Beyond the classic endocrine glands

Question 1

What do adipocytes store energy as?

Answer 1

Triglycerides and release energy as free fatty acids

Question 2

What is lipoprotein lipase?

Answer 2

Triglyceride hydrolysis (lipolysis)
Involved in receptor-mediated lipoprotein uptake

Refer to the diagram

Question 3

What is Hormone-sensitive lipase (HSL)?

Answer 3

When needed, fat stored as triacylglycerol (TG) is hydrolysed for energy use

Refer to the diagram

Question 4

What endocrine hormones does adipose tissue release?

Answer 4

1. Leptin - signals satiety centre in the brain
2. Adiponectin - Increases insulin sensitivity
3. Resistin - Cytokines
4. Androgens
5. Oestrogens

Question 5

What do mutations of the leptin (LEP) gene in adipose tissue or the leptin receptor (LEPR) gene expressed in the hypothalamus?

How do we cure leptin defficiency?

Answer 5

Lead to abnormal eating behaviour and the development of early-onset morbid obesity. Leptin deficiency has been successfully treated with leptin resulting in a reduction in fat mass

Question 6

What is the consequence of LEP mutations being rare?

What is obesity associated with?

Answer 6

However, LEP mutations are rare, and thus leptin treatment only rarely effective

Obesity is associated with leptin resistance (leptin levels are already (high in obesity)

Multiple interacting pathways control food intake and energy utilization

Question 7

Describe the levels of hormones in healthy adipose tissue

Answer 7

Leptin signals satiety to the brain

Adiponectin increases insulin sensitivity

Resistin levels low

Question 8

Describe the levels of hormones in obese tissue

Answer 8

Leptin secretion high but resistance to leptin

Adiponectin secretion low

Insulin resistance, diabetes and metabolic syndrome
Cytokines (e.g., IL-6, TNF-α)
  - Normal balance disturbed
Chemokines (chemotactic cytokines)
 - Attract macrophages

Question 9

What are the general disorders of energy metabolism associated with?

Answer 9

Obesity (especially visceral)

Hypertension

Hyperglycaemia (prediabetes)

High serum triglycerides (but low HDL)

Insulin resistance

Question 10

What is the difference between Visceral (VS) or intra-abdominal fat versus subcutaneous (SC) fat

Answer 10

VS and SC fat express different developmental genes

Different signalling profiles

Free fatty acids and adipocytokines released from VS fat drain directly to liver to alter metabolism

Question 11

How does the body fight weight loss for people with obesity?

Answer 11

On image

Question 12

What signals are sent when we regulate food intake?

What signals do these feed into?

Answer 12

1. Hormones secreted from the stomach and intestines
   and
2. Leptin secreted from adipocytes
   and
3. Vagal afferents to the nucleus of the tractus solitarius

Hypothalamus

Question 13

What are the non-classical endocrine organs?

Answer 13

Heart 
Kidney
Bone 
Tumours 
Pineal gland

Question 14

What does the kidney secrete?

What does it do?

Answer 14

The kidney as an endocrine organ – secretion of erythropoietin in response to low partial pressure of oxygen in the circulation. Stimulates the production of erythrocytes

Recombinant EPO used to treat anaemia due to renal failure, in critical illnesses and as a blood doping agent for endurance sports

Question 15

What control the circadian rhythms?

Answer 15

Cortisol

Question 16

What other physiological rhythms do the SCN control?

Answer 16

On image

Question 17

Pineal gland – the gland that measures time?

Answer 17

Neural inputs to the pineal
from retina->SCN
->superior cervical ganglion
-> pineal gland

Signals about the level of light reach the pineal gland via a rather circuitous route. Darkness is the signal that stimulates production and secretion of melatonin by the pineal, and light inhibits it. It seems to be involved in the control of sleep, synchronizing it to the time of day.

Question 18

What is Epidemiological?

Answer 18

Epidemiological studies in, for example shift workers, long-distance flight crews and patients with sleep disorders have shown that they have a higher prevalence of cancer, psychological disorders, metabolic syndrome, diabetes and cardiovascular diseases.