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4) Metabolic Endocrinology > 1) Introduction to Endocrinology > Flashcards

1) Introduction to Endocrinology Flashcards

1
Q

What is the classical definition of a hormone?

A

Chemical messenger released by one type of cell and carried in the bloodstream to act on specific target cells

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2
Q

What does the modern definition of a hormone include?

A

Factors produced and used locally without entering the bloodstream

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3
Q

What is endocrinology about?

A

Communication between cells in multicellular organisms

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4
Q

What is communication between cells required for?

A
  • Development
  • Homeostasis
  • Reproduction
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5
Q

How is the stability of a multicellular organism achieved?

A

By a complex communication network (gene interaction)

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6
Q

How many cells is composed within each adult?

A

10^14 cells

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7
Q

How many protein-encoding genes do we possess?

A

21 000

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8
Q

What are the three layers of signalling networks?

A
  • Within cells
  • Between groups of cells (tissues)
  • Between tissues
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9
Q

How do networks contribute to homeostasis?

A

Networks buffer against change

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10
Q

Why may dramatic changes, such as knocking-out a gene, not influence the output of the network?

A
  • Because we have mechanisms that allow us to bypass this change by tuning our networks
  • We have plasticity within our system
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11
Q

How many types of cells do we have?

A

200 to 250 types of cells

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12
Q

What accounts for the relative recent evolution of multicellular organisms?

A

The complexity of communication networks

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13
Q

When did life evolve? When did multicellular organisms evolve?

A
  • Life: 3.8 billion years ago

- Multicellular organisms: 600 million years ago

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14
Q

Where are signals generated?

A

Special hormone-producing cells

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15
Q

What are recipient cells?

A

Cells that recognize signals and respond to them

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16
Q

How do various signals affect the response of a recipient cell?

A

The various signals are exposed at the same time, and are integrated by the recipient cell, which modulates the response

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17
Q

What is the function of the nervous system?

A
  • Direct connection between concerned organs

- Rapid signals through nervous transmission

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18
Q

What is the function of the endocrine system?

A
  • Sending chemical messages (hormones) into circulation

- Slow signalling response

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19
Q

What are the main control systems of the body? What are they responsible for?

A
  • Nervous and endocrine system

- Responsible for monitoring internal and external environments and making adaptive changes (homeostasis)

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20
Q

What do endocrine cells secrete? What do they act on?

A
  • Secrete hormones into blood vessels

- Target cells may be distant

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21
Q

What do paracrine cells secrete? What do they act on?

A
  • Secrete hormones

- Act locally on neighboring cells

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22
Q

What do autocrine cells secrete? What do they act on?

A
  • Secrete hormones

- Act on themselves or on identical neighboring cells

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23
Q

What do neuroendocrine cells secrete? Where is it secreted from?

A
  • Secrete molecules

- From the axon terminals into the bloodstream

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24
Q

What do neurotransmitter cells secrete? What do they act on?

A
  • Secrete neurocrine molecules

- From axon terminals to activate adjacent neurons

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25
Q

What do neurocrine cells secrete? What do they act upon?

A
  • Secrete molecules

- From axon terminals to stimulate another neuron

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26
Q

What are the two general characteristics of hormones?

A
  • Very low in concentration

- Very specific receptor

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27
Q

What units of concentration are generally used to measure hormone concentration?

A

ng/mL or pg/mL

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28
Q

What occurs if hormones levels are too high?

A
  • The hormones activate other receptor types within that cell (inappropriate response)
  • Ex: steroids for muscle building increase mammary tissue as well
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29
Q

What is the response cascade of a cell to a signal?

A
  • Extracellular signal molecule binds to receptor protein
  • Intracellular signalling protein cascade
  • Signalling cascade acts on target proteins
  • Cellular response
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30
Q

Which proteins may be targeted in response to a signal? What may that alter?

A
  • Metabolic enzyme (altered metabolism)
  • Gene regulatory protein (altered gene expression)
  • Cytoskeletal protein (altered cell shape or movement)
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31
Q

What does the fate of a cell depend on?

A
  • A multitude of extracellular signals
  • Hormones never act in isolation
  • The cell is always bouncing around a set-point to regulate a specific function within a normal range for the cell
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32
Q

What occurs to most cells if signals are absent?

A

Programmed cell death (apoptosis)

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33
Q

How may cells that synthesize hormones be organized within the body? (2)

A
  • Clustered in endocrine glands (ex: thyroid gland)

- Interspersed as single cells in organs (ex: C-cells in the thyroid gland)

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34
Q

What are the three chemical types of hormones? What are the subtypes?

A
  • Lipids (steroids and eicosanoids)
  • Proteins (short polypeptides and large proteins)
  • Amino acid derivatives
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35
Q

Steroids are a derivative of what compound?

A

Cholesterol

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36
Q

Where are steroid hormones found? Give examples.

A
  • Gonads (estrogen, progesterone, testosterone)

- Adrenal cortex (cortisol, aldosterone)

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37
Q

Which steroid hormones are chemically very similar? How do they differ?

A
  • Testosterone and estrogen

- Their 3D structure is different, allowing for receptors to differentiate them

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38
Q

How is testosterone converted to estrogen?

A

Aromatase

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39
Q

What do mineralocorticoids affect?

A

Mineral homeostasis

40
Q

What do glucocorticoids affect?

A
  • Glucose metabolism

- Immune function

41
Q

What are eicosanoids?

A

Metabolites of arachidonic acid (20-carbon fatty acid)

42
Q

What functions are prostaglandins involved in?

A
  • Inflammation

- Reproduction

43
Q

Give three examples of prostaglandins.

A
  • Thromboxanes
  • Leukotrienes
  • Prostacyclins
44
Q

________ and related compounds are collectively known as eicosanoids.

A

Prostaglandins

45
Q

What is arachidonic acid?

A

20-carbon polyunsaturated fatty acid

46
Q

What are the two major pathways of eicosanoid metabolism?

A
  • Linear pathway

- Cyclic pathway

47
Q

What does the linear pathway of eicosanoid metabolism produce? What enzyme is required?

A
  • Leukotrienes are produced from arachidonic acid

- Requires lipoxygenase

48
Q

What does the circular pathway of eicosanoid metabolism produce? What enzyme is required?

A
  • Prostaglandin H2 is produced from arachidonic acid

- Prostaglandins H2 synthase (PGH2 synthase)

49
Q

What catalyzes the committed step in the cyclic pathway of eicosanoid metabolism?

A

PGH2 synthase

50
Q

What does prostaglandin H2 lead to? What enzymes are required?

A
  • Prostacyclins (prostacyclin synthase)

- Thromboxanes (thromboxane synthase)

51
Q

How does eicosanoid metabolism differ between different cell types?

A

Different cell types convert PGH2 to different compounds

52
Q

Do eicosanoids have a short or long half-life? How do they mainly function?

A
  • Short half-life

- They are rapidly degraded, so they are not transported to distant sites within the body

53
Q

Give examples of short-chain protein hormones.

A
  • GnRH
  • Oxytocin
  • Thyroid-releasing hormone (TRH)
54
Q

Which two protein hormones are extremely similar in terms of their amino acid sequence, but possess profoundly different physiological effects?

A
  • Arginine vasopressin (vasoconstriction and water retention)
  • Oxytocin (milk ejection and labour)
55
Q

How are subunits of large polypeptide protein hormones linked?

A

Disulfide bridge(s)

56
Q

Give examples of large polypeptide protein hormones.

A
  • Insulin

- Growth hormone

57
Q

What are the hormones that are derived from tyrosine? What endocrine organ are they derived from?

A
  • Thyroid: thyroid hormones

- Adrenal medulla: epinephrine, norepinephrine, dopamine

58
Q

Which hormones are often used as neurotransmitters in the CNS? What type of hormone are they?

A
  • Epinephrine, norepinephrine, dopamine

- Amino acid metabolites of tyrosine

59
Q

What are the three characteristics of endocrine glands?

A
  • Parenchyma (mass of secretory cells)
  • Blood vessels (highly vascularized)
  • No ducts
60
Q

What are examples of permanent and transient endocrine structures?

A
  • Permanent: pituitary, adrenal, pancreas

- Transient: ovarian follicle, corpus luteum

61
Q

How many hormones may a specialized secretory cell produce?

A
  • Usually, one type of cell produces one hormone

- A gland may be separated into lobes of cells; each lobe secreting a different hormone

62
Q

Which endocrine glands possess neurons that may be specifically used to produce hormones?

A
  • Hypothalamus
  • Posterior pituitary
  • Adrenal medulla
63
Q

Where does posttranslational modification occur in the cell?

A

In the cytosol following translation of mRNA into protein

64
Q

What are examples of posttranslational modifications?

A
  • Disulfide bond formation from two separate sequences (GH, PTH), or a single sequence (insulin)
  • Processing of polyproteins into smaller subunits (glucagon and calcitonin precursors)
  • Assemble multiple subunits together and glycosylate (hCG)
65
Q

What does the lipophilic leader sequence (signal peptide) enable the nascent peptide to do? What occurs afterwards?

A
  • To cross the endoplasmic reticulum into the cisternal space
  • The leader sequence is cleaved by a peptidase
66
Q

What posttranslational modifications occur in the Golgi?

A
  • Glycosylation
  • Proteolytic cleavage
  • Packaging into vesicles
67
Q

Where are peptide hormones stored?

A

In secretory vesicles (granules) in the cytoplasm

68
Q

What allows for the movement of secretory vesicles containing peptide hormones to the cell membrane?

A

Microtubules (cytoskeleton) and microfilaments

69
Q

What is required for the activation and release of a stored peptide hormone? What may the stimulus be? What does it normally involve?

A
  • A stimulus is required (stimulus-secretion coupling)
  • May be hormonal
  • Usually involves changes in calcium permeability of the cell membrane (opening of Ca2+ channels)
70
Q

What is the benefit of peptide hormones?

A

They may be pre-synthesized and stored in the cytoplasm as granules

71
Q

Where are steroid hormones stored?

A

They are NOT stored, but must be synthesized de novo since they are lipophilic

72
Q

What is the downside of steroid hormones?

A

They must be synthesized de novo, which requires more time for release

73
Q

In which organelle does the cleavage of the side chain of cholesterol occur? What does cholesterol become?

A
  • Mitochondria

- Becomes pregnenolone, which becomes progesterone

74
Q

Where are enzymes for steroid hormone synthesis located within the cell?

A

Mitochondria and smooth ER

75
Q

How does steroid hormone synthesis occur?

A
  • Cholesterol from cytosolic stores move into the mitochondria for conversion to pregnenolone
  • Transport into the smooth ER
  • Transformation into the appropriate hormone
  • Diffusion from the cell
76
Q

How do hydrophilic hormones circulate in blood?

A

In a free state

77
Q

How do hydrophobic hormones circulate in blood?

A

Require carrier proteins that are specific for the particular hormone

78
Q

What is the major function of binding proteins to hydrophobic hormones?

A

Binding proteins act as a buffer to protect the hormone from degradation in the liver

79
Q

What do binding proteins binding to hydrophobic hormones inhibit?

A

Only the free hormone is biologically active, so it must dissociate from the binding protein to bind to the receptor

80
Q

How does the half-life of peptide hormones differ from large protein hormones?

A
  • Peptide hormones have a very short half-life, as they are degraded by proteolytic enzymes
  • Large protein hormones are glycosylated, which extends their half-life
81
Q

What are the three levels of control of synthesis and secretion of hormones?

A
  • Neural input (brain, hypothalamus)
  • Hormonal stimulation/inhibition (inhibitory factors, feedback system)
  • Metabolic status (stress, blood concentrations of substances)
82
Q

What is the effect of a lack of GH in children? What about in adults?

A
  • Children: dwarfism

- Adults: atrophy of muscle tissue

83
Q

What is the effect of a lack of cortisol and aldosterone from the adrenal gland?

A
  • Addison disease
  • Increases ACTH secretion by the pituitary
  • Melanocyte-stimulating hormone secretion is also increased, which leads to excessive freckling
84
Q

What is the most common endocrine disorder? What are the two possible causes?

A
  • Diabetes mellitus
  • Lack of secretion of insulin from B-cells of the pancreas
  • Insulin receptor defect
85
Q

What are endogenous mechanisms?

A

Signals from the brain that are independent of external cues

86
Q

Give an example of a mechanism entrained by external cues?

A

Light-dark cycle

87
Q

What is the circadian rhythm? What is the infradian rhythm?

A
  • Circadian: 24h cycle

- Infradian: 28-day menstrual cycle

88
Q

When is cortisol secretion maximal?

A

Between 4 and 8 AM

89
Q

When is GH and PRL secretion maximal?

A

1 hour after going to sleep

90
Q

When may rhythms change?

A

During development

91
Q

How does gonadotrophin change during development (puberty and adulthood)?

A
  • Puberty: released mainly at night

- Adulthood: released in a pulsatile fashion

92
Q

What must be taken into account when measuring hormone levels?

A

Endocrine rhythms

93
Q

What are common techniques used in endocrinology?

A
  • Ablation and replacement
  • Bioassays
  • Immunoassays
  • Immunocytochemistry
  • Blot tests
  • Pharmacological techniques
  • Genetic techniques
94
Q

What are induced ovulators? What animal is an induced ovulator?

A
  • Females must mate in order to ovulate

- Rabbits

95
Q

What was the rabbit test?

A
  • If fertilization occurs, hCG is produced by the placenta 8 days afterwards
  • Urine from a pregnant woman is taken and injected into a rabbit, stimulating the ovary to cause ovulation
  • The rabbit is killed, and the ovaries are examined to determined if the woman is pregnant or not (+ corpus luteum)

4) Metabolic Endocrinology (15 decks)

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