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Endocrine System I: Superior Glands Homeostatic Mechanisms
Endocrine System vs Nervous System
Endocrine vs Exocrine Glands
Types and Actions of Hormones
Interaction of Hormones with Target Cells
Effects of Hormones on Target
Control Mechanisms of Endocrine Glands
Endocrine Signaling as Simple/Complex Reflexes
Major Superior Endocrine Organs
• Pituitary
Anterior: GH, Pl, FSH, LH, TSH, ACTH
Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Homeostasis Maintenance of a stable internal environment =
a dynamic state of equilibrium
Feedback Mechanisms Example of Negative feedback
Receptor and
Low blood glucose
Feedback Mechanisms Examples of Positive feedback
Endocrine System I: Superior Glands Homeostatic Mechanisms
Endocrine System vs Nervous System
Endocrine vs Exocrine Glands
Types and Actions of Hormones
Interaction of Hormones with Target Cells
Effects of Hormones on Target
Control Mechanisms of Endocrine Glands
Endocrine Signaling as Simple/Complex Reflexes
Major Superior Endocrine Organs
• Pituitary
Anterior: GH, Pl, FSH, LH, TSH, ACTH
Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
The Endocrine System A more broad-based and long-lasting
communication system than the nervous system
Uses chemical messages (hormones) that are released into the blood
Hormones control several major processes
• Reproduction
• Growth and development
• Mobilization of body defenses
• Maintenance of much of homeostasis
• Regulation of metabolism
Comparing Two Control Systems
System Mode of Messaging
Speed of Signaling
Length of Response Time Range of Focus
Nervous System
Endocrine System
Neuron “wiring” leading
directly to and from target
Hormones travel
through blood stream
systemically
Rapid, in milliseconds
Short duration; response stops in
seconds or minutes
Long-lasting;
minutes to days
Narrow & specific, a few cells to part of one organ
Broad & general; many target
tissues and organs stimulated
collectively
QuickTime™ and a decompressor
are needed to see this picture.
QuickTime™ and a decompressor
are needed to see this picture.
Slow; minutes,
hours, or days
Endocrine System I: Superior Glands Homeostatic Mechanisms
Endocrine System vs Nervous System
Endocrine vs Exocrine Glands
Types and Actions of Hormones
Interaction of Hormones with Target Cells
Effects of Hormones on Target
Control Mechanisms of Endocrine Glands
Endocrine Signaling as Simple/Complex Reflexes
Major Superior Endocrine Organs
• Pituitary
Anterior: GH, Pl, FSH, LH, TSH, ACTH
Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Glandular Epithelium Gland – one or more cells that secretes a
particular product
Two major gland types
• Endocrine gland
Ductless
Secretions are hormones
• Exocrine gland
Empty through ducts to the epithelial surface
Include sweat and oil glands
Types of Hormones Peptide-based hormones
Steroid hormones
Prostaglandins and catecholamines
Insulin Growth hormone
Hormones as Chemical Messengers
Endocrine gland (source)
Target organs or glands
Hormones move through the bloodstream to target organs
Endocrine System I: Superior Glands Homeostatic Mechanisms
Endocrine System vs Nervous System
Endocrine vs Exocrine Glands
Types and Actions of Hormones
Interaction of Hormones with Target Cells
Effects of Hormones on Target
Control Mechanisms of Endocrine Glands
Endocrine Signaling as Simple/Complex Reflexes
Major Superior Endocrine Organs
• Pituitary
Anterior: GH, Pl, FSH, LH, TSH, ACTH
Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Hormone Interaction with Target Cells Hormones bind to receptors sticking out from the plasma membrane of target
cells or within target cells
growth factor insulin epinephrine
Hormones
Examples of receptors found in the plasma membrane of cells
Receptors
Two Mechanisms of Hormone Action
Steroid hormone action1. Diffuses through the plasma membrane of target cells2. Enters the nucleus or binds to cytoplasmic receptor3. Binds to a specific protein within the nucleus if not
already bound4. Binds to specific sites on the cell’s DNA5. Activates genes that result in synthesis of new proteins
Non-steroid hormone action
1. Hormone binds to a membrane receptor; does not enter cell
2. Sets off a reaction where a G protein with bound GTP activates adenylate cyclase enzyme.
3. Adenylate cyclase produces cyclic AMP (second messenger) by converting ATP --> cAMP
5. cAMP, in turn, activates phosphorylating activation proteins (protein kinases) that trigger additional intracellular changes (enzyme activation, secretion, ion channel changes) to promote a specific response
(A few peptide hormones activate Ca+2 release via second messengers in the PIP2 calcium signaling system).
G protein
AdenylateCyclase
cAMP
Endocrine System I: Superior Glands Homeostatic Mechanisms
Endocrine System vs Nervous System
Endocrine vs Exocrine Glands
Types and Actions of Hormones
Interaction of Hormones with Target Cells
Effects of Hormones on Target
Control Mechanisms of Endocrine Glands
Endocrine Signaling as Simple/Complex Reflexes
Major Superior Endocrine Organs
• Pituitary
Anterior: GH, Pl, FSH, LH, TSH, ACTH
Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Effects Caused by HormonesChanges in target cells by hormonal activation
• Changes in plasma membrane permeability or electrical state
• Synthesis of proteins, such as enzymes
• Activation or inactivation of enzymes
• Stimulation of mitosis
• Activation of transcription of certain genes
Target cell activation depends on three factors
1. Blood levels of the hormone
2. Relative number of receptors on or in the target cell
3. Affinity of binding between receptor and hormone
Target Cell Activation
Hormones influence the number of their receptors
• Up-regulation—target cells form more receptors in response to the hormone
• Down-regulation—target cells lose receptors in response to the hormone
Hormones are removed from the blood by
• Degrading enzymes
• Kidneys
• Liver
• Half-life—the time required for a hormone’s blood level to decrease by half
Control of Hormone Release Hormone levels in the
blood are maintained by negative feedback
A stimulus or low hormone levels in the blood triggers the release of more hormone
Hormone release stops once an appropriate level in the blood is reached
Endocrine System I: Superior Glands Homeostatic Mechanisms
Endocrine System vs Nervous System
Endocrine vs Exocrine Glands
Types and Actions of Hormones
Interaction of Hormones with Target Cells
Effects of Hormones on Target
Control Mechanisms of Endocrine Glands
Endocrine Signaling as Simple/Complex Reflexes
Major Superior Endocrine Organs
• Pituitary
Anterior: GH, Pl, FSH, LH, TSH, ACTH
Posterior: Oxytocin, ADH
• Thyroid: TH synthesis and release; Calcitonin
• Parathyroids: PTH
Control Mechanisms of Endocrine Glands
Hormonal: Chemical stimulus (i.e. endocrine
glands are activated by other hormones
Humoral: Changing blood levels of certain ions
stimulate hormone release
Neural: Nerve impulses stimulate hormone release; most are under
control of the sympathetic nervous system
Endocrine Signaling (Reflexes)
Figure 9.3
Simple Endocrine Reflex • Involves only one hormone• Controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract
Complex Endocrine ReflexInvolves:
• One or more intermediary steps• Two or more hormones (tropic hormones cause secretion of a second hormone in target glands)• The hypothalamus
Location of Major Endrocrine Organs
Figure 9.3