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Neurohormones Flashcards

1
Q

How are neurohormones released?

A

→ DIrectly in the blood circulation

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2
Q

What is point to point communication like?

A

→ Fast and restricted

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3
Q

What are the secretory hypothalamus neurons like?

A

→ Slow but widespread

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4
Q

What are networks of interconnected neurons of the autonomic nervous system like?

A

→ Fast

→ widespread influence

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5
Q

What are diffuse modulatory systems like?

A

→ Slower and widespread

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6
Q

What are the 4 characteristics of the endocrine system?

A

→ Mediators travel within blood vessels
→ utilises chemical mediators

→ slow communication
→ long lasting effects

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7
Q

What are the 4 characteristics of the nervous system?

A

→ Signalling along nerve fibres
→ Transmission of electrical impulses

→ fast communication
→effects are short acting

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8
Q

What are neurohormones produced by?

A

→ specialised nerve cells called neurosecretory cells

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9
Q

What can neurohormones act like?

A

→ Neurotransmitters

→ autocrine or paracrine messengers

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10
Q

What are the 3 types of hormones?

A

→ Protein and peptide
→ amino acid derivatives

→ steroid hormones

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11
Q

What are the 4 features of protein and peptide hormones?

A

→ Vary considerably in size
→ Can be synthesised as large precursors prior to secretion

→ post translationally modified
→ can have multiple subunits synthesized independently and assembled

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12
Q

What are 2 features of amino acid derivative neurohormones?

A

→ Mostly tyrosine derived

→ Neurotransmitter that can also act as a hormon

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13
Q

What are 3 examples of amino acid derivative neurohormones?

A

→ adrenaline
→ noradrenaline

→ dopamine

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14
Q

Where are steroid hormones derived from?

A

→ Class of lipids derived from cholesterol

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15
Q

What are 5 examples of steroid neurohormones?

A

→ Cortisol
→ Aldosterone

→ testosterone
→ progesterone
→ estradiol

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16
Q

What is the base of the brain called?

A

→ Hypothalamus

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17
Q

What is the hypothalamus connected to?

A

→ pituitary

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18
Q

Where do magnocellular neurons project to?

A

→ posterior pituitary

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19
Q

What hormones are secreted from the posterior pituitary?

A

→ Vasopressin

→ oxytocin

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20
Q

Where are neurohormones released in the anterior pituitary?

A

→ Portal system

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21
Q

What time frame are circadian rhythms?

A

→ 24 hour cycle

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22
Q

What time frame are pulsatile rhythms?

A

→ less than 24 hours

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23
Q

What time frame are infradian rhythms?

A

→ longer than 24 hours

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24
Q

What is an example of hormones that follow the circadian cycle?

A

→ Cortisol
→ GH

→ PRL

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25
What is an example of a hormone that follows pulsatile cycles?
→ Gonadotrophins
26
What is an example of an infradian rhythm?
→ Menstrual cycle
27
Where is the pituitary?
→ Sella turcica | → in the sphenoid bone
28
Where are hypothalamic hormones secreted?
→ portal vein system | → at the median eminence
29
Describe the pathway of gonadotrophin releasing hormone?
→ neurons release GnRH → transported to the anterior hypothalamus and acts on receptors → Induces release of FSH and LH
30
Describe the pathway of growth hormone
→ Growth hormone releasing hormone is transported to the anterior pituitary →induces release of growth hormone
31
Describe the pathway of CRH
→ Corticotropin releasing hormone is a peptide released to the capillary system → it gets transported to the anterior pituitary → this releases ACTH and acts on the adrenal cortex → induces the release of cortisol
32
Describe the pathway of thyrotropin releasing hormone?
→ thyrotropin releasing hormone is delivered to the anterior pituitary → causes the release of TSH → TSH acts on the thyroid and induces the release of thyroxine
33
Describe the pathway of vasopressin
→ Magnocellular neurons release vasopressin in the posterior pituitary → Vasopressin acts on the kidney and has an anti-diuretic effect
34
Describe the pathway of oxytocin
→ Magnocellular neurons release oxytocin in the posterior pituitary → oxytocin acts on the uterus to induce uterine contraction → oxytocin acts on mammary glands to induce milk ejection
35
Describe the ACTH axis to release cortisol
→ Stress activates the HPA axis → Stress activates the hypothalamus to release corticotrophin releasing hormone (CRH) →This acts on receptors in the anterior pituitary which releases ACTH → ACTH is released in the blood → ACTH acts on receptors in the adrenal cortex to release cortisol
36
What is the effect of ACTH?
→ Mobilises energy for fight or flight
37
Describe how cortisol release is terminated
→ Cortisol induces a negative feedback effect | → It acts on cortisol receptors in the pituitary or in the hypothalamus to inhibit CRH or ACTH
38
What happens to the HPA axis during chronic stress?
→ Cortisol levels are increased → Hypersensitivity of the axis leads to high levels of basal cortisol → Depression and anxiety related disorders
39
Describe the TSH axis
→ Thyrotropin releasing hormone (TRH) from the hypothalamus stimulates the anterior pituitary to release TSH → TSH acts on the thyroid to increase T4/T3 secretion →Thyroxine exerts negative feedback on the pituitary receptors
40
What is the most potent thyroid hormone?
→ T3
41
What is the effect of TSH?
→ Targets tissues containing a deiodinase enzyme to convert T4 to T3
42
What does hyperthyroidism lead to?
→ Anxiety
43
What does hypothyroidism lead to?
→ Cognitive impairments such as apathy
44
Where is prolactin released from?
→ Lactotrophs in the anterior pituitary
45
What is the relationship between dopamine and prolactin?
→ Dopamine is released into the bloodstream and inhibits prolactin release
46
Where are vasopressin and oxytocin synthesized in?
→ Supraoptic and paraventricular nuclei in the hypothalamus
47
What is the difference between vasopressin and oxytocin?
→ 2 peptides | same length
48
What is vasopressin release stimulated by?
→ Changes in the activity of the osmoreceptor complex in the hypothalamus
49
What is the function of vasopressin?
→ Controls plasma osmolality by regulating water excretion | → Stimulates vascular smooth muscle contraction in the DCT to reduce water loss and raise blood pressure
50
When is oxytocin elevated?
→ Parturition → Lactation → Mating
51
What is oxytocin released in stimulus to?
→ Peripheral stimuli of cervical stretch receptors and suckling at the breast
52
What is the function of oxytocin?
→ Regulates contraction of smooth muscle → uterus during labour →stimulates placenta to make prostaglandins → contraction of vas deferens during ejaculation
53
Describe the RAAS system
→ Kidneys release renin → Renin cleaves angiotensinogen from the liver to angiotensin I → Angiotensin I → angiotensin II in the lungs → Angiotensin II constricts vessels → It acts on the subfornical organ which gives the signal to release vasopressin from the pituitary → blood pressure increases
54
Describe the role of oxytocin during childbirth
→ During labour the baby starts pushing on the uterus which stretches → There is stimulation of neurons that signal the magnocellular neurons to release oxytocin → Oxytocin acts on its receptors in the uterus to cause contractions → Baby moves forward which causes stretching → stretching causes further oxytocin release which is +ve feedback
55
What makes voles monogamous?
→ High levels of oxytocin in the reward centres of the brain
56
What does oxytocin deficiency lead to?
→ Antisocial behaviour
57
What stimuli activate the RAAS system?
→ dehydration | → low blood pressure due to blood loss
58
What are the 4 receptor mechanisms?
→ Dimerisation pathway → G protein/adenylate cyclase pathway → DAG/IP3 pathway → Nuclear and steroid pathways
59
How does the dimerisation pathway work?
→ Binding of insulin and growth hormone to cell surface receptors leads to dimerisation of receptors → this recruits tyrosine kinases which phosphorylates target proteins and induces biological responses
60
How does the G protein pathway work?
→ binding of a hormone to GPCR results in conformational changes in the receptor → leading to GTP exchange for GDP and activation of adenylate cyclse →Stimulation of adenylate cyclase leads to an increase in cAMP → cAMP activates PKA which phosphorylates target proteins to initiate gene expression
61
What 3 hormones use G proteins?
→ TSH and ACTH | → Oxytocin is Gq coupled
62
How does the DAG/IP3 pathway work?
→ Oxytocin binds to GCPRS → stimulates phospholipase C → PIP2 → IP3 and DAG → IP3 stimulates Ca2+ release from intracellular stores → DAG activates PKC → PKC stimulates the phosphorylation of proteins and alter enzyme activities to initiate a biological response
63
How do nuclear and steroid pathways work?
→ Steroid hormones diffuse across the plasma membrane of target cells and bind to intracellular receptors in the cytoplasm → The receptors function as hormone regulated transcription factors controlling gene expression
64
What do nuclear receptors share?
→ Transcriptional activation domain → Zn2+ finger DNA binding domain → Ligand binding domain
65
What are the 6 effects of a pituitary adenoma?
→ loss of visual field (pressure on optic nerve) → too much GH (acromegaly) → Hypogonadism and infertility → Hypopituitarism → Hyperprolactinemia → Cushing syndrome (too much ACTH)
66
What are the symptoms of hypothyroidism?
→ cold hands → cold feet → lack of energy

Neuroscience (21 decks)

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