Introduction to metabolic pathways Flashcards
Digestion, Absorption, and Transport
chew and swallow, food goes into stomach >
digestion: food is broken down into miniscule nutrients in the stomach
>absorption: the nutrients are absorbed into the blood stream from the small intestine
> after the nutrients are absorbed into the blood stream and travel to all cells of the body metabolism occurs
metabolism
Your body metabolises the food you eat, both, to use immediately or to store as energy for later demands
macronutrients
carbs: 130 g (45-65 %), fast, easy access energy,
fat: 65 g (<30 %), stored energy, insulin, vitamin storage, hormone-building, cell membranes
protein: 0.8 g/kg (12-20 %)
builidng cell structures, oxygen transport, immune defense and chemical reactions
• Vitamins
• Minerals 7 minerals: Ca2+, K+, P, S, Na+, Mg2+, Cl-. Also trace amounts of
about 12 others.
• Fibre
Primary energy / fuel sources
• Carbohydrates:
– Glucose is the principle fuel in the short term
– It yields is about 4kcal/g
– Stored as glycogen
– Humans can synthesis all the carbohydrates they need
• Lipids:
– Stored as triacylglycerols (fatty acids +
glycerol)
– Highest calorific value 9kcal/g
– Secreted as fatty acids
– Used when fuel is in short supply or prolonged energy expenditure
• Proteins:
– Polymers of amino acids
– 20 amino-acids, 9 cannot be synthesised by humans = essential amino acids
– Not stored for energy but can be used as a fuel source in times of need
Vitamins
• Organic compounds occurring in small amounts in food
• Assist with physiological function often as
coenzymes or as antioxidants
• 13 essential vitamins needed (4 fat soluble & 9
water soluble)
– Vitamins cannot be synthesised in the body (with the
exception of Vit D and Vitamin K)
– Some vitamins are often available from foods in inactive
forms known as precursors or provitamins
• Deficiencies are rare in developed economies
Minerals
• Minerals are involved in chemical reactions in the body including:
– 1. Cell growth and repair,
– 2.Metabolism,
– 3.Nerve and muscle function
• Balance of minerals in the body may be affected by:
– certaindiseases(GIT,kidney),
– anunbalanceddiet,
– takingmineralsupplements,
– removingcertainfoodsorfoodgroupsfromthediet-missingoutonimportant minerals
• Essential to good health include:
– Calcium, Chlorine, Iron, Magnesium, Phosphorus, Potassium, Sodium, Sulfur & Zinc
• Most common mineral deficiencies in Australia are:
– Calcium, leading to osteoporosis
– Iron, leading to anaemia
Fibre
• Fibre - plant substances that are resistant to digestion and absorption in the human small intestine and undergo complete or partial fermentation in the large intestine because
– Soluble (pectins, gums and mucilages) AND insoluble (Cellulose, hemicellulose & lignin)
– RDI – men 30g, women 25g
• The diets rich in fibre such as cereals, nuts, fruits and vegetables
• May protect against cardiovascular disease, diabetes and colon cancer
Metabolic Rate (MR) & Basal Metabolic Rate (BMR)
MR - the rate at which energy is spent in the body in a given period of time (kcal/hr or kcal/day)
BMR – is measured under ideal conditions: – Physicalandmentalrest;nofoodwithin12h – Comfortableroomtemperature
– Male BMR = 7,100 kJ/day (1,700 kcal/day)
– Female BMR = 5,900 kJ/day (1,400 kcal/day)
energy production
STAGE 1: GIT Nutrients are: • Digested into absorbable units. • Absorbed into the blood and transported to tissue cells.
Stage 2: Tissue Cells
Anabolism or catabolism:
• In anabolism, nutrients are built into macromolecules.
• In catabolism, nutrients are broken down to pyruvic acid and acetyl CoA.
• Glycolysis is the major catabolic pathway.
Stage 3: Mitochondria Oxidative breakdown of stage 2 products: • CO2 is released. • The H atoms removed are ultimately delivered to molecular oxygen, forming water. • Some of the energy released is used to form ATP. • The citric acid cycle and oxidative phoshorylation are the major pathways. Catabolic reactions Anabolic reactions PROTEINS Amino acids CARBOHYDRATES Glucose and other sugars FATS Triglycerides Proteins NH3 Glucose Pyruvic acid Acetyl CoA Citric acid cycle H Glycogen Infrequent CO2 Oxidative phosphorylation
Metabolism
- Metabolism refers to all chemical reactions that occur within the body cells.
- Provides energy to maintain homeostasis and perform essential functions.
- Involves reactions such as: degradation, synthesis & transformation of 3 classes of energy-rich organic molecules (carbohydrates/protein/fat) – known as intermediary metabolism
- Provides metabolites
Metabolism: Catabolic VS ANABOLIC Reactions
Metabolism is the sum of all reactions in the body: Metabolism = Catabolic Reactions + Anabolic Reactions
• Catabolic reactions break down larger molecules, such as carbohydrates, lipids, and proteins from ingested food, into smaller parts
• Anabolic reactions or biosynthetic reactions, synthesize larger molecules from smaller constituent parts, using ATP as the energy source.
Metabolic Tissues - Liver
•Extremely important metabolic organ:
– Intestinal blood supply flows directly to the liver - gets all
nutrients/metabolites
– Linked closely to pancreatic blood supply - insulin/glucagon hormones
exert their effects in the liver first
– Stores glucose as glycogen (Glycogenesis) which it can breakdown when
required (Glycogenolysis) and release to the rest of the body – Can synthesise “new glucose” (Gluconeogenesis)
– Can synthesise ketones, from fatty acids and amino acids (Ketogenesis) as an alternative energy source when carbohydrates are scarce
– Can synthesise lipids (fatty acids and triglycerides) from glucose and amino- acids (Lipogenesis)
Glycogenesis
- Synthesizes glycogen from glucose
* Occurs when glucose supplies exceed demand for ATP
Glycogenolysis
- Breaks down glycogen to release glucose
* Stimulated by low blood glucose
Metabolic Tissues – Muscle & Adipose tissue
•Muscle tissue - major mass tissue (approx 40% body weight): Utilises glucose as energy source during fed state and activity,utilises lipids
as energy source during fasting
Stores glucose as glycogen-only be used by muscle cells (Glycogenesis/ Glycogenolysis)
Adipose tissue - key metabolic regulator of lipid storage and release. Is now recognised as an endocrine organ releasing adipokines (e.g. Leptin)
– Storesfattyacidsastriglyceride – Releasesfattyacids
– Not ALL fat depots are the same!
– ie subcutaneous vs visceral fat, white fat vs brown fat
