Lecture One; How Hormones Work Flashcards
Give a brief overview of the function and properties of the endocrine system;
- Maintains homeostasis
- Cell;Cell communication
- Integrates with nervous system (neuroendocrinology) to maintain homeostasis
How does the nervous and endocrine system maintain homeostasis?
Nervous system: Responses are rapid short lived, triggered by change in environment
Endocrine system; Takes time, generates hormones to induce physiological changes of specific tissues. Can persist for a long time depending on the hormones
Define a hormone;
A chemical substrate released into circulation that acts a specific receptor and cell and creates the receptor induced response
“Classical endocrine signalling”
What is variation 1/3 for classical endocrine signalling?
Some neurons produce hormones that act in the classical endocrine signalling manner.
- These are neurohormones and are a variation because they are not produced by classical endocrine tissue
What is variation 2/3 for classical endocrine signalling?
Paracrine signalling; Hormones that act on another endocrine cell / neighbouring cell (paracrine event)
What is variation 3/3 for classical endocrine signalling?
Autocrine signalling; Hormones synthesised and stimulates the same self (autocrine event)
What are the classes of receptors that hormones can act on;
Intracellular Receptors
Extracellular Receptors
What are the types of hormones?
Peptide hormones
Steroid/Lipid hormones
Describe protein hormones;
Hydrophilic, act on extracellular receptors because they are lipophobic and cannot diffuse through the plasma lipid membrane.
Use secondary messenger cascades
Write brief notes on steroid/lipid hormones;
Hydrophobic, carrier transporters allow movement in blood i.e albumin, SBHG then diffuse into the cell and act on intracellular receptors
Binding affinity of receptors must be greater than that of transporter.
How are hormone receptors classified?
Based on structure
List the hormone receptors;
7 transmembrane receptor (GPCR)
Single transmembrane spanning receptor
Dimer (single spanning receptor)
Describe the 7 transmembrane receptor.
7 transmembrane protein with EC N terminus that hormones bind to.
This results in a conformational change activating the G subunits, which is further propogated by PKC etc to have nuclear effects
Whats a common affect following receptor/GPCR activation?
Raised IC cAMP levels.
Describe single spanning receptor;
One transmembrane protein with IC intrinsic kinase activity
Discribe the dimer;
- Two receptors i.e insulin that requires to molecules to be activated
- Changes in conformation of IC tyrosine kinase domains, which then phosphorylate residues on itself (autophosphorylation)
What do hormones typically do?
Once bound to receptors they alter gene expression, thus mRNA and proteins formed.
Regulate homeostasis!
What are the three endocrine reflexes?
1) Humoral stimuli (changes in ECF, i.e BG, ions, Temp)
2) Hormonal Stimuli (Arrival or removal of specific hormones)
3) Neural stimuli (Neuroglandular junctions - neurotransmitter stimulates H. release)
Once hormones achieve their purpose, what happens?
Endocrine reflexes must be turned off; Negative feedback
Direct or Indirect
What is the first step in negative feedback loops?
The endocrine cell responds to a disturbance in homeostasis by releasing its hormone into the circulatory system.
What is the second step in negative feedback?
The released hormone stimulates a target cell.
What is the third step in negative feedback?
The target cell releases regulatory hormones that eliminate the release of more hormone and eliminates endocrine cell stimuli. Also restores homeostasis
Give an example of negative feedback;
Glucose consumption
- Raised BG
- Beta cells in pancreas are stimulated and release Insulin
- Blood glucose falls and stimulus for insulin is stopped from being produced (negative stimulus)
Describe feedback loops
Direct (short)
Indirect (long)
Complex (long) negative feedback loops are most common in hormones and they can become severely complicated
Give the example of the stress response as negative feedback;
Hypothalamus - CTRH A. pituitary - Corticotrophin Adrenal Cortex - Cortisol
Cortisol has negative feedback on AP (D) and Hyp (Ind)
Corticotrphin acts on Hyp (D) via negative feedback
Does positive feedback play a role in hormones?
Oxytocin and Ovulation are examples of hormonal positive feedback
What is positive feedback limited to?
Hormone regulation through positive feedback is restricted to processes that must be rushed to completion
What is positive feedback?
The secretion of a hormone produces an affect that further stimulates hormone release.
Give an example of positive feedback;
Hyp. - GnRH A. Pituitary - LH Ovaries - Estradiol
Estradiol acts on A.pituitary positively
How is the brain critical in endocrine regulation?
Hyp. is key for homeostasis as it receives majority of sensory input and detects a lot
How does the hypothalamus respond to changes in homeostasis?
Hypothalamus responds by regulation pituitary gland hormones and neural projections to endocrine glands
What is the first hypothalamus action/regulation?
Neurons in the hypothalamus synthesise regulatory hormones which travel through the MEDIAN EMINANCE and act on the A.pituitary (Synthesises activating or inhibiting hormones)
What is the second hypothalamus action/regulation?
Neurosecretory neurons synthesise store and secrete hormones. (ADH and Oxytocin(
What is the third hypothalamus action/regulation?
Through nervous system (ANS), it can DIRECTLY regulate adrenal medulla release of corticotrophins
Direct Control
What are the anterior hypothalamic nuclie?
Sup.
PVN
SCN
SON
PON
Inf.
What are the posterior hypothalamic nuclie?
Sup.
DMN
VMN
AN
Inf.
