Animal Hormones

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Animal Hormones
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Introduction

• Chemical messages or hormones produce and
  coordinate anatomical physiological and
  behavioral changes in an animal.

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Hormones and Their Actions

• Control and regulation require information.
• In multicellular animals hormones provide
  chemical signals.
• Hormones are secreted by cells diffuse into the
  extracellular fluid and often are distributed by
  the circulatory system.

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Hormones and Their Actions

• Hormone-secreting cells are called endocrine
  cells.
• Cells receiving the hormonal message are called
  target cells and must have appropriate receptors.
• The binding of the receptor activates a response.
• The distance over which the signal operates
  distinguishes hormone groups some act close to
  the release site others at distant body
  locations.

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Hormones and Their Actions

• Hormones can be classified into three main
  groups
• Peptides or proteins water soluble transported
  by vesicles out of the cell that made them.
• Steroids lipid-soluble diffuse out of the cell
  that made them but in the blood they must be
  bound to carrier proteins.
• Amine derivatives of the amino acid tyrosine
  water-soluble and lipid-soluble.

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Hormones and Their Actions

• Some hormones act on distant cells these get
  into the circulatory system.
• Some hormones act locally these never get into
  the circulatory system.
• Autocrine hormones act on the secreting cell
  itself.
• Paracrine hormones act on cells near the site of
  release.
• released in tiny amounts
• are inactivated rapidly by enzymes
• are taken up efficiently by local cells.

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Figure 42.1 Chemical Signaling Systems
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Hormones and Their Actions

• Most hormones diffuse into the blood which
  distributes them throughout the body.
• When the hormone message encounters a cell with
  the proper receptor it binds and triggers a
  response.
• The same hormone can cause different responses in
  different types of cells.
• An example is epinephrine. The nervous system
  reacts to an emergency very quickly and
  stimulates adrenal cells to secrete epinephrine.
  The result is the fight-or-flight response.

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Hormones and Their Actions

• The epinephrine acts on different cells in the
  body
• In the heart it stimulates faster and stronger
  heartbeat.
• Blood vessels in some areas constrict to send
  more blood to muscles.
• In the liver glycogen is broken down to glucose
  to provide quick energy.
• In fat tissue fats are mobilized as another
  energy source.

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Hormones and Their Actions

• Endocrine refers to cells or glands that do not
  have ducts leading to the outside of the body
  they secrete their products directly into the
  extracellular fluid.
• Some endocrine cells are single cells within a
  tissue.
• Some endocrine cells aggregate into secretory
  organs called endocrine glands.
• In vertebrates nine major endocrine glands make
  up the endocrine system.

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Figure 42.2 The Endocrine System of Humans
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Vertebrate Endocrine Systems

• The pituitary gland of mammals is a link between
  the nervous system and many endocrine glands and
  plays a crucial role in the endocrine system.
• The pituitary gland sits in a depression at the
  bottom of the skull and is attached to the
  hypothalamus.
• The pituitary is made of two parts anterior and
  posterior.

The Pituitary Gland
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Vertebrate Endocrine Systems

• The posterior pituitary releases two hormones
  antidiuretic hormone and oxytocin.
• They are made by neurons in the hypothalamus and
  are packaged in vesicles.
• The vesicles are transported down the axons of
  the neurons that made them and are stored in the
  posterior pituitary.

- The function of antidiuretic hormone (ADH) is
to increase water conservation by the kidney. -
The function of oxytocin is to stimulate uterine
muscle contraction for the birth process.
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Vertebrate Endocrine Systems

• The Anterior Pituitary releases four tropic
  hormones which control activities of other
  endocrine glands.
• The four tropic hormones are
• thyrotropin (stimulates the thyroid gland)
• adrenocorticotropin
• luteinizing hormone
• follicle-stimulating hormone.

Anterior lobe of the human pituitary gland.
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Vertebrate Endocrine Systems

• Other peptide and protein anterior pituitary
  hormones influence tissues that are not endocrine
  glands.
• These include
• growth hormone (acts on many tissues to promote
  growth)
• prolactin (stimulates the production and
  secretion of milk in female mammals)
• melanocyte-stimulating hormone
• endorphins enkephalins (molecules that act as
  neurotransmitters in pain pathways)

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Vertebrate Endocrine Systems

• The anterior pituitary is controlled by
  neurohormones from the hypothalamus.
• The hypothalamus obtains data about body
  conditions and the external environment through
  both neuronal and hormonal signals.
• Secretions from hypothalamic nerves are
  transported by blood vessels to the anterior
  pituitary.

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Figure 42.8 Multiple Feedback Loops Control
Hormone Secretion
The anterior pituitary cells are also under
negative feedback control by the hormones of the
glands that they stimulate.
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Vertebrate Endocrine Systems

• The thyroid gland located near the trachea is
  an example of an endocrine gland that is
  controlled by negative feedback.
• The thyroid gland produces the hormone thyroxine
  in specialized structures called follicles.
• Thyroxine has many roles in regulating metabolism.

Thyroid and parathyroid
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Vertebrate Endocrine Systems

• The four parathyroid glands are embedded in the
  posterior surface of the thyroid gland.
• It is important in regulating blood calcium
  levels
• Low blood calcium release of parathyroid
  hormone
• causes specialized cells to dissolve bone and
  release calcium
• promotes calcium resorption by the kidney to
  prevent loss in the urine
• promotes vitamin D (actually a hormone)
  activation which stimulates the gut to absorb
  calcium from food.
• High blood calcium release of calcitonin
• lower calcium levels in the blood.

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Vertebrate Endocrine Systems

• Diabetes mellitus is a disease caused by a lack
  of the protein hormone insulin (Type I) or a lack
  of insulin receptors on target cells (Type II).
• Insulin binds to receptors on the cell membrane
  and allows glucose uptake.
• Without insulin or the receptors glucose
  accumulates in the blood until it is lost in
  urine.

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Vertebrate Endocrine Systems

• High glucose levels in the blood cause water to
  move from the cells into the blood by osmosis.
• The kidneys then increase urine output to get rid
  of the fluid excess.
• Cells not taking up glucose use fat and protein
  for fuel resulting in the bodys wasting away
  and tissue and organ damage.

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Vertebrate Endocrine Systems

• Insulin is produced in the pancreas in cell
  clusters called islets of Langerhans.
• The remainder of the pancreas acts as an exocrine
  gland with digestive functions.

Human Pancreatic Islet
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Vertebrate Endocrine Systems

• After a meal blood glucose levels rise and
  stimulate the b cells to release insulin.
• Insulin stimulates cells to use glucose and to
  convert it to glycogen and fat.
• When blood glucose levels fall the pancreas
  stops releasing insulin and cells switch to
  using glycogen and fat for energy.
• If blood glucose falls too low the cells release
  glucagon which stimulates the liver to convert
  glycogen back to glucose.

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Vertebrate Endocrine Systems

• The adrenal glands are made up of the adrenal
  medulla and the adrenal cortex.

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Vertebrate Endocrine Systems

• The medulla produces
• epinephrine (response to stress initiating
  fight-or-flight reactions - increased heart
  breathing rates elevated blood pressure)
• norepinephrine (a neurotransmitter involved in
  physiological regulation)

Adrenal medulla
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Vertebrate Endocrine Systems

• Adrenal cortex cells use cholesterol to produce
  three classes of steroid hormones called
  corticosteroids
• Glucocorticoids influence blood glucose
  concentrations and other aspects of fuel molecule
  metabolism.
• Mineralocorticoids influence extracellular ionic
  balance.
• Sex steroids stimulate sexual development and
  reproductive activity. These are secreted in only
  minimal amounts by the adrenal cortex.

Human adrenal gland
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Vertebrate Endocrine Systems

• The gonads (testes and ovaries) produce steroid
  hormones synthesized from cholesterol.
• Androgens are male steroids the dominant one
  being testosterone.
• Estrogens and progesterone are female steroids
  the dominant estrogen being estradiol.
• Sex steroids determine whether a fetus develops
  into a male or female.
• After birth sex steroids control maturation of
  sex organs and secondary sex characteristics such
  as breasts and facial hair.

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Vertebrate Endocrine Systems

• Sex steroid production increases rapidly at
  puberty or sexual maturation in humans.
• Control of sex steroids (both male and female) is
  under the anterior pituitary tropic hormones
  called luteinizing hormone (LH) and
  follicle-stimulating hormone (FSH).
• These gonadotropins are controlled by the
  hypothalamus.

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Vertebrate Endocrine Systems

• Synthetic androgens (anabolic steroids) can
  exaggerate body strength and muscle development.
• Negative side effects in females include more
  masculine body features such as shrinking the
  uterus and causing an irregular menstrual cycle.
• In males the negative side effects include
  shrinking of the testes enlarged breasts and
  sterility.
• Continued use of anabolic steroids may increase
  risk of heart disease some cancers kidney
  damage and personality disorders.