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Copyright 2009, John Wiley & Sons, Inc.
The Endocrine System
Copyright 2009, John Wiley & Sons, Inc.
Thyroid Gland
Located inferior to larynx 2 lobes connected by isthmus Thyroid follicles produce thyroid hormones
Thyroxine or tetraiodothyronine (T4)
Triiodothyronine (T3) Both increase BMR, stimulate protein synthesis, increase use
of glucose and fatty acids for ATP production
Parafollicular cells or C cells produce calcitonin Lowers blood Ca2+ by inhibiting bone resorption
Copyright 2009, John Wiley & Sons, Inc.
Thyroid Gland
Copyright 2009, John Wiley & Sons, Inc.
Control of thyroid hormone secretion
Thyrotropin-releasing hormone (TRH) from hypothalamus
Thyroid-stimulating hormone (TSH) from anterior pituitary
Situations that increase ATP demand also increase secretion of thyroid hormones
Low blood levels of T3
and T3 or low metabolicrate stimulate release of
HypothalamusTRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
1
Anteriorpituitary
TRH, carriedby hypophysealportal veins toanterior pituitary,stimulatesrelease of TSHby thyrotrophs
Low blood levels of T3
and T3 or low metabolicrate stimulate release of
Hypothalamus
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
1
2
Anteriorpituitary
TRH, carriedby hypophysealportal veins toanterior pituitary,stimulatesrelease of TSHby thyrotrophs
TSH released intoblood stimulatesthyroid follicular cells
Thyroidfollicle
Low blood levels of T3
and T3 or low metabolicrate stimulate release of
Hypothalamus
Anteriorpituitary
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
1
2
3
T3 and T4
released intoblood byfollicular cells
TRH, carriedby hypophysealportal veins toanterior pituitary,stimulatesrelease of TSHby thyrotrophs
TSH released intoblood stimulatesthyroid follicular cells
Thyroidfollicle
Low blood levels of T3
and T3 or low metabolicrate stimulate release of
Hypothalamus
Anteriorpituitary
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
1
2
3
4 T3 and T4
released intoblood byfollicular cells
ElevatedT3inhibitsrelease ofTRH andTSH(negativefeedback)
TRH, carriedby hypophysealportal veins toanterior pituitary,stimulatesrelease of TSHby thyrotrophs
TSH released intoblood stimulatesthyroid follicular cells
Thyroidfollicle
Low blood levels of T3
and T3 or low metabolicrate stimulate release of
Hypothalamus
Anteriorpituitary
TSH
TRH
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
1
2
3
5
4
Copyright 2009, John Wiley & Sons, Inc.
Parathyroid Glands
Embedded in lobes of thyroid gland Usually 4 Parathyroid hormone (PTH) or parathormone
Major regulator of calcium, magnesium, and phosphate ions in the blood
Increases number and activity of osteoclasts Elevates bone resorption
Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback
Copyright 2009, John Wiley & Sons, Inc.
Parathyroid Glands
Copyright 2009, John Wiley & Sons, Inc.
Roles of Calcitonin, Parathyroid hormone, Calcitrol in Calcium Homeostasis
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
2
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
3
2
1 High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.
3
4 2
1
PTH also stimulatesthe kidneys to releaseCALCITRIOL.
High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.
3
4 25
1
CALCITRIOL stimulatesincreased absorption ofCa2+ from foods, whichincreases blood Ca2+ level.
PTH also stimulatesthe kidneys to releaseCALCITRIOL.
High level of Ca2+ in bloodstimulates thyroid glandparafollicular cells to release more CT.
Low level of Ca2+ in bloodstimulates parathyroid gland chief cells to release more PTH.
CALCITONIN inhibitsosteoclasts, thus decreasingblood Ca2+ level.
PARATHYROID HORMONE (PTH)promotes release of Ca2+ frombone extracellular matrix intoblood and slows loss of Ca2+ in urine, thus increasing bloodCa2+ level.
3
4 25
6
Copyright 2009, John Wiley & Sons, Inc.
Adrenal Glands
2 structurally and functionally distinct regions Adrenal cortex
Mineralocorticoids affect mineral homeostasis Glucocorticoids affect glucose homeostasis
cortisol Androgens have masculinzing effects
Dehydroepiandrosterone (DHEA) only important in females Adrenal medulla
Modified sympathetic ganglion of autonomic nervous system
Intensifies sympathetic responses Epinephrine and norepinephrine
Copyright 2009, John Wiley & Sons, Inc.
Adrenal Glands
Copyright 2009, John Wiley & Sons, Inc.
Pancreatic Islets
Both exocrine and endocrine gland Roughly 99% of cells produce digestive enzymes Pancreatic islets or islets of Langerhans
Alpha or A cells secrete glucagon – raises blood sugar Beta or B cells secrete insulin – lowers blood sugar Delta or D cells secrete somatostatin – inhibits both insulin
and glucagon F cells secrete pancreatic polypeptide – inhibits
somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes
Copyright 2009, John Wiley & Sons, Inc.
Pancreas
Copyright 2009, John Wiley & Sons, Inc.
Negative Feedback Regulation of Glucagon and Insulin
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
1
GLUCAGON
Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
GLUCAGON
1
2 Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Glucose releasedby hepatocytesraises blood glucoselevel to normal
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
GLUCAGON
1
2
3
Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Glucose releasedby hepatocytesraises blood glucoselevel to normal
If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
GLUCAGON
1
2
3
4
Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Glucose releasedby hepatocytesraises blood glucoselevel to normal
If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
High blood glucose(hyperglycemia)stimulates beta cellsto secrete
GLUCAGON
1 5
2
3
4
INSULIN
Insulin acts on variousbody cells to:
• accelerate facilitated diffusion of glucose into cells• speed conversion of glucose into glycogen (glycogenesis)• increase uptake of amino acids and increase protein synthesis• speed synthesis of fatty acids (lipogenesis)• slow glycogenolysis• slow gluconeogenesis
Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Glucose releasedby hepatocytesraises blood glucoselevel to normal
If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
High blood glucose(hyperglycemia)stimulates beta cellsto secrete
INSULINGLUCAGON
1 5
2
3
4
6 Insulin acts on variousbody cells to:
• accelerate facilitated diffusion of glucose into cells• speed conversion of glucose into glycogen (glycogenesis)• increase uptake of amino acids and increase protein synthesis• speed synthesis of fatty acids (lipogenesis)• slow glycogenolysis• slow gluconeogenesis
Blood glucose level falls
Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Glucose releasedby hepatocytesraises blood glucoselevel to normal
If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
High blood glucose(hyperglycemia)stimulates beta cellsto secrete
INSULINGLUCAGON
1 5
2
3
4
6
7
Insulin acts on variousbody cells to:
• accelerate facilitated diffusion of glucose into cells• speed conversion of glucose into glycogen (glycogenesis)• increase uptake of amino acids and increase protein synthesis• speed synthesis of fatty acids (lipogenesis)• slow glycogenolysis• slow gluconeogenesis
If blood glucose continuesto fall, hypoglycemiainhibits release ofinsulin
Blood glucose level falls
Glucagon acts onhepatocytes(liver cells) to:
• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)
Glucose releasedby hepatocytesraises blood glucoselevel to normal
If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon
Low blood glucose(hypoglycemia)stimulates alphacells to secrete
High blood glucose(hyperglycemia)stimulates beta cellsto secrete
INSULINGLUCAGON
1 5
2
3
4
6
7
8
Copyright 2009, John Wiley & Sons, Inc.
Ovaries and Testes
Gonads – produce gametes and hormones Ovaries produce 2 estrogens (estradiol and estrone)
and progesterone With FSH and LH regulate menstrual cycle, maintain
pregnancy, prepare mammary glands for lactation, maintain female secondary sex characteristics
Inhibin inhibits FSH Relaxin produced during pregnancy
Testes produce testosterone – regulates sperm production and maintains male secondary sex characteristics Inhibin inhibits FSH
Copyright 2009, John Wiley & Sons, Inc.
Pineal Gland
Attached to roof of 3rd ventricle of brain at midline
Masses of neuroglia and pinealocytes Melatonin – amine hormone derived from
serotonin Appears to contribute to setting biological
clock More melatonin liberated during darkness
than light
Copyright 2009, John Wiley & Sons, Inc.
Thymus and Other Endocrine Tissues Thymus
Located behind sternum between the lungs Produces thymosin, thymic humoral factor
(THF), thymic factor (TF), and thymopoietin All involved in T cell maturation
Autocrine chemical signals include the chemical mediators of inflammation. Prostaglandins Thromboxanes Prostacyclins Leukotrienes
Collectively known as eicosanoids.
Autocrine Chemical Signals
These products are released from injured cells. Responsible for initiating some of the symptoms of
inflammation. Pain receptors are stimulated directly by
prostaglandins.
Autocrine Chemical Signals
Essential fatty acid deficiency and omega-6:omega-3 imbalance is linked with the following serious health conditions:
Prostaglandins
Heart attack Cancer Insulin resistance
Asthma
Lupus Schizophrenia Depression Stroke
Obesity Diabetes Arthritis Alzheimer’s Disease
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