Basic understanding of biochemistry rolls in the endocrine and nervous system, bringing “neuro” and “endocrine”
together. Neuroendocrine Cancer is both these aspects, I’m hoping to explain why both are involved.
The aim of this post is to gain a basic understanding of how these systems work together in a normal setting, ie a
healthy person, so that one can begin to master their endocrine systems and autonomic function and maybe
understand their pathology a little better. I’m trying to make this as simple as possible. I skipped info out on purpose to
spare paragraphs & relevance.
The Limbic System
So, what is the Limbic system? The Limbic system is a complete set of structures that lie just below the cerebrum in the brain. It has several parts to it including the hippocampus, amygdala and hypothalamus.
HYPOTHALAMUS FOCUS:
The hypothalamus is a tiny part of the Limbic system, but it
is very busy. It is located at the base, just above the pituitary
It is responsible for:
* Mostly homeostatic activity - it is like the body’s thermostat
* Regulates hunger, thirst, anger, pleasure & other emotions
* Regulates the autonomic nervous system: pulse, blood pressure & breathing
The hypothalamus receives direct sensory inputs from skin etc and inputs from the forebrain, and inputs signals back
to the autonomic nervous system and pituitary gland.
RECEIVES:
* From the vagus nerve it receives information about blood pressure and things like how full your belly is
* From the skin it receives information about body temperature
* From the optic nerve it receives information about light and dark ( this impacts your pineal gland & melatonin production)
* From neurons in the ventricles it receives information about the contents of cerebrospinal fluid, including toxins
that lead to vomiting (a natural response to being poisoned)
* Senses Leptin, released by fat cells. If we overeat, it tells our body with leptins to decrease our appetite
INPUTS:
The hypothalamus sends signals/instructions to two different systems
1. To the autonomic nervous system.
This controls blood pressure, heart rate, breathing,digestion, sweating, and all the sympathetic & parasympathetic functions.
The Autonomic Nervous System is made up of two parts opposite to each other;
Sympathetic Nervous System (SNS):
Starts in the spinal cord and travels to a variety of areas in the body. Its function is to prepare the body for vigorous
activity associated with “fight”, “fight” and “freeze”.
Activation of the SNS responds by:
- Dilates pupils
- Opens eyelids
- Dilates blood vessels in large muscles while restricts
elsewhere
- Increase heart rate
Stimulates sweat glands
- Opens up lungs (bronchial tubes)
- Inhibits secretion in the digestive system
Parasympathetic:
Roots for the parasympathetic nervous system are in the
brainstem of the spinal cord of the lower back. The
parasympathetic’s function is to pull the body out of what
the SNS has put it into.
Parasympathetic arousal includes:
- Pupils constructing
- Excess salivary glands
- Stimulates stomach secretions & other activity of the
intestines
- Stimulates secretion in lungs
- Constricts bronchial tubes
- Decrease heart rate
As we can see, this is why Dysautonomia (autonomic dysfunction such as POTS) has complex symptoms that present similar to Carcinoid Syndrome.
Adrenal Medulla:
The SNS stimulates the adrenal medulla to respond to information by pumping epinephrine (cortisol) into the
bloodstream. This triggers the release of glucose, the epinephrine subsides and tells the hypothalamus to activate
the...... HPA axis (the hypothalamus telling the endocrine system to go go go!!)
2. To the pituitary gland
The hypothalamus is neurally and chemically connected to the pituitary, it pumps hormones called releasing factors or regulatory hormones into the bloodstream The hypothalamus releases regulatory hormones into the
bloodstream ready for delivery to the anterior lobe of the pituitary gland.
The hypothalamus produces 7 regulatory hormones used to make your Endocrine glands do their job! These hormones
are : CRH/CRF, TRH, GH-PH, GH-IH, PFR, GnRH, PIH. The hormone is then “converted” to appropriate glands
individually so they can function. So essentially your hypothalamus makes the biochemical needed for the
pituitary to make another biochemical, to make a gland function... like dominos.
Endocrine glands function from the hormones signalled to them from the pituitary:
ACTH (adrenocorticotropic hormone) : stimulates the
adrenal glands to produce glucocorticoids (cortisol)
TSH (thyroid stimulating hormone): tells the thyroid to make
thyroxine which essentially stimulates metabolism to all the
body tissue
GH (growth hormone): peptide hormone that stimulates
growth and cell
production- for bones, muscles& other tissues
PRL (prolactin) : tells mammory glands to lactate
FSH & LH (luteinizing hormone & follicle stimulating
hormone): essential for reproduction. Stimulates Inhibin & testosterone for males, and estrogen, progesterone &
inhibin for females.
The hypothalamus also releases Direct Release Hormones into the posterior lobe of the pituitary. These stimulate
production of:
ADH (vasopressin one of many names): its role is to conserve fluid volume via the kidneys.
No ADH productionleads to Diabetes Insipidus.
OXT (oxytocin peptide hormone): acts on mammory &prostate glands
We can draw to a conclusion that one thing will take play on another, it is a system we are working with here after all, not an individual organ. It is easier to find tumours when you know how to follow your yellow brick road.
Remember that blood always flows in the same direction so one thing where there is an issue, there may be a negative feedback to the complimentary gland or organ in that direction. Liver NETs are a classic example of blood flow, the serotonin is excreted from the NET in the bloodstream and headed directly to the right heart valves. Another thing to consider with cortisol tests is your circadian clock, are your bloods
appropriate to yours? Your circadian clock is an internal timer as to how your body normally functions i.e., if you
have a regular bedtime, melatonin from the pineal gland will begin to release half an hour or so before your regular bed
time and you begin to “want” to go to bed. So a night shift worker needs to consider this factor. Obviously there is a lot more to this, but I hope it helps gain
some kind of insight as to how your endocrine system relates to your nervous system and the world around you
(stress!)
