Neurohormones Flashcards
What are neurohormones?
Neurohormones are neurotransmitters, released from brain neurons directly into the bloodstream
How do neurohormones produce their effect?
Neurohormones circulate in the bloodstream and diffuse out of capillaries and act on their receptors to produce an effect
How does neurohormone release directly into the blood stream affect their effects?
Point to point communication
- Fast, restricted
Neurons of secretory hypothalamus
- slow but widespread effect throughout body
Networks of interconnected neurons Autonomic Nervous System
- fast, widespread influence
Diffuse modulatory systems
- slower, widespread
What are the 2 main control systems of the body?
- Endocrine system
- Nervous system
Describe the endocrine system
Endocrine System
- Mediators travel within blood vessels
- Utilises chemical mediators (hormones)
- Slow communication
- Effects can be long-lasting
Describe the nervous system and its effects
Nervous System
- Signalling along nerve fibres
- Transmission of electrical impulses
- Fast communication
- Effects are generally short-acting
How are neurohormones produced?
Neurohormones are produced by specialised nerve cells called neurosecretory cells and released into the blood
What is the significance of neurohormones?
Because they are defined as hormones, they are secreted into the blood and have their effect on cells some distance away, but the same compounds can also act as neurotransmitters or as autocrine (self) or paracrine (local) messengers.
=> endocrine and nervous system
A number of these peptides act as both hormones and neurotransmitters
Sometimes the endocrine and neural functions are linked in others they are not
What are the principal endocrine organs of the body?
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid glands
- Adrenal gland
- Pancreas
- Ovary (F)
- Testes (M)
What hormones are released from the Hypothalamus?
- TRH (thyrotrophin-releasing hormone)
- GnRH (Gonadotrophin-releasing hormone)
- CRH (Corticotrophin-releasing hormone)
- GHRH (Growth hormone releasing hormone)
- Prolactin-inhibiting factor (Dopamine)
- Somatostatin
Which hormones are released from the anterior pituitary?
Anterior pituitary:
- TSH (thyroid stimulating hormone)
- LH (Luteinising hormone)
- FSH (Foliicle stimulating hormone)
- Growth hormone
- PL (prolactin)
- ACTH (adrenocorticotrophin)
Which hormones does the posterior pituitary release?
The 2 important neurohormones released via the posterior pituitary are:
- Vasopressin (ADH)
- Oxytocin
Which hormones are secreted from the adrenal cortex of the adrenal gland?
- aldosterone
- cortisol
Which hormones are released form the adrenal medulla of the adrenal gland?
- epinephrine (adrenaline)
- norepeinephrine (noradrenaline)
Which hormones are released from the pancreas?
Insulin, Glucagon and somatostatin
Which hormones are released from the gonads?
Ovaries:
- Oestrogens, progesterones
Testes:
- Testosterone
What are the different types of hormones?
- Protein and peptide hormones
- Amino acid derivatives
- Steroid hormones
Outline the features of peptide and protein hormones
Protein & Peptide Hormones
- Vary considerably in size
- Can be synthesised as a large 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)
Describe the features of amino acid derived hormones
Amino Acid Derivatives
- Mostly tyrosine derived
- Neurotransmitter that can also act as a hormone
E.g. epinephrine, norepinephrine, dopamine
What are steroid hormones?
Steroid is a class of lipids derived from cholesterol
Include cortisol, aldosterone, testosterone, progesterone, oestradiol
Where are neurohormones functionally required?
Neuropeptides (neurohormones) are functionally important transmitters in the Hypothalamo-pituitary axis
What are the 2 components of the HPA axis?
The HPA has 2 components (anterior and posterior pituitary)
How is the anterior pituitary connected to the hypothalamus?
Hypothalamus contains a network of blood vessels
The hypophyseal portal circulation connects to the adenohypophysis portal circulation in the anterior pituitary
⇒ project and release neurohormones into the portal capillary system, which activate their specific receptors, to induce further neurohormone release
How does the hypothalamus connect to the posterior pituitary?
The posterior pituitary is connected to the hypothalamus via magnocellular neurons
Describe the release of GnRH from the hypothalamus to the anterior pituitary
GnRH is released from the hypothalamus into the anterior pituitary, via the portal system to activate release of FSH and LH → acts on gonads
GHRH is also released directly into the capillary system to stimulate release of growth hormone
How is CRH released to the anterior pituitary?
CRH is a peptide released directly into the portal system and acts on the anterior pituitary to release ACTH. ACTH stimulates cortisol release from the adrenal cortex
Describe the release of TRH from the hypothalmus
TRH released into portal circulation from hypothalamus onto the anterior pituitary to induce TSH release which acts on thyroid to stimulate thyroxine release
How are the posterior pituitary hormones released?
In the posterior pituitary, activated magnocellular neurons cause the release of 2 neurohormones (ADH, oxytocin)
Describe the effects of the posterior pituitary hormones
ADH acts on the kidneys, producing an antidiuretic effect and water retention
Oxytocin acts on the uterus to induce uterine contractions or on the mammary glands induces milk ejection
Describe the endocrine rhythms
Most, if not all, bodily activities show periodic rhythms or cyclic changes
Many of the hormones show periodicity
What are circadian rhythms?
Circadian Rhythms: based on a 24-hour cycle
E.g. secretion of cortisol, GH, PRL
What are ultradian rhythms
Pulsatile (ultradian rhythms): periodicity of less 24 hours (usually every ½ - 2 hours)