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Distinguish between exocrine and endocrine glands.
- exocrine: not hormones, secrete to the surface through ducts
- endocrine: lack ducts, secrete hormones into the blood, well vascularized
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Compare and contrast the roles of the nervous system and endocrine system in
maintaining homeostasis.
- The Nervous System and the Endocrine System together act to direct the maintenance of homeostasis
- – in other words, to control internal conditions.
- Control by the Nervous System is rapid, localized (via nerve impulse transmission) and
- relatively short-lived.
- Control by the Endocrine System is slower, more global (hormones distributed through
- circulatory system) and more prolonged.
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Define hormone
long distance chemical signals, travel in blood or lymph.
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name and locate major endorcine organs
- Pituitary
- Thyroid
- Parathyroids
- Adrenals
- Pineal
- Thymus
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Why is the hypothalamus considered a neuroendocrine organ
has both nervous and endocrine functions and tissues
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Hormones can be classifed by their chemistry, by solubility in water and by their
mechanism of action. Name the classes for each category and explain the basis
for classification
- Chemistry: amino acid based derived from peptides proteins and amino acids steroids synthesized from cholesterol gonadal and adrenal cortical hormone
- Solubility: 1.Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
- •Act on plasma membrane receptors
- •Act via G protein second messengers
- •Cannot enter cell
- 2. Lipid-soluble hormones (steroid and thyroid hormones)
- •Act on intracellular receptors that directly activate genes
- •Can enter cell
- Mechanism of action:
•Though - hormones circulate systemically only cells with receptors for that hormone
- affected target cells
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how do hormones effect target cells
- –Alter plasma membrane permeability and/or membrane potential by opening or closing
- ion channels
- –Stimulate synthesis of enzymes or other proteins
- –Activate or deactivate enzymes
- –Induce secretory activity
- –Stimulate mitosis
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cAMP signalling mechanism
- 1.Hormone (first messenger) binds to receptor
- 2.Receptor activates G protein
- 3.G protein activates adenylate
- cyclase
- 4.Adenylate cyclase converts ATP to cAMP
- (second messenger)
- 5.cAMP activates protein kinases that phosphorylate proteins
- –Activated kinases phosphorylate various proteins, activating some and inactivating others
- –cAMP is rapidly degraded by enzyme phosphodiesterase
- –Intracellular enzymatic cascades have huge amplification effect
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PIP2-calcium signaling mechanism
- –Involves G protein and membrane-bound effector – phospholipase C
- –Phospholipase C splits PIP2 into two second messengers – diacylglycerol
- (DAG) and inositol trisphosphate (IP3)
- •DAG activates protein kinase; IP3 causes Ca2+ release
- •Calcium ions act as second messenger
- –Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin
- –Calcium-bound calmodulin
- activates enzymes that amplify cellular response
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What determines the ability of a target cell to respond to a hormone?
blood levels to hormone, number of receptors on/in target cell, affinity of binding between receptor and hormone
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Describe the three ways that hormones influence each other’s activity at target
cells.
- permissiveness: multiple hormones must be present to produce effect
- synergism: more than one hormone produces same effect on target cell-amplification
- antagonism: one or more hormones oppose action of another
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Name the anatomic regions of the pituitary gland. What is another name for the pituitary
and for each region
- pituitary (hypophysis)
- posterior lobe (neural)
- anterior lobe (gladular)
- -adenohypophysis
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name hormones released by each part of the pituitary gland
- posterior: store oxytocin and ADH(hormones made in the hypothalamus)
- anterior: GH, TSH, ACTH, FSH, LH, and PRL
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What is the hypophyseal portal system? What is its function?
primary capillary plexus, hypophyseal portal veins, secondary capillary plexus carries releasing/inhibiting hormones to anterior pituitary to regulate hormone secretion *slide 62*
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What are the tropic hormones? Why are they called tropic?
- TSH, ACTH, FSH, AND LS
- regulate secretory action of other endocrine glands
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Name the 3 hormones produced by the thyroid gland. What is the function of each
hormone?
- Thyroid hormone: =>increase rate of cell metabolism = increased O2 use
- & heat production
- =>required for normal growth and development of nervous system
- Extrafollicular cells secrete hormone calcitonin
- a. Action = decrease [Ca++]blood by stimulating osteoblast activity in bone
- b. Regulation by negative feedback:
- =>high blood Calcium stimulates secretion
- =>low blood Calcium inhibits secretion
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How is release of thyroid hormones regulated? How is release of calcitonin
regulated
- thyroid hormone:
- a. secretion stimulated by TSH
- b. inhibited by negative feedback of ant pituitary, hypothalamus via rising levels of thyroid hormones
- c. Consequences of misregulation:
- hyposecretion in infants = cretinism
- Grave’s disease = hyperthyroidism due to autoimmune stim
thyroidCalcitonin: - =>high blood Calcium stimulates secretion
- =>low blood Calcium inhibits secretion
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Describe
the structure of the hormone producing structures of the thyroid
- •Two lateral lobes connected by median mass called isthmus
- •Composed of follicles that produce glycoprotein thyroglobulin
- •Colloid (thyroglobulin + iodine) fills lumen of follicles and is precursor of thyroid
- hormone
- •Parafollicular cells produce the hormone calcitonin
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What is unique about the production of thyroid hormones?
thyroid gland stores thyroid hormone extracellularly
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Name the hormone produced by the parathyroid glands and describe its action.
Describe how it is regulated?
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