Physiology 3 - Normal Growth

Question 1

What hormone governs growth?

Answer 1

Growth Hormone aka Somatotrophin

Question 2

What class of hormone is Growth Hormone?

How is it transported in the blood?

Answer 2

A peptide hormone

Unusually about 50% of it is bound to a carrier proteins, more like a steroid hormone.

Question 3

Why does growth hormone bind to carrier proteins?

Answer 3

To provide a GH reservoir to smooth out the erratic pattern of secretion.

GHRH secretion surges and falls spontaneously and in response to stimuli making GH secretion very variable

Question 4

Which are the hormones affect the action of GH? and how?

Answer 4

Thyroid hormones and insulin are both permissive to GH.
Hence stunted growth can occur in uncontrolled diabetes & hypothyroidism

It is regulated by the balance between the production of GHRH and GHIH

Question 5

What does Growth hormone do?

Answer 5

• Growth and development - indirectly

- Cell growth and division-directly

Question 6

What is IGF-1?

Answer 6

Insulin-like Growth Factor 1 Aka somatomedin

Its very similar to insulin, binds to similar receptors and has similar hypoglycaemic effects.

Question 7

How is IGF-1 produced?

Answer 7

From liver and epiphyseal bone plates in response to GH

Question 8

What does IGF-1 do?

Answer 8

Stimulates cell division & hypertrophy.

Bone:
• GH causes the pre-chondrocytes in the epiphyseal growth plate of bone to differentiate into chondrocytes
• Chondrocytes then begin to secret IGF-1 and become sensitive to it
• IGF-1 acts at a paracrine/autocrine level and stimulates the chondrocytes to produce cartilage- foundation for bone growth- needed for bone growth
• Old chondrocytes then disintegrate and Osteoblasts lay done bone on top of the cartilage

Question 9

When does IGF-1 cease having an effect on long bones?

Answer 9

Near the end of puberty when sex steroid hormones fuse the epiphyseal plates

Question 10

Explain the -ve feedback loops involving GH?

Answer 10

GH itself inhibits GHRH release

IGF-1:

• Stimulates GHIH (Somatostatin) release
• Inhibits GH release
• Inhibits GHRH release

Question 11

Why is Growth Hormone said to be Diabetogenic?

Answer 11

3 of its 4 direct effects:

• Increased gluconeogenesis
• Reduction in Insulin’s glucose uptake effect
• Sensitizing adipocytes towards lipolytic stimuli

Are all Anti-insulin meaning Growth hormone overall raises Blood Glc

Question 12

Describe the secertion of GHRH & GHIH?

Answer 12

Both secreted from the hypothalamus

GHIH secretion is tonic (slow and responsive to need)

GHRH secretion surges both spontaneously and in response to certain stimuli

Question 13

What is the 24 hour mean value for blood [Growth hormone]

Answer 13

Adults 2-4ng/ml

Kids 5-8ng/ml

Question 14

What stimuli increase GHRH secretion?

Answer 14

-Decrease or potential decrease in energy in the cells: needed for cell energy. E.g
• Cold increases demand for energy
• Fasting hypoglycemia
- Increased blood [AAs]
- Stressfull stimuli e.g. infection or stress
- Delta Sleep
- Sex steroids

Question 15

How does delta sleep affect Growth hormone?

Answer 15

Delta sleep causes increased GHRH

Resulting in a roughly 20x spike in growth hormone levels during Delta Wave Sleep (Stage 3/4 aka deep sleep)

Question 16

What stimuli increase GHIH secretion?

Answer 16

• Glucose
• Free Fatty Acids
• REM sleep
• Cortisol

Question 17

How does cortisol inhibit growth?

Answer 17

It increases GHIH secretion but its main method is to increase protein catabolism

Question 18

What controls growth?

Answer 18

• GH which in turn is regulated by secretion of the GHRH and the GHIN
• Insulin
• Thyroid hormones
• Sex steroids
• Nutrients, genes, stress

Question 19

When is GH produced?

Answer 19

• It is produced in the pituitary in response to certain stimuli
• It reaches its highest peak during puberty
• It is mainly released in the first 2 hours of sleep when sleep is heaviest
• In children the amount released of GH increases by 20 x in the first 2 hours of sleep
• During wakeful hours the level of GH is low

Question 20

Do IGF-1 values change much?

Answer 20

No, despite the changes in GH

Question 21

What is IGF-II?

Answer 21

another form of IGF which tends to have effects in the neonatal stage

Question 22

Hypothyroidism and growth

Answer 22

Thyroid hormones
• Have permissive effect on GH and IGF-1
• People with hypothyroidism, they present with cretinism exhibit infantile facial features due to the inability in the body to produce IGF-1.
• In hypothyroidism GH levels are normal

Question 23

Which are the two periods of maximal growth?

Answer 23

-Infancy: 2.5 cm spurts
-Puberty :
• Release of sex steroids and androgens lead to IGF-1/GH secretion
• Same hormones inhibit growth by causing epyphysis of long bones to fuse

Question 24

Difference between gigantism and acromegaly?

Answer 24

• Gigantism: XS release of GH before the epiphyseal plates fuse
• Acromegaly: XS release of GH after the epiphyseal plates fuse. Patient can no longer grow longitudinally but can grow in other areas:
-Large hands and feet
-Gyconomastia
-Osteoarthiritic bone changes

Question 25

What is a major cause of hyper secretion of GH

Answer 25

Tumours of the pituitary

Question 26

What can lead to hypo secretion of GH?

Answer 26

• Dysfunction GHRH release
• GH secreting cells may be abnormal
• End organ responsiveness to GH may be low e.g. poor receptor response which prevents secretion of IGF-1
• Genetic abnormalities: prevents IGF-1 from being produced
• Precocious puberty: sex hormones cause the epiphyseal tissues to fuse earlier- stunted growth
• Hypothyroidism: loss of effect of TH on GH.