1. The Endocrine System
Chapter 45

2. Types of chemical messengers:
Hormone
Paracrine regulators
pheromones

3. Types of Chemical Messengers
Hormone
Regulatory chemical that is secreted into extracellular fluid and carried by the blood
Can act at a distance from source
Endocrine system
Organs and tissues that produce hormones
Only targets having the appropriate receptor can respond

4. Types of Chemical Messengers
Paracrine regulators do not travel in blood
Allow cells of an organ to regulate each other
Can be neurotransmitters
Pheromones are chemicals released into the environment to communicate among individuals of a single species
Not involved in normal metabolic regulation within an animal

5. Types of Chemical Messengers
Neurohormones
Some neurotransmitters are distributed by the blood and act as a hormone
Norepinephrine coordinates the activity of heart, liver, and blood vessels during stress

6. Endocrine System
The endocrine system includes all the organs that secrete hormones
Endocrine – product secreted into extracellular fluid and carried in blood
Exocrine – secrete product into a duct

7. 2 basic hormone characteristics
Must be sufficiently complex to convey regulatory information to their target cells
Must be adequately stable to resist destruction before reaching their target cells (having to survive in extracellular environments)
What’s with the beret & eye
patch?
I have to be both
Tough and complex!
HORMONE

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Hypothalamus
Hypothalamus
Pineal gland
Pineal gland
Neurohypophysis
Pituitary
gland
Adenohypophysis
Thyroid gland
Thymus
Parathyroid glands
(behind thyroid)
Adrenal
glands
Pancreas
Testes
(in males)
Ovaries (in females)

9. 1. Human Chorionic Gondadotrophin
3 Classes of Hormones
Peptides and proteins
Glycoproteins
Amino acid derivatives
Catecholamines
Thyroid hormones
Melatonin
Steroids
Sex steroids
Corticosteroids
1. Human Chorionic Gondadotrophin
( a glycoprotein)
2. Catecholamines
2. themedicalbiochemistrypage.org
3. Steroids 1. 3.

10. Hormones may be categorized as:
Lipophilic (nonpolar) – fat-soluble
Steroid hormones and thyroid hormones
Travel on transport proteins in blood
Bind to intracellular receptors
Tend to act over brief time period
Hydrophilic (polar) – water-soluble
All other hormones
Freely soluble in blood
Bind to extracellular receptors
Tend to have much longer active period

11. Lipophilic hormones
Transported by proteins
Cross cellular membrane
Bind to receptor in nucleus, activating transcription factors
Notice where the hormone ended up in this picture

12. Hydrophilic hormones Bind to receptors on cell surface
Initiates signal transduction through activation of protein kinases
Regulatory enzymes that activate intracellular proteins through phosphorylation

13. Paracrine Regulation occurs in most organs

14. Hydrophilic Hormones Second-messenger systems
Many hydrophilic hormones work through second messenger systems
Two have been described
One involving cyclic adenosine monophosphate (cAMP)
One that generates 2 lipid messengers: inositol triphosphate (IP3) and diacyl glycerol (DAG)

15. The Pituitary Gland Also known as the hypophysis
Hangs by a stalk from the hypothalamus
Consists of two parts
Anterior pituitary (adenohypophysis)
Appears glandular
Posterior pituitary (neurohypophysis)
Appears fibrous
Different embryonic origins
Different hormones

16. The Posterior Pituitary
Appears fibrous because it contains axons that originate in cell bodies within the hypothalamus and that extend along the stalk of the pituitary as a tract of fibers
Develops from outgrowth of the brain

17. The Posterior Pituitary
Releases 2 hormones:
ADH
Oxytocin

18. The Anterior Pituitary
Develops from a pouch of epithelial tissue of the embryo’s mouth
Not part of the nervous system
Produces at least 7 essential hormones
Tropic hormones or tropins
Act on other endocrine glands
Can be categorized into three families

19. 3 families of anterior pituitary hormones:
Peptide
Corticotropin – stimulates adrenal to make cortisol
Melanocyte-stimulating hormone – stimulates dispersion of pigment
Protein
Growth hormone
Prolactin – stimulate mammary glands
Glycoprotein
Thyroid-stimulating hormone – acts on thyroid
Luteinizing hormone – acts on ovaries, testes
Follicle-stimulating hormone – development of ovarian follicles, development of sperm

20. Anterior pituitary controlled by hormones from hypothalamus
Hypothalamus secretes neurohormones into anterior pituitary causing anterior pituitary to release hormones

21. The hypothalamus and the anterior pituitary are partially controlled by the very hormones whose secretion they stimulate (FEEDBACK)
Negative feedback (most)
Positive feedback (few)
Causes deviations from homeostasis
Control of ovulation and labor contractions

22. The Thyroid Gland
In humans, the thyroid gland is shaped like a bow tie, and lies just below the Adam’s apple in the front of the neck
Secretes
Thyroid hormones
Thyroxine
Triiodothyronine
Calcitonin

23. More Glands: Parathyroid Glands
4 small glands attached to the thyroid
Produce parathyroid hormone (PTH)
Raises blood Ca2+ levels by…
Pulling It out of bone (via osteoclasts)
Stimulating the kidneys to reabsorb Ca2+ from the urine
Vitamin D activated by a PTH controlled enzyme
Stimulates the intestinal absorption of Ca2+

24. The Adrenal Glands Medulla (inner portion) Cortex (outer portion)
Stimulated by the sympathetic division of the autonomic nervous system
Secretes the catecholamines epinephrine and norepinephrine (adrenalin and noradrenalin)
Cortex (outer portion)
Stimulated by anterior pituitary hormone ACTH
Corticosteroids
Glucocorticoids: maintain glucose homeostasis (e.g., cortisol)
Aldosterone: helps regulate mineral balance
Mayoclinic.com

25. The Pancreas Exocrine and endocrine glands
Connected to the duodenum of the small intestine by the pancreatic duct
Islets of Langerhans are scattered clusters of cells throughout the pancreas
These govern blood glucose levels through two hormones with antagonistic functions

26. The Pancreas Insulin Glucagon Secreted by beta (b) cells of the islets
Stimulates cellular uptake of blood glucose and its storage as glycogen in the liver and muscle cells, or as fat in fat cells
Glucagon
Secreted by alpha (a) cells of the islets
Promotes the hydrolysis of glycogen in the liver and fat in adipose tissue

27. The Gonads Ovaries and testes in vertebrates
Produce sex steroids that regulate reproductive development
Estrogen and progesterone
“Female” hormones
Androgens
“Male” hormones
Testosterone and its derivatives

28. The Pineal Gland
Located in the roof of the third ventricle of the brain
Secretes melatonin
Functions of melatonin
Reduces dispersal of melanin granules
Synchronizes various body processes to a circadian rhythm
Secretion of melatonin activated in the dark