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MCAT Biology > Chapter 12 - The Endocrine System > Flashcards

Chapter 12 - The Endocrine System Flashcards

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1
Q

What controls hormone activity and specificity?

A

Hormones must bind their receptors to be effective. Therefore, their activity is controlled not only by their release, but also by the presence of receptors on target cells

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2
Q

Autocrine signaling

A

Signaling where the cell releasing the hormones is stimulated, e.g. T-cells release IL-2 for self-activation

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3
Q

Paracrine signaling

A

Occurs between cells that are proximal to one another, e.g. two neurons signaling between the hypothalamus and pituitary.

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4
Q

Endocrine signaling

A

Classic action at a distance, e.g FSH is released by the anterior pituitary but exerts its effects at the level of the gonads

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5
Q

Endocrine glands

A

Glands that synthesize and secrete hormones directly into the circulatory system. Examples include the hypothalamus, pituitary gland, pineal gland, thymus, pancreas, testes, ovaries adrenal glands, thyroid gland, and parathyroid glands.

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6
Q

Exocrine glands

A

Glands that synthesize and secrete hormones through ducts. The gall bladder is an example of an exocrine gland.

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7
Q

What are the three molecular types of hormones

A
  1. Peptide hormones
  2. Amino acid-derived hormones
  3. Steroid hormones
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8
Q

Peptide hormones

A

Polar hormones incapable of permeating the cell membrane. They bind to surface receptors and act through second messengers.

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9
Q

Steroid hormones

A

Nonpolar hormones taht permeate the cell membrane and act by binding intracellular receptors

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10
Q

Amino Acid Derived Hormones

A

Hormones that are synthesized from amino acids (typically tyrosine). Some amino acid-derived hormones act via second messengers, while otehrs act in a fashion similar to steroid hormones

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11
Q

Endocrine glands (define and list)

A

Organs that are capable of producing hormones

  1. Hypothalamus
  2. Pituitary
  3. Gonads (testes and ovaries)
  4. Pineal gland
  5. Thyroid
  6. Kidneys
  7. Gastrointestinal glands (adrenal glands and pancreas)
  8. Heart
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12
Q

Endocrine system: effects

A
  • Slow, indirect, long lasting (compared to nervous system)
  • Alters metabolism
  • Regulates growth/development
  • Guides reproduction
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13
Q

Anterior pituitary hormones: list and type

A
  1. FSH
  2. LH
  3. ACTH
  4. hGH
  5. TSH
  6. Prolactin

These are all peptide hormones

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14
Q

Hypothalamus: function and location

A

The “master control gland” in the forebrain, dircetly above the pituitary gland and below the thalamus. The hypothalamusis capable of having organism-wide effects by regulating the pituitary through (paracrine) release of hormones.

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15
Q

Hypothalamus-Anterior Pituitary Connection

A

The hypothalamus secretes hormones into the hypophyseal portal system, a capillary network between the hypothalamus and anterior pituitary (hypophysis). These hormones travel through the capillary network and bind receptors on the anterior pituitary.

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16
Q

Hypothalamus hormones targeting the anterior pituitary: list and mode of function

A
  • Gonadotropin-releasing hormone (GnRH)
  • Growth hormone-releasing hormone (GHRH)
  • Prolactin Inhibitory Factor (PIF AKA Dopamine)
  • Thyroid-Releasing Hormone (TRH)
  • Corticotropin-Releasing Factor (CRF)

All of these hormones, with the exception of PIF (Dopamine), stimulate release of hormones in the anterior pituitary once they bind their receptors. PIF (Dopamine) is the opposite: as long as the hypothalamus releases it, no prolactin will be released.

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17
Q

Anterior pituitary hormones: list

A

Mnemomic: FLAT PEG

  • Follicle stimulating hormone (FSH)
  • Leutenizing Hormone (LH)
  • Adrenocorticotropic Hormone (ACTH)
  • Thyroid Stimulating Hormone (TSH)
  • Prolactin
  • Endorphins
  • Growth Hormone (GH)

NB: FLAT function tropically, PEG function directly

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18
Q

Hypothalamus-Anterior Pituitary: Hormone Cascades

A
  • GnRH → FSH + LH
  • GHRH → GH
  • PIF (Dopamine) –ø Prolactin
  • TRH → TSH
  • CRF → ACTH
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19
Q

Hypothalamus: mode of regulation

A

Since excessive levels of hormones can be detrimental, the hypothalamus and pituitary are subject to feedback inhibition to maintain hormone levels within a healthy range. For example, as concentrations of glucocorticoids rise, negative feedback to the hypothalamus and pituitary decreases their release of the upstream signals (CRH/CRF and ACTH)

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20
Q

Hypothalamus-Posterior Pituitary connection

A

Communication between the hypothalamus and posterior pituitary occurs through neuronal signal. Neurons in the hypothalamus send their axons down the pituitary stalk and into the posterior pituitary. Action potentials initiated in the hypothalamus result in synaptic signaling at the posterior pituitary, which triggers release of hormones stored in the posterior pituitary (Oxytocin and ADH).

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21
Q

Posterior pituitary hormones: list and functions

A
  • Oxytocin: secreted during childbirth and allows for coordinated contraction of uterine smooth muscle.
  • ADH: secreted in response to increased blood osmolarity or low blood volume. Acts at the collecting duct to increase water reabsorption.

Both oxytocin and ADH are peptide hormones synthesized in the hypothalamus but stored in the posterior pituitary. The posterior pituitary has no synthetic functions of its own.

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22
Q

Tropic hormones

A

Bind to receptors on target organs, resulting in the release of of effector hormones. Tropic hormones act as an intermediate in signaling. FSH, LH, ACTH, and TSH all act tropically (FLAT), as do their upstream signaling molecules.

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23
Q

Direct hormones

A

Bind to receptors on their target organs and have a direct effect (i.e. no intermediate is needed). Prolactin, Endorphins, and GH all act directly (PEG).

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24
Q

Growth Hormone (GH or hGH)

A

GH is a peptide hormone released by anterior pituitary in response to GHRH stimulation and inhibited by somatostatin.

Stimulates growth of bone and muscle by preventing glucose uptake in nongrowing tissues and stimulating the breakdown of fatty acids. This increases availability of glucose overall, allowing the bone and muscle to use it for growth. GH act directly.

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25
Q

Dysregulation of GH: resulting disorders

A

Dysregulation of GH during childhood can cause growth disorder. Gigantism is a result of excess GH, while dwarfism is due to a deficit. An excess of GH during adulthood leads to aberrant bone remodelling, a condition known as acromegaly, where smaller bones are disproportionately affected, resulting in the growth and expansion of hands, feet, fingers, etc.

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26
Q

Prolactin

A

Peptide hormone synthesized and released by the anterior pituitary that stimulates milk production and secretion in female mammary glands. Prolactin acts directly.

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27
Q

Endorphins

A

Synthesized and released by the anterior pituitary , endorphins inhibit the perception of pain. Many pharmaceuticals such as morphine mimic the effect of these naturally occurring painkillers. Endorphins act directly.

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28
Q

Tropic Hormones: Signaling Cascades

A
  • GNRH → FSH → Effectors (maturation of germ cells that give rise to gametes)
  • GNRH → LH → Testosterone (males) / Estrogen (females)
  • CRF → ACTH → Glucocorticoids (raise blood glucose levels)
  • TRH → TSH → T4 and T3 (increase metabolic activity)

In all cases, high plasma levels of the final effector molecule will lead to feedback inhibition.

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29
Q

Thyroid: location, regulation, major functions, and relavent hormones

A

Located on the fron surface of the trachea. The thyroid is regulated by the pituitary (via TSH) and the hypothalamus (via TRH). It is functions in

  1. setting basal metabollic rate (via T4 and T3)
  2. calcium homeostasis (via calcitonin)
30
Q

Thyroid Hormones

A

Synthesized and released by the thyroid gland in response to TSH, thyroid hormones (T4 and T3) are tyrosine derivatives that are capable of resetting the basal metabolic rate of the body by making energy production more or less efficient. They increase cellular respiration and protein and fatty acid turnover. High plasma levels of thyroid hormones will inhibit TSH and TRH synthesis.

TRH → TSH → T4 and T3

(T4 and T3)high –ø (TSH and TRH)

31
Q

Dysregulation of thyroid hormones: results

A
  • Hypothyroidism - insufficient secretion of thyroid hormones leads to lethargy, decreased body temperature, slow respiratory and heart rate, cold intolerance and weight gain. Deficient levels at birth can lead to mental retardation and developmental delay (cretinism)
  • Hyperthyroidism - excessive amounts of thyroid hormones leads to heightened activity level, increased body temperature, increased respiratory and heart rate, heat intolerance and weight loss.
32
Q

Calcitonin

A

Hormone released by the thyroid gland that decreases plasma Ca2+ concentrations. Acts by increasing excretion from the kidneys, decreaing absorption in the gut, and increasing storage in the bone. Antagonistic to PTH.

Mnemonic: calcitonin “tones down” Ca2+

33
Q

Parathyroid: location and major functions

A

Four small pea-shaped structures on the posterior surface of the thyroid. Produces parathyroid hormone (PTH) and functions in calcium homeostasis.

34
Q

Parathyhroid Hormone (PTH)

A

Synthesized and released by the parathyroid glands, PTH increases plasma Ca2+ concentrations. Acts by decreasing excretion from the kidneys, increasing absorption in the gut, and decreasing storage in the bone. Antagonistic to calcitonin.

35
Q

Adrenal glands: location, subdivisions, and functions.

A

Located on top of the kidneys (one on each side), the adrenal glands consist of the adrenal cortex and adrenal medulla. The adrenal glands are chiefly responsible for releasing hormones in response to stress.

36
Q

Adrenal cortex: embryonic tissue, hormones and regulation

A

Derived from the mesoderm, the adrenal cortex synthesizes and releases corticosteroids when stimulated by adrenocorticotropic hormone (ACTH). The corticosteroids consist of three functional classes:

  1. glucocorticoids: regulate glucose levels
  2. mineralocorticoids: regulate salt balance
  3. cortical sex hormones: androgen production

Mnemonic: recall the three s’s of the adrenal cortex: sugar, salt, sex. We spend most of our waking (and dreaming) hours fantasizing about, or actually pursuing, each of these.

CRF → ACTH → Corticosteroids

37
Q

Glucocorticoids: regulation, function, and example

A

Steroid hormones synthesized and released by the adrenal cortex in response to ACTH stimulation, glucocorticoids raise blood glucose levels while decreasing protein synthesis, inflammation, and immunological respones. Cortisol and cortisone are both important glucocorticoids.

CRF → ACTH → (Cortisol & Cortisone)

(Cortisol & Cortisone)high –ø (CRF & ACTH)

38
Q

Mineralocorticoids: function and example

A

Steroid hormones synthesized and released by the adrenal cortex in response to ACTH stimulation, mineralocorticoids control salt balance in coordination with the kidneys. Aldosterone is an important mineralocorticoid that increases sodium, and thereby water, reabsorption in the kidney.

39
Q

Aldosterone: function and regulation

A

Aldosterone is a mineralocorticoid secreted by the adrenal cortex that increases sodium, and thereby also water, reabsorption in the kidney, leading to increased blood pressure. Aldosterone secretion is regulated by the renin-angiotensin system in response to decreased blood volume (induces renin secretion):

40
Q

Cortical Sex Hormones

A

Steroid hormones synthesized and released by the adrenal cortex, cortical sex hormones consist of androgens. These are relatively unimportant in males given the high levels produced by the testes, but dysregulation in females may have masculinizing effects by increasing male secondary sex characteristics (facial hair, etc.).

41
Q

Adrenal medulla: embryonic tissue, hormones, and function

A

Derived from the embryonic neural crest (ectoderm), the adrenal medulla is a component the nervous system. It is responsible for the synthesis and release of the “fight or flight” sympathetic hormones epinephrine and norepinephrine, which function in stress response.

42
Q

Epinephrine and norepinephrine

A

Tyrosine derivatives (Catacholamines) synthesized in and released by the adrenal medulla. Responsible for the “fight or flight” response to stress.

Epinephrine and norepinephrine stimulate an increase in the heart, respiratory, and metabolic rates, and increase blood glucose levels by stimulating conversion of glycogen back to glucose. They divert blood flow away from the “rest and digest” organs (stomach, kidney, gut, and skin) and to the “fight or flight” organs (skeletal muscle, lungs, brain, and heart) through vasoconstriction and vasodilation (respectively).

43
Q

Pancreas: major endocrine and exocrine functions

A

The pancreas functions through secretion of compounds important in the regulation of digestion and overall metabolism. It has both exocrine and endocrine functions:

  • Exocrine: secretion of digestive enzymes into the duodenum (amylase, lipase, peptidases)
  • Endocrine: Secretion of digestive hormones (glucagon, insulin, and somatostatin)
44
Q

Islets of Langerhans

A

small group of pancreatic cells important in its endocrine function. Consists of alpha, beta, and delta cells.

45
Q

Alpha cells: location and secreted hormone?

A

Located in the pancreatic islets of langerhans, alpha cells secrete glucagon during times of famine to stimulate production of glucose alternatives and release of glucose stores.

46
Q

Beta cells: location and secreted hormone?

A

Located in the pancreatic islets of langerhans, Beta cells produce and secrete insulin during times of feast. Insulin induces glucose uptake and glycogen production in muscle and liver cells, and stimulates anabolic processes such as fat and protein synthesis.

47
Q

Insulin dysregulation: what are the results?

A

Excessive insulin results in hypoglycemia, or low blood glucose levels. Underproduction, insufficient secretion, or insensitivity to insulin can results in diabetes milletus, which is clinically characterized by hyperglycemia, excess glucose in the blood.

48
Q

Which hormones can regulate blood glucose levels?

A
  • Insulin - decrease plasma glucose levels
  • Glucagon - increase plasma glucose levels
  • Glucocorticoids - increase plasma glucose levels
  • Epinephrine - increase plasma glucose levels
49
Q

Insulin: production and function

A

Produced and secreted by the beta cells of the pancreas, insulin decreases blood glucose levels by facilitating the uptake of glucose by muscle and adipose cells and the conversionof glucose to glycogen in muscle and liver cells. Antagonistic to glucagon.

50
Q

Glucagon: production and function

A

Produced and secreted by the alpha cells of the pancreas, glucagon increases blood glucose levels bypromoting gluconeogenesis abd teh conversion of glycogen to glucose in the liver. Antagonistic to insulin

Mnemonic: Glucagon levels are high when glucose is gone

51
Q

Somatostatin

A

Produced and secreted by the delta cells of the pancreas, somatostatin inhibits the release of both glucagon and insulin.

52
Q

FSH and LH: targets and functions in the testes

A
  • FSH: stimulates Sertoli cells and is necessary for sperm maturation
  • LH: stimulates the interstitial cells to produce testosterone
53
Q

What are the major hormones that contribute to spermatogenesis in males, and what are their targets and effects?

A

Follicle Stimulating Hormone (FSH) stimulates the Sertoli cells and is necessary for sperm maturation, whereas Luteinizing Hormone (LH) causes the interstitial cells to produce testosterone, the major androgen in males. Testosterone is necessary for male embryonic differentiation, male sexual maturation at puberty, and maintenance of secondary sex characteristics, such as axillary and pubic hair. Testosterone provides negative feedback to FSH, LH, and GnRH.

54
Q

Testosterone: Production, regulation, and function

A

The major androgen in males, testosterone is produed by the interstitial cells of the testes in response to LH stimulation. It functions in spermatogenesis and is importatn in male embryonic differentiation and maintenance of masculine secondary sex characteristics. It provides negative feedback to FSH, LH and GnRH.

GnRH → LH → Testosterone

(Testosterone)high –ø (GnRH, LH, & FSH)

55
Q

Estrogen: production, regulation, and function

A

Hormone synthesized by the ovaries, the ovarian follicles, the corpus luteum, and the placenta in response to FSH and LH. Estrogen stimulates the development of the female reproductive tract and secondary sex characteristics, and is partly responsible for the LH spike that causes ovulation. Estrogen, along with progesterone produced by the placenta during the second trimester of pregnancy, helps inhibit the onset of a new menstrual cycle by blocking GnRH release.

GnRH → LH & FSH → Estrogen

(Estrogen)high –ø (GnRH, LH, & FSH)

56
Q

Progesterone

A

Hormone synthesized and released by the ovaries, corpus luteum, and placenta. During the luteal phase of the menstrual cycle, the corpus luteum secretes progesterone, which, along with estrogen, stimulates the development and maintenance of teh endometrial walls for implantation of the embryo.

57
Q

What hormones are produced in the ovaries? in the testes?

A

Estrogen and progesterone are produced in the ovaries, while testosterone and otehr male sex hormones (androgens) are produced in the testes. They function according to the following cascades:

GnRH → LH → Testosterone

GnRH → LH → Progesterone

GnRH → LH & FSH → Estrogen

(Testosterone/Estrogen)high –ø (GnRH, LH, & FSH)

58
Q

What are the four phases of the menstrual cycle, and what happens both physiologically and hormonally in each?

A

The menstrual cycle consists of

  • follicular (preovulatory) phase - follicles mature (driven by rise FSH and LH)
  • ovulation - release of the ovum from the ovary into the abdominal cavity (driven by abrupt spike in FSH, LH, and GnRH)
  • luteal (postovulatory) phase - ruptured follicle becomes corpus luteum and secretes estrogen and progesterone to build up uterine lining in preparation for implantation (LH and FSH are inhibited and levels drop)
  • menstruation - if fertilization doesn’t occur, corpus luteum atrophies, progesterone and estrogen levels decrease, and menses occurs (LH and FSH begin to rise again).
59
Q

Menstrual cycle diagram

A
60
Q

Corpus Luteum

A

Tissue that forms from the collapsed ovarian follicle by LH stimulation after ovulation. Secretes progesterone, which maintains the uterine lining for implantation. Must be maintained by Human Chorionic Gonadotropin (hCG), a hormone secreted by the blastocyst upon implantation. Without hCG to stimulate the corpus luteum, progesterone levels fall and the uterine lining is sloughed off (menstruation).

61
Q

What hormone is released upon implantation of the ovum in order to maintain pregnancy?

A

Human Chroionic Gonadotropin (hGC, and LH analog) will be generated by the blastocyst and the developing placenta to maintain the corpus luteum, the tissue that forms from the collapsed ovarian follicle. The corpus luteum will continue to secrete progesterone and estrogen, keeping the uterine lining in place.

62
Q

Hormonally speaking, what occurs after menopause and what is the general result?

A

Under normal function the ovaries contribute to a negative feedback loop for FSH and LH through the generation of estrogen and progesterone. After menopause the ovaries become less sensitive to their stimulating hormones (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]), cease to produce estrogen and progesterone, and eventually atrophy. This leads to a dramatic drop in estrogen and progesterone leves, and an accompanying spike in FSH and LH. This prompts profound physical and physiological changes to occur.

63
Q

Leutenizing Hormone (LH)

A

Syntehsized and released by the anterior pituitary in response to gonadotropin-releasing hormone (GnRH), LH stimulates ovulation and formation of the corpus luteum. LH is regulated by estrogen, progesterone, and GnRH.

64
Q

Follicle Stimulating Hormone (FSH)

A

Synthesized and released by the anterior pituitary in response to gonadotropin-releasing hormone (GnRH), FSH stimulates maturation of ovarian follicles in females and maturation of the semineferous tubules and sperm production in males. FSH is regulated by estrogen and positively regulated by GnRH.

65
Q

Pineal Gland: location, hormones, and functions

A

Located deep within the brain, the pineal gland secretes the hormone melatonin. Although the actual function of the hormone is unclear, it is hypothesized that it functions in the regulation of circadian rythms.

66
Q

Hormones of the digestive tract: locations and functions

A
  • Secretin - secreted by small intestine, induces release of pancreatic juice from the pancreas
  • Cholecyctokinin (CCK) - secreted by small intestine, induces release of bile from the gall bladder and pancreatic juice from the pancreas
  • Gastrin - secreted by G cells of the pyloric glands in the stomach, induces stomach acidification (HCl) and mixing.
67
Q

Hormones of the heart, kidney and thymus: locations and functions

A
  • Erythropoietin - secreted by the kidney in response to low blood oxygen levels, stimulates bone marrow to generate more erythrocytes.
  • Atrial natriuretic peptide (ANP) - secrted by the heart, helps to regulate salt and water balance.
  • Thymosin - secreted by the thymus, is important in proper T-cell development and differentiation
68
Q

Peptide hormones (characteristics and mode of action)

A
  • Bind cell surface receptors (not membrane permeable)
  • Derived from peptides
  • Made in the rough ER
  • Packaged/processed and released by Golgi
  • Water soluble (move freely in blood)
  • Receptor may act, or binding may activate intracellular second messenger (i.e., cAMP, cGMP, calmodulin
69
Q

Steroid hormones (characteristics and mode of action)

A
  • Intracellular receptors
  • Derived from / similar to cholesterol
  • Made in smooth ER / mitochondria
  • Require protein transport to dissolve in blood
  • Diffuse through cell membrane (lipid soluble)
  • Hormone-receptor binding to DNA promotes transcription of specific genes
70
Q

Amino acid derivative hormones (characteristics and mode of action)

A
  • Derived from one or two amino acids via minor modification
  • Fromed by enzymes in the rough ER or cytosol
  • Mode of action depends on polarity
  • May work through secondary messenger systems like peptide hormones (e.g epinephrine)
  • May cross membrane and act on intracellular receptors ilke steroid hormones (e.g. thyroxine)

MCAT Biology (15 decks)

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