Transcript Second Part
Anatomy CLIL Second Part Prof. Milvia Morocutti 13 All the organs can be classified in two types: solid and cave or hollow organs. Lobule Parenchima Secta Lobe Connectival Capsule Fig. 9a Solid organ The former, like liver or pancreas, are formed by an outermost capsule of dense connective tissue surrounding the entire organ, while the inside is filled with a tissue called parenchyma. 14 Fig. 9b Cave organ Despite the diverse and specialized processes that take place in different sections of the digestive tract, there is a fundamental consistency in the architecture of the tubular digestive tract. Inside cave organs like those of the G.I. tract, we can observe 3 basic concentric layers: tunica mucosa (with submucosa); tunica muscularis; tunica serosa or adventitia 15 The animal’s alimentary canal The animal’s alimentary canal is a long tube running from one end of its body to the other. Food is taken into the alimentary canal by ingestion. The food you eat usually contains some large molecules. Before they can be absorbed, they must be broken down into small ones. This is called digestion. Before food can be of any use to the animal, it has to get out of the alimentary canal and into the bloodstream. This is called absorption. To be absorbed, molecules of food have to get through the walls of the alimentary canal. They need to be quite small to be able to do this. At the end of this process, the food which could not be digested or absorbed is removed from the body by egestion. Fig.10 How an animal deals with food 16 food MOUTH Secretion of salivary glandules bolus ESOPHAGUS STOMACH Secretion of gastric glandules chimo SMALL INTESTINE Secretion of pancreas, liver and enteric glandules LARGE INTESTINE Absorption only of water and salts chilo The gastrointestinal tract has a uniform general histology with some differences which reflect the specialization in functional anatomy. The mucosa is the innermost layer, surrounding the lumen, or space within the tube. This is very important because it comes in direct contact with the food and is responsible for absorption and secretion. The mucosa is highly specialized in each organ of the G.I. tract, for example dealing with a low pH in the stomach, providing a multitude of different substances in the small intestine, and also absorbing specific quantities of water and salts in the large intestine (through blood vessels). The layer of the tunica mucosa also contains lymphatic nodules important for the immune function and fat absorption. c i r c u l a t o r y s y s t e m l y m p h a t i c s y s t e m Reflecting the varying needs of these organs, the structure of the mucosa can consist of invaginations of secretory glands (i.e. gastric pits), or it can be folded in order to increase surface area (i.e. villi, microvilli). These distinctive differences in architecture especially for the epithelium (the innermost part of the mucosa, the cell sheet in direct contact with the lumen), can be seen below to the right in the micrographs of mouse digestive tube. The magnification of all four images is identical and the epithelial layer is oriented toward the top. 17 Mouth Esophagus Glandule Stomach Glandule Duodenum S m a l l I n t e s t i n e Large Intestine Rectum Serosa Tunica Fig. 12 digestive tissue Submucosa Muscularis Mucosa Mouth Mechanical digestion by teeth and tongue. Chemical digestion by saliva. Esophagus Muscle tube, takes food down to the stomach. Stomach Mechanical digestion by contraction and relaxation of muscular walls. Heart Chemical digestion by gastric juice. Liver Pancreas Bile Gallbladder Duodenum Chemical digestion by bile pancreatic juice Small intestine Absorbs digested food by villis Large intestine Absorbs especially water and minerals Rectum 18 19