S1: Hormones, Energy Homeostasis and Obesity Flashcards
Name some uses of glucose
- Stored as glycogen
- Converted into proteins or lipids
- Metabolised to provide energy
What is glycogenesis and glycogenolysis?
Glycogenesis is the storage of glucose to glycogen (from glucose-6 phsophate)
Glycogenolysis is glycogen being broken down into glucose (from glucose-6 phsophate)
What is glycolysis and gluconeogenesis?
Glycolysis is glucose being broken down in pyruvate (from glucose-6 phsophate)
Gluconeogenesis is pyruvate (intermediate) forming glucose. It is the production of glucose from non carb sources.
What happens to pyruvate?
- It can be converted into protein
- It can be converted into fat (lipogenesis, the reverse being lipolysis) for storage
What are the 3 major metabolic pathways in the liver?
- Glucose metabolism (Glycogenesis, glycogenolysis, gluconeogenesis)
- Amino Acid metabolism (Lipogenesis, ketogenesis, gluconeogenesis)
- Fatty Acid metabolisn (Lipogenesis, keto acid formation)
What transporter can glucose be taken up into the liver by?
GLUT2 Transporter
What cycle can glucose be broken down through?
The krebs cycle (TCA cycle)
What are proteins broken down into in the liver?
Proteins can be broken down to ketoacids which can enter the Krebs cycle via ACoA.
What 2 products can you get from ACoA?
Ketogenesis into keto acids
Lipogenesis into Fatty Acids
What are fatty acids and glucose stored together as in the liver?
Triacyglycerol
What are fatty acids taken up in the liver as?
Fatty acyl-CoA
How are fatty acids transported out of the liver into the blood?
Low density lipoproteins
What is formed in the absence of glucose in the liver?
Beta oxidation stimulated by glucagon and there is formation of ketone bodies.
What are the major metabolic pathways in skeletal muscle?
- There is storage of glucose as glycogen and breakdown of glycogen (glycogenolysis) in the muscle for energy when required.
- Generation of ATP is through utilisation of glucose, fatty acids and amino acids taken up from the circulation and from the breakdown of glycogen.
- There is also storage of amino acids as muscle proteins and fatty acids as triacylglycerol in the skeletal muscle.
What is LPL?
It is a lipase transporter which breaks down triacyglycerides so they can be transported into the skeletal muscle cells
How are lipids transported in the circulation?
triacylglycerol bound to lipoprotein particles
What happens to fatty acids in the capillaries?
They are broken down to fatty acids by lipoprotein lipase (an enzyme) and absorbed into adipocytes (fat cells)
What hormone keeps blood glucose constant?
Insulin
What levels of glucose are normal?
4-6mmol
What percentage of the pancreas is exocrine tissue?
98%
Describe the exocrine function of the pancreas
It releases enzymes, bicarbonate ions and water which are released into the pancreatic duct ans transported to the small intestine for the digestion of food
What percentage of the pancreas comprises of special endocrine cells?
2%
Describe the endocrine function of the pancreas
The specialised endocrine cells are arranged in ‘islands’ and these cells are called ‘islets of Langerhans’.
They secrete insulin and glucagon which are two pancreatic hormones that regulate blood glucose levels
Explain the structure of Islets of Langerhans
The alpha cells are situated around the periphery while the beta cells make up the core and are more abundant (60%)
Beta cells: Secrete insulin
Explain the structure of Islets of Langerhans
The alpha cells are situated around the periphery while the beta cells make up the core and are more abundant (60%)
Alpha cells: Secrete glucagon
Beta cells: Secrete insulin
Glucagon and Insulin have antagonistic action meaning they have opposite functions in order to achieve regulated blood glucose levels.
Insulin is an Anabolic Hormone.
What does this mean?
It has a role in storage and taking up fuels
What happens when Insulin is stimulated (by rise in blood glucose concentrations)?
- Uptake of glucose into adipose tissue, skeletal muscle and cardiac tissue
- Uptake of amino acids in adipose/muscle tissue
- Stimulation of glycogen synthesis, inhibition of glycogenolysis
- Inhibition of gluconeogenesis, lipolysis and proteolysis
What type of hormone is glucagon known as?
Catabolic hormone
What stimulates an increase in glucagon?
- An decrease in blood glucose
- Amino acids
What happens when glucagon is stimulated?
- The significant effect is on the liver stimulating the production of glucose (gluconeogenesis and glycogenolysis)
- It promotes the formation of ketone bodies through fatty acid breakdown through beta oxidation which can be used as an alternative fuel source
Explain the regulation of insulin
If you have high blood glucose, there will be increased secretion of insulin from the pancreas and hence the levels of insulin the blood will rise. There will then be glucose uptake into the liver and adipose tissue. This will eventually lead to a decrease in circulating blood glucose, which negatively feedbacks on the production of insulin.
When blood glucose is low, insulin release is inhibited.
What type of receptor does insulin have?
Tyrosine kinase receptor
What enzyme converts glucose to glycogen?
Glycogen synthase
What enzyme converts glycogen to glucose?
Glycogen phosphorylase
What does glycogen transporters (GLUT) do when stimulated ?
They migrate from the cytoplasm where they usually are to the membrane so there is an increased number of glucose transporters on the membrane. Glucose then moves down its diffusion gradient into the cytoplasm.
What other hormones control blood glucose concentrations?
- Growth hormones
- Cortisol
- Adrenaline
How do growth hormones control blood glucose concentrations?
Stimulate fat mobilisation and glucose production in the liver
How does cortisol control blood glucose concentrations?
It is a stress hormone and will cause an increase in blood glucose levels. It does this through stimulating fat mobilisation and gluconegenesis and inhibiting uptake of glucose by muscle.
What general effect does cortisol have?
Anti- inflammatory effects on the body
How does adrenaline control blood glucose concentrations?
It mobilises stores of esterified fatty acids (triaglycerol) and glycogen (more rapid action)
Explain how the actions of glucagon and insulin prevail under the correct conditions
After an overnight fast, glucose is released into the circulation. There may also be release of free (non-esterified) fatty acids from adipose tissue as well as formation of ketone bodies in the liver. There may be production of glucose through gluconeogenesis also. Under this circumstance actions of glucagon have prevailed.
After breakfast, the actions of insulin prevail. Glucose is taken up into the liver, muscle and adipose tissue with formation of glycogen or TAG. Amino acids are taken up into the liver and muscle, lipolysis and proteolysis are inhibited. Ketogenesis is also inhibited. Action of insulin prevail.
What causes type 1 diabetes?
It is caused by autoimmune destruction of pancreatic islets resulting in absolute insulin deficiency
What causes type 2 diabetes?
This is caused by insulin resistance or partial loss of insulin production. It is often associated with obesity.
What causes obesity?
When food intake (energy input) is greater than the energy output
What is insulinopaenia?
Partial loss of insulin production
What 2 mechanisms regulate food intake and energy consumption?
- The hormone leptin (an adipocytokine)
2. Neural and hormonal signals from GI tract signalling brain that stomach is full
What produces leptin?
Adipose tissue
What does leptin do?
Inhibits food intake
Describe how increase or decrease in leptin affects food intake
- An increase in leptin will cause the feeling to reduce food intake (that you’ve had enough to eat) and increase energy expenditure (catabolic)
- Decrease in leptin gives urge to increase food intake
Why do obese people feel the urge to eat constantly?
Obese people show resistance to leptin
How is obesity measured?
BMI = kg/m2
How can body fat be assessed?
- Weighing under water
- Skinfold test
- CAT scan
- MRI scan
How can obesity be subdivided?
Class I
Class II
Class III
List some stats on obesity in the UK
1/4 of adults are obese
2/3 are overweight or obese
What diseases are associated with obesity?
CV disease
Diabetes mellitus type 2
Hypertension
OPD (obstructive pulmonary disorders)
How much does obesity cost the NHS?
£4 billion
What factors contribute to obesity?
▪ Genetic ▪ Illness (e.g. hypothyroidism) ▪ Eating disorders ▪ Certain medications ▪ Sedentary life-style ▪ High glycaemic diet (high postprandial blood sugar) ▪Weight cycling (dieting)
What is the correlation between diabetes and CVD?
The risk for cardiovascular disease increases as an individual progresses from insulin resistance to diabetes.
What does IFG and IGT stand for?
IFG: impaired fasting glucose
IGT: impaired glucose tolerance
What does obesity provide a risk for?
Obesity»_space; Insulin Resistance»_space; Athersclerosis
What is a metabolic syndrome?
This is a cluster of metabolic abnormalities which include: central obesity, dyslipidaemia (abnormality of lipids), insulin resistance and hypertension.
What fat is associated with increased risk of CVD?
Visceral adiposity (fat)
What are the 3 parts of abdominal fat?
- Visceral
- Subcutaneous
- Retroperitoneal
What are the factors that are thought (unknown) to contribute to metabolic syndrome?
Ageing
Lifestyle e.g. calorie intake, physical activity
Genetics
