Download Chemical Messengers

Communication critical for the survival of body cells.
2 major regulatory systems of the body
• Nervous
• Endocrine
communicate with the cells/tissues/organs/systems they
control.
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chemical Messengers
• Four types
1) Paracrines
• Local chemical messengers
• Exert effect only on neighbouring cells in immediate
environment of secretion site
2) Neurotransmitters
• Short-range chemical messengers
• Diffuse across narrow space to act locally on adjoining
target cell (another neuron, a muscle, or a gland)
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
1
Chemical Messengers
3) Hormones
• Long-range messengers
• Secreted into blood by endocrine glands in response to
appropriate signal
• Exert effect on target cells some distance away from
release site
4) Neurohormones
• Hormones released into blood by neurosecretory
neurons
• Distributed through blood to distant target cells
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chemical Messengers
• Extracellular chemical messengers: cell
response via signal transduction
– Membrane to cytosol
• Binding of extracellular messenger (first
messenger) to receptor brings about intracellular
response by affecting
– channels
– second-messenger systems
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
2
Chemical Messengers
ion channel
cAMP
effect
genes
nucleus
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Comparison of Nervous System and
Endocrine System
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
3
Hormones
Messengers of endocrine system
Released from endocrine gland
into blood
Transported in blood
Target cell:expresses specific
receptors
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Neurohormones
Released from neuron
into blood
Acts in manner similar
to hormones
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
4
Endocrine Glands
Derived from epithelial tissue
Primary endocrine organs
Secondary endocrine organs
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Negative Feedback
Gland 1
Hormone 1
Gland 1
↑ Hormone X
Gland 2
Hormone 2
Positive Feedback
Hormone 1
Gland 2
↓ Hormone X
-
↑ Hormone X
-
Hormone 2
Gland 3
Gland 3
Hormone 3
Hormone 3
↑ Hormone X
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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Physiological roles of Calcium
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Muscle contraction
Neurotransmitter release
Blood clotting
Intracellular signaling
Proliferation
Secretion
Fertilization
Cell motility
Maintenance of tight junctions
Structural integrity of bones and teeth
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine Control of Calcium Metabolism
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Calcium in the body:
Average adult human - 1.1kg Calcium
99% in crystalline form in bones and teeth
0.9% intracellularly in soft tissues
<0.1% in ECF
– Bound to plasma proteins
– Complexed with PO43– Freely diffusible: biologically active; subject to regulation
• Plasma Ca2+ : normally 2.5mmol/L (2.2 to 2.6mmol/L)
• Intracellular Ca2+ : normally 100nmol/L
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
6
Endocrine Control of Calcium Metabolism
Why regulate plasma Ca2+?
Primarily to prevent changes in neuromuscular excitability
–Hypocalcemia
•Overexcitability of nerves and muscles
•Decreased free Ca2+ causes increased Na permeability of cells
•Severe overexcitability can cause fatal spasmic contractions of
respiratory muscles
–Hypercalcemia
•Reduces excitability
•Increased free Ca2+ causes reduced Na permeability
•Cardiac arrhythmia
Changes in plasma Ca2+ will also impact on other physiological events
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine Control of Calcium Metabolism
• Three hormones regulate plasma concentration
of Ca2+ (and PO43-)
– Parathyroid hormone (PTH)
– Calcitonin
– Vitamin D (cholecalciferol)
• Regulation of plasma concentration of Ca2+
depends on hormonal control of exchange
between ECF and
– Bone (most important in short-term)
– Kidneys
– Intestine
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
7
Endocrine Control of Calcium Metabolism
• Parathyroid hormone (PTH)
– Secreted by parathyroid glands
– Primary regulator of Ca2+
• Raises free plasma Ca2+ levels by its effects on bone
kidneys, and intestines (via Vit D)
– Essential for life
• Prevents fatal consequences of hypocalcemia
– Facilitates activation of Vitamin D
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine Control of Calcium Metabolism
trachea
plasma
calcium
plasma
calcium
parathyroid
thyroid
Parathyroid hormone
Bone
Vitamin D (Intestines)
Kidney
parathyroid
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
8
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
9
Endocrine Control of Calcium Metabolism
• Vitamin D
– Stimulates Ca2+ and PO43- absorption from
intestine
– Can be synthesized from cholesterol derivative
when exposed to sunlight
• Often inadequate source
– Amount supplemented by dietary intake
– Must be activated first by liver and then by
kidneys before it can exert its effect on intestines
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine Control of Calcium Metabolism
• Calcitonin
– Hormone produced by C cells of thyroid gland
– Negative-feedback fashion
• Secreted in response to increase in plasma Ca2+
concentration
– Acts to lower plasma Ca2+ levels by inhibiting
activity of bone osteoclasts
– Unimportant except during hypercalcemia
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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Negative-feedback Loops Controlling
Parathyroid Hormone and Calcitonin Secretion
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Calcium Disorders
• PTH hypersecretion (hyperparathyroidism)
– Characterized by hypercalcemia and
hypophosphatemia
• PTH hyposecretion (hypoparathyroidism)
– Characterized by hypocalcemia and
hyperphosphatemia
• Vitamin D deficiency
– Children – rickets
– Adults – osteomalacia
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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