Introduction to Endocrinology Flashcards
Which of the following is a transient endocrine gland?
A. Pituitary gland
B. Hypothalamus
C. Pineal gland
D. Thymus gland
E. Heart
F. Stomach
G. Pancreas
H. Adipose Tissue
I. Testis
J. Ovary (corpus luteum)
Answer: J
Everything except for the corpus luteum, with its programmed 14 day survival span, is a permanent structure that secretes at least one hormone. Some are primary (pituitary, thymus, endocrine pancreas, and testis) and others are secondary (hypothalamus, pineal, heart, stomach, and adipose tissue) but none are transient. In this context one might say, “but the ovary is a primary endocrine gland.” In the larger scale, it is, but its actual hormone secretory structures are temporary, being located either in the maturing follicles or the corpus luteum. When these structures are finally depleted in the ovary, it ceases to be a working gland, leading to menopause. Contrast this with the testis, whose hormone secretory structures are permanent and theoretically function from puberty into advanced old age (70’s and beyond).
Which of the following is NOT a hormone secreted by a secondary endocrine gland?
A. Growth hormone
B. Growth hormone-releasing hormone
C. Melatonin
D. Atrial Natriuretic Peptide
E. Ghrelin
ANSWER A.
Explanation: Only the anterior pituitary gland has a clean primary endocrine gland function so growth hormone is excluded from the correct answers.
B. If we accept that the hypothalamus is first and foremost a part of the brain associated with the limbic system but it also secretes many hormones, it is easy to picture it as a secondary endocrine gland instead of a primary gland. Thus GHRH, a product of the hypothalamus that acts upon the anterior pituitary, is a product of a secondary endocrine gland.
C. Similarly, melatonin from the pineal falls in the it’s-first-a- part-of-the-brain category.
D. ANP is a product of the right atrium, and the heart is a secondary endocrine gland.
E. Finally, ghrelin is a product of the stomach.
A 35-year-old patient presents to his physician for a health maintenance examination. The patient says he has been tired lately. His vital signs are on the upper side of normal for heart rate, respiratory rate, and blood pressure. Nevertheless, he appears to be pale, and his gums are pale as well. Laboratory tests reveal a low red blood cell count resulting in anemia. A deficiency in hormone production from which secondary endocrine gland is most likely to be responsible for these signs and symptoms?
A. Stomach
B. Liver
C. Adipose tissue
D. Kidney
E. Duodenum
D
Explanation: Erythropoietin was first discussed in Heme & Lymph 1 back in Semester 1. It is a hormone, it’s secretory gland is the kidney whose primary job is cleaning the blood, and it won’t be discussed in lecture. Hormones like this, which are listed in the PDF table with this lecture, are legitimate endocrine hormones. They are therefore possible answers/distractors for both formative and summative examinations.
Which of the following classes of hormones is most likely to include both water- soluble and lipid-soluble hormones?
A. Amine
B. Peptide
C. Steroid
D. Prostanoid (includes Prostaglandins)
E. Gas
A.
Explanation: This is a “most likely” item, so it should have one best answer. And of these, the best answer is the amine class, which includes both short-half-life-water- soluble hormones like epinephrine and long-half-life-lipid-soluble hormones like thyroxin.
B. peptides are water soluble.
C. steroids are lipid soluble.
D. prostaglandins are often water soluble.
E. gases don’t usually have their water-vs-lipid soluble properties described.
For which of the following hormone classes can intracellular storage sites be identified with electron microscopy?
A. Amine
B. Peptide
C. Steroid
D. Prostanoid (includes Prostaglandins)
E. Gas
Answer: A and B
Explanation: The only two of these classes that are most clearly water-soluble and requiring vesicles are the water-soluble amines (e.g. epinephrine) and the peptides/protein hormones, which also need to be made in advance of need and then stored.
C-E. The other three classes are produced only when the signal comes in to start production, there is no between-signal synthesis and storage as there are with water- soluble amines and peptides.
For cortisol, which of the following patterns/modulations of hormone secretion are most likely?
A. Episodic Only
B. Pulsatile Only
C. Circadian Only
D. Episodic + Pulsatile
E. Episodic + Circadian
F. Pulsatile + Circadian
G. Episodic + Pulsatile + Circadian
Answer: F
This is an obsolete format for multiple choice questions. To obtain the correct answer you also have to know which are incorrect answers, which the NBME rejected for summative items. For formative items, however, it works well precisely because of the need to know or learn both for better understanding.
With this in mind, most cortisol secretion is typically dominated by a pulsatile pattern of secretion that is heavily modulated by the time of day (circadian modulation). Does this mean there is no episodic secretion in the presence of a strong stressor? No… but it is less likely that this will dominate the pattern of secretion. It is more likely that it will further modulate the primary pulsatile/circadian rythym control of cortisol secretion.
For insulin, which of the following patterns/modulations of hormone secretion are most likely?
A. Episodic Only
B. Pulsatile Only
C. Circadian Only
D. Episodic + Pulsatile
E. Episodic + Circadian
F. Pulsatile + Circadian
G. Episodic + Pulsatile + Circadian
Answer: A.
Explanation: Contrast insulin, which does not have a direct circadian component and does not undergo pulsatile secretion at all, with cortisol that does. Episodes of high plasma glucose result in insulin secretion until the excess glucose is stored/used in tissues.
Researchers have discovered a possible hormone Z, which is reported to increase plasma triglyceride levels. If it is controlled by a physiologic response-driven pattern of negative feedback, what would be the expected immediate effect if the levels of plasma triglycerides decreased?
A. Z would be secreted then plasma TGs would rise
B. Z would be secreted then plasma TGs would fall
C. Z secretion would stop then plasma TGs would rise D. Z secretion would stop then plasma TGs would fall E. Plasma TGs would rise then Z would be secreted
F. Plasma TGs would rise then Z secretion would stop G. Plasma TGs would fall then Z would be secreted
H. Plasma TGs would fall then Z secretion would stop
Answer: A, followed by F
Explanation: Negative feedback systems can include responses to changes above or below the desired set point. In this case the initial condition is a too-low triglyceride level. This would result in condition A, secretion of Z, and increased secretion turns into increased action, meaning triglyceride levels rise. When those TG levels rose enough, condition F, the rise of TG inhibiting further Z secretion, would provide the brake to stop the TG increase short of a pathological state.
For which of the following hormones would direct neural control of its secretion be most likely?
A. Testosterone
B. Norepinephrine
C. ACTH
D. Calcitonin
E. Thyroxine
Answer: B
Explanation: Norepinephrine, the classic sympathetic neurotransmitter, can be secfeted by cells within the adrenal medulla at the same time the more abundant epinephrine is secreted. Whether EPI or NE, though, the signal for release is sympathetic stimulation of the adrenal medulla, meaning neural control. For many of the others neural control modulates the secretory pathway but it is not the primary means of controlling secretion of the other hormones.
What is the one absolute requirement for a given tissue to be a target tissue for a given hormone?
A. The ability to produce a response that would correct the condition controlling the hormone secretion
B. The ability to synthesize products that are relevant to the effect of the hormone
C. The ability to synthesize receptors for that hormone
D. The ability to open ion channels and alter membrane potential in that cell
E. The ability to synthesize and secrete the hormone.
Answer: C
Explanation: Any cell with no receptors for a hormone is 100% resistant to being directly affected by that hormone, a first messenger. Without those receptors none of the other second messenger pathways would be or could be activated.
Rank the following hormones by their half-lives, from shortest to longest: Aldosterone, Angiotensin II, Cortisol, Growth hormone, Insulin, Progesterone, and Thyroxine.
Answer:
- AgII
- Insulin
- GH
- Aldosterone
- Cortisol
- Progesterone
- Thyroxine
Explanation: The water-soluble hormones have the shortest half lives. Of those, angiotensin II is cleared from the blood the fastest so it has the shortest half-life on any of the hormones on this list. I believe the table in the powerpoint has it as about 2 minutes for 50% clearance, a.k.a. one half-life. In contrast, thyroxine can last for seven DAYS before half of it has been removed from the plasma, giving it the longest half-life of any hormone.
Patterns of hormone secretion
Episodic Release
A specific stimulus arrives and the hormone is released. If only paracrine/autocrine substances are released, this can be called a “localized burst”.
Example: Insulin is an example of a hormone released when glucose levels rise in the bloodstream.
Patterns of hormone secretion
Pulsatile Release
A hormone is released in a series of regularly timed short bursts, typically with time between the bursts devoted to hormone action and metabolism
Example: Growth hormone is an example of a hormone released in short bursts when stimulated to do so by hypothalamic hormones
Patterns of hormone secretion
Circadian and other larger-timed rhythms
Significantly more hormone is released at certain times of the day (circadian), month, or year than at other points in the respective time cycle.
Example: Melatonin
Three Types of Hormone Control
- Homeostatic feedback
- Neural control
- Chronotropic control (modulation)
- Homeostatic feedback: almost always negative, but combined effects lead to normal amounts in body.
Physiological Response-Driven vs.Endocrine Axis-Driven
- Neural control: Nervous system directly commands hormone release; secretagogues
– Includes adrenergic, cholinergic, serotoninergic
– Can serve homeostatic feedback
- Chronotropic control (modulation): rise and fall of hormones during certain times of the day or month.
– Includes pulsatile, diurnal, menstrual, seasonal, and developmental rhythms;
– Involves neuronal signals
– Can modulate homeostatic feedback
