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Endocrinology > Pituitary gland > Flashcards

Pituitary gland Flashcards

1
Q

What are the three types of hormones?

A

Steroid hormones
Peptide hormones
Amino acid derived hormones

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2
Q

Which of the hormones acts on receptors in the cytoplasm and which acts on those on the cell surface and why?

A

Steroid hormones are lipophilic and therefore are able to cross the phospholipid bilayer which makes up the cell membrane so can acts on nuclear receptors located in the cytoplasm.
However, amino acid derived hormones and peptide hormones are both hydrophilic hormones and therefore are unable to cross the cell membrane so act on cell surface receptors.

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3
Q

What are some examples of steroid hormones?

A

Cortisol
Aldosterone
Testoesterone
Progesterone
Estrogen

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4
Q

What are some examples of amino acid derived hormones?

A

Epinephrine and Norephrine

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5
Q

What are some examples of peptide hormones?

A

Corticotrophins
Growth hormones
Insulin
Prolactin

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6
Q

How is hormones defined?

A

Hormones are chemical messengers that are secreted directly into the blood, which carries them to organs and tissues of the body to exert their functions often bound to proteins.

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7
Q

What is the function of the pituitary gland?

A

It is responsible for secreting hormones as directed by the hypothylamus, which controls/regulates the function of the other endocrine glands.

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8
Q

What are some of the endocrine glands in the body?

A

Testes
Ovaries
Pituitary
Pancreas
Adrenal
Thyroid
Parathyroid
Pineal

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9
Q

What is the function of the pineal gland (which hormone does it secrete)?

A

The pineal gland is responsible for the secretion of Melantonin which controls the sleep-wake cycle and circadian rhythms

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10
Q

How are the hypothylamus and the pituitary gland connected?

A

The hypothalamus is anatomically and functionally related to the pituitary gland, as the bean-sized organ is suspended from it by a stem called the infundibulum.

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11
Q

What is the function of the hypothylamus?

A

It releases hormones in response to environmental stimuli that control the
synthesis and release of the hormones of the pituitary gland.

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12
Q

Describe the anatomy of the pituitary gland.

A

The pituitary gland is a very small almost pea or bean like structure that is located at the base of the brain behind the bridge of the nose known as siting within a crevice of the sphenoid bone. It is composed of two derived lobes the posterior pituitary (made of nervous tissue) and the anterior pituitary (made of glandular epithelial tissue).

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13
Q

What does each of the pituitary lobes connect to?

A

The posterior pituitary connects to neural pathway
The anterior pituitary connects to vascular pathway

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14
Q

List the hormones released from the posterior pituitary.

A

Vasopressin (anti-diuretic)
Oxytocin

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15
Q

List the hormones released from the anterior pituitary.

A

Gonadotrophins
Prolactin
Growth hormone
Thyroid stimulating hormone
Follicle stimulating hormone
Adrenocorticotropic hormone
Luteinizing hormone
Melanocyte stimulating hormone

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16
Q

Describe the process in which either oxytocin or vasopressin is secreted from the posterior pituitary.

A

In the hypothylamus there are two types of neuron cell bodies known as supraoptic and paraventricular nuclei.
These neurosecretory neuronal cell bodies secrete the hormones (Vasopressin is normally produced in the supraoptic nucleus and oxytocin more in the paraventricular nucleus).
The secreted form of these hormones are packaged in secretory granules.
They then travel down the axon (in the Hypothylamic posterior pituitary stalk. These secretory granules reach and remain in the neuronal terminals in the posterior pituitary until excitation of neuron causes their release into the bloodstream.

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17
Q

What are some of the functions of oxytocin in females?

A

Aids the contraction of the uterine muscle to help expel infant during childbirth
(secretion of the hormone increased by reflexes within the birth canal)

Promotes ejection of milk from mammary glands during breast feeding
(Secretion increased by suckling)

Influences social behaviours
(bonding with infant)

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18
Q

What is a derivative of oxytocin used to initiate labour?

A

Syntocinon injection (also used to prevent postpartum haemorrhage).

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19
Q

What are the two receptors vasopressin binds to and what are the downstream effects?

A

Binds to V2 receptor on the distal and collecting ducts in the nephron increasing the water permeability and hence increases the amount of water reabsorbed (anti-diuretic effect)
Also binds to the V1 receptor on vascular smooth muscle inducing vasoconstriction (only a small regulator of blood pressure though).

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20
Q

What is the cause of diabetes insipidus?

A

Caused by lack of production of antidiuretic hormone (vasopressin) or lack of response to it.

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21
Q

What is the main characteristic of diabetes insipidus?

A

Passing large volumes of very dilute urine (more than 3 litres in 24 hours with a osmolality of less than 300 mOsmal per kg).

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22
Q

What are the main symptoms of diabetes insipidus and how are they caused?

A

The main symptoms are:
Polyuria (this is because the kidney is unable to concentrate the urine, there is no ADH acting to reabsorb some of the water)
Polydipsia (due to the concentrated blood)

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23
Q

What the two types of diabetes insipidious?

A

Nephrogenic (problem in the kidney)
Cranial (problem in the brain)

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24
Q

What is nephrogenic diabetes insipidious and what are some of the causes?

A

It is when ADH is produced normally but the collecting ducts do not respond to it.
Causes include
Drugs such as lithium
Genetic conditions such as a fault on the AUPR2 gene on the X chromosome
Intrinsic kidney disease
Electrokyte imbalance (hypokalaemia and hypercalcemia)

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25
Q

What is cranial diabetes insipidious and what are some of the causes?

A

Hypothylamus does not produce ADH for the pituitary gland to secrete
Causes:
Idiopathic
Brain tumours
Brain injuries
Brain surgery, radiotherapy
Brain malformations
Infections (Meningitis)

26
Q

What are some other symptoms of diabetes insipidious?

A

Hypernatremia
Postural hypotension

27
Q

What are some investigations you could make for diabetes insipidious?

A

Urea and electrolytes test
Urine osmolality (would expect it to be low, all diluted by water)
High serum osmolality (all concentrated in the blood)

28
Q

What does the water deprivation test involve?

A

Avoid eating or drinking for 8 hours prior to the test. Then the urine osmolality is measured before desmopressin is given. 8 hours later the urine osmolality is measured again.

29
Q

What results would you expect from the water deprivation test for cranial diabetes and why?

A

Before the 8 hours you would expect it to be the urine osmolality to be low, after the 8 hours you would expect it to be higher.

This is because in cranial diabetes there is a fault with the hypothylamus in the production of ADH and there is no fault with the kidneys and it would still be able to respond to ADH. Therefore when desmopressin is administered it is recognised by the kidney and is able to work on the distal and convoluted tubule in reabsorbing water and concentrating the urine output.

30
Q

What results would you expect from the water deprivation test for nephrogenic diabetes and why?

A

You would expect the results to remain low after administrating the desmopressin. This is because the kidneys are unable to respond to the ADH.

31
Q

What are some of the treatments available for diabetes insipidious?

A

Treat the underlying causes
Mild cases, treat conservatively
Desmopressin (cranial diabetes) and in high doses for nephrogenic diabetes under close monitoring

32
Q

What are the five major cell types in the anterior pituitary and what hormones do they secrete?

A

Somatotropes – GH (growth hormone (somatotropin))
Thyrotropes – TSH (thyroid stimulating hormone)
Corticotropes – ACTH (adrenocorticotrophic hormone)
Gonadotropes – FSH (follicle stimulating hormone) and LH
(luteinizing hormone)
Lactotropes – PRL (prolactin)

33
Q

Describe what is meant by the three hormone sequence.

A

Hormone number 1 (often known as a releasing hormone) is secreted from the hypothalamus, due to presence of an external stimuli, this hormone then acts on the anterior pituitary initiating the secretion of hormone number 2 (trophic hormone). This hormone is secreted into the bloodstream and travels to and acts on its target endocrine gland which it stimulates causing secretion of hormone number 3 (effector hormone) which then migrates in the bloodstream and acts on the target gland initiating a response. When hormone number 3 is secreted in substantial quantities this then acts on both the hypothalamus and anterior pituitary to stop production of hormone number 1 and number 2 and negative feedback control is achieved.

34
Q

What is the three hormone response for prolactin?

A

Prolactin secretion is stimulated by prolactin releasing factors (dopamine inhibits) and thyroid releasing hormone. It doesn’t act on an endocrine gland and just acts directly on the breast.

35
Q

What is the three hormone response for the thyroid gland?

A

Thyroid releasing hormone, (somatostatin inhibits) acts on the anterior pituitary initiating the secretion of thyroid stimulating hormone which then acts on the thyroid producing thyroxine and other thyroid hormones.

36
Q

What is the three hormone response for adrenal cortex?

A

Corticotrophin releasing hormone acts on the anterior pituitary initiating the secretion of adrenocotrophin hormone which then acts on the adrenal cortex stimulating production of cortisol.

37
Q

What is the three hormone response for growth hormone?

A

Growth hormone releasing factor and somatostatin (inhibits) act on the anterior pituitary initiating the secretion of growth hormone which then acts on the liver stimulating production of insulin-like growth hormone.

38
Q

What is the three hormone response for FSH and LH hormone?

A

Gonadotrophin releasing hormone act on the anterior pituitary initiating the secretion of FSH and LH which then acts on the endocrine cells of the gonads stimulating production of estrogens, progesterones and androgens.

39
Q

Are anterior pituitary hormones secreted constantly and at the same time?

A

No, their release is independent from each other and their release rate is not constant.

40
Q

What are the two major factors in controlling the rate of releasing of anterior pituitary hormones?

A

Feedback from target gland hormones
Hypothalamic hormones (releasing and inhibitory hormones)
Neural or hormonal inputs to stimulate or inhibit secretion

41
Q

What is the vascular link between the hypothalamus and the pituitary gland?

A

It is known as the hypophyseal portal system. The portal system is made up of two capillary beds, one in the median eminence and the other in the anterior pituitary and the hypothylamic hormone just travel locally within this. Upon arrival to the pituitary, the hypothalamic hormones bind to
specific receptors on specific cells in the anterior pituitary.

42
Q

What are some of the downstream effects of the growth hormone?

A

Net synthesis of proteins
Lengthening of long bones
Increase in size and number of cells in soft tissues

43
Q

Does the growth hormone have direct effects on tissue?

A

No, instead it works by increasing the insulin-like growth hormone by acting on the liver.

44
Q

What are some of the other factors that can affect growth?

A

Genetics
Adequate diet
Chronic disease
Stressful environment,
Other growth influencing hormones eg thyroid hormone, insulin, estrogens, androgens

45
Q

What are some of the complications of growth hormone deficiency?

A

Results in short stature due to reduced skeletal growth, reduced
muscle protein synthesis and increased fat deposition

GH deficiency occurring in adulthood (eg due to pituitary tumour)
results in muscle effects, eg at risk of heart failure

46
Q

What is the difference between primary and secondary growth hormone deficiency?

A

Primary is due to a defect with the pituitary gland in producing growth hormone
Secondary is due to a defect with the or target dysfunction – lack of GHRH or IGF or lack of tissue response

47
Q

Which ethnic group lacks IGF-1?

A

African pygmies

48
Q

What is the main treatment used in GH deficiency?

A

Somatotrophin (recombinant growth hormone)

49
Q

When is somatotrophin (recombinant GH) licensed?

A

Pituitary dwarfism
Turner’s syndrome
Chronic renal insufficiency in children. It is also used illicitly by athletes to increase muscle mass.

50
Q

What is one of the ethical considerations regarding somatotrophin?

A

Balance of improving stature vs the risk of cancer

51
Q

What are the two specific analogues given for GH defiency?

A

Somatorelin (human recombinant GHRF) is a 44 amino acid
residue peptide, which is sometimes given if relevant.

Mecasermin (human recombinant IGF-1) is given when there is
growth failure in children lacking adequate IGF-1

52
Q

What are some of the complications associated with acromegaly?

A

Thicker bones and soft tissue proliferation, bone thickening in the face
Extremities
Sometimes peripheral nerve disorders as
nerves can become trapped

53
Q

What is the difference between acromegaly and gigantism?

A

Acromegaly occurs in adulthood whilst gigantism occurs in childhood. With gigantism there is no body disproportions whereas there is with acromegaly.

54
Q

What is usually the cause of GH excess?

A

Most often this is due to a benign tumour of somatotrophs

55
Q

What is the two main treatment options for those with GH excess?

A

Surgery (trans-sphenoidal and/or debulking)
Medicines consisting of somatostatin analogues given in adjunct to surgery

56
Q

What are some examples of somatostatin analogues and where do they act?

A

Octreotide
Lanreotide,
Pasireotide

Unlike somatostatin which acts on all somatostatin receptors, the analogues act on specific receptors

57
Q

Depending on the cause what are some other drugs aside from the somatostatin analogues that may be given?

A

Dopamine agonists
Bromocriptine or
The GHRH antagonist Pegvisomant

58
Q

Describe somatostatin and the effects it has on certain hormones.

A

It is a 14 amino acid peptide and it inhibits the secretion of many hormones including glucagon, TSH, GH, insulin and most GI hormones.

59
Q

What are the indications of octreotide?

A

Carconoid and other hormone-secreting tumors
Acromegaly
Bleeding oesophageal varices (where it constricts splanchnic blood vessels)

60
Q

What are some of the side effects of octreotide, lanreotide and pasireotide?

A

Pain at the site of injection (due to s/c injection)
GI disturbances

61
Q

What is an additional indication of lanreotide?

A

Also used in the treatment of thyroid tumours

62
Q

What is an additional indication of pasireotide?

A

Used in the treatment of Cushing’s syndrome when surgery is ineffective or inappropriate

Endocrinology (13 decks)

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