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Biology 102 Chapter 42 Animal Hormones
1. Compare the response times of the two major systems of internal
communication: the nervous system and the endocrine system.
---nervous system is involved with high-speed messages
---endocrine system is slower and involves production,
release, and movement of chemical messages
2. Describe the relationships among endocrine system components:
Hormones, endocrine glands, target cells, and target cell receptors.
---most endocrine glands/tissues contain neurosecretory
cells that secrete hormones
--hormone is chemical signal that communicates
regulatory messages within body
---hormones may reach all parts of body, but only certain
types of cells, the target cells, are equipped to
---only target cells respond is because only they have
receptors for the hormone
3. Describe hormonal regulation of insect development including the
role of ecdysone, brain hormone, and juvenile hormone.
---in insects/crustaceans, molting triggered by ecdysone
--secreted (insects) by prothoracic glands just behind
--also favors development of adult characteristics
-from caterpillar to butterfly
---ecdysone production (insects) controlled by brain
hormone (BH)
---balanced by juvenile hormone (JH) secreted by corpora
allata (pair of small glands just behind brain)
--promotes retention of larval characteristics
4. List the general chemical classes of hormones and give examples
of each.
---peptide: oxytocin, ADH, calcitonin, PTH, thymosin
---protein: GH, prolactin, insulin, glucagon,
---glycoprotein: FSH, LH, TSH,
---amine: T3 and T4, epinephrine/norepinephrine, melatonin
---steroid: glucocorticoids, mineralocorticoids, androgens,
estrogens, progesterone
5. State which of the two classes of hormones is lipid soluble, and
explain how this property affects hormone action.
---nonsteroid hormones such as amines, peptides, and
proteins usually combine with receptors in target
cell membranes
--first messenger and second messenger
--signal-transduction pathways (convert extracellular
chemical signal to specific intracellular response)
---steroid hormones are lipid soluble & can easily
diffuse into cells
--once inside target cell, steroid hormones may
combine with specific protein molecules—the
6. Describe the mechanism of steroid hormone action, and explain the
location and role of steroid hormone receptors. (Chapter 15).
---steroid hormone easily crosses lipid bilayer of target
---binding of signal molecule with specific receptor
(usually in nucleus) initiates signal transduction
--signal initiates cascade of events in which proteins
interact with other proteins until final responses are
---in many cases, signal-receptor complex binds to DNA
to modify gene expression
7. Explain how to account for specificity in target cell response
to hormonal signals.
---each chemical signal has specific shape recognized by
that signal’s target cells
---signal’s action begins when it binds to specific
---receptor protein may be in plasma membrane of target
cell or inside the target cell
---diversity of responses of target cells depends on
nature of target cells & affinity of receptor molecules
on or within target cell
---cells are unresponsive to particular signal if they
lack appropriate receptor(s)
8. Describe the location of the hypothalamus, and explain how its
hormone-releasing cells differ from both endocrine gland secretory
cells and other neurons.
---hypothalamus is region of lower brain
---hormone releasing cells are 2 sets of neurosecretory
cells whose secretions are stored in posterior pituitary
---hormones released into capillaries in region at base
of hypothalamus
--capillaries drain into portal vessels; short blood
vessels that subdivide into second capillary bed
within anterior pituitary
---hypothalamic hormones have direct access to gland they
9. Describe the location of the pituitary, and explain the functions
of the posterior and anterior lobes.
---pituitary located at base of hypothalamus
---has 2 discrete parts that develop from 2 separate
regions of embryo and have very different functions
---anterior pituitary (adenohypophysis) consists of
endocrine cells that synthesize/secrete several hormones
directly into blood
---posterior pituitary (neurohypophysis) is extension of
--stores and secretes 2 hormones made by hypothalamus
10. List the posterior pituitary hormones, and describe their effects
on target organs.
---oxytocin stimulates contraction of uterus and mammary
gland cells; regulated by nervous system
---antidiuretic hormone (ADH) promotes water retention by
kidneys; regulated by water/salt balance
11. Using antidiuretic hormone as an example, explain how a hormone
contributes to homeostasis and how negative feedback can control
hormone levels.
---osmoreceptors in hypothalamus monitor blood osmolarity
---plasma osmolarity >s, osmoreceptors shrink slightly and
transmit nerve impulses to certain hypothalamic
neurosecretory cells
---these cells respond by releasing ADH into general
circulation from their tips in posterior pituitary
---target cells for ADH are cells lining collecting ducts
of nephrons in kidneys
---ADH binds to receptors on target cells & activates
signal-transduction pathway that increases water
permeability of collecting ducts
---water retention is >ed as water exits collecting ducts
and enters nearby capillaries
---osmoreceptors also stimulate thirst drive
---as more dilute blood (lower osmolarity) arrives at
brain, hypothalamus responds by reducing ADH secretion
and lowering thirst sensations
---this prevents overcompensation by stopping hormone
secretion and quenching thirst
---this negative feedback scheme includes hormonal action
and behavioral response
12. Define tropic hormone, and describe the functions of tropic
hormones produced by the anterior pituitary.
---trophic hormones have other endocrine glands as their
---four of the hormones secreted by anterior pituitary
gland are tropic hormones
---thyroid stimulating hormone (TSH) stimulates thyroid
---adrenocorticotropic hormone (ACTH) stimulates adrenal
cortex to secrete glucocorticoids
---follicle-stimulating hormone (FSH) stimulates production
of ova and sperm
---luteinizing hormone (LH) stimulates ovaries and testes
13. Explain how the anterior pituitary is controlled.
---set of neurosecretory cells in hypothalamus exerts
control over anterior pituitary by secreting 2 kinds
of hormones into the blood
---releasing hormones make the anterior pituitary secrete
its hormones
---inhibiting hormones make the anterior pituitary stop
secreting hormones
---is subtle blend (mix) of releasing and inhibiting hormones
that control timing and amount of hormonal release
14. List hormones of the thyroid gland, and explain their role in
development and metabolism.
---in humans and other mammals, thyroid gland consists of 2
lobes located on ventral surface of trachea
---produces 2 very similar hormones (from tyrosine)
--triiodothyronine (T3) and tetraiodothyronine (also
known as thyroxine (T4)
---in mammals, T3 is more active form
---thyroid important in human development
--thyroid deficiency (cretinism) results in markedly
retarded skeletal growth and poor mental development
---studies show thyroid hormones important for normal
functioning of bone-forming cells and for branching of
nerve cells during embryonic development of the brain
---in adult mammals, thyroid hormones help maintain normal
blood pressure, heart rate, muscle tone, digestion, and
reproductive functions
---hyperthyroidism (excessive secretion of thyroid
hormones) produces symptoms of high body temperature,
profuse sweating, weight loss, irritability, and high
blood pressure
---hypothyroidism (too little secretion of thyroid
hormones) produces cretinism in infants and symptoms
of weight gain, lethargy, and intolerance to cold in
--another condition associated with shortage of
thyroid hormones is enlargement of thyroid called
-associated with deficiency of iodine in diet
---thyroid also produces calcitonin
--lowers calcium levels in blood as part of
calcium homeostasis
15. Diagram the negative feedback loop that regulates the secretion
of thyroid hormones.
---hypothalamus-->TRH (thyroid releasing hormone) to
anterior pituitary-->TSH (thyroid stimulating hormone)
-->induces thyroid to manufacture and secrete T3 and T4
---increases levels of TSH and T3 and T4 signal hypothalamus
to reduce secretion of TRH
16. State the location of the parathyroid glands, and describe
hormonal control of calcium homeostasis.
---four parathyroid glands embedded in surface of thyroid
---function in homeostasis of calcium ions
---parathyroid glands secrete parathyroid hormone (PTH)
---raises blood levels of calcium and has effect opposite
of thyroid hormone calcitonin
---stimulates Ca2+ reabsorption in kidneys & induces
specialized bone cells (osteoclasts) to decompose
mineralized matrix of bone and release Ca2+ into
---vitamin D, synthesized in the skin and converted into
active form by many organs, essential to PTH function
---lack of PTH causes blood levels of calcium to drop
--leads to convulsive contractions of skeletal muscles
--if unchecked, tetany, is fatal
17. Distinguish between  and  cells in the pancreas and explain how
their antagonistic hormones (insulin and glucagon) regulate
carbohydrate metabolism.
---pancreas has both endocrine and exocrine functions
---islets of Langerhans are cluster of endocrine tissue
in pancreas
---secrete 2 hormones directly into circulatory system
---alpha () cells secrete peptide hormone glucagon
---beta () cells secrete the hormone insulin
---glucagon and insulin work together in antagonistic
manner to regulate the [] of glucose in blood
---in humans, blood glucose levels must remain about
90 mg/100 mL for proper body functioning
---at glucose levels above set point, insulin secreted
and lowers blood glucose [] by stimulating body
cells to take up glucose from blood
--also slows glycogen breakdown in liver and inhibits
conversion of amino acids/fatty acids to sugar
---when blood glucose levels drop below set point,
glucagon is secreted and increases blood glucose [] by
stimulating liver to increase hydrolysis of glycogen,
convert amino acids/fatty acids to glucose, and
slowly release glucose into blood
18. List hormones of the adrenal medulla, describe their function,
and explain how their secretion is controlled.
---medulla synthesizes/secretes catecholamines (epinephrine
and norepinephrine)
---secreted in times of stress
--nerve cells excited by stressful stimuli release the
neurotransmitter acetylcholine in medulla
--acetylcholine combines with cell receptors and
stimulates release of epinephrine
---norepinephrine released independently of epinephrine
---have rapid and dramatic effects on several targets
--glucose mobilized in skeletal and muscle cells
--fatty acid released from fat cells
--rate and stroke of heartbeat increased
--delivery of blood changed
--oxygen delivery to body cells increased
19. List the hormones of the adrenal cortex, describe their function,
and explain how their secretion is controlled.
---adrenal cortex synthesizes and secretes corticosteroids
---stressful stimuli cause hypothalamus to secrete
releasing hormone that simulates release of ACTH from
anterior pituitary
---ACTH stimulates release of corticosteroids from adrenal
---in humans, 2 primary types are glucocorticoids
(cortisol) and mineralocorticoids (aldosterone)
---glucocorticoids promote glucose synthesis from
noncarbohydrate substances such as proteins
--also have immunosuppressive effects and are used
to treat inflammation
---mineralocorticoids affect salt and water balance
--aldosterone stimulates kidneys to reabsorb sodium
ions and water from filtrate
---glucocorticoids/mineralocorticoids important to
maintaining body homeostasis during extended periods
of stress
20. Describe both the short-term and long-term endocrine responses
to stress.
---short-term stress responses trigger release of
epinephrine and norepinephrine
---long-term stress responses trigger the release of
mineralocorticoids and glucocorticoids
21. Identify male and female gonads, and list the three categories
of gonadal steroids.
---ovaries and testes
---androgens, estrogens, and progestins
---primary androgen is testosterone
---primary estrogen is estradiol
---progestins include progesterone
---gonadotropins from anterior pituitary (FSH & LH)
control synthesis of both androgens and estrogens
--FSH and LH controlled by gonadotropin-releasing
hormone (GnRH) from hypothalamus
22. Describe the location of the pineal and thymus glands, list their
hormone products, and describe their functions.
---pineal gland is small mass of tissue near center of
mammalian brain
---secretes melatonin; regulates functions related to
light and to seasons marked by changes in day length
--called biorhythms
---pineal contains light-sensitive cells or has nervous
connections from the eyes (depends on species)
---thymus is located just posterior to the sternum
---produces thymosin
--promotes development and maturation of lymphocytes
--important in immunity

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