Download 17 - Endocrine Systems

PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
Endocrine and Neurendocrine Systems!
!Spring 2010!
Figure 15.1 Chemical signals act over short and long distances
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Main function is to maintain internal
homeostasis in response to internal and external
(environmental) changes.!
Accomplished via chemical messengers that
travel different distances to target cells and
regulate their activity.!
 Short range: Neurons and local paracrine/autocrine
cells produce and release chemical messengers
within micrometers of target cells!
 Long range: neurosecretory cells and non-neural
endocrine cells make hormones: chemical messengers
that travel via the circulatory system to target tissues
throughout the body.!
Endocrine Glands that function
Primarily to Secrete Hormones!
Pituitary gland: antidiuretic hormone (ADH), oxytocin, and
tropic hormones!
Thyroid gland: thyroxin, triiodothyronine and calcitonin!
Parathyroid glands: parathyroid hormone (PTH)!
Adrenal glands: many corticosteroids (e.g., cortisol,
aldosterone, and androgens), aned medullary hormones
(e.g., epinephrine, norepinephrine)!
Pancreatic islet cells: alpha cells secrete glucagon and beta
cells secrete insulin !
Ovaries and testes: estrogens, progesterone, and androgens !
Pineal gland: melatonin!
Thymus gland: thymosine!
Figure 15.6 Discrete glands probably evolved from diffusely distributed secretory cells
Organs That Function
Secondarily as Endocrine Glands!
Heart: secretes atrial natriuretic peptide (ANP)!
 Occurs when there is an expansion in blood volume. ANP causes
diuresis, increasing secretion of Na+ into the distal tubule and
concentrating it in the urine. Water follows by osmosis, decreasing the
blood volume.!
Kidney: secretes erythropoietin, which stimulates the bone
marrow to produce more red blood cells!
Liver: secretes somatomedin, a growth factor.!
Skin: secrets 1,25-dihydroxyvitamin D3 which is
responsible for calcium homeostasis!
Gastrointestinal tract: secrets gastrin, CCk, and VIP.!
Adipose tissue: secretes leptin, which plays a role in obesity!
Hypothalamus: secretes several releasing and inhibiting
hormones.!
Chemical Classification of Hormones!
Steroid hormones!
 All based on cholesterol. Secreted by adrenal cortex,
testes, and ovaries!
 Examples: aldosterone, cortisol, testosterone,
progestrone!
 Nonpolar and hydrophobic (lipophilic), must be
carried in the plasma by a protein that will bind with
the hormone and transport it to the target call!
•  Once it reaches the target cell the hormone is released!
•  It enters the cell and binds to receptors that are either within
the cytoplasm (that carry the hormone into the nucleus) or
proceeds directly through the nuclear membrane.!
•  Once in the nucleus, the hormone binds to a domain on a
chromosome, promoting transcription and protein synthesis.!
Topic 17 - 1!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
!Spring 2010!
Chemical Classification of Hormones!
Figure 15.2 Steroid hormones are derived from cholesterol
Protein and (glyco)peptide hormones!
 Secreted by all endocrine glands except adrenal
cortex, gonads and thyroid, e.g., insulin, LH, FSH!
 Generally present as a prohormone, they undergo
modification and become the active form of the
hormone later.!
 Polar (hydrophilic): can t cross the lipid bilayer of
cell membrane and must bind to cell membrane
receptors!
•  Once the hormone binds to the receptor, several changes
occur in the cytoplasmic side of the cell membrane which
then stimulates a second messenger (c-AMP , c-GMP,
phospholipase C, Ca2+, or thyrosine kinase)!
•  These then activate cytoplasmic proteins.!
Chemical Classification of Hormones!
Figure 15.3 Peptide and protein hormones consist of assemblages of amino acids
Tyrosine derivatives!
 Examples: thyroid hormone, catecholamines!
 Thyroxine is nonpolar and crosses the cell
membrane easily!
•  Very similar to steroids in size and is very water insoluble!
•  Carried mainly by thyroxine-binding globulin (TBG:
which carries T4 more than T3)!
•  Location of receptor proteins is in the nucleus of the target
cells. !
 Catecholamines (dopamine, epinephrine, and
norepinephrine), however, usually have receptors on
the target cell membrane!
Storage Properties of Hormones!
Figure 15.4 Amine hormones are derived from amino acids
Steroids: limited storage of the hormone, usually
produced on demand !
Peptides, proteins and catecholamines: storage is
also limited, ranging from one to several days!
Thyroxine: usually stored for a much longer period
in the thyroid gland, about several weeks in adults
(less in children)!
 More active thyroxine synthesis in children made
them more vulnerable to radioactive 131I after the
Chornobyl nuclear power plant exploded!
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Topic 17 - 2!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
!Spring 2010!
Figure 15.5 Snapshots of insulin synthesis, processing, and packaging
Secretion Mechanisms!
Steroids: once synthesized, diffuse through
the plasma membrane when needed.!
Thyroid hormone: secreted by proteolysis of
thyroglobulin; breaking it down releases
thyroxine and triiodothyronine.!
Peptides, proteins, catecholamines: generally
stored in vesicles and are secreted by
exocytosis.!
Plasma Protein Binding and Transport!
Steroids: non-polar, hydrophobic, lipophilic, so
rarely in free form in the circulation-need plasma
proteins for transport. Their t1/2 in blood ranges
over hours.!
Thyroxine: also non-polar, hydrophobic,
lipophilic, so needs plasma protein for transport.
The t1/2 in blood ranges over several days.!
Peptides, proteins: polar and hydrophilic-most do
not need plasma proteins for transport. Their t1/2
in blood is a few minutes.!
Catecholamines: also are not bound to plasma
proteins. Their t1/2 in blood is a few seconds. !
Hormone Receptors and Action!
Steroids: can pass through the cell membrane. Receptors
located either with the cytoplasm or in the nucleus.!
  Receptor-hormone complex controls DNA transcription.!
Thyroxine: Receptors located either with the cytoplasm or
in the nucleus.!
  Receptor-hormone complex controls transcription.!
Peptides, proteins, catecholamines: cannot pass through the
plasma membrane, so their receptors are on the outside of
the plasma membrane.!
  In peptides and proteins, hormone binding triggers synthesis
of cytolic second messengers or triggers protein kinase
activity.!
  In catecholamines, hormone binding causes change in
membrane potential or triggers synthesis of cytolic second
messengers.!
Hormonal Rhythm !
Pituitary Gland (Hypophysis)!
Pattern of secretion of the hormone over time. Actual
secretion is pulsatile (the hormone secretion starts and
stops, over and over).!
Circadian or diurnal rhythm: hormone is secreted every 24
hours. For example:!
  Cortisol is secreted about 2 hours before awakening. Its secretion pattern
depends on the light:dark cycle (which is cued by the photoperiod).!
  Growth hormone secretion, however, peaks during stages 3 and 4 of sleep,
whether at night or during the day. Its secretion pattern depends on what
is known as the sleep:wake cycle, which is an endogenous (internal)
rhythm.!
Connected to the hypothalamus by an infundibulum,
structurally and functionally divided into 2 lobes:!
  Posterior pituitary or neurohypophysis (neural of the
pituitary; pars distalis)!
  Anterior hypophysis (adenohypophysis)!
Ultradian Rhythm: hormone more frequently than once a
day (often every ½, 1, or 2 hours). Examples include:!
  Hormones involved in menstruation or seasonal breeding
(LH, FSH).!
  Hormones involved in sex cell production (e.g., testosterone).!
Topic 17 - 3!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
!Spring 2010!
Posterior Pituitary Hormones!
Figure 15.7 The vertebrate pituitary gland has two parts (Part 1)
Does NOT have cells that produce OR store hormones.
Neurosecretory cells of hypothalamus release hormones
directly into posterior pituitary, which are then rapidly
released into the systemic bloodstream:!
Oxytocin:!
  In females, it stimulates the contraction of the uterus during
labor, required for parturition ( childbirth ). Also stimulates
milk release in a lactating female mammals (contractions of
the mammary gland alveoli and ducts).!
•  When the baby suckles, touch receptors located in the nipple send
sensory signals to the hypothalamus, oxytocin is released, and milk
is ejected.!
•  When the baby stops suckling, stimulation ends and milk ejection
stops.!
  In males, it is secreted during ejaculation, causing uterine
contractions that aid movement of the sperm up the oviducts
where they then fertilize the egg. !
Posterior Pituitary Hormones!
Other Hypothalamic Hormones!
Antidiuretic hormone (ADH), also known as arginine
vasopressin (AVP)!
Control releases of anterior pituitary hormones:!
  Stimulates retention of water by the kidneys. High osmolarity
stimulates ADH: !
•  When osmolarity is high, more water will leave the osmoreceptors,
so they will shrink. This shrinking will stimulate the hypothalamus
to produce ADH, which is then released from the posterior
pituitary.ADH acts on the collecting ducts of the kidney, closing
water transport channels and thus decreasing water excretion. !
•  When there is an increase in blood volume, it is sensed by receptors
in the left atrium. These send signals to the hypothalamus that stop
it from producing ADH and thus increasing water excretion.!
  At high doses, causes ADH also causes vasoconstriction of
blood vessels (and is therefore also known as arginine
vasopressin, AVP)!
 Corticotropin releasing hormone (CRH) controls
release of ACTH.!
 Gonadotropin Releasing Hormone (GnRH) controls
release of LH and FSH.!
 Thyroid Releasing Hormone (TRH) controls release
of TSH.!
 Growth Hormone Releasing Hormone (GHRH)
promotes release of GH.!
 Somatostatin (SS) inhibits the secretion of GH
hormone. !
 Prolactin is regulated by hypothalamic inhibitory
hormone known as Prolactin-inhibiting hormone
(PIH).!
Anterior Pituitary Hormones!
Figure 15.7 The vertebrate pituitary gland has two parts (Part 2)
Secreted by pars distalis of adenohypophysis:!
Thyroid-stimulating hormone (TSH) acts on the thyroid
gland to produce T3 and T4.!
Adrenocorticotropic hormone (ACTH) acts on the
adrenal gland to secret glucocorticoids (e.g., cortisol),
mineralocorticoids (e.g., aldosterone) and sex steroids.!
Growth hormone (GH) acts all over the body, e.g.,!
  Stimulates the liver to produce IGF-I, which promotes cell
growth throughout the body.!
  Increases mass of body, including bones, muscle, and adipose
tissue (anabolic on proteins increases protein synthesis).!
  Acts catabolically on carbohydrates and lipids: increases
blood concentration of glucose and free fatty acids. Also has
an anti-insulin effect, stimulating carbohydrate breakdown.!
Topic 17 - 4!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
!Spring 2010!
Anterior Pituitary Hormones!
Figure 15.7 The vertebrate pituitary gland has two parts (Part 3)
Follicle-stimulating hormone (FSH) acts on gonads!
  In females: during the first part of the menstrual cycle, it
stimulates growth of ovarian follicle.!
  In males: FHS + testosterone induces maturation of
seminiferous tubules and stimulates beginning of sperm
production. Stimulates Sertoli cells, which guide developing
sperm cells through the stages of spermatogenesis and also
act as phagocytes, consuming the residual cytoplasm during
spermatogenesis. Translocation of germ cells from the base to
the lumen of the seminiferous tubules occurs by
conformational changes in the Sertoli cells.!
Luteinizing hormone (LH) also acts on gonads!
  In females: stimulates ovulation and conversion of ovulated
ovarian follicle into a corpus luteum.!
  In males: stimulates the secretion of male sex hormones
(mainly testosterone) from interstitial cells in testes.!
Figure 15.7 The vertebrate pituitary gland has two parts (Part 4)
Figure 16.8 The human female reproductive system (Part 3)
Figure 16.9 A synoptic view of events in the human female reproductive cycle
Figure 16.10 Hormonal control of estrogen production and secretion by an ovarian follicle
Topic 17 - 5!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
Figure 16.11 The human male reproductive system (Part 2)
!Spring 2010!
Figure 16.11 The human male reproductive system (Part 3)
Anterior Pituitary Hormones!
Figure 16.16 Mammary glands and lactation
Melanin-stimulating hormone (MSH) stimulates melanocytes,
causing darkening of the skin in fishes, amphibians, and
reptiles.!
  Darkening of the skin in these animals is#
temporary, and important in#
thermoregulation (darker animals absorb#
more heat).!
  The darkening occurs as granules of melanin#
(a brownish-black pigment that absorbs UV#
light) are spread through the branches of#
specialized melanocytes (melanophores).!
Prolactin (PL) is important in water and salt balance in many
vertebrates. Also acts on the breasts of mammals:!
  It stimulates breast development during pregnancy (not during
puberty).!
  In males, it facilitates reproductive function, however, too high levels
of PRL interfere with the secretion of LH and FSH which are needed
for spermatogenesis.!
Figure 15.8 The adrenal gland consists of an inner medulla and an outer cortex
Figure 15.9 Both hormonal and neural mechanisms modulate the action of the HPA axis
Topic 17 - 6!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
Figure 15.10 Interactions of insulin, glucagon, and epinephrine
!Spring 2010!
Figure 15.11 The mammalian stress response
Circadian Rhythms!
Figure 15.12 The CNS and the immune system interact during the stress response
Found in most organisms. All animals
produce endogenous circadian rhythms!
 Internal mechanisms that operate on an
approximately 24 hour cycle (generally 23-25
hours)!
 Regulates the sleep/wake cycle.!
 Also regulates the frequency of eating and
drinking, sensory sensitivity, nervous
sensitivity/synaptic excitability, body
temperature, secretion of hormones, mitotic
activity, volume of urination, and sensitivity
to drugs and toxicants.!
Figure 14.12 Daily rhythm of several physiological functions in a human
Topic 17 - 7!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
Endogenous Rhythms and External Cues!
!Spring 2010!
Figure 14.13 Circadian rhythm of metabolic rate (O2 consumption) and motor activity for a chaffinch
Endogenous rhythms remain remain consistent
despite lack of environmental cues indicating the
time of day. In the lack of such cues, the rhythm is
known as free-running.!
Rhythms also be entrained to an environmental cue
(daylight, tides, temperature).!
 Setting the phase of an environmental rhythm is a
phase factor (zeitgeber: time giver ).!
According to Ashoff s Rule, the period length of a
diurnal organism shortens as light intensity
increases (and vice-versa for a nocturnal organism).!
  In humans, rhythms run faster in bright light conditions and
subjects have trouble sleeping.!
  In constant darkness, humans have difficulty waking.!
Entrainment!
Figure 14.14 Activity rhythms of two nocturnal flying squirrels (Glaucomys volans)
Circadian period must be equal to or a multiple of the driver
(environmental oscillation) for the two to be coupled.!
Entrainment in many animals is due to extraocular
photoreceptors (entrainment is still seen in enucleated, or in
eyeless animals):!
  Insects in eclosion (pupation) often emerge at the same time.!
  Crayfish: 6th tail ganglion essential for setting the clock.!
  Birds: have about 20 extraretinal photoreceptors in the brain.!
  Photoreceptors known in amphibians and some reptiles!
  Mammals: may have a few located throughout the body.!
Entrainment can occur without light:!
  In Uta (a diurnal lizard) entrainment follows light:dark cycle,
regardless of temperature.!
  In Coleonyx (a nocturnal lizard) entrainment follows temperature and
light:dark cycle.!
Figure 14.16 The paired suprachiasmatic nuclei in the brain together constitute the major circadian
clock of mammals
Control of Circadian Rhythms!
In all vertebrates except mammals: control is in the pineal.
In mammals, a part of the hypothalamus, the
suprachiasmatic nucleus (SCN) is the main control center
of the circadian rhythms of sleep and temperature.!
  Damage to the SCN results in less consistent body rhythms
that are no longer synchronized to environmental patterns of
light and dark.!
The SCN is genetically controlled and independently
generates the circadian rhythms (a single cultured cell
continues to produce rhythmic action potentials).!
  SCN regulates waking and sleeping by controlling activity
levels in other areas of the brain.!
  The SCN regulates the pineal gland, an endocrine gland
located posterior to the thalamus.!
  The pineal gland secretes melatonin, a hormone that increases
sleepiness.!
Topic 17 - 8!
PSLY 4210/5210
!Comparative Animal Physiology
!Endocrine Systems!
Control of Circadian Rhythms!
Two types of genes are responsible for
generating the circadian rhythm.!
1.  Period - produce proteins called Per.!
2.  Timeless - produce proteins called Tim.!
Per and Tim proteins increase the activity of
certain kinds of neurons in the SCN that
regulate sleep and waking.!
Mutations in the Per gene result in odd
circadian rhythms.!
Topic 17 - 9!
!Spring 2010!