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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.

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chapter 45

Chapter 45

Hormones and the Endocrine System

internal communication
Internal Communication
  • Animals have 2 systems of internal communication and regulation:
  • 1. The nervous system.
  • 2. The endocrine system.
1 the nervous system
1. The Nervous System
  • The nervous system is the pathway of communication involving high speed electrical signals.
2 the endocrine system
2. The Endocrine System
  • The endocrine system is all of the animal’s hormone secreting cells.
  • The endocrine system coordinates a slow, long-lasting response.
endocrine glands
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
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
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 cells8
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
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 effector.
3 general hormonal pathways
3 General Hormonal Pathways
  • 1. A simple endocrine pathway.
  • 2. A simple neurohormone pathway.
  • 3. A simple neuroendocrine pathway.
1 a simple endocrine 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 pathway12
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
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 pathway14
2. Simple Neurohormone Pathway
  • For example:
    • A suckling infant’s 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
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 pathway16
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
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
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
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 cell’s behavior.
signal transduction
Signal Transduction
  • Receptors for most water soluble proteins are embedded in the plasma membrane.
  • Binding of a hormone initiates a signal transduction pathway.
signal transduction21
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 transduction22
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.
water soluble hormones
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
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 hormone26
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 muscles.
    • Decreased blood flow to the digestive tract.
lipid soluble hormone
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 pathway.
    • Binding to DNA stimulates transcription of genes.
    • mRNA produced is translated into protein within the cytoplasm.
estrogen example lipid soluble hormone
Estrogen Example-Lipid Soluble Hormone
  • Estrogen induces cells within the female bird’s reproductive system to make large amounts of ovalbumin.
paracrine signaling
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
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
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
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
  • The pituitary gland has 2 parts.
  • The anterior and the posterior.
the anterior pituitary gland
The Anterior Pituitary Gland
  • It is regulated by hormones produced by neurosecretory cells in the hypothalamus.
  • Some inhibit hormone release, others stimulate it.
  • The adenohypophysis consists of endocrince cells that make and secrete at least 6 different hormones.
  • Many of them target and stimulate endocrine glands.
the anterior pituitary gland35
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 Posterior Pituitary Gland
  • The neurohypophysis is an extension of the hypothalamus.
  • It stores and secretes 2 hormones: ADH and oxytocin.
    • ADH acts on the kidneys increasing H2O retention.
    • Oxytocin signals uterine muscle contraction and mammary gland excretion of milk.
the thyroid gland
The Thyroid Gland
  • The thyroid produces 2 hormones.
    • Triiodothyroxine (T3)
    • Thyroxin (T4)
  • In mammals, T4 is converted to T3 by target cells.
  • T3 is mostly responsible for the cellular response.
the thyroid gland38
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 gland39
The Thyroid Gland
  • The thyroid creates calcitonin.
  • It works in conjunction with the parathyroid to maintain calcium homeostasis.
parathyroid hormone
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 hormone41
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 food.
  • 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 gland.
    • 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.
blood glucose
Blood Glucose
  • Glucagon gets released when blood glucose falls below a setpoint.
  • Insulin gets released when blood glucose is elevated.
  • Insulin stimulates most cells to take up glucose from the blood.
  • It also acts to slow glycogen breakdown in the liver.
diabetes mellitus
Diabetes Mellitus
  • Diabetes is an endocrine disorder caused by a deficiency in insulin or decreased response to insulin.
  • There are 2 types:
  • Type I-insulin dependent.
  • Type II-non-insulin dependent.
type i diabetes
Type I Diabetes
  • Insulin dependent. It’s an autoimmune disease resulting in the destruction of the body’s b-cells.
  • The pancreas can’t produce insulin and the person requires insulin injections.
type ii diabetes
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
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
Adrenal Cortex
  • Responds to endocrine signals.
  • ACTH released from the anterior pituitary stimulates the release of corticosteriods.
    • Glucocorticoids-cortisol involved in bioenergetics.
    • Mineralcorticoids-aldosterone acts on salt balance.
  • The cortex also releases sex hormones.
adrenal medulla
Adrenal Medulla
  • The medulla responds to endocrine signals.
  • Produces the catecholamines epinephrine and norepinephrine.
  • These are involved in the ‘fight-or-flight’ response.