The hypothalamo-adenohypophyseal axis: anterior pituitary

Question 1

What is the alternative name for the pituitary gland?

Answer 1

HYPOPHYSIS

Question 2

Why is the pituitary gland know as the master gland?

Answer 2

Regulates a series of other and it controls many body systems

Question 3

What is the alternate name for the anterior pituitary gland?

Answer 3

adenohypophysis

Question 4

What is the alternate name for the posterior pituitary gland?

Answer 4

neurohypophysis

Question 5

Describe the embryology of the pituitary gland?

Answer 5

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The 2 components of the pituitary gland develop from different structures. There is a upward growth from the buccal cavity called Rathke’s pouch towards a downward growth from the base of the brain - these two growths combine to make one gland.

So the pituitary gland has 2 components, 1 secretory part derived from the buccal cavity the adenohypophysis and 1 neural part, the neurohypophysis, made up of nerve axons derived from the base of the brain.

Glandular Tissue - Buccal Cavity (pharyngeal region of the mouth) has an extension that starts growing upwards Nervous Tissue - there is a downwards movement of tissue from the developing hypothalamus .

These two tissues then fuse and normally lose contact with the rest of the buccal cavity. So one part of the pituitary is derived from glandular tissue (adenohypophysis) and the other part is derived from neural tissue (neurohypophysis)

Question 6

Besides hormonal effects, what can a tumour of the pituitary gland cause and why can it do this?

Answer 6

The optic chiasm is near the anterior pituitary and this will become relevant n Y2 Endocrinology lectures when you learn that tumours of the pituitary gland can cause visual disturbance. add pic

Question 7

What are groups of nueronal cell bodies known as?

Answer 7

Groups of neuronal cell bodies are called nuclei.

Question 8

The hypothalamus surrounds one of the ventricles of the brain What is the name of this ventricle?

Answer 8

3rd Ventricle

Question 9

What is the region of median eminence?

Answer 9

Median Eminence = an area that lies between the top of the pituitary stalk and the hypothalamus add pic

Question 10

A different population of neurons have shorter axons and these terminate in the part of the hypothalamus which abuts the pituitary gland Name this region?

Answer 10

Region of median eminence

Question 11

What is the body of the anterior putituary gland known as?

Answer 11

Pars distalis is the body of the anterior pituitary add pic

Question 12

What is the part of the pituitary gland that wraps around the pituitary stalk?

Answer 12

the pars tuberalis is the part of the anterior pituitary which wraps around the pituitary stalk add pic

Question 13

What is the Neurohypophysis mainly made up of ?

What does the Adenohypophysis consist of?

Answer 13

Neurohypophysis- (mainly nerve axons and nerve terminals) Adenohyphysis- Secretory cells add pic

Question 14

Where do some of the axons coming from the hypothalmic nuclei terminate at?

Answer 14

Neurohypophysis and the Region of median eminence add pic

Question 15

Describe the THE HYPOTHALAMIC – HYPOPHYSIAL PORTAL CIRCULATION? Start at the superior hypophyseal artery

Answer 15

It starts with blood arriving in the SUPERIOR hypophyseal artery and this enters a capillary network in the median eminence.

From this capillary network, blood drains to a second capillary network in the anterior pituitary – a portal network.

From the secondary capillary system, blood would flow out into the venous system via the cavernous sinus.

This system is critical for control of anterior pituitary function. The importance of the HYPOTHALAMIC – HYPOPHYSIAL PORTAL CIRCULATION is that it can carry messages from the hypothalamus to the anterior pituitary gland

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Question 16

What is a portal network?

Answer 16

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

Question 17

What does fenestrated mean?

Answer 17

Fenestrated capillary is a leaky capillary

Question 18

What in the hypothalmic-hypophysial portal circulation is fenestrated?

Answer 18

Primary Capillary Plexus Secondary Capillary Plexus

Question 19

Where do many nuerones (not all) coming from the hypothalmic nuclei terminate at?

Answer 19

Lots of neurones coming from the hypothalamic nuclei terminate on the walls of the PRIMARY CAPILLARY PLEXUS

Question 20

How does the hypothalamus play a major part in controlling anterior pituitary function?

Answer 20

Those short hypothalamic neurones which terminate in the median eminence lie on the surface of that primary capillary plexus.

These specific hypothalamic neurones, which abut the primary capillary network, when stimulated, release neurosecretion – hormones – which are going to get into the blood flowing through this primary capillary plexus and then they will be transported to the anterior pituitary where there will exert their effects and stimulate release of anterior pituitary hormones.

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Question 21

What two types of Nuerosecretions from the nureons in the hypothalamus are there?

Answer 21

HYPOTHALAMIC RELEASING/INHIBITING HORMONES

Question 22

What do Samatotrophs produce?

Answer 22

Growth Hormone (Somatotrophin)

Question 23

What do Lactotrophs produce?

Answer 23

Prolactin

Question 24

What do thyrotrophs produce?

Answer 24

Thyroid Stimulating Hormone (TSH, Thyrotrophin)

Question 25

What do Gonadotrophs Produce?

Answer 25

Luteinising Hormone, Follicle Stimulating Hormone (LH and FSH)

Question 26

What do Corticotrophs produce?

Answer 26

AdrenoCorticoTrophic Hormone (ACTH, Corticotrophin)

Question 27

Name the cells that make up the anterior pituitary gland and name their coressponding hormone?

Answer 27

REMEBER THERE ARE 6 HORMONES AND 5 CELL TYPES add pic

Question 28

Name the 2 Protein hormones (Very large in size) produced by the anterior pituitary gland?

Answer 28

GROWTH HORMONE (SOMATOTROPHIN ) 191 aa PROLACTIN 199 aa

Question 29

Name the Glycoprotein hormones made by the Anterior pituitary gland?

Answer 29

THYROID STIMULATING HORMONE (TSH, THYROTROPHIN) b-sub-unit 110 aa 2 GONADOTROPHINS both have 115 aa b-sub-unit - LUTEINISING HORMONE (LH) - FOLLICLE STIMULATING HORMONE (FSH)

Question 30

What is similar to all of the Glycoprotein Hormones (in terms of their structure) and what distinguishes them?

Answer 30

Alpha subunit is common to all, Beta subunit is different and hence determines the characteristics of the molecule

Question 31

Name the Stimulatory and Inhibitory hypothalmic hormones for somatotrophin (Growth hormone).

Answer 31

Growth Hormone Releasing Hormone (GHRH, somatotrophin releasing hormone )- STIMULATORY Somatostatin (SS)-INHIBITORY Neurosecretions from different hypothalamic nuclei – GHRH in bold as this is the dominant signal and stimulates GH release. SS is a short polypeptide which is inhibitory on GH release – minor compared to dominant GHRH. It is the pulse of these hormones in relation to each other which will dictate GH release.

Question 32

Name the Stimulatory and Inhibitory hypothalmic hormones for Prolactin?

Answer 32

Dopamine (DA)-INHIBATORY Thyrotrophin releasing hormone (TRH)-STIMULATORY

Question 33

Name the stimulatory hypothalmic hormone for TSH

Answer 33

TRH- Thyrotropin-releasing hormone

Question 34

Name the stimulatory hypothalmic hormone for LH and FSH?

Answer 34

Gonadotrophin releasing hormone (GnRH

Question 35

Name the stimulatory hypothalmic hormone for ACTH (corticotrophin).

Answer 35

Corticotrophin releasing hormone (CRH) Vasopressin (VP)

Question 36

Some hypothalamic hormones are dominant over their counterpart Name 2 examples of this

Answer 36

Somatrotophin Releasing Hormone (SRH or GHRH) - dominant over somatostatin Dopamine - dominant over thyrotrophin releasing hormone

Question 37

How are hypothalmic hormones released and how does this effect the way that the anterior pituitary hormones are released?

Answer 37

Hypothalamic hormones are released in pulsatile fashion and hence, anterior pituitary hormones are released in a pulsatilefashion

Question 38

Name the only hypothalmic hormone where it is the dominant single is the inhibatory signal?

Answer 38

Dopamine

Question 39

List all of the ADENOHYPOPHYSIAL HORMONES AND THEIR MAIN TARGET CELLS?

Answer 39

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Question 40

Name ALL of the effects of the Growth hormone in the body?

Answer 40

Lots of GH Rs on hepatocytes – binding of GH to these receptors causes production of IGF-1 (and 2) which mediates some of the effects of GH in the tissues. Somatomedins are a group of proteins that promote cell growth and division in response to stimulation by growth hormone (GH) also known as somatotropin (STH). Somatomedins have similar biological effects to somatotropin. add pic

Question 41

Name some examples of somatomedins

Answer 41

IGF 1 and IGF 2

Question 42

Name the two ways somatotrophins work?

Answer 42

Direct Effect - binding to somatotrophin receptors in general cells of the body Hepatocytes - stimulating hepatocytes to produce IGF I Both these pathways mean that somatotrophin controls large aspects of metabolism

Question 43

List the 4 Metabolic Actions of Somatotrophin ?

Answer 43

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

Question 44

Why can Growth hormone predispose you to Diabetes Mellitus?

Answer 44

GH increases gluconeogenesis

Question 45

Why does growth hormone cause the increase of amino acids into cells?

Answer 45

Certain glucogenic amino acids can stimulate growth hormone release. Makes sense because after a meal you will have lots of amino acids coming in so by stimulating growth hormone release, you increase amino acid movement into the cells and increase protein synthesis at the nuclear level

Question 46

Name things that stimulate growth hormone release?

Answer 46

Sleep (stages III and IV) Stress Oestrogens Exercise Fasting (hypoglycaemia) Amino acids eg arginine (Maramite is rich in arginine) Ghrelin (from stomach) add pic

Question 47

Name the direct and indirect inhibotors of somatotrophin?

Answer 47

Inhibitors of somatotrophin: Direct - IGF I back to the pituitary. Indirect - IGF I back to the hypothalamus . Somatotrophin also has its own negative feedback effects - back to the hypothalamus - auto-negative feedback loop. add same pic as before

Question 48

Describe the feedback loop for prolactin?

Answer 48

Stimulationn of Tactile receptors (SUCKLING) This cause the suppression of hypothalmic dopaminergic neurones hence less dopamine release. add pic