hormone transport and kinetics

Question 1

what are the four characteristics of a hormone

Answer 1

• chemical agent
• synthesized and secreted by glands
• circulate in the blood to other parts of the body
• circulate in the blood to other parts of the body
• stimulate specific tissues

Question 2

what are the 3 classifications of hormones

Answer 2

• classical hormones
• neurohormones
• local hormones

Question 3

what are classical hormones

Answer 3

• secreted from endocrine cells
• diffues into the blood
• transported by transported via blood to target tissues

example: cortisol

Question 4

what are neurohormones

Answer 4

• synthesised within neuroendocrine cells
• secreted from nerve terminals
• diffuse into blood vessels and transported

example: corticotropin-releasing hormone

Question 5

what are local hormones

Answer 5

• diffusion of hormone into interstitial fluid
• paracrine function on neighbouring cells via interstitial fluid, not blood
• autocrine function acts on itself

Question 6

list lipid soluble hormone binding proteins

Answer 6

specific:
- cortisol-binding protein (for cortisol)
- vitamin D binding globulin (vitamin D)
- thyroid binding globulin (T3 and T4)

non specific:
- albumin (steroids)
- prealbumin (T3 and T4)

Question 7

where are transport proteins produced

Answer 7

liver
also degraded in liver
(consequence of liver damage?)

Question 8

is free T3/T4 or bound T3/T4 more abundant

Answer 8

bound (70-80%) to TBG
more free T3 than T4

Question 9

what are the functions of transport proteins

Answer 9

• serve as a hormone reservoir
• act as hormone buffers
• reduce hormone loos via the kidneys

Question 10

how do transport proteins act as hormone reservoirs

Answer 10

• free hormone diffuses into cells
• consumed as binds to receptors
• equilibrum
• reservoir replaces free hormone in blood

Question 11

how do transport proteins act as hormone buffers

Answer 11

• respond to increase hormone production
• only using 50% of binding capacity
• short-term peaks in synthesis absorbed
• raise in amount of hormone in circulation
• doesnt necessarily stimulate tissues

Question 12

how do transport proteins reduce hormone loss

Answer 12

• some hormones excreted via the kidney
• hormone loss reduced by protein binding

Question 13

hormone plasma concentrations are a net result of:

Answer 13

• rate of secretion into the blood
• rate of removal from the blood

Question 14

list elimination mechanisms of hormones

Answer 14

• enzymatic degradation
• within target cells after binding receptor
• via liver and kidneys

Question 15

what factors affect homrone responses

Answer 15

• variation by tissue (tissues repond differently to the same hormone)
• variation by time (initial response may differ from delayed response, and depends on species, age and hormone)
• variation by dose (example, pred short term no side effects, long term can see clinical signs or excess cortisol)
• status of target tissue (overstim = hypertrophy, understim = atrophy)

Question 16

discuss hormone feedback loops

Answer 16

• negative feedback if hormone level exceeds needs, high level sensed by hypothalamus/pituitary, hormone synthesis decreases
• it is free hormone that is monitored
• adapt to changes in binding protein