Basics of Endocrinology II Flashcards Preview

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Flashcards in Basics of Endocrinology II Deck (57):
1

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

a single amino acid, 2-3 minutes

2

What are catecholamines derived from

A single tyrosine

3

What are indolamines derived from?

A single tryptophan

4

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

Two tyrosines - the exception to amines

Half life T4 = 8 days, T3 = 24 hours

5

What chemical classification are most hormones?

peptides/proteins

6

What is the half life of peptide/protein hormones?

4-170 minutes

7

What is the half life of steroid hormones?

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

8

What are the three chemical classifications of hormones?

amines, peptide/proteins, steroid

9

What are the common features of catecholamines and indolamines?

short half life - act quickly and are degraded quickly

travel freely in the blood

always activate a membrane receptor to activate a signaling cascade

10

What is the major difference between catecholamines and indolamines?

synthesis

Catecholamines synthesized from tyrosine via tyrosine hydroxylase (rate limiting)

Indolamines synthesized from tryptophan via ryptophan hydroxylase (rate limiting)

11

What are some tyrosine derived catecholamines?

Dopamine, Norepi, Epi

12

How can tyrosine hydroxylase be used clinically?

It can be used as a marker of dopaminergic activity

13

What are the two ways in which dopamine can act?

NT and a hormone

14

What organs is dopamine made in?

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

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

15

What is the function of dopamine in the brain?

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

16

What is the hormone action of dopamine?

Inhibits prolactin release from the anterior pituitary (tonic inhibitor)

17

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

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

18

What are the two ways in which norepinephrine can act?

NT, hormone

19

From what is norepi derived from?

dopamine (which is derived from tyrosine)

20

What is required to convert dopamine to norepi?

sympathetic stimulation

21

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

dopamine-beta-hydroxylase

22

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

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

23

What do sympathetic post-ganglionic fibers release?

NE!

24

Through what kind of receptors does NE act through?

alpha and beta adrenergic receptors

25

How is the adrenal medulla involved in NE release?

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

26

What is the rate limiting enzyme of indoleamine synthesis?

tryptophane hydroxylase

27

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

Serotonin

28

What can be formed from serotonin?

Melatonin

29

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

SNA

30

Where is melatonin produced?

Pineal gland

31

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

the brain, is the 'happiness hormone'

32

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

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

33

What is serotonins activity in the gut?

vasoconstrictor
stimulates smooth muscle contraction in intestine

34

How do SSRIs work?

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

35

What can happen with long term SSRI use?

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

36

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

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

37

What do MAOIs do?

inhibit MAOand thus are used for depression and anxiety disorders

38

What is the primary metabolite of catecholamines in extraneural tissues?

DHPG

39

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

Vanillylmandelic acid (VMA)

40

from what is melatonin synthesized, and where?

from serotonin in the pineal gland

41

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

N-acetyltransferase, at night

42

What does melatonin inhibit?

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

43

Discuss the events required for melatonin secretion

light info transmitted to the SCN via the retinohypothalamic tract

the SCN transmits the info to the pineal gland and regulates its circadian activity

44

Describe the path of a gene to a protein hormone

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

45

What are all steroids derived from?

Cholesterol

46

What are the steroid hormones of the adrenal cortex?

Cortisol, mineralocorticoid, DHEA, androstenedione

47

What is the steroid hormone of the kidney?

Vit. D

48

What are the steroid hormones of the placenta?

progesterone, estriol

49

What is the steroid hormone of the testis?

testosterone

50

What are the steroid hormones of the ovaries?

17beta-estradiol, progesterone

51

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

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

52

What are the different fates of pregnenolone?

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

53

What is an endocrine axis?

Three-tiered endocrine system involving hypothalamic neurons, anterior pituitary cells, and peripheral endocrine glands

hormones can regulate any part of this sequence

54

What is short and long loop negative feedback?

short loop: hormone from pituitary acts on hypothalamus

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

55

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

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

56

What are four examples of positive feedback?

parturition

lactation

ovulation

blood clotting

57

What factors affect circulating hormone levels?

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