Endocrine System

Nestor T. Hilvano, M.D., M.P.H.(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain,

Textbook, 2012.)

Learning Objectives

1. Describe the 3 types of hormones by chemical structure.

2. Describe the endocrine system as to types and functions of endocrine organs including its regulatory control. - pituitary gland, pineal gland, thyroid and parathyroid glands, pancreas, adrenal glands, and gonads.

4. Define hypothyroidism, hyperthyroidism, goiter, diabetes mellitus, and hypoglycemia.

5. Describe the benefits and risks of using glucocorticoids.

Endocrine System• Ductless glands• Hormones – chemical signals secreted and pass directly

into the blood circulation to reach the target organs

3 Types of Hormones 1. Proteins and peptides – most numerous group; H2O

soluble; ex. TSH, LH, FSH, ADH, prolactin

2. Amine – derivatives of tyrosine; some H2O soluble, some lipid soluble; ex. TH, Epi, Nor-Epi, dopamine

3. Steroids – not H2O soluble ex. sex hormones

Mechanisms of Action on target cells:

1. Lipid soluble hormones – bind to cytoplasm or nuclear receptors (inside the cell)

2. Water soluble hormones – bind to receptor on plasma (cell) membrane; w/ second messenger

Hypothalamus • Master control center• Signals pituitary gland, which in turn secretes

hormones that influence many body functions• Secretes releasing and inhibitory hormones

Brain

Posterior pituitary

Anterior pituitary

Bone

Hypothalamus

Hypothalamus: The Master Gland

Figure 18–9 Pituitary Hormones and Their Targets.

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Pituitary Gland • Posterior pituitary –

stores and secretes hormones made in the hypothalamus

- ADH, and oxytocin• Effect of ADH- increase

reabsorption of water in kidney tubules (DCT/ CT)

• Effect of oxytocin- uterine contraction; milk ejection

Hypothalamus

Neurosecretorycell

Hormone

Posteriorpituitary

Bloodvessel

Oxytocin ADH

Uterine musclesMammary glands

Kidney tubules

Anteriorpituitary

Pituitary Gland1. Tropic hormones (control

other glands)•TSH (thyroid stimulating hormone)•ACTH (adrenocorticotropic hormone)•LH and FSH (luteinizing hormone and follicular stimulating hormone)

2. GH (growth hormone)

3. Prolactin (lactogenic hormone)

4. Endorphins (pain receptors in

brain)

5. MSH (melanocytes stimulating

hormone)

Neurosecretorycell

Bloodvessel

Releasing hormonesfrom hypothalamus

Pituitary hormones

TSH ACTH FSHandLH

Growthhormone

(GH)

Prolactin(PRL)

Endorphins

Thyroid Adrenalcortex

Testes orovaries

Entirebody

Mammaryglands

(in mammals)

Painreceptors

in the brain

Endocrine cells ofthe anterior pituitary

Figure 26.4E

Hypothalamus

Anteriorpituitary

Thyroid

Thyroxine

Inhibition

Inhibition

TRH

TSH

Pineal Gland

• Brain outgrowth • Secretes melatonin,

with rhythmical activity and biologic clock functions

• SAD syndrome

Thyroid Gland • Located beneath the larynx• Secretions: Thyroid Hormones

(T3, T4); increase BMR • Cretinism – congenital

deficiency of thyroxine in children resulting to physical and mental retardation

• ___ – increase TH• ___ – decrease TH• ___ – enlarged gland; caused

by iodine deficiencya. Hypothyroidism

b. Goiter

c. Hyperthyroidism

Calcium Homeostasis• Calcium level in the blood and

interstitial fluids are essential• Maintained by calcitonin (to decrease

calcium) from thyroid gland and PTH (parathyroid hormone, to increase calcium) from the parathyroid glands

• PTH- increase blood calcium level by: increase bone destruction, increase calcium reabsorption in kidneys, and increase calcium absorption in GIT

Pancreatic Hormones• Regulate blood glucose levels• Islets of Langerhans – endocrine part

- Insulin is a protein hormone produced by beta cells; lower BS

- Glucagon is a peptide hormone produced by alpha cells; increase BS

• Diabetes Mellitus:

Type I = destruction of beta cells; no insulin produced

Type II = low or not responsive to

insulin (insulin resistance) *DM= hyperglycemia, glycosuria (polydipsia, polyuria,

polyphagia)

• Hypoglycemia – secrete too much insulin, lower the blood sugar

Adrenal Gland • Adrenal cortex – produces hormones that provide

slower, longer term responses to stress; secretes steroid hormones – mineralocorticoids (aldosterone), glucocorticoids, and androgens

* Glucocorticoids offer relief of pain; suppress body’s defense system

• Adrenal medulla – ensures a rapid, short term response to stress; releases epinephrine and norepinephrine.

* Secretions stimulate liver and muscle cells to release glucose for energy use

Gonads

• Male = testes; testosterone• Female = ovaries; estrogen; progesterone• Sex hormones

1.affect growth and development

2. regulate reproductive cycles and sexual behavior.

Homework 1. Define terms: endocrine gland, hormones,

goiter, hyperthyroidism, hyperglycemia, hypoglycemia, and hypothyroidism.

2. Discuss the hormonal effects in regulation of blood calcium level and regulation of blood glucose level.

3. List the hormones secreted and its functions (effects) of the following endocrine organs: thyroid, posterior pituitary, anterior pituitary, adrenal gland, pineal gland, pancreas, testes, and ovaries.