3B Scientific The Digestive System Chart - Manual (Page 4)

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Large Intestine
Small Intestine
4
English
I Representation of the Alimentary Canal
1 Parotid gland
2 Sublingual gland
3 Submandibular gland
4 Esophagus
5 Stomach
6 Liver
7 Pancreas
8 Duodenum
9 Jejunum
10 Ileum
11 a) Caecum
b) Vermiform appendix
12 Colon
a) Ascending colon
b) Transverse colon
c) Descending colon
d) Sigmoid colon
Brown area marks the zone of acid reaction, while the blue zone is an area where alkaline reaction occurs.
II Schematic Outline of the Physiological Processes in the Alimentary Canal
(chemical breakdown of carbohydrates, proteins and fats)
1. Oral Cavity
a) Fats
b) Proteins
c) Carbohydrates
Three pairs of large salivary glands (parotid, submandibular and sublingual glands), together with
numerous small glands in the oral cavity cooperate in producing saliva. The principal places of enzyme
formation are the parotid glands. The amylase ptyalin is an important enzyme in the reduction of polysac-
carides, primarily starch. Because food remains in the oral cavity for only from 0,5 to 1 minute, the fermen-
tation processes probably are deemed of only secondary importance here.
2. Stomach
Even before food is taken in, unconditioned reflexes elicit the secretion of gastric juice. This is further acce-
lerated when food comes into contact with the oral mucosa. Stimuli of this kind are conducted the stoma-
ch by the pneumogastric nerve (nervus vagus). When food reaches the stomach, secretion of gastric juice is
stimulated directly by the gastric contents. Food itself contains substances stimulating secretion which are
also produced during the digestive process. The protein-splitting enzymes pepsin and cathepsin, together
with hydrochloric acid, are the gastric juice‘s most important constituents.
Pepsinogen is converted into the active protein-splitting enzyme pepsin by acid reaction. In the process
albumin is broken down into polypeptides. Reflex action opens and closes the pylorus. The pylorus closes
when acid gastric contens passed into the duodenum. When the alkaline intestinal juice has attenuated the
acid reaction, the pylorus opens again.
Digestion