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
Neuron
“wiring”
leading
Rapid, in
directly to and milliseconds
from target
Quic kTime™ and a
dec ompres sor
are needed to see this pic ture.
Nervous
System
Endocrine
System
Hormones
travel
through
blood
stream
systemically
QuickTime™ and a
decompressor
are needed to see this picture.
Slow;
minutes,
hours, or days
Length of
Response Time
Range of Focus
Short
duration;
response
stops in
seconds or
minutes
Narrow &
specific, a
few cells
to part of
one organ
Longlasting;
minutes to
days
Broad & general;
many target
tissues and organs
stimulated
collectively
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
Insulin
 Steroid hormones
 Prostaglandins and catecholamines
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
Receptors
Examples of receptors found in the plasma membrane of cells
Two Mechanisms of Hormone Action
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).
Steroid hormone action
1.
2.
3.
4.
5.
Diffuses through the plasma membrane of target cells
Enters the nucleus or binds to cytoplasmic receptor
Binds to a specific protein within the nucleus if not
already bound
Binds to specific sites on the cell’s DNA
Activates genes that result in synthesis of new proteins
Adenylate
Cyclase
G
protein
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 Hormones
Changes 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)
Simple Endocrine Reflex
• Involves only one hormone
• Controls hormone secretion by the heart, pancreas,
parathyroid gland, and digestive tract
Complex Endocrine Reflex
Involves:
• One or more intermediary steps
• Two or more hormones (tropic hormones cause
secretion of a second hormone in target glands)
• The hypothalamus
Figure 9.3
Location of Major Endrocrine Organs
Figure 9.3