structural:summarization, quality:correction
System overview

The common ostrich is well-adapted to hot, arid environments through specialization of excretory organs. The common ostrich has an extremely long and developed colon – a length of approximately 11–13 m (36–43 ft) – between the coprodeum and the paired caeca, which are around 80 cm (30 in) long. A well-developed caeca is also found and, in combination with the rectum, forms the microbial fermentation chambers used for carbohydrate breakdown. The catabolism of carbohydrates produces around 0.56 grams (9 grains) of water that can be used internally. The majority of their urine is stored in the coprodeum, and the feces are separately stored in the terminal colon. The coprodeum is located ventral to the terminal rectum and urodeum (where the ureters open). Found between the terminal rectum and coprodeum is a strong sphincter. The coprodeum and cloaca are the main osmoregulatory mechanisms used for the regulation and reabsorption of ions and water, or net water conservation. As expected in a species inhabiting arid regions, dehydration causes a reduction in fecal water, or dry feces. This reduction is believed to be caused by high levels of plasma aldosterone, which leads to rectal absorption of sodium and water. Also expected is the production of hyperosmotic urine; cloacal urine has been found to be 800 mOsm. The U:P (urine:plasma) ratio of the common ostrich is therefore greater than one. Diffusion of water to the coprodeum (where urine is stored) from plasma across the epithelium is voided. This void is believed to be caused by the thick mucosal layering of the coprodeum.

Common ostriches have two kidneys, which are chocolate brown in color, are granular in texture, and lie in a depression in the pelvic cavity of the dorsal wall. They are covered by peritoneum and a layer of fat. Each kidney is about 300 mm (12 in) long, 70 mm (3 in) wide, and divided into a cranial, middle, and caudal sections by large veins. The caudal section is the largest, extending into the middle of the pelvis. The ureters leave the ventral caudomedial surface and continue caudally, near the midline into the opening of the urodeum of the cloaca. Although there is no bladder, a dilated pouch of ureter stores the urine until it is secreted continuously down from the ureters to the urodeum until discharged.