structural:scholar_edition, stylistic:style_transfer, structural:expansion, stylistic:tone
Biochemistry

The majority of the common ostrich's internal solutes are made up of sodium ions (Na), potassium ions (K), chloride ions (Cl), total short-chain fatty acids (SCFA), and acetate. The caecum contains a high water concentration with reduced levels nearing the terminal colon and exhibits a rapid fall in Na concentrations and small changes in K and Cl. The colon is divided into three sections and takes part in solute absorption. The upper colon largely absorbs Na and SCFA and partially absorbs KCl. The middle colon absorbs Na and SCFA, with little net transfer of K and Cl. The lower colon then slightly absorbs Na and water and secretes K. There is no net movements of Cl and SCFA found in the lower colon.

When the common ostrich is in a dehydrated state, plasma osmolality, Na, K, and Cl ions all increase; however, K ions return to controlled concentration. The common ostrich also experiences an increase in haematocrit, resulting in a hypovolemic state. Two antidiuretic hormones, Arginine vasotocin (AVT) and angiotensin (AII), are increased in blood plasma as a response to hyperosmolality and hypovolemia. AVT triggers antidiuretic hormone (ADH) which targets the nephrons of the kidney. ADH causes a reabsorption of water from the lumen of the nephron to the extracellular fluid osmotically. These extracellular fluids then drain into blood vessels, causing a rehydrating effect. This drainage prevents loss of water by both lowering volume and increasing concentration of the urine. Angiotensin, on the other hand, causes vasoconstriction on the systemic arterioles and acts as a dipsogen for ostriches. Both of these antidiuretic hormones work together to maintain water levels in the body that would normally be lost due to the osmotic stress of the arid environment.

Ostriches are uricotelic, excreting nitrogen in the form of uric acid and related derivatives. Uric acid's low solubility in water gives a semi-solid paste consistency to the ostrich's nitrogenous waste.