The schematic representation of gaseous exchange in tissues typically involves the movement of oxygen (O2) from the bloodstream into the cells and the exchange of carbon dioxide (CO2) from the cells into the bloodstream. In tissues, oxygen diffuses from the capillaries into the interstitial fluid and then into the cells where it is used for cellular respiration. Simultaneously, carbon dioxide produced during cellular respiration diffuses out of the cells into the interstitial fluid and then into the capillaries to be transported back to the lungs for exhalation.

Alveoli in the lungs and nephrons in the kidneys serve different physiological functions but share some structural and functional characteristics. Both have a high surface area for efficient exchange processes. Alveoli are tiny air sacs in the lungs where gas exchange occurs, characterized by thin walls and a dense network of capillaries. Nephrons are the functional units of the kidneys responsible for filtering blood and producing urine, consisting of a renal corpuscle and a renal tubule. While alveoli facilitate the exchange of gases (oxygen and carbon dioxide) between the air and the blood, nephrons filter waste products and regulate electrolyte balance and blood pressure through processes such as filtration, reabsorption, and secretion.

Emulsification of fats is significant because it breaks down large fat globules into smaller droplets, increasing the surface area available for enzymatic action. This process, usually aided by bile salts produced by the liver and stored in the gallbladder, enhances the efficiency of fat digestion by lipase enzymes, allowing for better absorption of fatty acids and fat-soluble vitamins in the small intestine.

The small intestine in herbivores is larger than in carnivores primarily because plant matter requires more extensive digestion and absorption. Herbivores typically consume diets rich in complex carbohydrates like cellulose, which require longer processing times and more surface area for absorption. Therefore, a larger small intestine provides ample space for microbial fermentation and absorption of nutrients from plant material.

A four-chambered heart provides efficient separation of oxygenated and deoxygenated blood, ensuring that oxygen-rich blood is pumped to the body tissues and oxygen-depleted blood is sent to the lungs for reoxygenation. This separation prevents mixing of oxygenated and deoxygenated blood, allowing for a more effective oxygen supply to the body tissues, which is particularly important for sustaining high metabolic rates in warm-blooded animals like mammals and birds.