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Physiology 2 > Neuro: Neurohormones > Flashcards

Neuro: Neurohormones Flashcards

1
Q

What is a neurohormone?

A

A hormone produced by neurons within the brain that gets secreted into the circulation

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2
Q

What are some of the differences between the endocrine system and the the nervous system?

A
  • Signalling in nervous system occurs along nerve fibres while signalling for endocrine system occurs via neurohormones travelling in circulation
  • Nervous system siganlling is fast while endocrine signalling is slower
  • Nervous sysyem effects are generally short-acting while endocrine system effects are more long-lasting
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3
Q

What is the name of the cells that secrete neurohormones?

A

Neurosecretory cells

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4
Q

What are the different types of neurohormone?

A
  • Protein and peptide hormones e.g. FSH and LH
  • Amino acid derivatives e.g. Dopamine, adrenaline and Noradrenaline
  • Steroid hormones e.g. Oestradiol and Progesterone
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5
Q

How is the hypothalamus connected to the anterior pituitary?

A
  • Hypothalamus connected to the anterior pituitary via the hypophaseal portal system
  • Hypophaseal portal system made of primary capillary plexus in hypothalamus which is connected to secondary capillary plexus in the anterior pituitary
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6
Q

How is the hypothalamus connected to the posterior pituitary?

A
  • Hypothalamus connecetd to the posterior pituitary via the hypophaseal nerve tract
  • This nerve tract is made up of magnocellular neurons which connect to nerosecretory cells in anterior pituitary
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7
Q

What are the 2 main neurohormones secreted from the posterior pituitary?

A
  • Vasopressin
  • Oxytocin
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8
Q

Name some neurohormones secreted by the anterior pituitary as well as neurohormones secreted from the hypothalamus

A
  • Anterior pituitary: LH, FSH, Prolactin, GH (Growth hormone)
  • Hypothalamus: CRH (Corticotrophin-releasing hormone), GnRH, Prolactin-inhibiting factor (dopamine)
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9
Q

The levels of neurohormones within the circulation show periodic rhythms. What are the different types of periodic rhythms that neurohormones show?

A
  • Circadian rhythms - based on a 24 hour cycle
  • Pulsatile (ultradian rhythms) - based on a cycle shorter than 24 hours
  • Infradian rhythms - based on a cycle longer than 24 hours
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10
Q

Describe the effect of some neurohormones released from the hypothalamus have on the anterior pituitary

A
  • Corticotrophin-releasing hormone (CRH) acts on anterior pituitary causing it to release adrenocorticotrophic hormone (ACTH)
  • Thyrotrophin-releasing hormone (TRH) acts on anterior pituitary causing it release Prolactin and Thyroid-stimulating hormone (TSH)
  • Gonadotrophin-releasing hormone (GnRH) acts on anterior pituitary causing it to release FSH and LH
  • Dopamine (prolactin-inhibiting factor) acts on anterior pituitary to prevent release of prolactin
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11
Q

What are the different cell types within the anterior pituitary responsible for synthesising and secreting the different neurohormones of anterior pituitary?

A
  • Gonadotroph cells - secrete FSH and LH in response to GnRH
  • Corticotrophs - secrete ACTH in response to CRH
  • Thyrotrophs - secrete TSH in response to TRH
  • Lactotrophs - secrete prolactin in response to TRH and are inhibited from releasing prolaction in response to dopamine (prolactin-inhibiting factor)
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12
Q

Explain how stress causes release of cortisol from adrenal glands with HPA-axis

A
  1. Increased sress levels stimulates hypothalamus to release Cortiotrophin releasing hormone (CRH)
  2. CRH travels through hypophyseal portal system to anterior pituitary where it binds to CRH receptors on corticotroph cells
  3. Corticotroph cells synthesise and secrete Adrenocorticotrophin hormone (ACTH) into circulation
  4. ACTH binds to receptors on adrenal cortex causing it to secrete cortisol (stress hormone)
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13
Q

What effect does cortisol have on the HPA-axis?

A

Cortisol places negative feedback on hypothalamus and anterior pituitary thus reducing release of CRH and ACTH

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14
Q

How does chronic stress affect the HPA-axis and cortisol release?

A
  • Chronic stress (constant stress) will lead to hyperactivation of HPA-axis which will lead to high levels of cortisol release
  • Due to stress being constant however, cortisol levels won’t go down and will remain high within the circulation leading to conditions such as depression
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15
Q

Describe the rhythmic changes in cortisol levels in a 24 hour cycle

A
  • Plasma cortisol levels are highest first thing in the morning
  • Decline during the day (reflecting the pattern of ACTH secretion by the anterior pituitary)
  • At night cortisol levels start to rise until they reach peak levels first thing in the morning
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16
Q

Explain how activation of HPT-axis results in secretion of thyroid hormone (T3/T4)

A
  1. Stimulation of hypothalamus results in it secreting thyrotrophin-releasing hormone (TRH) into hypophyseal portal system
  2. TRH travels via hypophyseal portal system to anterior pituitary where it binds to receptors on thyrotrophs
  3. Thyrotrophs synthesise and secrete thyroid-stimulating hormone which then binds to receptors on thyroid gland
  4. This causes thyroid gland to produce and secrete Thyroid hormone (T3/T4)
17
Q

What is the name of the enzyme responsible for converting T4 into T3 when T4 binds to target tissue

A

Deiodinase

18
Q

Why does the anterior pituitary also express the deiodinase enzyme?

A
  • T3 more potent version of thyroid hormone so conversion of T4 into T3 helps with prodcution of negative feedback on anterior pituitary
19
Q

Where are vasopressin (ADH) and oxytocin synthesised withhin the brain?

A

Synthesised in the Suprapotic nucleus and the Paraventricular nucleus within the hypothalamus

20
Q

What are some of the functions of vasopressin (Anti-diruetic hormone, ADH)?

A
  • Stimulates smooth muscle contraction of distal tubules of kidney to reduce water loss and increase blood pressure
  • Also increases feeling of thirst
21
Q

What are some of the functions of oxytocin?

A
  • Causes smooth muscle contraction of uterus during labour
  • Causes smooth muscle contraction of myoepithelial cells of mammary ducts to cause lactation
  • Causes smooth muscle contraction of vas deferens to induce ejaculation
22
Q

Explain how thirst/low blood pressure causes Vasopressin (ADH) to be released from the kidneys

A
  1. Thirst/low blood pressure causes the kidneys to release renin
  2. Renin causes angiotensinogen in the liver to be converted into angiotensin I
  3. Angiotensin I then gets converted to Angiotensin II
  4. Angiotensin II detected by subfornical organ in the brain which sends a signal to the magnocellular neurons in hypothalamus to activate and produce vasopressin
  5. Vasopressin travels to and is secreted from posterior pituitary and acts on kidneys
23
Q

Explain how labour leads to release of oxytocin and how that oxytocin release results in positive feedback

A
  • During labour Baby stretches uterus which causes magnocellular neurons in hypothalamus to activate
  • This leads to secretion of oxytocin from posterior pituitary
  • Oxytocin binds to recptors within the uterus increasing uteruine contractions
  • Uterine contractions push baby further which stretches uterus more which leads to more oxytocin release (positive feedback)
    *
24
Q

What are the different types of receptor that neurohormones can bind to? For each type name a neurohormone that binds to that receptor

A
  • Tyrosine kinase receptors - Growth hormone (GH)
  • G-protein coupled receptors - Gi/o, Gs and Gq
  • Cytoplasmic/nuclear receptors - Progesterone
25
Q

How does activation of tyrosine kinase receptors lead to a biological response?

A
  • Substrate binds to thyroid hormone receptor and causes it to dimerise
  • Once dimerisation occurs receptor activates tyrosine kinase
  • Tyrosine kinase phosphorylates a particular substrate leading to a biological response
26
Q

How does activation of cytoplasmic/nuclear receptors lead to a biological response?

A
  • Steroid hormone diffuses through plasma membrane as it’s lipophillic
  • Steroid hormone then binds to specific receptor in the cytoplasm to form cell/receptor complex
  • Cell/receptor complex diffuses into nucleus and binds to specific genes within DNA causing their transcription
  • mRNA produced is then translated into protein
27
Q

What is hypothyroidism?

A

Condition in which too little thyroid hormone (T3 and T4) is secreted from the thyroid gland

28
Q

What is the most common cause of hypothyroidism?

A
  • Hashimoto’s disease
  • This is an autoimmune disease in which the immune system produces antibodies against the thyroid gland
29
Q

What is hyperthyroidism?

A

Condition in which too much thyroid hormone (T3 and T4) is produced from the thyroid gland

30
Q

What is the most common cause of hyperthyroidism?

A
  • Grave’s disease
  • Autoimmune diease in which the immune system produces antibodies against the thyroid gland
  • Antibodies act like Thyroid stimulating hormone (TSH) and cause secretion of thyroid horomone (T3 and T4) from thyroid gland
31
Q

What is Addison’s disease?

A

Disease in which adrenal gland doesn’t secrete enough steroid hormone

32
Q

What is cushing’s syndrome?

A

Disorder in which the adrenal galnd secretes too much cortisol

Physiology 2 (29 decks)

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