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 2 kinds

1. Mechanical Digestion chewing, chopping, grinding breaks food into smaller pieces increases surface area for:

2. 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. EliminationLarge 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 BladderLiver: 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