Chapter 7 - Endocrine Flashcards
What organs are the endocrine system composed of?
Thyroid Gland Ovaries Testicles Pancreas Adrenal Glands And other glands that produce hormones
Negative Feedback Regulatory Mechanism
Endocrine gland producing its hormone until concentrations of the hormone reach a certain level, at which point the cells in the endocrine gland detect this and shut off further hormone production
Exogenous
A compound that originates outside the body
Endogenous
Naturally occurring hormone
Basal Metabolic Rate
The overall rate at which cellular functions occur
What hormone producing organ has the most effect on the basal metabolic rate?
Thyroid
Thyrotropin-Releasing Hormone (TRH)
Hypothalamus produces TRH when low concentrations of thyroid hormone in the blood are detected. TRH then stimulates the pituitary gland to release TSH into the blood
Thyroid-Stimulating Hormone (TSH)
Pituitary gland releases TSH into the blood when stimulated by TRH.
Circulating TSH stimulates the follicular cells of the thyroid gland to absorb iodine and incorporate it into tyrosine molecules to produce two functional thyroid hormones (T3 and T4)
The numbers in T3 and T4 refer to what?
The numbers of iodine’s attached to the thyroid hormone molecule
Triiodothyronine
T3
Tetraiodothyronine / Thyroxine
T4
T3 Hormone
- Released from the thyroid gland, enters body cells and combines with receptors in the nucleus
- T3 considered the hormone that produces the physiologic effect of thyroid hormones - even though it is produced in smaller quantities
T4 Hormone
Serves as a storage pool for the more active T3 because the majority of tissues derives most of their needed T3 by enzymatically removing one iodine from T4 and converting it to T3
Hypothyroidism
Low production of thyroid hormone
Hyperthyroidism / Thyrotoxicosis
Excessive production of thyroid hormone caused by a functional, hormone-secreting tumor of the thyroid gland causing an increase in the circulating concentrations of T3 and T4
_______ are more prone to Hyperthyroidism
Cats
_______ are more prone to Hypothyroidism
Dogs
Primary Hypothyroidism
Disease of the thyroid gland itself that results in lower T3 and T4 hormones
Secondary Hypothyroidism
The thyroid gland itself functions normally, but the low quantities of T3 and T4 hormones result from the pituitary gland being unable to produce TSH for some reason (No TSH = Thyroid hormones not produced)
Tertiary Hypothyroidism
Thyroid gland is normal, the pituitary is normal, the problem is in the hypothalamus - it does not produce TRH, so it does not stimulate TSH to stimulate the thyroid gland to produce T3 and T4 hormones
Goiter
Form of hypothyroid condition that results not from a damaged thyroid gland, but from lack of iodine needed to manufacture T3 or T4 hormones (Rare)
Hypertrophies
Increases in size
Signs of hypothyroidism
Lethargy, weight gain despite normal appetite, heat seeking behavior, bradycardia, hair loss, dry and scaly skin
Signs of hyperthyroidism
Increased physical activity, diarrhea from increased GI motility, weight loss despite a voracious appetite, tachycardia (exceeding 240 bpm), heat intolerance, polyuria, polydypsia
Euthyroid state
Normal thyroid state
Is the thyroid hormone T3 or T4 more readily absorbed by the GI tract?
T3 - (0.95) 95% absorbed form the GI tract
T4 - 40-80% absorption
What are the 4 treatment modalities for Hyperthyroidism?
1) Thyroidectomy (cure)
2) I-131 (radioactive iodine) (cure)
3) Methimazole (antithyroid drug) (treatment)
4) Iodine-Limited Diets (treatment)
The pancreas plays a role in what two body functions?
Endocrine (hormone)
Exocrine (digestive enzyme)
What are the 3 hormones produced by the pancreas
Insulin, Glucagon and Somatostatin
What is the major effect of insulin?
To move glucose from the blood into tissue cells (decrease blood glucose concentrations by enhancing distribution of glucose to the body tissues)
Beta Cells
Produce insulin
Diabetes Mellitus
Lack of insulin, resulting in high blood glucose levels. Most commonly caused by destruction or lack of function to the pancreatic beta cells
Hyperglycemia
High blood glucose
Hypoglycemia
Low blood glucose
Glucosuria
Presence of glucose in the urine
Type I / Insulin Dependent Diabetes Mellitus (IDDM)
Characterized by decreased insulin related to the number of functional pancreatic beta cells
Type II / Non-insulin-Dependent Diabetes Mellitus (NIDDM)
Decreased effectiveness of insulin even though the pancreatic beta cells are potentially capable of producing adequate insulin (Decreased # of insulin receptors, sensitivity of insulin receptors present, sensitivity of pancreatic beta cells)
Why can insulin not be given PO?
Insulin is a protein, it would be denatured (destroyed) by the stomachs gastric acid and not absorbed. Even if it was not denatured, the insulin molecule is too large to be absorbed through the bowel mucosa