6. NEUROHORMONES Flashcards
1
Q
What are the 8 principal endocrine glands of the body?
A
- HYPOTHALAMUS
- PITUITARY GLAND
- THYROID GLAND
- ADRENAL GLAND
- Adrenal cortex = Aldosterone, cortisol
- Adrenal medulla = Adrenaline, noradrenaline - PARATHYROID GLAND
- PANCREAS
- OVARY
- TESTES
2
Q
What hormones does the anterior & posterior pituitary release?
A
- Anterior pituitary = ACTH, FSH, LH. TSH, GH, PRL
- Posterior pituitary = oxytocin & vasopressin (ADH)
3
Q
What hormones does the adrenal medulla & cortex release?
A
- Adrenal medulla = Adrenaline, Noradrenaline
- Adrenal cortex = Aldosterone, cortisol
4
Q
Describe the principles of the endocrine system
A
- Mediators travel in the blood stream, slow communication but long term effect
- Chemical mediators - hormones
5
Q
Describe the principles of the nervous system
A
- The nervous system has fast communication but the effects are short lasting or temporary
- Transmission of electrical impulses
6
Q
What are neurohormones?
A
- Neurohormones are produced by NEUROSECRETORY CELLS which are specialised nerve cells
- The neurohormones are then released into the blood & act on receptors at a distance
- However, neurohormones can also act as neurotransmitters, autocrine (self) or paracrine (local) factors
7
Q
Give three classes of hormones
A
- PEPTIDE/PROTEIN - synthesised as large precursors which can be cleaved or post-translationally modified.
- E.g FSH, LH, TSH - AMINO ACID DERVIATIVES - Hormones derived from tyrosine, can also act as neurotransmitters
- E.g adrenaline, noradrenaline - STEROID HORMONES - Lipids that are derived from cholesterol
- E.g sex steroids , cortisol
8
Q
How are the hypothalamus & pituitary associated?
A
- The hypothalamus & pituitary are joined by the HYPOPHYSEAL NERVE TRACT
- The infundibulum of the pituitary stalk also connects the two structures
9
Q
How do hormones released by the hypothalamus act on the pituitary?
A
- Neurohormones synthesised by the hypothalamus will be carried by neurones projecting into the pituitary
- The neurohormones will be released into the hypophyseal portal circulation which is a capillary network & portal vein system
- The hormones will then be released from the pituitary gland
10
Q
What are the two major hypothalamic neurones?
A
- Magnocellular neurones
2. Parvocellular neurones
11
Q
Describe the magnocellular neurones
A
- The magnocellular neurones project from the hypothalamus to the posterior pituitary
- The posterior pituitary is also known as neurohypophysis & produces vasopressin & oxytocin
- The cell body of the magnocellular neurones is located in the hypothalamus but it projects to the pituitary
- Magnocellular neuronal cell bodies are located in the:
1. Paraventricular nuclei
2. Supra optic nuclei
12
Q
Describe the parvocellular neurones
A
- Parvocellular neurones project from the hypothalamus to anterior pituitary
- The anterior pituitary is also known as adenohypophysis
- The neurohormones will be released from the neurones into the capillary network to activate specific cells of the pituitary
13
Q
What does corticotrophin releasing hormone do?
A
- CRH released from hypothalamus
- CRH acts on corticotrophs of anterior pituitary
- ACTH released from anterior pituitary
- Cortisol released from adrenal cortex
14
Q
What does the thyrotrophic releasing hormone do?
A
- TRH released from hypothalamus
- TRH cats on thyrotrophs of anterior pituitary
- TSH released from anterior pituitary
- Thyroid hormones released from thyroid gland
15
Q
What does growth hormone releasing hormone do?
A
- GHRH controls release of GH from anterior pituitary
16
Q
What does somatostatin do?
A
- Somatostatin/ Growth hormone inhibiting hormone inhibits the release of GH, VIP, TSH, PRL & insulin
17
Q
What are the specialised cells of the anterior pituitary?
A
- Gonadotrophs - release FSH & LH in response to GnRH
- Corticotrophs - Release ACTH in response to CRH
- Thyrotrophs - Release TSH in response to TRH
- Somatotrophs - Control LH in response to GHRH
- Lactotrophs - control PRL, in response to dopamine, somatostatin, TRH
18
Q
What is ACTH & what does it do?
A
- ACTH (adrenocorticoptrophin hormone) is released in response to CRH produced by the hypothalamus
- ACTH stimulates the release of glucocorticoids (cortisol) & sex steroids (androgens) from the zona fasciculata of the adrenal cortex
19
Q
Describe the mechanism of cortisol release via the HPA axis?
A
- CRH released from hypothalamus
- CRH acts on corticotrophs of anterior pituitary
- Anterior pituitary releases ACTH
- ACTH causes release of cortisol & adrenal androgens from adrenal cortex
20
Q
How do cortisol levels change throughout the day?
A
- Cortisol levels are highest in the morning & decline throughout the day due to the pattern of ACTH secretion from the anterior pituitary
21
Q
Describe the HP-Thyroid axis
A
- TRH released by hypothalamus
- TRH acts on thyrotrophs of anterior pituitary
- TSH released from anterior pituitary
- Thyroid hormones released from thyroid glad (T3 & T4)
22
Q
What are the two thyroid hormones?
A
- T3 - TRIIODOTHRYOXINE
- T4 - THYROXINE
- T4 can be converted to T3 with DEIODINASE
- T4 is responsible for basal metabollic rate, high T4 = weight loss
23
Q
Describe the synthesis of vasopressin & oxytocin?
A
- Vasopressin & oxytocin are released from the posterior pituitary
- They are synthesised in the supraoptic & paraventricular nuclei of the magnocellular neurones which project into the posterior pituitary, where they’re released
24
Q
What is vasopressin & it’s effects?
A
- Vasopressin is also known as antidiuretic hormone
- It’s released from the posterior pituitary in response to changes in osmoreceptors of the hypothalamus
1. Controls osmolalilty - regulates water excretion & thirst
2. Stimulates contraction of smooth muscle of the kidney to cause vasoconstriction - Both of these changes help to regulate blood volume
25
Describe RAAS & it's interaction with the hypothalamus to release ADH
1. A drop in blood pressure or plasma volume causes teh kidneys to release RENIN
2. RENIN converts ANGIOTENSINOGEN into ANGITENSIN I
3. ANGIOTENSIN I circulates in the blood & is converted to ANGIOTENSIN II
4. ANGIOTENSIN II causes vasoconstriction
5. ANGIOTENSIN II is detected by the SUB-FORNICAL REGION
6. Neuronea of the sub-fornical region project to the magnocellular neurones of the hypothalamus releasing vasopressin/ADH
7. Vasopressin affects the kidneys & increases water retention to regulate blood volume
26
What is oxytocin?
- Oxytocin is synthesised in the hypothalamus & is released by the posterior pituitary
- Oxytocin levels can elevated during lactation & mating
- Oxytocin can be produced in response to cervical stretch receptors, stroking, grooming etc.
27
What are the peripheral effects of oxytocin?
1. Stimulates contraction of uterine wall smooth muscle during labour
2. Contracts myoepithelial cells of mammary glands - lactation
3. Contracts reproductive duct during sperm ejaculation in males
28
What are the central nervous system effects of oxytocin?
- Oxytocin can be released into central areas of the brain such as the cortex
- The functions of oxytocin in these areas are not well understood, but it's thought to be involved in trust, empathy, social bonding & cognition
- It can therefore be used as treatment for autism, OCD, depression
29
Give examples of hormones that bind to a tyrosine kinase receptor?
- Growth hormone
| - Insulin
30
Describe the mechanism of action for tyrosine kinase receptors
1. (GH or insulin) Peptide hormone binds to tyrosine kinase receptor
2. Leads to dimerisation of the receptor
3. Activates tyrosine kinases (JAK2/MAPIC)
4. Tyrosine kinases phosphorylate target proteins to cause signalling cascade
31
Give examples of hormones that bind to a G-protein adenylate cyclase receptor?
- TSH
| - ACTH
32
Describe the pathway for G-protein adenylate cyclase receptors
1. TSH or ACTH bind to receptor & activate Gs or Gi protein
2. Adenylate cyclase can be stimulated or inhibited depending on G protein
3. Stimulation of AC= increased cAMP & increased PKA
4. PKA phosphorylates target proteins to cause signalling
33
Give examples of hormones that bind to a G-protein phospholipase C receptor?
- Oxytocin
| - GnRH
34
Describe the pathway for G-protein phospholipase C receptors
1. Oxytocin & GnRH bind to receptor coupled to Gq
2. Phospholipase C is activated which converts PIP2 -> IP3 + DAG
3. IP3 causes increase in intracellular Ca2+
4. DAG activates PKC which phosphorylates target proteins
35
Give examples of hormones that bind to a nuclear receptor?
- Sex steroids (testosterone, oestrogen)
| - Cortisol
36
Describe the pathway for nuclear receptors receptors
1. Steroid hormones pass through cell membrane as they're lipophillic, don't act on surface receptors
2. Bind to receptors within cytoplasm to form hormone-receptor complex
3. Hormone-receptor complex enters nucleus
4. Hormone-receptor complex acts as a transcription factor by binding to a motif in the DNA sequence
5. Initiates protein synthesis
37
What are diseases caused by too much GH & PRL?
- Too much GH = Acromegaly or Gigantism
| - Too much PRL = Hyperprolactinaemia
38
What is hyperthyroidism & hypothyroidism?
- Hyperthyroidsim = too much thyroid hormone
| - Hypothyroidism = too little thyroid hormone
39
Give an example of a hypothyroidism disease
- Hashimoto's disease = too little thyroid
- Autoimmune disease, antibodies to thyroid hormone
- Causes: Radioactive iodine treatment, thyroid surgery, pituitary dysfunction
40
Give an example of a hyperthyroidism disease
- Grave's disease = too much thyroid
- Autoimmune disease, antibodies attack thyroid gland which mimic TSH causing thyroid production
- Symptoms: fatigue, goitre, anxiety, weight loss
41
What is adrenal insufficiency & give an example of a disease
- Adrenal insufficiency is when too little adrenal hormones are produced e.g cortisol. The adrenal glands don't produce enough cortisol
- Addison's disease is an example of primary adrenal insufficiency
- Symptoms: fatigue, darkened skin, irregular menstruation
42
What is Cushing's syndrome?
- Cushing's syndrome occurs when there's too much cortisol production
- Causes:
- External steroids (medications e.g asthma)
- Surgery
- Adrenal adenoma
- Cushing's disease - produces too much ACTH leading to too much cortisol
43
What's the difference between Cushing's disease & Cushing's syndrome?
- Both Cushing's disease & Cushing's syndrome result in elevated cortisol levels but have different cortisol
- Cushing's disease can lead to Cushing's syndrom
- In Cushing's disease, a pituitary adenoma scretes too much ACTH which results in adrenal hyperplasia causing too much cortisol
- Whereas, Cushing's syndrome is simply an increase in cortisol due to other reasons
