Download Option D.5 Hormones and metabolism

Option D.5 Hormones and
metabolism
Essential idea: Hormones are not secreted at a uniform rate and exert
their effect at low concentration
D.5 Hormones and metabolism
Understandings:
• Endocrine glands secrete hormones directly into the bloodstream
• Steroid hormones bind to receptors proteins in the cytoplasm of the target cell to
form a receptor-hormone complex
• The receptor-hormone complex promotes the transcription of specific genes
• Peptide hormones bind to receptors in the plasma membrane of the target cell
• Binding of hormones to membrane receptors activates a cascade mediated by a
second messenger inside the cell
• The hypothalamus controls hormone secretion by the anterior and posterior
lobes of the pituitary gland
• Hormones secreted by the pituitary control growth, developmental changes,
reproduction, and homeostasis
D.5 Hormones and metabolism
Application and skills:
• Application: Some athletes take growth hormones to build muscles
• Application: Control of milk secretion by oxytocin and prolactin
Hormone
• Hormone- chemical messengers secreted by endocrine glands into
the blood and transported by the blood to specific target cells. Long
distance signaling molecules
Two major types of hormones:
1. Lipid soluble hormones- ex: steroid hormones come from gonads
(testosterone, estradiol (estrogen), and progesterone (progestin))
and the adrenal cortex (cortisol and aldosterone).
2. Water soluble hormones: ex: peptide hormones include oxytocin
(posterior pituitary) and ADH (posterior pituitary), calcitonin
(thyroid gland), tyrosine derivatives (epinephrine and
norepinephrine, thyroxin also known as T4 and Triiodothyronine)
Catecholamines (Tyrosine Derivatives)
• From phenylalanine
• Includes hormones such as epinephrine,
norepinephrine, and dopamine
• Water soluble
Steroid Hormones
Endocrine vs exocrine
• Endocrine glands release hormones directly into the bloodstream
• Pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland,
parathyroid gland, hypothalamus, and adrenal gland
• Exocrine glands release chemical substances through ducts
• Sweat, salivary, mammary, etc.
Hormones of the endocrine system
General mechanisms for chemical signaling
• A chemical signal secreted by a cell either
Binds to a receptor protein on the surface of a target cell, triggering
a signal-transduction pathway
Penetrates the target cell’s plasma membrane and binds to a
receptor inside the cell
Chemical signaling mechanism
Signal Transduction Pathway
• Peptide hormones act through signal transduction pathways
• A signal transduction pathway is a series of molecular changes that
convert an extracellular chemical signal to a specific intracellular
response
• Components of signal-transduction pathway include:
Reception of signal- signal receptor located in the plasma membrane
Transduction- might involve phosphorylation by a kinase, the
generation of a second signal using cyclic AMP (cAMP) or Ca++. In any
case a 2nd signal or 2nd message is generated
Third event is a cellular response
Signal Transduction Pathway
Signal That Binds to a
Surface Receptor That
Activates a Gene
Enzyme Cascade
• ATP is used to create
unstable phosphorylated
intermediates
cAMP can act as a second messenger
cAMP= Cyclic AMP
G Protein Receptor
Specific Mechanism of Action: Steroid
Hormones
Steroids hormones are able to pass through the
plasma membrane
1. Hormones such as estrogen and
testosterone bind to a receptor protein in
the cytosol activating it
2. Receptor-hormone complex enters the
nucleus and binds to specific genes
3. The bound protein stimulates the
transcription of the gene into mRNA
4. The mRNA is translated into specific protein
In other words…
• When the signal is bound to an intracellular receptor, the receptor
acts as a transcription factor, causing a change in gene expression
• The binding of signal to a surface receptor can lead to either a change
in gene expression or a change in cytoplasmic activity
Hormones of the hypothalamus and pituitary
glands
• The pituitary gland is located at the base of the brain and is
surrounded by bone
• It consists of the posterior pituitary (neurohypophysis) and the
anterior pituitary (adenohypophysis).
• The posterior pituitary is actually an extension of the hypothalamus
• Hormones secreted by the pituitary control growth, developmental
changes, reproduction, and homeostasis
Pituitary Gland Secretions
• Growth- Growth Hormone (GH) which stimulates mitosis and organism
growth. Targets liver to release insulin-like growth factor which
stimulates bone and cartilage growth
• Reproduction- LH (luteinizing hormone) and FSH (follicle stimulating
hormone). Prepares ovarian cells for ovulation in females, and needed for
sperm production in males.
• Developmental Changes- GH, LH, and FSH. GH is necessary for all
developmental growth throughout adulthood. LH and FSH secretions
increase during puberty, leading to ovulation and sperm production,
among other functions.
• Homeostasis- ADH (antidiuretic hormone): Secretion of ADH is needed for
the reabsorption of water from the collecting ducts in the kidneys.
Involved in osmoregulation
Posterior Pituitary
• Neurosecretory cells: many
endocrine organs and tissues
contain specialized nerve cells that
secrete hormones
• Animals have neurosecretory cells
in their brain that secrete
hormones into the blood
• The hypothalamus plays an
important role in integrating the
vertebrate endocrine and nervous
system
Posterior Pituitary
• Neurosecretory cells in the hypothalamus synthesize antidiuretic
hormone (ADH) and oxytocin
• These hormones are transported down the axons to the posterior
pituitary, where they are stored
• The posterior pituitary releases them upon stimulation into the
blood circulation
• ADH binds to target cells in the kidneys (collecting duct). Increases
water retention, thus decreasing urine volume.
• Oxytocin binds to target cells in the mammary glands (regulates milk
release during nursing) and uterus (induces muscular contraction).
Also functions in regulating mood and sexual arousal in both males
and females
Hormonal control of the kidney by negative
feedback circuits
• ADH enhances fluid retention by making the kidneys permeable to
water
• Neurosecretory cells in the supra-optic nucleus of the hypothalamus
synthesize ADH, transport it down axons, and store it in nerve endings
in the posterior pituitary gland
• The release of ADH is triggered by osmoreceptor cells in the
hypothalamus that detect an increase in osmolarity of blood
• If plasma becomes too concentrated impulses are passed to ADHsecreting neurosecretory cells, which convey the impulses to their
nerve endings in the posterior pituitary
• Impulses stimulate release of ADH into the blood from the stores in
nerve endings
• ADH causes reduction in the concentration of blood plasma by
stimulating the kidney to produce hypertonic urine
• Osmoreceptor cells also promote thirst. Drinking reduces osmolarity
of blood, which inhibits secretion of ADH, completing circuit
• If detectors sense low concentration of blood plasma, neurosecretory
cells are not stimulated to release ADH and blood levels of ADH levels
rapidly drop
Anterior Pituitary
Anterior Pituitary
• The release of hormones from the anterior pituitary gland is
controlled by the hypothalamus
• Neurosecretory cells in the hypothalamus secrete releasing
hormones and inhibiting hormones into a capillary network located
above the stalk of the pituitary
• The capillaries drain into the portal vessels (short blood vessels that
subdivide into a second capillary bed within the anterior pituitary)
• In this way, hypothalamic hormones have direct access to the gland
they control
D.A.5.2 Prolactin: Diversity of effects among
vertebrates
1. Stimulates mammary gland growth and milk synthesis in mammals
2. Regulates fat metabolism and reproduction in birds
3. Delays metamorphosis in amphibians
4. Regulates salt and water balance in freshwater fish
Suggests that prolactin is an ancient hormone with functions that have
diversified during the evolution of vertebrate groups
D.A.5.2 Control of milk secretion
Regulated by pituitary hormones
1. Prolactin is secreted by anterior
pituitary which stimulates mammary
glands to grow and to produce milk
2. During pregnancy, high estrogen levels
increase prolactin production but
inhibit its effects
3. Abrupt decline in estrogen following
birth ends this inhibition and milk
production begins
Control of milk secretion
4. Milk is produced in small spherical
chambers (alveoli) distributed
throughout gland
5. Oxytocin stimulates the let-down of
milk to a central chamber where it is
accessible to the baby
6. Physical stimulus of sucking (nursing)
by a baby (or breast pump) stimulates
oxytocin secretion by posterior
pituitary gland
Regulation of milk release: mediated by a
simple neurohormone pathway
1. Stimulus is received by a sensory neuron which stimulates a
neurosecretory cell
2. The neurosecretory cell then secretes a neurohormone which diffuses
into the blood stream and travels to target cells
3. In the case of oxytocin pathway, the initial stimulus is the infant’s
sucking (could also be the sight/sound/thought of the baby)
4. Stimulation of sensory nerve cells in the nipples generates signals in the
nervous system that reach the hypothalamus
5. A nerve impulse from the hypothalamus then triggers the release of
oxytocin from the posterior pituitary gland
6. In response to circulating oxytocin, the mammary gland secretes milk
• Have you ever wondered how breast milk production keeps up with
the growth of the infant?
• The answer involves positive feedback
• An example of positivefeedback mechanisms
• Oxytocin stimulates milk
release which leads to more
suckling and therefore more
stimulation
• Sustained until the baby stops
suckling
• Increased sucking also leads to
increased prolactin secretion
which leads to increased milk
production
D.A.5.1 Growth hormone (GH): Peptide
hormone
1. Secreted by the anterior pituitary
2. Major target is the liver which
responds by releasing insulin-like
growth factors (IGFs), which
circulate in the blood and directly
stimulate bone and cartilage
growth
3. Also exerts diverse metabolic
effects that tend to raise blood
glucose levels (opposing insulin)
Metabolic Effects of Growth Hormone
• Stimulates the synthesis of protein
• Stimulates the breakdown of fat
• Increases mitosis of cartilage cells and the mineralization of bone
• Stimulates increases in muscle mass and growth of all organs apart
from the brain
• GH has been used by athletes since the 1960s to help build muscles
• Some evidence that it does enhance performance in events
depending on muscle mass such as home-run hitting and weightlifting
Human Growth Hormone production
decreases with age
• Hypersecretion during childhood can
result in Gigantism (growth as tall as 8
feet)
• In adulthood, excessive GH production
stimulates bony growth in the few
tissues that are still responsive to the
hormone: face, hands and feet
• Hyposecretion results in pituitary
dwarfism (less than 4 ft.)
• Genetic engineering of bacteria allows
HGH to be made and is used in
treatment
Adverse effects of taking HGH
• Increased cholesterol levels
• Increased risk of diabetes
• Carpal tunnel syndrome
• Acromegaly (growth of bones of
face)
• Bloated gut