Human Digestive System

Ingest food Break down food Move through digestive tract Absorb digested food and water Eliminates waste materials HowStuffWorks Videos "Assignment Discovery: Breaking Down Digestion"

1. Ingestion Eating and drinking

2. Digestion Bite Size Science 2 kinds Mechanical Digestion chewing, chopping, grinding breaks food into smaller pieces increases surface area for: Chemical Digestion breaks chemical bonds within macronutrients hydrolysis reaction (releases water) BiologySource

Mouth Breaks down food into small pieces Begins starch digestion (amylase) Saliva produces amylase and lubricates food Moves food into esophagus Epiglottis covers trachea Peristalsis moves food to stomach

Oesophagus (esophagus) ~ 24 cm long tube takes food from pharynx to stomach made up of circular, longitudinal & smooth layers of muscles work together to push food along

Peristalsis circular & longitudinal muscles contract rhythmically lubricant mucin added together push bolus (ball of food) along in waves to stomach Peristaltic Wave in the Gastric Antrum - YouTube

Stomach First opening – cardiac sphincter Muscles churn food – more mechanical digestion Inner layer folded into ridges called rugae that contain gastric glands Glands produce gastric juice = pepsin + HCl Mucous secreted that protects stomach wall Pepsin breaks down proteins (only at pH 2) creates chyme (thick liquid), which leaves after 2-4 hrs Second opening – pyloric sphincter Stomach Digestion - YouTube

3. Absorption proteins, starches, sugars, fats & vit. Small Intestine: ~ 7 m long chyme leaves stomach into duodenum jejunum middle section illium passes chyme into lg intestine lined with finger-like villi (inc SA) each villus had artery, vein & lymph vessels to it nutrients absorbed into blood by diffusion or active transport

Large Intestine (aka the colon) ~ 1.5 m long absorbs water from wastes e. coli bacteria further break down wastes (produce methane) other bact. produce vitamin B & K which get absorbed

4. Elimination Large Intestine, Rectum & Anus Rectum - last 20-30 cm of LI stores wastes (toxins) when fills with wastes nerves send message to brain to empty wastes exit through anal sphincter low cellulose (fibre) diet results in less elimination, so toxins in rectum for longer increased risk of colon cancer

Endocrine Glands Pancreas, Liver & Gall Bladder * chyme doesn’t enter these organs but they help in digestion* Pancreas produces: insulin lowers blood glucose glucagon raises bld glucose pancreatic juices & NaHCO3:

Digestive Enzymes (Pancreas) neutralize chyme & contain digestive enzymes break down macromolecules Ex: Protease – protein into a.a. Lipase – fat into glycerol and 3 fatty acids Maltase, Sucrase, Lactase – sugars into glucose

Liver & Gall Bladder Liver: produces bile which contains salts to break down lg fat globules (inc. SA) stores carbs and vitamins detoxifies Gall Bladder: stores bile until needed Digestive System.notebook