2. The Endocrine System Defined:
the glands and parts of glands that
secrete hormones that integrate and
control the body's metabolic activity.
Endocrine glands include the pituitary,
thyroid, parathyroids, adrenals,
pancreas, ovaries, and testes.
3. Endocrine System
• Regulates long-term processes:
– growth
– development
– reproduction
• Uses chemical messengers to relay
information and instructions between
cells
4. What are the modes of intercellular
communication used by the
endocrine and nervous systems?
5. 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
6. Paracrine Communication
• Paracrine
• Uses chemical signals to transfer information
from cell to cell within single tissue
• Most common form of intercellular
communication
7. Endocrine Communication
• Endocrine cells release chemicals (hormones)
into bloodstream
• Alters metabolic activities of many tissues and
organs simultaneously
8. Target Cells
• Are specific cells that possess receptors
needed to bind and “read” hormonal
messages
9. Hormones
• Stimulate synthesis of enzymes or structural
proteins
• Increase or decrease rate of synthesis
• Turn existing enzyme or membrane channel
“on” or “off”
10. Endocrine System
• Is unable to handle crisis management
•
Nervous System
• split-second responses
11. How do the cellular components
of the endocrine system
compare with those of other
tissues and systems?
20. Peptide Hormones
• Chains of amino acids
• Synthesized as prohormones:
– inactive molecules converted to active hormones
before or after secretion
21. 2 Groups of Peptide Hormones
• Group 1:
– glycoproteins:
• more than 200 amino acids long, with carbohydrate side
chains:
– thyroid-stimulating hormone (TSH)
– luteinizing hormone (LH)
– follicle-stimulating hormone (FSH)
22. 2 Groups of Peptide Hormones
• Group 2:
– all hormones secreted by:
•
•
•
•
•
•
•
hypothalamus
heart
thymus
digestive tract
pancreas
posterior lobe of pituitary gland
anterior lobe of pituitary gland
23. 2 Classes of Lipid Derivatives
• Eicosanoids:
– derived from arachidonic acid
• Steroid hormones:
– derived from cholesterol
24. Eicosanoids
• Are small molecules with five-carbon ring at
one end
• Are important paracrine factors
• Coordinate cellular activities
• Affect enzymatic processes in extracellular
fluids
25. Leukotrienes
• Are eicosanoids released by activated white
blood cells, or leukocytes
• Important in coordinating tissue responses to
injury or disease
26. Prostaglandins
• A second group of eicosanoids produced in
most tissues of body
• Are involved in coordinating local cellular
activities
27. Steroid Hormones
• Are lipids structurally similar to cholesterol
• Released by:
– reproductive organs (androgens by testes,
estrogens, and progestins by ovaries)
– adrenal glands (corticosteroids)
– kidneys (calcitriol)
28. Steroid Hormones
• Remain in circulation longer than peptide
hormones
• Are absorbed gradually by liver
• Are converted to soluble form
• Are excreted in bile or urine
31. Free Hormones
• Remain functional for less than 1 hour:
– diffuse out of bloodstream:
• bind to receptors on target cells
– are absorbed:
• broken down by cells of liver or kidney
– are broken down by enzymes:
• in plasma or interstitial fluids
32. Thyroid and Steroid Hormones
• Remain in circulation much longer
• Enter bloodstream:
– more than 99% become attached to special
transport proteins
34. What are the general mechanisms
of
hormonal action?
35. Hormone Receptor
• Is a protein molecule to which a particular
molecule binds strongly
• Responds to several different hormones
36. Cells
• Different tissues have different combinations
of receptors
• Presence or absence of specific receptor
determines hormonal sensitivity
37. Catecholamines and
Peptide Hormones
• Are not lipid soluble
• Unable to penetrate cell membrane
• Bind to receptor proteins at outer surface of
cell membrane (extracellular receptors)
38. Eicosanoids
• Are lipid soluble
• Diffuse across membrane to reach receptor
proteins on inner surface of membrane
(intracellular receptors)
39. Hormone
• Binds to receptors in cell membrane
• Cannot have direct effect on activities inside
target cell
• Uses intracellular intermediary to exert effects
40. Intracellular Intermediaries
• First messenger:
– leads to second messenger
– may act as enzyme activator, inhibitor, or cofactor
– results in change in rates of metabolic reactions
41. Important Second Messengers
• Cyclic-AMP (cAMP):
– derivative of ATP
• Cyclic-GMP (cGMP):
– derivative of GTP
• Calcium ions
42. G Protein
• Enzyme complex coupled to membrane
receptor
• Involved in link between first messenger and
second messenger
• Activated when hormone binds to receptor at
membrane surface
44. G Protein
• Changes concentration of second messenger
cyclic-AMP (cAMP) within cell
• Increased cAMP level accelerates metabolic
activity within cell
45. Increased cAMP Levels (1 of 2)
1. Activated G protein:
– activates enzyme adenylate cyclase
2. Adenylate cyclase:
– converts ATP to cyclic-AMP
46. Increased cAMP Levels (2 of 2)
3. Cyclic-AMP (second messenger):
– activates kinase
4. Activated kinases affect target cell:
– depends on nature of proteins affected
50. G Proteins and
Calcium Ions (1 of 2)
• Activated G proteins trigger:
– opening of calcium ion channels in membrane
– release of calcium ions from intracellular stores
51. G Proteins and
Calcium Ions (2 of 2)
1. G protein activates enzyme phospholipase C
(PLC)
2. Enzyme triggers receptor cascade:
– production of diacylglycerol (DAG) and inositol
triphosphate (IP3) from membrane
phospholipids
52. Steroid Hormones
• Cross cell membrane
• Bind to receptors in cytoplasm or nucleus,
activating or inactivating specific genes
54. Steroid Hormones
• Alter rate of DNA transcription in nucleus:
– change patterns of protein synthesis
• Directly affect metabolic activity and structure
of target cell
56. Thyroid Hormones
• Cross cell membrane:
– primarily by transport mechanism
• Bind to receptors in nucleus and on
mitochondria:
– activating specific genes
– changing rate of transcription
63. Hypothalamus (1 of 2)
•
Integrates activities of nervous and
endocrine systems in 3 ways:
1. Secretes regulatory hormones:
– special hormones control endocrine cells in
pituitary gland
64. Hypothalamus (2 of 2)
2. Acts as an endocrine organ
3. Contains autonomic centers:
– exert direct neural control over endocrine cells
of adrenal medullae
•
Neuroendocrine response
74. Median Eminence
• Swelling near attachment of infundibulum
• Where hypothalamic neurons release
regulatory factors:
– into interstitial fluids
– through fenestrated capillaries
88. Adrenocorticotropic
Hormone (ACTH)
• Also called corticotropin
• Stimulates release of steroid hormones by
adrenal cortex
• Targets cells that produce glucocorticoids
91. Follicle-Stimulating
Hormone (FSH) (2 of 2)
• Stimulates sustentacular cells in males:
– promotes physical maturation of sperm
• Production inhibited by inhibin:
– peptide hormone released by testes and ovaries
92. Luteinizing Hormone (LH)
• Also called lutropin
• Causes ovulation and progestin production in
females
• Causes androgen production in males
93. FSH and LH Production
• Stimulated by gonadotropin-releasing
hormone (GnRH) from hypothalamus:
– GnRH production inhibited by estrogens,
progestins, and androgens
94. Prolactin (PRL)
• Also called mammotropin
• Stimulates development of mammary glands
and milk production
• Production inhibited by prolactin-inhibiting
hormone (PIH)
103. Oxytocin
• Stimulates contractile cells in mammary
glands
• Stimulates smooth muscles in uterus
• Secretion and milk ejection are part of
neuroendocrine reflex
104. Where is the thyroid
gland located, and
what is its structure?
105. Thyroid Gland
• Lies anterior to thyroid cartilage of larynx
• Consists of 2 lobes connected by narrow
isthmus
117. Transthyretin
• Also called thyroid-binding prealbumin (TBPA)
• Is a transport protein
• Attaches to most remaining T4 and T3
molecules
118. Unbound Thyroid Hormones
• Diffuse out of bloodstream and into other
tissues
• Disturb equilibrium
• Carrier proteins release more thyroid
hormones until new equilibrium is reached
119. Thyroid-Stimulating
Hormone (TSH)
• Absence causes thyroid follicles to become
inactive:
– neither synthesis nor secretion occur
• Binds to membrane receptors
• Activates key enzymes in thyroid hormone
production
120. What are the functions
of thyroid hormones, and what are
the results of abnormal levels of
thyroid hormones?
121. Thyroid Hormones
• Enter target cells by transport system
• Affect most cells in body
• Bind to receptors in:
– cytoplasm
– surfaces of mitochondria
– nucleus
126. Iodide Ions
• Are actively transported into thyroid follicle
cells:
– stimulated by TSH
• Reserves in thyroid follicles
• Excess removed from blood at kidneys
• Deficiency limits rate of thyroid hormone
production
127. C (Clear) Cells
• Produce calcitonin (CT):
– helps regulate concentrations of Ca2+ in body
fluids
132. 4 Effects of PTH
1. It stimulates osteoclasts:
– accelerates mineral turnover
– releases Ca2+ from bone
2. It inhibits osteoblasts:
– reduces rate of calcium deposition in bone
3. It enhances reabsorption of Ca2+ at kidneys,
reducing urinary loss
4. It stimulates formation and secretion of
calcitriol at kidneys
142. Zona Fasciculata
• Produces glucocorticoids
• Endocrine cells are larger and contain more
lipids than zona glomerulosa
143. Zona Fasciculata
• Secretes cortisol (hydrocortisone) with
corticosterone:
– liver converts cortisol to cortisone
144. Glucocorticoids
• Secretion regulated by negative feedback
• Have inhibitory effect on production of:
– corticotropin-releasing hormone (CRH) in
hypothalamus
– ACTH in anterior lobe
145. Glucocorticoids
• Accelerate glucose synthesis and glycogen
formation
• Show anti-inflammatory effects:
– inhibit activities of white blood cells and other
components of immune system
146. Zona Reticularis
• Network of endocrine cells
• Forms narrow band bordering each adrenal
medulla
• Produces androgens under stimulation by
ACTH
147. Adrenal Medullae
• Secretory activities controlled by sympathetic
division of ANS
• Produces epinephrine (adrenaline) and
norepinephrine
• Metabolic changes persist for several minutes
148. Where is the pineal gland, and
what are the functions of
the hormone it produces?
149. Pineal Gland
• Lies in posterior portion of roof of third
ventricle
• Contains pinealocytes:
– synthesize hormone melatonin
150. Functions of Melatonin
• Inhibiting reproductive functions
• Protecting against damage by free radicals
• *Setting circadian rhythms
– (your 24 hr cycle)
151. Where is the pancreas, and
what is its structure?
152. Pancreas
• Lies between:
– inferior border of stomach
– and proximal portion of small intestine
• Contains exocrine and endocrine cells
161. 3 Effects of Glucagons
1. Stimulates breakdown of glycogen in skeletal
muscle and liver cells
2. Stimulates breakdown of triglycerides in
adipose tissue
3. Stimulates production of glucose in liver
162. What are the functions of
hormones produced by the kidneys,
heart, thymus, testes, ovaries, and
adipose tissue?
166. Effects of Calcitriol
on Calcium Metabolism
• Stimulates formation and differentiation of
osteoprogenitor cells and osteoclasts
• Stimulates bone resorption by osteoclasts
167. Effects of Calcitriol
on Calcium Metabolism
• Stimulates Ca2+ reabsorption at kidneys
• Suppresses parathyroid hormone (PTH)
production
172. Heart
• Produces atrial natriuretic peptides (ANP and
BNP):
– when blood volume becomes excessive
173. Natriuretic Peptide
• Action opposes angiotensin II
• Resulting in reduction in blood volume and
blood pressure
174. Thymus
• Produces thymosin hormones:
– that helps develop and maintain normal immune
defenses
– Promotes T cell maturation
175. Testes
• Produce androgens in interstitial cells:
– testosterone:
• is most important male hormone
• Secrete inhibin in sustentacular cells:
– support differentiation and physical maturation of
sperm
176. Ovaries
• Produce estrogens:
– principle estrogen is estradiol
• After ovulation, follicle cells:
– reorganize into corpus luteum
– release estrogens and progestins, especially
progesterone
177. Adipose Tissue Secretions
1. Leptin:
– feedback control for appetite
– controls normal levels of GnRH, gonadotropin
synthesis
2. Resistin:
– reduces insulin sensitivity
179. Autonomic Nervous System (ANS)
• Operates without conscious instruction
• Part of peripheral nervous system
• Coordinates systems functions:
– cardiovascular
– respiratory
– digestive
– urinary
– reproductive
180. Visceral Motor Neurons
• In brain stem and spinal
cord, are known as
preganglionic neurons
• (Ganglia- clusters of neuronal cell
bodies and their dendrites)
183. Postganglionic Fibers
• Axons of ganglionic
neurons
• Begin at autonomic
ganglia:
– extend to peripheral
target organs
184. What are the divisions and
functions of the ANS?
185. Sympathetic Division
• “Kicks in” only during exertion, stress, or
emergency
Parasympathetic Division
• Controls during resting
conditions
186. Divisions of the ANS
• 2 divisions may work together or
independently:
187. Sympathetic Division
• Preganglionic fibers (thoracic and superior
lumbar) synapse in ganglia near spinal cord
• Preganglionic fibers are short
• Postganglionic fibers are long
189. 7 Responses to Increased Sympathetic
Activity (Fight or Flight)
1. Heightened mental alertness
2. Increased metabolic rate
3.Reduced digestive and urinary functions
4.Energy reserves activated
1. 5. Increased respiratory rate and respiratory
passageways dilate
5. 6. Increased heart rate and blood pressure
6. 7. Sweat glands activated
190. Parasympathetic Division
• Preganglionic fibers originate in brain stem
and sacral segments of spinal cord
• Synapse in ganglia close to (or within) target
organs
• Preganglionic fibers are long
• Postganglionic fibers are short
191. Parasympathetic-Rest and Repose
or Breed, Feed, & Read
• Parasympathetic division stimulates visceral
activity
• Conserves energy and promotes sedentary
activities
192. Pattern of Responses to Increased
Levels of Parasympathetic Activity
• Decreased:
– metabolic rate
– heart rate and blood pressure
• Increased:
– salivary and digestive glands secretion
– motility and blood flow in digestive tract
– Urination and defecation stimulation
194. Structure of the
Sympathetic Division
• Preganglionic neurons located between
segments T1 and L2 of spinal cord
• Ganglionic neurons in ganglia near vertebral
column
199. The Adrenal Medullae
Modified Sympathetic Ganglion
• At the center of each adrenal gland in area
known as adrenal medulla
• Very short axons
• When stimulated, release neurotransmitters
into bloodstream (not at synapse)
• Functions as hormones affect target cells
throughout body
200. What are the mechanisms of
neurotransmitter release in the
sympathetic division?
204. Differences from Sympathetic
Postganglionic Fiber Stimulation
• Cells not innervated by sympathetic
postganglionic fibers
• Effects last longer:
– hormones continue to diffuse out of bloodstream
205. Sympathetic Division
• Can change activities of tissues and organs
by:
– releasing NE at peripheral synapses
– distributing E and NE throughout body in
bloodstream
206. Crisis Mode
• Entire division responds (sympathetic
activation)
• Are controlled by sympathetic centers in
hypothalamus
• Effects are not limited to peripheral tissues
• Alters CNS activity as well
209. NE Released by Varicosities
• Affects targets until reabsorbed or inactivated
• 50–80% of NE is reabsorbed by varicosities:
– is reused or broken down by MAO
• The rest diffuses out or is broken down by
COMT
211. Duration of Effects on Postsynaptic
Membrane
• NE persist for a few seconds
• ACh only for 20 msec
224. Beta-2 (b2)
• Causes inhibition
• Triggers relaxation of smooth muscles along
respiratory tract
225. Beta-3 (b3)
• Is found in adipose tissue
• Leads to lipolysis, the breakdown of
triglycerides in adipocytes
• Releases fatty acids into circulation
226. Sympathetic
Postganglionic Fibers
• Mostly adrenergic (release NE)
• A few cholinergic (release ACh)
• Innervate sweat glands of skin and blood
vessels of skeletal muscles and brain
• Stimulate sweat gland secretion and dilates
blood vessels
227. ACh
• Released by parasympathetic division
• Body wall and skeletal muscles are not
innervated by parasympathetic division
• Both NE and ACh needed to regulate visceral
functions
228. What are the structures
and functions of the
parasympathetic division of the
autonomic nervous system?
230. Autonomic Nuclei
• Are contained in the mesencephalon, pons,
and medulla oblongata:
– associated with cranial nerves III, VII, IX, X
• In lateral gray horns of spinal segments S2–S4
231. Ganglionic Neurons
in Peripheral Ganglia
• Preganglionic fiber synapses on 6–8 ganglionic
neurons:
– terminal ganglion:
• near target organ
• usually paired
– intramural ganglion:
• embedded in tissues of target organ
• interconnected masses
• clusters of ganglion cells
232. Pattern of
Parasympathetic Division
• All ganglionic neurons in same ganglion
• Postganglionic fibers influence same target
organ
• Effects of parasympathetic stimulation more
specific and localized
233. What are the mechanisms of
neurotransmitter release in the
parasympathetic division?
242. 10 Effects of
Parasympathetic Activation
1. Constriction of pupils:
– restricts light entering eyes
2. Secretion by digestive glands:
– exocrine and endocrine
243. 10 Effects of
Parasympathetic Activation
3. Secretion of hormones
4. Changes in blood flow and glandular activity:
– associated with sexual arousal
244. 10 Effects of
Parasympathetic Activation
5. Increases smooth muscle activity:
– along digestive tract
6. Defecation:
– stimulation and coordination
245. 10 Effects of
Parasympathetic Activation
7. Contraction of urinary bladder:
– during urination
8. Constriction of respiratory passageways
246. 10 Effects of
Parasympathetic Activation
9. Reduction in heart rate:
– and force of contraction
10. Sexual arousal:
– stimulation of sexual glands
249. ACh
• Inactivated by by enzyme
acetylcholinersterase (AChE) at synapse
• Ach is also inactivated by
pseudocholinesterase in surrounding
tissues
250. 2 Types of ACh Receptors
on Postsynaptic Membranes
• Nicotinic receptors
• Muscarinic receptors
251. Nicotinic Receptors
• On surfaces of ganglion cells (sympathetic
and parasympathetic)
• At neuromuscular junctions of somatic
nervous system
252. Action of Nicotinic Receptors
• Exposure to ACh causes excitation of
ganglionic neuron or muscle fiber
• Open chemically gated channels in
postsynaptic membrane
253. Dangerous Environmental Toxins
• Muscarine:
– binds to muscarinic receptors
– targets parasympathetic neuromuscular or
neuroglandular junctions
256. Summary:
Parasympathetic Division
• All neurons are cholinergic:
– ganglionic neurons have nicotinic receptors,
excited by ACh
– muscarinic receptors at neuromuscular or
neuroglandular junctions produce either
excitation or inhibition
258. Comparing Sympathetic and
Parasympathetic Divisions
• Sympathetic:
– widespread impact
– reaches organs and tissues throughout body
• Parasympathetic:
– innervates only specific visceral structures
260. What is the relationship between
the two divisions
of the autonomic nervous system,
and the significance
of dual innervation?
261. Dual Innervation
• Most vital organs receive instructions from
both sympathetic and parasympathetic
divisions
• 2 divisions commonly have opposing effects
262. Anatomy of Dual Innervation
• Parasympathetic postganglionic fibers
accompany cranial nerves to peripheral
destinations
• Sympathetic innervation reaches same
structures by traveling directly from superior
cervical ganglia of sympathetic chain
263. Structure: Autonomic Plexuses
• Nerve networks in the thoracic and
abdominopelvic cavities:
– are formed by mingled sympathetic
postganglionic fibers and parasympathetic
preganglionic fibers
• Travel with blood and lymphatic vessels that
supply visceral organs
266. Autonomic Tone
• Is an important aspect of ANS function:
– if nerve is inactive under normal conditions, can
only increase activity
– if nerve maintains background level of activity,
can increase or decrease activity
267. Autonomic Tone
and Dual Innervation
• Significant where dual innervation occurs:
– 2 divisions have opposing effects
• More important when dual innervation does
not occur