Chemical Signals in Animals

							Chemical Signals in
    Animals
     Chapter 47
    Chemical Signals in Animals
►  Hormone - chemical signal that circulates
  through the blood or other bodily fluids and
  affects distant target cells.
► The endocrine system is responsible for the
  production and secretion of hormones.
► There are six major categories of chemical
  signals in animals
► Six chemical messenger classes do not coincide
  with six structurally distinct classes of molecules
Hormone Structure
  and Function
             Autocrine Signals
► Autocrine signals act on the same cell that
 secretes them.
► An example is cytokines; most cytokines
 amplify the response of a cell to a stimulus
     Like in bone marrow cells for defense
► IL-1    is one of the most important immune
    responses, enhances the activation of T-
    cells in response to antigen
           Paracrine signals
► Paracrinesignals diffuse locally and act
 on neighboring cells
   May be due to degradation
► Growth  factors that are important in
  coordination of development
► Responses to allergens
► Has been linked to tumor growth and
  cancer
           Endocrine Signals
► Endocrine   signals are produced by cells
  that may be organized into discrete organs
  called glands or may be interspersed
  among the cells of other organs
► May be carried by blood or interstitial fluid
► Act on target cells throughout the body
► Hormones such as testosterone and
  estrogen
              Neural Signals
► Neuralsignals are the chemical
 messengers called neurotransmitters
► Causean action potential to be created in a
 neuron and create a neural signal
► Held   in vacuoles within the neuron
► Acetylcholine   stimulates muscle neurons
► Norepinephrine    stimulates wakefulness
       Neuroendocrine Signals
► Neuroendocrine      signals are released
  from neurons but act on distant cells
  instead of acting at the adjacent synapse
► Signals from stomach stimulate pituitary
  and brain cells to tell the brain and
  pituitary gland that it is full or it is empty
         Chemical Characteristics
             of Hormones
► The three types of chemical
 messengers: polypeptides, amino acid
 derivatives, and steroids
►All are similar in that they are
     Organic compounds
     Synthesized and secreted from the cells
     Act on target cells remote from their
      point of origin
        Chemical Characteristics
            of Hormones
► Similarities:
   Present in extremely small concentrations yet
    have large effects
► Key  difference in these hormone types is
  that steroids are lipid soluble but
  polypeptides and amino acid derivatives
  are not.
► Steroids cross cell membranes much more
  readily than do other types of hormones.
The Human Endocrine System—an
Overview

►  Organs that secrete
  hormones into the
  bloodstream are
  called endocrine
  glands
► The major human
  endocrine glands
  are:
             Hypothalamus
► Thehypothalamus,
 a region of the
 lower brain
   Contains different
    sets of
    neurosecretory cells
   Receive nerve
    signals from
    throughout the body
             Pituitary Gland
2.   The pituitary
     gland, which sits
     just below the
                                                    Hypothalamus




     hypothalamus and      Neurosecretory
                           cells of the                                Axon


     has distinct
                           hypothalamus




     anterior and
                            Posterior
                            pituitary
                                                                              Anterior
                                                                              pituitary

     posterior regions   HORMONE        ADH             Oxytocin


                         TARGET    Kidney tubules   Mammary glands,
                                                     uterine muscles
   Posterior Pituitary Hormones
► The two hormones released from the
  posterior pituitary
   Act directly on nonendocrine tissues
► Oxytocin
   Induces uterine contractions and milk ejection
► Antidiuretic   hormone (ADH)
   Enhances water reabsorption in the kidneys
        Anterior Pituitary Glands
► The   anterior pituitary
   Produces both tropic and nontropic hormones
► The   four strictly tropic hormones are
     Follicle-stimulating hormone (FSH)
     Luteinizing hormone (LH)
     Thyroid-stimulating hormone (TSH)
     Adrenocorticotropic hormone (ACTH)
             Thyroid Gland
►The   thyroid gland
  Situated in the Neck
  Consists of two
   lobes located on the
   ventral surface of
   the trachea
  Produces two
   iodine-containing
   hormones,
   triiodothyronine (T3)
   and thyroxine (T4)
            Thyroid Hormones
► The    thyroid hormones
   Play crucial roles in stimulating metabolism and
    influencing development and maturation
► Also important in maintaining homeostatic
  functions
► Hyperthyroidism, excessive secretion of
  thyroid hormones
   Can cause Graves’ disease in humans
► Hypothyroidism    can cause weight gain
         Thyroid and Parathyroid
                Hormones
► The  four parathyroid glands are embedded in
  the thyroid gland
► Act in opposition to thyroid
► 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
    therefore raises Ca2+ levels
   Also has an indirect effect, stimulating the kidneys to
    activate vitamin D, which promotes intestinal uptake of
    Ca2+ from food
         Kidneys and Adrenal Glands
5.   The two kidneys, which lie in the
     posterior part of the abdominal cavity
6.   The two adrenal glands, which sit atop
     the kidneys and have an outer cortex and
     a central medulla
     •    The adrenal medulla secretes epinephrine
          and norepinephrine
     •    In response to stress-activated impulses from
          the nervous system
                         Pancreas
7.Located in the anterior
  part of the abdominal
  cavity
► Two types of cells in the
  pancreas
        Secrete insulin and
         glucagon, antagonistic
         hormones that help
         maintain glucose
         homeostasis and are
         found in clusters in the
         islets of Langerhans
        Gonadal Sex Hormones
8.   Suspended below
     the pelvic cavity,
     respectively
►    Produce most of
     the body’s sex
     hormones:
     androgens,
     estrogens, and
     progestins
     What Do Hormones Do?
►  Hormones coordinate the activities of
  diverse groups of target cells
► Change according to environment or
  signals
► The stimuli to which hormones respond can
  be simple or complex
► Coordinate responses to environmental
  change
► Direct developmental processes
          Digestive Hormones
► Digestive  hormones function in simple stimulus-
  and-response circuits
► When acidic food passes from the stomach to the
  upper part of the small intestine, the food
  triggers intestinal cells to release secretin and
  cholecystokinin into the bloodstream
► Secretin induces the pancreas to secrete a
  solution that neutralizes acid
► Cholecystokinin causes the pancreas to
  secrete digestive enzymes into the small intestine
  and the gallbladder to eject bile salts into the
  intestine to emulsify fats
           Responses to Stress
►  When a person is in danger, hormones
  regulate both the short-term and long-term
  responses
► The short-term reaction—the fight-or-flight
  response—occurs through the activation of
  the sympathetic nervous system
► Long-term stress involves glucocorticoids
  produced in the adrenal cortex.
     Ensures the continued availability of fuel
      molecules to support important body functions
Stress and the Adrenal Gland
                                                                                        Stress



                                              Nerve                                              Hypothalamus
                            Spinal cord
                                              signals
                            (cross section)
                                                                       Releasing
                                                                       hormone
                                                              Nerve
                                                              cell
                                                                                      Anterior pituitary

                                                                                       Blood vessel

    Adrenal medulla                                       Nerve cell
secretes epinephrine
 and norepinephrine.                                                                                                       Adrenal cortex
                                                                                                                           secretes
                                                                               ACTH                                        mineralocorticoids
                                                                                                                           and glucocorticoids.

                                                            Adrenal
                                                            gland

                                                           Kidney


           (a) Short-term stress response                                             (b) Long-term stress response

            Effects of epinephrine and norepinephrine:                               Effects of                   Effects of
                                                                                     mineralocorticoids:          glucocorticoids:
         1. Glycogen broken down to glucose; increased
            blood glucose                                                          1. Retention of sodium       1. Proteins and fats
         2. Increased blood pressure                                                  ions and water by            broken down and
                                                                                      kidneys                      converted to glucose,
         3. Increased breathing rate
                                                                                                                   leading to increased
         4. Increased metabolic rate                                               2. Increased blood              blood glucose
                                                                                      volume and blood
         5. Change in blood flow patterns, leading to                                 pressure                  2. Immune system may
            increased alertness and decreased digestive
                                                                                                                   be suppressed
            and kidney activity
    How Do Hormones Direct
    Developmental Processes?
►  Growth hormones and sex hormones
  promote cell division, increase overall body
  size, and promote sexual differentiation as
  an individual matures.
► Certain hormones direct the development
  of particular cells and tissues at critical
  junctures in an individual’s life
► The major hormonal effects on
  development are:
    Primary Sex Determination
•   Events early in development that dictate
    whether the sex organs become male
    (testes) or female (ovaries)
•   Once they develop, they begin producing
    male-specific hormones (testosterone)
    or female-specific hormones (estradiol,
    a member of the estrogen family of
    hormones).
                 Puberty
•   At puberty, surges of sex hormones lead
    to the physical and emotional changes
    associated with adolescence
•   These developmental changes create the
    adult phenotype and the ability to
    produce offspring.
      Full Growth and Development

•   In humans and other mammals, the
    attainment of full adult stature is
    mediated by growth factors that are
    regulated by growth hormone produced
    in the pituitary gland.
             Reproduction
•   Most long-lived animals reproduce
    seasonally
•   In many species, environmental cues
    trigger the release of sex hormones
•   Although humans do not breed
    seasonally, sex hormones regulate sperm
    production and the menstrual cycle
    Hormones and Homeostasis
►  Hormones that act as messengers in
  homeostatic systems include antidiuretic
  hormone (ADH), aldosterone, and
  erythropoietin (EPO).
► Calcitonin and parathyroid hormone
  work together to keep Ca2+ levels in the
  blood close to a set point
 How are Hormones Regulated?
►  In many cases, hormone production is
  directly or indirectly controlled by the
  nervous system.
► Adrenocorticotropic hormone (ACTH)
  is a regulatory hormone that controls
  release of glucocorticoids from the adrenal
  cortex
► These hormones act as regulators and all
  are involved in negative feedback, or
  feedback inhibition
      47.4 How Do Hormones
        Act on Target Cells?
► Differences in lipid solubility influence
  where a target cell receives the chemical
  message.
► Steroids often act inside the cell, whereas
  most amino acid derivatives and all
  polypeptides act at the cell surface.
   Steroid hormone-receptor complexes bind to
    specific sites in DNA called hormone-
    response elements
     Hormones That Bind to Cell-
         Surface Receptors
►    Epinephrine and the peptide hormones are
    not lipid soluble and cannot enter the
    target cell
     They bind to receptors on the cell surface
► Activate the receptor on the cell surface by
  signal transduction
► Epinephrine produces two distinct patterns
  of responses because there are two types
  of receptor, alpha and beta
   Identifying the
Epinephrine Receptor
►  Epinephrine and its agonists
(molecules that bind to the same
receptors as the hormone itself)
produce two distinct patterns of
responses because there are two
types of receptor, alpha and beta.
In turn, there are two types of
alpha and two types of beta
receptor.
Signal Transduction and
   the Role of Second
       Messengers
 ►  Epinephrine activates
 phosphorylase, the enzyme that
 catalyzes the formation of glucose
 from glycogen (Figure 47.15).
    Epinephrine Signal
      Transduction
►    Epinephrine triggers
    a signal
    transduction
    cascade that includes
    cyclic adenosine
    monophosphate
    (cAMP) as a second
    messenger to
    amplify the signal