endocrine 2

Question 1

Regulation of Hormone Activity

Answer 1

• Secretion:
  stimulation, feedback, reflexes, rhythms

•Transport:
binding proteins, free/bound balance

•Metabolism
activation/inactivation, differs for hydrophilic vs lipophilic due to accessibility

• Excretion
unregulated (but can be affected by renal/urinary

Target cell responsiveness
- receptor expression,

amplification
-combination with other hormones - ‘permissiveness, synergism and antagonism

Question 2

Secretion:

Answer 2

Two control pathways:
Central regulation
• controlled by the brain
• affected by negative-feedback loops, neuroendocrine reflexes, rhythms (eg diurnal)
• Can be fast, slow or long term responses

Direct regulation
• endocrine cells respond directly to changes in extra- cellular fluid (especially plasma) levels of substances (eg glucose, calcium)
• very rapid response to critical needs

Question 3

Central regulation:

Answer 3

Coordinated by the hypothalamus & pituitary gland

Influenced by feedback ‘loops’ (+ or -)

Question 4

direct regulation

Answer 4

Cells respond directly to changes in extracellular fluid levels

Question 5

Transport – (for lipophilic hormones)

Answer 5

Availability of binding proteins, some specific for particular hormone, some (eg albumin) are non-specific.
Carrier-bound hormone in equilibrium with free hormone
Binding proteins are synthesised in liver, deficiency (eg from liver disease) alters balance between bound and free hormone in plasma

Question 6

Metabolism –

Answer 6

A few hormones activated when metabolised by enzyme (eg thyroid hormone), metabolised form may have much greater activity than original.
Inactivation (mostly in liver) usually unregulated, but may be affected by liver disease.
Metabolism takes place at a higher rate for hydrophilic hormones (peptides & catecholamines) than lipophilic (bound) hormones as they are accessible to blood & tissue enzymes.

Question 7

Excretion

Answer 7

– usually unregulated, urinary excretion (so urinary levels are a good way to measure hormones), but may be affected by kidney or urinary disease.

Question 8

Target cell responsiveness

Answer 8

Amplification of hormones effects via second messenger cascade
* Variations in receptor expression on target cell - a cell must have functional receptors specific for the hormone to be able to respond.
– Number and type of cell receptors can vary by down- regulation or up-regulation

Question 9

Permissiveness, Synergism & Antagonism

Answer 9

Permissiveness, Synergism & Antagonism
P - need hormone A for B to work
S - when hormana A is present, hormone B works better
A - prescence of A, b doesn’t work

Presence or absence of one hormone can influence effects of another through receptor regulation, activation or inactivation

Question 10

Endocrine system basics: summary

Answer 10

• Classes of hormones: peptides, amines, steroids
• Hydrophilic (peptides & catecholamines): dissolve in blood, can’t pass through membranes (act on surface receptors), stored, fast acting, fast breakdown
• Lipophilic (TH & steroids): dissolve in fat, can diffuse through membranes (act within cell), hard to store, longer to act, slow to breakdown
• Regulation: secretion, transport, metabolism, responsiveness of target cells