Lecture Six Flashcards
What do the main regulatory centres include (nervous system)?
-Nervous System
-Somatic Nervous System – voluntary system, skeletal muscle contraction
oAutonomic Nervous System – involuntary system, maintains a state of homeostasis (steady state)
-Sympathetic System = “fight-or-flight”
-Prepares the body for strenuous situations (e.g. physical activity)
-Parasympathetic System = “rest and digest”
-Assists during the quiet phases (e.g. digestion)
What are the similarities between the Nervous & Endocrine system?
- Both systems use the brain and hypothalamus
- Some molecules are used as both neurotransmitters and hormones
- Both systems work to regulate bodily functions
- Some neurons secrete hormones (neurohormones)
What are the differences between the Nervous & Endocrine system?
oMode of transport
-Endocrine secretes hormones into the blood stream
-Nervous system secretes neurotransmitters which are directly released onto target cells.
oSpeed of response
-The endocrine system is slower compared to the nervous system
oDuration of response
-Hormones remain in the blood stream for min, days, weeks
-Nervous system is active for as long as the action potentials are sent
What is the role of the Endocrine System?
- Metabolism
- Control of food intake and digestion
- Tissue development n Ion levels
- Water balance
- Heart rate and blood pressure changes
- Control of blood glucose and other nutrients
- Control of reproductive functions
- Uterine contractions and milk release
- Immune system function
What are the classes of Chemical Messages and how are they produced/secreted from?
- Autocrine – Secreted from an individual cell and influences the same cell it is secreted from
- Hormonal Control- Produced by a wide variety of tissues and secreted into extracellular fluid and has a localised effect
- Neurotransmitter – Produced by neurons and secreted into the synaptic cleft and travels a short distance to influence postsynaptic cells
- Endocrine – Hormones secreted into the bloodstream, which travel some distance to target tissues
What is Chronic Hormone Secretion?
- A relatively stable concentration is maintained in the blood stream over a long time period
- e.g. Lipid-soluble hormones
What is Acute Hormone Secretion?
- Hormone concentration alters irregularly and dramatically and changes with each stimulus
- e.g. Water-soluble hormones
What is Episodic Hormone Secretion?
- Hormones are secreted at regular intervals and concentrations
- e.g. Lipid-soluble hormones
How are hormones regulated?
- Neural Activation
- Hormone Activation
- Hormone Control
What is Neural Activation, what does it cause, what happens if it stops and what do some neurons secrete?
-A neuron releases a neurotransmitter that signals the endocrine gland to release a hormone
oA stimulus causes neural action potentials to release neurotransmitters into the synapse of hormone-producing cells which stimulate the release of a hormone.
oIf the stimulus stops then the neural stimulation will stop = hormone release will stop.
oSome neurons secrete chemical messengers into the blood, these hormones are called neurohormones (neuropeptides). These can then cause the secretion of releasing hormones, primarily from the
What is Hormone Activation, what are tropic hormones and what is inhibition?
-A hormone (typically called a hormone-releasing factor) will stimulate an endocrine organ/gland to release a different hormone.
oTropic Hormones
-Stimulate the secretion of other hormones from other endocrine glands or organs.
-Inhibition – some hormones prevent the secretion of other hormones
What is Hormone Control, what are hormones sensitive to and what is inhibition?
- Circulating blood-borne molecules stimulate the release of hormones
- Hormones are sensitive to changes in blood levels of substances.
- Inhibition – often a hormone with opposing effects is secreted to inhibit the effects of the stimulating hormone.
- Hormones work together to maintain homeostasis.
What do the main regulatory centres include (endocrine system)?
-Endocrine system
oEndocrine glands secrete hormones that travel in the bloodstream to target tissues
oGreek = endo ‘within’ krino ‘to secrete’
oAllows cells to communicate with each other
What does an increased demand for a hormone cause?
-Increased demand for a hormone causes appropriate stimuli to induce the endocrine gland to secrete a hormone
When a hormone has done its job what does it need to be?
- Removed from circulation
- The endocrine gland must receive an inhibitory message
How is regulation of a stimulus for homeostatic control done?
-Regulation of this stimuli and inhibition in order to maintain homeostatic levels of hormones are done by two major mechanisms;
o Positive Feedback
o Negative Feedback
What is a positive feedback?
- When a hormone:
1. Stimulates their target cell AND
2. Promotes the synthesis and secretion of the hormone = further secretion of the hormone. - Self-propagating system.
What is a negative feedback?
-Most common regulatory mechanism.
-Hormone secretion is inhibited by itself when there
are adequate hormone levels in the blood.
-Self-Limiting system.
What do hormones bind to?
-Hormones bind to receptors (proteins) on the target cells.
What do hormones only stimulate and what do they bind to?
- Generally, hormones can only stimulate those cells that have the matching receptor.
- Some hormones can bind to many (family) receptors which have similar structures.
How do you decrease and increase sensitivity to a hormone?
- Decrease sensitivity to a hormone by ‘down-regulation’ whereby the number of receptors decrease.
- Increased sensitivity through ‘up-regulation’ results from the increase in the rate of receptor synthesis.
What is the hypothalamus, what does it receive and what is it connected to?
- Is a major control site of the nervous and endocrine systems.
- It receives information from hormones, emotions and the central nervous system.
- The hypothalamus is connected to the pituitary gland by an extension = infundibulum.
