MLAB 2401: Clinical Chemistry
Keri Brophy-Martinez
Introduction to Endocrinology
Terms
• Endocrinology
– Study of hormones and
disorders of these hormones
– Endocrine System
–
–
–
–
Hypothalamus & pituitary
Thyroid & parathyroid
Adrenals
Others (Islets of Langerhans,
ovaries, testicles, placenta)
Hormones
– Any substance normally produced by
specialized cells in some part of the body,
carried by the blood stream to another part,
where it effects the body as a whole
– Vehicles for intracellular & extracellular
communication
Characteristics of Hormones
• Specificity
– Only target cells respond
• Multiple actions
• Variable half-life
– Often depends on solubility properties
• Variable forms
– Depends on weight
• Excretion rates
– Diurnal variation
– Cyclic patterns
– Stimulus response
Functions of Hormones
• Maintain homeostasis
• Regulate growth and development
• Promote sexual maturation, sexual rhythms and
facilitate reproduction
• Regulate energy production
• Adapt/adjust body to stressful/emergency
situations
• Promote/inhibit production or release or other
hormones
Chemical Types of Hormones
• Peptides/proteins
– Polypeptides or glycoproteins
– Soluble in plasma
– Interact with target cell membrane receptors to trigger a
second messenger to complete the specific action of the
hormone.
– Short term effects
• Amines
–
–
–
–
Amino acid derivatives
Poorly soluble in plasma
Interact with membrane receptors of target cells
Provide long and short term effects
Chemical Types of Hormones
• Steroids
– Composed of lipids (cholesterol)
– Can transverse through the cell membrane
– Produced by ovaries, testis, placenta, and adrenal
cortex
– Insoluble in water
– Long-lasting
Functional Types of Hormones
• Tropic
– Originate from anterior pituitary gland
– Specific for another endocrine gland
• Non-tropic or Direct effector
– Secreted by non-pituitary endocrine glands
– Act directly on peripheral tissue
– Exert a feedback effect on the hypothalamus or
anterior pituitary gland
Hormone Receptors
• Located on cell membrane or within cell
cytoplasm
• Binding of hormone to receptor initiates a
signal
• Results in changes in gene expression
• Ultimately causes a biological response
Regulation and Control of
Hormones
• Occurs by controlling the rate of synthesis
rather than the rate of degradation
• Primary control= Hypothalamus
– Small gland next to pituitary gland
– Connected to the pituitary by the “pituitary stalk”
• Pituitary Gland
– Releases both tropic and effector hormones
Feedback Control
• Negative feedback
 An increase in the product
causes a decreased in the
system
 Serves to stabilize a process
 Primary means of hormone
regulation
• Positive feedback
 An increase in the product
causes an increase in the
activity of the system
Sunheimer, R., & Graves, L. (2010). Clinical
Laboratory Chemistry. Upper Saddle River:
Pearson
Hypothalamus Hormones
Hormone
Action
Thyrotropin releasing hormone (TRH)
Releases TSH and prolactin
Gonadotropin releasing hormone
(GnRH)
Releases LH and FSH
Corticotropin releasing hormone ( CRH)
Releases ACTH
Growth hormone releasing hormone
(GHRH)
Releases GH
Somatostatin
Inhibits GH and TSH release
Dopamine
Inhibits prolactin release
Anatomy of the Pituitary
• 3 distinct parts and their functions
– Anterior pituitary (adenohypophysis)
• Hormones which target other endocrine glands
• Forms the lactotrophs, somatotrophs, throtrophs,
corticotrophs and gonadotrophs
– Intermediate lobe (pars intermedialis)
• Little functional capacity
– Posterior pituitary (neurohypophysis)
• Stores and releases oxytocin and vasopressin (ADH)
Anatomy of Pituitary
Anterior Pituitary Hormones
Hormone
Target Gland
Classification
Feedback
Hormone
Function
Luteinizing
hormone (LH)
Gonad :
Ovary/testes
Tropic
Sex steroids
Ovulation
Testosterone
production
Follicle
stimulating
hormone (FSH)
Gonad :
Ovary
Tropic
Inhibin
Ovarian
recruitment
Thyroid
stimulating
hormone (TSH)
Thyroid
Tropic
Thyroid hormones Stimulates thyroid
(T4/T3)
hormone
production
Adrenocorticotro
pin hormone
(ACTH)
Adrenal cortex
Tropic
Cortisol
Growth hormone
(GH)
Multiple
Direct effector
Insulin-like growth Stimulates tissue
factor
growth
Prolactin
Breast
Direct effector
Unknown
Stimulates
synthesis &
secretion of
glucocorticoid
hormones
Secretion
LH & FSH
• Luteinizing hormone (LH):
– Serves to promote ovulation, formation of corpus
luteum, and secretion of progesterone
– Stimulates and secretes of androgens
• Follicle-stimulating hormone (FSH):
– Stimulates growth of follicles, and along with LH,
secretion of estrogens and ovulation
– Stimulates development of seminiferous tubules,
spermatogenesis
Actions of LH & FSH
Male Hormonal Control
Female Hormonal Control
Sunheimer, R., & Graves, L. (2010). Clinical Laboratory
Chemistry. Upper Saddle River: Pearson
TSH
• Tropic hormone
• Used to confirm adult hypothyroidism
ACTH
• Target cell= adrenal cortex
• Promote growth of adrenal cortical tissue
• Stimulate the production of adrenal steroids
– Glucocorticoids
– Mineralocorticoids
– Androgen
• Diurnal variation
– Highest levels between 6-8 am
– Lowest levels between 6-11 pm
Growth Hormone
• Also called somatotropin
• Peptide with direct effector functions
• Release of GH is stimulated by GHRH
– Secretion occurs in pulse ~ every 2-3 hours
– Peaks at the onset of sleep
• Inhibited by somatostatin
Growth Hormone
• Amphibolic: influences both anabolic & catabolic processes
• Allows effective transition from a fed state to a fasting state without
shortage of substrates
• Directly antagonizes effect of insulin on glucose metabolism
• Provides hepatic gluconeogenesis
• Stimulates lipolysis
• Enhances protein synthesis in skeletal muscle & other tissues
• Stimulates production of insulin-like growth factors
Growth Hormone
Stimulators
• Meals
• Exercise
• Sleep
• Hypoglycemia
Inhibitors
• Glucose loading
• Epinephrine
• Emotional/psychogenic
stress
• Nutritional deficiencies
• Insulin deficiency
Prolactin
• Functions in relation to reproduction
– Breast growth during pregnancy
– Milk secretory activity
• Direct effector hormone
• Stimulated by thyrotropin-releasing hormone
• Inhibited by dopamine
Posterior Pituitary Hormones
• Posterior Pituitary is a storage region for 2
hormones
• Oxytocin
– Function
• Lactation
– Stimulates milk let down
• Stimulator of smooth muscle (uterine)
– Synthetic oxytocin (Pitocin)
» Used to induce or enhance labor contractions
Posterior Pituitary Hormones
• ADH/vasopressin
– Action
• Regulates water excretion in the renal tubules
– Receptors for vasopressin found in the tubules
• Assists in water balance
– Hypothalamic osmoreceptors & vascular
baroceptors regulate release of vasopressin from
posterior pituitary.
References
• Bishop, M., Fody, E., & Schoeff, l. (2010).
Clinical Chemistry: Techniques, principles,
Correlations. Baltimore: Wolters Kluwer
Lippincott Williams & Wilkins.
• Sunheimer, R., & Graves, L. (2010). Clinical
Laboratory Chemistry. Upper Saddle River:
Pearson .