Human Anatomy and Physiology - I. V. Gayvoronsky 2011

Anatomy and Physiology of the Excretory System
Excretory Functions of Other Organs

As already noted, In addition to the Urinary System, the excretory function is performed by the Skin, Liver, mucous membranes of the Digestive System, and Lungs.

Skin. The Excretory Function of the skin is ensured by Sweat Glands and, to a lesser extent, Sebaceous Glands. Under normal conditions, a human secretes between 300 and 1000 ml of sweat per day. This amount depends on ambient Temperature, as well as the duration and intensity of physical activity. For instance, under heavy physical exertion, sweat glands can secrete up to 10 L of sweat. At rest, sweat removes up to 1|₃ of the total Water eliminated from the body, along with 5–10% of all urea. In addition, sweat eliminates uric acid, chloride, sodium, potassium, and Calcium Ions, as well as other organic substances and Trace Elements. When renal function is impaired, The excretion of these substances through the skin increases significantly as the body attempts to partially compensate for the disruption in the urinary system. It is well known that patients suffering from severe chronic renal failure emit a urine-like odor from their skin surface. The sweat of such patients contains high concentrations of urea, uric acid, and various ions. It should be noted that the active functioning of sweat glands only partially compensates for renal failure. Ultimately, metabolic products accumulate, their toxic effects on the body increase, and this leads to irreversible Changes in the functioning of the entire Organism.

Sebaceous glands play a minor role in excretion. The secretion produced by these glands (about 20 g/day) consists of ²/₃ water and ¹/₃ Cholesterol, sex hormone metabolites, and corticosteroids.

Liver. The excretory function of the liver is carried out through Bile secretion (500–1000 ml/day). Bile eliminates the End products of Hemoglobin METABOLISM (bilirubin and its derivatives) and cholesterol metabolites in the form of bile acids. It also excretes heavy metal salts, Calcium and phosphorus ions, medications, and toxic substances. Notably, the water, bile acids, and ions contained in bile are largely reabsorbed in the intestine. An equally important excretory mechanism is the liver's ability to convert toxic substances into non-toxic compounds, which are subsequently eliminated from the body by other Organs.

Stomach and intestines. These organs excrete urea, uric acid, and various medicinal and toxic substances (such as mercury, iodine, salicylates, and quinine) as part of digestive juices. In addition, they participate in the elimination of heavy metal salts, magnesium, and calcium. Feces remove approximately 100 ml of water per day. Strictly speaking, feces are not an excretory product; the actual excretory components are limited to those substances that were secreted with bile and digestive juices and were not subsequently reabsorbed into the bloodstream.

Substances representing undigested food residues and Bacteria make up that portion of excrement which, without ever entering the body's internal environment, essentially passes in transit through the gastrointestinal tract.

Lungs. They eliminate volatile substances from the body's internal environment: carbon dioxide, water vapor, ammonia, acetone, ethanol, and others. When alcohol is consumed, alcohol and its metabolites can be detected in exhaled breath. In patients with Diabetes Mellitus, breathing emits a distinct odor of acetone. Furthermore, the respiratory tract eliminates metabolic products of the lung tissue itself and altered surfactant.

Water evaporates through the mucous membrane of the respiratory tract (ranging from 300 ml/day at rest to up to 1 L/day during rapid breathing). When renal excretory function is impaired, the excretion of urea via the bronchial mucosa and lungs increases. Its breakdown produces ammonia, causing a characteristic bad breath.

Review Questions

1. Define The process of excretion.

2. What structures form the renal fixation apparatus?

3. Name the PARTS OF THE nephron and describe their Functions.

4. What are the Specific features of the Kidney's Blood supply?

5. List the urinary structures of the kidney.

6. Describe The Role of The Kidneys in the body.

7. What are the parts of the Ureter?

8. Name the parts and layers of the Urinary Bladder.

9. Describe the excretory function of the skin, liver, hollow organs, gastrointestinal tract, and lungs.