2. Principles of Chemical Communication
• Chemical Messengers
– Allow cells to communicate with each other to
regulate activities
– 4 classes of chemical messengers based on the
source of the chemical messenger and its mode of
transport in the body
• Autocrine chemical messengers
• Paracrine chemical messengers
• Neurotransmitters
• Endocrine chemical messengers
3.
4. Characteristics of the Endocrine
System
• Composed of endocrine glands and
specialized endocrine cells located throughout
the body
• Secrete minute amounts of chemical
messengers (hormones) into the bloodstream
• Hormones travel a distance from their source
through the bloodstream to specific sites
(target tissues or effectors)
5.
6.
7. Comparison of the Nervous System
and Endocrine Systems
• Nervous system and the endocrine system
regulate and coordinate the activities of
essentially all body structures to achieve and
maintain homeostasis
– Nervous system functions as a communication
system
– Endocrine system sends information to the cells it
controls in the form of hormones, which are
carried by the bloodstream to all parts of the body
8. Similarities
• Structures associated with the brain
– E.g. hypothalamus
• Same molecule is a neurotransmitter for the
nervous system and a hormone for the
endocrine system
– E.g. epinephrine
• Work together to regulate critical body
processes
– E.g epinephrine
10. Differences
• Mode of transport
– Endocrine system secretes hormones which are
transported in the bloodstream
– Nervous system secretes neurotransmitters which
are released directly onto their target cells
• Speed of response
– Nervous system responds faster than the
endocrine
11. Differences cont.
• Duration of response
– Nervous system activates its targets quickly
– Endocrine system tends to have longer-lasting
effects
12. Hormones
• Characteristics
– Stability
• Life span of hormone varies with its chemical nature
• Expressed as half-life – amount of time it takes for 50% of
the circulating hormone to be removed from the circulation
and excreted
– Communication
• Able to regulate specific cellular pathways once they arrive
at their targets
– Distribution
• Transported by the blood to many locations
13. Chemical Nature of Hormones
• Lipid soluble
– Steroid hormones, thyroid hormones and fatty
acid derivative hormones
– Travel in bloodstream bound to binding proteins
• Water soluble
– Protein hormones, peptide hormones and most
amino acid derivative hormone
– Circulate as free hormones
– Relatively short half-lives
14.
15.
16. Patterns of Hormone Secretion
• 3 main patterns of hormone secretion
– Chronic hormone secretion
– Acute hormone secretion
– Episodic hormone secretion
• Steroid reproductive hormones
17. Control of Hormone Secretion
• 3 types of stimuli regulate hormone release
– Humoral
• Blood-borne molecules can directly stimulate the
release of some hormones
– Neural
• Involves neural stimuli of endocrine glands
– Hormonal
• Hormone is secreted that stimulates the secretion of
other hormones
23. Hormone Receptors and Mechanisms
of Action
• Hormones exert their actions by binding to
proteins called receptors
– Only can stimulate cells that have the receptor for
that hormone
– Specific
26. Classes of Receptors
• Lipid-soluble hormones bind to nuclear
receptors
– Relatively small
– Able to diffuse through the plasma membrane and
bind to nuclear receptors
27. • Water-soluble hormones bind to membrane-
bound receptors
– Large molecules and cannot pass through the
plasma membrane
– Interact with membrane-bound receptors
29. Membrane-Bound Receptors and
Signal Amplification
• Membrane-bound receptors activate
responses in 2-ways
– Receptors may alter the activity of G proteins at
the inner surface of the plasma membrane
– Receptors may directly alter the activity of
intracellular enzymes
– Second messenger system
30. Receptors that activate G Proteins
• G proteins
– 3 subunits
• Alpha, beta and gamma
• Guanine nucleotide bound to alpha subunit
– Inactive state – GDP bound
– Active state – GTP bound
35. Receptors that Phosphorylate
Intracellular Proteins
• Hormones bind to
membrane-bound
receptors.
• Part of receptor protein
on inside of membrane
acts as an enzyme to
phosphorylate proteins
• E.g., insulin receptors
bound to insulin cause
phosphorylation of
proteins and cell
responds to presence of
insulin.