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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