Basics of Endocrinology II

Question 1

What are amine hormones derived from and what is their half life?

Answer 1

a single amino acid, 2-3 minutes

Question 2

What are catecholamines derived from

Answer 2

A single tyrosine

Question 3

What are indolamines derived from?

Answer 3

A single tryptophan

Question 4

What is T4/T3 derived from and what are their half lives?

Answer 4

Two tyrosines - the exception to amines

Half life T4 = 8 days, T3 = 24 hours

Question 5

What chemical classification are most hormones?

Answer 5

peptides/proteins

Question 6

What is the half life of peptide/protein hormones?

Answer 6

4-170 minutes

Question 7

What is the half life of steroid hormones?

Answer 7

minutes to several hours - generally the longest half life of the hormones (exception, thyroid hormones)

Question 8

What are the three chemical classifications of hormones?

Answer 8

amines, peptide/proteins, steroid

Question 9

What are the common features of catecholamines and indolamines?

Answer 9

short half life - act quickly and are degraded quickly

travel freely in the blood

always activate a membrane receptor to activate a signaling cascade

Question 10

What is the major difference between catecholamines and indolamines?

Answer 10

synthesis

Catecholamines synthesized from tyrosine via tyrosine hydroxylase (rate limiting)

Indolamines synthesized from tryptophan via ryptophan hydroxylase (rate limiting)

Question 11

What are some tyrosine derived catecholamines?

Answer 11

Dopamine, Norepi, Epi

Question 12

How can tyrosine hydroxylase be used clinically?

Answer 12

It can be used as a marker of dopaminergic activity

Question 13

What are the two ways in which dopamine can act?

Answer 13

NT and a hormone

Question 14

What organs is dopamine made in?

Answer 14

Brain: Substantia nigra, ventral tegmental area, arcuate nucleus (for release to pituitary)

Adrenal glands: the adrenal medulla is where it is converted into norepinephrine

Question 15

What is the function of dopamine in the brain?

Answer 15

Regulates many pathways as a NT, involved in reward pathways, attention, and mood

Question 16

What is the hormone action of dopamine?

Answer 16

Inhibits prolactin release from the anterior pituitary (tonic inhibitor)

Question 17

In the control of prolactin release, where do the dopaminergic neurons arise from, and where do they synapse?

Answer 17

Arise from the arcuate nucleus, synapse on the hypophyseal capillary bed

Question 18

What are the two ways in which norepinephrine can act?

Answer 18

NT, hormone

Question 19

From what is norepi derived from?

Answer 19

dopamine (which is derived from tyrosine)

Question 20

What is required to convert dopamine to norepi?

Answer 20

sympathetic stimulation

Question 21

What is the rate limiting enzyme in the conversion of dopamine to norepi?

Answer 21

dopamine-beta-hydroxylase

Question 22

Where does the conversion of dopamine to norepi happen, and how do we know?

Answer 22

The tissue concentrations are equivalent to that of the synapse - thus the conversion must take place within the neurons

Question 23

What do sympathetic post-ganglionic fibers release?

Answer 23

NE!

Question 24

Through what kind of receptors does NE act through?

Answer 24

alpha and beta adrenergic receptors

Question 25

How is the adrenal medulla involved in NE release?

Answer 25

splanchic nerve innervates the adrenal medulla where conversion to NE occurs Chromaffin cells of the adrenal medulla are homologous to post-ganglionic fibers and will release NE into the blood

Question 26

What is the rate limiting enzyme of indoleamine synthesis?

Answer 26

tryptophane hydroxylase

Question 27

What is an example of an indoleamine that is both a hormone and a NT?

Answer 27

Serotonin

Question 28

What can be formed from serotonin?

Answer 28

Melatonin

Question 29

What is the enzyme in the synthesis of melatonin from serotonin?

Answer 29

SNA

Question 30

Where is melatonin produced?

Answer 30

Pineal gland

Question 31

What is serotonins action as a NT, and where is it located?

Answer 31

the brain, is the 'happiness hormone'

Question 32

Where is the majority of serotonin produced, and by what cells?

Answer 32

over 95% of serotonin is produced by enterochromffin cells of the gut

Question 33

What is serotonins activity in the gut?

Answer 33

vasoconstrictor | stimulates smooth muscle contraction in intestine

Question 34

How do SSRIs work?

Answer 34

Block the reuptake of serotonin (inhibit 5-HT) thus increasing serotonin concentrations in the synaptic cleft

Question 35

What can happen with long term SSRI use?

Answer 35

down-regulation of serotonin receptors or the neuron can stop making endogenous serotonin if used for prolonged periods

Question 36

What are the two primary methods of mono-amine metabolism and what are the enzymes involved?

Answer 36

deamination and methylation MAO: oxidative deamination - inactivates indoleamines and catecholamines via removal of an amine group resulting in aldehyde and ammonia (aldehyde degraded via aldehyde dehydrogenase) COMT: metabolism of catechoamines - adds a methyl group

Question 37

What do MAOIs do?

Answer 37

inhibit MAOand thus are used for depression and anxiety disorders

Question 38

What is the primary metabolite of catecholamines in extraneural tissues?

Answer 38

DHPG

Question 39

What is a metabolite in urine that can indicate excessive catecholamines?

Answer 39

Vanillylmandelic acid (VMA)

Question 40

from what is melatonin synthesized, and where?

Answer 40

from serotonin in the pineal gland

Question 41

What is the rate limiting enzyme in melatonin synthesis, and when is it most active?

Answer 41

N-acetyltransferase, at night

Question 42

What does melatonin inhibit?

Answer 42

It is a potent inhibitor of reproduction - it causes decreased spermatogenesis and testis size in males

Question 43

Discuss the events required for melatonin secretion

Answer 43

light info transmitted to the SCN via the retinohypothalamic tract the SCN transmits the info to the pineal gland and regulates its circadian activity

Question 44

Describe the path of a gene to a protein hormone

Answer 44

DNA - mRNA - translated to a preprohormone - NH2 signal is cleaved to give a prohormone - additional peptides cleaved to give hormone

Question 45

What are all steroids derived from?

Answer 45

Cholesterol

Question 46

What are the steroid hormones of the adrenal cortex?

Answer 46

Cortisol, mineralocorticoid, DHEA, androstenedione

Question 47

What is the steroid hormone of the kidney?

Answer 47

Vit. D

Question 48

What are the steroid hormones of the placenta?

Answer 48

progesterone, estriol

Question 49

What is the steroid hormone of the testis?

Answer 49

testosterone

Question 50

What are the steroid hormones of the ovaries?

Answer 50

17beta-estradiol, progesterone

Question 51

What is a common precursor of steroid hormones, and how is it formed?

Answer 51

StAR moves cholesterol from the outer to the inner mitochondrial membrane and forms pregnenolone

Question 52

What are the different fates of pregnenolone?

Answer 52

Cortisol via several hydroxylation steps Estrogens and androgens via DHEA and the enzyme 3betaHSD progesterone via 3betaHSD and subsequent metabolism to aldosterone via hydroxylation rxns and the enzyme aldosterone synthase

Question 53

What is an endocrine axis?

Answer 53

Three-tiered endocrine system involving hypothalamic neurons, anterior pituitary cells, and peripheral endocrine glands hormones can regulate any part of this sequence

Question 54

What is short and long loop negative feedback?

Answer 54

short loop: hormone from pituitary acts on hypothalamus long loop: hormone released from peripheral gland can act on both the pituitary and the hypothalamus

Question 55

What is the difference between endocrine axis driven- and physiological response driven- negative feedback?

Answer 55

physiological response driven (used to be called feed forward) - the physiological effect of the hormone is what results in a change, not the hormone itself as in endocrine axis driven

Question 56

What are four examples of positive feedback?

Answer 56

parturition lactation ovulation blood clotting

Question 57

What factors affect circulating hormone levels?

Answer 57

Age, sex, time of day, body weight, diet