English for

Avian
 
Birds have particular difficulties getting the nutrition they need from food. Since they lack 
teeth, Figure 143's depiction of their digestive system implies that it is capable of processing 
unmasticated food. Birds' diverse beak types have evolved over time to reflect the wide range of foods 
they consume, from seeds and insects to fruits and nuts. Most birds can fly, so they have high 
metabolic rates to process food quickly and maintain low body weights. The stomach of birds has 
two chambers: the 
proventriculus
, where gastric juices are produced to digest the food before it 
enters the stomach, and the 
gizzard
, where the food is stored, soaked, and mechanically ground. Food 
pellets made of the undigested material are occasionally regurgitated. The intestine is where most 
chemical digestion and absorption takes place, and the cloaca is where waste is expelled. 

---

205 
 
Figure 143.
The crop, a pouch found in the avian esophagus, is used to store food. Food travels from the 
crop to the proventriculus, the first of the two stomachs, where it is broken down by digestive juices. The 
food enters the gizzard, also known as the second stomach, from the proventriculus, where it is ground. 
Some birds ingest grit or stones that are kept in their gizzards to help with the grinding process. In birds, the 
openings used to expel feces and urine are not separate. Instead, waste products from digestion are mixed 
with uric acid secreted from the kidneys into the large intestine. Through a hole called the cloaca, this waste 
is expelled. 
Ruminants
 
Ruminants
are mainly herbivores like cows, sheep, and goats, whose entire diet consists of 
eating large amounts of 
roughage
or fiber. Due to their highly developed digestive systems, they can 
easily digest large amounts of cellulose. The absence of upper incisor teeth in ruminants' mouths is 
an intriguing trait. To tear and chew their food, they use their lower teeth, tongue, and lips. The food 
moves from the mouth through the esophagus and into the stomach. 
Ruminants have multi-chambered organs in their stomachs to aid in the digestion of the 
substantial amount of plant material, as shown in Figure 144. The rumen, reticulum, omasum, and 
abomasum are the names of the stomach's four distinct compartments. Numerous microbes that 
ferment ingested food and break down cellulose can be found in these chambers. The equivalent of 
the monogastric stomach chamber, the abomasum is the "true" stomach and is where gastric juices 
are secreted. The four-compartment gastric chamber gives ruminants the extra room and microbial 
support they need to digest plant matter. Large amounts of gas are produced during the fermentation 
process and must be expelled from the stomach chamber. Similar to other animals, the small intestine 
is crucial for nutrient absorption, and the large intestine aids in waste removal. 

---

206