Endocrine System
Chapter 16
The Endocrine System
• Specialized glands throughout the body
• Regulates metabolic activity
– Secrete hormones into ECF
• Slow acting
• Long living
• Act on target cells
– Signaling molecules
• Other tissues produce
hormones too
Categories of Hormones
• Amino acid based
– Chains of AA’s
– Not membrane soluble (hydrophilic)
– Regulatory G proteins and 2nd messengers
– e.g. oxytocin, insulin, and prolactin
– e.g. epinephrine, norepinephrine, and thyroxine
– Derived from AA tryptophan and tyrosine
• Steroids
– Lipids made from cholesterol
– Membrane soluble (hydrophobic)
– Direct gene activation
– e.g. testosterone, estrogen, and cortisol
Amino Acid Action (cAMP)
• Binds to PM receptors (1st messenger)
– Conformation change binds inactive G protein
– Activated by GTP replacing GDP
• Active G protein binds to adenylate cyclase
(effector)
– Stimulatory (Gs) or inhibitory (Gi)
– cAMP (2nd messenger) from ATP
• cAMP activates protein kinase A
– Phosphorylates proteins causing signaling cascade
• Target cell specificity produces/inhibits hormone production
– Phosphodiesterase rapidly degrades
Amino Acid Action (PIP2)
• Binds to PM receptors (1st messenger)
– Conformation change binds inactive G protein
– Activated by GTP replacing GDP
• Active G protein binds to phospholipase C
(effector)
– Stimulatory (Gs) or inhibitory (Gi)
– DAG and IP3 (2nd messengers) from PIP2
• DAG activates protein kinase C
• IP3 triggers Ca2+ (2nd messenger) release
Steroid Action
• Binds to intracellular receptors
• Hormone-receptor complex binds to DNA
– Activates or inhibits
– Gene transcription (mRNA production)
• mRNA translated into proteins
Hormonal Functioning
• Stimulating release
– Humoral: concentration of ions & nutrients in blood
• Drop in Ca2+ signals PTH or increased glucose signals insulin
– Neural: nerve fibers
• Stress (SNS) signals NE and Epi
– Hormonal: other endocrine gland secretions
• Hypothalamus signals anterior pituitary
• Interactions at target cells
– Permissiveness: requirement of 1+ hormone for full effect
• Reproductive hormones need thyroid hormone
– Synergism: 1+ hormone produces same effect  both amplifies
• Glucagon and epinephrine signal liver to release glucose
– Antagonism: hormones oppose one another
• Glucagon increases and insulin decreases blood glucose levels
• Generally regulated by negative feedback
– Oxytocin is positive feedback
Pituitary Gland
• Posterior lobe is neural tissue
– Store hypothalamic hormones
– Exocytic release on demand
• Anterior lobe is glandular
tissue
– Produce hormones
– Release of hormones to blood
portal system
• Hypothalamic control
• Releasing or inhibiting hormones
Posterior Lobe
• Oxytocin
– Uterine contractions (smooth muscle)
– Milk letdown (glandular muscle)
– Sexual arousal, satisfaction, and
‘bonding’ behavior in males &
nonlactating females
• Antidiuretic hormone
– Water balance and loss
– Vasoconstriction of visceral blood
vessels
• Raises blood pressure  vasopressin
Anterior Lobe
• Tropic hormones
–
–
–
–
TSH
ACTH
FSH
LH
• Non-tropic
– GH
– PRL
– Melanocyte-stimulating
hormone (MSH): controls
appetite
Growth Hormone
• Growth hormone releasing (GHRH) and inhibiting (GHIH) hormones
regulate
• Increase size of multiple target cells
– Promotes protein synthesis/growth
• Primarily skeletal muscle mass and bone length
– Metabolic effects (glucose conservation)
• Mobilize fat from adipose
• Hypersecretion
– Gigantism: in children; tall stature w/ normal body proportions
– Acromegaly: in adults; disproportionately large hands, feet, face
• Hyposecretion
– Pituitary dwarfism: in children; short stature w/normal body
proportions
• TSH, LH, and FSH reduced can misproportioned and/or delay sexual maturity
• Artificial production w/ pros and cons
Prolactin
• Prolactin inhibiting hormone (PIH) regulates
• Stimulates milk production
– Rise and fall w/ estrogen levels in females
• Breast tenderness prior to menstrual period
• Elevates at end of pregnancy; suckling maintains
– Role in males is not understood
• Hypersecretion
– Inappropriate lactation, lack of menses, impotence in
males
• Hyposecretion only problem for nursing females
Thyroid Gland
• Thyrotropin-releasing hormone (TRH) regulates
TSH release to regulate
• Anatomy
– Bilobed structure w/connecting isthmus
– Composed of follicles surrounded by follicular cells w/
thyroglobin
• Colloid in lumen is thyroglobin bound to iodine  thyroid
hormone
– Parafollicular cells w/i follicular epithelium secretes
calcitonin
• Inhibits osteoclast activity and Ca 2+ release; stimulates Ca 2+
uptake
Thyroid Hormone (TH)
• Most processes in body (table 16.2)
– Steroid hormone action
– Oxidizes glucose to up metabolic rate & heat
production
– Maintains blood pressure
– Regulates tissue growth and development
– Skeletal and nervous system development
– Reproductive maturation
• Thyroxine (T4) primarily produced, but converted
to triiodothytonine (T3) by targets
Thyroid Imbalances
• Hypothyroidism
– Myxedema in adults
• Low metabolic rate, chills, dry skin, puffy eyes, lethargy, edema
– Goiter from lack of iodine
• Gland enlargement
– Cretinism when severe in infants
• Mental retardation and short, disproportionate body
• Hyperthyroidism
– Graves’ disease from autoimmune attack of follicle cells
• Elevated metabolic rate, sweating, rapid heart rate, weight loss,
protruding eyeballs
Adrenal Gland
• Adrenal cortex is glandular tissue
– Long-term stress responses
• Corticosteroids derived from cholesterol
– Corticotropic releasing hormone (CRH) regulates
ACTH to regulate
• Adrenal medulla is neural tissue
– Short-term stress responses
• Epinephrine (Epi)
• Norepinephrine (NE)
– Hypothalamic neural signal (SNS)
Adrenal Cortex
• Zona glomerulosa produce
mineralcorticoids
– Aldosterone (chpts. 25 & 26)
• Zona faciculata produce
glucocorticoids
– Cortisol stimulates gluconeogenesis
– Excessive levels cause antiinflammatory and –immune
functions
• Zona reticularis produce sex steroids
(androgens)
– Onset of puberty, hair production,
and sex drive in women
– Testosterone (and estrogen)
precursors
Adrenal Cortex Imbalances
• Hyposecretion
– Addison’s disease (mineral- and glucocorticoids)
• Loss of weight, drop in glucose and Na+, increase in K+
• Dehydration and hypotension are common
• Hypersecretion
– Cushing’s disease (glucocorticoids)
• Chronic elevated blood glucose, loss of muscle and bone, H2O and
NaCl retention
• Hypertension, edema, swollen face, neck hump, bruise tendency
– Masculinization prepubescently (sex steroids)
• Strong sex drive in males
• Masculine body hair patterns and clitoris resembling a penis in
females
Adrenal Medulla
• SNS regulates
• Secrete epinephrine (Epi)
and norepinephrine (NE)
– Similar effects
– Tyrosine  dopamine 
NE  Epi
• Hypersecretion increases
SNS effects
Gonads
• Gonadotropin-releasing hormones (GnRH) regulates FSH and LH to
regulate
• Ovaries and testes contain all types, but ratios vary
– Estrogens (estradiol)
•
•
•
•
Maintain female system
Development of 2° sex characteristics
Derived from androgens
Masculinize male brain in early development
– Progesterone
• Prepare and maintain uterus
• Breast development
• Can be converted to testosterone
– Testosterone
• Maintain and stimulate development of male system
• Development of 2° sex characteristics and sex drive
• 7th week level determines sex
Parathyroid Gland
• Tiny glands on the posterior thyroid
• Chief cells secrete parathyroid hormone (PTH)
– Regulates blood Ca2+ levels (fig 16.12)
• Skeleton: stimulates osteoclast activity
• Intestine: increases Ca2+ reabsorption (vitamin D)
• Kidneys: activates vitamin D and enhances Ca2+ reabsorption in
nephrons
• Hyperparathyroidism is rare
– Ca2+ leaches from bones causing softening and deformation
– Elevated Ca2+ depresses nervous system and kidney stones
form
• Hypoparathyroidism
– Low Ca2+ levels increases excitability of neurons
Pancreas
• Acinar cells produce
enzyme rich digestive
juices
• Islets of Langerhans
produce hormones
– Alpha (α) cells
produce glucagon w/
fasting
– Beta (β) cells produce
insulin w/feeding
Diabetes Mellitus
• Blood glucose levels high after feeding
• Type I (insulin dependent)
– Autoimmune disease
– WBC’s attack beta cells (hyposecretion)
• Type II (non-insulin dependent)
– Older onset
– Cells can’t use insulin (hypoactivity)
Other Hormone Producing Structures
• Heart: ANP reduces blood pressure, volume,
and [Na+]
• GI tract: enteroendocrine cells release local
digestive hormones (gastrin, secretin, CCK)
• Placenta: human chorionic gonadotrophic
(hCG) to sustain fetus and pregnancy
• Kidneys: secrete erythropoietin (EPO) to
signal erythropoiesis
Other Hormone Producing Structures
• Skin: choleocalciferol produce precursor of
vitamin D
• Adipose tissue: leptin signals stored energy
levels and satiety; increase activity levels
• Thymus: large in children, diminishes in size
w/age; thymosin and thymopoietins stimulate
T-cells
• Pineal gland: releases melatonin to regulate
rhythmic variation of physiological processes