Download Hydrophilic Insulin Vasopressin Oxytocin Hydrophilic Adrenaline

ENDOCRINOLOGY
PRINCIPLES OF ENDOCRINE FUNCTION
Intercellular Communication
 The way in which signals are transmitted are classified by 2 criteria:
1. Type of secreting cell
2. Route taken by signal in reaching target
 5 types of signalling:
Type
Distance
Type of cell
Description
Endocrine
Long
Synaptic
Endocrine cells
Hormones transported via bloodstream /
hemolymph to target cells throughout body.
Neurons
Neurotransmitters diffuse vry short distance
across synaptic cleft to target
Neuroendocrine
Neurosecretory
cells
(specialised
neurons)
Paracrine
Endocrine cells
Short
Autocrine
Endocrine cells
Neurohormones secreted from nerve cell
endings into bloodstream and transported
to target cells throughout body.
Local regulators reach nearby target cells
via diffusion through extracellular fluid
Local regulators diffuse & bind to secreting
cell itself
Types of Hormones
 Hormone molecules vary in size & chemical properties:
Polypeptide
(Proteins & Peptides)
Function
Maintain homeostasis
Mediate response to environmental
stimuli
Regulates growth & development
Sensation, movement
Memory & cognition
Water balance
e.g. ADH, Oxytocin, Releasing
hormones from hypothalamus,
epinephrine from adrenal medulla
Physiological processes:
Blood pressure regulation
Nervous system function
Reproduction
Hydrophilic
Insulin
Most are formed by cleavage of one long
Vasopressin
polypeptide chain.
Oxytocin
Hydrophilic
Adrenaline /
Epinephrine Synthesised from a single amino acid (Tyrosine
insulin
Amines
adrenaline
Hydrophobic
Thyroxine
Hydrophobic
Cortisol
Ecdysteroid
Estradiol
Steroid
or tryptophan)


Derived from cholesterol
Contain 4 fused C rings

Action mechanism differ according to solubility:
Hydrophilic
Location of
Cell surface membrane
receptor
Transport
Dissolve in bloodstream and transported freely
mechanism
Hydrophobic
Intracellular (cytoplasm / nucleus)
Binds to transport proteins that keep them soluble
Pathway
1. Hormone binds to signal receptor.
2. This triggers responses including:
 Cytoplasmic response
Activation of enzyme
Change in uptake / secretion of molecules
Rearrangement of cytoskeleton
 Gene regulation
Alter transcription of genes
**Which in turn cause cytoplasmic response
Onset of
effect
Fast
Adrenaline
1. Hormone diffuses into cell and binds to intracellular
signal receptor.
2. Intracellular receptors perform entire task of
transducing signal.
3. This triggers response including:
 Gene regulation
Slow
(Takes time for gene products to bulid up / become depleted)
Steroid – Estrogen
Example
1. Adrenaline binds to GPCR of target cells in liver.
2. This triggers synthesis of cAMP which activates
protein kinase A.
3. Protein kinsase A
 Activates enzyme required for glycogen
breakdown.
 Inactivates enzyme required for glycogen
synthesis
4. This results in increased glucose levels.
1. Estrogen binds to receptor in cytoplasm.
2. Hormone-receptor complex formed moves into
nucleus.
3. Receptor portion of the complex alters transcription
of particular genes by interacting with a specific
DNA-binding protein / response element in the DNA.