Test 3 - Quiz 8 - Thyroid & GI Endocrinology Flashcards
What is the largest gland in the body?
Thyroid
- Larger in men than women
- Increases with age and body weight
- decreases as dietary iodine intake decreases
**EXTREMELY WELL VASCULARIZED
Increasing or decreasing thyroid hormone does what?
Changes basal metabolic rate
If its cold outside, hypothalamus stimulates thyroxin (T3, T4) from what?
Thyroid
*This increases metabolic rate and generates heat to raise body temp
If it is warm outside, hypothalamus inhibit’s thyroxin (T3, T4) release from what?
Thyroid
*This decreases metabolic rate, reducing heat production
When you hear thyroid hormone, what is being referred to?
T3 AND T4
T3 can work independently from the what?
Thyroid
T4 is dependent upon what?
Thyroid
Know the negative feedback loop on slide 5 of her lecture.
In your photos..
T4 is turned into what two things?
rT3, and T3
*rT3 is inactive, while T3 is very active
Thyroglobulin is what and found where and what is in it?
Colloid proteins
Found in thyroid
T3 and T4
The size of the follicle determines what in regards to the gland?
Inactive - Large follicles
Active - Small follicles
What are the two main endocrine functions of the thyroid gland?
Secretion of T4 and T3
Secretion of calcitonin
Calcitonin is secreted by what cells?
Parafollicular cells (aka C cells)
What does calcitonin do?
Lowers Ca2+ in serum
-Decreases osteoclast activity
What does parathyroid hormone (PTH) do?
Stimulates osteoclasts
What secretes PTH?
Chief cells in parathyroid glands (in response to low blood calcium)
1,25-Dihydroxycholecalciferol is formed from what?
Vitamin D in skin via sun and hydroxylation in liver and kidneys
What does 1,25-dihydroxycholecalciferol do?
Increases Ca2+ absorption in intestines
Increases Ca2+ stored in bones
T3 and T4 are _______ - philic.
LIPO
What can synthesize T3 and T4?
Iodine
And tyrosine portions of thyroglobulin
T4 is produced exclusively where?
Thyroid only
T3 is primarily produced from what?
Extrathyroidally from T4
- Liver
- Intestines
Almost all T4 produced is quickly converted to what once released from thyroglobulin stores?
T3
T3 is ____ times more potent than T4.
4
rT3 is inactive and made mostly where?
Liver
What enzyme converts T4 to T3?
5’ deiodinase enzyme
If the enzyme catalyzes another rxn, after T3 is formed, what is formed?
rT3
T3 and T4 are considered what? (______genic)
Calorigenic
T3 can act independently of what?
HPT axis regulation
Many chronic stress-like conditions lead to what?
Hypothyroidism
Stress, dietary iodine, illness, fasting, and cortisol (steroids) are all able to alter the activity of what enzyme?
Deiodinase
W/o sufficient iodine, one may develop what?
Goiter
*W/o iodine, thyroid hormones are not released from thyroglobulin and TSH builds up
Look at practice question on slide 14 of her lecture.
In your photos
Look at practice question on slide 15 of her lecture.
In your photos
Thyroid hormones:
Synthesis and storage
Release from parent cell
T-port in blood
1/2 half
Location of receptor
Example
Made in advance
Simple diffusion
Bound to carrier proteins
Long
Nucleus (Lipophilic)
Thyroxine
What are the only cells in the body that can absorb iodine?
Thyroid cells
*Good outlook for thyroid cancer patients
Urine iodine excretions of >70% of dietary iodine intake is what?
Iron deficiency
*For adults, that is urine excretion of >/= 105 mcg/day
Goiter is the result of too much what? (2 things)
TSH
Human chorionic gonadotropin (HCG)
Goiters are found in what autoimmune disease and what type of cancer?
Hashimoto’s
Thyroid cancer
What are two disorders with iodine deficiency?
Iodine deficiency disorder (goiter)
Cretinism
-Growth retardation
Hypothyroidism and hyperthyroidism can both give the patient goiter. Tell me why each one can.
Hypo (Hashimoto’s) - Reduced T3 and T4 causes ant pit to overproduce TSH, causing thyroid to enlarge - goiter
Hyper (Graves) - TSH levels decrease, auto-antibodies attack thyroid, and thyroid hypertrophies. Thyroid overproduced T3 and T4 leading to goiter.
4 GI functions.
Secretion
Digestion
Absorption
Gut motility
What types of hormonal communication involves the GI?
Endocrine, paracrine, neurocrine
What hormone acts in all three hormonal communication fashions?
CCK
The are two types of events that maintain homeostasis. Name and describe them.
Stimulatory - Smelling food, food hitting stomach
Inhibitory - bowel dissension
**Constant balance for homeostasis
What is the enteric nervous system?
The GI’s own localized nervous system, INDEPENDENT of parasympathetic and sympathetic innervations.
GASTRIN
Type
Source
Stimuli for release
Action
GI hormone
G cells
Stomach distention, peptides
Stim gastric acid secretion and proliferation of gastric mucosa
CHOLECYSTOKININ (CCK)
Type
Source
Stimuli for release
Action
GI hormone
I cells
Digestive products from fats, fatty acids, monoglycerides
Contracts gall bladder - expelling bile into duodenum
SECRETIN
Type
Source
Stimuli for release
Action
GI hormone
S cells
Acidic pH in small intestine
Stims pancreas to release bicarb (neutralize acids)
GASTRIC INHIBITORY PEPTIDE (GIP)
Type
Source
Stimuli for release
Action
GI hormone
Mucosa of upper small intestine
FA, AA, carbs
Inhibits gastric secretions and motility, increases insulin release when food in duodenum and blood glucose is high
GLUCAGON
Type
Purpose
Action
Release due to:
Inhibition due to:
Deficiency due to:
Excess
Pancreatic hormone
Counter-regulatory assistance for insulin
Release of glucose from cells
Low blood sugar
High blood sugar
Hypoglycemia
Hyperglycemia
INSULIN
Type
Purpose
Action
Release due to:
Inhibited by:
Deficiency
Excess
Pancreatic hormone
Regulate blood glucose
Absorption of glucose from cells
High blood sugar
Low blood sugar
Diabetes
Hypoglycemia
SOMATOSTATIN
Type
Purpose
Action
Release due to:
Inhibited by:
Deficiency
Excess
Pancreatic hormone
Regulates GI hormones in pancreas and GI tract
Slows production of insulin, glucagon, gastrin, and other hormones
High hormone levels
Low hormone levels
No deficiency
Diabetes
What is the continuous process by which thyroid hormones are produced and stored w/in thyroid follicles?
Iodine ions absorbed
Diffusion and attaches 1 or 2 activated iodide ions to the tyrosine portions of a thyroglobulin resulting in 4 to 8 molecules of T3, T4, or both
Thyroglobulin from follicle by endocytosis
Lysosomal enzymes break down thyroglobulin, AA are then recycled and used to synthesize more thyroglobulin
T3 and T4 diffuse across bsmt membrane into blood. Attached to blood transport proteins called thyroid-binding globulins.
T/F - T3 and T4 release into blood and into follicles is a continuous process.
TRUE
