Hypothalamic pituitary axis and growth hormone

Question 1

What is the hypothalamic pituitary axis?

Answer 1

a functional unit that links the endocrine and nervous system (hypothalamus and pituitary)

Question 2

What is the sella turcica?

Answer 2

A socket of bone below the hypothalamus where the pituitary gland sits

Question 3

What is the Infundibulum?

Answer 3

The pituitary stalk that physically connects the hypothalamus with the posterior pituitary

Question 4

List a few processes that is regulated by the hypothalamic pituitary axis

Answer 4

• Body growth
• Reproduction
• Adrenal gland function
• Milk secretion
• Lactation
• Water homeostasis

Question 5

What are the two parts of the pituitary gland and where to they originate from?

Answer 5

1) Anterior (adenohypophysis) = evagination of oral ectoderm (Rathke’s pouch)
2) Posterior (neurohypophysis) = neuroectoderm

Question 6

Describe the function of the posterior pituitary gland

Answer 6

Stores and releases oxytocin and ADH (synthesised in supraoptic and paraventricular nuclei of the hypothalamus)

Question 7

Describe the function of the anterior pituitary gland

Answer 7

Produces and secretes 6 hormones that is stimulated (or inhibited) by tropic hormones from the hypothalamus

Question 8

Describe how the tropic hormones from the hypothalamus stimulate/inhibit the target endocrine cells of the anterior pituitary

Answer 8

• transported down to the median eminence

- released to the hypophyseal portal system (blood supply)

Question 9

Oxytocin (effect and where its produced/secreted)

Answer 9

• Milk let down and uterus contraction in birth

- Produced in the hypothalamus; secreted from posterior pituitary

Question 10

ADH/Vasopressin (effect and where its produced/secreted)

Answer 10

• Regulates body water volume

- Produced in the hypothalamus; secreted from posterior pituitary

Question 11

TRH (effect and where its produced/secreted)

Answer 11

• Tropic
• Thyroid releasing hormone
• Produced and released from hypothalamus

Question 12

PIH/Dopamine (effect and where its produced/secreted)

Answer 12

• Tropic
• Prolactin release-inhibiting hormone
• Produced and released from the hypothalamus

Question 13

CRH (effect and where its produced/secreted)

Answer 13

• Tropic
• Corticotropin releasing hormone
• Produced and released from hypothalamus

Question 14

GnRH (effect and where its produced/secreted)

Answer 14

• Tropic
• Gonadotropin releasing hormone
• Produced and released from hypothalamus

Question 15

GHRH (effect and where its produced/secreted)

Answer 15

• Tropic
• Growth hormone releasing hormone
• Produced and released from hypothalamus

Question 16

GHIH/Somatostatin (effect and where its produced/secreted)

Answer 16

• Tropic
• Growth hormone-inhibiting hormone
• Produced and released from hypothalamus

Question 17

TSH (effect and where its produced/secreted)

Answer 17

• Thyroid stimulating hormone

- Produced and released from anterior pituitary

Question 18

ACTH (effect and where its produced/secreted)

Answer 18

• Adrenocorticotropic hormone
• Secretion of hormones from adrenal cortex
• Produced and released from anterior pituitary

Question 19

LH (effect and where its produced/secreted)

Answer 19

• Lutenising hormone
• Ovulation and secretion of sex hormones
• Produced and released from anterior pituitary

Question 20

FSH (effect and where its produced/secreted)

Answer 20

• Follicle stimulating hormone
• Development of eggs and sperm
• Produced and released from anterior pituitary

Question 21

PRL (effect and where its produced/secreted)

Answer 21

• Prolactin
• Mammary gland development and milk secretion
• Produced and released from anterior pituitary

Question 22

GH (effect and where its produced/secreted)

Answer 22

• Growth hormone
• Growth and energy metabolism and stimulates IGFs
• Produced and released from anterior pituitary

Question 23

What mechanism are the hormones of the hypothalamic pituitary axis regulated?

Answer 23

Negative feedback loop

Question 24

What are the effects of GH in childhood and teenage years?

Answer 24

• Stimulates long bone growth

- IGFs stimulate both bone and cartilage growth

Question 25

What are the effects of GH in adults?

Answer 25

- Maintain muscle and bone mass - Promote healing and tissue repair - Modulating metabolism and body composition

Question 26

How is the production and release of GH regulated

Answer 26

- GHRH stimulates release - GHIH/Somatostatin inhibits release - Long loop negative feedback = mediated by IGFs - Short loop = mediated by GH itself

Question 27

List a few factors that INCREASES GH secretion

Answer 27

- After onset of deep sleep - Exercise - Decrease in glucose or fatty acids - Fasting - Stress

Question 28

List a few factors that DECREASES GH secretion

Answer 28

- REM sleep - Increase in glucose or fatty acids - Obesity

Question 29

Describe growth hormone deficiency

Answer 29

- Growth rated in childhood slower than expected for age - No sexual development in teen years - Leads to pituitary dwarfism - Height is below 3rd percentile on standard growth charts

Question 30

Describe growth hormone excess

Answer 30

- Leads to gigantism (from childhood) - Rare, often caused by Pituitary adenoma - Leads to acromegaly (large extremities -> hands, feet, lower jaw)

Question 31

Describe the mechanism of how GH brings on its effect

Answer 31

1) Growth hormone binds to Growth hormone receptor 2) GH receptor activates Janus kinase (similar to tyrosine kinase) 3) Cross phosphorylation of JAK 4) Phosphorylation of GH receptor 5) Activates signalling pathway 6) Transcription factors activated and IGF produced

Question 32

What is IGF?

Answer 32

- Insulin growth receptors | - Bind to IGF receptors and modulate: hypertrophy, hyperplasia, protein synthesis and lipolysis

Question 33

What are the 2 IGFs in mammals and which period are they normally needed?

Answer 33

- IGF2 = mainly in fetal growth | - IGF1 = major growth factor in adults

Question 34

What other hormones influence growth and what are their effects?

Answer 34

- Insulin = enhances somatic growth; interacts with IGF receptors - Thyroid hormone = Promote CNS development and enhances GH secretion - Androgens = Accelerate pubertal growth spurt; increase muscle mass - Oestrogen = Decrease somatic growth; promote closure of epiphyseal plates - Glucocorticoids = Inhibit somatic growth