Endocrine System Flashcards
Describe what a myelinated neuron looks like
Axon in the middle surrounded by myelin sheath which has been secreted by Schwann cell sitting around the outside
Describe what a non-myelinated neuron looks like
Multiple axons sitting inside a Schwann cell
Describe how a nerve impulse is transmitted
Nerve impulse generated
Voltage causes membrane structure change so voltage gated calcium channels open allowing calcium to flow freely from the presynaptic neuron into the synaptic cleft
This sets up a gradient allowing neurotransmitter containing vesicles to fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft
Sodium channels open allowing sodium to flow into the postsynaptic neuron causing ligand gated channels to open
Sodium flows from the synaptic cleft into the postsynaptic neuron, having transmitted the nerve impulse
Symptoms of the alarm response
Increased heart rate Increased sweating Pupil dilation Decreased salivation Peripheral vasoconstriction Bronchi dilation Increased blood sugar Increased blood pressure Decreased digestion
Symptoms of the relaxation response
Decreased heart rate Pupil contraction Peripheral vasodilation Bronchi constriction Increased digestion Increased salivation
Sympathetic division
Associated with
Exercise
Emotion
Excitement
Parasympathetic division
Associated with
Rest
Relaxation
Repletion
Autonomic nervous system properties
Mainly interoreceptors
Involuntary from limbic system, hypthothalamus, brain stem and spinal cord
Two-neuron pathway
Acetylecholine
Norepinephrine (postganglionic sympathetic fibres to areas other than sweat glands)
Smooth muscle, cardiac muscle, glands
Somatic nervous system properties
Special sense and somatic sense Voluntary from cerebral cortex One-neuron pathway Acetylcholine Skeletal muscle
Describe the sympathetic division innervation to effector tissues other than sweat glands
ACh travels along a cholinergic sympathetic preganglionic neuron
ACh released into autonomic ganglion where it is picked up by nicotinic receptors
ACh travels along adrenergic sympathetic poatganglionic neuron
NE released near effector cell where it is picked up by adrenergic receptors
Describe the sympathetic division innervation to sweat glands
ACh travels along a cholinergic sympathetic preganglionic neuron
ACh released into autonomic ganglion where it is picked up by nicotinic receptors
ACh travels along cholinergic sympathetic poatganglionic neuron
ACh released near sweat gland cell where it is picked up by muscarinic receptors
Describe the parasympathetic division innervation
ACh travels along a cholinergic sympathetic preganglionic neuron
ACh released into autonomic ganglion where it is picked up by nicotinic receptors
ACh travels along cholinergic sympathetic poatganglionic neuron
ACh released near effector cell where it is picked up by muscarinic receptors
Hypothalamus
Controls internal organs via autonomic nervous system and pituitary gland
Regulates behavioural patterns, circadian rhythms and body temperature
Regulates eating and drinking behaviour
HPA axis
Hypothalamus
Pituitary
Adrenal glands
Paracrine hormone
Released by paracrine cell to be used by a nearby cell
Autocrine hormone
Released by autocrine cell to be used by the original cell
Describe control of hormone release
Synthesis, storage and release of hormone into blood by hormone producing cell Travels through the bloodstream to target cell with receptors for specific hormone to achieve desired response Hormone disposal by breakdown or excretion Feedback signal (usually negative) acts on original hormone producing cell to stop (or continue) production
Lipid soluble hormone action
Hormone cannot move through blood because it isn’t water soluble so it binds to a carrier protein to carry it through
Hormone dissociates from carrier protein and diffuses into cell through lipid membrane
Hormone binds intracellular receptor activating a receptor complex and altering gene expression
Newly formed mRNA directs synthesis of specific proteins on ribosomes
New protein alters cell activity
Water soluble hormone action
Hormone can move through blood alone
Binds to receptor on cell surface because it can’t diffuse through lipid membrane
G protein is activated which in turn activates adenyl cyclase
Adenyl cyclase is cleaved by ATP to produce cAMP which acts on protein kinases
Phosphorylation cascade occurs
Phosphorylated enzymes catalyse reactions that produce physiological response
Number of hormones synthesised by hypothalamus
9
Number of hormones synthesised by pituitary
7
Describe hypothalamic control of the pituitary gland
Hypothalamic neurosecretory cell releases hormone or hormone precursor into the top of the pituitary where they travel through hypophyseal portal veins to the secondary plexus and then to pituitary target cells
Describe how the alarm response is enhanced
Sympathetic preganglionic neuron terminates in the adrenal medulla and stimulates (via ACh) epinerphrine and NE release into the bloodstream which enhances and sustains the alarm response
Hormones from the adrenal medulla
Epinephrine and NE
Hormones from the adrenal cortex
Mineralo-corticoids e.g. aldosterone
Glucocorticoids e.g. cortisol
Describe how mineralo-corticoids work
Stimulated by increased potassium and angiotensin II which increases sodium and water levels and decreases blood potassium levels
This leads to increased blood volume and increased blood pressure
Describe how cortisol work
Stimulated by ACTH which is released from the anterior pituitary by CRH from hypothalamus
Causes resistance reaction to stress, dampens inflammation and depresses immune responses
Cortisol then negatively feeds back on CRH
7 properties of the resistance reaction (actions of cortisol)
Protein breakdown Gluconogenesis Lipolysis Resistance to stres Vasoconstriction Anti-inflammatory Immune depression
Summarise the stress response (alarm + resistance reaction)
Stressor stimulates sympathetic nerves to act on adrenal medulla to secrete NE, immediately acting on visceral effectors causing the alarm response
At the same time but slower, stressor stimulates hypothalamus to secrete CRH into primary hypophyseal plexus then portal vein to secondary plexus to anterior pituitary
Anterior pituitary releases ACTH into bloodstream which acts on the adrenal cortex to release cortisol into the bloodstream which causes the resistance reaction
Once the stressor is removed, high levels of cortisol in the blood inhibits ACTH and CRH secretion
3 links between the neuroendocrine and immune systems
Autonomic nerves
Hormones
Cytokines
Stress cardiomyopathy syndrome
Overactivation of the stress response
Habitually hostile people
Long term sympathetic activation
Heart working harder, capillaries constantly constricted
Increased risk of cardiac infarction
