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Chapter 18: The Endocrine System

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Title: Chapter 18: The Endocrine System


1
Chapter 18 The Endocrine System
2
Endocrine System
  • Regulates long-term processes
  • growth
  • development
  • Reproduction
  • Uses chemical messengers to relay information and
    instructions between cells

3
What are the modes of intercellular communication
used by the endocrine and nervous systems?
4
Direct Communication
  • Exchange of ions and molecules between adjacent
    cells across gap junctions
  • Occurs between 2 cells of same type
  • Highly specialized and relatively rare

5
Paracrine Communication
  • Chemical signals transfer information from cell
    to cell within single tissue
  • paracrine factors may enter blood stream and
    function as hormones
  • Most common form of intercellular communication

6
Endocrine Communication
  • Endocrine cells
  • release chemicals (hormones) into bloodstream
  • Alters metabolic activities of many tissues and
    organs simultaneously
  • Target Cells
  • possess receptors needed to bind and read
    hormonal messages

7
  • Hormones
  • Stimulate synthesis of enzymes or structural
    proteins
  • Increase or decrease rate of synthesis
  • Turn existing enzyme or membrane channel on or
    off

8
Synaptic Communication
  • Releases neurotransmitter at a synapse that is
    very close to target cells
  • Ideal for crisis management

9
What are the cellular components of the endocrine
system?
10
  • Includes all endocrine cells and tissues that
    produce hormones or paracrine factors
  • Endocrine Cells
  • Glandular secretory cells that release their
    secretions into extracellular fluid
  • Exocrine Cells
  • Secrete their products onto epithelial surfaces

11
Endocrine System
Figure 181
12
What are the major structural classes of hormones?
13
Hormones
  • Can be divided into 3 groups
  • amino acid derivatives
  • peptide hormones
  • lipid derivatives

14
Amino Acid Derivatives
  • Small molecules structurally related to amino
    acids
  • Synthesized from the amino acids tyrosine and
    tryptophan

15
  • Tyrosine Derivatives
  • Thyroid hormones
  • Catacholamines epinephrine (E), dopamine
    norepinephrine (NE)
  • Tryptophan Derivative
  • Melatonin produced by pineal gland

16
Peptide Hormones
  • Chains of amino acids
  • Synthesized as prohormones
  • inactive molecules converted to active hormones
    before or after secretion
  • ADH, prolactin, oxytocin, growth hormone

17
Lipid Derivatives
  • Eicosanoids
  • important paracrine factors
  • Leukotrienes, Prostaglandins
  • Steroid hormones
  • derived from cholesterol
  • androgens (estrogens, and progestins)
    corticosteroids, calcitriol

18
What are the general mechanisms of hormonal
action?
19
  • Receptors are protein molecules to which a
    particular molecule binds strongly
  • Different tissues have different combinations of
    receptors
  • Presence or absence of specific receptor
    determines hormonal sensitivity

20
  • Hormones bind to receptors in cell membrane
  • Cannot have direct effect on activities inside
    target cell

21
  • Hormones indirectly
  • alter cellular operations by altering protein
    composition and activity
  • stimulate protein synthesis
  • activate proteins
  • modulate current levels of protein synthesis

22
  • First messenger
  • leads to second messenger (cAMP, cGMP, Ca)
  • A single hormone promotes release of more than 1
    type of second messenger

23
  • Down-regulation
  • Presence of a hormone triggers decrease in number
    of hormone receptors
  • Up-regulation
  • Absence of a hormone triggers increase in number
    of hormone receptors

24
G Protein
  • Enzyme complex coupled to membrane receptor
  • Involved in link between first messenger and
    second messenger
  • Binds GTP
  • Activated when hormone binds to receptor at
    membrane surface

25
  • Activated G protein
  • activates enzyme adenylate cyclase
  • Adenylate cyclase
  • converts ATP to cyclic-AMP
  • Cyclic-AMP (second messenger)
  • activates kinase
  • Activated kinases affect target cell
  • depends on nature of proteins affected

26
  • Activated G proteins trigger
  • opening of calcium ion channels in membrane
  • release of calcium ions from intracellular stores

27
  • Activated G protein stimulates phosphodiesterase
    (PDE) activity
  • Inhibits adenylate cyclase activity
  • Levels of cAMP decline
  • cAMP breakdown accelerates cAMP synthesis is
    prevented

28
G Proteins and Hormone Activity
Figure 183
29
Steroid Hormones
  • Cross cell membrane
  • Bind to receptors in cytoplasm or nucleus,
    activating or inactivating specific genes

30
Steroid Hormones
Figure 184a
31
Steroid Hormones
  • Alter rate of DNA transcription in nucleus
  • change patterns of protein synthesis
  • Directly affect metabolic activity and structure
    of target cell

32
How are endocrine organs controlled?
33
Hypothalamus
  • Integrates activities of nervous and endocrine
    systems in 3 ways
  • Secretes regulatory hormones
  • special hormones control endocrine cells in
    pituitary gland

34
  • Acts as an endocrine organ
  • manufactures hormones released into the
    bloodstream via the posterior pituitary
  • Contains autonomic centers
  • exert direct neural control over endocrine cells
    of adrenal medullae

35
Hypothalamus
Figure 185
36
Where is the pituitary gland located, and what
is its relationship to the hypothalamus?
37
Pituitary Gland
  • Hangs inferior to hypothalamus
  • connected by infundibulum
  • Releases 9 important peptide hormones
  • Hormones bind to membrane receptors
  • use cAMP as second messenger

38
Pituitary Gland
Figure 186
39
What are the hormones produced by the anterior
lobe, and what are the functions of those
hormones?
40
Anterior Pituitary
  • Thyroid-Stimulating Hormone (TSH)
  • Also called thyrotropin
  • Triggers release of thyroid hormones
  • hypothalamic regulatory hormone
  • Thyrotropin Releasing Hormone (TRH)

41
  • Adrenocorticotropic Hormone (ACTH)
  • Also called corticotropin
  • Stimulates release of steroid hormones by adrenal
    cortex
  • hypothalamic regulatory hormone
  • Corticotropin Releasing Hormone (CRH)

42
  • Prolactin (PRL)
  • Also called mammotropin
  • Stimulates development of mammary glands and milk
    production
  • hypothalamic regulatory hormone
  • prolactin-inhibiting hormone (PIH)

43
  • Growth Hormone (GH)
  • Also called somatotropin
  • Stimulates cell growth and replication
  • hypothalamic regulation
  • growth hormonereleasing hormone (GHRH)
  • growth hormoneinhibiting hormone (GHIH)

44
  • Melanocyte-Stimulating Hormone (MSH)
  • Also called melanotropin
  • Stimulates melanocytes to produce melanin
  • Inhibited by dopamine

45
  • Gonadotropins
  • Regulate activities of gonads (testes, ovaries)
  • hypothalamic regulation
  • gonadotropin-releasing hormone (GnRH)
  • GnRH production inhibited by estrogens,
    progestins, and androgens

46
  • Follicle-Stimulating Hormone (FSH)
  • Also called follitropin
  • Stimulates follicle development and estrogen
    secretion in females
  • Stimulates sustentacular cells in males
  • promotes physical maturation of sperm
  • Production inhibited by inhibin released by
    testes and ovaries

47
  • Luteinizing Hormone (LH)
  • Also called lutropin
  • Causes ovulation and progestin production in
    females
  • Causes androgen production in males

48
What hormones are secreted by the posterior lobe,
and what are their functions?
49
  • Antidiuretic Hormone
  • Decreases amount of water lost at kidneys
  • Elevates blood pressure
  • Release inhibited by alcohol

50
  • Oxytocin
  • Stimulates contractile cells in mammary glands
  • Stimulates smooth muscles in uterus

51
Summary The Hormones of the Pituitary Gland
Figure 189
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