1. The Endocrine System
Chapter 46

2. How chemical messengers regulate body processes?
Hormones are regulatory chemicals secreted by endocrine glands (table 46.1) into extracellular fluid and carried by blood.
Pheromones are regulatory chemicals released into environment to communicate among individuals of a single species
Exocrine glands secrete saliva or milk (exocrine secretions) into a duct for transport to outside
Hormones must satisfy two characteristics – must be complex to convey regulatory information to their targets and must be able to resist destruction before reaching their target cells
Hormones act within a body whereas pheromones act between organisms

3. What are the three chemical classes of hormones?
Peptides and proteins are composed of chains of amino acids. Example: Peptide hormones are antidiuretic hormone, insulin and proteins are glycoproteins – TSH, LH etc
Amino acid derivatives – are hormones manufactured by enzymatic modification of specific amino acids. Secreted from adrenal medulla (catecholamines), thyroid (tyrosine) and pineal (melatonin) glands
Steroids – lipids manufactured by enzymatic modification of cholesterol – like progesterone, testosterone, cortisol etc.
Steroid hormones can be divided into sex steroids secreted by testes, ovaries, placenta and corticosteroids secreted by adrenal cortex
These work to coordinate the activity of specific target cells through out the body

4. Chemical nature of hormones
Chemical nature of hormone determines its mode of transportation and interaction with their targets
Hormones categorized as lipophilic (nonpolar and fat soluble) and hydrophilic (polar and water soluble)
Hydrophilic hormones activate their receptors of target cells from outside the cell membrane (activity for minutes to hours). Lipophilic hormones attach to transport proteins and their lipid solubility allows them to cross cell membranes and bind to intracellular receptors (days to weeks)
Destroyed or deactivated after use and get excreted via bile or urine

5. What are the posterior pituitary or neurohypophysis hormones?
Pituitary gland (hypophysis) hangs as a stalk from hypothalamus (a part of central nervous system)
Pituitary gland is a compound endocrine gland which has two parts – glandular part called anterior pituitary or adenohypophysis and fibrous part called posterior pituitary or neurohypophysis
Posterior pituitary releases two neurohormones – Antidiuretic hormone stimulates water reabsorption by kidneys and inhibits urine production. ii) Oxytocin stimulates milk ejection reflex and uterine contractions in women during childbirth
Produced by neuron cell bodies located in hypothalamus-----transported along axon tracts from hypothalamus------to posterior pituitary for storage-----Upon appropriate stimulation the neurohormones get released into blood

6. What are the seven hormones produced by anterior pituitary?
Anterior pituitary secretes seven hormones that stimulate growth of their target organs as well as production and secretion of other hormones from additional endocrine glands.
Collective term – tropic hormones or tropins
Classification of secreted proteins – peptide hormones (adenocorticotropic hormones, Melanocyte stimulating hormone), protein hormones (growth hormone and Prolactin) and glycoprotein hormones (Thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone) – page 930.

7. How releasing and inhibiting hormones regulate anterior pituitary?
Hypothalamus secretes releasers and inhibiters into blood capillaries at the base of hypothalamus via portal system
These blood capillaries drain into small veins that run within stalk of pituitary to a second bed of capillaries in anterior pituitary – hypothalamohypophysial portal system/portal system
Releasing hormones are peptide neurohormones that stimulate release of other hormones – thyrotropin-releasing hormone, corticotropin-releasing hormone and gonadotropin-releasing hormone.
Inhibitors can inhibit release of anterior pituitary hormones – Somatostatin or growth-inhibiting factor and prolactin-inhibiting factor.

8. What is negative feedback theory?
Some endocrine organs are not directly regulated by hypothalamic control system
The hypothalamus and the anterior pituitary are partially controlled by the very hormones whose secretion they stimulate
This is called negative feedback and is important to maintain constant levels of target cell hormone (example thyroxine)

9. Negative feedback: Thyroid gland control
Hpothalamus secretes TRH
Portal system
TRH stimulates anterior pituitary to secrete TSH
Metabolism
TSH stimulates thyroid gland to release thyroxine
Contains iodine
Thyroxine acts on hypothalamus and anterior pituitary to inhibit secretion of TRH and TSH
Negative feedback keeps thyroxine levels constant
Less iodine- hypothalamus and anterior pituitary receive far less negative feedback inhibition than normal
Results in elevated increase of TSH and TRH
Stimulates thyroid gland to produce more thyroxine (-iodine)
Consequence is overgrowth of thyroid gland-GOITER

10. Read 46. 4 (examples of major peripheral endocrine glands) and 46
Read 46.4 (examples of major peripheral endocrine glands) and 46.5 (Other Hormones and their effects)

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