Digestive System: From Mouth to Anus

• Digestion: Function is to breakdown food into smaller molecules (nutrients) to be absorbed by the body. All undigested food is removed as solid waste.

• Two parts: digestive tract and digestive glands.

Digestive Glands• is a long tube ~27 feet that starts at mouth, where food and drink enter the body, and ends at the anus, where leftover food and waste leaves the body.

• Includes: Mouth, pharynx, esophagus, stomach, small intestines, large intestines, rectum, anus

• Produce chemical secretions needed to

breakdown food.• Includes: salivary

glands, gastric glands, the liver, pancreas, and

intestinal glands.

Digestive Tract

Food Digestion• Ingestion and propulsion of food• Digestion of food• Absorption of nutrients• Elimination of fecal matter• Mechanical digestion/transformation:

physically mixing and breaking down food into smaller parts

• Chemical digestion/transformation: chemically breaking down food from complex molecules into simpler molecules. Occur due to secretions from the digestive glands.

Mouth• Ingestion: taking substances into

body via mouth.• Teeth: rips, cuts, crushes and

grind food [mastication: chew food] into a soft pulp that is easy to swallow (mechanical digestion).– Incisors: cut and tear– Canines: tear– Premolars and Molars: chew and

grind• Masticating mixes food with

saliva, from the salivary glands, to make it moist and easy to swallow.

• Tongue: moves the food in your mouth and helps to swallow

Saliva• Secreted by the salivary glands– The glands are found in and around

your mouth and throat. – Salivary glands produce the saliva

used to moisten your mouth and food, initiate digestion, and help protect your teeth from decay.

• Contains:– enzyme called Amylase, which helps

breakdown starch into simple sugars (chemical digestion).

– Enzyme called Lingual Lipase, begins breakdown of lipids.

Deglutition (Swallowing) • Food moves to the back of your

mouth to your pharynx: where there is the opening to both the trachea (windpipe) and esophagus.

• Swallowing is a voluntary action involving many muscles.

• When swallowing the epiglottis (flap of cartilage) prevents food from going into the trachea allowing the food to move into the esophagus.

Esophagus• A muscular tube ~25 cm long. • Passage for food and drink between pharynx and stomach. • Food moves by rhythmic waves of muscle contractions

called peristalsis. (mechanical digestion)• Note: peristalsis also occurs in the stomach, small and

large intestines.

Stomach• Food moves into the stomach from the esophagus by

passing through the cardiac sphincter (muscle at top of stomach).

• Acts like a blender churning and mixing the food (mechanical digestion).

• Mixes food with HCl (hydrochloric acid) and other gastric juices that uncoils proteins (chemical digestion).

• Food now known as chyme moves through the pyloric sphincter (muscle at bottom of stomach) into the small intestines.

Small Intestines• Major sight of digestion.• Chymes moves by peristalsis into small

intestines at the duodenum (first section).• Secretes digestive juices.

• Liver produces bile that is stored in the gallbladder. • Gallbladder releases bile into the small intestines.• Bile aids to break down fat into droplets (chemical). Pancreas secretes pancreatic juices (enzymes) into the small intestines that helps to neutralize stomach acid. Also, aids in the further digestion of carbohydrates glucose, fats fatty acids and glycerol, and proteins amino acids (chemical).• Peristalsis moves the chyme mixing it with digestive enzymes

(mechanical digestion).Absorption: passage of nutrients from digestive tract into blood stream or lymph.• 90% of nutrients absorbed through the villi: folds in the walls of

the small intestines.

Large Intestines• Liquid matter with little nutrients move into large intestines

by peristalsis. • ~4 feet long • No villi• No further digestion• Reabsorbs excess water• Contains bacteria that releases vitamin B and K that gets

absorbed (symbiotic relationship).• Stores and concentrates feces• Peristalsis moves feces to rectum for storage.• Signal sent to brain triggers need for bowel movement and

feces exits via anus (anal sphincter).