Lectures 5-8
Lecture 5 - Hormones
- hormones can travel all throughout the body
- A.A Berthold - removing testes from a developing rooster, it became more docile capon
- hormones: chemicals secreted by one cell group that travel through the bloodstream to act on
targets (organs, cells)
- typically released by glands
- endocrine glands: release hormones within the body
- exocrine glands: use ducts to secrete fluid such as tears and sweat outside the body
Hormonal vs neural signaling
- Synaptic: or endocrine signaling involves chemical release and diffusion across a
synaptic cleft
- Endocrine: signalling involves hormones being released into the bloodstream to act on
target tissues
Principles of hormone action
- Act in gradual fashion
- Act by changing the probability/intensity of a behaviour (not like on/off switch)
- Relationship between behaviors and hormones is reciprocal
- A hormone can have multiple effects and one behaviour can affect several hormones
- Hormones have a pulsatile secretion pattern - in bursts
- Some hormones are controlled by circadian clocks
- Hormones can interact with other hormones and change their effects
Hormonal vs neural signaling
- Similar in 3 basic ways:
- Neurons and endocrine glands produce and store chemicals
(neurotransmitters or hormones) and release them upon stimulation
- Neurotransmitters and hormones both bind to receptors to stimulate target
cells
- Some chemicals can act as either hormones or neurotransmitters, depending
on where they are released Ex. norepinephrine
- Differ in 4 basic ways:
- Neural communication travels to precise destinations. Hormonal
communication spreads throughout the body, and is picked up by cells within the
proper receptor
- Neural messages are rapid, spread in milliseconds. Hormonal messages are
slower, measured in seconds and minutes
- Distance traveled varies - the synaptic cleft is small while hormones may travel
over a meter
- Neural communications are sometimes under voluntary control, while hormones
are involuntary
Major classes of hormones
, Based on chemical composition, not function.
- Peptide/protein hormone - a strong of amino acids i.e. insulin
- Monoamine hormones - a modified amino acid, found in brain as neurotransmitters a
well i.e. norepinephrine
- Steroid hormones - four rings of carbon atoms i.e. testosterone
Effects of hormones on cells
- Unlike many neurotransmitter receptors, hormone receptors are not ion channels
- Rather than affecting the membrane potential, when hormones bind to their receptors
that trigger the release of intracellular second messenger
- Hormones considered first messenger
- These second messengers spread throughout the cell and cause a variety of
physiological changes
- Changes metabolism, hormone release receptor trafficking, cell growth
- Second messenger mediated effects inode cell are rapid
Effect of steroid hormones on cells
- Steroid hormones (like testosterone, esterogen, cortisol etc) are all made from
cholesterol, a fatty substance
- Steroid hormone receptors are inside the cell, usually floating freely within the the
cytoplasm
- The steroid receptor complex bind to DNA and acts as a transcription factor
- Controlling gene expression
- Transcription factor mediated mechanisms are slow, but effects are long-lasting
Effects of hormones on organs
Three basic categories:
- Hormones may promote proliferation, growth and differentiation of cells
- Hormones may modulate cell activity and metabolism
- Hormones may modulate hormone secretion from endocrine glands
Hierarchical control of hormones
- 4 levels
- Hypothalamus
- Pituitary gland
- Target endocrine glands
- Target organs and tissues
- Hormones affect almost every neuron in the brain
- Can also influence genetic expression, synthesis of proteins
The pituitary gland
- The pituitary gland is the ‘master gland’ of the body, secreting hormones that affect
function of glands and organs throughout the entire body
- Is located at the base of the brain and connected to the hypothalamus to by the
pituitary stalk
- There are two parts of the pituitary gland
- Anterior pituitary: connected to the hypothalamus by blood vessels
- Posterior pituitary: directly connected to hypothalamus by axons extending
from hypothalamic neurons
Lecture 5 - Hormones
- hormones can travel all throughout the body
- A.A Berthold - removing testes from a developing rooster, it became more docile capon
- hormones: chemicals secreted by one cell group that travel through the bloodstream to act on
targets (organs, cells)
- typically released by glands
- endocrine glands: release hormones within the body
- exocrine glands: use ducts to secrete fluid such as tears and sweat outside the body
Hormonal vs neural signaling
- Synaptic: or endocrine signaling involves chemical release and diffusion across a
synaptic cleft
- Endocrine: signalling involves hormones being released into the bloodstream to act on
target tissues
Principles of hormone action
- Act in gradual fashion
- Act by changing the probability/intensity of a behaviour (not like on/off switch)
- Relationship between behaviors and hormones is reciprocal
- A hormone can have multiple effects and one behaviour can affect several hormones
- Hormones have a pulsatile secretion pattern - in bursts
- Some hormones are controlled by circadian clocks
- Hormones can interact with other hormones and change their effects
Hormonal vs neural signaling
- Similar in 3 basic ways:
- Neurons and endocrine glands produce and store chemicals
(neurotransmitters or hormones) and release them upon stimulation
- Neurotransmitters and hormones both bind to receptors to stimulate target
cells
- Some chemicals can act as either hormones or neurotransmitters, depending
on where they are released Ex. norepinephrine
- Differ in 4 basic ways:
- Neural communication travels to precise destinations. Hormonal
communication spreads throughout the body, and is picked up by cells within the
proper receptor
- Neural messages are rapid, spread in milliseconds. Hormonal messages are
slower, measured in seconds and minutes
- Distance traveled varies - the synaptic cleft is small while hormones may travel
over a meter
- Neural communications are sometimes under voluntary control, while hormones
are involuntary
Major classes of hormones
, Based on chemical composition, not function.
- Peptide/protein hormone - a strong of amino acids i.e. insulin
- Monoamine hormones - a modified amino acid, found in brain as neurotransmitters a
well i.e. norepinephrine
- Steroid hormones - four rings of carbon atoms i.e. testosterone
Effects of hormones on cells
- Unlike many neurotransmitter receptors, hormone receptors are not ion channels
- Rather than affecting the membrane potential, when hormones bind to their receptors
that trigger the release of intracellular second messenger
- Hormones considered first messenger
- These second messengers spread throughout the cell and cause a variety of
physiological changes
- Changes metabolism, hormone release receptor trafficking, cell growth
- Second messenger mediated effects inode cell are rapid
Effect of steroid hormones on cells
- Steroid hormones (like testosterone, esterogen, cortisol etc) are all made from
cholesterol, a fatty substance
- Steroid hormone receptors are inside the cell, usually floating freely within the the
cytoplasm
- The steroid receptor complex bind to DNA and acts as a transcription factor
- Controlling gene expression
- Transcription factor mediated mechanisms are slow, but effects are long-lasting
Effects of hormones on organs
Three basic categories:
- Hormones may promote proliferation, growth and differentiation of cells
- Hormones may modulate cell activity and metabolism
- Hormones may modulate hormone secretion from endocrine glands
Hierarchical control of hormones
- 4 levels
- Hypothalamus
- Pituitary gland
- Target endocrine glands
- Target organs and tissues
- Hormones affect almost every neuron in the brain
- Can also influence genetic expression, synthesis of proteins
The pituitary gland
- The pituitary gland is the ‘master gland’ of the body, secreting hormones that affect
function of glands and organs throughout the entire body
- Is located at the base of the brain and connected to the hypothalamus to by the
pituitary stalk
- There are two parts of the pituitary gland
- Anterior pituitary: connected to the hypothalamus by blood vessels
- Posterior pituitary: directly connected to hypothalamus by axons extending
from hypothalamic neurons
