BIOB33H3 Study Guide - Midterm Guide: Exocytosis, Menopause, Glycogen

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Lecture 9: Endocrine System I
Readings: pgs. 122-137
Key Thoughts
Overview of endocrine system
Evolution and diversity
Mechanism of action
Endocrine reflexes
Pituitary glands
Connection between Nervous System and Endocrine System…
The nervous system directs an immediate response to stimuli, usually by coordinating the
activities of other organ systems
Could lead to a long-term change directed by the endocrine system
Both the endocrine and nervous system…
o Rely on chemicals that bind to receptors on target cells
o Share many chemical messengers
Norepinephrine and epinephrine can be neurotransmitters and hormones
o Regulated primarily by negative feedback mechanisms
o Share the common goal to preserve homeostasis
By coordinating and regulating activities of other cells, tissues, organs and
Vertebrate endocrine system
o The endocrine system includes all the endocrine cells and tissues of an animal
o Endocrine cells are glandular secretory cells that release their secretions into the
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Secretory Tissue
Chemical Class
Pineal gland
Circadian and seasonal rhythms
Hypothalamus (clusters
of secretory neurons)
Trophic hormones
Regulation of anterior pituitary
Posterior pituitary
(extensions of
hypothalamic neurons)
Breast & uterus in mammals: also
involved in social bonding & behaviour
Water reabsorption in excretory
Vasotocin (fish,
amphibians, birds)
Activates similar to both oxytocin and
Anterior Pituitary gland
Milk production in mammals,
osmoregulation, growth, metabolism
Growth Hormone (GH)
Growth, metabolism
Hormone (ACTH)
Release of corticosteroids
Thyroid stimulating
hormone (TSH)
Synthesis and release of thyroid
Follicle stimulating
hormone (FSH)
Egg or sperm production; sex hormone
Luteinizing hormone
Sex hormone production; egg or sperm
o Endocrine system of vertebrates are all similar, same endocrine cells and tissues
o Chemical messengers, receptor and cell signaling mechanisms of animals share many
similarities (suggests common ancestor)
Animals can use hormones for long-term effects
o Substantial differences in endocrine system of different animals (ie. vertebrate vs.
o Invertebrates have few endocrine glands and most endocrine signaling utilizes
neurohormones rather than hormones
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Evolution of endocrine system
o Evolutionary changes in way the tissues respond to a hormone, rather than a change
in hormone molecules
o Some hormones have different effects in different animals
o The endocrine system is quite diverse mostly because they are connected to the
circulatory system and the circulatory system was thought to have arisen
independently across different taxa (also substantial similarities)
Examples of hormones having similar effects include: HGH in fish and
humans, Estrogen from pregnant mares can be used in post-menopausal
Examples of hormones having different effects include: Prolactin stimulates
milk production in mammals, but inhibits metamorphosis and promotes
growth in amphibians, and regulates water balance in fish
Generally in the endocrine system…
o Hormones are released into the blood and transported by blood
o Hormones are released at low amounts and circulate the blood in low concentrations
o Hormones act on cells through interaction with specific receptors (act as first
messengers in a series of messengers that lead to a specific response in target
Hydrophilic Hormones
o Biological amines are derived from amino acids
Catecholamines such as epinephrine and norepinephrine (produced in the
adrenal glands)
o Peptide & protein hormones are chains of amino acids
Insulin is produced by beta islet cells in pancreas
o Free in the plasma
o Receptors are located on the plasma membrane
o Signaling mechanisms
Second messengers (cAMP, Ca2+, H+)
Enzyme activation by receptor
Intrinsic enzymatic activity of receptor (tyrosine, autophosphorylation)
o Fast excretion/metabolism (minutes)
Hydrophobic Hormones
o Steroid hormones are lipids, mostly from the adrenal glands and gonads
Testosterone and estrogen (synthesized from precursor cholesterol)
o Protein-bound in plasma
o Receptors are location: intracellular
o Signaling mechanisms
Intracellular receptors directly alter gene transcription
o Slow excretion/metabolism (hours/days)
Hormone mechanism of action
o Hormone interacts with a receptor on a target cell
o The presence of absence of a receptor determine the cell’s sensitivity (whether the
cell will respond to the hormone or not) to a hormone
o Hormone receptors are located either in the cell membrane
(hydrophilic/catecholamines, peptide/protein) or inside the cell
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