Transcript Principals of General Zoology (Zoo-103)

Principals of General Zoology (Zoo-103)
Zoology Department, 1431-1432H
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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.