S8 Hypothalamic Pituitary Axis and Growth Hormone

Question 1

What processes do the hypothalamus and pituitary gland modulate?

Answer 1

• body growth
• milk secretion
• reproduction
• lactation
• adrenal gland function
• thyroid gland function
• water homeostasis
• puberty

Question 2

What are the two parts of the pituitary gland?

Answer 2

Anterior and posterior gland

Question 3

What is the embryological origin of the anterior pituitary gland?

Answer 3

Arises the evagination of the oral ectoderm (Rathke’s pouch) which is primitive gut tissue

Question 4

What is the embryological origin of the posterior pituitary gland?

Answer 4

Originates from the neuroectoderm which is primitive brain tissue

Question 5

What connects the hypothalamus to the pituitary gland?

Answer 5

The infundibulum (pituitary stalk)

Question 6

What is released from the posterior pituitary?

Answer 6

• oxytocin

* antidiuretic hormone (ADH)

Question 7

Where are oxytocin and ADH produced?

Answer 7

Produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus

Question 8

What type of signalling transports oxytocin and ADH to the posterior pituitary?

Answer 8

Neurocrine signalling

Transported down nerve cell axons

Question 9

Where are hormones that act on the anterior pituitary synthesised in the hypothalamus stored before release in the hypophyseal portal system?

Answer 9

Stored in median eminence

Question 10

What is the hypophyseal portal system?

Answer 10

Between the hypothalamus and pituitary gland - connection of two capillary beds

Question 11

What action do hormones that are released from the hypothalamus to act on the anterior pituitary have?

Answer 11

Stimulate or inhibit target endocrine cells in anterior pituitary (via neurocrine signalling)

Question 12

What do endocrine cells in the anterior pituitary do?

Answer 12

Secrete a variety of hormones into the blood stream to act on distant target cells (endocrine signalling)

Also have autocrine and paracrine functions

Question 13

What does oxytocin do?

Answer 13

Involved in the milk let down reflex and uterus contractions during birth

Question 14

What does ADH do?

Answer 14

Regulation of body water volume

Question 15

What are the 6 tropic hormones of the hypothalamus?

Answer 15

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

Question 16

What does tropic mean?

Answer 16

Affect the release of other hormones in the target tissue

Question 17

What 6 hormones are produced by the anterior pituitary?

Answer 17

• thyroid stimulating hormone (TSH)
• adrenocorticotropic hormone (ACTH)
• luteinising hormone (LH)
• follicle stimulating hormone (FSH)
• prolactin (PRL)
• growth hormone (GH)

Question 18

On which gland does TSH act? What does it cause the release of?

Answer 18

Thyroid gland

Thyroid hormone (T3 and T4) which affect metabolic rate

Question 19

On which gland does ACTH act? What does it cause the release of?

Answer 19

Adrenal gland

Cortisol part of the stress response and involved in metabolic actions

Question 20

On which gland does prolactin act? What it cause the effect of prolactin?

Answer 20

Mammary glands

Breast growth and milk secretion

Question 21

On which tissues does growth hormone act? What does it cause the release of?

Answer 21

Liver and many tissues

IGFs released from liver for growth

Question 22

On which gland does LH act? What does it cause the release of?

Answer 22

Ovaries in females, testes in males

Sex hormone secretion

Question 23

On which gland does FSH act? What effect does it have?

Answer 23

Ovaries in females, testes in males

Gamete production

Question 24

How are the pathways of hypothalamic and anterior pituitary hormone release/production regulated?

Answer 24

By negative feedback

Question 25

What is the hypothalamic-pituitary-adrenal axis?

Answer 25

Stress occurs (pain, fever, etc) casing the hypothalamus to release CRH which stimulates the anterior pituitary to release ACTH which stimulates the adrenal cortex to release cortisol which acts on target tissues Cortisol inhibits the anterior pituitary releasing ACTH and the hypothalamus releasing CRH

Question 26

What factors influence growth?

Answer 26

* genetics * nutrition * environment * hormones e.g. growth hormone

Question 27

Where is growth hormone produced? What is it stimulated by, what is it inhibited by?

Answer 27

Produced in anterior pituitary Stimulates by hypothalamic GHRH, inhibited by hypothalamic somatostatin

Question 28

What type of hormone is growth hormone? How is it folded properly?

Answer 28

A protein hormone that has a signal peptide that needs to be cleaved before proper folding can occur

Question 29

How are the growth-promoting effects of growth hormone usually exerted?

Answer 29

Exerted via insulin-like growth factors (somatomedins) - GH causes the liver and skeletal muscle to produce and secrete IGFs

Question 30

Why is GH essential for normal growth during childhood and teenage years?

Answer 30

* it stimulates long bone growth (length and width before epiphyseal closure, width after) * IGFs stimulate bone and cartilage growth

Question 31

Why are GH and IGFs essential in adults?

Answer 31

* help maintain muscle and bone mass * promote healing and tissue repair * modulate metabolism and body composition

Question 32

When is GH secretion at it’s highest?

Answer 32

During deep sleep

Question 33

Does REM sleep decrease or increase GH secretion?

Answer 33

Decrease

Question 34

Does stress increase or decrease GH secretion?

Answer 34

Increase

Question 35

Does exercise increase or decrease GH secretion?

Answer 35

Increase

Question 36

What does a decrease in glucose and/or fatty acids mean for GH secretion? So what does an increase in glucose or free fatty acid lead to?

Answer 36

GH secretion increases A decrease

Question 37

In fasting and obesity does GH secretion increase or decrease?

Answer 37

Fasting - increase Obesity - decrease Increases in fasting to break down fatty tissue to release energy

Question 38

What is GH secretion related by in terms of negative feedback?

Answer 38

* long loop - mediated by IGFs - they inhibit release of GHRH from hypothalamus, stimulate release of somatostatin from hypothalamus and inhibit the release of GH from the anterior pituitary * short loop - mediated by GH - stimulates somatostatin release

Question 39

What is the name of a growth hormone deficiency in childhood?

Answer 39

Pituitary dwarfism

Question 40

What is pituitary dwarfism? What are the signs of it? How is it treated?

Answer 40

* proportionate type of dwarfism * can be a complete or partial deficiency * growth rate is slower than normal * there’s delayed or no sexual development during teenage years * height is below 3rd percentile on standard growth charts * treated with GH therapy

Question 41

What is the name of the growth hormone excess condition that occurs in childhood?

Answer 41

Gigantism This is rare

Question 42

What is the name of the growth hormone excess condition that occurs in adulthood?

Answer 42

Acromegaly Large extremities e.g. hands, feet, lower jaw

Question 43

How does GH exert its effects on cells?

Answer 43

GH receptors activate Janus kinases (JAKs) - tyrosine kinase receptors and these receptors cause activation of signalling pathways that lead to transcription factor activation and IGF production

Question 44

What are the 2 IGFs in mammals? What is each mainly involved in?

Answer 44

IGF1 - major growth factor in adults IGF2 - mainly involved in fetal growth

Question 45

What modulates the availability of IGFs?

Answer 45

Binding proteins

Question 46

What type of signalling actions do IGFs carry out?

Answer 46

Paracrine, autocrine and endocrine

Question 47

What do IGFs act through? What are their actions?

Answer 47

IGF receptors Hypertrophy (cell growth), hyperplasia (cell number increase), increase in rate of protein synthesis and increase in rate of lipolysis in adipose tissue

Question 48

Insulin and IGF1 can act on the same receptor, what is this receptor? What is the main effect of this receptor type?

Answer 48

A hybrid receptor The main effect from this receptor are mitogenic effects

Question 49

The effects of insulin and IGF1 are both metabolic effects and mitogenic effects, which has the main effect on metabolism and which on mitosis?

Answer 49

Metabolism - insulin | Mitosis - IGF1

Question 50

What is the growth related action of insulin?

Answer 50

Enhances somatic growth and interacts with IGF receptors

Question 51

What is the growth related action of thyroid hormones?

Answer 51

Promote CNS development and enhance GH secretion

Question 52

What is the growth related action of androgens?

Answer 52

* accelerate pubertal growth spurts * increase muscle mass * promote closure of epiphyseal plates

Question 53

What is the growth related action of estogens?

Answer 53

* decrease somatic growth | * promote closure of epiphyseal plates

Question 54

What is the growth related action of glucocorticoids?

Answer 54

Inhibits somatic growth

Question 55

What can IGF1 do in some tissues? How does this relate to tumours?

Answer 55

Inhibits apoptosis Some types of tumours express abundant ICF1 receptors to inhibit apoptosis

Question 56

When can synthetic oxytocin, pitocin, be administered? And why?

Answer 56

To increase uterine tone and control bleeding after birth and to help induce uterine contractions during birth Oxytocin/pitocin bind too oxytocin receptors on uterine smooth muscle cells and activate uterine contractions

Question 57

What is another role of ADH/vasopressin other than reabsorption of water in the kidneys? What is a clinical advantage of this?

Answer 57

Increase peripheral vascular resistance by activating ADH receptors on smooth muscle cells of blood vessels and causing vasoconstriction which increases arterial blood pressure Restoring blood pressure in hypovolaemic shock during haemorrhage

Question 58

What hormone does TRH have a minor positive control on?

Answer 58

Prolactin

Question 59

Why is prolactin releasing hormone (PRH) not often considered one of the tropic hormones of the hypothalamus?

Answer 59

Because it may not exist