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Hormones and the Endocrine System


Chapter 45 Hormones and the Endocrine System Internal Communication Animals have 2 systems of internal communication and regulation: 1. The nervous system. – PowerPoint PPT presentation

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Title: Hormones and the Endocrine System

Chapter 45
  • Hormones and the Endocrine System

Internal Communication
  • Animals have 2 systems of internal communication
    and regulation
  • 1. The nervous system.
  • 2. The endocrine system.

1. The Nervous System
  • The nervous system is the pathway of
    communication involving high speed electrical

2. The Endocrine System
  • The endocrine system is all of the animals
    hormone secreting cells.
  • The endocrine system coordinates a slow,
    long-lasting response.

Endocrine Glands
  • Endocrine glands are hormone secreting organs.
  • They are ductless glands.
  • Their product is secreted into extracellular
    fluid and diffuses into circulation.

Endocrine and Nervous Systems
  • It is convenient to think of the nervous system
    and the endocrine as separate.
  • They are actually very closely linked.
  • Neurosecretory cells are specialized nerve cells
    that release hormones into the blood.
  • They have characterisitics of both nerves and
    endocrine cells.

Neurosecretory Cells
  • The hypothalamus and the posterior pituitary
    gland contains neurosecretory cells.
  • These produce neurohormones which are
    distinguishable from endocrine hormones.
  • Some hormones serve as both endocrine hormones
    and neurotransmitters.

Neurosecretory Cells
  • They can stimulate a response, or they can induce
    a target cell to elicit a response.
  • For example, a suckling infant and oxytocin
    release is an example.

Biological Control Systems
  • Recall,
  • These are comprised of a receptor/sensor which
    detects a stimulus and sends information to a
    control center that controls an effector.
  • The control center processes the information and
    compares it to a set point.
  • The control center sends out processed
    information and directs the response of the

3 General Hormonal Pathways
  • 1. A simple endocrine pathway.
  • 2. A simple neurohormone pathway.
  • 3. A simple neuroendocrine pathway.

1. A Simple Endocrine Pathway
  • A stimulus elicits a response on an endocrine
    cell causing a hormone release.
  • The hormone diffuses into the blood where it
    reaches a target effector eliciting a response.

1. A Simple Endocrine Pathway
  • For example
  • A low glucose level in the blood stimulates the
    pancreas to release glucagon.
  • Glucagon acts on liver cells to release glycogen.
  • Glycogen breaks down into glucose and gets into
    the blood.

2. Simple Neurohormone Pathway
  • In the simple neurohormone pathway, a stimulus
    travels via a sensory neuron to the
    hypothalamus/posterior pituitary gland.
  • Neurosecretory cells here release hormones into
    the blood.
  • These hormones travel to the target cells and
    elicit a response.

2. Simple Neurohormone Pathway
  • For example
  • A suckling infants stimulation is sent via a
    sensory neuron to the hypothalamus/posterior
    pituitary where oxytocin is made and released
    into the blood.
  • The hormones travel to the smooth muscle in the
    breast which responds by contracting and
    releasing milk.

3. A Simple Neuroendocrine Pathway
  • A stimulus sends the signal to the hypothalamus
    via a sensory neuron.
  • The neurosecretory cells of the hypothalamus
    release hormones into the blood.
  • These act on endocrine cells to release hormones
    into the blood.
  • These hormones have an effect on target cells and
    elicit a response.

3. A Simple Neuroendocrine Pathway
  • For example
  • Neural and hormonal signals tell the hypothalamus
    to secrete prolactin releasing hormone.
  • The hormone travels through the blood to the
    anterior pituitary which releases prolactin.
  • Prolactin travels through the blood to the
    mammary glands stimulating milk production.

Positive and Negative Feedback
  • Recall,
  • Positive feedback acts to reinforce the stimulus.
    It leads to a greater response.
  • Negative feedback acts to reduce the response of
    the stimulus.

Molecules Functioning as Hormones
  • There are 3 major classes of molecules that
    function as hormones
  • 1. Proteins/peptides-water soluble.
  • 2. Amines-water soluble.
  • 3. Steroids-not water soluble.

Key Events
  • There are 3 key events involved in signaling
  • 1. Reception-is when the signal binds to the
    receptor protein in or on the target cell.
  • Receptors can be inside or outside the cell.
  • 2. Signal transduction-signal binds and triggers
    events within the cell (cascade events).
  • 3. Response-changes a cells behavior.

Signal Transduction
  • Receptors for most water soluble proteins are
    embedded in the plasma membrane.
  • Binding of a hormone initiates a signal
    transduction pathway.

Signal Transduction
  • The pathway is a series of changes where cellular
    proteins convert an extracellular chemical signal
    into an intracellular response.
  • Examples
  • Activation of an enzyme
  • Uptake or secretion of a specific molecule
  • Rearrangement of a cytoskeleton

Signal Transduction
  • The signals can activate proteins that can act to
    directly or indirectly regulate transcription of
    certain genes.
  • Hormones can cause a variety of responses in
    target cells with different receptors.
  • These responses are types of signal transductions.

(No Transcript)
Water Soluble Hormones
  • Most water soluble hormones have receptors
    embedded in the membrane.
  • Surface receptor proteins activate proteins in
    the cytoplasm which then move into the nucleus
    and regulate transcription.

Epinephrine Example-Water Soluble Hormone
  • Liver cells and smooth muscle of blood vessels
    supplying skeletal muscle contain b-type
    epinephrine receptors.

Epinephrine Example-Water Soluble Hormone
  • Smooth muscle of intestinal blood vessels contain
    a-type receptors.
  • The tissues respond differently to epinephrine.
  • Increased blood flow and glucose to the skeletal
  • Decreased blood flow to the digestive tract.

Lipid Soluble Hormone
  • Lipid soluble hormones have their receptors
    located inside of the cell. Either in the
    cytoplasm or the nucleus.
  • Entrance of the signal and binding of the signal
    to the receptor initiates the signal transduction
  • Binding to DNA stimulates transcription of genes.
  • mRNA produced is translated into protein within
    the cytoplasm.

Estrogen Example-Lipid Soluble Hormone
  • Estrogen induces cells within the female birds
    reproductive system to make large amounts of

Paracrine Signaling
  • Neighboring cells signal local regulators that
    convey signals between these neighboring cells.
  • Neurotransmitters, cytokines, and growth factors
    are all examples of local regulators.

Paracrine Signaling-Example
  • Nitric oxide (NO).
  • When blood O2 levels fall, endothelial cells in
    the blood vessel walls synthesize and release NO.
  • NO activates an enzyme that relaxes neighboring
    smooth muscle.
  • This results in the dilation of blood vessels and
    improves blood flow.

Endocrine Control
  • The hypothalamus integrates the vertebrates
    nervous and endocrine systems.
  • It is found on the underside of the brain.
  • It receives information from nerves throughout
    the body and brain.
  • It initiates the appropriate endocrine signals
    for varying conditions.

The Hypothalamus
  • Contains 2 sets of neurosecretory cells.
  • The secretions from these cells are stored in or
    regulate the activity of the pituitary gland.

The Pituitary
  • The pituitary gland has 2 parts.
  • The anterior and the posterior.

The Anterior Pituitary Gland
  • It is regulated by hormones produced by
    neurosecretory cells in the hypothalamus.
  • Some inhibit hormone release, others stimulate
  • The adenohypophysis consists of endocrince cells
    that make and secrete at least 6 different
  • Many of them target and stimulate endocrine

The Anterior Pituitary Gland
  • FSH-stimulates production of ova and sperm.
  • LH-stimulates ovaries and testes.
  • TSH-stimulates the thyroid gland.
  • ACTH-stimulates production and secretion of the
    hormones of the adrenal cortex.
  • MSH-stimulates concentration of melanin in skin.
  • Prolactin-stimulates mammary gland growth and
    milk synthesis.

The Posterior Pituitary Gland
  • The neurohypophysis is an extension of the
  • It stores and secretes 2 hormones ADH and
  • ADH acts on the kidneys increasing H2O retention.
  • Oxytocin signals uterine muscle contraction and
    mammary gland excretion of milk.

The Thyroid Gland
  • The thyroid produces 2 hormones.
  • Triiodothyroxine (T3)
  • Thyroxin (T4)
  • In mammals, T4 is converted to T3 by target
  • T3 is mostly responsible for the cellular

The Thyroid Gland
  • The thyroid is crucial to development.
  • It controls metamorphosis in frogs.
  • It is required for normal functioning of
    bone-forming cells.
  • It promotes branching of nerves in utero.
  • It helps skeletal growth and mental development.
  • It helps maintain muscle tone, digestion,
    reproductive functions, b.p., h.r.

The Thyroid Gland
  • The thyroid creates calcitonin.
  • It works in conjunction with the parathyroid to
    maintain calcium homeostasis.

Parathyroid Hormone
  • Released by the parathyroid gland in response to
    low blood calcium levels.
  • PTH induces the breakdown of osteoclasts.
  • Ca2 is then released into the blood.
  • PTH stimulates Ca2 uptake by the renal tubules.

Parathyroid Hormone
  • PTH also promotes the conversion of vitamin D
    into its active form.
  • The active form of vitamin D acts on the
    intestines stimulating the uptake of Ca2 from
  • When Ca2 gets above a certain setpoint, it
    promotes the release of calcitonin which opposes
    the effects of PTH lowering blood Ca2 levels.

  • The pancreas is both an endocrine and a exocrine
  • Exocrine-releases secretions into ducts.
  • Endocrine-secretions diffuse into bloodstream.
  • Islets of Langerhans are scattered throughout the
    exocrine portion of the pancreas.

  • Each islet contains a-cells and b-cells.
  • a-cells produce glucagon.
  • b-cells produce insulin.
  • Insulin and glucagon oppose each other and
    regulate the concentration of glucose in the

Blood Glucose
  • Glucagon gets released when blood glucose falls
    below a setpoint.
  • Insulin gets released when blood glucose is
  • Insulin stimulates most cells to take up glucose
    from the blood.
  • It also acts to slow glycogen breakdown in the

Diabetes Mellitus
  • Diabetes is an endocrine disorder caused by a
    deficiency in insulin or decreased response to
  • There are 2 types
  • Type I-insulin dependent.
  • Type II-non-insulin dependent.

Type I Diabetes
  • Insulin dependent. Its an autoimmune disease
    resulting in the destruction of the bodys
  • The pancreas cant produce insulin and the person
    requires insulin injections.

Type II Diabetes
  • Non-insulin dependent.
  • It is caused either by a deficiency in insulin,
    or usually by a reduced responsiveness by the
    cells to insulin.

Adrenal Glands
  • They are adjacent to the kidneys.
  • They are made up of 2 different cell types.
  • Adrenal cortex-the outer portion.
  • Adrenal medulla-the inner portion.

Adrenal Cortex
  • Responds to endocrine signals.
  • ACTH released from the anterior pituitary
    stimulates the release of corticosteriods.
  • Glucocorticoids-cortisol involved in
  • Mineralcorticoids-aldosterone acts on salt
  • The cortex also releases sex hormones.

Adrenal Medulla
  • The medulla responds to endocrine signals.
  • Produces the catecholamines epinephrine and
  • These are involved in the fight-or-flight
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