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Transcript
BIOLOGY 11
DIGESTIVE SYSTEM
DIGESTIVE SYSTEM = digestive tract (=alimentary canal)
plus associated glands and organs
DIGESTION = breaking down of large complex molecules to
simple molecules that can be used by body’s cells
Molecules must be small enough to be absorbed by columnar
epithelium of small intestine
Organs involved:
Digestive tract
mouth  pharynx  esophagus  stomach 
small intestine  large intestine  rectum  anus
Cavity in digestive tract is the lumen
Associated glands:
Salivary glands (3 pair)
Liver
Gall bladder
Pancreas
Glands in intestinal lining and stomach
Digestive process
Mouth Teeth
Tongue & teeth
Taste buds
Salivary glands
Parotid glands
Submandibular glands
Sublingual glands
Saliva
Pharynx Swallowing
Soft palate seals nasal passage
Epiglottis seals glottis
Esophagus Peristalsis
Cardiac sphincter -
Stomach Functions
Food storage
Formation of chyme
Initiation of protein digestion
Gastric glands
Gastrin  hydrochloric acid release
Mucus
Pepsin
Pyloric sphincter
Small intestine
Structure designed to increase surface area for absorption
coiled
circular folds
villi
microvilli
3 sections
duodenum
jejunum
ileum
Chyme contains
nucleic acids
polypeptides (from proteins)
carbohydrates
fats
Chemoreceptors in duodenum wall detect type of food
molecules present and pH (acidity)
Glands in duodenum wall release hormones
Secretin
stimulates pancreas to secrete bicarbonate
neutralizes acidity of chyme
stimulates liver to produce bile
Cholecystokinin (CCK)
stimulates pancreas to secrete digestive enzymes
stimulates gall bladder to release bile
Liver produces bile
Stimulated by presence of fats or low pH in chyme
Bile breaks down large fat droplets into smaller droplets
increases surface area for enzyme action
Gall bladder stores bile
When stimulated, gall bladder releases bile into intestine
Pancreas releases digestive enzymes
Pancreatic amylase
polysaccharides (carbohydrates)  disaccharides
Lipases
fats  fatty acids + glycerol
Nucleases
RNA and DNA  nucleotides
Proteases
polypeptides  amino acids
Absorption of most of water and all nutrients in small intestine
Ileocaecal valve - one-way valve allows undigested material to
pass into large intestine
Large intestine
Functions
absorption of water from undigested food
formation of feces
anaerobic bacteria (E. coli) break down wastes
produce gas
produce vitamin K and B vitamins
absorption of vitamins produced by E. coli
vitamin K important for blood clotting factor
storage of feces
caecum - short pouch where small intestine joins
large intestine
appendix hangs off caecum
colon - parts named for position or shape
ascending colon
transverse colon
descending colon
sigmoid colon
rectum - muscular walls
stores feces until elimination
anal canal - two sphincters to control defecation
internal anal sphincter - smooth muscle
defecation reflex
external anal sphincter - skeletal muscle
control of defecation reflex
Anus - opening through which defecation occurs