Human Digestive System

Functions Ingest food Break down food Move through digestive tract Absorb digested food and water Eliminates waste materials

Gastrointestinal Tract

Mouth Incisors- sharp, front teeth used to tear food Molars- flat, back teeth used to grind it up Hard and soft palates- roof of mouth for tongue to push against Begins starch digestion (amylase) Saliva produces amylase and lubricates food Moves food into esophagus

Esophagus Pharynx- the opening at the back of the mouth for air and food Epiglottis- flap of tissue that covers trachea (windpipe) so food doesn’t go down Esophagus- muscular tube about 25 cm long connecting pharynx to stomach Peristalsis- rhythmic muscular contractions and relaxations that moves food to stomach

Stomach First opening – cardiac sphincter Muscles churn food – more mechanical digestion. Glands called gastric pits produce gastric fluid = pepsin + HCl Pepsin breaks down proteins (only at pH 2) Food leaves after 2-4 hrs Chyme- pastelike substance containing various nutrients. Second opening – pyloric sphincter

Stomach

Liver Stores glycogen and breaks down toxic substances Produces bile: breaks down fat globules into small droplets Allows more surface area so digestive enzymes can break down Ex.-aminotransferases Bile is stored in the gallbladder: releases bile into small intestine when chyme is present

Pancreas Lies just behind the stomach Secretes pancreatic fluid with digestive enzymes into small intestine Contains sodium bicarbonate- changes pH of chyme from acid to base. Enzymes break down carbs, fats, and proteins. Examples- pancreatic amylase, lipase, trypsin

Liver and Pancreas

Small Intestine Split into three sections: Duodenum- makes up first 25 cm Jejunum- makes up middle 2.5 m Ileum- finishes with about 4 m Digestion is finished here Peristalsis finishes mechanical digestion Pancreatic juice produces enzymes to finish chemical digestion of fats, proteins and carbohydrates Broken down nutrients then diffuse into blood vessels Mucous lines the intestinal walls to protect from digesting enzymes and acidic chyme

Small Intestine Enzymes include maltase and peptidases.

Villi Villi are finger-like projections that line the small intestine. Increases surface area to increase absorption! Also has digestive enzymes on surface.

Large Intestine Broken into four parts: Ascending, transverse, descending and sigmoid colon. Absorbs water left from small intestine Bacteria live here (produce methane) Bacteria produce B vitamins and Vitamin K Stores solid waste in rectum until elimination.

Large Intestine

Endocrine Glands Release hormones into blood. Pancreas – insulin = blood sugar Thyroid – thyroxine = metabolic rates Thyroid – calcitonin = blood calcium levels Parathyroid – PTH = calcium, phosphorus absorption rates and helps make Vitamin D