Download Lecture 13 – Endocrine System 1

Lecture 13 – Endocrine System 1
Slower process, more widespread, longer lasting
Organs & tissues of the endocrine system
Compare & contrast the nervous & endocrine systems
Nervous system
Neurotransmitters
Delivery via synapse
Endocrine system
Hormones
Delivery via bloodstream
Similarities
Specific receptors
Noradrenaline, Adrenaline
Maintains homeostasis
Regulated by negative feedback
Compare the major chemical classes of hormones
Amino acid derivatives
Hormones are divided into 3 groups based on their chemical structure
The chemical composition determines how it can travel in the blood & how it interacts with a
specific cell
 Water soluble – travel in the blood in their own state as blood is water based
Amin acid hormones
Also referred to as
amine hormones.
Amine hormones
are synthesized
from the amino
acids tryptophan or
tyrosine
Peptide/Protein
Steroid hormones
hormones
Consist of short
The primary hormones derived from lipids
chains of amino acids are steroid hormones & are derived from the
whereas protein
lipid cholesterol.
hormones are longer No soluble in water (hydrophobic)  must
polypeptides
travel to their target cell bound to a transport
protein
Peptide hormones
Travel in the blood in their natural state
Peptide/protein hormones
Peptide hormones consist of short chains of amino acids whereas protein hormones are longer
polypeptides
 Glycoproteins – Consist of more than 200 amino acids in length & accommodate CHO side
chains. They include hormones such as thyroid stimulating hormone (TSH), luteinizing
hormone (LH), & follicle stimulating hormone (FSH) produced in the anterior lobe of the
pituitary gland
 Short
polypeptides/small proteins – this is a large & diverse group of hormones which range in
size from short chain polypeptides such as oxytocin & vasopressin, to small proteins which
includes such hormones as growth hormone & prolactin.
This group of hormones includes all hormones secreted by the hypothalamus, posterior
pituitary, heart, thymus, digestive tract & the pancreas in addition to several others
Lipid Derivatives
Steroid hormones (e.g. cortisol, oestrogen, thromboxane A2, Prostaglandin E)
The primary hormones derived from lipids are steroid hormones & are derived from the lipid
cholesterol. Steroid hormones are not soluble in water hydrophobic) therefore must travel to their
target cell bound to a transport protein


Steroid Hormones – because blood is water-based, lipid derived hormones must travel to
their target cell bound to a transport protein. This more complex structure extends the halflife of steroid hormones much longer than that of hormones derived from amino acids. A
hormone’s half-life is the time required for half the concentration of the hormone to be
degraded. E.g. the lipid-derived hormone cortisol has a half-life of approx. 60-90 mins. In
contrast, the amino acid-derived hormone adrenaline/epinephrine has a half-life of approx.
1 minute
Eicosanoids – These are important paracrine factors which are involved in the coordination
of cellular activities & enzymatic processes. Eicosanoids include leukotriene’s &
prostaglandins, the later of which can be converted into thromboxane’s & prostacyclin’s in
some tissues
Cell membrane hormone action
e.g. Catecholamine’s, peptide hormones
Hormone (first messenger)

Receptor on cell membrane

Second Messenger

Metabolic reactions to alter cell activity
G proteins & hormone activity (water-soluble)
Figure 1 (17.5) Binding of water soluble hormones
Figure 17.5 Binding of water-soluble hormones –
Water soluble hormones cannot diffuse through
the cell membrane. These hormones must bind to
a surface cell-membrane receptor. The receptor
then initiates a cell-signaling pathway within the
cell involved G proteins, adenylyl cyclase, the
secondary messenger cyclic AMP (cAMP), and
protein kinases. In the final step, these proteins
kinases phosphorylate proteins in the cytoplasm.
This activates proteins in the cell that carry out the
changes specified by the hormone
The hormone remains outside the
cell but triggers a cascade of events
Intracellular hormone action
lipid derived hormones. E.g. steroid hormones ( can diffuse straight through the cell)
Lipid hormone

Diffuses through cell membrane

Forms hormone-receptor complex

Activates/inactivates specific genes

Changes target cell structure