Download Chapter 41 Animal Hormones

Chapter 42 Animal Hormones
Biology 102
Tri-County Technical College
Pendleton, SC
Two Major Systems
Nervous system involved with high-speed
messages
Estes and the Dutch Oven…oh yeah!!!!
Endocrine system is much slower and
involves production, release, and movement
of chemical messages
As always, it is the subtle interplay between
the two systems that COUNTS…
Endocrine System
Components
Most endocrine glands/tissue contain
neurosecretory cells that secrete
hormones
Chemical signal that communicates regulatory
messages within body
Hormones reach all parts of body but only
certain types of cells [target cells] are
equipped to respond
Only target cells respond because ONLY they
have receptors for that hormone
Target Cell Visual
Insect Development
Hormones
In insects/crustaceans, molting triggered by
ecdysone
Secreted (insects) by prothoracic glands just
behind head
Favors development of adult characteristics
i.e., from caterpillar to butterfly
Ecdysone production in 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
General Chemical Classes
Peptide hormones: oxytocin, ADH,
calcitonin, PTH, and thymosin
Protein hormones: GH, prolactin, insulin,
and glucagon
Glycoprotein hormones: FSH, LH, TSH
Amine hormones: T3 and T4, epinephrine
and norepinephrine, and melatonin
Steroid hormones: glucocorticoids,
mineralocorticoids, androgens, estrogens, and
pregesterone
Two General Classes
Hormones can be divided into two
general classes: steroid and nonsteroid
Nonsteroid hormones such as amines,
peptides, and proteins usually combine
with receptors in target cell membrane
First messenger/second messenger
Signal transduction pathway: converts
extracellular chemical signal to specific
intracellular response
Classes, cont.
Steroid hormones are lipid-soluble and
easily diffuse into cells
Once inside target cell, steroid hormone
MAY combine with specific protein
molecules (the receptor[s]) or they may
exert their influence directly
Typically, steroid hormone bind with
their specific protein receptor
Stirring the Steroids…
Steroids easily cross plasma membrane
Binding of steroid (signal molecule) with
specific receptor (usually in nucleus) initiates
signal transduction process
Signal initiates cascade of events in which
proteins interact with other proteins until final
response(s) are achieved
In many cases, signal-receptor complex binds
to DNA to modify gene expression
Target Cell Specificity
Each chemical signal has specific shape
recognized by that signal’s target cells
Signal’s action begins when it binds to specific
receptor
Receptor protein may be in PM of target cell
or inside the cell
Diversity of responses of target cells depends
on nature of target cell and the affinity of
receptor molecules on or within cell
Cells are unresponsive to signal if they lack
appropriate receptors
Hypothalamus
Hypothalamus is region of lower brain
Hormone releasing cells are 2 sets of
neurosecretory cells whose secretions are
stored in posterior pituitary (antidiuretic
hormone/oxytocin)
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
Hypothalamus, cont.
Hypothalamic hormones have direct
access to gland they control
(releasing/release-inhibiting hormones)
Pituitary: Location/Function
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 and
secrete several hormones directly into blood
Pituitary, cont.
Posterior pituitary (neurohypophysis) is
extension of the brain
Stores and secretes 2 hormones made by
hypothalamus
Oxytocin: contraction of uterus and
mammary gland cells; regulated by nervous
system
Antidiuretic hormone (ADH): promotes
water retention by kidneys; regulated by
water/salt balance
ADH/Homeostasis/Neg. FB
Osmoreceptors in hypothalamus monitor
blood osmolarity
Plasma osmolarity >s; osmoreceptors shrink
slightly and transmit nerve impulse 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 the kidneys
ADH, cont.
ADH binds to receptors on target-cells
and activates signal-transduction
pathway that increases water
permeability of collecting ducts
Water retention is >ed as water exist
collecting ducts and enters nearby
capillaries
Osmoreceptors also simulate thirst drive
ADH III
As more dilute blood (lower osmolarity)
arrives at brain, hypothalamus responds by
reducing ADH secretion and lowering thirst
sensation
This prevents overcompensation by stopping
hormone secretion and quenching thirst
This negative feedback scheme includes
hormonal action and behavioral response
Tropic Hormones
Have other endocrine glands as their targets
Four of hormones secreted by anterior
pituitary gland are tropic hormones
Thyroid-stimulating hormone (TSH))
stimulates thyroid gland
Adrenocorticotropic hormone (ACTH)
stimulates adrenal cortex to secrete
glucocorticoids
Tropic Hormones, cont.
Follicle-stimulating hormone (FSH)
stimulates production of ova and sperm
Luteinizing hormone (LH) stimulates
ovaries and testes
Anterior pituitary also secretes other
hormones with profound effects on body:
Growth hormone (GH), Prolactin; Melanocytestimulating hormone; Endorphins and
enkephalins
Control of Anterior Pituitary
Neurosecretory cells in hypothalamus exert
control over anterior pituitary by secreting 2
kinds of hormones into blood
Releasing hormones: anterior pituitary
secretes its hormones
Inhibiting hormones: make A.P. stop secreting
hormones
Is subtle blend of R and I hormones that
control timing and amount of hormonal
release by A.P.
Thyroid Gland
In humans/other mammals, thyroid
gland consists of 2 lobes located on
ventral side of trachea
Produces 2 very similar hormones from
tyrosine
Triiodothyronine (T3) and
Tetraiodothyronine (T4)/thyroxine
In mammals, T3 is more active form
Thyroid, cont.
Thyroid important in human development
Deficiency (cretinism) results in markedly
retarded skeletal growth/poor mental
development
Thyroid hormones important for normal
functioning of bone-forming cells and for
branching nerve cells during embryonic
development of the brain
In adults, help maintain normal BP, heart
rate, muscle tone, digestion, and reproductive
functions
Thyroid III
Hyperthyroidism (> amounts)
produces high body temperature,
profuse sweating, weight loss,
irritability, and high BP
Hypothyroidism (< amounts)
produces cretinism in infants and
symptoms of weight gain, lethargy, and
intolerance to cold in adults
Thyroid IV
Deficiency of iodine in diet can lead to
shortage of thyroid hormones and
cause enlargement of thyroid called a
goiter
Thyroid also produces calcitonin which
lowers calcium levels in blood as part of
calcium homeostasis
Stimulates osteoblasts to use circulating
calcium to deposit new bone
Thyroid Hormones Loop
HypothalamusTRH (thyroid releasing
hormone) [some texts call thyrotropinreleasing hormone or TRH] to anterior
pituitaryTSH (thyroid stimulating
hormone)induces thyroid to manufacture
and release T3 and T4
Increasing levels of TSH, T3, and T4 signal
hypothalamus to reduce secretion of TRH
Parathyroid Glands
Four parathyroid glands embedded in
surface of thyroid
Function in homeostasis of calcium ions
Parathyroids secrete parathyroid
hormone (PTH)
Raises blood levels of calcium [has
opposite effect of thyroid hormone
calcitonin
Parathyroids, cont.
Stimulates Ca2+ reabsorption in kidneys and
induces osteoclasts to decompose
mineralized matrix of bone and release Ca2+
into blood
Vitamin D (synthesized in skin) essential to
PTH function
Lack of PTH causes blood levels of calcium to
drop dramatically
Leads to convulsive contractions of skeletal
muscles
If unchecked, tetany follows which is FATAL!!!
Pancreas
Pancreas has both endocrine and exocrine
functions
Islets of Langerhans are cluster of
endocrine tissue in the pancreas which
secretes 2 hormones directly into circulatory
system
Alpha (α) cells secrete peptide hormone
called glucagon
Beta (β) cells secrete the hormone insulin
Hormones of Pancreas
Glucagon and insulin work together
(antagonistic) to regulate [ ] 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
Pancreas III
Insulin also slows glycogen breakdown in liver
and inhibits conversion of AAs/fatty acids to
sugar
Blood glucose levels drop below set point,
glucagon is secreted and increases blood
glucose [ ] by stimulating liver to increase
hydrolysis of glycogen, convert AAs/Fas to
glucose, and slowly release glucose into blood
Adrenal Medulla
Adrenal medulla synthesizes/secretes
catecholamines (epinephrine and
norepinephrine)
Secreted in times of stress
Nerve cells excited by stressful stimuli release
neurotransmitter acetylcholine in medulla
Acetylcholine combines with cell receptors
and stimulates release of epinephrine
Norepinephrine released independently of
epinephrine
Adrenal Medulla, cont.
Have rapid/dramatic effect on several
targets
Glucose mobilized in skeletal muscle
cells
Fatty acid released from fat cells
Rate and stroke of heartbeat increased
Delivery of blood changed
Oxygen delivery to body cells increased
Adrenal Cortex
Adrenal cortex synthesizes and secretes
corticosteroids
Stressful stimuli cause hypothalamus to
secrete releasing hormone that stimulates
release of ACTH from anterior pituitary
ACTH stimulates release of corticosteriods
from adrenal cortex
In humans, 2 primary types are
glucocorticoids (cortisol) and
mineralocorticoids (aldosterone)
Adrenal Cortex, cont.
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
Aldosteone stimulates kidneys to reabsorb
sodium ioins and water from filtrate
Adrenal Cortex III
Glucocorticoids/mineralocorticoids important
to maintaining body homeostasis during
extended periods of stress
Short-term stress responses triggers
release of epinephrine and norepinephrine
(fight or flight)
Long-term stress responses trigger the
release of mineralocorticoids and
glucocorticoids
Gonadal Hormones
In humans, gonads are ovaries and
testes
Hormones are androgens, estrogens,
and progestins
Primary androgen is testosterone
Primary estrogen is estradiol
Progestins include progesterone
Gonadal Hormones, cont.
Gonadotropins from anterior pituitary
(FSH and LH) control synthesis of both
androgens and estrogens
FSH and LH controlled by gonadotropinreleasing hormone (GnRH) from
hypothalamus
Wrapping it up…so to speak
Pineal gland is small mass of tissue near
center of mammalian brain
It secretes melatonin which regulates
functions related to light and to seasons
marked by changes in day length
(biorhythms)
Pineal contains light sensitive cells or has
nervous connections from the eyes (depends
on species)
Some studies indicate it has role in fertility
Wrapping, cont.
Thymus is located just posterior to sternum
Produces thymosin
Promotes development and maturation of
lymphocytes
Important in immunity
Larger and most active in younger years, by
adulthood, has atrophied and is mostly just
gone….as is this chapter…