Hormones

Question 1

Endocrine system

Answer 1

• Collection of glands of an organism that secrete hormones

Question 2

Amine and peptide hormones

Answer 2

• Act on Metabotropic receptors (G-coupled proteins)
• Relatively quick (seconds to minutes): act on the surface of target cells via second messengers
• Examples include:
  
  • Oxytocin - produced in the hypothalamus and released by the posterior pituitary
    
    • “pro-social”
    • Implicated in social bonding, trust
    • Released during childbirth, breastfeeding
  • Ghrelin – produced by the stomach
  • Leptin – produced by fat cells
    
    • These are “appetite hormones” – act to stimulate or suppress hunger

Question 3

Steroid hormones

Answer 3

• Lipid-soluble → cross the plasma membrane
• Receptors are typically localized in the cytosol and nucleus of a cell
• Bind to transcription factors → capable of binding to DNA and altering gene synthesis → Alterations in the number of receptors, amount of neurotransmitter, peptides, proteins or hormones synthesized and stored within a cell.
• Slow action (hours to days) - may also act by nongenomic means
• Glucocorticoids (e.g. cortisol) – produced by the adrenal gland, affect immune/metabolic activity
• Sex hormones (androgens/estrogens) – produced by ovaries/testes

Question 4

Hypothalamus

Answer 4

• Located at the base of the brain, near the pituitary gland
• Acts to maintain homeostasis (maintenance of body’s internal environment): temperature, blood pressure, blood glucose ⇒ Synthesizes and secretes hormones

Question 5

Secretory hypothalamus

Answer 5

• The hypothalamus has control of the pituitary gland which then releases hormones into the bloodstream:
  
  • the hypothalamus releases its own hormones called either releasing (RH) or inhibiting (IH) hormones
  • RH and IH will travel a short distance to the pituitary gland and regulate it to release its own hormones into the bloodstream
  • Pituitary cells can secrete: growth hormones, sex hormones, adrenocorticotropic-stimulating hormone (ACTH - implicated in production of cortisol)

Question 6

Stress response

Answer 6

1. Hypothalamus decides whether a stimulus is stressful or not
2. Secretes CRH which travels to the pituitary
3. The pituitary releases ACTH
4. Adrenocorticotropic hormone (ACTH) travels to the adrenal cortex
5. Cortisol release - important in stress response

⇒ Pathway is called the Hypothalamic Pituitary Adrenal (HPA) pathway (also known as HPA axis)

Question 7

Hypothalamic Pituitary Adrenal (HPA) axis

Answer 7

• Responds to stress
• Short-term ⇒ Sympathetic nervous system (fight or flight, prepare for action)
  
  • Increases metabolism
  • Supresses Immune system
  • Increases perception & attention
  • Norepinephrine release
• Long-term
  
  • Immune changes
  • Loss of muscle and bone mass
  • Hippocampus neuronal death

Question 8

Sex hormones

Answer 8

• Pituitary and Hypothalamus Control of Sex Hormones
• Gonadotropin-releasing hormone triggers Pituitary release of the Gonadotropins :
  
  • luteinizing hormone (LH)
  • follicle-stimulating hormone (FSH)
• Males- LH signals testes to produce testosterone;
  
  • FSH aids sperm maturation
• Females- FSH initiates follicular growth;
  
  • LH triggers ovulation when follicle has matured
• Those hormones determine the sexual differentiation of the foetus.