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Principals of General Zoology (Zoo-103) Zoology Department, 1431-1432H 1 Digestion الهضم • Digestion: is the mechanical and chemical breaking down تكسيرof food into smaller components, to a form that can be absorbed تُمتص. Digestion is a form of catabolism that means break down of macro-food molecules أجزاء الطعام الكبيرةto smaller one. a)- Extracellular digestion الهضم خارج الخلية: In mammals, food enters the mouth, being chewed by teeth, and broken down by the saliva اللعابfrom the salivary glands. Then it travels down the esophagus البلعومinto the stomach المعدة, where acid begins physical break down of some food. The food go through the small intestine األمعاء الدقيقة, through the large intestine األمعاء الغليظة, and are excreted outside. b)- Intracellular digestion الهضم داخل الخلية: Some other unicellular organisms الكائنات وحيدة الخليةuse different mechanisms to digest food inside the cell. Digestive systems الجهاز الهضمي • Once food is inside the organism, digestion can be conducted in the cytoplasm, in a vesicle , through a tube, or through specialized organs aimed at making the absorption of nutrients more efficient. • Diggestive systems are classified into two kategories: a)- Gastrovascular cavity التجويف الوعائي المعوي: functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Digestion takes place within this central cavity التجويف المركزيwhich has only one opening to the outside that functions as both a mouth فمand an anus شرج. So, it is described as an incomplete gut معي غير كامل. b)- Complete gut المعي الكامل: has specialized organs أعضاء متخصصةthat aid in the digestion of their food. Here, animals were created with organs such as beaks مناقير, tongues ألسنة, teeth أسنان, a crop حوصلة, gizzard القانصة, and others. Digestive systems 1. Beaks: birds eat primarily seeds, nuts, and fruit, using their beaks to open even the toughest seed البذور الجافة. 2. Tongue: is skeletal muscle on the floor of the mouth that manipulates food for chewing ( )المضغand swallowing ()البلع. The underside of the tongue is covered with a smooth mucous membrane غشاء مخاطي. The tongue is utilized يوظفto transport food down to the esophagus. 3. Teeth: (singular, tooth) are small whitish structures found in the jaws ( )الفكوكof many vertebrates that are used to chew food مضغ الطعام. They are not made of bone, but rather of tissues of varying density and hardness. - Teeth of carnivores آكالت اللحومare shaped to kill and tear meat وتمزق اللحم. - Teeth of herbivores آكالت العشبare made for grinding طحنplant parts. Digestive systems 4. Crop: is a thin-walled expanded portion جزء واسع رفيع الجدارof the alimentary canal used for the storage of food prior to digestion تخزين الطعام قبل الهضم. In some birds it is an expanded, muscular pouch كيس near throat قرب الزور. In adult pigeons, the crop can produce crop milk لبن الحوصلةto feed newly hatched birds. Certain insects may have a crop or enlarged oesophagus. 5. Gizzard: is a specialized stomach with thick سميك, muscular walls used for grinding up food طحن الطعام. Birds and cockroaches have developed gizzards to assist in the digestion of tough materials. The gizzard can grind food with stones that have been swallowed and pass it back to the true stomach and vice versa. Digestive systems 6. Abomasum المعدة الحقيقية Herbivores have evolved cecums (or an abomasum in the case of ruminants )الحيوانات المجترة. Ruminants have a fore-stomach معدة أماميةwith four chambers. These are the rumen الكرش, reticulum الشبكية, omasum الورقية, and abomasum) األنفحة (المعدة الحقيقية: In the first two chambers (the rumen & the reticulum) the food is mixed with saliva and separates into solid and liquid materials. The solid is then regurgitated يُسترجع, chewed slowly يمضغ ببطءto completely mix it with saliva and to break down the particle size. In the 3rd chamber (omasum) water and many of the inorganic mineral elements are absorbed into the blood stream. The 4th chamber (abomasum) which is equivalent of the human stomach. It serves primarily as a site for digestion of microbial and dietary protein. Digesta is finally moved into the small intestine for absorption of nutrients.