Introduction to the Endocrine System Hormones, Receptors and Signalling Flashcards Preview

Endocrine > Introduction to the Endocrine System Hormones, Receptors and Signalling > Flashcards

Flashcards in Introduction to the Endocrine System Hormones, Receptors and Signalling Deck (43)
Loading flashcards...
1
Q

where does endocrine secretion originate?

A

either single cells

more commonly collection of cells forming a ductless endocine gland

2
Q

endocrine vs exocrine secretion?

A
exocrine = secretes into ducts
endocrine = ductless secretion
3
Q

how do glands communicate with other tissues in the body/other endocrine glands in the body?

A

via secretion of hormone into the blood and bulk transport to the target site

4
Q

how do endocrine glands interact? give an example

A

glands are anatomically distinct strucures but form integrated functional systems
- e.g hypothalamus releases CRF which stimulates anterior pituitary to release ACTH which causes adrenal cortex to synthesise and release cortisol

5
Q

what 3 factors are involved in the specificity of hormone signalling?

A

chemically distinct hormones
specific receptors for each hormone
distinct distribution of receptors across target cells

6
Q

what are the 7 major endocrine organs in the body?

A
pituitary
thyroid
parathyroid
adrenal glands
pancreas
ovary
testes
- others do exist - hypothalamus, pineal, heart etc
7
Q

what classifies an endocrine organ?

A

secretes a hormone

therefore many organs in the body can technically be considered an endocrine hormone - heart, kidneys etc

8
Q

what are the 4 main classes of hormones?

A

modified amino acids
steroids - synthesised from cholesterol
peptides
proteins

9
Q

give an example of each hormone type

A

amino acid - adrenaline, thyroid hormones
steroids - cortisol, progesterone, testosterone
peptides - ACTH, ADH, oxytocin
proteins - insulin

10
Q

peptide vs protein hormones?

A

peptides derived from larger precursor proteins

11
Q

significance of hormone structure?

A

half life

where it acts

12
Q

what are the 3 types of signalling?

A

autocrine - hormone released from cell into ECM and acts back upon itself
paracrine - hormone released from cell and acts on cells immediately adjacent (e.g histamine in stomach)
endocrine - hormone released into ECM and enters the blood stream and travels to target cells and leaves the blood

13
Q

do all hormones have a single distinct signalling action?

A

no

e.g - somatostatin

14
Q

how potent are hormones?

A

very potent
only very small concentration required to activate receptors at distant sites
- receptors have high affinity for the hormones

15
Q

each hormone has a single specific target, true or false?

A

false

single hormone can act on several targets and several hormones can act on same target

16
Q

how does a hormone elicit a biological response?

A

hormone binds to its cognate receptor which is expressed in a tissue selective manner
activated receptor engages a signal transduction cascade that differs between individual receptors but typically causes amplification of the original signal. This is important because of the scarcity of the original signal

17
Q

how does hormone action differ?

A

speed of onset
duration of action
- most are slower and more long lasting compared to neurotransmitters

18
Q

how is hormone action terminated?

A

enzyme mediated metabolic inactivation in either the liver or site of action

19
Q

what 2 broad actions can a hormone have?

A

complementary

antagonistic

20
Q

describe a complementary action

A

action of several hormones regulates many complex physiological functions on short and long time scales
- e.g adrenaline, cortisol and glucagon contribute to body’s response to exercise

21
Q

describe antagonistic action

A

occurs via balance of opposing influences

- e.g insulin lowers plasma glucose while glucagon increases plasma glucose

22
Q

describe the lifecycle of amine hormones

A

presynthesised via enzymatic steps from tyrosine
stored in vesicles in endocrine cell
released into ECM via C2+ dependant exocytosis in response to stimuli
transported free in the plasma (dissolved in blood) as amines are hydrophillic

23
Q

describe the life cycle of peptides and proteins hormones

A

presynthesised from long precursor protein via proteolytic steps
mature hormones stored in vesicles in endocrine cells
released into ECM via Ca2+ dependant exocytosis in response to stimuli
transported free in the blood plasma like amines

24
Q

describe the life cycle of steroid hormones

A

synthesised from cholesterol upon demand
released immediately once formed
transported in plasma bound to plasma transport proteins (90%) as hydrophobic

25
Q

how are steroid hormones synthesised?

A

stimuli increases cellular uptake and availability of cholesterol and rate of conversion of cholesterol to pregnenolone
(all steroids hormones formed via pregnenolone intermediate)

26
Q

which part of steroid hormone is biologically active?

A

only free, unbound hormone in the blood

27
Q

which hormones are insoluble in plasma? how are they transported?

A

steroids
thyroid hormones
mainly bound to carrier proteins

28
Q

what are the functions of carrier proteins?

A

increase amount of insoluble hormones in blood
provide reservoir of hormone
extend half life of hormone in circulation

29
Q

name 3 carrier proteins and their specific functions

A

cortisol binding globulin
thyroxine binding globulin
sex steroid binding globulin

30
Q

name 2 general carrier proteins

A

albumin
transthyretin
- bind several hormones

31
Q

how do carrier proteins help maintain constant concentration of hormone in the blood?

A

bound hormones are too large to cross capillary wall
allows equilibrium between free and bound equilibrium as hormone can unbind and replace free hormone which has crossed the capillary wall - therefore free concentration of hormone doesn’t rise abruptly during a surge of hormone secretion

32
Q

what is the primary determinant of plasma concentration?

A

rate of secretion

33
Q

how is secretion of hormone generally controlled, give an example?

A

negative feedback - eg HPA axis

*see diagram in lecture

34
Q

give an example of how the nervous system and endocrine system can interact

A

HPA axis

neurological stress can trigger hypothalamus to produce CHF etc

35
Q

what is the general pattern of hormone secretion (e.g cortisol)?

A

diurinal (circadium) rhythm

- secretion rate goes up and down as a function of time (entrained to external cue - i.e night and day)

36
Q

via what routes are hormones usually eliminated?

A

metabolism locally]
by the liver
excretion by the liver

37
Q

how can plasma concentration of hormone be calculated?

A

rate of secretion - rate of elimination

38
Q

what are the major types of hormone receptors?

A
g protein coupled receptors (cell surface)
receptor kinases (cell surface)
nuclear receptors (intracellular)
39
Q

what activates GPCRs?

A

amines and some proteins/peptides

signalling pathways involve coupling to Gs, Gi or Gg

40
Q

what activates receptor kinases?

A

some proteins/peptides

41
Q

what are the 3 classes of nuclear receptors?

A
class 1 = in cytoplasm bound to HSP and move to nucleus when activated by steroid hormones
class 2 = in nucleus, activated by lipids
hybrid = activated by thyroid hormones, similar action to class 1
42
Q

what are the general effects of Gs and Gi?

A

Gs increases adenylyl cyclase activity = increases cAMP = increased PKA = cellular effects
Gi = suppresses adenylyl cyclase activity etc

43
Q

what happens in receptor kinases when insulin binds

A

beta subunits gain enzyme activity (by increasing tyrosine kinase activity) so can facilitate phosphorylation of tyrosine > IRS1 binds > IRS1 phosphorylated > activates PKB > metabolic effects