Lecture 2 part 2 Flashcards
Hormone can influence activity of another hormone at given target cell in one of three ways
- permissiveness
- synergism
- antagonism
Permissiveness
One hormone must be present in adequate amounts for full exertion of another hormones effect
Synergism
- Occurs when actions of several hormones are complimentary
- Combined effect is greater than the sum of their separate effects
Antagonism
- Occurs when one hormone causes loss of another hormone’s receptors
- Reduces effectiveness of second hormone
Example of synergism
Cortisol +5 mg/100 ml
Glucagon +10 mg/100 ml
Epinephrine +20 mg/100 ml (added = +35)
Synergistic effect + 140 mg glucose /100 ml blood
Example of antagonism
progesterone prevents estrogen function during pregnancy
Example of permissiveness
need 2nd hormone to get full expression (thyroid hormone & reproductive hormones; thyroid hormone & epinephrine)
Endocrine dysfunction causes
- Can arise from a variety of factors
- Most commonly result from abnormal plasma concentrations of a hormone caused by inappropriate rates of secretion
Endocrine dysfunction - Hyposecretion
Too little hormone is secreted
Endocrine dysfunction - hypersecretion
Too much hormone is secreted
Primary hyposecretion
Too little hormone is secreted due to abnormality within gland
Causes:
Genetic
Dietary
Chemical or toxic
Immunologic
Other disease processes such as cancer
Iatrogenic
Idiopathic
Secondary hyposecretion
Gland is normal but too little hormone is secreted due to deficiency of its trophic hormone
Causes of hypersecretion
Tumors that ignore normal regulatory input and continuously secrete excess hormone
Immunologic factors
Primary hypersecretion
Too much hormone is secreted due to abnormality within gland
Secondary hypersecretion
Excessive stimulation from outside the gland causes oversecretion
Pathologies:
Over or Under Production
“no bad hormones – just too much or too little“
Hypersecretion exaggerates a hormone’s effect (e.g. cortisol)
- Benign (adenomas) & cancerous tumors
- Exogenous medication (iatrogenic – caused by physician)
> Causes atrophy of gland
> Cortisol treatment must be tapered of gradually to allow pituitary and
adrenal gland to gain back normal hormone production
Pathologies:
Hyposecretion
- due to atrophy of gland
E.g. thyroid hormone
- due to insufficient iodine in diet
- absence or low levels of thyroid hormone
- result: trophic hormone levels rise (negative feedback)
E.g. adrenal cortex atrophies due to tuberculosis
- decrease cortisol production
- result: increased CRH & ACTH production to stimulate adrenal gland to increase cortisol
Down-regulation of receptors
Due to abnormal high hormone secretion
E.g. Hyperinsulinemia – sustained high levels of insulin – target cells remove receptors from cell membrane – patients show symptoms of diabetes despite high blood insulin levels
Mutations alters protein sequence of receptor
E.g. testicular feminizing syndrome
Androgen receptors are nonfunctional in male fetus
Androgens are unable to influence development of genitalia – child appears to be female with lack of uterus & ovaries
Genetic alterations in signal transduction pathways
E.g. pseudohypoparathyroidism
Inherited defect in G-protein that links hormone receptor to cAMP amplifier, adenyl cyclase
PTH levels are normal to high
Symptoms of hormone deficiency
Diagnosis of Pathologies depends on complexity of reflex
