1. Endocrine System Nestor T. Hilvano, M.D., M.P.H.
(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain, Textbook, 2012.)

2. Learning Objectives
Describe the 3 types of hormones by chemical structure.
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.

3. Endocrine System Ductless glands
Hormones – chemical signals secreted and pass directly into the blood circulation to reach the target organs

4. 3 Types of Hormones
Proteins and peptides – most numerous group; H2O soluble; ex. TSH, LH, FSH, ADH, prolactin
Amine – derivatives of tyrosine; some H2O soluble, some lipid soluble; ex. TH, Epi, Nor-Epi, dopamine
Steroids – not H2O soluble ex. sex hormones
Mechanisms of Action on target cells:
Lipid soluble hormones – bind to cytoplasm or nuclear receptors (inside the cell)
Water soluble hormones – bind to receptor on plasma (cell) membrane; w/ second messenger

5. Figure 29.3 Hormonal Signals Are Amplified within the Cell and Elicit Specific Responses in the Target Cell
Hormones are active at very low concentrations because tiny amounts of a hormone can generate a large internal signal within a target cell. A hormone that docks to a plasma membrane receptor triggers an internal signal relay, known as a signal transduction pathway, in the course of which the original signal becomes magnified. In addition to changing gene expression (1), hormones can bring about a change in cell activity by altering metabolism (2), cytoskeletal organization (3), or membrane transport (4).

6. Figure 29.1 The Endocrine System Is Composed of Hormone-Secreting Cells
The endocrine system consists of ductless glands, as well as scattered endocrine cells and tissues, that release hormones directly into the circulatory system. The hypothalamus is the main coordinator of the endocrine system; it also integrates the endocrine system with the nervous system.

7. 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

8. Hypothalamus: The Master Gland
Figure 18–9 Pituitary Hormones and Their Targets.
1) Direct neuronal innervation of adrenal medulla (come back to)
2) Neuronal innervation of posterior pituitary
3) Portal system release to anterior pituitary
2A) Pathway: Supraoptic neurons → posterior pituitary → ADH → kidneys
Affect: ↑ H2O reabsorption in distal convoluted tubule (DCT) & collecting duct (CD)
~5% daily urine output
Release
stimulated by: ↑ osmotic pressure (↑ solute = ↓ H2O)-detected in hypothalamus
↓ blood pressure &/or volume-detected in heart called osmoreceptors
diabetes insipidus: central-don’t make ADH; nephrogenic-don’t respond to ADH
Notes: EtOH ↓ ADH release = ↑ urine output
2B) Pathway: Paraventricular neurons → posterior pituitary → oxytocin → uterus/mammary gland [female] OR vas deferens/prostate [male]
Affect: female: uterine contractions during labor (+ feedback); contractions during breastfeeding (let down)
male: contractions during emission-get sperm out
stimulated by: pressure on cervix; nipple stimulation
sexual arousal
List hormone produced by anterior pituitary
List hormone produced by hypothalamus that goes to anterior pituitary
List target organ
Effects
blood levels nearly 0 in humans except:
3A) weirdo-pars intermedia-secretes melanocyte stimulating hormone (MSH); secretion inhibited by dopamine
1) fetal development 2) young children 3) pregnant women 4) disease state
also released by skin after sun exposure = paracrine effect
3B) prolactin release factor (dopamine acts as inhibitor)
The rest follow pathway to pars distalis portion of anterior pituitary
prolactin → breasts→ development and milk production (also involves additional hormones for dev. Esp estrogen)
3C) Gonadotropin Releasing Hormone (GnRH)
Lutenizing Hormone (LH) → ovaries → ovulation; estrogen & progesterone release
→ testes → androgen release
Follicle Stimulating Hormone (FSH) → ovaries → estrogen release; follicle development/maturation
→ testes → sperm development/maturation
Growth Hormone (GH) → kidney/liver → somatomedins → ↑ amino acid uptake/protein synthesis everywhere
3D) Growth Hormone Releasing Hormone (GHRH) & Growth Hormone Inhibiting Hormone (GHIH)
epithelial/CT → cell division & differentiation
adipose → b.d. triglycerides → fatty acid → ATP synthesis
liver → b.d. glycogen → ↑ [glucose] in blood
depends on genetics and diet too (also increase: exercise, non-REM sleep, thyroid and sex hormones = increase GH release)
all together = growth!
imbalances: hypo-pituitary dwarfism-small stature, normal brain; Rx inject GH
hyper-gigantism before growth plates close; acromegaly after growth plates close
Adrenocorticotropic Hormone (ACTH) → adrenal cortex → glucocorticoids (cortisol) [come back to w/stress]
3E) Corticotropic Releasing Hormone (CRH)
3F) Thyrotopin Releasing Hormone (TRH)
Thyroid Stimulating Hormone (TSH) → thyroid → T3/T4
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

9. 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
Neurosecretory
cell
Hormone
Posterior
pituitary
Blood vessel
Oxytocin
ADH
Uterine muscles Mammary glands
Kidney tubules
Anterior

10. Pituitary Gland 1. Tropic hormones (control other glands)
Neurosecretory
cell
Blood vessel
Releasing hormones from hypothalamus
Pituitary hormones
TSH
ACTH
FSH and LH
Growth hormone (GH)
Prolactin (PRL)
Endorphins
Thyroid
Adrenal cortex
Testes or ovaries
Entire body
Mammary glands (in mammals)
Pain receptors in the brain
Endocrine cells of
the anterior pituitary
Pituitary Gland
1. 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)

11. Anterior pituitary Thyroxine
Figure 26.4E
Hypothalamus
Inhibition
TRH
Anterior pituitary
Inhibition
TSH
Figure 26.4E Control of thyroxine secretion
Thyroid
Thyroxine 11

12. Pineal Gland Brain outgrowth
Secretes melatonin, with rhythmical activity and biologic clock functions
SAD syndrome

13. 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 deficiency
Hypothyroidism
Goiter
Hyperthyroidism

14. 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

15. Figure 29.7 Balancing Calcium Levels in the Blood
The thyroid and parathyroid glands secrete hormones that control calcium levels in the blood. The width of the red circuit indicates the relative levels of calcium in the bloodstream at different times.

16. 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

17. Figure 29.4 Balancing Levels of Glucose in the Blood
Two hormones—insulin and glucagon—work in opposite ways to regulate blood levels of glucose. The width of the red circuit indicates the relative amounts of glucose in the bloodstream at different times.

18. 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

19. Figure 29.6 Adrenal Hormones Produce a Rapid Response to Stress
The adrenal glands produce epinephrine (adrenaline) and norepinephrine (noradrenaline), which trigger rapid release and delivery of stored energy.

20. Gonads Male = testes; testosterone
Female = ovaries; estrogen; progesterone
Sex hormones
affect growth and development
regulate reproductive cycles and sexual behavior.

21. Homework
Define terms: endocrine gland, hormones, goiter, hyperthyroidism, hyperglycemia, hypoglycemia, and hypothyroidism.
Discuss the hormonal effects in regulation of blood calcium level and regulation of blood glucose level.
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.