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CH 50 Endocrine system
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Hormones are chemicals produced by cells in the body, circulate within the bloodstream
o Act on one/more target tissues
o Chief function is to counter body-challenges within and maintain homeostasis
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 taken to another part of the body (circulatory system)
o Ex of endocrine gland: Pituitary gland
Hormone producing cells (endocrine glands) and other organs with hormone secreting cells make up the
endocrine system
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Glucocorticoids (cortisol) regulates metabolism, development, growth, immune system,
and body’s response to stress
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1: Mechanisms of Hormone Action and Control
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Long distance signaling allows remote organs and tissues to communicate
Hormones can have long and short term effects
Three classes of hormones:
o Amines  derived from amino acid, tyrosine or tryptophan, water soluble,

location of target cell: Plasma Membrane, but in thyroid hormones (via intracellular
receptors),
 Mechanism of action: stimulate second messengers, but in thyroid hormones ( via changes in
gene transcription)
 Ex: epinephrine, norepinephrine, dopamine, thyroid hormones, melatonin(pineal gland, major
hormone)
o Protein/Peptides (most abundant, participate in metabolism, mineral balance, reproduction, and growth)
 water soluble
 Location of target cell: Plasma membrane
 Mechanism of action: Stimulate second messenger pathways
 Ex: insulin, glucagon, leptin
o Steroids, usually bounded to large proteins in blood that serve as carriers (reach high blood
concentration)  Derived from cholesterol, mostly lipid soluble
 Location of target cell: Cytosol, or nucleus
 Mechanism of action: Gene transcription directly
 Ex: Aldosterone, cortisol, testosterone, estradiol
Hormones act through membrane or intracellular receptors
o Amines and peptide/protein classes of hormones are unable to cross plasma membranes and must use
receptors on the cell surface
 Three activated pathways activated by water soluble hormones: cyclic AMP,
calcium/phosphatidylinositol
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 Rapid, involve changing the activity of enzymes
o Steroids can diffuse across plasma membranes and access receptors within the cytosol or nucleus
o All steroid hormones and thyroid hormones are lipophilic(lipid soluble) and bind to intracellular
receptors
Hormone levels in blood depend on rates of synthesis and removal
o The increase and decrease in concentration of hormones when circulated in the blood are accomplished
in two ways:
 Changing the rate of hormone production and released by a endocrine cell
 Changing the rates at which hormones are removed from the blood or inactivated
o Synthesis of amine hormones are mediated by enzymatic conversion of tyrosine or tryptophan into
their respective hormones
 Require enzymes that add or remove chemical side groups
 Depends on amounts and activities of the synthesized enzymes
 Always present in cell, stimulated when more hormone is required
o Synthesis of protein/peptide hormones are at a steady rate in unstimulated cell, until additional
hormone is required
 Transcription factors direct increased transcription of gene coding for the hormone in
question
 When less hormone is required, gene transcription is slowed, or stopped
 Too large and hydrophilic to diffuse across the plasma membrane, so the hormone is packed
into secretory vesicles
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Ready for secretion of hormones via exocytosis and stored for immediate use
When call is stimulated to secrete the store hormone, it is stimulated to synthesize
new hormone molecules to replace them
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 Allow the blood hormone levels to remain at normal range

50
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o Hormones of Anterior Pituitary Gland(refer to pg 1052):
 Adrenocorticotropic Hormone (ACTH)stimulate cells of adrenal cortex to synthesize and
release cortisol or related steroid hormones
 Follicle-Stimulating Hormone (FSH) act on ovaries or testes to stimulate egg or sperm
development…
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 Thyroid-Stimulating Hormone (TSH)act on cells of thyroid gland to stimulate growth of gland
and production of thyroid hormones
The Posterior Pituitary Gland contains axon terminals from hypothalamic neurons that store and secrete oxytocin
and antidiuretic hormone

o Not connected to the hypothalamus by portal veins and does NOT RESPOND TO NEUROHORMONES FROM
THE HYPOTHALAMUS
 Extension of hypothalamus that lies in close contact with anterior pituitary gland
o Store oxytocin or antidiuretic hormone (ADH)
 At high concentrations, ADH increases blood pressure by stimulating vasoconstriction of blood
vessels, like oxytocin
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(Oxytocin) stimulates contractions
of smooth muscle cells both during birth and during lactation
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3 Hormonal Control of Metabolism and Energy Balance
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Thyroid hormones contain iodine and regulate metabolic rate
o Colloid contains thyroglobulin(TG) which plays a large role in synthesizing thyroid hormones
o Are produced when hypothalamic neurohormone thyrotropin-releasing hormone (TRH) stimulates the
anterior pituitary gland to secrete thyroid stimulating hormone into the blood (which stimulate the
cell follicles of thyroid gland to begin the process of producing thyroid hormones)
 Negative feedback on anterior pituitary and hypothalamus, which prevents them from
overproducing TRH and TSH
o Synthesis of Thyroid Hormones:
 Iodide is diffused from the bloodstream into interstitial fluid, then transported across
basolateral membrane of the thyroid follicular cells
Diffuses through apical membrane  colloid (where it is oxidized and bonds to tyrosine side
chains in thyroglobulin)
 Iodinated TG(thyroglobulin) enters follicular cells by endocytosis(apical membrane undergoes
this) when the cell is stimulated by TSH(thyroid stimulating hormone)
 Endocytotic vesicles fuse with lysosomes, lysosomal enzymes cleave iodinated tyrosines from
thyroglobuline to form thyroxine (T4) and triidothyronine (T3)
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o Major action of thyroid hormones include stimulating energy consumption by many different types of
cells (regulate metabolism)
 By increasing number and activity of sodium/potassium-ATPase pumps in plasma membranes
 As these pumps hydrolyze ATP, the cellular level of ATP decrease (compensated by
increasing the cell’s metabolism of glucose)
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 When T3 and T4 are in low amounts, due to lack of iodine, TRH and TSH are
overstimulated and overstimulates the thyroid (enlarged thyroid), reduced negative
feedback on the hypothalamus and the anterior pituitary gland
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4 Hormonal control of mineral balance
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Vitamin D and parathyroid hormone regulate the calcium ion level in blood
o Calcium obtained from the diet and absorbed in the small intestine (homeostasis of blood calcium:
10mg/100mL)
o Vitamin D is consumed in food and made in the skin in the presence of sunlight
 OH group added to vitamin D in the liver
 Second OH added in kidneys producing 1, 25-dihydroxyvitamin D (active hormone)
 Active hormone reaches small intestine, absorption of calcium from small intestine into the
blood is increased
Due to parathyroid hormone(PTH), secreted from parathyroid glands, blood Calcium levels do not decrease
dramatically
o Act on bone to stimulate the activity of cells that dissolve mineral part of bone  releases calcium
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50
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1 Cellular components of nervous systems
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Central nervous system (CNS) consists of a brain and a nerve cord, in vertebrates this extends from the brain
through the vertebral column (spinal cord)
Peripheral nervous system (PNS) consists of all neurons and projections of their plasma membranes that are
outside of but connect, such as projections that end on muscle and gland cells
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o 2 Classes of Cells include: Neurons and Glia
 Neurons (refer to myelinated cell)
 Dendrites receive electrical and chemical messages, Axons send outgoing messages to axon
terminals
 All animals except for sponges have neurons
 Glia cells outnumber neurons, and contribute to blood brain barrier and play numerous roles
 Some glia form tracks along which neurons migrate to form nervous system
 Specialized glial cells wrap around axons at regular intervals to form myelin sheath
 Myelin producing glial cells are called oligodendrocytes(brain and spinal cord)
 Schwann cells are glial cells that form myelin on axons that travel outside the brain
and spinal cord

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Myelin and the nodes of Ranvier increase the speed with which electrical signals
pass down the axon
 Ex: Astrocytes( provide metabolic stability for neurons and involved in formation of
blood brain barrier, helps maintain constant ion concentrations in extracellular fluid),
microglia(remove cellular debris)
Sensory and motor neurons as well as interneurons form pathways in a nervous system
o There are three main types of Neurons( refer to drawings):
 Sensory: detect or sense information from outside world, such as light, taste, smell, or heat
 Detect internal body conditions, such as blood pressure and body temperature
 Afferent, transmit signals to CNS
 Arrangement allows for rapid transmission of sensory signal to CNS
 Motor: send signals away from CNS and produce a response
 Causes movement, secretion of hormones
 Efferent, do not branch into two main processes
 Interneuron: forms interconnections between other neurons in CNS
 Signals set between interneurons are critical in interpretation of information that
CNS receives and the response it produces
 Arrangements allow for complex connections with other cells
Neurons transmit information to each other through a series of connections that form a circuit
o Simple circuit(reflex arc) allows an organism to respond rapidly to inputs from sensory neurons and
consists of only a few neurons
 Stimulus from sensory neurons  sent to CNS, but signal is not really interpreted (not very
many interneurons involved)  motor neurons, where a response is produced (knee jerk)
 Allows animals to respond quickly to dangerous situations

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 Plasma membrane contains ion specific channels that affect permeability of sodium and
potassium across membrane
 Ungated channel is one that is open at rest and that does not respond to other
stimuli such as voltage, ligand binding, or mechanical stimulation
 At rest, the membrane is more permeable to potassium channels than sodium,
because there are more potassium channels than ungated sodium channels
 Na+ tends to diffuse into cells, K+ tends to diffuse out of cells when the cell is at rest
 Presence of negatively charged molecules such as proteins that are more abundant inside the
cell ( do not readily move through plasma membrane, so they contribute to some negative
charge to the interior)
An electrochemical gradient governs the movement of ions across a membrane (pg
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o Direction that an ion will move depends on electrochemical gradient for ion, which is combined effect of
both an electrical and chemical gradient

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o Hyperpolarization occurs when the cell membrane becomes more polarized (more negative inside of
the cell relative to the surrounding fluid)
o Excitable cells = neuron and muscle cells
o Gated ion channels allow for swift change in membrane potential, in order to communicate with other
cells using electrical signals
 Volted gated ion channel: open and close in response to changes in voltage
across membrane
 Ligand gated ion channel: chemically gated, open or close when ligands
(neurotransmitters) bind to them
o Volted gated ion channel and Ligand gated ion channel are responsible
for two types of neuron’s membrane potential:
 Graded Potential: Depolarization or hyperpolarization that varies
depending on the strength of stimulus
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 Read pgs 858-865

Ch 42: Neuroscience II: Evolution and Function of the Brain and Nervous System
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Nervous systems evolved to sense and respond to changes in the environment
More Complex body types have been associated with cephalization, which is the formation in the head of an
increasingly complex brain that controls sensory and motor functions of the entire body
In all chordates: the brain is connected to spinal cord
Brains of Vertebrates have three basic divisions
o Vertebrate brains begin with formation of neural tube (from which entire nervous system develops)
o Anterior end develops into brain, posterior portion becomes spinal cord
3 major divisions:
o Hind Brain includes:
 medulla oblongata, coordinates breathing, maintain homeostatic processes of animals
 , pons and cerebellum, monitor and coordinate body movements
o Midbrain
 Processes different types of sensory inputs, including vision, olfaction (smell), and hearing
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 Surface layer of cerebrum is called the cerebral cortex
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2 Structure and Function of the human nervous system
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Nervous system is composed of central and peripheral nervous systems
Ganglion refers to group of neuronal cell bodies located in PNS
Within the vertebrate nervous system, many myelinated axons may run in parallel bundles, such as tract (found in
CNS)
o Convey information from region to region within the brain and between the brain and spinal cord
White matter gets color from myelin, consists of myelinated axons bundled together in large numbers to form
tracts
Grey matter consists of neuronal cell bodies, dendrites, and unmyelinated axons
Primary function of somatic nervous system Is to sense external environment and control skeletal muscles
o Receive stimuli and transmit to CNS
o Voluntary, because responses can be controlled consciously
Autonomic nervous system regulates homeostasis and organ function
o Efferent nerves are subdivided into(act on same organs and have opposing actions):
 Sympathetic: Rapidly activating systems that prepare the body for danger or stress
 Ex: Fight-or-flight response
 Increases heartbeat and force of contraction, inhibits digestion and stomach activity,
stimulates release of glucose into blood, inhibits insulin release from pancreas,
inhibits activity of small intestines, stimulates secretion of epinephrine and
norepinephrine from adrenal glands, promotes ejaculation and vaginal contractions
 Parasympathetic: maintains and restores body function
 Ex: rest-or-digest(promotes digestion)
 Slows heartbeat, stimulates digestion and stomach activity, increase glucose
utilization by liver cells, stimulates insulin secretion from pancreas, increases
activity of small intestines to promote absorption of nutrients, stimulates urinary
bladder to contract, promotes erection of genitals
Hindbrain: maintains homeostasis and coordinates bodily functions
o Medulla Oblongata: responsible for swallowing, vomiting, digestion, breathing, heart rate, and
cardiovascular function
o Cerebellum: receives sensory inputs from cerebral cortex and auditory and visual areas of brain, inputs
from spinal cord that covey information about the position of joints and contraction or relaxation of
muscles… Main Function: maintain balance and coordinate hand-eye movement
o Pons: serve as relay between cerebellum and other areas of brain, give rise to some cranial nerves, and
contain nuclei that help regulate rate of breathing
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 Major role is production of hormone
 Suprachiasmatic nuclei act as “master clock” of CNS (establishment of circadian
rhythms, (control expression of behavioral, psychological, and hormonal rhythms
over 24-hr day)
 Epithalamus: collection of structures
 Pineal gland (produces melatonin – responsible for seasonal reproductive behaviors
in mammals)



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