15 Hypothalamic Pituitary Axis and Growth Hormone

Question 1

Where is the Pituitary Gland located?

Answer 1

Beneath Hypothalamus, in sella turcica (=socket of bone)

Question 2

What are the hypothalamus and pituitary gland a link between?

Answer 2

Endocrine and nervous system

Question 3

What processes do the hypothalamus and pituitary gland modulate?

Answer 3

1 Body growth 2 Lactation 3 Milk Secretion 4 Reproduction 5 Adrenal Gland function 6 Water homeostasis 7 Puberty 8 Thyroid gland function

Question 4

What is the structure of the pituitary gland?

Answer 4

Anterior (adenohypophysis) Posterior (neurohypophysis) (Infundibulum= pituitary stalk)

Question 5

How do the anterior and posterior pituitary glands differ?

Answer 5

1, Distinct embryological origins: Anterior- oral ectoderm Posterior- neuroectoderm= physically connected to hypothalamus 2, Distinct functions

Question 6

How does the posterior pituitary gland function?

Answer 6

NEUROCRINE FUNCTION 1-Oxytocin and ADH - produced- neurosecretory cells in supraoptic+ paraventricular nuclei of hypothalamus 2- Transported down nerve cell axons 3- Stored and released in posterior pituitary- into general circulation via capillary bed

Question 7

How does the anterior pituitary function?

Answer 7

1-Hormones-synthesised in hypothalamus- transported down axons- stored in median eminence 2- Hormones released into hypophyseal portal system- stimulate/inhibit endocrine cells in anterior pituitary 3- Endocrine cells secrete hormones into blood stream (hormones in anterior pituitary= also autocrine and paracrine)

Question 8

What are the functions of the 2 hormones which are produced by the hypothalamus for release in the posterior pituitary?

Answer 8

1- Oxytocin- milk let down+ uterus contractions 2- Anti-Diuretic Hormone- regulation of body water volume

Question 9

What is a tropic hormone?

Answer 9

A hormone that has a direct effect on the release of ANTERIOR pituitary hormones.

Question 10

What are the 6 tropic hormones produced in the hypothalamus?

Answer 10

Releasing hormones: 1 TRH: Thyrotropin releasing hormone 2 CRH: Corticotropin releasing hormone 3 GnRH: Gonadotropin releasing hormone 4 GHRH: Growth hormone releasing hormone Inhibiting hormones: 5 GHIH: Growth hormone inhibiting hormone (SOMATOSTATIN) 6 PIH: Prolactin release inhibiting hormone (DOPAMINE)

Question 11

What do trophic hormones do?

Answer 11

Affect growth

Question 12

What are the 6 hormones produced by the anterior pituitary?

Answer 12

1- FSH- Follicle stimulating hormone (development- eggs and sperm) 2-LH- Lutenising Hormone (ovulation and secretion- sex hormones) 3- GH- Growth Hormone (stimulates IGFs- growth+energy metabolism) 4-Prolactin (mammary gland development and milk secretion) 5-TSH- Thyroid stimulating hormone 6- ACTH- Adrenocorticotropic hormone (secretion- hormones from adrenal cortex

Question 13

Outline to negative feedback mechanism of the Hypothalamic-Pituitary- Adrenal Axis.

Answer 13

Stress- e.g. low BP- Hypothalamus- CRH–> anterior pituitary- ACTH–> adrenal cortex-cortisol. Cortisol then has negative feedback on Hypothalamus and Anterior pituitary

Question 14

What is the main mechanism for growth promotion of Growth Hormones?

Answer 14

IGFs (insulin-like growth factors) (aka Somatomedins)- produced by Liver&Skeletal muscle- response to GH (Actions of IGFs can be endocrine, paracrine or autocrine) (Insulin and IGF1 can have Metabolic and Mitogenic effects)

Question 15

Why is GH so important in childhood and teenage years?

Answer 15

Stimulates long bone growth (IGFs stimulate bone and cartilage growth)

Question 16

What do GH and IGFs do in adults?

Answer 16

=Help maintain muscle and bone mass =Promote healing and tissue repair =Modulate metabolism and body composition

Question 17

How is GH secretion controlled?

Answer 17

CNS-inputs to hypothalamus- affect GHRH and Somatostatin (GHIH)

Question 18

What causes GH secretion to increase?

Answer 18

1. Onset of deep sleep 2. Stress (trauma, surgery, fever) 3, Exercise 4, Decrease in glucose/fatty acids 5, Fasting

Question 19

What causes GH secretion to decrease?

Answer 19

1, Obesity 2, REM sleep 3, Increase in glucose/fatty acids

Question 20

What are the two negative feedback loops regulating GH secretion?

Answer 20

LONG LOOP: IGFs - inhibit GHRH release -stimulate GHIH (somatostatin release) therefore inhibits GH release SHORT LOOP: GH -stimulates GHIH (somatostatin) release

Question 21

What happens if someone has Growth Hormone Deficiency (complete/partial)?

Answer 21

Pituitary dwarfism (proportionate) Growth rate slower than expected- below 3rd percentile Delayed/no sexual development in teenage years

Question 22

How is GH deficiency treated?

Answer 22

GH therapy (response= good)

Question 23

What happens if someone has Growth Hormone Excess?

Answer 23

Childhood: Gigantism (rare) Adulthood: Acromegaly (large extremities)

Question 24

How does GH exert its effects on cells?

Answer 24

GH receptors activate Janus Kinases –> Activate transcription factor–> IGF production

Question 25

What are the 2 IGFs found in mammals?

Answer 25

IGF1: Mainly involved- fatal growth IGF2: Major GF- in adults

Question 26

How do IGFs act?

Answer 26

On IGF receptors, modulate: Hypertrophy Hyperplasia Increase protein synthesis rate Increase lipolysis in adipose tissue

Question 27

Apart from GH, what other hormones influence growth and how? (5)

Answer 27

1, Insulin- interacts w./ IGF receptors 2, Thyroid Hormones- promote CNS development&GH secretion 3, Androgens- accelerate pubertal growth spurt, increase muscle mass, promote closure- epiphyseal plates 4, Estrogens- decrease somatic growth- promote closure- epiphyseal plates 5, Glucocorticoids- inhibit somatic growth