SBI3U Digestive system

Importance of Nutrition

Provides energy for body metabolism and raw materials for building cells

Macronutrients

Nutrients consumed in large amounts daily to supply energy, carbohydrates, proteins, and fats

Micronutrients

Minerals and vitamins required in smaller amounts for body functions

Water

Essential nutrient critical for survival, involved in all bodily processes

Carbohydrates

Major sources of quick energy

Monosaccharide

Simple sugar with chemical formula (C6H12O6): Fructose, galactose, glucose

Dehydration synthesis

Process removing a water molecule to combine two monosaccharides into a disaccharide

Hydrolysis

Process adding water to break disaccharides back into monosaccharides

Disaccharide

Two monosaccharides linked : maltose, sucrose, lactose

Maltose

Disaccharide formed from glucose + glucose

Sucrose

Disaccharide from glucose + fructose, common table sugar

Lactose

Disaccharide from glucose + galactose, sugar found in milk

Polysaccharide

Complex carbohydrate from many monosaccharides linked together

Starch

Polysaccharide stored in grains and vegetables, serves as plant energy storage

Glycogen

Animal polysaccharide made from excess glucose converted by insulin and stored in liver, released back to glucose by glucagon when blood sugar is low

Cellulose

Polysaccharide in plant cell walls, undigested in humans but provides roughage for intestinal waste elimination

Fats

Organic molecules with carbon, hydrogen, oxygen in different ratios from carbs, protect organs and joints, insulate body under skin

Triglyceride

Fat structure consisting of a 3-carbon glycerol’s

Saturated fats

Fats where all carbon bonds are filled with hydrogen, solid at room temperature, sources include animal fat, butter, lard, artificially saturated margarines

Unsaturated fats

Fats with some carbon bonds not filled with hydrogen, liquid at room temperature, sources include vegetable oils, nut oils, some fish oils, certain margarines

Lipoprotein

Structure with proteins and lipids on outside to transport fats in bloodstream

Proteins

Organic molecules used in cells and body structure

Polypeptides

Long protein chains broken down by digestive enzymes into dipeptides and amino acids

Amino acids

20 building blocks for all proteins, 8 essential ones not made in body so obtained from food

Complete protein

Protein containing all 8 essential amino acids, found in meat, legumes, milk, eggs, cheese, whole grains

Vitamins

Act as coenzymes to enable enzyme function, support tissue growth and disease defense

Fat-soluble vitamins

Vitamins K, E, D, A stored in fat, important for eyes and skin

Water-soluble vitamins

Vitamins B and C, act as antioxidants to resist disease, excess removed in urine

Minerals

Inorganic elements without carbon, build bones and hormones

Food pyramid

Guide for balanced diet with base as grains, cereals, potatoes and top as sweets, chocolates, cakes

Digestion

Mechanical and chemical breakdown of food into smaller absorbable components

Macromolecules

Large molecules providing nutrition and energy, including proteins, carbohydrates, fats, but not nucleic acids

Saliva

Secretion containing mucus and enzymes like amylase to break polysaccharides

Pharynx

Connects oral cavity to epiglottis and esophagus

Epiglottis

Flap preventing food from entering lungs through larynx

Esophagus

Muscular tube 2cm diameter passing food from pharynx to stomach via peristalsis

Peristalsis

Radially symmetrical muscle contractions moving food bolus, involving circular muscles narrowing and longitudinal muscles shortening ahead

Stomach

J-shaped organ holding up to 1.5L food, performs mechanical churning and chemical digestion with gastric juice

Rugae

Thick folds of smooth muscle lining stomach inner wall, allow expansion

Ulcer

Damage from acid burning through stomach lining

Cardiac Sphincter

Controls food entry to stomach, improper closure causes acid reflux

Pyloric sphincter

Ring connecting stomach to small intestine, controls flow of chyme

Gastric Juice

Produced in stomach glands, contains HCl, pepsinogen converted to pepsin for polypeptide breakdown

Chyme

Semi-digested acidic food mixture exiting stomach

Small Intestine

About 6m long, major site for digestion and absorption, divided into duodenum, jejunum, ileum

Duodenum

First 10-12 inches of small intestine, receives secretions from gall bladder and pancreas, site of most chemical digestion

Cholecystokinin

Hormone from duodenum cells signaling pancreas to secrete substances and stomach to slow digestion

Gall Bladder

Stores bile produced by liver, releases to emulsify fats increasing surface area for lipases

Bile

Made from cholesterol and salts, emulsify fats

Liver

Produces bile and cholesterol, converts and stores glucose as fat, stores vitamins K E D A, detoxifies poisons like alcohol and medicines

Villi

Finger-like projections in small intestine lining increasing surface area for nutrient absorption

Crypts

Glands in epithelial lining producing enzymes like maltase and sucrase

Absorption of water-soluble nutrients

Nutrient molecules absorbed through mucosal epithelium into blood capillaries of villi, transported to body

Absorption of fat-soluble nutrients

Fatty acids, cholesterol, fat-soluble vitamins absorbed by membrane transport into lacteals, transported via lymphatic system

Simple diffusion

Passive transport where simple ions move from high concentration to low in epithelial cells

Facilitated diffusion

Passive transport of larger molecules like water-soluble minerals and vitamins through channel proteins along concentration gradient

Active transport

Energy-requiring process using ATP and membrane protein pumps to move monosaccharides and amino acids from low to high concentration against gradient

Caecum

First part of large intestine, attached to appendix, separated from ileum by ileocaecal valve

Appendix

Blind-ended tube sheltering beneficial digestive bacteria, can become infected causing appendicitis

Colon Cancer

Fourth most common cancer, starts as benign polyps becoming malignant

Diverticula

Small pouches in colon lining causing diverticulosis