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Endocrinology > The hypothalamo adenohypophysial axis (2) > Flashcards

The hypothalamo adenohypophysial axis (2) Flashcards

1
Q

What is the anatomy of the pituitary gland/hypophysis

A

The pituitary is attached to the base of the brain . It lies within a bone lined cavity called Sella Turcica

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2
Q

Why is Sella Turcica important

A

Sella Turcica is important from a clinical point of view because a tumour will be constrained by the walls of the bony cavity. Pituitary tumours may protrude out towards the brain or it may go through the bone (if it is really malignant)

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3
Q

Where is the hypothalamus

A

it lies just above the pituitary gland

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4
Q

How does the pituitary gland develop

A

The anterior lobe(adenohypophysis) is derived from glandular tissue. Its an extension of the buccal cavity that grows upwards and attaches to the base of the brain. The posterior lobe (neurohypophysis) is derived from neural tissue. It is formed from downward movement of tissue from the developing hypothalamus. It attaches to the anterior lobe; consists mainly of nerve axons and nerve terminals. These two tissues then fuse and normally lose contact with the rest of the buccal cavity.

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5
Q

Features of the hypothalamus

A

Regulates the endocrine system. it surrounds the 3rd ventricle in the brain. Optic Chiasma lies at the front (anterior) of the hypothalamus, and has an important role in sight. Mammillary body is at the back (prosterior) of the hypothalamus is important in the development of the nervous system

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6
Q

What is the link between the hypothalamus and the pituitary gland

A

The Median Eminence

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7
Q

What is present in hypothalamus

A

Hypothalamic nuclei. These are clusters of nerve cell bodies.

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8
Q

What are the two types of neurones within the hypothalamic

A

Neurones that pass through the region of median eminence and end at the NEUROHYPOPHYSIS within the pituitary gland. Neurones that terminate at the region of median eminence

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9
Q

What is the adenohypophysis mainly made up of

A

secretory cells

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10
Q

What is the neurohypophysis mainly made up of

A

nerve axons and nerve terminals

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11
Q

What is the hypothalamo-hypophysial portal system

A

The median eminence is essentially a mass of capillaries receiving blood form the superior hypophysial artery. Lots of neurones coming from the hypothalamic nuclei terminate on the walls of the primary capillary plexus. The primary capillary plexus feeds blood down into portal vessels which run down through the pituitary stalk to terminate within the adenohypophysis.

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12
Q

What happens after the primary capillary plexus feeds blood down into portal vessels?

A

Blood drains to a second capillary plexus in the anterior pituitary – a portal network. From the secondary capillary plexus , blood would flow out thorough jugular veins via the cavernous sinus. This system is critical for control of anterior pituitary function.

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13
Q

What is a portal network

A

A portal network is where blood from the systemic circulation drains from one capillary network to another before returning to the heart.

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14
Q

Where is the primary capillary plexus

A

The median eminence which lies outside the blood-brain barrier meaning that the capillary walls have lots of holes so they are Fenestrated (leaky) Capillaries

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15
Q

Where is the seconday capillary plexus

A

in the anterior pituitary

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16
Q

Why does the hypothamalus plays a major part in controlling anterior pituitary function

A

There is important hypothalamic control over the anterior pituitary through hormones that are released by neurones which originate in the hypothalamus. The hypothalamic neurones which terminate in the median eminence lie on the surface of that primary capillary plexus. When stimulated they release neurosecretion (hormone). The portal system carries these chemicals to their target cells in the anterior pituitary. These hypothalamic hormones will bind to their target cells and stimulate release of anterior pituitary hormones into the circulation

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17
Q

What kind of neurosecretions are released from the hypothalamus

A

hypothalmic releasing and inhibiting hormones

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18
Q

What are the different adenohypophysial cells

A

somatotrophs, lactotrophs, thyrotrophs, gonadotrophs, corticotrophs

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19
Q

What do somatotrophs produce

A

Growth Hormone (Somatotrophin)

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20
Q

What do lactotrophs produce

A

prolactin

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21
Q

What do corticotrophs produce

A

AdrenoCorticoTrophic Hormone (ACTH, Corticotrophin)

22
Q

What do thyrotrophs produce

A

Thyroid Stimulating Hormone (TSH, Thyrotrophin)

23
Q

What do gonadotrophs produce

A

Luteinising Hormone, Follicle Stimulating Hormone (LH and FSH)

24
Q

How are adenohypophysial hormones synthesised, stored and released

A

Synthesised as prohormones. Enzymatic cleavage of the prohormone yields the bioactive hormone. Hormone is stored in secretory granules and released by exocytosis into the bloodstream.

25
Q

What effects can other molecules (not hormones) produced by Adenohypophysial cells

A

paracrine or autocrine effects

26
Q

Give an example of hormone production from precursor prohormone

A

Example: POMC —–> CORTICOTROPHIN + Pro-gMSH + bLPH

27
Q

What 3 forms can adenohypophysial hormones be

A

proteins, glycoproteins and polypeptides

28
Q

Example of protein adenohypophysial hormones and how many amino acids they are made up of

A

Somatotrophin (growth hormone) - 191aa

Prolactin - 199aa

29
Q

Example of glycoprotein adenohypophysial hormones and how many amino acids they are made up of

A

Glycoproteins consist of alpha and beta subunits. The alpha subunit is common to all, beta subunit is different and hence determines the characteristics of the molecule

Thyrotrophin (Beta subunit - 110aa)

LH and FSH (Beta subunit - 115aa)

30
Q

Example of polypeptide adenohypophysial hormones and how many amino acids they are made up of

A

Corticotrophin (ACTH) - 39aa

31
Q

What does each adenohypophysial hormone have

A

two hypothalamic hormones that control them: one which stimulates release of the adenohypophysial hormone and one that inhibits it

32
Q

What is somatotrophin releasing hormone (SRH) /growth hormone releasing hormone (GHRH)

A

a hypothalamic hormone that stimulates the release of somatotrophin. It is dominant over somatostatin

33
Q

What is somatostatin (SS)

A

a hypothalamic hormone that inhibits the release of somatotrophin

34
Q

what is dopamine

A

a hypothalamic hormone that inhibits the release of prolactin. it is dominant over thyrotrophin releasing hormone

35
Q

what is Thyrotrophin releasing hormone (TRH)

A

a hypothalamic hormone that stimulates the release of prolactin and thryotrophin

36
Q

What are the target cells of thyrotrophin

A

the thyroid

37
Q

What is Gonadotrophin releasing hormone (GnRH)

A

a hypothalamic hormone that stimulates the release of Luteinising hormone (LH) and Follicle stimulating hormone (FSH). It is dominant over gonadotrophin inhibitory hormone

38
Q

What are the target cells of gonadotrophins (LH and FSH)

A

testes in men and ovaries in women

39
Q

What are Corticotrophin releasing hormone (CRH) and Vasopressin (VP)

A

hypothalamic hormones that stimulate the release of ACTH (corticotrophin)

40
Q

What are the target cells of somatotrophin (growth hormone)

A

general body tissues, particularly in the liver (endocrine functions)

41
Q

What are the target cells of prolactin

A

breasts - lactating women

42
Q

What are the target cells of corticotrophin

A

adrenal cortex

43
Q

What is the action of somatotrophin

A

It stimulates various metabolic actions in body tissues and is involved in growth. It binds to receptors on the hepatocytes (liver cells) and stimulates the production of hormone from those cells. The molecules produced Somatomedins aka Insulin-like Growth Factor (IGF) I and II

44
Q

What is IGF I is particularly important for

A

growth and development

45
Q

What two ways does somatotrophin work in

A

Direct Effect - binding to somatotrophin receptors in general cells of the body. Hepatocytes (indirectly) - stimulating hepatocytes to produce IGF I

46
Q

What are the metabolic actions of somatotrophin/growth hormone

A

Stimulation of amino acid transport into cells (e.g. muscle) and protein synthesis. Increased gluconeogenesis. Stimulation of lipolysis leading to increased fatty acid production. Increased cartilaginous growth and somatic cell growth

47
Q
A
48
Q

What stimulates the release of growth hormone releasing hormone/somatotrophins from the hypothalamus

A

Certain glucogenic amino acids (arginine). hypoglycaemia (fasting). Exercise. Stress. Oestrogen. Sleep. Ghrelin (from stomach)

49
Q

What are growth hormones released as

A

pulses

50
Q

What is the direct negative feedback in the control of somatotrophin

A

somatomedians (mainly IGF 1) directly stops the release of somatotrophins from the anterior pituitary.

51
Q

What is the indirect negative feedback in the control of somatotrophins

A

somatomedians (mainly IGF 1 ) has an indirect effect on the hypothalamus to reduce the release of GHRH. Somatotrophin also has an effect on the hypothalamus

52
Q

What is the neuro endocrine reflex arc for prolactin

A

Suckling of the breast causes stimulation of the tactile receptors. The afferent neural pathway is stimulated to higher centres. This suppresses the hypothalamic dopaminergic neurones. There is direct stimulation of thyrotrophin releasing hormone - this leads to release of prolactin. This is the efferent endocrine pathway. Prolactin causes milk production is post partum breast

Endocrinology (12 decks)

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