Chemical Coordination

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Chemical Coordination

• Chapter 34

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Hormones

• A hormone is a chemical signal that is secreted
  into the circulatory system and communicates
  regulatory messages within the body.
• Hormones may reach all parts of the body, but
  only certain types of cells, target cells, are
  equipped to respond.

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Systems of Internal Communication

• Animals have two systems of internal
  communication and regulation
• The nervous system
• The endocrine system

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Systems of Internal Communication

• The nervous system conveys high-speed electrical
  signals along specialized cells called neurons.
• The endocrine system, made up of endocrine
  glands, secretes hormones that coordinate slower
  but longer-acting responses to stimuli.

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Hormones

• Advantages of using chemical messengers
• Chemical molecules can spread to all tissues
  through the blood.
• Chemical signals can persist longer than
  electrical ones.
• Many different kinds of chemicals can act as
  hormones different hormones can target different
  tissues.

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Glands

• Many hormones are secreted by ductless endocrine
  glands.
• Obtain raw materials from and secrete hormones
  directly into the bloodstream.
• Exocrine glands have ducts for discharging
  secretions onto a free surface.
• Sweat glands, salivary glands, enzyme-secreting
  glands in the digestive tract.

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Hormones

• Hormones convey information via the bloodstream
  to target cells throughout the body.
• Pheromones carry messages outside the body to
  other individuals.

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Hormones

• Three major classes of molecules function as
  hormones in vertebrates
• Proteins and peptides
• Amines derived from amino acids
• Steroids

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Hormones

• Signaling by any of these molecules involves
  three key events
• Reception
• Signal transduction
• Response

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Hormones

• The hypothalamus regulates the neuroendocrine
  system, maintaining homeostasis in the body.
• The hypothalamus can use motor nerves to send
  short-lived electrical messages or hormones to
  send chemical messages with a longer duration.

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The Chain of Command

• The hypothalamus produces seven different
  releasing hormones that travel to the pituitary
  gland.
• Each releasing hormone stimulates the pituitary
  to release a corresponding hormone which travels
  to an endocrine gland and causes it to start
  producing a particular endocrine hormone.

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Membrane-Bound Receptors

• Many hormones are too large, or too polar, to
  pass through plasma membranes.
• Bind to transmembrane proteins that act as
  receptor sites on target cell membranes.
• Hormone is first messenger.
• Causes activation of a second messenger in the
  cytoplasm.
• cAMP

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Nuclear Receptors

• Steroid hormones are lipid soluble molecules that
  bind to hormone receptors in the cytoplasm of the
  target cell.
• Site of activity is the nucleus.
• Steroids are manufactured from cholesterol.
• Estrogen, progesterone, testosterone, cortisol.

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Nuclear Receptors

• Thyroid hormones and insect-molting hormone
  (ecdysone) also act through nuclear receptors.
• Binds to transmembrane protein that uses ATP to
  move it into the cell.

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Control Pathways and Feedback Loops

• A common feature of control pathways is a
  feedback loop connecting the response to the
  initial stimulus.
• Negative feedback regulates many hormonal
  pathways involved in homeostasis.

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Invertebrate Hormones

• Ecdysone regulates molting in insects.
• Juvenile hormone favors the retention of juvenile
  characteristics.

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The Pituitary

• The pituitary gland is located below the
  hypothalamus.
• Nine major hormones are produced here.
• These hormones act primarily to influence other
  endocrine glands.

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The Pituitary

• The posterior lobe of the pituitary regulates
  water conservation, milk letdown, and uterine
  contraction in women.
• The anterior lobe regulates the other endocrine
  glands.

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The Anterior Pituitary

• Thyroid stimulating hormone (TSH) stimulates
  the thyroid gland to produce thyroxine which
  stimulates oxidative respiration.
• Luteinizing hormone (LH) plays an important role
  in the menstrual cycle. It also stimulates the
  production of testosterone in males.

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The Anterior Pituitary

• Follicle-stimulating hormone (FSH) plays an
  important role in the menstrual cycle. In males,
  it causes the testes to produce a hormone that
  regulates sperm production.
• Adrenocorticotropic hormone (ACTH) stimulates
  the adrenal gland to produce steroid hormones.
  Some regulate glucose production, others balance
  sodium potassium in the blood.

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The Anterior Pituitary

• Growth hormone (GH) stimulates the growth of
  muscle and bone.
• Prolactin stimulates milk production.
• Melanocyte-stimulating hormone (MSH) in
  reptiles amphibians, this hormone stimulates
  color change.

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The Posterior Pituitary

• Antidiuretic hormone (ADH) regulates the kidneys
  retention of water.
• Oxytocin initiates uterine contraction during
  childbirth and milk release in mothers.
• These hormones are actually synthesized in the
  hypothalamus and stored in the posterior
  pituitary.

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Biological Clocks

• The pineal gland is located in the brain of most
  vertebrates.
• Evolved from a light sensitive third eye.
• Primitive fish some reptiles still have a third
  eye.

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Biological Clocks

• In other vertebrates it functions as an endocrine
  gland secreting melatonin.
• Melatonin controls color change in amphibians
  reptiles.
• Release of melatonin is controlled by light/dark
  cycles.
• The primary functions of melatonin appear to be
  related to biological rhythms associated with
  reproduction.
• Circadian rhythms 24 hours long.

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The Thyroid

• The thyroid gland, located in the neck, produces
• Thyroxine increases metabolic rate and promotes
  growth.
• Two iodine-containing hormones, triiodothyronine
  (T3) and thyroxine (T4).
• Calcitonin stimulates calcium uptake by bones.

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The Thyroid

• The hypothalamus and anterior pituitary control
  the secretion of thyroid hormones through two
  negative feedback loops.

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The Thyroid

• The thyroid hormones play crucial roles in
  stimulating metabolism and influencing
  development and maturation.

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The Parathyroids

• The parathyroid glands are four small glands
  attached to the thyroid.
• The hormone they produce is parathyroid hormone
  (PTH) which regulates the level of calcium in the
  blood.
• Essential that calcium is kept within narrow
  limits for muscle contraction, including the
  heart.

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Calcium Homeostasis

• Two antagonistic hormones, parathyroid hormone
  (PTH) and calcitonin, play the major role in
  calcium (Ca2) homeostasis in mammals.

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Calcium Homeostasis

• Calcitonin, secreted by the thyroid gland,
  stimulates Ca2 deposition in the bones and
  secretion by the kidneys, thus lowering blood
  Ca2 levels.
• PTH, secreted by the parathyroid glands, has the
  opposite effects on the bones and kidneys, and
  raises Ca2 levels.
• Also has an indirect effect, stimulating the
  kidneys to activate vitamin D, which promotes
  intestinal uptake of Ca2 from food.

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The Adrenals

• Mammals have an adrenal gland above each kidney.
• Adrenal medulla is the inner core which produces
  adrenaline (epinephrine) and norepinephrine.
• Adrenal cortex is the outer shell that produces
  the steroid hormones cortisol and aldosterone.

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Adrenal Medulla

• The adrenal medulla releases adrenalin
  (epinephrine) and norepinephrine in times of
  stress.
• Identical to the effects of the sympathetic
  nervous system, but longer lasting.
• Accelerated heartbeat, increased blood pressure,
  higher levels of blood sugar and increased blood
  flow to heart and lungs.

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Adrenal Cortex

• The adrenal cortex produces the steroid hormone
  cortisol (hydrocortisone).
• Reduces inflammation.
• Synthetic derivatives such as prednisone are used
  as anti-inflammatory agents.
• Stimulates carbohydrate metabolism.

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Adrenal Cortex

• The adrenal cortex also produces aldosterone.
• Aldosterone acts in the kidney to promote the
  uptake of sodium other salts from the urine.
• These salts are important in nerve conduction.
• Aldosterone and PTH are the only two hormones
  essential for survival.

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The Pancreas

• The pancreas is located behind the stomach and is
  connected to the small intestine by a small tube.
• It secretes digestive enzymes into the digestive
  tract (exocrine function).
• Endocrine function production of insulin and
  glucagon.

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Glucose Homeostasis

• The islets of Langerhans in the pancreas secrete
  insulin and glucagon.
• Insulin removes glucose from the blood.
• Glucagon returns glucose to the blood.

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Diabetes

• Diabetes mellitus, perhaps the best-known
  endocrine disorder, is caused by a deficiency of
  insulin or a decreased response to insulin in
  target tissues.
• Marked by elevated blood glucose levels.

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Diabetes

• Type I diabetes mellitus (insulin-dependent
  diabetes) is an autoimmune disorder in which the
  immune system destroys the beta cells of the
  pancreas.
• Type II diabetes mellitus (non-insulin-dependent
  diabetes) is characterized either by a deficiency
  of insulin or, more commonly, by reduced
  responsiveness of target cells due to some change
  in insulin receptors.