Unit 2 BHS: Endocrine control of growth

Question 1

Physiological growth

Answer 1

• Net synthesis of proteins
• Lengthening of long bones
• Increased in number and size of cells comprising soft tissue

Question 2

Normal growth depends on

Answer 2

1. Hormones - GH, TH, insulin, sex hormones
2. Genetics - potential adult size
3. Absence of stress - cortisol is catabolic and inhibits growth
4. Adequate diet - protein, calorie intake, vitamins, minerals. obtained from diet or manufactured in the body

Question 3

Growth Hormone

Answer 3

• produced by somatotropes
• anabolic
• major targets: bone and skeletal muscle
• regulated by GHIH and GHRH

Question 4

Outline the mechanisms of GH action

Answer 4

1. Indirect: through IGF1 and acts on wide variety of cells
2. Direct: selective, involved in regulation of blood glucose and amino acid concentrations & cell division and differentiation

Question 5

Explain the indirect action of GH

Answer 5

• IGF-1 acts on bone and soft tissue to bring about growth-promoting actions
• protein synthesis, cell division and lengthening and thickening of long bones
• uptake of sulphur into cartilage matrix

Question 6

Factors affecting IGF-1 synthesis (besides GH)

Answer 6

1. Age: increase at puberty which corresponds to increase in GH
2. Nutrition: inadequate nutrition reduces production of IGF despite GH level increasing

Question 7

Explain the direct action of GH

Answer 7

1. increase plasma fatty acid level - increase breakdown of triglyceride in fat
2. increase blood glucose level - decrease glucose uptake by muscles
3. stimulates stem cell division and differentiation in epithelial and connective tissue

Question 8

The role of thyroid hormone in growth

Answer 8

1. required for normal growth
2. indirect effect on growth - permissive effect on GH
3. increase BMR and heat production by stimulating enzymes involved in glucose oxidation
4. enhances protein synthesis and lipid breakdown
5. regulates tissue growth and development
6. NB for skeletal muscle growth and development
7. controlled by negative feedback

Question 9

The role of PTH and calcitriol in growth

Answer 9

1. PTH - promotes absorption of calcium salts
2. calcitriol - promotes deposition of ca in bone

in absence of PTH and calcitriol, bones can still enlarge but poorly mineralised and weak.