Chapter 13: THE
ENDOCRINE SYSTEM
Endocrine Functions: Hormones
• Hormones:
– Come from endocrine glands
– Circulate in the blood stream
– Act on specific cells in the body
Endocrine Functions: Hormones
Figure 13.1
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Endocrine System Characteristics
• Access to every cell
• Each hormone acts only on specific cells
(target cells)
• Only specific cells have receptors for specific
hormones
• Endocrine control slower than nervous system
• Endocrine and nervous systems interact
Classification of Hormones: Steroid
• Steroid Hormones:
– Lipid soluble, chemically derived from cholesterol
– Enter target cells
– Activate specific genes to produce specific
proteins
– Slower acting than non-steroid hormones, minutes
to hours
PLAY
Press to play Steroid Hormone animation
Steroid Hormone Action on a
Target Cell
Figure 13.2
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Classification of Hormones:
Nonsteroid
• Nonsteroid hormones:
– Water soluble
– Bind to receptors on target cell membranes
– Work through intermediate mechanisms to activate
existing enzymes
– Faster action than steroid hormones, seconds to
minutes
PLAY
Press to play Non-Steroid Hormones animation
Nonsteroid Hormone Action on a
Target Cell
Figure 13.3
Role of Negative Feedback Loops
Figure 13.4
3
Hypothalamus and the Posterior
Pituitary Gland
• Posterior pituitary
– Connection to hypothalamus:
hormones made in
hypothalamus, stored in
posterior pituitary
– Hormones: nonsteroidal
• Antidiuretic hormone (ADH):
conserves water in kidneys,
regulates water balance in body
• Oxytocin: causes uterine
contractions during labor and
milk ejection through
neuroendocrine reflex
Figure 13.5
Hypothalamus and the Posterior
Pituitary Gland
Figure 13.6
Hypothalamus and the Anterior
Pituitary Gland
• Anterior pituitary
– Connection to hypothalamus: releasing and inhibiting
hormones from hypothalamus travel to pituitary
through pituitary portal system
– Hormones: nonsteroidal
• ACTH: stimulates adrenal cortex
• TSH: acts on thyroid gland
• FSH, LH, Prolactin: related to control of reproductive cycles
and lactation
• Growth Hormone: widespread effects on body
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Hypothalamus and the Anterior
Pituitary Gland
Figure 13.7
Hormones of the Pituitary Gland
Pituitary Disorders
• Syndrome of inappropriate ADH
Secretion (SIADH): hypersecretion
of ADH, excessive water retention
• Diabetes Insipidus: hyposecretion
of ADH, inability to conserve water
appropriately
• Gigantism: hypersecretion of
growth hormone
• Pituitary Dwarfism: hyposecretion
of growth hormone
Figure 13.8
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Pancreas: Endocrine Functions
• Structures: islets of Langerhans
• Hormones: nonsteroidal
– Glucagon: made by alpha cells, raises blood sugar
– Insulin: made by beta cells, lowers blood sugar
– Somatostatin: made by delta cells, inhibits
secretion of glucagon and insulin, regulates other
hormones
Roles of Insulin and Glucagon in
Regulating Blood Glucose
Figure 13.9
Adrenal Glands: Cortex
• Adrenal cortex
– Secretion: mediated through hypothalamuspituitary secretions
– Hormones: steroidal
• Glucocorticoids: cortisol
• Mineralocorticoids: aldosterone
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Secretion of Cortisol
Figure 13.10
Adrenal Glands: Medulla
• Adrenal medulla:
neuroendocrine organ
– Secretion: sympathetic
nervous system
– Hormones: nonsteroidal
• Epinephrine and
norepinephrine: enhance
function of sympathetic
nervous system
(Fight or flight)
Figure 13.11
Thyroid and Parathyroid Glands
Figure 13.12
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Thyroid Gland
• Secretion: mediated through hypothalamus-pituitary
secretions
• Steroidal hormones:
– Thyroxine (T4) and Triiodothyronine (T3): both regulate
production of ATP from glucose, affects metabolic rate
– Calcitonin: lowers blood calcium levels
Negative Feedback Control of
Thyroxine Secretion
Figure 13.13
Figure 13.14
Parathyroid Glands
• Secretion: response to lowered blood calcium levels
• Hormone: Parathyroid hormone (PTH),
nonsteroidal
– Removes calcium and phosphate from bone
– Increases absorption of calcium by the digestive tract
– Increases renal retention of calcium and excretion of
phosphate
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Homeostatic Regulation of Blood
Calcium Concentration
Figure 13.15
Testes
• Hormone: testosterone (steroidal)
– Functions:
• Regulates development and normal functioning of
sperm, male reproductive organs, male sex drive
• Development of male secondary sex characteristics
Ovaries
• Hormones (steroidal) and functions:
– Estrogen: initiates development of secondary sex
characteristics, regulates menstrual cycle
– Progesterone: regulates menstrual cycle
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Other Hormone Sources
• Thymus: thymosin and thymopoietin, assist
maturation of T lymphocytes
• Pineal gland: melatonin
Other Hormone Sources
• Heart: atrial natriuretic hormone (ANH)
• Digestive system: gastrin, secretin,
cholecystokinin
• Kidney: erythropoietin, renin
Other Chemical Messengers
•
•
•
•
Histamine: inflammation
Prostaglandins: local control of blood flow
Nitric oxide: multiple functions
Growth factors: local acting
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Disorders of the Endocrine System
• Thyroid
– Hypothyroidism:
• Children: cretinism—mental retardation and stunted growth
• Adults: myxedema—swelling under skin, lethargy, weight gain,
low body temperature
– Hyperthyroidism:
• Graves Disease—autoimmune disorder leads to antibodies
stimulating thyroxine production, leads to bulging eyes
Disorders of the Endocrine System
• Adrenal glands
– Addison’s Disease: failure of adrenal cortex, cortisol
deficiency
• Slower development
– Cushing’s Syndrome: excessive cortisol
• Leads to fat on back of neck
Figure 13.16
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