Neurohormones Flashcards
What are neurohormones?
Compound neurotransmitters that are released from the brain neurons, not into the synapse, directly into the blood circulation.
How do neurohormones act?
They circulate around the blood and diffuse out of the capillaries and act on receptors for the neurohormone. It can have a potential widespread effect all around the body.
What are the two main control systems in the body?
- Endocrine system
- Nervous system
How does the endocrine system work?
- Mediators travel within blood vessels
- Utilises chemical mediators (hormones)
- Slow communication
- Effects can be long-lasting
How does the nervous system work?
- Signalling along nerve fibres
- Transmission of electrical impulses
- Fast communication
- Effects are generally short-acting
Which cells produce neurohormones?
Produced by specialised nerve cells called neurosecretory cells and released into the blood.
Why are neurohormones defined as hormones?
They are defined as hormones as they are secreted into the blood and have their effect on cells some distance away.
What is different about neurohormones and normal hormones?
They can also act as neurotransmitters or as autocrine (self) or paracrine (local) messengers
What are the three types of hormones?
- Protein and peptide hormones
- Amino acid derivatives
- Steroid hormones
Protein and peptide hormones
- Vary considerably in size
- Can be synthesised as a larger precursor and processed prior to secretion (e.g. GH, somatostatin, insulin)
- Can be post-translationally modified (e.g. Glycosylation)
- Can have multiple subunits synthesised independently and assembled (e.g. FSH, LH, TSH)
Amino acid derivatives
- Mostly tyrosine derived
- Neurotransmitter that can also act as a hormone
- E.g. epinephrine, norepinephrine and dopamine
Steroid hormones
- Steroid is a class of lipids derived from cholesterol
- Include cortisol, aldosterone, testosterone, progesterone, oestradiol
What are the principle endocrine organs of the body?
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Adrenal gland
- Pancreas
- Ovary
- Testes
What hormones does the hypothalamus release?
Thyrotrophin-releasing hormone, GnRH, CRH, GHRH, Prolactin-inhibiting factor (dopamine), somatostatin
What hormones is released from the anterior pit?
Thyroid-stimulating hormone, LH, FHS, GH, Prolactin and adrenocorticotrophin
WHat hormones are released from the posterior pit?
Vasopressin and Oxytocin
Hormones released from thyroid gland
Thyroxine
Triiodothyronine
Calcitonin
Hormones released from parathyroid glands
PTH
Hormones released from adrenal cortex of adrenal gland
Aldosterone
Cortisol
Hormones released from adrenal medulla of adrenal gland
Adrenaline
Noradrenaline
Hormones from pancreas
Insulin
Glucagon
Somatostatin
Hormones from ovary
Oestrogen
Progesterone
Hormones from testes
Testosterone
Where are neuropeptides most important?
They are functionally important transmitters in the hypothalamo-pituitary axis
What are the two components of the HPA?
Anterior and posterior pituitary
What is the capillary network system in the hypothalamus?
The hypophyseal portal circulation - this connects to another portal system in the anterior pituitary.
How does the hypophyseal portal circulation work with the neurohormones?
- There are neurons that project and release neurohormones directly into the portal system in the hypothalamus.
- Once released, the neurohormones are transported along the system and activate receptors in the anterior pituitary which release other neurohormones into blood circulation.
- These are circulated throughout the body and activate other receptors
How is the posterior pituitary connected to the hypothalamus differently?
It is connected through neurons called magnocellular neurons that project from the hypothalamus directly to the posterior pituitary. This is called the hypophyseal nerve tract.
Why type of rhymthms are most endocrine hormones?
Periodic rhythms
Circadian rhythms
- Based on a 24-hour cycle
- Example: secretion of cortisol, GH, PRL
- Blood cortisol levels fluctuate throughout the day - it’s highest in the morning and decreases after this. Before bed, there is another increase.
Pulsatile (ultradian) rhythms
- Periodicity of less 24 hours (usually 1/2-2 hours)
- e.g. secretion of gonadotrophins in adults
Infradian rhythms
Periodicity longer than 24 hours e.g. Menstrual cycle
Where are the neuroendocrine secretory cells?
Scatted in the hypothalamus but key nuclei are the medial pre-optic, the arcuate and the paraventricular nuclei
What are the hypothalamic neurohormones that control the anterior pituitary?
- Corticotrophin Releasing Hormone (CRH)
- Thyrotrophin releasing hormone (TRH)
- Gonadotrophin Releasing Hormone (GnRH)
- Growth Hormone Releasing Hormone (GHRH)
- Growth Hormone Releasing Inhibiting Hormone (Somatostatin)
- Dopamine
What is the CRH?
41 amino acid peptide that controls the release of adrenocorticotrophin (ACTH)