Endocrine- Bergfelt Flashcards
Endocrine System
Collection of ductless glands that secrete hormones directly into the circulatory system that target distant organs
Endocrine Glands
ductless glands of the endocrine system that secret heir products, hormones, directly into teh cirulatory system
Examples of endocrine glands
pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland
Hormone signaling
hormone-receptor interactions
Exocrine Glands
glands not of the endocrine system that secret their product through a duct or canal
Examples of exocrine glands
salivary, sweat, mammary glands
What are the two major systems involved in homeostasis?
nervous and endocrine system
Where is the thyroid located?
on either side of the trachea, below the larynx
Where are the parathyroid glands located?
external and internal to the surface of each lobe of the thyroid gland in cats and dogs
What is the function of thyroid follicles?
epithelial cells that produce thyroid hormones
What is colloid?
intracellular fluid rich in thyroglobulin
Where are parafollicular cells located?
between thryoid follicles
What do parafollicular cells secrete?
produce calcitonin
What do cheif cells produce?
parathyroid hormone
What are the two main precursor substances to thyroid hormone synthesis?
Iodide and thyroglobulin (tyrosine aa)- from colloid
What is the most bioactive form of thyroid hormone?
T3
What is the most abundant form of thyroid hormone?
T4
What produces thyroid- releasing hormone?
produced by the hypothalamus, binds to TRH receptors on anterior pituitary gland thyrotropes
What is the function of thyroid stimulating hormone?
stimulates T3 and T4 synthesis
How does T3 and T4 function as a negative feedback loop?
As T3 and T4 blood concentrations increase, inhibit TSH and TRH, inhibiting thryoid epithelial hormone production
The T3 and T4 negative feedback loop acts on what two organs?
hypothalamus and anterior pituitary
What are external control factors to the thyroid gland?
cold, diet and stress
What is the effect of cold on the thyroid?
increases T3 levels
What is the effect of high carb. diet on the thyroid?
increase in T3 levels, increase metabolic rate
What is the effect of low carb. diet on the thyroid?
decrease in T3 levels, decrease in metabolic rate
The transport of T3 and T4 requires what and why?
Requires the binding to transport proteins because T3 and T4 are fat soluble (hydrophobic)
what are some examples of thyroid binding proteins?
thyroid binding globulin, transthyrein and albumin
What does T3 bind to?
mitochondria nd nuclear receptors
What does the binding of T3 to mitochondria create?
activates oxidative phosphorylation and ATP synthesis
What does the binding of T3 to nuclear receptors create?
increases mRNA transcription, translation and an increase in protein synthesis
What are the primary organs for clearance of thyroid hormones and metabolites?
liver and kidneys
T4 glucuronidation is facilitated by which liver enzyme?
T4, UDP-glucuronyltransferase
What can happen if you increase UDP-glucuronyltransferase production in the liver with drugs or toxins?
increase the loss of T4, increases loss of T3: acute hypothyroidism
the production of calcitonin is stimulated by?
high extracellular or blood calcium levels
What is the function of calcitonin?
decrease Ca levels
What tissues do calcitonin target?
bone, kidney and digestive tract
What is the effect of calcitonin on bone?
inhibits osteoclast activity, stimulates storage of Ca
What is the effect of calcitonin on the kidney?
inhibits tubular reabsortion of Ca, stimulates excretion of Ca
What is the effect of calcitonin on the digestive tract?
inhibits uptake of Ca, stimulates excretion of Ca
What stimulates increased production and secretion of parathyroid hormone?
low extracellular or blood Ca levels
What organs do PTH target?
bone, kidney and digestive tract
what is the effect of PTH on bone?
stimulates osteoclast activity, increasing bone digestion
What is the effect of PTH on the kidney and GI?
reabsorption of Ca and inhibiting Ca excretion
Hypothyroidism
decreased synthesis and secretion of thyroid hormones, associated with decreased metabolic rate
Primary hypothryoidism is classified as
thyroid gland dysfunction and is the most common
Secondary hypothyroidism is classified as
pituitary gland dysfunction and is rare (pituitary gland tumor)
Tertiary hypothyroidism is classified as
hypothalamic dysfunction, rare/ not described
Congenital hypothyroidism is classified as
thyroid gland hyperplasia
reported in foals as a result of mares diet, low I- during pregnancy
