Endocrine lecture 2

Question 1

Major hormones that control growth and describe their actions.

Answer 1

1. Growth hormone, secreted by the anterior pituitary.
2. Insulin-like growth factors
3. Thyroid hormones
4. Sex steroids (pubertal growth and growth spurt)
5. Glucocorticoids (however excess glucocorticoids –> premature fusion of the epiphyses of the bones and thus stunt growth)

Question 2

What are the actions of GROWTH HORMONE (GH)

Answer 2

Growth hormone is secreted by the anterior pituitary.
it stimulates the release of Insulin-like growth factor from the liver, which acts on osteoblasts to increase bone growth.
It also leads to increase Calcium retention and increases muscle mass/sarcomere hypertrophy, as well as protein synthesis.

Question 3

What stimulates the release of Growth hormone?

Answer 3

• SLEEP.
• Hypoglycaemia
• exercise
• stress and trauma
• fasting and protein deficiency
• Ghrelin

Question 4

What inhibits the release of Growth Hormone?

Answer 4

• Hyperglycaemia (post prandial)
• increase free fatty acids
• age
• Negative feedback IGF-1
• somatostatin

Question 5

Growth hormone mechanism of action.

Answer 5

Growth hormone results in increase muscle and bone mass. It has anabolic effects.
It decreases glucose uptake and muscles rely on glycogen stores, stimulating glycolysis in adipose tissues.
The stimulation of fatty acid breakdown, allows glycerol and fatty acids to be used by the live run gluconeogenesis.
This increases the glucose levels in the blood, which can be used by other body tissues for growth.

It also stimulates production of insulin-like growth factor 1 from the liver, which acts on osteoblasts to increase bone growth.

Question 6

What is meant by growth hormone having anti-insulin effects?

Answer 6

Rather than increasing glucose uptake, and fatty acid stores, it breaks down these stores. Increases blood glucose levels.

Question 7

What is the action of thyroid hormones?

Answer 7

It stimulates growth during puberty.

Question 8

What happens in Hypothyroidism?

Answer 8

Lack of pre-pubescent thyroid hormone can result in growth and mental retardation. It can lead to smaller stature (decreased growth) and mental retardation.

Question 9

What can be used to treat hypothyroidism/reverse effects?

Answer 9

Growth hormone can be given, to reverse decreased growth, however cannot fix mental retardation.

Thyroid hormones can also be given to treat hypothyroidism.

Question 10

What period of development is insulin an important growth factor for?

Answer 10

In-utero. Stimulates the growth of the foetus.

diabetic mothers

Question 11

What happens during insulin deficiency?

Answer 11

Muscle wasting/ catabolism, for use in gluconeogenesis.

High insulin levels have an anabolic effect.

Question 12

What are the sex steroids?

Answer 12

they include androgens and oestrogen’s.

Question 13

What are there effects?

Answer 13

Excess of sex steroids accelerates pubertal growth spurts and bone growth.

Increases the rate of bone maturation, and sealing of the epiphyseal plates.

Precocious puberty: Tall for age, but then short, due to increased androgen and oestrogen sealing the epiphyseal plates.

Question 14

Actions of glucocorticoids?

Answer 14

inhibits growth in excess.
Use of synthetic glucocorticoids for treatment, stunts growth. e.g. asthma treatment, and children with trauma are shorter.

Question 15

Insulin and growth hormone

Answer 15

Just as important for growth as each other.

Question 16

Can thyroid hormone work in absence of growth hormone?

Answer 16

Thyroid hormone is essential for growth, but does not function in the absence of Growth Hormone.

Question 17

Importance of calcium?

Answer 17

1. Muscle contraction (skeletal and cardiac)
2. Nerves. Sympathetic transmission, learning and memory.
3. Hormone release
4. Blood clotting.

Question 18

How is calcium regulated?

Answer 18

1. calcium is absorbed by the gut.
2. calcium enters the ECF
3. Excrete calcium into urine and in faeces.

10% excreted in urine, 35% absorbed.

Question 19

What hormones regulate Ca2+?

Answer 19

• Vitamin D increase absorption.
• Thyroid hormones and cortisol decrease absorption.
• Parathyroid hormone increases tubular reabsorption, as It converts inactive vitamin D to active.

Thus, vitamin D, cortisol, T3 and T4, and parathyroid hormone regulate calcium levels.

Question 20

Describe the actions of the actions of the parathyroid hormone.

Answer 20

The parathyroid hormone stimulates resorption of phosphate and calcium into the plasma.
It detects when calcium levels are low, and increase calcium plasma concentrations, however it does not increase phosphate plasma concentrations.
It stimulates excretion of phosphate by the kidneys.

PTH increases the activity of 1 hydroxylase. This converts inactive vitamin D to the active from.
= decreased phosphate
= increased levels of biologically active Vitamin D, which acts on the gut, to increase calcium reabsorption.

Question 21

The two hormones that regulate Ca2+

Answer 21

Parathyroid hormone and calcitriol.

Question 22

What part does Parathyroid hormone play in bone remodelling?

Answer 22

PTH works on the osteoblasts, that build up bone (rather than on osteoclasts to break down bone).

PTH stimulates resorption by acting on osteoblasts.
Osteoblasts produce RANK LIGAND. Rank ligand, binds to RANK RECEPTOR, present on osteoclasts and stimulation osteoclast activity.

Thus, PTH stimulates osteoclast activity by working on osteoblasts.

Question 23

How do sex steroids interfere with Parathyroid hormone action?

Answer 23

Sex steroids stimulate the production of OPG protein, which sits on the Rank ligand and prevents it from binding to osteoclasts.

Thus, increased androgens and oestrogen, increase OPGs which prevents rank ligand from working, and inhibiting bone resorption.

Question 24

What are the three organs targeted by PTH?

Answer 24

1. PTH is secreted by the parathyroid glands.

BONE: causes bone resorption. Increased calcium plasma and phosphate excretion.

2. Kidney: induces hydroxylase activity which converts inactive vitamin D to active vitamin D. Induced by PTH.

PTH doesn’t act on gut, but increases reabsorption of calcium in the gut, converting inactive vitamin D to active vitamin D.

Oestrogen and androgens increase bone formation/mineralisation.

Glucocorticoids increase bone resorption.

Question 25

Role of vitamin D and calcium?

Answer 25

Vitamin D is important for normal bone growth.
Vitamin deficiency leads to hypocalcemia and skeletal abnormalities e.g. Ricketts (bowed legs)

• lipid soluble, present in food or synthesised in the skin under UV light.

Question 26

5. Describe the actions of calcitonin

Answer 26

Important in fish and rats but not in humans.
Calcitonin is a hormone that controls calcium levels, but doesn’t have much effect under normal physiology.
- it decreases plasma calcium and phosphate.

Minor actions in the small intestine to decrease absorption.
Minor actions in the kidney is there for fine tuning (not a big effect on plasma calcium levels).

Opposite action of PTH
acts on bone to inhibit osteoclastic bone resorption and is used clinically to treat Paget’s disease, hypercalcemia and osteoporosis.

Question 27

6. Explain the importance of vitamin D3, in the regulation of Ca++ homeostasis

Answer 27

Decreases plasma calcium and phosphate.
It suppresses PTH secretion.

It stimulates the kidney to reabsorb calcium and phosphate.

and increase calcium reabsorption in the gut

Question 28

Hypercalcemia

Answer 28

Commonly caused by hyperparathyroidism (excess parathyroid hormone).

• increased bone resorption.
• increases absorption of calcium from gut.
• decreased renal excretion of calcium.

calcium levels are high.
Symptoms:
- CNS: lethargy
- muscle weakness
- makes it hard for cells to depolarise 
- kidney stones 
- osteoporosis