Download Unit 5 Digestive System

Human Biology 11
Human Digestive System
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Objective: make food/ nutrients small enough to enter cells; must be small molecule size
Types of digestion:
o Mechanical digestion: grinding, chewing, physical breakdown of food into smaller pieces
 Occurs in mouth, stomach
o Chemical digestion: adding of chemicals (acids, enzymes) to break large molecules into
smaller molecules
 Occurs in mouth, stomach, small intestine
Teeth: used for breaking food into smaller pieces before entering digestive
o Types:
 Wisdom: no purpose
 Molar: grinding food
 Bicuspid: breaking hard
objects (e.g. nuts)
 Cuspid: tearing food
 Incisor: cutting food
Tongue: mix food with saliva to form
bolus (ball of food that is swallowed)
o Senses; heat, extreme heat, cold, taste
o Taste: sensed by taste buds (salty, sweet, sour, bitter)
Esophagus: mucus lubricated tube that moves bolus to stomach
o Peristalsis: muscle contraction that moves the bolus through the digestive tract
Stomach: used for storage, mechanical digestion and chemical digestion
o Mechanical digestion: moving of abdominal muscles churns food and controls the amount of
material released into the small intestine.
 Sphincters: round muscles that close off digestive tubes.
 Cardiac sphincter: top of stomach
o Stops movement of food from stomach to esophagus
 Pyloric sphincter: bottom of stomach
o Controls the movement of food from stomach to small intestines
o Mucus; produced by mucus glands in sinuses/ esophagus/ stomach lining
 Protect stomach lining from acids
 Breaks in mucus can cause ulcers (chemical ‘burns’ caused by HCl and
pepsin
o Chemical digestion: adding of gastric juice (HCl and enzymes) breaks down food into smaller
particles to change bolus into chyme
 HCl changes pH of stomach so that enzymes work more efficiently and kills bacteria
that may be with food
 Gastric enzymes;
 Pepsin; digests protein (makes the molecules smaller)
 Renin; curdles milk so that enzymes can digest it properly
 Lipase; digests fats
Human Biology 11
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Small intestine: has many folds and is responsible for completing digestion and absorbing nutrients
from food
o ~7m long
o Three parts;
 duodenum; completes most digestive processes
 jejunum; has villi to absorb nutrients
 villi; finger like projections that link digestive system and circulatory system
 ileum; absorbs materials that were not absorbed by the jejunum
o Associated digestive organs add bile and digestive enzymes here
Large intestine: responsible for absorbing excess water from waste material before passing the
material onto rectum
o Sphincter at beginning of large Intestine controls amount of material passing from small
intestine to large intestine
o Appendix: although attached to large intestine, serves no present function in humans
 Thought to have been needed for digesting leaves
Associated Digestive Organs
o Liver; produces bile and converts excess blood sugar into fat for storage
 Liver also produces vitamin A; stores vitamin A,D, B12, iron and glycogen
 When blood sugar is low, glycogen is converted into glucose to increase
blood sugar levels
 Filters blood (removes waste and toxic chemicals from blood.
 Bile; stored in gall bladder
 Breaks fat into tiny droplets (emulsification); (Acts like dish soap.)
o Pancreas; produces pancreatic juice to be added to small intestine for digestion
 Pancreatic juice includes;
 Protease; digest proteins
 Lipase; digest fats
 Amylase; digest starches and sugars
 Pancreas also produces insulin and glycogen
 Insulin allows cells to absorb sugar for energy
 Glycogen tells liver to convert fat into sugar