How is it determined what's waste and what's not?
Shown above is a major process of maintaining homeostasis. Getting rid of waste and excess water. Such a basic process is actually very complex. It involves an intricate exchange of material through the kidney.
are part of the
, which is shown in
. The main function of the urinary system is to filter waste products and excess water from the blood and excrete them from the body.
The kidneys are the chief organs of the urinary system.
The kidneys are a pair of bean-shaped organs just above the waist. A cross-section of a kidney is shown in
. The function of the kidney is to filter blood and form urine.
is the liquid waste product of the body that is excreted by the urinary system.
are the structural and functional units of the kidneys. A single kidney may have more than a million nephrons!
Each kidney is supplied by a renal artery and renal vein.
The kidney and nephron are discussed at
Additional information about the nephron is shown at
Filtering Blood and Forming Urine
As shown in
, each nephron is like a tiny filtering plant. It filters blood and forms urine in the following steps:
Blood enters the kidney through the
, which branches into capillaries. When blood passes through capillaries of the
of a nephron, blood pressure forces some of the water and dissolved substances in the blood to cross the capillary walls into
The filtered substances pass to the
of the nephron. In the renal tubule, some of the filtered substances are reabsorbed and returned to the bloodstream. Other substances are secreted into the fluid.
The fluid passes to a collecting duct, which reabsorbs some of the water and returns it to the bloodstream. The fluid that remains in the collecting duct is urine.
The parts of a nephron and their functions are shown in this diagram.
From the collecting ducts of the kidneys, urine enters the
, two muscular tubes that move the urine by peristalsis to the bladder (see
is a hollow, sac-like organ that stores urine. When the bladder is about half full, it sends a nerve impulse to a sphincter to relax and let urine flow out of the bladder and into the urethra. The
is a muscular tube that carries urine out of the body. Urine leaves the body through another sphincter in the process of
. This sphincter and the process of urination are normally under conscious control.
The kidneys filter blood and form urine. They are part of the urinary system, which also includes the ureters, bladder, and urethra.
Each kidney has more than a million nephrons, which are the structural and functional units of the kidney.
Each nephron is like a tiny filtering plant.
Use these resources to answer the questions that follow.
Describe the following:
loop of the nephron
Describe the structure of the nephron.
Describe how the nephron filters blood.
How many nephrons are in a kidney?
How does the urinary system work?
What is urea? Where does urea come from?
What is the primary role of the kidneys?
Describe the bladder.
1. Describe how nephrons filter blood and form urine.
2. State the functions of the ureters, bladder, and urethra.