Negative and Positive Feedback Mechanisms

What is negative feedback?

Regulatory mechanism where a change in a system triggers a response that counteracts the initial change, maintaining homeostasis.

Give 2 examples of negative feedback

There are 3 hormones here:

• Hypothalamic releasing hormone

• Pituitary hormone

• Target gland hormone

• Hypothalamic releasing hormone triggers release of hormone by anterior pituitary gland

  • This triggers release of a second hormone by the target gland

  • This hormone suppresses secretion of both hypothalamic releasing hormone and pituitary hormone

The body could also use both releasing and inhibiting hormones to control a process.

Give an example with growth hormone

• What influences the hypothalamic growth hormones

• How

• What releases it

What influences the hypothalamic growth hormones: Somatomedins

How:

• Inhibit release of growth hormone-releasing hormone

• Stimulate release of growth hormone-inhibiting hormone

What releases it: Liver releases somatomedins

NEG FED: What are the steps in glucose homeostasis when there is increasing blood glucose levels

What are the

• Stimulus

• Receptors

• Effectors

  • Results in (5)

• Stimulus: Homeostasis disturbed by increasing blood glucose level

• Receptors: Beta cells in pancreatic islets

  • Secrete insulin

• Effectors: All body cells

  • Increase rate of glucose transport

  • Increase rate of glucose use and ATP generation for:

    • Increase amino acid absorption and protein synthesis

    • Increase fat synthesis in adipose tissue

  • Increase conversion of glucose —> glycogen

• Homeostasis restored by decreasing blood glucose level

NEG FED: What are the steps in glucose homeostasis when there is decreasing blood glucose levels

What are the

• Stimulus

• Receptors

  • Location

  • Secretes

• Effectors

  • Results in (3)

Stimulus: Decreasing blood glucose level

Receptors: Alpha cells

• Location: Pancreatic islets

• Secrete: Glucagon

Effectors: Liver, skeletal muscle and adipose cells

• Respond with increased

  • Breakdown of glycogen —> glucose (liver, skeletal muscle)

  • Breakdown of fat —> fatty acids (adipose tissue)

    • For gluconeogenesis

  • Synthesis and release of glucose (liver)

What is positive feedback mechanism

A mechanism by which output is enhanced

Give an example of positive feedback

Contractions in childbirth

• Contractions stimulates oxytocin which stimulate more muscle contraction