Hormone Signalling

Question 1

What is a hormone?

Answer 1

• Chemical synthesised by highly vascularised endocrine cells
• Released into the bloodstream to send a message to another part of the body (usually by cell signalling)

Question 2

Give examples of organs that release hormones.

Answer 2

• Pituitary and hypothalamus
• Thyroid
• Pancreas
• Adrenal
• Gonads
• Heart, kidneys, skin and placenta

Question 3

Describe peptide hormones.

Answer 3

• Water soluble
• Bind to extracellular receptors
• Half life determined by enzymatic degradation
• EXAMPLE: Insulin

Question 4

Describe steroid hormones.

Answer 4

• Lipid soluble
• Bind to intracellular receptors. Activation causes changes in gene expression
• Derived from cholesterol
• EXAMPLE: testosterone

Question 5

Describe eicosanoid hormones.

Answer 5

• Water soluble
• Involved in inflammation e.g prostaglandins

Question 6

Describe endocrine signalling

Answer 6

• Cell releases hormone into the systemic circulation
• Bind to receptors on and cause changes in distal tissue

Question 7

Describe paracrine sigalling.

Answer 7

• Cell releases hormone into the systemic circulation
• Binds to receptors and induces changes in neighbouring cells in locality

Question 7

Describe autocrine signalling

Answer 7

• Chemical is released from a cell which acts on itself
• Used in hormone regulation e.g binding of a hormone on its own cell to slow down production

Question 8

Define intracrine signalling.

Answer 8

• Signalling chemical acts on intracellular receptors within the same cell.
• Alter DNA transcription or initiate intracellular signalling cascades

Question 9

Describe negative feedback.

Answer 9

• Increase in a controlled variable
• Processes occur that will eventually decrease that variable and its effects.
• Example: HPA axis

Question 10

Describe positive feedback.

Answer 10

• Increase in a controlled variable
• Body amplifies the effect of that variable
• Response of effector reinforces stimulus.
• EXAMPLE: Oxytocin release

Question 11

Describe the positive feedback control of uterine contractions in labour by oxytocin.

Answer 11

• Oxytocin stimulates contraction of the uterine muscles.
• Cervix dilates and activates stretch receptors.
• Action potentials send signals to the hypothalamus.
• Stimulates a further release of oxytocin.

Question 12

What are the three types of hormone receptors?

Answer 12

• Enzyme receptors - water soluble hormones bind.
• GPCRs - water soluble hormones bind. Causes biochemical cascades
• Intracellular receptors - lipid soluble hormones bind

Question 13

Describe the hypothalamic pituitary axis. PART 1

Answer 13

• Anterior pituitary responds to hormones released by hypothalamus. Secretes hormones into circulation
• Posterior pituitary - secretes vasopressin and oxytocin (synthesised by hypothalamus)

Question 14

Describe the hypothalamic pituitary axis. PART 2

Answer 14

• Hypothalamus receives multiple inputs relating to parameters such as stress, metabolic rate, body temp.
• In response to signals, hormone secretions from pituitary gland either increases or decreases.

Question 15

What are circadian fluctuations and what are they mediated by?

Answer 15

• Change in levels of hormones associated with time of day. Single cycle of hormone in 24 hour period.
• Mediated by ‘internal body clock’ genes - regulator is the SCN
• Example: melatonin

Question 16

Describe ultradian rhythmicity.

Answer 16

• Cycle of hormones occur more than once in 24 hour period
• EXAMPLE: Ghrelin