Endocrine System Part I

Question 1

endocrinology

Answer 1

the study of hormones and the endocrine organs

Question 2

speed of endocrine system

Answer 2

responses are slower but longer lasting than those of the nervous system

Question 3

endocrine system controls and integrates

Answer 3

• reproduction
• growth/development
• maintenance of electrolyte, water, and nutrient balance
• regulation of cellular metabolism and energy balance
• mobilization of body’s defenses

Question 4

exocrine glands

Answer 4

• produce nonhormonal substances (sweat, saliva)
• have ducts to carrry secretions to membrane surfaces

Question 5

endocrine glands

Answer 5

• produce hormones
• lack ducts

Question 6

hypothalamus

Answer 6

neuroendocrine organ
*pancreas, gonads, and placenta have exocrine and endocrine functions

Question 7

all endocrine glands

Answer 7

• pituitary, thyroid, parathyroid, adrenal, pineal

Question 8

other tissues and organs that produce hormones

Answer 8

adipose cells, thymus, cells in walls of small intestine, stomach, kidneys, heart

Question 9

paracrines

Answer 9

locally acting chemicals that affect cells other than those that secrete them
- local, not considered part of the endocrine system

Question 9

hormones

Answer 9

long-distance chemical signals; travel through blood or lymph

Question 10

autocrines

Answer 10

chemicals that exert effects on the same cells that secrete them
- local, not considered part of the endocrine system

Question 11

steroids

Answer 11

synthezised from cholesterol; gonadal and adrenocortical hormones

Question 12

amino acid based hormones

Answer 12

amino acid derivatives, peptides, and proteins

Question 13

how endocrine system works

Answer 13

hormones circulate systemically, but only cells with receptors for a specific hormone will be affected

Question 14

target cells

Answer 14

tissues with receptors for a specific hormone
- hormones alter target cell activity

Question 15

upon arrival at target cells, hormones may be able to:

Answer 15

• alter plasma membrane permeability and/or membrane potential by opening/closing ion channels
• stimulate synthesis of enzymes or other proteins
• activate/deactivate enzymes
• induce secretory activity
• stimulate mitosis

Question 16

water soluble hormones

Answer 16

all amino acid based hormones except thyroid hormone
- cannot directly enter a cell
- act on plasma membrane receptors
- typically, receptors are coupled to 1+ intracellular second messengers via regulatory molecules called g proteins

Question 17

except for thyroid hormone, amino acid based hormones exert effects through second-messenger systems:

Answer 17

• cyclic AMP
• PIP 2-calcium

Question 17

lipid soluble hormones

Answer 17

steroid and thyroid hormones
- can directly enter a cell
- act on intracellular receptors that directly activate genes

Question 18

cAMP is degraded by

Answer 18

phosphodiesterase

Question 18

cAMP signaling mechanism

Answer 18

1. Hormone (First Messenger) binds to receptor
2. Receptor activates a G Protein
3. G Protein activates or inhibits amplifier enzyme adenylate cyclase
4. Adenylate cyclase converts ATP to cAMP (Second Messenger)
5. cAMP activates proteins kinases that phosphorylate other proteins and generate responses within the cell

Question 19

molecular relay race analogy

Answer 19

hormone (1st messenger) > receptor > G protein > enzyme > 2nd messenger

Question 20

pip 2 calcium signaling mechanism

Answer 20

hormone activated g protein activates phospholipase c - an effector enzyme

Question 21

activated phospholipase c splits membrane protein, pip 2, into 2nd messengers:

Answer 21

• dialglycerol (DAG); activates protein kinases and triggers responses within target cells
• inositol triphosphate (IP3) causes Ca2+ to be released from intracellular storage sites

Question 22

freed ca2+ ions act as another second messenger

Answer 22

• ca2+ either alters enzyme and channel activity or binds to a regulatory protein called calmodulin
• once ca2+ binds to calmodulin, it activates enzymes that amplify the cellular response

Question 23

intracellular receptors and direct gene activation

Answer 23

• Lipid-soluble steroid hormones and thyroid hormone can diffuse into target cells and bind with their intracellular receptors
• Receptor-hormone complexes then enter the nucleus and bind to specific regions of the DNA
• Binding helps to initiate transcription of DNA to produce mRNA
• mRNA is then translated into specific proteins
• The proteins synthesized have various functions – metabolic activities, structural purposes, or exportation from the cell

Question 23

other signaling mechanisms

Answer 23

• cyclic guanosine monophosphate (cGMP) is a 2nd messenger for selected hormones
• other hormones work without any second messenger system
• ex insulin receptor is a tyrosine enzyme that autophosphorylates upon insulin’s binding; the activated tyrosine kinases provide docking sites for relay proteins that trigger cell responses

Question 24

endocrine glands are stimulated to synthesize and release hormones in response to 1 of 3 stimuli

Answer 24

• humoral stimuli
• neural stimuli
• hormonal stimuli

Question 25

release of hormones

Answer 25

• negative feedback loop
• internal/external stimulus triggers release of hormone
• rising hormone levels cause effects at target hormones
• additional rise in hormone levels inhibits further release
• hormonal levels vary within a narrow, desirable range

Question 26

humoral stimuli

Answer 26

changing blood levels of ions and nutrients directly stimulates secretion of hormones
- ex. level of ca2+ in blood > when it declines PTH is secreted

Question 27

neural stimuli

Answer 27

nerve fibers stimulate hormone release
- ex. in times of stress, fibers of the sympathetic nervous system stimulate the adrenal medulla to secrete catecholamines

Question 28

hormonal stimuli

Answer 28

hormones can stimulate other endocrine glands to release their hormones
- ex. Hypothalamic hormones stimulate the release of most anterior pituitary hormones
- Anterior pituitary hormones stimulate their targets to secrete still more hormones
- Hormones from the final target organs inhibit the release of anterior pituitary hormones – the hypothalamic-pituitary-target endocrine organ feedback loop

Question 29

nervous system modulation

Answer 29

nervous system can adjust hormone levels when needed - can modify stimulation/inhibition of different endocrine glands
- nervous sytem can override mechanical endocrine controls
- ex. under severe stress, the hypothalamus and sympathetic nervous system override insulin controls to allow blood glucose levels to rise

Question 30

target cell specificity

Answer 30

target cells must have the specific receptors to which a hormone binds
- ex. receptors for ACTH are only on certain cells of adrenal cortex but thyroxin receptors are found on nearly every cell of the body

Question 30

target cell activation 3 factors

Answer 30

1. blood levels of the hormone
2. relative # of receptors on/in a target cell
3. affinity (strength) of binding between receptor and hormone

Question 31

permissiveness

Answer 31

one hormone cannot exert its effects without another hormone being present
- ex. reproductive hormones need thyroid hormone to have effect

Question 32

synergism

Answer 32

more than one hormone produces the same effects on the target cell - causes amplification
- ex. glucagon and epinephrine both cause the liver to release glucose

Question 33

antagonism

Answer 33

one or more hormones oppose the action of another hormone
- ex. insulin and glucagon