Endocrine%20signals%20are%20produced%20by%20endocrine%20cells%20that%20release%20signaling%20molecules,%20which%20are%20specific%20and%20can%20travel%20long%20distances%20through%20the%20blood%20to%20reach%20all%20parts%20of%20the%20body

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Cells communicate with each other through direct
contact with other cells or from a distance via
chemical signaling

• Endocrine signals are produced by endocrine cells
  that release signaling molecules, which are
  specific and can travel long distances through
  the blood to reach all parts of the body

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Endocrine Communication

• Animal hormones are chemical signals that are
  secreted into the circulatory system and
  communicate regulatory messages within the body
• Hormones reach all parts of the body, but only
  target cells are equipped to respond

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Two systems coordinate communication throughout
the body the endocrine system and the nervous
system

• The endocrine system secretes hormones that
  coordinate slower but longer-acting responses
  including reproduction, development, energy
  metabolism, growth, and behavior

• The nervous system conveys high-speed electrical
  signals along specialized cells called neurons
  these signals regulate other cells

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Endocrine Signaling

• Endocrine signals (hormones) are secreted into
  extracellular fluids and travel via the
  bloodstream

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Paracrine and AutocrineSignaling

• Local regulators are chemical signals that travel
  over short distances by diffusion
• Local regulators help regulate blood pressure,
  nervous system function, and reproduction
• Two types
• Paracrine signals act on cells near the secreting
  cell
• Autocrine signals act on the secreting cell
  itself

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Synaptic Signaling and Neuroendocrine Signaling

• At synapses, neurons often secrete chemical
  signals called neurotransmitters that diffuse a
  short distance to bind to receptors on the target
  cell
• Neurohormones are a class of hormones that
  originate from neurons in the brain (i.e.
  hypothalamus) and diffuse through the bloodstream
  to act on target cells (possibly an endocrine
  gland to produce a 2nd hormone).

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Receptor Location Varies with Hormone

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

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One Hormone Different Effects

• The same hormone may have different effects on
  target cells that have
• Different receptors for the hormone
• Different signal transduction pathways
• Different proteins for carrying out the response
• A hormone can also have different effects in
  different species

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Fig. 45-10
Major endocrine glands
Hypothalamus
Pineal gland
Pituitary gland
Organs containing endocrine cells
Thyroid gland
Thymus
Parathyroid glands
Heart
Liver
Adrenal glands
Stomach
Pancreas
Kidney
Testes
Small intestine
Kidney
Ovaries
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• A negative feedback loop inhibits a response by
  reducing the initial stimulus
• Negative feedback regulates many hormonal
  pathways involved in homeostasis

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Insulin Glucagon control blood glucose

• Pancreas contains clusters of endocrine cells
  known as Islets of Langerhans
• Islets of Langerhans contain alpha and beta cells
• Beta cells secrete insulin which triggers uptake
  of glucose from the blood
• Alpha cells secrete glucagon which promotes the
  release of glucose into the blood
• Hormones secreted into the interstitial fluid and
  enter circulatory system

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Insulin Glucagon

• Insulin stimulates nearly all body cells to
  take up glucose
• Insulin slows glycogen breakdown in liver and
  glucose production
• Glucagon targets cells in liver to increase
  glycogen hydrolysis release glucose into the
  bloodstream
• Negative Feedback stimulus leads to release of
  hormone which works on target cell to bring about
  response response shuts off hormone

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Diabetes Melitus

• Causes
• Deficiency of insulin
• Decreased response to insulin
• Results in increased blood glucose levels
• Body forced to use fat as main fuel can result
  in acidic metabolite build up lowering pH
• Kidney cant handle high level of glucose in
  blood sugar in urine leading to frequent
  urination and extreme thirst

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Type I Diabetes

• Insulin-dependent diabetes is an autoimmune
  disorder in which the immune system destroys the
  beta cells of the pancreas
• Often thought of as childhood diabetes
• Destroys a persons ability to produce insulin
• Treatment insulin injections

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Type 2 Diabetes

• Target cells fail to respond to insulin blood
  glucose levels remain high
• Develops with age usually around 40
• Excess weight and lack of exercise can
  contribute to type 2 diabetes
• Most common form of diabetes

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Human Growth Hormone

• Releasing hormones from hypothalamus trigger
  anterior pituitary to secrete growth hormone
• Growth Hormone has Tropic effects (regulates
  other endocrine cells) and Nontropic effects
  (targets nonendocrine cells)
• Major target of GH is the liver which secretes
  IGFs (insulin-like growth factors) which
  stimulate bone and cartilage growth

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Gigantism

• Hypersecretion of GH during childhood can lead to
  gigantism
• Person grows unusually tall
• Results in overgrowth of extremities in adults
  (acromegaly)

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Dwarfism

• Hyposecretion of GH in childhood retards long-bon
  growth and can pituitary dwarfism
• If diagnosed before puberty, can be treated with
  HGH

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Thyroid Hormones

• The thyroid gland consists of two lobes on the
  ventral surface of the trachea
• It produces two iodine-containing hormones
  triiodothyronine (T3) and thyroxine (T4)
• The thyroid is regulate by Thyroid Stimulating
  Hormone (TSH) from the antior pituitary

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Thyroid Gland

• Triiodothyroxine (T3) called T3 because it has
  three iodine atoms
• thyroxine (T4) called T4 because it has four
  iodine atoms
• Both have basically the same effect
• Bone and nerve cell development
• Help maintain normal blood pressure, heart rate,
  muscle tone, digestion reproductive function

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Hyperthyroidism

• Hyperthyroidism, excessive secretion of thyroid
  hormones, causes high body temperature, weight
  loss, irritability, and high blood pressure
• Graves disease is a form of hyperthyroidism in
  humans
• In Graves disease, the body's natural defense
  (immune) system attacks the thyroid gland. The
  thyroid fights back by making too much thyroid
  hormone

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Hypothyroidism

• Hypothyroidism, low secretion of thyroid
  hormones, causes weight gain, lethargy, and
  intolerance to cold

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Iodine Deficiency
Goiter Excess TSH enlarge the thyroid gland
results in a large swelling just above the breast
bone. Rarely, it may constrict the trachea
(windpipe) or esophagus and cause difficulty
breathing or swallowing. The rest of the symptoms
come from thyroxin or the lack of it.

• Severe iodine deficiency causes problems because
  the thyroid can never produce enough T3 and T4
  but is still continually stimulated by TSH
  resulting in elargement
• childhood can cause cretinism
• Adulthood can cause goiter

Cretinism congenital condition due to thyroid
hormone deficiency during fetal development and
marked in childhood by dwarfed structure, mental
retardation dystrophy of the bones, and low basal
metabolism
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Antidiuretic Hormone

• Neurosecretory cells extend from the hypothalamus
  into the posterior pituitary where ADH is
  released into the blood stream
• Antidiuretic hormone (ADH) enhances water
  reabsorption in the kidneys

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Luteinizing Hormone and Follicle Stimulating
Hormone

• Male

• Females

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Estrogen

• Estrogens, most importantly estradiol, are
  responsible for maintenance of the female
  reproductive system and the development of female
  secondary sex characteristics

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Testosterone

• The testes primarily synthesize androgens, mainly
  testosterone, which stimulate development and
  maintenance of the male reproductive system
• Testosterone causes an increase in muscle and
  bone mass and is often taken as a supplement to
  cause muscle growth, which carries health risks

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Fig. 45-16
Pathway
Example
Stimulus
Suckling

Sensoryneuron
Hypothalamus/posterior pituitary
Neurosecretorycell
Posterior pituitarysecretes oxytocin ( )
Positive feedback
Bloodvessel
Targetcells
Smooth muscle inbreasts
Response
Milk release
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Positive Feedback Hormones

• Oxytocin induces uterine contractions and the
  release of milk
• Suckling sends a message to the hypothalamus via
  the nervous system to release oxytocin, which
  further stimulates the milk glands