digestion and absorption of the food nutrients chapter 3

Digestion and Absorption of the Food Nutrients

Chapter 3

Nutrient Digestion and Absorption

Hydrolysis reactions• Catabolic

Breakdown Split of chemical bonds

• Separates water molecules into • H+ - hydrogen ions• OH- - hydroxyl ions

• These ions then added to by-products of reaction

Hydrolysis

Nutrient Digestion and Absorption

Hydrolysis reactions• Examples:

Polysaccharides (starches) to disaccharides to monosaccharides

Proteins to amino acids Lipids to glycerol and fatty acids

Nutrient Digestion and Absorption

Condensation reactions • Anabolic (building up)• Join H+ and OH- to form a water molecule• Source of metabolic water

Condensation

Enzymes

Accelerate chemical reactions Specific protein catalyst Reduce activation energy (energy input)

Reusable Enzymes don’t get changed during the

reaction Substrate

Any substance acted upon by an enzyme

Lock and Key Mechanism

Coenzymes

Coenzymes Facilitate enzyme action

Nonprotein Additional ions (minerals) Smaller organic molecules (like B-vitamins)

Coenzymes

Coenzymes

Temporary carrier NAD+

NADH Carry electrons and H+

This carrier allows the enzymes of the electron transport chain to extract the electrons and H+

Passive Transport

Cell membranes Selectively permeable

Maintain consistency in chemical composition

Passive Transport (4 types-does not require energy input) Simple diffusion Facilitated diffusion Osmosis Filtration

Simple Diffusion

Continuous molecular movement Higher to lower

concentration Until they are evenly

dispersed

Examples Almost all gases Ex. Oxygen, Carbon

dioxide Concentration

gradients allow movement of gases

Facilitated Diffusion

Membrane proteins Channels in cell

membrane Open under specific

conditions Chemical messenger

Neurotransmitter Ions ( + or - )

Voltage gated channels

Thus, they facilitate the movement of molecules

Facilitated Diffusion

Examples Glucose

Lipid insoluble

Uncharged Binds to site

on membrane

Structural change

Osmosis

Water moves based on differences in solute concentration

It can move freely between these compartments Intracellular Extracellular Plasma

Osmosis

Osmolality Concentration of dissolved particles in a solution

• Isotonic solution No gain or loss of water between cells and fluid surrounding

them• Hypertonic

Higher solute concentration outside cell than inside (causes cell to shrink)

• Hypotonic Higher water concentration outside cell than inside (causes

cell to swell)

Osmolality

Filtration

Hydrostatic pressure Pressure in blood stream is higher than

surrounding tissues Causes flow of fluid from capillaries to

interstitial space Higher protein content in plasma Osmotic pressure causes absorption of

interstitial fluid back into capillaries

Filtration

Active Transport

Requires energy (ATP) Ex. Sodium-Potassium Pump

Moves ions against electrochemical gradients Sodium-potassium ATPase

Sodium-Potassium Pump

Na+ leak into cell Action potential

Depolarization K+ moves out to re-

establish charge Sodium-potassium

pump “resets” cell to resting gradients

Coupled Transport

Linked, simultaneous transport Two substances Across cell membrane Same direction – symport Opposite directions – antiport

Coupled Transport

Bulk Transport

Movement of large particles and molecules

Exocytosis Hormones, Neurotransmitters, Secretions,

wastes ICF to ECF Stages

Enclosed in pouch Pouch migrates to membrane Contents ejected into ECF

Bulk Transport

Endocytosis Water, lipids Plasma membrane of cell surrounds

substance Pinches away Moves into cytoplasm

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Acid-Base Concentrations

Acid: any substance that dissociates (ionizes) in solution and releases hydrogen ions (H+)

Base: any substance that picks up or accepts H+ to form hydroxide ions (OH-) in water solutions

pH: provides a quantitative measure of the acidity or alkalinity (basicity) of a liquid solution

Acid-Base Concentrations

pH 1.0 to 14.0 Examples

HCl – 1.0 (acid) Blood – 7.4 Lye – 14.0 (base)

Acid-Base Concentrations

Enzymes Activated/inactivated by pH

Example Salivary amylase

Mouth Inactivated by stomach pH Denatured

Acid-Base Concentrations

Chemical buffers• Use a base to “neutralize” an acid

Acid + base → weaker acid → dissociates into harmless or less harmful products

Acid-Base Concentrations

Ventilatory buffer• Increases or decreases in pulmonary

ventilation Lactic acid (Hla)

• H+ + La-

• H+ + HCO3- → H2CO3 → CO2 + H2O

• Tissues → Lungs

Acid-Base Concentrations

Renal buffer• Kidneys excrete or conserve H+ to

maintain acid–base stability of body fluids