55 Urinary Integration of Systems
The urinary system is responsible for only a part of our body’s ability to exchange material with the environment. It is not the only excretory system in the body. Several other organs, tissues, and processes are also involved in excretion. These structures temporarily store wastes, transport them for removal, or excrete the wastes and excess materials from the body.
Excretory Organs
| Organ System | Organ | Major Excretory Function |
|---|---|---|
| Digestive | Large intestine | Defecation removes solid waste and some water |
| Integumentary | Skin/sweat glands | Remove water, salts, other wastes |
| Respiratory | Lungs | Remove carbon dioxide |
| Urinary | Kidneys | Remove wastes and excess substances from blood |
The digestive system participates in waste removal in two ways. First, the liver detoxifies some substances. One example is the conversion of ammonia into urea. The large intestine is also considered an excretory organ. It eliminates a number of substances through defecation, including undigested food, water, carbon dioxide, water, salts, cholesterol and heat. The respiratory system may seem like an unlikely waste remover, but when we exhale, the lungs excrete carbon dioxide and also rid the body of heat and some water vapor. Finally, the sweat glands in the skin are important excretory structures. They help dispose of excess water, heat, and carbon dioxide, as well as small amounts of salts and urea.
The kidneys are critical organs because they regulate blood volume and blood pressure. These organs perform this regulatory role by altering the amount of water that is eliminated in urine, as well as by releasing the chemicals renin and erythropoietin. When blood pressure drops, the kidneys secrete renin, which is both a hormone and an enzyme. Renin activates a hormonal pathway that increases blood pressure. When oxygen levels in body tissues decrease, the kidneys secrete the hormone erythropoietin. Erythropoietin stimulates the bone marrow to increase production of red blood cells.
The kidneys regulate ion concentrations in blood plasma by returning some ions to the bloodstream and by excreting excess ions in urine. They control blood pH by adjusting the amount of hydrogen ions and bicarbonate ions that are reabsorbed or secreted in urine. The kidneys also reclaim valuable nutrients from the filtrate and return them to the systemic circulation.
The urinary system also affects all other body systems, whether directly or indirectly.
| Body System | Urinary System Interaction | Effects |
|---|---|---|
| All Systems | Eliminates metabolic wastes
Maintains fluid, electrolyte, and acid-base balances |
Controls volume, pH, and composition of body fluids· Homeostasis |
| Cardiovascular | Kidneys increase/decrease reabsorption of water filtered from blood
Cells in kidneys release renin when blood pressure decreases |
Helps regulate blood volume and blood pressure
Renin-angiotensin-aldosterone system increases blood pressure |
| Digestive | Kidneys help synthesize calcitriol, the active form of vitamin D synthesized in the liver | Calcitrol is necessary for the absorption of dietary calcium |
| Endocrine | Kidneys help synthesize calcitriol
Kidneys release erythropoietin |
Calcitriol is an endocrine hormone that promotes bone reabsorption
Erythropoietin stimulates red blood cell production |
| Integumentary (skin) | Kidneys work with skin to synthesize calcitriol
Kidneys maintain fluid balance |
Calcitriol is necessary for the absorption of dietary calcium
Fluid balance necessary for perspiration |
| Lymphatic/ immune | Kidneys increase/decrease reabsorption of water filtered from blood | Helps regulate volume of lymph and interstitial fluid |
| Muscular | Kidneys help regulate calcium and phosphate levels in blood | Calcium and phosphate balance important for muscular contractions |
| Nervous | Kidneys are responsible for gluconeogenesis | Glucose is necessary for the production of adenosine triphosphate in neurons |
| Reproductive | Urethra is dual passageway in males
In pregnant women, urinary system eliminates wastes for mother and fetus |
Allows passage and direction of sperm
Eliminates metabolic wastes of fetus |
| Respiratory | Kidneys work with lungs to adjust pH of body fluids | Prevent abnormal function of enzymatic pathways |
| Skeletal | Kidneys help regulate calcium and phosphate levels in blood | Calcium and phosphates are essential for bone deposition |