22. Metabolic and Endocrine Control During Special Circumstances

Question 1

What is the average weight gain during pregnancy?

Answer 1

About 8kg.

Question 2

What are the two metabolic phases in pregnancy?

Answer 2

Anabolic phase - preparatory increase in maternal nutrient stores and increase in insulin sensitivity during early pregnancy.
Catabolic phase - decreased insulin sensitivity so increase in maternal glucose and free fatty acid concentration to allow for foetal growth in late pregnancy.

Question 3

How are most substances transferred from mother to foetus?

Answer 3

By simple diffusion down concentration gradients.

Question 4

How is glucose, the principal fuel, delivered to the foetus?

Answer 4

By facilitated diffusion through GLUT1 transporter primarily.

Question 5

What is the new endocrine entity that develops during pregnancy?

Answer 5

The foetoplacental unit. It consists of the placenta, foetal adrenal glands and foetal liver.

Question 6

What are two important placental steroid hormones?

Answer 6

Oestriol and progesterone.

Question 7

What is the anabolic phase in pregnancy, during the first 20 weeks, in preparation for?

Answer 7

More rapid growth rate of the foetus, birth and subsequent lactation.

Question 8

How is nutrient concentration kept high in maternal circulation during the second 20 weeks of pregnancy?

Answer 8

Reducing maternal utilisation of glucose by switching tissues to use of fatty acids, delaying maternal disposal of nutrients after meals and releasing fatty acid stores built up in the 1st half of pregnancy.

Question 9

How does the insulin/anti-insulin ratio fall in the second half of pregnancy?

Answer 9

Because although insulin levels increase, anti-insulin hormones production by the foetal-placental unit increases more quickly.

Question 10

What are three anti-insulin hormones in pregnancy?

Answer 10

Corticotropin releasing hormone, human placental lactogen and progesterone.

Question 11

What is the overall blood glucose levels change in late pregnancy?

Answer 11

It’s about 10% lower.

Question 12

How do oestrogen and progestones increase insulin synthesis and secretion?

Answer 12

They increase sensitivity of maternal pancreatic B-cells to blood glucose.

Question 13

What are the three known causes of gestations diabetes?

Answer 13

1. Autoantibodies similar to those in type I DM.
2. Genetic susceptibility similar to maturity onset DM.
3. B-cell dysfunction in setting of obesity and chronic insulin resistance (most common).

Question 14

How many pregnancies are affected by gestational DM?

Answer 14

3-10%.

Question 15

What effect on the pregnancy does gestational DM have?

Answer 15

Increased incidence of miscarriage, 4x higher incidence of congenital malformation, foetal macrosomia (large body), risk of shoulder dystocia (fat around shoulders meaning baby could get stuck during birth), hypertensive disorders of pregnancy - e.g. preeclampsia.

Question 16

What affects whether a pregnancy will be affected by gestational DM?

Answer 16

The women’s starting point in terms of insulin resistance before pregnancy. If it was low originally, the peak in pregnancy may not take it over the threshold for gestational DM.

Question 17

What are some risk factors of gestational diabetes?

Answer 17

Maternal age over 25 years, BMI over 25kg/m2, race/ethnicity (more common in Asian, Black and Hispanic groups), personal or family history of DM and family history of macrosomia (large body).

Question 18

How is gestational DM managed?

Answer 18

Dietary modification (calorific reduction in obesity), insulin injection if persistent hyperglycaemia is present and regular ultrasound scans to assess foetal growth and well being.

Question 19

What must the metabolic response to exercise ensure?

Answer 19

The increased energy demands of skeletal and cardiac muscle are met by mobilisation of energy stores, minimal disturbances to metabolic homeostasis - keep rate of mobilisation = rate of utilisation, glucose to brain maintained and end products of metabolism are removed ASAP.

Question 20

What does the magnitude and nature of metabolic response to exercise depend on?

Answer 20

Type of exercise, intensity and duration of exercise and physical condition and nutritional state of individual.

Question 21

How much ATP is stored in muscle?

Answer 21

A limited amount, 5mmol/kg.

Question 22

Where does energy come from in exercise after muscle stores of ATP are used?

Answer 22

Muscle creatine phosphate stores replenish ATP for immediate energy.

Question 23

Beyond the initial burst of energy, where is further ATP supplied by?

Answer 23

Glycolysis and oxidative phosphorylation.

Question 24

What are two key differences between getting ATP from glycolysis and oxidative phosphorylation?

Answer 24

Glycolysis is inefficient but can be done anaerobically. Whereas oxidative phosphorylation is efficient but requires oxygen.

Question 25

What can intensive exercise by sustained by?

Answer 25

Muscle glycogen.

Question 26

What happens in the Cori cycle?

Answer 26

Lactate produced by the muscle is taken to the liver and converted to glucose. That glucose is taken back to the muscle, where is is metabolised to produce my lactate.

Question 27

How does muscle take up blood glucose?

Answer 27

Via GLUT4 and GLUT1 transporters.

Question 28

What happens to metabolism during a 100m sprint?

Answer 28

Not enough oxygen to muscles. High energy phosphate stores are used then ATP is created anaerobically (inefficient and incomplete metabolism of glucose). This produces lactate and causes fatigue. Muscle stores of glycogen are used.

Question 29

What happens to metabolism during a 1500m middle distance run?

Answer 29

Some extra oxygen is delivered to muscles. 40% anaerobic metabolism. Initial start - creatine phosphate and anaerobic glycogen metabolism. Middle phase - ATP produced aerobically from muscle glycogen. Finishing sprint - anaerobic metabolism of glycogen.

Question 30

What happens to metabolism during a marathon?

Answer 30

95% aerobic. Uses muscle glycogen, liver glycogen and fatty acids. The muscle glycogen stores are depleted within a few minutes and glucose from the liver peaks at about 1 hour and then decreases. Use of fatty acids rises steadily from 30 minutes.

Question 31

Order the following energy sources in the order they'd be used in exercise. ATP, muscle glycogen (anaerobic), plasma free fatty acids, plasma glycogen, adipose tissue triglycerides, creatine phosphate, muscle glycogen (aerobic) and liver glycogen.

Answer 31

ATP and creatine phosphate. Muscle glycogen (anaerobic). Muscle glycogen (aerobic), plasma glycogen and liver glycogen. Plasma free fatty acids and adipose tissue triglycerides.

Question 32

How is metabolic response to a marathon hormonally controlled?

Answer 32

Insulin levels fall slowly - inhibition of secretion by adrenaline. Glucagon level rise - stimulates glycogenolysis (glycogen phosphorylase), gluconeogenesis (PEPCK and fructose 1,6 biphosphatase) and lipolysis (hormone sensitive lipase). Adrenaline and growth hormones rise - stimulates glycogenolysis and lipolysis, mobilises fatty acids. Cortisol slowly rises - stimulates gluconeogenesis and lipolysis.

Question 33

What are the benefits of exercise?

Answer 33

Body compositional changes - decreased adipose and increased muscle. Glucose tolerance imporves - increased muscle glycogenesis. Insulin sensitivity of tissues increases. Blood TAGs decrease - reduced VLDL and LDL and increased HDL. Bloody pressure falls. Psychological effect - feelings of well being.