Overview of Endocrine System Flashcards
Define and discuss the following terms: Hormone; Hypothalamic-Pituitary Axis; Negative Feed back; Primary vs. Secondary Disorders. Outline the feedback mechanisms of common endocrine systems and hormones encountered in primary care.
A molecule that functions as a message within an organism. It’s only function is to convey information. Essentially, a “signal.”
Hormone
Class of Hormones including Dopamine, Catecholamines, and T3/T4
Amino Acid Derivatives
Class of Hormones including GnRH (Gonaotropin-Releasing Hormone), TRH (Thyrotropin Releasing Hormone), and ADH (Antidiuretic Hormone, Vasopressin, Arginine Vasopressin).
Neuropeptides
What is Endocrinology?
Intracellular Chemical Communication (NOT OBJECTIVE)
Functions of Endo?
- Maintain Internal Homeostasis, 2. Support Cell Growth, 3. Coordinate Development, 4. Coordinate Reproduction, 5. Facilitate Responses to External Stimuli (NOT OBJECTIVE)
Cellular Proteins that bind with high affinity to hormones, causing altered shape and function. Limited number of these.
Hormone Receptor (NOT OBJECTIVE)
Two types of Hormone Receptors
Membrane and Nuclear (NOT OBJECTIVE)
Proteins that convert the information in hormone signals into chemical signals understood by cellular machinery. This occurs when they interact with the protein-hormone complex
Transducers (NOT OBJECTIVE)
Two types of feedback
Negative and Positive
These maintain hormonal balance and are often linked to homeostatic processes. A signal in the lower section of a hierarchy is sent to a higher section to inhibit action.
Negative Feedback
These cause physiologic changes in the system involved. A signal in the lower section of a hierarchy is sent to a higher section to excite an action.
Positive Feedback
Class of Hormones including Insulin and Gonadotropins
Proteins
Class of Hormones including cortisol and estrogen
Steroids
Class of Hormones including retinoids and Vitamin D
Vitamin Derivatives
How are hormones stored?
Precursors or Prohormones (preproinsulin, POMC)
Three types of cells in the Endocrine System
- Endocrine Cell
- Paracrine Cell
- Autocrine Cell
Cell –> Anywhere in body
Endocrine Cell
Cell –> Proximal Cell
Paracrine Cell
Cell –> Itself
Autocrine Cell
Hormone –> Cellular Effect –> Physiological Response & Feedback
Homeostatic Principle of Endocrinology
Two types of Endocrine Environmental Adaptation
Pulsatile and Circadian Rhythms (Note: Hormones commonly activated by light or sleep)
Brain Stem Rule #1
Hormones Obey Newton’s 3rd Law
Brain Stem Rule #2
Plasma accumulation of ANYTHING reflects balance between rate of formation and rate of removal
Brain Stem Rule #3
Most protein hormones have short plasma half lives and some (like ACTH) are very susceptible to ex vivo proteolysis.
This is predominantly connected to the hypothalamus by vascular connections
Adenohypophysis or Anterior Lobe of Pituitary Gland
This is predominantly connected to the hypothalamus by neural connections
Neurohypophysis or Posterior Lobe of Pituitary Gland
Tea Time, Praise The Lord
TRH –> TSH + PRL –> Thyrotroph and Lactotrophs
Function of Thyrotrophs
Metabolism
Function of Lactotrophs
Lactation
Lovely Lola F*cks George
LHRH –> LH + FSH –> Gonadotrophs
Function of Gonadotrophs
Reproduction
Crazy Andrew Cries
CRH –> ACTH –> Corticotroph
Function of Corticotroph
Stress
Growing Gary Stilts
GHRH –> GH –> Somatotroph
Function of Somatotroph
Growth
Shrinking Gary Shrinks
Somatostatin –> GH –> Somatotroph (Note: Shrinking is opposite of Growing, so this is an inhibitory process)
Dolly Parton Lactates?
Dopamine –> PRL –> Lactotroph (Note: Dolly Parton probably can’t lactate, so this is an inhibitory process)
Common Hormones from the Neurohypophysis
Oxytocin and ADH (aka Vasopressin aka Arginine Vasopressin)
Functions of the Hypothalamus
- Sympathetic and Parasympathetic Nervous Systems
- Body temperature
- Biological Rhythms
- Electrolyte Balance
- Emotional Behavior (Anger, fear, euphoria)
- Motivational Behavior (sex, hunger, aggression, thirsty)
- Hormone Secretion
What is the thyroid feedback loop?
TRH from the hypothalamus is released to the Pituitary Thyrotroph to produce TSH that is released to the thyroid gland which excited it to produce T3 and T4. With elevated T3 and T4, they inhibit this process by acting on either the hypothalamus OR the Pituitary Gland.
Somatostatin from the hypothalmus is released to the pituitary thyrotroph to inhibit synthesis of TRH
Thyroid Anatomy
Right Lobe, Left Lobe, Pyrimidal Lobe, Isthmus
This is synthesized by the thyroid epithelial cells and secreted into the lumen (colloid) of the follicle.
Thyroglobulin
The colloid is primarily filled with ____________.
Thyroglobulin
Functions of the Thyroid Hormone
- Development and function of the CNS
- Fat oxidation and increase in metabolic rate
- Skeletal muscle strength
- Myocardium contractility
- Protein Synthesis
- Vascular endothelial function and coagulation
Lab Tests for Thyroid
TSH, Free T4, Total T3, Reverse T3
High TSH levels with Low T4
Primary Hypothyroidism
Low TSH levels with High T4
Primary Hyperthyroidism
Low TSH and T4 levels
Secondary Hypothyroidism (Central Hypothyroidism)
High TSH and T4
Screen for an adenoma!
Thyroxine
T4
First line test for thyroid function? Why?
TSH because it is highly reliable and cheap to do. Does have pitfalls and can be inaccurate if in a dynamic state.
Causes of elevated TSH
- Hypothyroidism
- Recovering from a non-thyroid illness
- Central Hypothyroidism
- Adrenal insufficiency
- Thyroid Hormone Resistance
- Heterophilic Antibodies
- Nocturnal TSH surges
- TSH-secreting adenoma
- Drugs (lithium, iodide/contrast agents, dopamine antagonists, metaclopramide, amiodarone)
Causes of low TSH
- Hyperthyroidism
- Hypopituitaryism
- Non-thyroidal illness
- Starvation
- Cushing’s Syndrome
- Elderly with normal response to TRH
- Drugs (dopamine and dopaminergic agents, glucocorticoids, somatostatin, opiates, NSAIDs, amphetamines, cocaine)
Causes of Elevated T4
Heparin/Furosemide/NSAIDs! This can cause lipoprotein lipase to lyse triglycerides to form free fatty acids that can displace T4 from the receptors
