Transcript PowerPoint
Fig 7-2
__________________: the study of hormones, their receptors, the intracellular signaling pathways they invoke, and the diseases and conditions associated with them.
What are hormones?
Major endocrine glands?
Physiological processes controlled by hormones?
Hormones
Known since ancient times Secreted by cells into the blood Transported to distant targets Effective at very low concentration Bind to receptors Hormone action must be of limited duration
Classification of Hormones
3 main types:
–
Peptides and proteins
–
Steroids
–
Amines Differ on basis of synthesis, storage, release, transport and cellular mechanism of action
(review Table 7-1)
Peptide (Protein) Hormones
Synthesis as preprohormone translational modification to prohormone
then hormone
post-
Fig 7-4
Storage – release?
Short half-life (mins.)
Most common type
Fig 7-3
Cellular Mechanism of Action for Peptide Hormones
Lipophobic does message get into cell?
how
Usually rapid cellular response because existing proteins are modified
cAMP 2 nd messenger system most common
Steroid Hormones
All derived from cholesterol
Fig 7-6
Where synthesized?
Storage – release?
Transport in blood?
Longer half-life
Mechanism of action
Fig 7-7
Amine Hormones
Derived from one or two amino acids
3 groups
–
Tryptophan
Melatonin
–
Tyrosine
Catecholamines behave like peptide hormones
–
Tyrosine
Thyroid hormones behave like steroid hormones
Fig 7-8
Control of Hormone Release
All endocrine reflex pathways have similar components
– Stimulus / input signal – Integration (where?) – Output signal (hormone / neurohormone) – Physiological action – Negative feedback – turns off reflex
One Hormone may follow > 1 reflex pathway pattern
Simple Endocrine Reflex
Endocrine cell acts as sensor AND integrating center
no afferent pathway
responds by secreting hormone Example: PTH
increases [Ca 2+ ] in plasma
Fig 6-31/➅
Neurohormone Reflex
NH release by modified neurons upon NS signal
3 major groups of Neurohormones:
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Catecholamines from adrenal medulla
–
Hypothalamic neurohormones posterior pituitary from
–
Hypothalamic neurohormones anterior pituitary acting on
Fig 6-31/②
Neurohormones of Posterior Pituitary
Other name of gland?
2 neurohormones
Both are peptides (9 aa) transported in secretory vesicles via axonal transport
Fig 7-12
Anterior Pituitary
Secretes 6 Hormones (names?)
A Trophic (tropic) hormone controls the secretion of another hormone
Hypothalamic trophic hormones and the hypothalamic-hypophyseal portal system
Negative Feedback Loops in the Hypothalamic-anterior pituitary axis Hypothalamus IC1 Ant. pituitary IC2 Endocrine gland IC3 Target tissue Hormones serve as negative feedback signals: Short-loop vs. long-loop negative feedback.
Feedback patterns important in diagnosis of ES pathologies
Hormone Interactions
Multiple hormones can affect a single target simultaneously
Three types of hormone interactions:
Synergism
Permissiveness
Antagonism
Synergism
Combined action of hormones is more than just additive!
Example: Blood glucose levels & synergistic effects of glucagon, cortisol and epinephrine
Fig 7-18
Permissiveness
Hormone A will not exert full effect without presence of hormone B.
Example: Thyroid hormone & growth hormone
Antagonism
Antagonistic hormones have opposing physiological actions – Hormone B diminishes the effect of hormone A
(mechanisms?)
Hormone Antagonists and Cancer: Tamoxifen
Endocrine Pathologies
“Unbalance leads to disease”
Due to:
1.
Hypersecretion (excess) 2.
Hyposecretion (deficiency) 3.
Abnormal target tissue response
Hypersecretion:
Due to ?
– –
Iatrogenic (could lead to gland atrophy) ________
Symptoms: Exaggerated Effects
Examples:
Cushing’s Syndrome
Gigantism
Example:
Hyperthyroidism (Review pp. 756 – 761)
Most common cause: Graves' disease Autoantibodies (TSI) bind to TSH receptor and stimulate thyroid hormone production This activation by TSI is not subject to the normal negative feedback loop.
Left exophthalmus in Graves disease
Hyposecretion:
Due to ?
Symptoms: Normal effects of hormone diminished or absent
Examples:
Addison’s disease
Dwarfism
Example:
Hypothyroidism
Most common cause in US: chronic autoimmune thyroiditis (Hashimoto's thyroiditis = Chronic thyroiditis ) Other causes
surgical removal of the thyroid gland radioactive iodine treatment
external radiation a deficiency in dietary iodide consumption (= endemic or primary goiter )
Hypothyroidism cont.
Symptoms: During childhood:
stunted growth retardation lethargy low body temp.
In adulthood:
Bradycardia weight gain lethargy low body temp.
Abnormal Tissue Responsiveness
Hormone levels normal, target unresponsive
Due to:
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Abnormal hormone / receptor interaction
–
Abnormal signal transduction
Diagnosis of Endocrine Pathologies
Primary Pathology
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Defect arises in last integration center in the reflex
–
Examples?
Secondary Pathology
–
Defect arises in one of the trophic integration centers
–
Examples?
Which of the sets of lab values below would indicate Grave’s disease? Explain.
Patient A B C D Normal Serum T4 6 µg/dl 14 µg/dl 2.5 µg/dl 16 µg/dl 4.6 12 µg/dl Serum TSH 1.5 µU/ml .25 µU/ml 20 µU/ml 10 µU/ml 0.5 6 µU/ml
Graves’ disease