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MCAT Biology > Endocrine System 1 > Flashcards

Endocrine System 1 Flashcards

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1
Q

What is the function of the endocrine system?

A

Allows communication within the organism, regulation in response to stimuli in internal and external environment

Acts more slowly but exerts effects that are more general and sustained

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2
Q

What are hormones secreted by the nervous system called and what are hormones secreted by the endocrine system called?

A

Nervous System: local hormones
- secreted by neurons and cause action potentials

Endocrine System: general hormones
- released into body fluids (blood), affect many cell types

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3
Q

Exocrine Glands

A

Release enzymes to external environment through ducts

E.g. sudoriferous (sweat), sebaceous (oil), mucous, and digestive glands

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4
Q

Endocrine Glands

A

Release hormones directly into the bloodstream

E.g. pancreas is both exocrine and endocrine gland: release enzymes through pancreatic duct and releasing insulin and glucagon directly into the blood

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5
Q

How are hormones detected by the cells?

A

Hormones act by binding to protein receptors specific to a particular hormone type
- Some hormone receptors are on virtually all cells while some are on specific tissues only

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6
Q

What are the effects of the endocrine system

A

To alter metabolic activities, regulate growth and development, and guide reproduction

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7
Q

How can the endocrine system be tightly regulated by specific neural control?

A

Endocrine glands are sometimes stimulated by neurons to secrete hormones
- nervous system can tightly control the stimulation of the glands which then release hormones to act via generalized communication with multiple parts of the body

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8
Q

What evolutionary advantage would there be in the brain not having precise control over all aspects of physiology, such as the endocrine system?

A

In an example with metabolism, action potentials are metabolically expensive, and the endocrine system is used to coordinate uptake of consumed nutrients after a meal with coordination of the liver, musculature, and adipose tissues
- Would be expensive for nervous system to stimulate all of these systems simultaneously over time

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9
Q

What are the three basic chemistry types of hormones?

A

Peptide Hormones
Steroid Hormones
Tyrosine Derivatives

Each differ in solubility which affects physical characteristics, mechanisms of action, and ultimate effects on targets

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10
Q

Peptide Hormones

A

Derived from peptides and are water soluble

  • Move freely through blood but cannot travel through cell membrane
  • Attach to membrane-bound receptor
  • Large or small
  • Often include a carbohydrate
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11
Q

How does the membrane-bound receptor that responds to a peptide hormone act?

A

Receptor can activate an enzyme, or activate a second messenger system (cAMP, cGMP, calmodulin)

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12
Q

Where are all peptide hormones manufactured?

A

Manufactured in Rough ER as preprohormones (larger than active hormone)

  • Preprohormone cleaved in ER lumen -> prohormone
  • Prohormone transported to Golgi apparatus where cleaved and a carbohydrate may be added -> final hormone form
  • Golgi packages hormone into secretory vesicles and cell will release vesicle via exocytosis when ready
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13
Q

Peptide Hormones you should know for MCAT

A

Anterior pituitary hormones: FSH, LH, ACTH, HGH, TSH, and prolactin
Posterior pituitary hormones: ADH, oxytocin
Parathyroid hormone PTH
Pancreatic hormones: glucagon, insulin
Thyroid C cell hormone calcitonin

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14
Q

Effector

A

Target cell of the hormone

Receptor on effector is sometimes referred to as cognate receptor

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15
Q

In general, where do polar hormones bind and where do nonpolar steroid hormones bind?

A

Polar hormones tend to bind extracellular receptors

Nonpolar hormones typically bind cytoplasmic or nuclear receptors

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16
Q

Steroid Hormones

A

Derived from and are chemically similar to cholesterol

  • Nonpolar, hydrophobic because they are lipids
  • Usually require a protein transport molecule (carrier protein) to dissolve in bloodstream
  • Diffuse through cell membrane of effector
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17
Q

Where are steroid hormones produced?

A

Formed in a series of steps that take place mainly in smooth ER and mitochondria (they are lipids)

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18
Q

cAMP

A

Cyclic adenosine monophosphate

Same as ADP, with only one phosphate which attaches to ribose sugar in two places to make ring

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19
Q

How do steroid cells act on effector cells?

A

Diffuse through cell membrane (nonpolar), combine with a receptor in cytosol or nucleus

  • Act at level of transcription
  • Usually increase certain membrane or cellular proteins within effector
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20
Q

Important Steroid Hormones for MCAT

A

Glucocorticoids and Mineral corticoids of adrenal cortex: cortisol, aldosterone
Gonadal hormones: Estrogen, Progesterone, Testosterone

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21
Q

Important Tyrosine Derivative Hormones for MCAT

A

Thyroid Hormones: T_3 (triiodothyronine), T_4 (thryoxine)

Catecholamines formed in adrenal medulla: epinephrine, norepinephrine

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22
Q

How are tyrosine derivative hormones formed?

A

Formed by enzymes in the cytosol or on the rough ER

- Not all water or lipid soluble, a mix

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23
Q

Thyroid Hormones

A

Lipid-soluble, so carried by plasma protein carriers
Slowly released to target tissues and bind to receptors inside nucleus
Have latent period of response and prolonged effect due to strong binding to protein receptors in plasma and nucleus

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24
Q

How do Thyroid hormones carry out their effect?

A

Increase transcription of large numbers of genes in nearly all cells of body

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25
Q

Catecholamine Tyrosine Derivative Hormones

A

Epinephrine and Norepinephrine

  • Water soluble, dissolve in blood
  • Bind to receptors on effector
  • Act mainly through second messenger cAMP
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26
Q

How does negative feedback relate to endocrine hormones?

A

Some aspect of hormones effect on target tissue will inhibit secretion of hormone
This means that the endocrine gland will over-secrete hormone until negative feedback turns off secretion
Body works to maintain constant level of metabolites using hormones

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27
Q

What should you assume if the blood sugar in the body is high?

A

That levels of insulin are also high, because pancreas released insulin in response to high blood sugar to lower and return body to homeostasis

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28
Q

How do hormones function in the HPA axis?

A

Corticotrophin releasing hormone (CRH) is secreted from hypothalamus
CRH secretion causes secretion of adrenocorticotropic hormone (ACTH) from anterior pituitary
ACTH secretion causes secretion of cortisol from adrenal cortex
Cortisol has negative feedback to inhibit release of CRH and release of ACTH

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29
Q

Which endocrine hormones are more fast and fleeting?

A

Polar hydrophilic hormones

  • readily soluble in water, do not need a carrier protein to travel
  • Can be cleared quickly from blood (shortish half life)
  • Concentration can be adjusted on minute-to-minute basis
  • Activating enzyme or opening channel is a fast process
30
Q

Which endocrine hormones are slower and more sustained?

A

Hydrophobic hormones

  • Slower to arrive at targets, not readily soluble in water
  • Carrier proteins in blood transport and protect from breakdown (hormone inactive in this form)
  • Can dissolve in fatty tissues of body and hide indefinitely from breakdown (long half-life)
  • Adjust concentration on hour to hour basis
  • Transcription of target genes is slower response
31
Q

Do glands secrete a mix of hydrophobic and hydrophilic hormones?

A

Almost all glands only secrete either hydrophilic or hydrophobic hormones
Glands can be organized along a spectrum according to polarity (and solubility) of hormones that they secrete

32
Q

Tropic Hormones

A

AKA Regulatory hormones
All peptide hormones
Targets are glands that secrete hydrophobic hormones
Every hydrophobic hormone has a correlating hydrophilic control hormone

33
Q

Why are hydrophilic hormones more suited for regulatory function?

A

Effects of a hydrophilic hormone are faster and more fleeting than those of hydrophobic hormones

34
Q

Tyrosine

A

Amino acid tyrosine is precursor to both polar and nonpolar hormones
Hydroxyl functional group allows formation of ether linkages -> nonpolar hormones like T3
Addition of second hydroxyl group to benzene ring allows for formation of polar hormones such as epinephrine

35
Q

Name all the glands that secrete peptide hormones

A

Anterior/Posterior Pituitary
Pancreas
Parathyroid & Thyroid C cells
Placenta & Blastocyst

36
Q

How do the hypothalamus and the pituitary glands link the nervous and endocrine systems?

A

Fine nervous control over hypothalamus causes hormone secretion from pituitary gland

  • Pituitary gland has regulatory affect on other endocrine glands
  • Nervous system therefore has widespread impact on functioning of endocrine system
37
Q

Posterior Pituitary Gland

A

Continuation of nervous system; bundle of axons whose cell bodies are in hypothalamus, AKA neurohypophysis
Stores peptide hormones that are synthesized in hypothalamus
Releases anti-diuretic hormone (ADH) or vasopressin- regulates plasma volume, stimulates receptors on kidney collecting ducts to facilitate reabsorption of water, increases blood pressure
Also releases oxytocin- stimulates labor and milk ejection for nursing, effectors in uterus and milk ducts of breasts, periodic contraction of smooth muscle

38
Q

What benefit does close nervous system control have over the release of ADH and Oxytocin from the Posterior Pituitary?

A

ADH: Allows changes in ADH level to occur rapidly in response to body’s needs
Oxytocin: Can be quickly released by posterior pituitary in response to suckling or other stimuli that indicate infant’s need for milk

39
Q

Anterior Pituitary Gland

A

AKA adenohypophysis
Higher regulatory gland of endocrine system which effects other glands
Subject to nervous control
Group of endocrine cells
Hypothalamus communicates with AP by releasing hormones into shared blood vessels (portal system)
- signaling faster and more direct

40
Q

What hormones does the Anterior Pituitary release?

A

Hormones that regulate secretion of steroid hormones
6 major, several minor, all peptide hormones
Thyroid-stimulating hormone (TSH), Adrenocorticotropin (ACTH), Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), Human growth hormone (HGH), Prolactin

41
Q

Parathyroid Glands

A

Release parathyroid hormone (PTH) in response to low calcium in bloodstream
Receptors located on osteoblasts, but intercellular signaling causes osteoclasts to breakdown bone and release calcium

42
Q

Thyroid Gland

A

Responsible for basal metabolic rate and for calcium regulation
Secretes thyroid hormones T3 and T4 from follicular cells to stimulate higher basal metabolic rate
- receptors on almost all cells in body (widespread effect)
Secretes calcitonin from C cells to inhibit osteoclasts in response to high blood calcium levels

43
Q

How do parathyroid glands and thyroid glands act in opposition?

A

Physically adjacent glands that have complementary roles in blood calcium regulation
Parathyroid secretes parathyroid hormone (PTH) which stimulates increase in blood calcium
Thyroid secretes calcitonin which stimulates decrease in blood calcium
Both act through effect on osteoclasts, and both hormones secreted are polar

44
Q

What hormones does the pancreas secrete?

A

Insulin and glucagon, which act antagonistically to regulate cellular metabolism and control blood glucose levels
Insulin: released when blood glucose high, causes glucose to be converted to glycogen and store for later
Glucagon: released when blood glucose low, causes glycogen breakdown from liver and stimulates processes like beta oxidation or usage of ketone bodies for nutrients

45
Q

Adrenal Medulla

A

Gland contained in adrenal gland
Involved in stress response
Secretes polar tyrosine-derived hormones epinephrine and norepinephrine (adrenaline and noradrenaline, catecholamines or amine derivatives which are also used by sympathetic nervous system to facilitate fight-or-flight)
- Into bloodstream as response to SNS input for more sustained and general signaling

46
Q

Adrenal Cortex

A

Secretes steroid hormones
Involved in blood pressure regulation and production of body’s stress response
Secretes glucocorticoids (cortisol) and mineralocorticoids (aldosterone)
Cortisol produces long term stress response (chronic stress)
Aldosterone affects blood pressure by increasing reabsorption of mineral Na+ which causes increased water reabsorption and plasma volume

47
Q

What hormones do the testes and ovaries secrete?

A

Release hormones that stimulate reproductive development and functions
- Secrete hormones in response to regulation by anterior pituitary
- Ovaries secrete estrogen and progesterone to control pubertal development, menstruation, and pregnancy
HCG affects hormones, and then placenta becomes endocrine gland
- Testes secret testosterone to facilitate male puberty and spermatogenesis

48
Q

Placenta

A

Secretes a peptide hormone that regulates secretion of steroid hormones
- causes uterus to prepare to support pregnancy
Blastocyst secretes human chorionic gonadotrophin after implantation (HCG)
Placenta secretes HCG secretion as develops
Effects ovaries which signal to continue to secrete estrogen and progesterone to maintain uterus

49
Q

What are the only glands that secrete polar and nonpolar hormones?

A

Placenta (polar peptide hormone HCG, and then nonpolar steroid as develops)
Thyroid Gland
Adrenal Gland (actually two glands)

50
Q

What do the regulation of blood calcium levels and blood glucose levels have in common?

A

Both have antagonistic set of peptide hormones which act quickly and are secreted by either the same organ or organs in close proximity
Blood glucose: glucagon and insulin
Blood calcium: calcitonin and PTH

51
Q

How does the hypothalamus control the secretion of hormones from the anterior pituitary?

A

Secretes releasing and inhibitory hormones into common duct which carries hormones to capillary bed of anterior pituitary

52
Q

Thyroid-stimulating hormone (TSH)

A

AKA thyrotropin
Peptide that stimulates the thyroid to release T3 and T4
- T3 and T4 released via secondary messenger cAMP
- Increases thyroid cell size, number, and rate of T3 and T4 secretion
High T3 and T4 have negative feedback on TSH at anterior pituitary and hypothalamus

53
Q

Adrenocorticotropioc hormone (ACTH)

A

Peptide hormone that stimulates the adrenal cortex to release glucocorticoids using cAMP

  • Stimulated by many types of stress
  • Glucocorticoids are stress hormones
54
Q

Human growth hormone (HGH)

A

AKA somatotropin
Peptide hormone that stimulates growth in almost all cells of body
Increases rate of mitosis, cell size, protein synthesis, use of fatty acids for energy, rate of transcription and translation, and decreases use of glucose and breakdown of proteins and AAs as well as mobilizing fat stores

55
Q

Prolactin

A

Peptide hormone that promotes lactation (milk production) by breasts
Before birth, milk not normally produced due to estrogen and progesterone inhibition

Anterior pituitary mainly inhibits release of prolactin
Suckling by infant stimulates hypothalamaus, which stimulates AP to release prolactin inhibits menstrual cycle, although actual evidence uncertain

56
Q

Parathyroid Hormone (PTH)

A

Peptide hormone that increases blood calcium
Increases osteocyte absorption of calcium, stimulates proliferation of osteoclasts to break down calcified bone for increase of calcium in blood
Increases renal calcium absorption and renal phosphate excretion
Calcium and phosphate react to form insoluble calcium phosphate, leaving less free calcium in the blood
increases renal production of steroid derived from vitamin D -> increases calcium uptake from gut

57
Q

Triiodothyronine and Thyroxine

A

T3 and T4
Both Tyrosine derived hormones released by thyroid gland
Work to increase basal metabolic rate (amount of energy expended when body is at rest for a day)
Lipid soluble hormones that diffuse through the bilayer and act in the nuclei of the effectors
Secretion regulated by thyroid stimulating hormone (TSH) released by anterior pituitaryt

58
Q

Basal Metabolic Rate

A

AKA resting metabolic rate
Amount of energy expended at rest in one day
Measured as rate of oxygen consumption
Determinants of basal metabolic rate include heart rate and muscle mass

59
Q

Calcitonin

A

Large peptide hormone released by thyroid gland
Works to lower levels of blood calcium
Decreases osteoclast activity and number
Humans can survive and regulate calcium without calcitonin
Calcitonin “tones down calcium”

60
Q

Adrenal Glands

A

Endocrine glands located on top of kidneys
Adrenal cortex is outside portion of gland and secretes only steroid hormones (glucocorticoids and mineralcorticoids, but small amount of sex hormones in females)
Adrenal medulla is inside portion of gland

61
Q

Mineralcorticoids

A

Steroid hormone that affects the electrolyte balance in the bloodstream
Aldosterone: increases uptake of Na+ in kidneys so more water is retained

62
Q

Glucocorticoids

A

Steroid hormones that increase blood glucose concentration and have even greater effect on fat and protein metabolism
Major glucocorticoid is cortisol (released in stress response)

63
Q

Aldosterone

A

Steroid, mineralocorticoid acts on distal convoluted tubule and collecting duct to increase Na+ and Cl- reabsorption and K+ and H+ secretion
Increases water absorbed through aquaporins in distal convoluted tubule, but no change in salt level in blood
Eventually increases blood pressure
Smaller effect on salivary glands, sweat glands, and intestines

64
Q

Cortisol

A

Steroid glucocorticoid that increases blood glucose levels by stimulating gluconeogenesis in liver
Mobilizes fatty acids from fat cells for energy
Moderate decrease in use of glucose by all cells
Stimulates protein degradation in nonhepatic cells (increase in AA conc in liver)
AA serve as C source for gluconeogenesis
High levels of cortisol diminish immune system ability to fight infection

65
Q

Epinephrine and Norepinephrine

A

Catecholamine hormones that are tyrosine derivatives synthesized in adrenal medulla
Similar effects as in sympathetic nervous system, but much longer lasting
Constrict blood vessels of most internal organs and skin, dilate blood vessels of skeletal muscle
Increases blood flow and oxygen to muscles

66
Q

Somatostatin

A

Endocrine hormone released by delta cells of pancreas
Inhibits both insulin and glucagon
May be to extend the period of time over which nutrients are absorbed

67
Q

Insulin

A

Peptide hormone released by the beta cells of the pancreas when blood levels of carbohydrates or proteins are high
Insulin increases glycogenesis in liver and muscles
Insulin increases fat storage in adipose tissue, fatty acid synthesis
Amino acids are used to create protein in the cells of the body
Ends up lowering blood glucose levels

68
Q

What happens when insulin binds to its effector?

A

Insulin binds to membrane receptor and activates the opening of a membrane bound glucose transporter
Increases permeability of the membrane to amino acids
Activates intracellular metabolic enzymes
Affects transcription and translation

69
Q

Glucagon

A

Peptide hormone released by the alpha cells in the pancreas
Acts via second messenger system of cAMP
Stimulates glycogenolysis (breakdown of glycogen)
Stimulates gluconeogenesis in the liver
Breaks down adipose tissue
Net effect is to raise blood glucose levels

70
Q

Type I diabetes

A

Autoimmune diabetes in which the body attacks the beta cells of the pancreas
Pancreas becomes unable to secrete insulin and cannot regulate blood glucose levels
Can be fatal- confusion, seizures, coma, death

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