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Chemical Signals in Animals

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Title: Chemical Signals in Animals


1
Chemical Signals in Animals
  • Chapter 47

2
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

3
Hormone Structure and Function
4
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

5
Paracrine signals
  • Paracrine signals 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

6
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

7
Neural Signals
  • Neural signals are the chemical messengers called
    neurotransmitters
  • Cause an 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

8
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

9
Chemical Characteristicsof 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

10
Chemical Characteristicsof 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.

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12
The Human Endocrine Systeman Overview
  • Organs that secrete hormones into the
    bloodstream are called endocrine glands
  • The major human endocrine glands are

13
Hypothalamus
  • The hypothalamus, a region of the lower brain
  • Contains different sets of neurosecretory cells
  • Receive nerve signals from throughout the body

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15
Pituitary Gland
  • The pituitary gland, which sits just below the
    hypothalamus and has distinct anterior and
    posterior regions

16
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

17
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)

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19
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)

20
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

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22
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

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Kidneys and Adrenal Glands
  • The two kidneys, which lie in the posterior part
    of the abdominal cavity
  • 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

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Pancreas
  • 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

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Gonadal Sex Hormones
  • Suspended below the pelvic cavity, respectively
  • Produce most of the bodys sex hormones
    androgens, estrogens, and progestins

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30
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

31
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

32
Responses to Stress
  • When a person is in danger, hormones regulate
    both the short-term and long-term responses
  • The short-term reactionthe fight-or-flight
    responseoccurs 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

33
Stress and the Adrenal Gland
34
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 individuals life
  • The major hormonal effects on development are

35
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).

36
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.

37
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.

38
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

39
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

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41
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

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43
47.4 How Do HormonesAct 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

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45
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

46
Identifying theEpinephrine 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.

47
Signal Transduction and the Role of Second
Messengers
  • Epinephrine activates phosphorylase, the enzyme
    that catalyzes the formation of glucose from
    glycogen (Figure 47.15).

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49
Epinephrine Signal Transduction
  • Epinephrine triggers a signal transduction
    cascade that includes cyclic adenosine
    monophosphate (cAMP) as a second messenger to
    amplify the signal
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