T24. INTRODUCTION TO ENDOCRINOLOGY

Question 1

What is the purpose of internal communication between cells?

Answer 1

It is necessary for the coordination of cell functions.

Question 2

What are the four principal mechanisms of communication between cells?

Answer 2

1. GAP junctions (electrical synapses) 2. Neurotransmitters (chemical synapses) 3. Paracrine and autocrine hormones 4. Endocrine (systemic) hormones

Question 3

What are endocrine hormones?

Answer 3

Chemical messengers that travel in the bloodstream to other tissues and organs.

Question 4

Compare the nature of nervous and endocrine communication.

Answer 4

Nervous: electrical and chemical; Endocrine: only chemical

Question 5

Compare the speed and persistence of response in nervous vs endocrine communication.

Answer 5

Nervous: reacts quickly (1–10 ms), stops quickly; Endocrine: reacts slowly (seconds or days), effect may last weeks

Question 6

Compare the adaptation to long-term stimuli in nervous vs endocrine systems.

Answer 6

Nervous: response declines quickly; Endocrine: response persists and adapts slowly

Question 7

Compare the targets affected by nervous vs endocrine communication.

Answer 7

Nervous: targeted and specific (one organ); Endocrine: general, widespread effects (many organs)

Question 8

What are endocrine glands?

Answer 8

Ductless glands that secrete hormones into the bloodstream.

Question 9

How do hormones interact with target cells?

Answer 9

Hormones are carried in the blood to cells with specific receptors that bind in a high specificity, high affinity, and low capacity manner, causing a change in the cell.

Question 10

What non-endocrine organs also secrete hormones?

Answer 10

Heart (ANP), liver (IGF), kidney.

Question 11

What are amine hormones derived from?

Answer 11

They are derived from tyrosine and tryptophan.

Question 12

Where are amine hormones synthesized?

Answer 12

Adrenal medulla (epinephrine), thyroid (T3 and T4), pineal gland (melatonin).

Question 13

What are steroid hormones derived from and where are they synthesized?

Answer 13

They are lipids derived from cholesterol, synthesized on demand in the adrenal cortex and gonads.

Question 14

List some steroid hormones.

Answer 14

Testosterone, estradiol, progesterone, cortisol, aldosterone.

Question 15

Are steroid hormones soluble in plasma?

Answer 15

No, they are insoluble in plasma and require carrier proteins.

Question 16

Are protein and glycoprotein hormones water-soluble?

Answer 16

Yes, they are soluble in water and plasma.

Question 17

List examples of protein/glycoprotein hormones.

Answer 17

ADH, insulin, renin, angiotensin, growth hormone, FSH, LH, and others.

Question 18

Describe step 1 of protein hormone synthesis.

Answer 18

mRNA on ribosomes binds amino acids into a preprohormone, directed to ER lumen by a signal sequence.

Question 19

Describe step 2 of protein hormone synthesis.

Answer 19

Enzymes in the ER remove the signal sequence, creating an inactive prohormone.

Question 20

Describe step 3 of protein hormone synthesis.

Answer 20

The prohormone passes from the ER to the Golgi Complex.

Question 21

Describe step 4 of protein hormone synthesis.

Answer 21

Secretory vesicles containing enzymes and prohormone bud off the Golgi; enzymes cleave it into active peptides and fragments.

Question 22

Describe step 5 of protein hormone synthesis.

Answer 22

Vesicle releases contents into extracellular space via exocytosis.

Question 23

Describe step 6 of protein hormone synthesis.

Answer 23

The hormone enters circulation for transport to target cells.

Question 24

How are steroid hormones synthesized?

Answer 24

They are synthesized on demand from cholesterol in the adrenal cortex and gonads.

Question 25

What determines hormone solubility in water?

Answer 25

Polarity: Polar chemicals are water-soluble; nonpolar are not.

Question 26

What are polar (hydrophilic) hormones?

Answer 26

Proteins that are soluble in water and plasma, do not need carriers, and bind to membrane receptors.

Question 27

Can polar hormones pass through membranes?

Answer 27

No, they cannot; they trigger second messenger cascades instead.

Question 28

How must polar hormones be administered as drugs?

Answer 28

They must be injected.

Question 29

What are nonpolar (lipophilic) hormones?

Answer 29

Steroids and thyroid hormones that are insoluble in water and need carrier proteins.

Question 30

Can lipophilic hormones enter cells directly?

Answer 30

Yes, they can diffuse through membranes and bind to intracellular receptors.

Question 31

How can nonpolar hormones be administered?

Answer 31

They can be taken orally as pills.

Question 32

What are prohormones?

Answer 32

Inactive hormones that are activated by cutting and splicing within target cells.

Question 33

What are prehormones?

Answer 33

Inactive hormones that require modification within target cells to become active.

Question 34

How do water-soluble hormones circulate?

Answer 34

Catecholamines and polypeptides circulate dissolved in plasma.

Question 35

How do fat-soluble hormones circulate?

Answer 35

Thyroid and steroid hormones circulate bound to plasma proteins (e.g., albumin, TBG).

Question 36

Which hormone form is biologically active?

Answer 36

Only the free (unbound) hormone is active.

Question 37

Where are hormones mainly eliminated?

Answer 37

In the liver and kidneys via enzymatic degradation and conjugation.

Question 38

What are the types of intracellular hormone receptors?

Answer 38

Cytoplasmic and nuclear receptors for lipophilic hormones.

Question 39

How do lipophilic hormones reach intracellular receptors?

Answer 39

They dissociate from carriers, diffuse across the membrane, and bind to receptors.

Question 40

What do hormone/receptor complexes do in cells?

Answer 40

They activate gene transcription as transcription factors, creating new proteins/enzymes.

Question 41

Where do hydrophilic hormones bind?

Answer 41

To extracellular (cell surface) receptors.

Question 42

Why can't hydrophilic hormones cross membranes?

Answer 42

Because they are water-soluble and cannot diffuse through the lipid bilayer.

Question 43

What mechanisms do extracellular receptors activate?

Answer 43

Second messenger systems: adenylate cyclase, phospholipase C, tyrosine kinase, calcium.

Question 44

Describe the adenylate cyclase/cAMP pathway.

Answer 44

Epinephrine binds β-receptor → G-protein activates adenylate cyclase → cAMP made → activates protein kinases → proteins phosphorylated → cAMP inactivated by phosphodiesterases.

Question 45

Describe the phospholipase C system.

Answer 45

Epinephrine binds α-receptor → G-protein activates phospholipase C → DAG + IP3 → Ca²⁺ release → calmodulin activation → kinase activation.

Question 46

Describe the tyrosine kinase system.

Answer 46

Receptor autophosphorylates → activates (e.g. by insulin) → phosphorylates substrates → alters enzymatic activity.

Question 47

What determines hormone effects on target cells?

Answer 47

Affinity, receptor number, competition, saturation.

Question 48

What is hormone affinity?

Answer 48

Higher affinity means less hormone is needed to produce a response.

Question 49

How does receptor number affect hormone sensitivity?

Answer 49

More receptors = higher sensitivity to hormone.

Question 50

What is hormonal competition?

Answer 50

Other molecules can bind receptors, reducing hormone effect.

Question 51

What is receptor saturation?

Answer 51

Point at which all receptors are occupied by hormone.

Question 52

What is hormone half-life?

Answer 52

Time it takes for hormone concentration to reduce by half in blood.

Question 53

How does hormone concentration affect response?

Answer 53

Tissues respond only when hormone is at normal physiological levels.

Question 54

What can happen at high hormone concentrations?

Answer 54

Effects may differ; cross-reactivity with related hormone receptors can cause side effects.

Question 55

What is meant by hormone interaction?

Answer 55

Target cells can respond to multiple hormones that may act synergistically, permissively, or antagonistically.

Question 56

What are synergistic hormone effects?

Answer 56

Two or more hormones produce a greater combined effect than individual actions.

Question 57

What are additive hormone effects?

Answer 57

E.g., epinephrine and norepinephrine both increase heart activity in the same way.

Question 58

What are complementary hormone effects?

Answer 58

Each hormone contributes a different role to achieve one function (e.g., milk production).

Question 59

What are permissive hormone effects?

Answer 59

One hormone increases the response of a cell to another hormone (e.g., estrogen → progesterone response).

Question 60

What are antagonistic hormone effects?

Answer 60

Two hormones work in opposition (e.g., insulin promotes fat storage, glucagon promotes fat breakdown).

Question 61

How is hormone secretion regulated neurally?

Answer 61

Neurons affect endocrine cells: autonomic innervation (e.g., pancreas), adrenal medulla, hypothalamic neurosecretory cells.

Question 62

What are the general functions of hormones in reproduction?

Answer 62

Regulate gametogenesis, sexual differentiation, and sexual behavior.

Question 63

What is the role of hormones in growth and development?

Answer 63

Multiple hormones (peptide, steroid, thyroid) interact to regulate growth and development processes.

Question 64

How do hormones affect energy production and storage?

Answer 64

They mediate conversion of digestion products into stored energy or usable energy.

Question 65

What is the role of hormones in homeostasis?

Answer 65

Regulate body fluids, electrolytes, blood pressure, heart rate, acid-base balance, temperature, and body mass.

Question 66

What type of feedback regulates most hormones?

Answer 66

Negative feedback.