The endocrine system is made up of glands that secrete hormones directly into the bloodstream to regulate processes like growth, metabolism, and reproduction. The major glands include the pituitary, thyroid, parathyroids, adrenals, pancreas, ovaries, and testes. The hypothalamus integrates the nervous and endocrine systems by secreting hormones that control the pituitary gland, and contains centers that exert neural control over endocrine cells in other glands like the adrenals. The pituitary gland, located at the base of the brain, releases hormones in response to signals from the hypothalamus via a portal blood vessel system.

1. Chapter 18:
The Endocrine System

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?

12. Endocrine System
• Includes all endocrine cells and body tissues
that produce hormones or paracrine factors

13. Endocrine Cells
• Glandular secretory cells that release their
secretions into extracellular fluid (blood and
lymph)

14. Exocrine Cells
• Secrete their products onto epithelial surfaces
• Use ducts instead of circulation

15. What are the major structural
classes of hormones?

16. Hormones
• Can be divided into 3 groups:
– amino acid derivatives
– peptide hormones
– lipid derivatives

17. Amino Acid Derivatives
• Small molecules structurally related to amino
acids
• Synthesized from the amino acids tyrosine and
tryptophan

18. Tyrosine Derivatives
• Thyroid hormones
• Compounds:
– epinephrine (E)
– norepinephrine (NE)
– dopamine, also called catecholamines

19. Tryptophan Derivative
• Melatonin:
– produced by pineal gland

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

29. Classes of Hormones
Figure 18–2

30. Hormones
• Circulate freely or bound to transport proteins

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

33. Bloodstream
• Contains substantial reserve of bound
hormones

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

43. G Proteins and Hormone Activity
Figure 18–3

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

47. G Proteins and Hormone Activity
Figure 18–3

48. Lower cAMP Levels
1.
2.
3.
4.
Activated G protein stimulates PDE activity
Inhibits adenylate cyclase activity
Levels of cAMP decline
cAMP breakdown accelerates; cAMP
synthesis is prevented

49. G Proteins and Hormone Activity
Figure 18–3

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

53. Steroid Hormones
Figure 18–4a

54. Steroid Hormones
• Alter rate of DNA transcription in nucleus:
– change patterns of protein synthesis
• Directly affect metabolic activity and structure
of target cell

55. Thyroid Hormones
Figure 18–4b

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

57. How are endocrine
organs controlled?

58. Endocrine Reflexes
• Functional counterparts of neural reflexes
• In most cases, controlled by negative feedback
mechanisms

59. Simple Endocrine Reflex
• Involves only 1 hormone
• Controls hormone secretion by:
– Heart (ANF)
– Pancreas (insulin, glucagon)
– parathyroid gland (calcitonin)
– digestive tract

60. Complex Endocrine Reflex
• Involves:
– 1 or more intermediary steps
– 2 or more hormones
• Stimulating, releasing, inhibitory hormones

61. Endocrine System
Figure 18–1

62. Hypothalamus
Figure 18–5

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

65. Neuroendocrine Reflexes
• Pathways include both neural and endocrine
components

66. Complex Commands
• Issued by changing:
– amount of hormone secreted
– pattern of hormone release
• (continuous, pulsed)

67. Pulses
• Hypothalamic and pituitary hormones
released in sudden bursts
• Frequency varies response of target cells

68. Where is the pituitary
gland located, and
what is its relationship
to the hypothalamus?

69. Pituitary Gland
Figure 18–6

70. Pituitary Gland
• Also called hypophysis
• Lies within sella turcica
• Hangs inferior to hypothalamus:
– connected by infundibulum

71. Diaphragma Sellae
• Locks pituitary in position
• Isolates it from cranial cavity

72. Pituitary Gland
• Releases 9 important peptide hormones
• Hormones bind to membrane receptors:
– use cAMP as second messenger

73. Anterior Lobe
•
Also called adenohypophysis:

74. Median Eminence
• Swelling near attachment of infundibulum
• Where hypothalamic neurons release
regulatory factors:
– into interstitial fluids
– through fenestrated capillaries

75. Median Eminence
Figure 18–7

76. Portal Vessels
• Blood vessels link 2 capillary networks
• Entire complex is portal system

77. Hypophyseal Portal System
• Ensures that regulatory factors reach intended
target cells before entering general circulation

78. What are the hormones produced
by the anterior lobe, and what are
the functions of those hormones?

79. 2 Classes of Hypothalamic Regulatory
Hormones
1. Releasing hormones
2. Inhibiting hormones

80. Hypothalamic
Regulatory Hormones
• Rate of secretion
is controlled by
negative
feedback
Figure 18–8a

82. Hypothalamic
Regulatory Hormones
Figure 18–8b

83. Releasing Hormones (RH)
• Stimulate synthesis and secretion of 1 or more
hormones at anterior lobe

84. Inhibiting Hormones (IH)
• Prevent synthesis and secretion of hormones
from anterior lobe

85. Anterior Lobe
• Hormones “turn on”
endocrine glands or
support other organs
Figure 18–8a

87. Thyroid-Stimulating
Hormone (TSH)
• Also called thyrotropin
• Triggers release of thyroid hormones

88. Adrenocorticotropic
Hormone (ACTH)
• Also called corticotropin
• Stimulates release of steroid hormones by
adrenal cortex
• Targets cells that produce glucocorticoids

89. Gonadotropins
• Regulate activities of gonads (testes, ovaries)
• Follicle-stimulating hormone
• Luteinizing hormone

90. Follicle-Stimulating
Hormone (FSH) (1 of 2)
• Also called follitropin
• Stimulates follicle development and estrogen
secretion in females

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)

95. Prolactin (PRL)
• Stimulates PIH release
• Inhibits secretion of prolactin-releasing factors
(PRF)

96. Prolactin (PRL)
Figure 18–8b

97. Growth Hormone (GH)
• Also called somatotropin
• Stimulates cell growth and replication
• Production regulated by:
– growth hormone–releasing hormone (GH–RH)
– growth hormone–inhibiting hormone (GH–IH)

98. Melanocyte-Stimulating
Hormone (MSH)
• Also called melanotropin
• Stimulates melanocytes to produce melanin
• Inhibited by dopamine

99. Melanocyte-Stimulating
Hormone (MSH)
• Secreted during:
– fetal development
– early childhood
– pregnancy
– certain diseases

100. What hormones are produced
by the posterior lobe, and
what are their functions?

101. Posterior Lobe
• Also called neurohypophysis
• Contains unmyelinated axons of hypothalamic
neurons
• Supraoptic and paraventricular nuclei
manufacture:
– antidiuretic hormone (ADH)
– oxytocin (OT)

102. Antidiuretic Hormone
• Decreases amount of water lost at kidneys
• Elevates blood pressure
• Release inhibited by alcohol

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

106. Thyroid Gland
Figure 18–10a, b

107. Thyroid Follicles
• Hollow spheres lined by cuboidal epithelium
• Cells surround follicle cavity that contains
viscous colloid

108. Thyroid Follicles
• Surrounded by network of capillaries that:
– deliver nutrients and regulatory hormones
– accept secretory products and metabolic wastes

109. Thyroid Follicles
Figure 18–11a, b

110. Thyroglobulin
•
•
•
•
Globular protein
Synthesized by follicle cells
Secreted into colloid of thyroid follicles
Molecules contain amino acid tyrosine

111. Thyroglobulin
Figure 18–10c

112. What hormones are produced by
the thyroid gland?

113. Thyroxine (T4)
• Also called tetraiodothyronine
• Contains 4 iodide ions

114. Triiodothyronine (T3)
• Contains 3 iodide ions

115. Rate of Thyroid
Hormone Release
• Major factor:
– TSH concentration in
circulating blood
Figure 18–11b

116. Thyroid-Binding Globulins (TBGs)
• Transport proteins
• Attach to most T4 and T3 molecules

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

122. Calorigenic Effect
• Cell consumes more energy resulting in
increased heat generation

123. Thyroid Hormones
• In children, essential to normal development
of:
– skeletal, muscular, and nervous systems

124. Thyroid Gland
• Is responsible for strong, immediate, and
short-lived increase in rate of cellular
metabolism

125. Thyroid Gland
Table 18–3

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

128. Where are the
parathyroid glands?

129. Parathyroid Glands
• Embedded in posterior surface of thyroid
gland
Figure 18–12

130. What is the function
of the hormone produced
by the parathyroid glands?

131. Parathyroid Hormone (PTH)
• Produced by chief cells
• In response to low concentrations of Ca2+

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

133. Calcitriol
• Effects complement or enhance PTH
• Enhances Ca2+, PO43— absorption by digestive
tract

134. Parathyroid Glands
• Primary regulators of
blood calcium I levels in
adults
Figure 18–13

135. What are the location, structure,
and general functions of the
adrenal gland?

136. Adrenal Glands
• Lie along superior border of each kidney
• Subdivided into superficial adrenal cortex and
an inner adrenal medulla

137. Adrenal Cortex
•
Subdivided into 3 regions:
1. zona glomerulosa
2. zona fasciculate
3. zona reticularis

138. What hormones are produced
by the adrenal glands, and
what are their functions?

139. Zona Glomerulosa
• Outer region of adrenal cortex
• Produces mineralocorticoids:
– e.g., aldosterone

140. Aldosterone
• Stimulates:
– conservation of sodium ions
– elimination of potassium ions
• Increases sensitivity of salt receptors in
taste buds

141. Aldosterone
• Secretion responds to:
–
–
–
–
Rise in blood Na+
drop in blood K+ concentration
blood volume
blood pressure

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

153. Pancreas
Figure 18–15

154. Endocrine Pancreas
• Cells form clusters:
– pancreatic islets, or islets of Langerhans

155. What hormones are
produced by the pancreas, and
what are their functions?

156. 4 Types of Cells
in Pancreatic Islets
• Alpha cells:
– produce glucagon
• Beta cells:
– secrete insulin

157. Blood Glucose Levels
• When levels rise:
– beta cells secrete insulin, stimulates transport of
glucose across cell membranes
• When levels decline:
– alpha cells secrete glucagons, stimulates glucose
release by liver

158. Insulin
• Is a peptide hormone released by beta cells
• Affects target cells

159. 5 Effects of Insulin
1. Accelerates glucose uptake
2. Accelerates glucose utilization and enhanced
ATP production
3. Stimulates glycogen formation
4. Stimulates amino acid absorption and
protein synthesis
5. Stimulates triglyceride formation in adipose
tissue

160. Glucagons
• Released by alpha cells
• Mobilize energy reserves
• Affects target 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?

163. Intestines
• Produce hormones important to coordination
of digestive activities

164. Kidneys
• Produce the hormones calcitriol and
erythropoietin
• Produce the enzyme (hormone?) renin

165. Calcitriol
• Stimulates calcium
and phosphate ion
absorption along
digestive tract
Figure 18–17a

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

168. Erythropoietin (EPO)
• Stimulates red blood cell production by bone
marrow:
– increased RBCs elevate blood volume

169. Renin
• Converts angiotensinogen to angiotensin I in
liver
• Angiotensin I is converted to angiotensin II (in
lungs via ACE)

170. Angiotensin II
1. Stimulates adrenal production of
aldosterone
2. Stimulates pituitary release of ADH
3. Promotes thirst
4. Elevates blood pressure

171. The Renin–Angiotensin System
Figure 18–17b

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

178. Chapter 16
Autonomic Nervous System

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)

181. Preganglionic Fibers
• Axons of preganglionic
neurons
• Leave CNS and synapse
on ganglionic neurons

182. Autonomic Ganglia
• Peripheral ganglia
• Contain many ganglionic
neurons
• Ganglionic neurons
innervate visceral (pertaining
to the internal organs) effectors:
– cardiac muscle
– smooth muscle
– glands
– adipose tissues

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

188. Sympathetic Chain
•
•
•
•
•
3 cervical ganglia
10–12 thoracic ganglia
4–5 lumbar ganglia
4–5 sacral ganglia
1 coccygeal ganglion

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

193. ANS: Sympathetic Division
Figure 16–3

194. Structure of the
Sympathetic Division
• Preganglionic neurons located between
segments T1 and L2 of spinal cord
• Ganglionic neurons in ganglia near vertebral
column

195. Ganglionic Neurons
• Occur in 3 locations:
– sympathetic chain ganglia
– collateral ganglia
– adrenal medullae
Figure 16–4

197. Collateral ganglia

198. The Adrenal Medullae
Figure 16–4c

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?

201. Neuroendocrine Cells
of Adrenal Medullae
• Secrete hormones epinephrine (E) and
norepinephrine (NE)

202. Epinephrine
• Also called adrenaline
• Is 75–80% of secretory output
• Remaining is noradrenaline (NE)

203. Distribution
• Bloodstream carries hormones through body
• Causing changes in metabolic activities of
different cells

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

207. Cholinergic Synapses
• Use ACh as transmitter
• Excitatory effect on ganglionic neurons

208. Adrenergic Neurons
• Use NE as neurotransmitter

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

212. Effects of
Sympathetic Stimulation
• Primarily from interactions of NE and E with
adrenergic membrane receptors

213. 2 Classes of
Sympathetic Receptors
• Alpha receptors
• Beta receptors

214. Norepinephrine
• Stimulates alpha receptors to greater degree
than beta receptors

215. Epinephrine
• Stimulates both classes of receptors

216. Localized Sympathetic Activity
• Involves release of NE at varicosities
• Primarily affects alpha receptors near active
varicosities

217. Generalized
Sympathetic Activation
• Release of Epinephrine by adrenal medulla
• Affect alpha and beta receptors throughout
body

218. Alpha and Beta Receptors
• G proteins

219. What are the effects of sympathetic
neurotransmitters on target organs
and tissues?

220. Stimulation of
Alpha (a) Receptors
• Activates enzymes on inside of cell membrane

221. Alpha Receptors
• Alpha-1 (a1)
• Alpha-2 (a2)

222. Beta Receptors
• Two types:
– Beta-1 (b1)
– Beta-2 (b2)

223. Beta-1 (b1)
• Increases metabolic activity

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?

229. ANS: The
Parasympathetic Division
Figure 16–7

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?

234. Parasympathetic
Preganglionic Fibers
• Leave brain as components of cranial nerves:
– III (oculomotor)
– VII (facial)
– IX (glossopharyngeal)
– X (vagus)

235. Parasympathetic Innervation
Figure 16–8

236. Vagus Nerve
• Preganglionic parasympathetic innervation to
structures in:
– neck
– thoracic and abdominopelvic cavity
– distal portion of large intestine

237. Vagus Nerve
• Provides 75% of all parasympathetic outflow
• Branches intermingle with fibers of
sympathetic division

238. Sacral Segments of Spinal Cord
• Preganglionic fibers carry sacral
parasympathetic output
• Do not join ventral roots of spinal nerves

239. Pelvic Nerves
• Innervate intramural ganglia in walls of:
– kidneys
– urinary bladder
– portions of large intestine
– sex organs

240. What are the effects
of parasympathetic
neurotransmitters on
target organs and tissues?

241. Parasympathetic Activation
• Centers on relaxation, food processing, and
energy absorption
• Localized effects, last a few seconds at most

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

247. Anabolic System
• Stimulation increases nutrient content of
blood
• Cells absorb nutrients

248. Parasympathetic Neurons
• All release ACh as neurotransmitter
• Effects vary widely

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

254. Summary:
Parasympathetic Division
• Ganglionic neurons located in or next to target
organs

255. Summary:
Parasympathetic Division
• Innervates areas served by:
– cranial nerves
– organs in thoracic
– organs in abdominopelvic cavities

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

257. Summary:
Parasympathetic Division
• Effects of stimulation are brief and restricted
to specific organs and sites

258. Comparing Sympathetic and
Parasympathetic Divisions
• Sympathetic:
– widespread impact
– reaches organs and tissues throughout body
• Parasympathetic:
– innervates only specific visceral structures

259. Differences between Sympathetic and
Parasympathetic Divisions
Figure 16–9

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

264. 6 Autonomic Plexuses
1.
2.
3.
4.
5.
6.
Cardiac plexus
Pulmonary plexus
Esophageal plexus
Celiac plexus
Inferior mesenteric plexus
Hypogastric plexus

265. Why is autonomic
tone important?

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