Topic Two: Endocrine Function Revision Flashcards
Define ‘Endocrine system’
- Second control system (after nervous system)
- Influences cell metabolic activity by means of hormones
- Contains endocrine glands - secrete hormones into blood stream/interstitial fluid
What are hormones?
Hormones are specialised chemical messengers that act to alter the activity of its target cell.
Every cell in the body contains receptors to some or many hormones.
What are endocrine glands?
Glands that secrete their chemical messengers into the bloodstream
What are exocrine glands?
Secrete their secretions by way of a duct onto an epithelial surface (skin, mucosa of digestive tract)
Can some organs be exocrine and endocrine?
Yes - the pancreas is.
How does communication differ between endocrine and nervous systems?
Endocrine - communicates only via chemicals (hormones)
Nervous - electrical and chemical means (action potentials and neurotransmitters)
How does distribution differ between endocrine and nervous systems?
Endocrine - more widespread
Nervous - Relatively local, specific effects
How does reaction to stimuli differ between endocrine and nervous systems?
Endocrine - reacts more slowly to stimuli and may continue responding long after stimulation stops.
Nervous - Responds in a few milliseconds and stops responding almost immediately once stimulation stops
What are some similarities of the endocrine and nervous systems?
- Chemicals act both as neurotransmitters and hormones e.g. noradrenalin & dopamine
- Both act as receptors
- neuroendocrine cells - indicating a close association between the two systems as these modified neuronal cells release their hormones (adrenaline & oxytocin) into the blood stream
- Hormones and neurotransmitters produce overlapping effects on same organ (e.g. glucagon & norepinephrine - both stimulate liver to break down glycogen)
What is the MOA for autocrine agents?
Autocrine act on the cell that secreted it
What is the MOA for paracrine agents?
Paracrine act on adjacent cells
What is the MOA of endocrine agents?
Endocrine agents:
- Secreted into the blood and act on distant target cells
- Also known as hormones
- Act to maintain homeostasis using feedback loops
Functionally classify hormones.
Trophic hormones: Hormones that target other endocrine glands and stimulate their growth and secretion
Sex hormones - Target reproductive tissues
Anabolic hormones - stimulate anabolism in their target cells.
Chemically classify hormones.
Steroid hormones
Non steroid hormones:
- Amino acid derivatives
- Peptides/proteins/glycoproteins
Name some steroid hormones:
Cortisol (hydro cortisol) Aldosterone Oestrogen Progesterone Testosterone
Name two examples of non steroid hormone proteins:
Growth hormone GH
Prolactin
Name two examples of non steroid hormone glycoproteins:
Follicle-stimulating hormone (FSH)
Human chorionic gonadotropin (hCG)
Name two examples of non steroid hormone peptides:
Antidiuretic hormone (ADH) Oxytocin (OT)
Name two examples of non steroid hormone amino acid derivatives:
Norepinephrine (NE)
Epinephrine (Epi)
Melatonin
Thyroxin (Iodinated amino acid)
Steroid hormones examples and description:
Synthesized from cholesterol
Lipid Soluble
e.g. Progesterone, testosterone, cortisol
Hormone transport for amines and peptides?
- Hydrophilic (water loving)
- Mix easily with blood plasma
Hormone transport for steroids and thyroid hormones?
- Hydrophobic
- Must bind to transport proteins (albumin + globulins) in the blood stream
- When carried by a transport protein proteins in the blood must unbind to leave the capillary
- Bound hormones have a longer circulating time (1/2 life) in the bloodstream as the transport protein protects the hormone from being broken down by enzymes
- Free hormones circulate for minutes whereas bound hormones can circulate for hours to weeks.
What are the general principles of hormone action?
- Hormones delivered by blood
- Act only at target cells
- Specific receptors for each hormone
- Signalled by target cell binding (lock and key)
- Receptors located (on/in)
- Nucleus or cytoplasm
- Cell membrane (protein, peptide and amine hormones)
Action of hydrophilic hormones?
Must bind to cell surface receptors
Action of hydrophobic hormones?
Penetrate plasma membrane - enter nucleus
MOA of steroid hormone action?
- They are lipid soluble
- Receptors usually found in target cells cytosol
- Once diffused into a target cell - binds to a receptor molecule to form a hormone -receptor complex
- Amount of steroid hormone present determines the magnitude of a target cells response
- Transcription and protein synthesis is slow thus response to steroid hormones is slow
MOA of steroid hormone action RE Mobile receptor model:
Hormone passes into the nucleus, where it binds to a mobile receptor and activates a certain gene sequence to begin the transcription of messenger ribonucleic acid mRNA
MOA of non steroid.
- Peptide and amine hormones cannot pass through the cell membrane
- Binds to receptor proteins on the outer surface of the plasma membrane - G - Protein coupled receptors a good example
- This activates systems within the cytoplasm which mediate the actions of the hormone
Non steroid hormone action RE: Second messengers?
- Many different 2nd messenger systems
- Cyclic adenosine monophosphate (cAMP) is the best known
- Many 2nd messenger systems involve kinase enzymes which add phosphate groups to proteins (phosphorylation) thus changing its 3D shape and usually activating it.
What is up regulation?
Means number cell receptors is increased
Sensitivity to hormone is increased
What is down regulation?
Reduces number of cell receptors:
- Cell less sensitive to hormone
- Happens with long term exposure to high hormone concentrations
What are the four possible outcomes of hormone interaction?
- Antagonistic
- Additive
- Permissive
- Integrative
What is an antagonistic interaction?
When opposing hormones interact:
- effects are weaker than those produced by either hormone acting unopposed
Response is attenuated
What is an additive interaction?
Hormones add together to increase effect
What is a permissive interaction?
First hormone needed for the second one to have an effect
What is an integrative interaction?
Hormones have different complimentary effects.
