7.1- The Hypothamic Pituitary Axis

Question 1

Where does the pituitary gland sit in relation to the hypothalamus?

Answer 1

Sits below the hypothalamus in a socket of bone called the sella turcica

Question 2

What do the hypothalamus and pituitary form together?

Answer 2

A complex functional unit

Question 3

What are the two components of the pituitary gland?

Answer 3

Anterior pituitary

posterior pituitary
Is physically connected to the hypothalamus

Question 4

What is the neurocrine function of the posterior pituitary?

Answer 4

Oxytocin and ADH
- produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus

• transported down nerve axons to posterior pituitary
• stored and released from posterior pituitary in general circulation to act on distant target sites

Question 5

What’s the function of the anterior pituitary?

Answer 5

Hormones made in hypothalamus are transported down axons and stored in the median eminence before released into the hypophyseal portal system
These hormones stimulate target endocrine cells in the anterior pituitary gland (neuroendocrine function)

Endocrine cells of ant pit secrete hormones into bloodstream for endocrine function

Hormones in ant pit also have autocrine and paracrine function

Question 6

What are the two distinct neurocrine pathways for hormones made by nerve cells in the hypothalamus?

Answer 6

Direct effects on distant target tissues with oxytocin and ADH are released from posterior pituitary

Hormones secreted into hypophyseal portal system affect endocrinecells within anterior pituitary

Question 7

What’s the role of ADH and oxytocin?

Answer 7

Oxytocin - milk and uterus contractions during birth

ADH - regulation of body water volume

Question 8

What’s a tropic hormone?

Answer 8

Hormone that affects the release of other hormones in the target tissue

Question 9

What are the 6 tropic hormones of the hypothalamus and what do they do?

Answer 9

TRH - thyrotropin releasing hormone 
PIH - prolactin release inhibiting hormone (dopamine)
CRH - corticotropin releasing hormone 
GnRH - gonadotropin releasing hormone 
GHRH - growth hormone releasing hormone 
GHIH - growth hormone inhibiting hormone

Question 10

What do tropic hormones from the hypothalamus effect?

Answer 10

Have direct effects on the release of anterior pituitary hormones

Question 11

What hormones are produced by the anterior pituitary?

Answer 11

TSH - thyroid stimulating hormone
( secrete thyroid hormone from thyroid gland)

ACTH - adrenocorticotropic hormone
( secreting of hormones from adrenal cortex)

LH - leutinising hormone
( ovulation and secretion of sex hormones)

FSH - follicle stimulating hormone
( development of eggs and sperm)

PRL - prolactin
( mammary gland development and milk secretion)

GH - growth hormone
( growth and energy metabolism)

Question 12

How would the negative feedback loop of the release of corticotropin releasing hormone work?

Answer 12

1) stimulus e.g pain, fever, low blood pressure
2) change detected by hypothalamus
3) corticotropin releasing hormones (CRH) goes to ant pit
4) ant pit releases Adrencocorticotropic hormone
5) goes to adrenal cortex and cortisol is released
6) levels of cortisol rise = less CRH produced by hypothalamus

Question 13

What is hyperplasia?

Answer 13

Cell growth due to increase in number

How tumours grow

Question 14

What is growth hormone responsible for

Answer 14

• stimulates long bone growth = length and width prior to epiphyseal closure, width after epihyseal closure
• in adults GH and IGF help maintain muscle and bone mass and promote healing and tissue repair as well as modulating metabolism and body composition

Question 15

What inhibits growth hormone?

Answer 15

Somatostatin

Question 16

How do growth promoting effects exert?

Answer 16

Via insulin like growth factors (somatomedin)

In response to GH cells of the liver and skeletal muscles produce and secrete IGF

Question 17

What movements cause levels of growth hormone to fluctuate?

Answer 17

Increase

• surge in GH after deep sleep
• surge if stressed
• exercise increases
• fasting: decrease in glucose or fatty acids

Decrease

• rapid eye movement sleep = decrease in GH
• increase in glucose or free fatty acids = decrease in secretion
• obesity

Question 18

How is GH secretion regulated in its negative feedback loop?

Answer 18

Long loop

• mediated by IGF
• inhibit release of GHRH from hypothalamus
• stimulates the release of somatostatin from hypothalamus
• inhibit release of GH from anterior pituitary

Short loop
- mediated by GH itself via stimulation of somatostatin release.

Question 19

What is the consequence of growth hormone deficiency?

Answer 19

In childhood, results in pituitary dwarfism

• proportionate type of dwarfism
• complete or partial deficiency
• both types respond to GH therapy
• delayed or no sexual development during teen years

Question 20

What are the consequences of growth hormone excess?

Answer 20

In childhood, results in gigantism

In adulthood leads to acromegaly = large extremities

• hands
• feet
• lower jaw

Question 21

How does GH exert its effects on cells?

Answer 21

GH receptors activate Janus kinases (JAK)

• binding causes phosphorylation of JAK and after phosphorylation of GH receptor
• activation of signalling pathways
• transcription factor activation and IGF production

Question 22

What are insulin like growth factors?

Answer 22

Main types

• IGF1 (fetal growth) and IGF2 (adults)
• binding proteins modlate their availability
• actions can be paracrine autocrine and endocrine
• act through IGF receptors to modulate hypertrophy, hyperplasia, increase the rate of protein synthesis, increase the rate of lipolysis.

Question 23

What hormones other than GH influence growth?

Answer 23

• insulin:interacts with IGF
• thyroid hormones: enhance GH secretion
• androgens: accelerate pubertal growth spurt, increase muscle mass
• estrogens: decrease somatic growt, promote closure of epiphyseal plates
• glucocorticoids: inhibit somatic growth