Nutrition (nourishment) is a process of intake of nutrients المواد الغذائية (like carbohydrates, fats, proteins,vitamins, minerals and water) by the organism and the utilisation of these nutrients by the organism.nutrients The diet الوجبة of an organism is what it eats. A poor diet can have a negative impact on health, causing deficiency diseases such as scurvy الإسقربوط, beriberi, health- threatening conditions like metabolic syndrome متلازمة أيضية.scurvyberiberimetabolic syndrome Lecture 22: Nutrition التغذية

Nutrients: المواد الغذائية There are seven major classes of nutrients: carbohydrates, fats, fiber, minerals, protein, vitamin, and water.carbohydratesfats fibermineralsproteinvitaminwater They are classified into two categories: I)- Macronutrients مغذيات كبيرة : needed in relatively large amounts. They are carbohydrates, fats, fibers, proteins, and water.Macronutrients II)- Micronutrients مغذيات صغيرة : needed in smaller quantities. They are minerals الأملاح المعدنية and vitamins.icronutrients

The macronutrients (but not fibers and water) provide structural material مواد بنائية for example, amino acids from which proteins are built and lipids from which cell membrane is built. Some of the structural materials can be used to generate energy internally لتوليد الطاقة داخليا, and measured in kilocalories كيلو كالوري (often called "Calories"). I- Carbohydrates and proteins provide 4 kcal of energy per gram. II- while fats provide 9 kcal per gram. Vitamins, minerals, and water do not provide energy. Fibers (i.e., non-digestible materials such as cellulose), seems to be required, for both mechanical and biochemical reasons.

Fats are triglycerides, made of fatty acid monomers bound to glycerol backbone. They cannot be synthesized in the body. Protein molecules contain amino acids, some of which are essential (the body can not make them internally). Some of the amino acids are convertible to glucose and can be used for energy production just as ordinary glucose during prolonged starvation التجويع. Some nutrients can be stored internally (eg, some vitamins), while others are required more or less continuously. Poor health results from a lack of required nutrients or, too much of a required nutrient. For example, both salt and water (both are required) but cause illness (or even death) in too large amounts.

Digestion: الهضم Digestion: is the mechanical and chemical breaking down of food into smaller components, to a form that can be absorbed. Digestion is a form of catabolism that means break down of macro-food molecules أجزاء الطعام الكبيرة to smaller one. a)- Extracellular digestion الهضم خارج الخلية : In mammals, food enters the mouth, being chewed by teeth, and broken down by the saliva اللعاب from the salivary glands. Then it travels down the esophagus المرئ into the stomach المعدة, where acid begins physical break down of some food. The food go through the small intestine الأمعاء الدقيقة, through the large intestine الأمعاء الغليظة, and are excreted outside. b)- Intracellular digestion الهضم داخل الخلية : Some other unicellular organisms use different mechanisms to digest food inside the cell.

Digestive systems: Once food is inside the organism, digestion can be conducted in the cytoplasm, in a vesicle, through a tube, or through specialized organs. Diggestive systems are classified into two categories: 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 المركزي which has only one opening to the outside. So, it is described as an incomplete gut معي غير كامل. b)- Complete gut: المعي الكامل has specialized organs أعضاء متخصصة that 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.

1- Beaks: birds eat primarily seeds, nuts, and fruit, using their beaks to open even the toughest seed البذور الجافة. 2- Tongue: is a skeletal muscle on the floor of the mouth that manipulates food for chewing ( المضغ ) and swallowing ( البلع ). The underside of the tongue is covered with a smooth mucous membrane غشاء مخاطي. The tongue is utilized يوظف to transport food down to the esophagus. 3- Teeth: (singular, tooth) are small whitish structures found in the jaws ( الفكوك ) of many vertebrates that are used to chew food مضغ الطعام. - Teeth of carnivores are shaped to kill and tear meat تمزق اللحم. - Teeth of herbivores are made for grinding طحن plant parts.

4- Crop: is a thin-walled expanded portion جزء واسع رفيع الجدار of the alimentary canal used for the storage of food prior to digestion تخزين الطعام قبل الهضم. 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.

6- Abomasum المعدة الحقيقية : Herbivores have evolved cecums. Ruminants الحيوانات المجترة have a fore-stomach معدة أمامية with four chambers. These are the rumen الكرش, reticulum الشبكية, omasum الورقية, and abomasum الأنفحة ( 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 ببطء to completely mix it with saliva and to break down the food. In the 3 rd chamber (omasum) water and many of the inorganic mineral elements are absorbed into the blood stream. The 4 th chamber (abomasum) which is equivalent of the human stomach. It serves primarily as a site for digestion of microbial and dietary protein. Digestion is finally moved into the small intestine for absorption of nutrients.