THE DIGESTIVE SYSTEM C15L2

The food you eat goes through four steps: Ingestion: intake of nutrients; the act of eating, or putting food in your mouth Digestion: breakdown of food into small particles and molecules that your body can absorb and use Absorption: uptake of nutrient molecules Defecation: elimination of undigested residues

Two types of digestion mechanical digestion chemical digestion

mechanical digestion the process of breaking food into smaller pieces and mixing it with the digestive juices food is physically broken down

chemical digestion the breaking down of food into smaller molecules

Enzymes are proteins that help break down larger molecules into smaller molecules.Enzymes Enzymes also speed up, or catalyze, the rate of chemical reactions. The digestive system produces enzymes that are specialized to help break down each type of food molecule. Chemical Digestion

Amylase: breaks down starch in the mouth Lipase: breaks down fats when it enters the stomach Pepsin: digests proteins in the stomach Renin: digests milk in the stomach Some Digestive Enzymes

GROUPING OF ORGANS OF THE DIGESTION SYSTEM alimentary canal (digestive tract) accessory organs

alimentary canal the digestive tract: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus

accessory organs organs that secrete substances that are carried through ducts (tubes) to the alimentary canal

accessory organs liver pancreas gallbladder salivary glands

MOUTH mixed with saliva from the salivary glands (3 pairs of salivary glands) the saliva moistens and lubricates the food for easy swallowing

MOUTH salivary glands secrete a digestive enzyme--amylase

amylase A digestive enzyme that begins the breakdown of starch to sugar and neutralizes acidic foods

mastication The chewing of food

4 different types of teeth are involved in mastication  incisors (8): flat, narrow, bladelike surfaces for cutting and biting food  canines [cuspids] (4): tear food  premolar (8): crush food  molars (12): grinding food

4 different types of teeth are involved in mastication

ESOPHAGUS a muscular tube that connects the mouth to the stomach

ESOPHAGUS the word esophagus means "I will carry down."--its only function it only requires 3-6 seconds for food to move from the mouth to the stomach

peristalsis muscular contractions that move food along the alimentary canal

cardiac sphincter Lower Esophageal Sphincter muscular valve that controls food going into the stomach; keeps food in the stomach

STOMACH The stomach is a large, hollow organ that temporarily stores food and aids in chemical digestion.

STOMACH the thick, muscular walls of the stomach churn the food and mix it with the acidic gastric juices which contains the enzyme pepsin for protein digestion

STOMACH The acid would also digest the walls of the stomach if the walls were not protected by the slimy mucous from the mucous membrane lining the stomach

STOMACH the duration of churning may be 4 hours for coarse foods like celery and spinach; foods like oatmeal and pudding move through the stomach quickly

STOMACH chyme: food in a semi-liquid state Food mixes with gastric juice in the stomach to form a thin, watery liquid called chyme.chyme

STOMACH Although the stomach lining does not absorb many food molecules, it does absorb alcohol, water, and certain drugs.

STOMACH pyloric sphincter : muscles that control the pyloric valve; controls food moving into the small intestine

SMALL INTESTINE about 7 m (23 feet) long; about 2.5 cm (1 inch) in diameter

SMALL INTESTINE Most of the chemical digestion and absorption of food occurs here.

SMALL INTESTINE duodenum: first section of the small intestine; about 10 inches Chemical digestion of proteins, carbohydrates and fats takes place in the first part of the small intestine, called the duodenum.

SMALL INTESTINE As partially digested food from the stomach passes into the duodenum, the acidity of the

SMALL INTESTINE food stimulates the intestinal lining to secrete hormones

SMALL INTESTINE these hormones stimulate the pancreas, gallbladder, and intestinal lining to secrete

SMALL INTESTINE enzymes and other materials into the duodenum for digestion.

Small Intestine The remainder of the small intestine absorbs nutrients from food.

The folds of the small intestine are covered with fingerlike projections called villi.villi

VILLUS villi: (singular, villus) microscopic, fingerlike structures that line the wall of the small intestine

VILLI

LARGE INTESTINE (COLON) about 1.5 M (5-6 feet) long; 5 cm (2 1/2 inches) in diameter

Large Intestine (colon) Food not absorbed in the small intestine move by peristalsis into the large intestine, also called the colon. Materials that pass through the large intestine are the waste products of digestion.

LARGE INTESTINE (COLON) little or no digestion occurs

LARGE INTESTINE (COLON) functions: 1)removal of waste materials (called feces) 2) absorb water and minerals

LARGE INTESTINE (COLON) also serves as an ideal site for growth of bacteria and yeasts

LARGE INTESTINE (COLON) there are many beneficial bacteria and yeasts reproducing in the colon

LARGE INTESTINE (COLON) Bacteria and yeasts produce vitamins (B1, B2, B12, and K) and some amino acids.

accessory organs liver pancreas gallbladder salivary glands

LIVER called "master chemist of the body"

LIVER Liver receives blood by way of the portal vein

LIVER makes bile, a greenish fluid that breaks up lipids into droplets so they can be digested.

GALLBLADDER bile is stored in the gallbladder

PANCREAS a soft, pinkish- white gland about 6-9 inches long; 1 inch wide pancreas

PANCREAS about 97% of the pancreas cells produce digestive juices that contain enzymes for digesting carbohydrates, fats, and proteins pancreas

PANCREAS most of the remaining pancreas cells produce hormones (insulin) involved in regulating the amount of sugar in the blood

Nutrients absorbed by the body through the digestive system are necessary for other body systems to maintain homeostasis. The Digestive System and Homeostasis