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Chapter 45: Hormones and the Endocrine System
Hormone: a chemical signal that is secreted into the extra cellular fluid, carried by the
circulatory system – communicates regulatory messages within the body
Endocrine system: all of an animal’s hormone-secreting cells
Coordinates slower, longer acting responses to stimuli
Regulates long-term developmental processes
Overlap Between Endocrine and Nervous Regulation
Neurosecretory cells: release hormones (sometimes called neurohormones) into the
blood via extracellular fluid
Control Pathways and Feedback Loops
Biological control system: sensor detects stimulus and sends info to control center,
which sends signal to effector which creates and efferent signal, which causes changes to
occur
negative feedback: effector response reduces the initial stimulus, so the response ceases
positive feedback: effector reinforces the stimulus and increases the response
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3 major classes of molecules can function as hormones: proteins and peptides,
amines from amino acids, and steroids
3 key events: reception, signal transduction, response
o reception: signal molecule binds to a receptor protein and is recognized
o signal transduction: events are triggered within the target cell
o response: the cell’s behavior changes
Cell-Surface Receptors for Water-Soluble Hormones
 Signal transduction pathway: series of changes in cellular proteins that converts
extracellular chemical signal to intracellular response (i.e. activation of an enzyme,
change in the uptake or molecules, or rearrangement of cytoskeleton)
 One hormone can have different effects in different target cells
o i.e. epinephrine, which affects stress affects different parts of the body
differently
Intracellular Receptors for Lipid-Soluble Hormones
 Intracellular receptors transducer a signal within the target cell – almost always
creates a change in gene expression
o mRNA produced in response to the stimulation is translated into new
protein in the cytoplasm
o can also have different effects on different cells
Paracrine Signaling by Local Regulators
Paracrine signaling: local regulators convey messages between neighboring cells
Several types of compounds: amino acid derivatives, cytokines, growth factors, or nitric
oxide
Nitric oxide: activates an enzyme to improve blood flow
Prostaglandins: a type of local regulators involved in reproduction, the immune system,
blood clotting, and the respiratory system
Relationship between the hypothalamus and pituitary gland
Hypothalamus: integrates endocrine and nervous systems
Receives information from nerves and brain; initiates endocrine signals
Pituitary gland: located at the base of the hypothalamus – has two parts
Posterior pituitary: stores and secretes hormones,
Anterior pituitary: sysnthesizes and secretes different hormones, including tropic
hormones; regulated by tropic hormones from the hypothalamus
Tropic hormones: hormones that regulate the function of endocrine organs
Posterior Pituitary Hormones
Antidiuretic hormone: increases water retention in kidneys, helping regulate osmolarity
of blood
Oxytocin: induces uterine muscles to contract during childbirth and causes mammary
glands to eject milk
Anterior Pituitary Hormones
Tropic
FSH, LH, and TSH: protein molecues with carbohydrates attached
ACTH: peptide hormone derived by cleavage of a large precursor protein
These hormones participate in complex neuroendocrine pathways
Nontropic
Prolactin: has a diversity of effects in different vertebrate species
MSH: regulates pigment-containing cells
Endorphins: dull perception of pain
Growth Hormone
Signals liver to release IGFs
Hypersecretion of GH leads to unusual height, while hyposecretion leads to
dwarfism
Thyroid Hormones
Thyroid gland: two lobes on the ventral surface of the trachea; produces
triiodothyronine (T3) and thyroxine (T4)
- Important in vertebrate development and maturation and homeostasis functions
Parathyroid Hormone (PTH) and Calcitonin: Control of Blood Calcium
- Calcium ions are essential to the normal functioning of all cells
PTH: raises the level of blood calcium ions
Calcitonin: lowers the level of calcium ions
- They work together to maintain homeostasis
Insulin and Glucagon: Control of Blood Glucose
Pancreas: important in endocrine and digestive system; contains islets of Langerhans
Islets of Langerhans: produce glucagons and insulin
Insulin: lowers blood glucose concentration
Glucagon: raises blood glucose concentration
Diabetes mellitus: deficiency of insulin – results in high blood glucose
Adrenal Hormones: Response to Stress
Adrenal glands: contain adrenal cortex and adrenal medulla
Adrenal Medulla: produces epinephrine (adrenaline) and norepinephrine (nonadrenaline)
during stress
Adrenal Cortex: produces glucocorticoids and mineralocorticoids over extended periods
of stress
Gonadal Sex Hormones
Androgens: stimulate the development and maintenance of the male reproductive
systems (i.e. testosterone)
Estrogens: responsible for the maintenance of the female reproductive system and
development of female secondary sex characteristics (i.e. estrogen and progestins)
Melatonin and Biorhythms
Pineal gland: secretes melatonin, which regulates functions related to light and seasons
Invertabrates also involve hormones, including brain hormone, which promotes the
development of adult characteristics; and juvenile hormone, which promotes juvenile
characteristics