Lecture 21--Hormonal regulation of growth

Question 1

What does growth depend upon?

Answer 1

Nutritional status and endocrine control by the brain

Question 2

What hormone stimulates growth?

Answer 2

Growth Hormone

Question 3

Where is growth hormone most abundant?

Answer 3

Adenohypophysis

Question 4

What regulates the release of growth hormone?

Answer 4

Hypothalamus

Question 5

What does the hypothalamus release that stimulates GH release?

Answer 5

Growth hormone releasing hormone

GHRH

Question 6

Where does GHRH act?

Answer 6

Anterior pituitary

Question 7

What does GHRH on the anterior pituitary do?

Answer 7

Stimulates release of GH

Question 8

What inhibits GH release from the anterior pituitary?

Answer 8

Somatostatin

Question 9

What are the direct effects of GH?

Answer 9

Acts on skeletal muscle, adipose and bone

Question 10

What are the indirect effects of GH?

Answer 10

Acts on liver to release IGF-1 acting on GH

Question 11

What effects the release of GH?

Answer 11

Stress, exercise and sleep

Question 12

Can GH release affect weight gain?

Answer 12

YES

Question 13

What are the effects of GH on the body?

Answer 13

• Activates metabolic processes
• ++ protein synthesis
• ++ amino acid transport
• ++ lipolysis
• Reduces glucose transport and metabolism
• ++ fibroblast differentiation
• ++ in bone density
• ++ IGF production in the liver and fibroblasts

Question 14

What are IGFs?

Answer 14

Insulin-like growth factors, which are produced in the liver. They are multifunctional homrones that regulate cellular proliferation and cellular metabolism

Question 15

Are IGFs similar to insulin?

Answer 15

Yes, they resemble insulin in structure and function

Question 16

Does IGF have autocrine and paracrine effects?

Answer 16

Yes

Question 17

How are IGF-I and IGF-II different in adults and babies?

Answer 17

IGF-I is prevalent in adults while IGF-II is the major form in the fetus

Question 18

What growth does IGF have the most profound effect upon?

Answer 18

• Cartilage
• Bone
• Soft tissues

Question 19

What do IGFs stimulate in the body?

Answer 19

Amino acid uptake and activate protein and DNA synthesis

Question 20

What do IGFs act as?

Answer 20

Mitogens, to increase proliferation of target cells

Question 21

Where Is autocrine/paracrine IGF-I released?

Answer 21

Released from the muscles/organs in which it acts, for instance skeletal muscle and bone both release IGF-1 that act back on these organs

Question 22

When do serum IGF-1 levels peak?

Answer 22

In the young-adolescence age, around puberty. More IGF, the taller/larger the child is going to grow

Question 23

Does insulin stimulate IGF production?

Answer 23

YES

Question 24

Can GH increase IGF levels in the absence of insulin?

Answer 24

NO

Question 25

What nutrients stimulate IGF release? How?

Answer 25

High AAs ==> ++ GH release ++GH ==> ++ IGF High blood glucose==> ++ insulin ++Insulin ==> ++ IGF ++IGF ==> growth

Question 26

Why don’t you grow during starvation?

Answer 26

Decreased blood sugar ==> decreases insulin. Even though fasted/starved state increases GH, this does not result in growth because of the =lack of insulin.

Question 27

What does excess GH cause?

Answer 27

>>Gigantism (excess before puberty) | >>Acromegaly (excess after puberty)

Question 28

What causes an excess secretion of GH?

Answer 28

A benign tumour known as the ADENOMA

Question 29

What causes the problems associated with excess GH release after puberty?

Answer 29

Growing ends of bone fuse and completely stop growing in length, so over-secretion of GH after puberty causes increased thickness of bones but not length

Question 30

What is the main difference in the symptoms of pre-and post-puberty excess GH secretion?

Answer 30

Whether the growth is proportional or not. Gigantism (pre-puberty) is proportional growth

Question 31

What are the side effects of acromegaly?

Answer 31

* Cartilage enlargements, ++ size of nose and eyes * Impinges on nerves (++ bone and cartilage) * Visual field losses (pressure on the optic nerves) * Bell’s palsy (pressure on facial nerve) * Spreading teeth or bite difficulties * Joint & bone aches and pains * Soft tissues enlarge => cardiac hypotrophy * Hypertension * Carpal tunnel (pressure on median nerve in wrist by excessive bone/tendon growth)

Question 32

What is carpal tunnel syndrome and what causes it?

Answer 32

It is tingly or pain in the hands/wrists and is caused by pressure on the median nerve in the wrist by excessive bone/tendon growth

Question 33

What are the symptoms of limited GH pre-puberty?

Answer 33

Dwarfism

Question 34

What are the symptoms of limited GH release post- puberty?

Answer 34

Few symptoms

Question 35

What can cause reductions in pituitary GH output?

Answer 35

* Tumours of the hypothalamus which cause oversecretion of somatostatin * Infections which can affect hypothalamic GNRH or somatostatin secretion * GH secretion is very susceptible to irradiation (e.g. after radiotherapy)

Question 36

What is an example of people who have short stature due to low GH or IGF?

Answer 36

Laron dwards and African pygmies respectively

Question 37

What are some other factors that work with GH to stimulate growth?

Answer 37

• Steroid hormones (increase weight gain and muscle mass) • Androgens act synergistically with GH to stimulate the hypothalamus to release more GH • Testosterone and oestrogen enhance the growth hormone rhythms Thyroid hormones – T3 and T4.

Question 38

Where are hormonal growth promoters used?

Answer 38

* Food production androgens * Growth hormone treatment in children who are GH deficient * Sports * GRH peptides act on anterior pituitary to increase lean muscle mass and also reduce injury

Question 39

What are the side effects of IGF use

Answer 39

* Carpal tunnel syndrome * Hypertension * Joint and bone aches * Cancers * Tumours

Question 40

GH cannot increase IGF in absence of _______

Answer 40

INSULIN GH + Insulin => IGF1

Question 41

Stunted growth in thyroid deficient individuals -->

Answer 41

Due to deficiency in GH

Question 42

How do the thyroid hormones promote growth?

Answer 42

Act synergistically with GH to produce effects (stimulate GH synthesis, increase GH secretion, act on target cells to increase their sensitivity to GH)

Question 43

What happens to promote growth during puberty?

Answer 43

GH & IGF levels increase simultaneously

Question 44

What causes Laron dwarfism?

Answer 44

Genetic defect in expression of GH receptors (absent GH signalling before puberty)

Question 45

What causes african pygmism?

Answer 45

Impaired IGF production, normal GH levels

Question 46

Gigantism = _______ growth

Answer 46

PROPORTIONAL growth