Chapter 5: Principle of Endocrinology Flashcards
1
Q
Tropic Hormones
A
- regulates hormone secretion by another endocrine gland
- stimulates and maintains their endocrine target tissues
ex. TSH- secreted from anterior pit. and stimulates thyroid hormone secretion by thyroid gland
2
Q
Plasma Hormone Concentration
A
- plasma concentration of each hormone is normally controlled by regulated changes in rate of hormone secretion
- direct regulatory inputs that influence secretory output of endocrine cells
- neural input- neuroendocrine reflexes
- input from another hormone
- effective plasma concentration also influenced by: rate of removal from blood by metabolic inactivation and excretion and rate of activation or its extent of binding to plasma proteins
3
Q
Negative-Feedback Control
A
- negative exists when the ouput of a system counteracts a change in input
- maintains the plasma concentration of a hormone at a given level
- given level is referred to as a “set point”
4
Q
Neuroendocrine Reflexes
A
- neural and hormonal components
- quick increase in secretion of hormone
- E release, vasopressin, and cortisol
5
Q
Diurnal Rhythm
A
- cycle 1/day with external cues (entrained)
- set by CNS
- other cycles (menstrual)
6
Q
Endocrine Dysfunction
A
- can arise from a variety of factors
- most commonly by inappropriate rates of secretion
- hyposecretion and hypersecretion
7
Q
Hyposecretion
A
primary: too little hormone is secreted due to abnormailty within gland
- causes: genetic, dietary, chemical or toxic, immunologic, other disease processes such as cancer, latrogenic “healer”, idiopathic
secondary: gland is normal but too little hormone is secreted due to deficiency of its tropic hormone
- replacement therapy to alleviate symptoms
8
Q
Hypersecretion
A
- causes: tumors that ignore normal regulatory input and continuously secrete excess hormone
- immunological factors- Ab-mimicking TSH
primary: too much hormone is secreted due to abnormality within gland
secondary: excessive stimulation from outside the gland causes oversecretion
9
Q
Hormone Influence at Target Cell
A
- permissiveness: one hormone must be present in adequate amounts for full exertion of another hormone’s 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
10
Q
2 Hormones Based on Solubility
A
- Hydrophilic: peptide hormone and catecholamines
2. Lipophilic: steroid and thyroid hormones
11
Q
Peptide and Protein Hormones
A
- most common are polypeptides
- synthesized, processed, and packaged
12
Q
Insulin Release
A
- preparation and release of insulin
- C-peptide also released but inactive
13
Q
Steroid Hormones
A
- derived from cholesterol
- mostly from in cell stores
- sequential modifications by enzymes
- final product depends on cell type: Testosterone to estradiol in ovaries
- cannot be stored
- final product depends on cell type
14
Q
Amine hormones
A
- derivatives of amino acid tyrosine
- thyroid hormones (2 tyrosines)
- melatonin derived from tryptophan (pineal gland)
15
Q
Catecholamines
A
- cytosolic enzymes make changes to chemicals
- this pathway occurs in adrenal gland
16
Q
Hormone Receptors
A
- cell response to hormone
- presence of receptors for that hormone on or in target cell
- most surface-binding hydrophilic hormones function by activating second-messenger systems: cAMP and Ca2+
- Lipophilic hormones function mainly y activating specific genes in target cell
17
Q
Pituitary Gland
A
- Hypophysis
- thin stalk connects pituitary gland to hypothalamus called infundibulum
- posterior (neurohypophysis): nervous tissue
- anterior (adenohypophysis): glandular tissue
18
Q
Posterior Pituitary
A
- along with hypothalamus forms neuroendocrine system
- does not actually produce any hormones
- stores and releases two small peptide hormones:
- vasopressin
- oxytocin: stimulates uterine contraction and milk ejection
19
Q
Relationship of Hypo. and Post. Pit.
A
- paraventricular and supraoptic nuclei both contain neurons that produce vasopressin and oxytocin
- hormone travels down axon to be stored in neuronal terminals within post. pit.
- on excitation of the neuron, stored hormone is released from these terminals into systemic blood
20
Q
Anterior Pituitary
A
- 6 different peptide hormones that it produces itself
Tropic hormones: - TSH: stimulates secretion of thyroid hormone
- ACTH: secretion of cortisol by adrenal cortex
- LH: females (ovulation, luteinization, regulates ovarian secretion of female sex hormones) males (stimulates testosterone)
- FSH: females (growth and development of ovarian follicles, secretoin of estrogen by ovaries)
- GH: primary hormones for regulating overall body growth; important in intermediary metabolism
Non-tropic hormone: - Prolactin (PRL): enhances breast development and milk production in females
21
Q
Control of Pituitary Hormone Release
A
- Hypothalamic (hypophysitropic) hormones
- regulate release of anterior pituitary hormones
- releasing and inhibiting hormones - feedback by target-gland hormones
22
Q
Hypothalamic Releasing and Inhibiting Hormones
A
- secretion of each anterior pit. hormone is stimulated or inhibited by one or more of the 7 hypothalamic hypophysiotrophic hormones
- gonadotropic hormones (LH and FSH) secreted by same cells
23
Q
Hypothalamic-Hypophyseal Portal System
A
- portal system is a vascular arrangement in which blood flows from one capillary bed through a connecting vessel to another capillary bed
- critical link between the brain and much of the endocrine system
24
Q
Hypothalamic Releasing and Inhibiting Hormones
A
- minute quantities of hypothalmic hormones are carried directly to their target cells in anterior pituitary, and are not diluted out in the systemic circulaiton
- reach ant. via:
1. branch of the hypophyseal artery ramifies into a capillary bed in the lower hypothalamus and hypothalmic hormones are secreted into that capillary blood
2. blood from capillaries drains into hypothalamic-hypophyseal portal veins- branch again into another series of capillaries within the anterior pituitary
3. capillaries within anterior pit. which carry hormones secreted by that gland, coalesce into the veins that drain into the systemic venous blood
25
Q
Growth: other influencing factors
A
- genetic determination of an individual’s max. growth capacity
- an adequate diet
- freedom from chronic disease and stressful environmental conditions
- normal levels of growth-influencing hormones
26
Q
Growth Summary
A
- not continuous
- factors do not remain the same throughout growth period
- fetal growth: promoted largely by hormone from placenta, GH plays no role in fetal development
- postnatal growth spurt: displayed during first two years of life
- pubertal growth spurt: occurs during adolescence
27
Q
Endocrine Control of Growth Spurt
A
- involves cell division and net protein synthesis
- height determined by bone growth- vertebral column and legs
28
Q
Growth hormone: Somatomedin
A
- promotes growth indirectly
- stimulating production of somatomedins from liver
- somatomedin= insulin-like growth factor (IGF-1)
- acts on bone and soft tissues to bring about most growth-promoting actions
- stimulates: protein synthesis, cell division, lengthening and thickening of bones (hyperplasia and hypertrophy)
29
Q
Growth Hormone
A
- promotes bone thickness and length
- stimulates osteoblast activity and proliferation of epiphyseal cartilage
- growth only when plate is cartilaginous “open”
- when plate ossify “close”, no more growth (end of adolescence)
- bone growth: chondrocytes and stopes after puberty
- increase cell division
- increased protein synthesis- predominantly in muscle
30
Q
Growth Hormone: Metabolic Effect
A
- not related to growth
- increases blood fatty acid levels
- enhancing breakdown of triglyceride fat stored in adipose tissue
- increases blood glucose levels
- decreasing uptake/use by muscles
31
Q
Growth Hormone and Age
A
- Gh secretion highest in adolescence
- next highest in childhood
- lowest in adults:
- decrease in lean body fat and bone mass, expansion in adipose tissue, thinning of skin
32
Q
Growth Hormone Abnormailites
A
- hyposecretion
- Dwarfism in childhood: also less muscle, more fat in adults
- deficiency in adults produces relatively few symptoms
- hypersecretion in childhood= Gigantism; before epiphyseal plate closes
- hypersecretion as an adult= Acromegaly
- tumour of GH-producing cells
- most often caused by tumour GH producing cells of anterior pituitary
33
Q
Pineal Gland
A
- Melatonin: hormone of darkness
- peak levels during darkness and secretion falls to low levels during light of day
- functions: helps keep body’s circadian rhythms in synchrony with light-dark cycle
- promotes sleep, influences reproductive activity,acts on antitoxidant to remove free radicals, enhances immunity
34
Q
Circadian Rhythms
A
- daily changes in light intensity
- major environmental cue used to adjust SCN master clock
- photoreceptors in retina pick up light signals and transmit them directly to SCN
- SCN relays message regarding light status to pineal gland
