25 Chapter 25 The Urinary System
By Ganesan Kamatchi
Motivation.
Hemodialysis, also spelled haemodialysis, or simply dialysis, is a process of purifying the blood of a person whose kidneys are not working normally. This type of dialysis achieves the extracorporeal removal of waste products such as creatinine and urea and free water from the blood when the kidneys are in a state of failure. Hemodialysis is one of three renal replacement therapies (the other two being kidney transplant and peritoneal dialysis). An alternative method for extracorporeal separation of blood components such as plasma or cells is apheresis. Hemodialysis can be an outpatient or inpatient therapy. Routine hemodialysis is conducted in a dialysis outpatient facility, either a purpose built room in a hospital or a dedicated, stand-alone clinic. Less frequently hemodialysis is done at home. Dialysis treatments in a clinic are initiated and managed by specialized staff made up of nurses and technicians; dialysis treatments at home can be self-initiated and managed or done jointly with the assistance of a trained helper who is usually a family member.
Learning Objectives
Upon completion of the work in this chapter students should be able to:
- Describe the external structure of the kidney, including its location, support structures, and covering
- Identify the major internal divisions and structures of the kidney
- Identify the major blood vessels associated with the kidney and trace the path of blood through the kidney
- Provide specific examples to demonstrate how the urinary system responds to maintain homeostasis in the body in relation with other systems
Background.
The urinary system consists of two kidneys, two ureters, a single urinary bladder, and a single urethra (Figure 25.2). This system has roles that you may already be aware of, such as cleansing the blood and ridding the body of wastes. However, there are additional, equally important functions played by the system. Take for example, regulation of pH, a function shared with the lungs and the buffers within the blood. Additionally, the regulation of blood pressure is a role shared with the heart and blood vessels. What about regulating the concentration of solutes in the blood? Did you know that the kidney is important in determining the concentration of red blood cells?
Most importantly, the urinary system works to remove the dissolved materials from the blood through the process of filtration. Filtration occurs when one or more substances pass through a selectively permeable membrane, while others are retained. Within the kidneys, filtration involves both metabolic waste products, such as urea or toxins, as well as materials that are beneficial to the body. Any filtered material that is not desirable though will be excreted from the body. If the kidneys fail, these functions are compromised or lost altogether, with devastating effects on the homeostasis. Affected individuals may experience weakness, lethargy, sh