Urinary System Overview

Function: Primarily responsible for urine production and water conservation.
Roles: Critical for determining what stays in the body and what is excreted.

Two Main Groups:
1. Kidneys: Major excretory organs.
- Function: Filter blood and produce urine.
1. Urinary Tract: Includes three components that transport urine out of the kidneys:
- Ureters: Tubes that carry urine from the kidneys to the urinary bladder.
- Urinary Bladder: Temporary storage for urine before expulsion.
- Urethra: Controls the expulsion of urine from the bladder to outside the body.

Homeostasis: The kidneys play a critical role in maintaining bodily balance through various mechanisms:
- Fluid Balance: Regulates water volume in the body, determining how much water to retain or expel.
- Electrolyte Balance: Maintains levels of essential electrolytes by regulating their loss or retention.
- Acid-Base Balance: Provides long-term regulation of blood pH, contrasting with the instant effects of the respiratory system.
- Metabolic Waste Removal: Eliminates metabolic byproducts.
- Blood Pressure Maintenance:
- Involves fluid balance regulation and the hormonal influence of angiotensin II on blood volume and peripheral resistance.
- Regulation of Erythropoiesis:
- Produces the hormone erythropoietin, which stimulates red blood cell production.
- Activation of Vitamin D: Necessary for calcium homeostasis.
- Gluconeogenesis: Produces glucose from non-carbohydrate sources during fasting.

Filtrate:
- Initial fluid produced in the kidneys through blood filtration.
- Consists of blood plasma components excluding proteins (e.g., water, ions, nutrients).
Urine:
- Heavily modified filtrate after processing within the kidneys.
- Primarily composed of water, electrolytes, and metabolic waste.
- Represents less than 1% of the filtrate produced (99% reclaimed by the body), indicating how vital the reabsorption process is to life.