hormone response element on DNA
• Synthesis of RNA (called genomic action) takes at least 30 minutes

Review Question (Which of these hormones have nuclear receptors?)

• Possible answers: adrenal cortex, gonads, both A & B

Hormones That Use 2nd Messengers

• Water-soluble hormones cannot pass through plasma membrane, so use cell surface receptors
• Actions are mediated by 2nd messengers
• Hormone is the 1st messenger
• 2nd messenger carries signal from receptor to inside of cell

Three Types of 2nd Messenger Systems

• Adenylate cyclase – cAMP system
• Phospholipase C – Ca++ system
• Tyrosine Kinase system

Adenylate Cyclase-cAMP

• Hormone binds to receptor, G-proteins dissociate
• Activates adenylate cyclase (ATP)
• Converts ATP to cAMP (2nd messenger)
• cAMP activates protein kinase
• Protein kinase phosphorylates enzymes
• Examples: epinephrine, norepinephrine, glucagon, FSH

Phospholipase C- Ca++ system

• Hormone binds to receptor
• G proteins signal phospholipase C (PLC)
• PLC forms inositol triphosphate (IP3)
• IP3 causes Ca++ channel to open in ER
• Ca++ is a 2nd messenger
• Ca++ binds to calmodulin
• Activates enzymes to bring about desired responses
• Examples: epinephrine and α-receptors

Tyrosine Kinase System: for insulin

• Receptor itself is an enzyme (tyrosine kinase)
• Insulin binds to 2 units of receptor
• Receptors dimerize (come together)
• Tyrosine kinase phosphorylates itself > activated
• Glucose uptake

Glucose Uptake by Insulin

Review Question (Which of these hormones uses cAMP as a second messenger?)

• Possible answer: Epinephrine

Review Question (Which of these correctly describes the role of inositol triphosphate (IP3)?

• Possible answer: It stimulates the release of Ca++ from the endoplasmic reticulum

Hormonal Actions and Interactions

Hormone Levels and Tissue Responses

• Effects of hormones depend on concentration
• Abnormally high concentration can have bad side effects (e.g., male athletes, anabolic steroids)
• Desensitization/downregulation of receptors decreases hormone effect on target

The Pituitary Gland

Posterior Pituitary Gland

• Stores and releases 2 hormones made in the hypothalamus
  • ADH: increases H2O absorption in kidneys
  • Oxytocin: Uterus contraction during labor, milk let-down in lactating women

Clinical Example: Oxytocin

• Synthetic injections (pitocin) are given to pregnant women to induce labor during prolonged pregnancy or fetal membrane rupture leading to infection
• Preeclampsia
• Used post-delivery to reduce uterus size, preventing hemorrhage

Anterior Pituitary

• Growth hormone (GH): Promotes growth of cartilage and bone, protein synthesis, amino acid movement into cells
• Thyroid-stimulating hormone (TSH): Stimulates thyroid to produce and secrete T4 and T3
• Adrenocorticotropic hormone (ACTH): Stimulates adrenal cortex to secrete cortisol and aldosterone

GH Disorders

• Pituitary dwarfism (hyposecretion of GH during childhood)
• Gigantism (hypersecretion of GH during childhood)
  • Height over ~8'
  • Puberty often delayed
• Acromegaly (hypersecretion of GH during adulthood)

Anterior Pituitary (cont.)

• Follicle-stimulating hormone (FSH): Stimulates growth of ovarian follicle, and sperm production
• Luteinizing hormone (LH): Causes ovulation, and secretion of testosterone in testes
• Prolactin (PRL): Stimulates milk production by mammary glands

Hypothalamic control of anterior pituitary via Hypothalamic-Pituitary Portal System

• Hypothalamus controls anterior pituitary secretion
• Receives input from higher brain centers (emotional states, psychological stress, circadian rhythms, menstrual cycle, adrenal hormones)

Review Question (Compare and contrast the control that the hypothalamus has over anterior and posterior pituitary glands)

Thyroid Hormones

• Made in thyroid follicles using iodine and tyrosine amino acids
• T4 (thyroxine) and T3 (triiodothyronine)
• Set BMR, protein synthesis
• Needed for growth and development

Clinical Examples involving TH

• Hypothyroidism (low T4 & T3 levels): low BMR, weight gain, lethargy, cold intolerance
• Endemic Goiter (iodine deficiency): High TSH (low T3 & T4), thyroid growth
• Cretinism (fetal development hypothyroidism): severe mental retardation

Endemic Goiter (iodine deficiency)

Hyperthyroidism

• High thyroxine (T4) secretion
• High BMR, weight loss, nervousness, irritability, intolerance to heat
• Graves disease: autoimmune disease
• Antibodies have TSH-like effects
• Not inhibited by negative feedback
• Excess thyroid stimulation > excess T4
• Exopthalmos (bulging eyes)

Review Question (The secretion of which of these hormones would be increased in a person with endemic goiter?)

• Possible answer: TSH

Review Question (The hormone primarily responsible for setting the BMR & for promoting the maturation of the brain is...)

• Possible answer: Thyroxine (T4)

Parathyroid Glands

• Secrete parathyroid hormone (PTH)
• Most important hormone for controlling blood Ca2+ levels

Adrenal Medulla: Amine hormones

• Epinephrine and norepinephrine
• Controlled by sympathetic nervous system
• Activated during "fight or flight" response

Adrenal Cortex: Steroid hormones

• Mineralocorticoids (aldosterone): Salt and H2O absorption in kidneys
• Glucocorticoids (cortisol): Inhibits glucose uptake, inhibits inflammation, suppresses immune system, weak androgens (supplements sex steroids of gonads)

Melatonin

• Secretion regulated by suprachiasmatic nucleus (SCN) of hypothalamus (circadian rhythms)
• Reset by daily environmental light/dark changes
• Synchronizes physiology with sleep/wake cycle and seasons
• Secreted at night and inhibited by light
• Antigonadotropic effects in many animals (in humans, delays puberty)

Gonads & Placenta

• Ovaries: estrogen and progesterone
• Testes: testosterone
• Placenta: estrogen, progesterone, hCG
• Discussed in reproductive system

Test your knowledge on the human endocrine system with this quiz. Explore various hormones, their functions, and the mechanisms of action within the body. Dive into topics like basal metabolic rate, hormone secretion, and the effects on puberty.