Introduction to the endocrine system

Question 1

What is the endocrine system?

Answer 1

• a communication system based on chemical messengers called hormones

Question 2

How are hormones distributed?

Answer 2

• hormones are distributed in the blood from their site of production to their site of action - endocrine mode of action

Question 3

What are the main components of the endocrine system?

Answer 3

• endocrine glands ( secrete product directly into blood)
• hormones
• target tissue/cells
• hormone receptor ( on tissue or cells)
• 2nd messengers

Question 4

What are neuroendocrine cells & give an example of one?

Answer 4

• cells that receive a neural input ( eg NT’s released by nerve cells or neurosecretory cells) and after input they release hormones into the blood
• interaction between the NS and the endocrine system
  EXAMPLE - chromaffin cells in adrenal medulla

Question 5

Compare the main differences between the NS and the ES

Answer 5

• nervous system - wired system with structural arrangement between neurons and target cells, NT’s released into cleft, rapid response
• endocrine system- wireless system, endocrine glands are widely dispersed and not structurally related to one another, hormones released into blood, slow response

Question 6

What are the 6 major functions of the endocrine system?

Answer 6

1. regulate organic metabolism eg glucagon, insulin
2. regulate inorganic metabolism eg Ca2+, Na+
3. regulate water and electrolyte balance
4. promote linear growth and development eg growth hormone
5. control sexual development eg estrogen, testosterone, FSH & LH
6. adaptive response to stress eg adrenaline, cortisol

Question 7

What is a simplified function of the endocrine system?

Answer 7

to maintain homeostasis - maintain physiological variables eg PH and temp within narrow range that is optimal for body function

Question 8

What are the (8) major endocrine glands in the body?

Answer 8

• Hypothalamus
• Pituitary gland
• Thyroid gland
• Parathyroid gland
• Adrenal gland
• Pancreas
• Ovaries
• Testes

Question 9

What hormones do the (8) major endocrine glands release?

Answer 9

1. Hypothalamus - eg GHRH, TRH, GnRH
2. Pituitary gland - eg oxytocin, vasopressin, growth hormone, FSH & LH
3. thyroid gland - eg thyroid hormones T3 & T4
4. Parathyroid hormones - eg parathyroid hormone
5. Adrenal gland - eg cortisol, aldosterone
6. Pancreas - eg insulin & Glucagon
7. Testes - testosterone
8. Ovaries - Estrogen & progesterone

Question 10

What is the difference between endocrine and exocrine glands?

Answer 10

• Exocrine - maintain contact with body surface through a duct eg sweat gland & mammary glands
• Endocrine - do not have contact with body surface, they have no ducts.. they secrete hormones directly into blood

Question 11

What are the 3 main classes of hormones?

Answer 11

• Peptide hormones
• Amines
• Steroid hormones

Question 12

What are peptide hormones?

Answer 12

• hormones made of many amino acids linked together by peptide bonds
  they are water soluble so they bind to receptors on outer surface
• synthesized in rough ER and stored in secretory vesicles as they go through golgi apparatus
• examples : insulin and glucagon of the pancreas

Question 13

What are amine hormones?

Answer 13

• hormones derived from amino acid tyrosine
• catecholamines - adrenaline and noradrenaline
• thyroid hormones - T4 & T3 ( note the number indicates the number of iodine’s)

Question 14

What are steroid hormones?

Answer 14

• hormones that are derived from cholesterol
• corticosteroids ( includes glucocorticoids - cortisol & mineralcorticoids - aldosterone )
• sex steroids ( progesterone, androgens and estrogens)

Question 15

What are androgens?

Answer 15

• natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics

Question 16

What are the hypothalamus and the pituitary gland?

Answer 16

• 2 endocrine glands that control the production of and release of hormones of the other endocrine glands in the body
• each lobe of the pituitary gland ( anterior and posterior) secrete different hormones in response to signals from the hypothalamus

Question 17

What stimuli can decrease or increase the production and release of a hormone?

Answer 17

• ions
• nutrients
• PH and temp
• neuron
• biological rhythms

Question 18

What is the difference between positive and negative feedback regulation of hormone production?

Answer 18

• positive feedback increases the stimulus and increases productivity eg Ferguson reflex ( oxytocin causing uterine contractions in childbirth
• negative feedback reduces the stimulus and decreases activity eg testosterone release, FSH and inhibin

Question 19

How many messengers are there in the endocrine system?

Answer 19

• 1st messengers - hormones
• signal is relayed to cells via hormone receptors eg G protein coupled receptor
• 2nd messengers - cAMP/cGMP or Ca2+/calmodulin, PIP3 and DAG

Question 20

Compare up vs down regulation of receptor

Answer 20

1. down regulation - high hormone conc - reduce the no of receptors to prevent overstimulation ie more degradation and lower gene expression
2. up regulation - low hormone conc - increase no of receptors ie higher gene expression of receptors and more receptor synthesis

Question 21

what is the sensitivity of a hormone usually defined as?

Answer 21

the concentration needed to produce a half maximal response

Question 22

in this curve, B is normal curve response, but is A and C increased or decreased sensitivity?

Answer 22

• B = normal curve
• A = increased sensitivity - ie less hormone is required to produce a half maximal response
• C= decreased sensitivity - ie more hormone is requird to produce a half maximal response