Metabolism Flashcards
What is glucose?
- stored as glycogen
- can be converted to amino acids or fat
- oxidised for energy, principle fuel in short term
What are fatty acids?
- stored as fat = triaclglycerides (TGs)
- TGs are glycerol + fatty acids
- FAs can be oxidised, high energy yield, important in starvation
- cannot be converted to glucose or amino acids
What are amino acids?
- stored as protein polymers of AAs
- not a primary energy source except starvation
- excess amino acids are: converted to glucose, converted to fat or some oxidised
Define metabolism
The sum of all reaction in the body; metabolism = catabolic + anabolic reactions
Define catabolic reactions
The breakdown of large macro molecules, such as carbohydrates, lipids and proteins from ingested food or storage molecule into smaller parts, yields energy
Define anabolic reactions
- synthesis of large molecules from smaller constituent parts, requires energy
List the anabolic and catabolic reactions of carbohydrates, lipids and proteins
Carbohydrates:
glucose -> glycogen (anabolic) glycogen -> glucose (catabolic)
Lipids:
fatty acids -> triacylglycerides (anabolic) triacylglycarides -> fatty acids (catabolic)
Proteins:
amino acids -> proteins (anabolic) proteins -> amino acids (catabolic)
What is the function of the liver in digestion?
- intestinal blood supply flows directly to the liver, so ‘first pass’ metabolism occurs in the liver
- linked closely to the pancreatic blood supply, so hormones insulin/glucagon exert their effects at the liver first
- liver stores glucose as glycogen (glycogenesis) which it can breakdown when required (glycogenolysis) and release to the body - muscles are the main store + utilisation of glycogen
What other substances can the liver synthesise?
- can synthesise ketones, from fatty acids and amino acids (ketogenesis), as an alternative energy source when carbohydrates are sparse (synthesis of ‘new glucose - gluconeogenesis)
- can also synthesise lipids (TGs) from glucose and amino-acids (lipogenesis)
What is fat/adipose tissue?
- major site (normally) of lipids (TGs) storage and release
- releases glycerol backbone and FAs during starvation
- glycerol backbone + fatty acids = new glucose
- glycerol is used to make new glucose by liver
- FAs are an alternative energy source to glucose
- not all fats are the same
Discuss metabolism and the brain
- the brain has a very high metabolic rate and high blood supply
- depends mainly on glucose
- blood glucose levels are under strict control by insulin/glucagon
- if levels fall between severely low (2 mmol/L) results in impaired brain function, coma and death
What are the key tissues in metabolism?
liver - produces glucose and stores glycogen
brain - obligate glucose user
muscle - stores glycogen
white adipose tissue - stores fat
What are the key hormones responsible for promoting storage?
- insulin (promotes anabolic reactions; formation of storage molecules)
- GH (protein)
What are the key hormones responsible for promoting mobilisation?
- glucagon
- catecholamines (adrenaline and noradrenaline) and cortisol - both involved in sympathetic response to starvation
- GH (fats, CHOs) - (roids) growth hormone: protein anabolic, fat catabolic
What type of hormone is insulin?
An anabolic hormone
What type of hormone is glucagon?
A catabolic hormone
What are some WHO criteria for metabolic syndrome?
- impaired glucose regulation/insulin resistance
- abdominal/central obesity
- hypertriglycemia
- low levels of HDL cholesterol
- raised blood pressure
- microalbuminuria
Discuss fat accumulation
- adipose tissue is a highly active metabolic and endocrine organ
- adipocytes are the primary cell type of adipose tissue
- adipose is the primary site of storage for excess energy
- adipocytes synthesise a number of biologically active compounds that regulate metabolic homeostasis
Why is a pro-inflammatory profile dangerous?
- the distance between cells and their blood supply needs to be short to allow diffusion
- if this distance is greater, and too great, it can cause hypoxia and necrosis
What is insulin insensitivity/resistance?
- insulin signalling regulates glucose, lipid and fat metabolism
- insulin receptors are expressed on the cells of the Skm, liver and adipose tissues
- insulin insensitivity is defined where insulin levels are normal or elevated, but target cells become less sensitive to insulin
- consequences: hyperglycaemia and compensatory hyperinsulinemia
What is diabetes mellitus, and some symptoms?
- disease of impaired carbohydrate, fat and protein metabolism
- characterised by hyperglycaemia
- more frequent urination (polyuria)
- increased thirst (polydipsia)
- increased appetite (polyphagia)
What are some features of type 1 DM?
- insulin secretion, age of onset, speed of onset, defect, treatment and management
- no insulin secretion
- early age of onset
- rapid onset
- destruction of beta cells (produce insulin; anabolic, increases storage of glucose, fatty acids and amino acids)
- treated with insulin, exercise, diet
What are some features of type II DM?
- insulin secretion, age of onset, speed of onset, defect, treatment and management
- normal or increased insulin secretion
- late-adult/obesity
- slow onset
- insulin resistance
- weight reduction, diet, exercise, drug
What are the purposes of metabolic pathways?
- extraction of energy
- storage of fuels
- synthesis of important building blocks
- elimination of waste materials
What is ATP, and what does it supply energy for?
ATP is temporary energy storage molecules in all cells
Energy for:
- synthesis, to make macromolecules
- transport (pumps) often against concentration gradient
- muscle contractions and cell motility
List some important metabolic reactions for humans
- glycolysis
- citric acid cycle
- oxidative phosphorylation
- urea cycle
- fatty acid beta cell oxidation
- gluconeogenesis
What are the major lipid pathways?
- lipolysis: hydrolysis of mainly TGs produce glycerol and FAs
- beta-oxidation: conversion of FAs into acetyl choline acid
- lipogenesis: cholesterol and other lipids synthesis
- ketogenesis: formation of ketone bodies
