Gastrointestinal System Part 2

Week 2

Two categories of micronutrients

• Vitamins

• Minerals

Vitamins functions

• energy production

• immune function

• blood clotting

Minerals function

• growth

• bone health

• fluid balance

Fat-soluble vitamins

• fat soluble

• bile salts are required for absorption

• transported by carrier protein

• stored in liver and fatty tissues

• during excretion, surplus is stored

• required in periodic doses

Water-soluble vitamins

• water soluble

• simple intestinal absorption

• travel freely in the body without carrier proteins

• minimal storage capacity

• surplus vitamins are detected in kidney and excreted in urine

• required in frequent doses (1-3 days)

Co-enzymes/factors (vitamins)

act as acceptors or donors of functional groups (e.g., transfer of electrons)

Antioxidants (vitamins)

donate electrons to prevent damage to other atoms

types of water-soluble viatmins

• thiamin

• folate

• niacin

• riboflavin

• vitamin B6

• vitamin B12

• pantothenic acid

• biotin

• vitamin C

types of fat-soluble vitamins

• vitamin A

• vitamin D

• vitamin E

• vitamin K

vitamins are…. minerals are….

organic…inorganic

major minerals

• sodium

• chloride

• potassium

• calcium

• magnesium

• sulphate

trace element minerals

• iron

• copper

• manganese

• zinc

• iodine

• selenium

Anabolism

• synthesis or production of more complex molecules from simpler molecules

• process of -building’ compounds needed by cells

• generally endergonic reactions that consume more energy that they produce

• anabolic processes generally end in genesis

• e.g. glycerol and fatty acids may be assembled into triglycerides

Catabolism

• breakdown of molecules

• breakdown of more complex molecules to simpler molecules

• release/help obtain energy

• generally exergonic reactions that produce more energy than they consume

• generally end in lysis

Amphibolic pathways

• chemical processes that involve both catabolic and anabolic reactions

• e.g. Krebs cycle/Citric Acid Cycle

During photosynthesis

• plants make sugars which are able to capture the sun’s light energy in their chemical bonds

• then as humans, we either eat plants or animals who have eaten plants

How does the body get energy from foods

• plants and animals who have eaten plants provide our own bodies with energy

• first our body consumes and breaks down foods into smaller molecules to be absorbed into blood/lymph systen

• then the body is able to use the molecules for energy metabolism

Cellular Respiration

• key pathway in converting food into energy

• energy stored in food is converted to the body’s energy currency (ATP)

• oxidation of glucose (cellular respiration) doesn’t consume glucose as an energy source

basic components of energy balance

• energy intake

• energy expenditure

• energy storage

body weight can only change when…

energy intake is not equal to energy expenditure over a given period of time

three components that determine energy expenditure

• Basal Metabolic Rate (BMR)

• Thermic Effect of Food (TEF)

• Physical activity

Basal Metabolic Rate (BMR)

• the energy our body expends at rest to maintain normal bodily functions

• Physiological functions that contribute to BMR include respiration, circulation, nervous system activity, protein synthesis and temperature regulation

• can vary amoung individuals depending on gender, height, age and body composition

Thermic Effect of Food (TEF)

• the energy the body needs to digest, absorb and store nutrients from food

• energy is expended through active transportation of nutrients, secreting digestive juices and the gastrointestinal tract speed of contractions

• accounts for 5-10% of total energy expenditure with little variation between individuals

Physical Activity

• any bodily movement that is produced by the skeletal muscles involved in energy

• can contribute between 15-30% of energy expenditure

• Exercise related activity thermogenesis (EAT) - planned, structures and repetitive activities, usually with the objective to improve health

• Non-exercise-related activity Thermogenesis (NEAT) - energy expended during unstructured or unplanned activities, such as usual daily activities

Metabolism is…

all chemical reactions in the body

Digestion is…

breakdown of food into smaller molecules (a part of metabolism)

Oxidation

• loss of electrons

Reduction

• gain of electrons

Oxidation reduction reactions

-transfer of electrons from one molecule to another

Phosphorylation

• process where phosphate group is added to another molecule

Electrons and protons

• negatively charged particle found in atoms

• positively charged particle found in atoms

Metabolism of Carbohydrates

• glucose is preferred fuel source

oxidation of glucose to produce ATP occurs in 4 steps

• Glycolysis

• Formation of acetyl coenzyme A (acteyl-CoA) - transitional step

• Krebs Cycle

• Electron transport chain

Glycolysis

Occurs in 10 steps

Has three phases

• Sugar activation

• Sugar cleavage

• Sugar oxidation and ATP production

Glycolysis 1 - 5

• glycolysis stars when glucose is phosphorylated

• phosphofructokinase is key regulator of rate of glycolysis

• Uses 2 ATP molecules

Glycolysis 6 - 10

• NAD+ steals H atoms (NAD → NADH/H+)

• Steps 6 - 10 occur twice for each glucose molecule

• 4 ATP molecules produced

Pyruvate

• End-product of glycolysis

• two metabolic fates

1. conversion to lactate (in anaerobic conditions, remaining steps in glucose oxidation do not occur)

2. conversion to acetyl-CoA (aerobic conditions, all four steps occur)

Pyruvate conversion to lactate

In the absence of oxygen (anaerobic)

• end-product = 2 lactic acid molecules and 2 NAD+

• NAD+ regenerated to keep glycolysis running

• Lactic acid → pyruvic acid → can be converted to glucose (occurs in liver)

Pyruvate conversion to acetyl CoA

• transitional step between glycolysis and Krebs cycle

• Occurs in presence of oxygen

• occurs in the mitochondria

• reaction is irreversible

• one carbon lost from each pyruvate and replaces with CoA

• 2 CO2 and 2 NADH+ 2 H+ produced

The Krebs Cycle

• Acetyl CoA enters Krebs Cycle

• Series of eight reactions

• its a cycle and is amphibolic

• two ‘turns’ for each glucose molecule

• each ‘turn’ produces 3 NADH 3 H+, FADH2 and 1 GTP/ATP, 2 CO2

• reduced coenzymes contain energy

Electron Transport Chain - Chemiosmosis

• uses energy of the proton gradient to synthesis ATP

• H+ atoms diffuse through ATP synthase (go from high → low H+ concentration)

• proton motive force allows generation of ATP from ADP

Electron Transport Chain

• series of electron carriers

• reducing equivalents generate proton gradient across inner mitochondrial membrane

• requires oxygen → oxygen accepts electrons

• Chemiosmosis → major source of ATP for cells

• H20 byproduct

Glycogenesis

• synthesis of glycogen from glucose

• occurs when ATP levels are high

• glycogen stored in liver and skeletal muscles

Glycogenolysis

• breakdown of glycogen back to glucose

• occurs when the body requires energy - when blood glucose levels drop/during fasting periods

Gluconeogenesis

• metabolic pathway for production of new glucose from non-carbohydrate precursors

• occurs in the liver when unable to produce enough glucose from glycogen

• can be avoided by eating

• plays important role in starvation/fasting or following a low carb diet

• reversal of glycolysis

Metabolism of dietary fats

• dietary fats broken down into glycerol and free fatty acids during digestion

• can be oxidises to produce ATP - triglycerides must first be split into glycerol and fatty acids through lipolysis

• if not needed for ATP, stored in adipose tissue - known as lipgenesis

Lipid metabolism - glycerol

• converted to glyceraldehyde-3-phosphate

• can enter glycolysis to form glucose via gluconeogenesis or be converted to pyruvate

• conversion to glucose when ATP levels are high

• conversion to pyruvate when ATP levels are low

Lipid metabolism - fatty acids

• converted to acetyl CoA through process of beta-oxidation

• fatty acids are not used to make glucose - cannot make pyruvate from acetyl CoA

Beta-oxidation

Fatty acid → acetyl CoA

• two carbon atoms are removed at a time and attach to coenzyme A

Acetyl CoA can enter Krebs cycle

occurs in the mitochondria

cycle repeats until all carbon=carbon bonds are broken

Why does the body prefer glucose?

ATP production from fatty acids requires oxygen

• cannot be achieved under anaerobic conditions

Glucose is the brain’s preferred fuel source

• brain has high energy requirements and needs constant supply of glucose

Mature RBC only perform glycolysis

• lack mitochondria

• limited ATP produced → need constant supply of glucose

Lipogenesis

• liver and adipose cells synthesis lipids from glucose or amino acids

• occur when consuming more energy than body needs

Metabolism of protein

• proteins from food break down into amino acids

• not stored for energy use

• oxidised for ATP OR synthesised to make new proteins

• excess proteins converted to glucose bia gluconeogenesis or triglycerides via lipogenesis - used to make glucose when glucose/glycogen supplies are exhausted

Amino Acids - glucogenic

can be converted to glucose through pyruvate (majority of amino acids)

Amino Acids - ketogenic

enter the Krebs cycle as acetyl CoA or an intermediate molecule

Amino Acid Deamination

• before amino acids can be used for energy, the must be deaminated

• occurs in hepatocytes (liver cells)

• two products: Ammonia (NH3) → toxic to cells and Carbon structure without amino group (keto acid)

Amino acid transamination

Amino acids are either

• essential: cannot be made by the body and must be obtained from food

• non-essential: can be make by the body

process of making non-essential amino acids from keto acids

Involves:

• transfer of amino group from amino acid to its corresponding keto acid

• creates new amino acid and keto acid

Excess glucose (energy balance)

• stored as glycogen in the liver and muscles

• limited conversion to fatty acids or amino acids as it requires a lot of energy

Excess protein (energy balance)

• cannot be stored

• small amounts of protein used

• conversion to glucose: transported back to liver

deaminated → oxidised → converted to glucose via gluconeogenesis

Excess dietary fat (energy balance)

• does not promote its own oxidation

• Fat, more than energy needs requirements is stored - virtually unlimited capacity for fat stores