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MEH session 8 Flashcards

1
Q

Where is the hypothalamus located?

A

At the base of the brain beneath the thalamus

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2
Q

Where is the pituitary gland located?

A

Beneath the hypothalamus in a socket of bone called the sella turcica

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3
Q

What is the infundibulum?

A

(pituitary stalk)- axons from the hypothalamus pass down here and terminate in the posterior pituitary.

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4
Q

The anterior and posterior pituitary gland have distinct embryonic origins. What are they?

A

Anterior pituitary
Arises from invagination of oral ectoderm (primiative gut tissue) rathke’s pouch

Posterior pituitary
Originates from neuroectoderm
(Primitive brain tissue)

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5
Q

Is the anterior or posterior pituitary gland physically connected to the hypothalamus?

A

Posterior pituitary via infundibulum

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6
Q

Where are hormones that are released from the posterior pituitary gland synthesised?

A

Hypothalamus

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7
Q

Which hypothalamic nuclei are involved in the control of:

  1. Appetite
  2. Biological clock
  3. Milk secretion
  4. Blood pressure
A
  1. Arcuate nuclei
  2. Suprachiasmatic nuclei
  3. Supraoptic nuclei and paraventricular
  4. Paraventricular nuclei and supraoptic
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8
Q

Which hormones are synthesised in the hypothalamus and transported to the posterior pituitary? How?

A

ADH
Oxytocin

Neurocrine secretion

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9
Q

How are hormones synthesised in the hypothalamus and transported to the anterior pituitary?

A

Transported down axons and released into the median eminence by neurocrine secretion.
Enter the hypothalamic-hypophyseal portal to reach target cells in the anterior pituitary gland

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10
Q

What effect to the hormones synthesised in the hypothalamus have on target cells in the anterior pituitary?

A

They are tropic hormones.

They either stimulate or inhibit target cells in the anterior pituitary gland.

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11
Q

What methods of communication do hormones synthesised and secreted by the anterior pituitary gland use?

A

Autocrine
Paracrine
Endocrine

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12
Q

What are the seven tropic hormones synthesised and released by the hypothalamus?

A
  • TRH - thyrotropin releasing hormone
  • PRH - prolactin releasing hormone
  • PIH - prolactin release-inhibiting hormone (dopamine)
  • CRH - corticotropin releasing hormone
  • GnRH - gonadotropin releasing hormone
  • GHRH - growth hormone releasing hormone
  • GHIH - growth hormone inhibitory hormone (also called somatostatin)
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13
Q

The hormones produced by nerve cells of the hypothalamus act via two distinct neurocrine pathways. What are they?

A
  • direct effects on distant target tissues via oxytocin and ADH from the posterior pituitary
  • hormones secreted exclusively into the hypophyseal portal system via the median eminence to affect endocrine cells in the anterior pituitary
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14
Q

What is the difference between tropic and trophic hormones?

A

Tropic hormones affect the release of other hormones in the target tissue.
Trophic hormones affect growth

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15
Q

What is the hypothalamic stimulating and inhibitory hormone for the release of TSH from thyrotropes in the anterior pituitary?
What does TSH do?

A

Thyrotropin releasing hormone

Growth hormone inhibiting hormone (somatostatin)

TSH stimulates secretion of thyroid hormones from the thyroid gland.

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16
Q

What is the hypothalamic stimulating and inhibitory hormone for the release of prolactin from lactotropes in the anterior pituitary?
What does prolactin do?

A

Prolactin releasing hormone (minor stimulatory control on prolactin)

Prolactin release-inhibiting hormone
Growth hormone-inhibiting hormone (somatostatin)

Prolactin stimulates milk production in mammary glands

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17
Q

What is the stimulating hormone for the release of ACTH from corticotropes in the anterior pituitary?

What does ACTH do?

A

Corticotropin releasing hormone (CRH)

ACTH stimulates glucocorticoid (mainly cortisol) secretion from the adrenal cortex

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18
Q

What is the hypothalamic stimulatory and inhibitory hormones for the release of growth hormone from somatotropes in anterior pituitary gland?
What does growth hormone do?

A

Growth hormone releasing hormone (GHRH)

Growth hormone inhibiting hormone (GHIH)

Growth hormone stimulates IGF production by the liver. It also has direct growth effects on some target cells.

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19
Q

What is the hypothalamic stimulating hormone for the release of LH and FSH from gonadotropes in the anterior pituitary?

What do LH and FSH do?

A

Gonadotropin releasing hormone (GnRH)

LH - stimulates progesterone and oestrogen production in females and testosterone in males. Initiates ovulation.

FSH - stimulates gamete production (egg in female, sperm in male)

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20
Q

Which hormones are produced by the anterior pituitary?

A 
TSH - thyroid stimulating hormone 
ACTH - adrenocorticotropic hormone
LH - luteinising hormone 
FSH - follicle stimulating hormone 
PRL - prolactin 
GH - growth hormone
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21
Q

Which hormones that are produced and secreted by the anterior pituitary are tropic hormones?

A

F-L-A-T

TSH stimulates release of thyroid hormones from thyroid gland
ACTH stimulates release of cortisol from adrenal cortex
LH stimulates release of oestrogen and progesterone in females, and testosterone in males
FSH stimulates gamete production

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22
Q

In the ultra-short loop, what produces the negative feedback and what does it inhibit the production of?

A

What produces the negative feedback?
Hypothalamic releasing hormone

Inhibits production of?
Hypothalamic releasing hormone

How?
Autocrine

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23
Q

In the short loop, what produces the negative feedback? What does this influence the production of?

A

What produces the negative feedback?
Anterior pituitary hormone released in response to hypothalamic releasing hormone

Inhibits production of?
Hypothalamic releasing hormone

Stimulates production of?
Hypothalamic inhibiting hormone

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24
Q

In the direct long loop, what produces the negative feedback and what does this influence the production of?

A

What produces the negative feedback?
Peripheral effector hormone

Inhibits production of?
Anterior pituitary hormone

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25
In the indirect long loop, what produces the negative feedback? What does this influence the production of?
What produces the negative feedback? Peripheral effector hormone Inhibits production of? Hypothalamic releasing hormone Stimulates production of? Hypothalamic inhibiting hormone
26
What is growth influenced by?
Nutrition Genetics Environment Hormones - growth hormone is the most important endocrine regulator of postnatal growth
27
Where is growth hormone produced?
Somatotrope cells in the anterior pituitary gland
28
Is growth hormone orally active?
No- it is a protein hormone so is denatured Only steroid hormones are biologically active when taken orally.
29
How does growth hormone exert a majority of its effects?
In response to growth hormone, liver and skeletal muscle produce insulin-like growth factors. IGFs act on target cells through their own specific receptor which shows similarities to the insulin receptor (tyrosine kinase).
30
Why is growth hormone essential for normal growth during childhood and teenage years?
Growth hormone stimulates long bone growth. - length and width prior to epiphyseal plate closure - width after epiphyseal closure IGFs stimulate both bone and cartilage growth
31
What does growth hormone do in adults?
Growth hormone and IGFs: - maintain muscle mass - maintain bone mass - promote healing and tissue repair - modulate metabolism (promote anabolic processes)
32
What principally controls the release of growth hormone?
Hypothalamus Growth hormone releasing hormone Growth hormone inhibiting hormone (somatostatin)
33
What factors stimulate the release of growth hormone?
Endocrine: • Hypothalamic hormone - GHRH (growth hormone releasing hormone) • Ghrelin Metabolic: • A decrease in plasma glucose or plasma free fatty acid concentrations • Fasting Central nervous system-inputs into hypothalamus affecting GHRH and GHIH levels • Surge in GH secretion after onset of deep sleep • Stress eg. Trauma, surgery fever • Exercise
34
What factors inhibit the release of growth hormone?
Endocrine: • Hypothalamic hormone - Somatostatin/GHIH (growth hormone inhibiting hormone) Metabolic: • An increase in plasma glucose or plasma free fatty acid concentrations • Obesity Central nervous system-inputs into hypothalamus affecting GHRH and GHIH levels • Light sleep (Rapid Eye Movement REM) sleep
35
In childhood, what does growth hormone deficiency result in?
Pituitary dwarfism - proportionate type of dwarfism - complete or partial deficiency - height below third percentile on standard growth charts - growth rate slower than expected for age - delayed or no sexual development Responds well to GH therapy
36
In childhood, what does growth hormone excess result in? | What is it often caused by?
Gigantism This is often caused by a pituitary adenoma
37
In adulthood, what does excess growth hormone result in?
Acromegaly Large extremities: Hands, feet, lower jaw
38
What kind of receptor is the growth hormone receptor? | What does activation of this receptor cause?
Kinase-linked receptor, Janus kinases (JAK) Coupled to janus kinase This results in activation of a transcription factor that turns on production of IGFs
39
What kind of cell communication are IGFs involved in?
Paracrine Autocrine Endocrine
40
What effects to IGFs have?
Hypertrophy Hyperplasia Increased protein synthesis Increased lipolysis in adipose tissue
41
IGF1 can produce a hybrid receptor with which type of receptor?
Insulin receptor
42
Which hormones other than growth factor influence growth?
Insulin - influences somatic growth by interacting with IGF receptors Thyroid hormones - promote CNS development and enhance GH secretion Androgens - accelerate pubertal growth spurt, increase muscle mass, promote closure of epiphyseal plate Oestrogens - decrease somatic growth, promote closure of epiphyseal plates Glucocorticoids - inhibit somatic growth
43
What effect would a superior growth of a pituitary tumour have on vision?
Bitemporal hemi-anopia (vision is missing on outer half of left and right field)
44
How do pituitary tumours present?
--->Mass of tumour on local structures leading to: Visual loss Headache --->Abnormality of pituitary function Hyposecretion Hypersecretion
45
Which anterior pituitary hormone is under tonic inhibitory control by the hypothalamus and which hormone mediates this?
Prolactin Prolactin inhibitory hormone (dopamine)
46
How can a pituitary tumour cause hyposecretion of hormones from the anterior pituitary gland?
The pituitary tumour may block the hypothalamic tropic hormones from reaching target cells in the anterior pituitary. Therefore, hormones that are usually under stimulatory/inhibitory influence change in concentration: FSH/LH decreases ACTH decreases TSH decreases Growth hormone decreases Prolactin increases
47
How can you tell whether hypothyroidism is due to a tumour in the pituitary gland (secondary hypothyroidism) or due to a problem in the thyroid gland itself (primary hypothyroidism)?
Primary hypothyroidism T3 and T4 is low TSH is high Secondary hypothyroidism T3 and T4 is low TSH is low
48
What does growth hormone deficiency cause in adults?
Reduced quality of life - fatigue, muscle weakness
49
What does LH/FSH deficiency present as?
In children, this results in delayed puberty In adults, this results in loss of secondary sexual characteristics in adults (males develop breasts, loss of periods is an early sign in women).
50
What does ACTH deficiency present as?
Low cortisol | Tired, dizzy, low blood pressure, low sodium, can be life threatening
51
Pituitary tumours can result in hyposecretion of which hormones...
TSH ACTH FSH/LH Growth hormone
52
Pituitary tumours commonly results in hypersecretion of which hormones?
Commonly, Prolactin Growth hormone ACTH
53
What processes are involved in the investigation and diagnosis of a pituitary tumour?
* Delineation of the anatomy, size and topographical location of the pituitary or parapituitary mass (usually by MRI scan) * Assessment of visual field defects * Assessment of endocrine function determine whether there is a hormonal excess/deficiency
54
In biochemical assessment of pituitary disease, which axes is a basal blood test sufficient for?
Thyroid axis Gonadal axis Prolactin axis The levels of these hormones do not fluctuate significantly throughout the day.
55
In the biochemical assessment of pituitary disease, which axes require dynamic blood tests?
HPA axis - levels of cortisol vary throughout the day (diurnal rhythm) GH axis - growth hormone released in a pulsatile fashion
56
How is the dynamic assessment of the adrenal axis carried out?
Suspected hormone deficiency ---> stimulation test - direct stimulation of adrenals by ACTH - response to hypoglycaemic stress (insulin stress test) Suspected hormone excess ---> suppression test -suppress ACTH axis with steroids
57
How is dynamic assessment of the GH axis carried out?
Suspected hormone deficiency---> stimulation test -Response to hypoglycaemic stress (insulin stress test) Suspected hormone excess---> suppression test -suppress GH axis with glucose load (glucose tolerance test)
58
How are prolactinomas treated?
Dopamine receptor agonists such as cabergoline are usually the first line of treatment. The tumour will shrink. Prolactin secretion from the anterior pituitary is mainly under the negative influence of dopamine.
59
Give some signs of hyperprolactinaemia in women.
Galactorrhoea - unexplained milk production higher level of dopamine in the hypothalamus resulting from negative feedback of increased plasma prolactin which inhibits GnRH secretion from the hypothalamus and therefore FSH and LH secretion from the anterior pituitary. This results in: Menstrual disturbance Fertility problems
60
What are the symptoms of hyperprolactinaemia in men?
Men present later than women Usually larger tumours Symptoms of low testosterone are non-specific eg. Loss of libido May present with mass symptoms such as visual loss
61
Which hormone of the anterior pituitary gland is the only hormone which would show an increase in a non-functional or functional tumour of the pituitary gland if pituitary function is affected and why?
Prolactin It is the only anterior pituitary hormone under tonic inhibitory control by dopamine from the hypothalamus so is the only one that would be raised in a non-functional tumour that affects pituitary function.
62
How can you tell if prolactinaemia is due to a non-functional tumour or a functional tumour?
If prolactin is <5000, high prolactin may be due to disinhibition rather than active secretion If prolactin is >5000, high prolactin is likely to be due to active prolactin secretion (prolactinoma)
63
Why is it important to recognise whether a prolactinaemia is caused by a functional or non-functional pituitary adenoma?
prolactinomas are treated with dopamine agonists non functioning pituitary tumours are treated surgically
64
Why is it important to check if anyone with hyperprolactinaemia is taking any anti-sickness or anti-psychotic drugs?
These could be dopamine antagonists. Dopamine inhibits prolactin release. Therefore, the drug may be the cause of high prolactin in the blood.
65
What is the treatment for acromegaly?
Surgical removal of the tumour Radiotherapy Drugs: dopamine receptor agonists have some efficacy is reducing GH levels but a much higher dose than that used for prolactin-secreting pituitary adenoma is required somatostatin - the hypothalamic hormone which limits GH secretion has limited use due to its very short half-life but the synthetic somatostatin analogs have been developed which produce a prolonged suppression of GH secretion Pegvisomant - antagonists of the GH receptor
66
What are the symptoms of Cushing's disease?
Round pink face with round abdomen • Skinny and weak arms and legs • Thin skin and easy bruising • Red stretch marks (‘striae’) on abdomen • High blood pressure and diabetes • Osteoporosis (thin bones)
67
What is the difference between Cushing's disease and Cushing's syndrome?
Cushing's disease is due to a pituitary tumour. Cushing's syndrome may be caused by other pathologies.
68
What causes diabetes insipidus?
ADH deficiency Less expression of aquaporins in collecting ducts of kidney nephrons Less water reabsorbed into the blood
69
What are the symptoms of diabetes insipidus?
Excess secretion of dilute urine Dehydration Increased thirst sensation If untreated, can result in: Reduced consciousness Coma Death
70
Do standard pituitary tumours affect both the anterior and posterior pituitary?
No. They usually just affect the anterior pituitary If they affect the posterior pituitary, it is due to some other sort of pathology: - inflammation - infiltration - malignancy - infection
71
What is the treatment for cranial diabetes insipidus?
synthetic vasopressin | Desmopressin nasal spray, tablets or injection
72
What is pituitary apoplexy?
Sudden vascular event within a pituitary tumour. Haemorrhage with in the tumour (bleeding) Infarction within the tumour (blood supply cut off)
73
What is the clinical presentation of pituitary apoplexy?
``` Sudden onset headache Double vision Cranial nerve palsy Hypopituitarism - cortisol deficiency most dangerous Visual field loss ```
74
In which nuclei of the hypothalamus are the neurones that synthesis oxytocin located?
Supraoptic and paraventricular nuclei
75
Describe the embryonic origin of the anterior lobe of the pituitary gland.
The anterior lobe of the pituitary gland arises from an up-growth of ectodermal cells from the roof of the primitive pharynx
76
Which organ releases IGF-1 into the blood in response to growth hormone stimulation?
Liver
77
Which disease results from excess growth hormone secretion occurring after puberty after the epiphyseal plates have closed?
Acromegaly
78
Why might a patient with a pituitary adenoma develop visual field loss?
Growth of the adenoma can cause physical compression of the optic chiasma. (Mass-effect)
79
What is galactorrhoea?
Milky secretion from the breasts not due to breastfeeding which can be caused by hyperprolactinaemia
80
Which biochemical finding would you expect in. Patient with acromegaly?
Plasma growth hormone above the normal range | Plasma IGF-1 above the normal range as liver and muscle is stimulated to release more
81
Which term is used to describe a sudden vascular event such as haemorrhage or infarction to a pituitary tumour?
Pituitary apoplexy Patients with pituitary apoplexy may show sudden onset headache, double vision, cranial nerve palsy, visual field loss and hypopituitarism (cortisol deficiency is the most dangerous). Apoplexy needs prompt diagnosis and treatment
82
Which of the following is a typical clinical consequence of untreated central diabetes insipidus? Glucosuria Hypernatraemia Hyperkalaemia Hypocalcaemia
Hypernatraemia -dehydration can develop in patients when they do not drink adequately
83
Which pattern of plasma cortisol concentration is normal? Highest at midnight, lowest level in the morning Constant throughout the day Highest in the morning, lowest level at midnight
Plasma cortisol reaches its peak at around 7:00 to 8:00 AM and then gradually declines throughout the day to a lowest levels at around midnight before gradually increasing again through the night. For this reason it is essential to always record the time a blood sample for cortisol measurement was taken and to take repeated samples the same timne of day. Typically cortisol is measured in the morning.
84
What is the role of LH in men?
Control of the production of testosterone by the testis by acting on the Leydig cells
85
Name the type of surgical procedure that can be used to remove a pituitary tumor by inserting an endoscope and/or surgical instruments through the nose.
Transphenoidal surgery

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