PY411 Lectures

• How do animal cells signal each other? (through which systems)

  Endocrine system

  Paracrine system

  Neuronal system

  Contact-dependent system
• What is the endocrine system?


  It is a collection of glands and tissues that produce hormones, which regulate internal processes.
• What are examples of reactions involved in the endocrine system?


  Metabolism

  Growth and development

  Tissue function

  Sexual& reproductive function

  sleep and mood
• What is an endocrine gland/tissue?


  -A group of cells that synthesise a chemical messenger to be released into the surrounding medium _> usually blood.
• What is a "classic" endocrine gland?

  
  

  Can you give examples?

  They have clearly defined intracellular secretory machinery.

  
  

  eg: adrenal and thyroid gland
• What are some tissues which AID the endocrine glands?

  The liver/heart aid the role of the glands.
• What is a chemical messenger?

  a hormone
• What are the types of hormones? and give an example of each.


  - Peptide hormones -> insulin

  
  

  -Steroid Hormones -> Oestrogen

  
  

  -Amino Acids-derived Hormones -> Thyroid Hormone
• How does a hormone work? (GENERAL)


  They are carried to a target by the blood

  
  

  These target cells with the appropriate hormone receptor, which then response in a specific way

  
  

  Each hormone may act on several target tissues.
• What is a peptide hormone? can it cross the cell membrane and why?


  -> Chains of amino acids, often synthesised and stored as an inactive precursor.

  
  

  -> They can be susceptible to protease attack.

  
  

  They cannot cross the cell membrane without acting on membrane bound receptors, such as carrier/channel proteins.
• What are some properties of peptide hormones?


  water soluble

  not orally active

  rapid onset of action

  short plasma half-life

  short duration of action
• What are steroid hormones?

  Can they cross the cell surface membrane?

  They are derived from lipids

  Generally synthesised on demand

  Transported in blood bound to plasma protein

  
  

  Can cross the cell membrane as is lipid soluble.
• Why are steroid hormones synthesized on demand?


  Because they are lipophilic molecules, so they can cross the membrane rapidly. Therefore, there isn't a need to have back-up amounts
• What are properties of steroid hormones?


  -Poorly water soluble

  -Orally active

  -Slow onset of action

  -Long plasma half-life

  -Long duration of action
• What are the types of thyroid hormones?


  T3 and T4
• How are T3 and T4 thyroid hormone made?

  Through Tyrosine and Iodine
• What is the t3 version of the thyroid hormone?

  It is the active hormone
• What is the T4 version of the thyroid hormone?

  More abundant but less active form
• What happens in the tissues to the T3 and T4 hormone?


  T4 can be converted to the T3 within tissues
• What are the major receptors involved in hormone action?


  Steroid Hormone Receptors

  
  

  G-Protein coupled receptors

  
  

  Tyrosine kinase receptors

  
  

  Nuclear receptors
• What are the major endocrine glands?


  The hypothalamus, pituitary, thyroid, parathyroid, adrenal glands, pancreas, testes, and ovaries
• What is the pituitary gland?

  "master gland"
• What is the role of each section of pituitary gland?

  Posterior pituitary -> ADH and Oxytocin release

  
  

  Anterior Pituitary ->

  Growth Hormone

  Thyroid Stimulating Hormone

  Adrenocorticotropic hormone (ACTH)

  Luteinizing hormone (LH)

  Prolactin

  Melanocyte-stimulating hormone
• What is the role of the thyroid and parathyroid gland?


  Thyroid Gland -> it is important for controlling the metabolic rate

  
  

  -> controlled by the hypothalamus and pituitary

  
  

  Also important for calcium homeostasis
• Where do we find the adrenal glands?

  Found on top of the kidneys

  
  

  Separated into inner medulla and outer cortex.
• What is the role of the medulla in adrenal glands?


  - Concerned with stress response.

  
  

  - release of adrenaline and noreadrenaline
• What is the role of the cortex?


  Involved in stress response, glucose and sodium homestasis
• What is the medulla controlled by, and what is the cortex controlled by?

  Medulla -> Hypothalamus

  
  

  Cortex -> ACTH
• What are the gonads?


  - Ovaries/testis

  
  

  secret female/male reproductive hormones.
• What is the role of the gonads?


  - Metabolic activity

  -Sperm production

  -Egg maturation

  -Uterus preparation
• What is an extra role of oestrogen?

  Clacium homeostasis
• What types of cells are found in the pancrease?

  Enodcirne and Ecorcine cells
• What type of hormones are released by the hypothalamus? and why's that same/different to ones that come from the anterior pituitary gland?

  Hypothalamus -> "Release" Hormones

  
  

  
  

  Anterior pituatary gland -> stimuate and trophic hormones
• What is hormone secretion controlled by? and can you give examples


  Controlled by negative feedback

  
  

  Thyroid Hormone acts to decrease TRH and TSH secretion

  
  

  Cortisol acts to decrease CRH and ACTH secretion

  
  

  Oestrogen act to decrease GnRH and FSH secretion
• How is thyroid triggered?

  Hypothalamus released TRH (Thyroid releasing hormone), which stimulates release of TSH (Thyroid stimulating hormone) from anterior pituitary gland, which is going to cause the thyroid to make T4 and T3
• What does thyroid contain?

  follicles made of follicular cells, surrounding viscous colloid
• Where are T3 & T4 made and stored?


  Made from tyrosine (and iodine) and stored in colloid
• How is T3 and T4 made?


  The body collects iodine in the colloid of thyroid follicles, tyrosine residues on a protein called thyroglobulin, which gains one or two iodine molecules.

  
  

  These iodine bound tyrosine are coupled together, forming the thyroid hormones T4/T3
• How is thyroid transported in the blood?


  Thyroid hormones are insoluble in water, so they are transported in the blood by plasma proteins.

  
  

  Mainly by TBG (75%).
• What type of thyroxine is active?

  only free (unbound( hormone is biologically active