1 - Pituitary and Thyroid Hormones Flashcards
The pituitary gland lies in a bony cavity called the _______
It is connected to the hypothalamus by ________
sella turcica
pituitary stalk
The anterior pituitary is also known as:
The psosterior pituitary is also known as:
adenohypophysis
neurohypophysis
List the six major hormones of the anterior pituitary
- growth hormone
- adrenocorticotropic
- TSH
- Prolactin
- FSH
- Luteinizing
List the two major hormones of the posterior pituitary
- ADH
- Oxytocin
Name the cell types of the anterior pituitary and the hormones they produce
Somatotropes - hGH
Corticotropes - ACTH
Thyrotropes - TSH
Gonadotropes - LH and FSH
Lactotropes - Prolactin (PRL)
Why are tumors that secrete hGH called acidophilic tumors?
Somatotropes stain strongly with acid dyes
These tumors have large numbers of somatotropes, so they stain strongly with acid dye
Where are posterior pituitary hormones synthesized?
Cell bodies in the hypothalamus
Almost all pituitary secretion is controlled by the ______
hypothalamus, either through nervous or hormonal signalling
Another word for pituitary is
hypophysial
Prolactin inhibitory hormone is also known as _______
Dopamine
All the major anterior pituitary hormones except GH exert heir effects by:
Stimulating target glands
Where does GH exert its effects?
Directly on all or almost all tissues of the body
What are two other names for GH?
Somatotropic hormone
Somatotropin
GH promotes:
increased size, mitosis, and differentiation of cells
GH has three metabolic effects:
- Enhances body protein
- Decreases fat stores
- Conserves carbohydrates
What effect does blood glucose level have on growth hormone?
increased BG = inhibition of GH secretion
decreased BG = stimulation of GH secretion
How does growth hormone effect amino acid and protein level?
enhances amino acid uptake and protein synthesis
reduces the breakdown of proteins
Growth hormone is only effective if _____ and _____ are present
insulin
carbohydrates
Function of osteoblasts:
Function of osteoclasts:
deposit new bone
remove old bone
Does growth hormone stimulates osteoblasts or osteoclasts?
Osteoblasts
thickens the bones
The growth effects of GH are probably the result of the action of _______
rather than the direct effects of GH
insulin-like growth factors
Growth hormone has a ____ duration
IGF-1 has a ______ duration
short (20 min)
long (20 hours)
GH secretion follows a _____ pattern
pulsatile
Starvation with protein deficiency will have what effect on growth hormone?
Stimulate secretion of GH
Exercise, excitement, and trauma have what effect on GH?
increased secretion
In severe conditions of protein malnutrition, why does it not work to just give adequate calories?
It has to be protein
If you give adequate calories via carbs, the level of GH won’t change
______ hormone is responsible for stimulating GH release
_______ hormone is responsible for supressing GH release
GHRH
Somatostatin (GHIH)
Where are GHRH and somatostatin stored?
The hypothalamus, in the same areas that are sensitive to blood glucose levels and satiety
Most of the control of GH is via _____ hormone
GHRH rather than somatostatin
ADH and Oxytocin are both synthesized in the ______
hypothalamus
Minute concentrations of ADH cause _______
Higher concentrations of ADH cause _______
water conservation
vasoconstriction
How does the body sense when ADH is needed to restore fluid balance?
Osmoreceptors in the hypothalamus sense osmolarity/tonicity by monitoring their cell size. If the cells are shrinking, they interpret that as hyperosmolar plasms
If they’re getting bigger, they interpret that as hypoosmolar plasma
When the osmolarity is too high, ADH is secreted
When osmolarity is too low, ADH secretion is inhibited
The thyroid hormone secretes two hormones:
Thyroxine (T4)
Triiodothyronine (T3)
Complete lack of thyroid secretion decreases BMR by ___%
Extremely excessive thyroid secretion can raise BMR by ___%
40-50% below normal
60-100% above normal
Thyroid secretion is controlled by _______
which is secreted by _______
TSH
Anterior Pituitary
Besdies T3 and T4, what else does the thyroid secrete?
Calcitonin
Which is produced in larger quantities: Thyroxine or Triiodythonine?
Thyroxine, but it is the precursor to Triidothynonine, and pretty much all thyroxine gets converted to T3 in the tissues
Which is more potent: T3 or T4?
T3 is four times more potent, but is present in the blood in very low concentrations
The thyroid gland is comprised of large numbers of _____ that are filled with:
follicles
secretory substance called colloid
The major constituent of the colloid in thyroid cells is:
thyroglobulin, which contains the thyroid hormones
How much iodine is required per week to prevent deficiency?
1 mg/wk
50 mg/yr
How is iodine trapping acheived?
the sodium-iodide symporter cotransports one iodid alongw ith two sodium into the cell
Sodium is actively pumped out of the cell by the Na-K ATPase
It passes back through its concentration gradient through the sodium-iodid pump, carrying to iodine with it which are then trapped in the cell
The rate of iodide trapping is mainly determined by:
the concentration of TSH
How is iodine transported into the cuboidal epithelial cell of the thyroid?
How is it transported into the follicle?
the sodium iodide pump
a chloride-iodid ion counter-transporter called pendrin
What is the role of iodine in formation of thyroid hormones?
Oxidized iodine binds with thyroglobulin and “organifies” it, assisted by a peroxidase enzyme
Tyrosine substrates are formed
Eventually they couple to form lots of T4 and a little bit of T3
If your thyroid stops making hormones, how long will it take for symptoms to show up?
2-3 months
Each thyroglobulin contains up to _____ thyroxine molecules and ___ T3 molecules
30
a few
How is thyroglobulin released into the blood stream?
It isn’t
The apical surface of the thyroid cell forms pinocytic vesicles around thyroglobulin
These join up with lysosomes that break thyroglobulin into T3 and T4
T3 and T4 freely diffuse across the membrane into the blood
What is the role of the deiodinase enzyme?
75% of the iodinated tyrosine never becomes thyroid hormone
When the vesicles digest thyroglobulin, these tyrosines are also freed from the thyroglobulin molecules
They are cleaved by a deiodinase enzyme to recycle that iodine to make more thyroid hormone
How are T3 and T4 circulated in the blood?
99% protein bound
The high affinity of plasma proteins for T3 and T4 allow slow release into the tissue cells
Once they enter the target cell, what happens to T3 and T4?
They are again bound to intracellular proteins and stored for
used slowly over a period of days or weeks
What is the onset and peak to T4?
T3?
2-3 days, 10-12 days
6-12 hours, 2-3 days
Why do the latency periods of T3 and T4 vary so intensely?
Mostly due to T3’s relatively smaller affinity for plasma proteins
It’s released more easily and more rapidly
What changes do thyroid hormones incite once they enter the cell?
Increases transcription of many genes
increases the size and number of mitochondria
Increases Na-K ATPase activity
When thyroid hormone levels rise, the concentrations of plasma cholesterol, phospholipids and triglycerides ______
decrease
The opposite is also true
Why is hypothyroidism associated with atherosclerosis?
Increased circulating plasma cholesterol level
How does thyroid hormone stimulate carb metabolism?
Increases rapid glucose uptake by cells
enhances glycolysis and gluconeogenesis
increased rate of absoprtion from GI tract
increased insulin secretion
How does thyroid hormone increase fat metabolism?
rapidly mobilizes lipids from fat tissue
Thyroid hormone increases the need for _____, and may cause a deficiency if repletion isn’t present.
Vitamins
Why don’t you lose weight when you have excess thyroid?
It also increases appetite
Why does the thyroid hormone cause increased blood flow and cardiac output?
Increased metabolism means increased release of metabolic end products, which causes vasodilation
Cardiac output increases to compensate
Why does the heart rate increase with thyroid hormone?
It’s NOT just due to the increase in cardiac output
seems to have a direct excitatory effect on the heart
Often one of the first s/s of thyroid issues is heart rate
How does blood pressure change in response to thyroid hormone?
The MAP is unchanged, but the pulse pressure is greater in hyperthyroidism
How does thyroid hormone dysfunction effect menstruation?
Hyperthyroidism causes amenorrhea
Hypothyroidism causes menorrhagia and polymenorrhea
What are the five ways TSH effects the thyroid gland?
- increases proeolysis of thyroglobulin
- increased activity of iodide pump
- increased iodination of tyrosine
- increased size and increased secretory activity of thyroid cells
- increased number of thyroid cells (plus changes them from cuboidal to columnar)
After TSH is released, how long does it take for T3 and T4 release to occur?
30 minutes
What intracellular signalling pathway does TSH utilize to effect thyroid cells?
cAMP- adenylyl cyclase
TSH release from the anterior pituitary is regulated by which hormone?
TRH from the hypothalamus
What intracellular signalling pathway does TRH utilize to release TSH from the Anterior pituitary?
Phospholipase second messenger system
What is one of the best known stimulants for TRH and TSH secretion?
Cold!
The anterior pituitary is composed of two main cell types:
Chromophobes (nonsecretory)
Chromophils (secretory)
What are the three categories of tropic hormones secreted by the anterior pituitary?
- Corticotropin related hormones (ACTH, MSH)
- Glycoproteins (LH, FSH, TSH)
- Somatotropins (GH and Prolactin)
GH secretion from the anterior pituitary is controlled by two hormones from the hypothalamus:
- GHRH (increases secretion)
- Somatostatin (inhibits secretion)
When does growth hormone secretion peak?
adolescence
What is the difference between somatotropic hormones and somatomedins?
Name an example of each
Somatotropic hormones induce increased cellular function and reproduction (GH, Prolactin)
Somatomedins promote cell growth and division (IGFs)
How does IGF mediate GH function?
binds to IGF-1 receptors and mediates anabolic effect
binds to insulin receptors, providing insulin-like efffect on skeletal muscle (moves glucose into the muscle)
The major stimulating substance for ADH secretion is:
The major inhibitory stimulus is:
Glutamate
GABA
The effects of ADH may be inhibited by:
hypercalcemia
prostaglandin E
hypokalemia
Melatonin release is stimulated by ______ and inhibited by _______
exposure to dark
exposure to light
What is the function of the pineal gland?
Melatonin secretion
circadian rhythm
Why does hyperthyroidism cause cardiac hyperactivity?
T3 stimulates the synthesis of alpha myosin havey chain, sarcolemmal ion pumps, and beta membrane receptors
more receptors = more sensitivity
the heart is overreacting to a normal amout of beta stimulation, and as a result it is beating harder and faster
