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
Insulin is classified into what?
Their duration of activity - short acting, intermediate acting and long acting insulins
Differences in insulin structures between species are thought to contribute to what?
Development of insulin antibodies - which leads to erratic control of BG levels
Most insulin’s are suspensions, meaning what?
The insulin is not dissolved in the liquid and needs to be resuspended before each withdrawal of insulin from the bottle
What brand of insulin specifically states it is ideal to shake the bottle in order to achieve more uniform suspension of the drug?
Vetsulin - shaking has no adverse effect to the insulin’s activity if shaken
Insulin doses are time when?
They have their maximal effect near the time when the BG concentrations are peaking after consumption of a meal
Where is it ideal to administer insulin?
In SQ areas that have consistent perfusion
What is the idea diet for a diabetic patient?
Low in absorbable sugars with NO “treats”
What is the name of the oral drug that has been used in cats to control diabetes mellitus?
Glipizide
What is a side effect of Glipizide?
May accelerate beta cell loss, rendering the Glipizide ineffective and making the diabetic condition worse
Hormone drugs are used in horses and cattle for what purposes?
Synchronize estrous cycles, terminate pregnancies and induce ovulation
Hormone drugs are used in dogs and cats for what purposes?
Primarily to prevent pregnancy or alter the state of the uterus
Theriogenology
The study of reproduction
How do hormone therapies typically work in female animals?
Block of enhance the effect of the endogenous reproductive hormones by either mimicking the effect of the natural hormone or by triggering the normal negative feedback mechanism
What are the 2 phases of the estrous cycle?
Follicular and Luteal
Follicular Phase (proestrus and estrus)
Hormones produced by the ovarian follicle exert predominant control and prepare the animal to become inseminated
Luteal Phase (metestrus/diestrus)
Hormones of the CL on the ovary predominate, focusing on sustaining a fertilized egg
Proestrus
When follicles are developing
Estrus
When the female animal is receptive to mating and ovulates
Estrus/Diestrus
The follicle turns into a CL to prepare for and sustain pregnancy
Anestrus
Period of time in which little or no cycling activity is occurring and hormone levels in general are very low
Myometrium
Uterine smooth muscles
Progesterone
Produced by the CL, principal hormone in charge of the Luteal phase (both preparation for implantation of the ovum, and during pregnancy it creates an environment conducive to fetal development)
Inhibin
Hormone produced by the developing follicular tissue and serves as a negative feedback mechanism to decrease the release of GnRH and FSH (allowing only the most developed follicle to continue maturation until it can release an ovum)
Estrus
Referring to the state of being in heat
Estrous is a complex cycle coordinated and integrated between the…..
Hypothalamus (brain), pituitary gland (just below the hypothalamus), and the gonads (testicles or ovaries)
Estrogen
Hormone, changes in estrogen levels are known for causing the behavioral and physical changes associated with estrus - making the uterus more prone to contraction during parturition
Luteinizing Hormone (LH)
Hormone released from the pituitary gland, the surge of LH lyses the mature ovarian follicles, releases the ova, and transforms the ruptured follicle into a CL, ushering in the luteal phase
Parturition
The birth process
Adenocorticotropic Hormone (ACTH)
Produced by the pituitary gland, stimulates production or cortisol
Cortisol
Natural corticosteroid released from the the adrenal glands of both the fetus and the pregnant female animal
Lyse
Destroy
Prostaglandins
Produced by the uterus and lyse the CL, terminating its production of progesterone and removing the ‘calming’ effect on the myometrium - making the uterus more prone to contraction during parturition
Gonadotropin - Releasing Hormone Drugs (GnRH Analogs) / Gonadorelins
Stimulate release of LH and FSH. Analogs cannot exactly mimic the natural GnRH.
Oxytocin
Endogenous hormone released from the pituitary gland that causes contraction of the myometrium (and milk ejection)
GnRH analogs or Gonadorelins drugs are used for what?
- Approved for short term use in beef and dairy cattle to lyse persistent ovarian follicles or follicular cysts.
- Timed AI protocol’s to bring an entire groups of cattle into estrus at the same time
Gonadotropins
Pituitary gonadotropins FSH and LH have an affinity for, and produce their effects on the gonads (ovaries, testes)
Equine Chorionic Gonadotropin
Produced by certain fetal cells in horses, has FSH and LH effects
Progestins
Refers to a group of progesterone-like hormones
Progestagen
Refers to a synthesized drug that mimics progestins
Controlled-Internal Drug Release (CIDR)
Apparatus that can be used in cattle to provide a continuous supply of progesterone for several days to prolong diestrus
Metritis
Inflammation of the uterus
Pyometra
Uterine infection with pus
Gestational Diabetes
Effect of Progesterone and other progestins during pregnancy (antagonistic effect on insulin receptors) causing hyperglycemia and a temporary diabetic-like syndrome
What is the most common estrogen product used in vet med?
Incurin - Primarily used in spayed dogs to treat urinary incontinence
Carcinogenic
Cancer-producing
Aplastic Anemia
Estrogen induced, usually appears 2-8 weeks after estrogen administration manifested by (low platelet counts, pinpoint hemorrhages in the skin, bruising, leukopenia, and severe anemia) May slowly resolve on its own after discontinuation of estrogen therapy
What 3 hormones play a major role in synchronizing estrous cycles?
Prostaglandins, GnRH and Progestins
True/False
Prostaglandins can function in both the Follicular and Luteal phases of estrous?
FALSE.
Prostaglandins can ONLY function in the luteal phase when an active CL is present to lyse
What drugs can cause both bronchoconstriction and CL lysis (unintended abortion) when handled incorrectly in both humans and animals?
Prostaglandins
In 2009 the AVMA warned veterinary practices to tightly control inventory of what reproductive products?
Prostaglandin products - it was thought teenage girls were stealing/obtaining these drugs to terminate unwanted pregnancies
Foal Heat
Mares that come into heat soon after foaling, these mares generally have a significantly lower conception rate
Nymphomania
Animals that remain in a prolonged estrus and often exhibit aggressive behavior
Short cycling
Shortening the diestrus phase of the first cycle by using prostaglandins to lyse the CL and initiate a new cycle
Seasonal Anestrus
Occurs in autumn when the days grow shorted and the photoperiod decreases, the reproductive hormones in mares begin to decrease to minimal amounts causing the mares to stop cycling
Dopamine Antagonist Drugs
Promote the release of prolactin from the pituitary (have been shown to increase follicular activity in anestrus mares)
Mammary Hyperplasia
Proliferation of mammary tissue, cause by prolonged use of Megestrol
Dopamine Agonists
Group of compounds that bind with and stimulate dopamine receptors
Dystocia
Difficult labor
