the excretory system

formation of urine

Blood with wastes enters each kidney through an artery, which branches into many capillaries. After passing through capillaries and being filtered, the clean blood leaves the kidney through a vein. The part of each nephron called the glomerulus is where blood in the capillaries is filtered. Excess water and wastes are filtered out of the blood. The tubule of the nephron collects these substances. Some of the water is reabsorbed. The remaining fluid is urine.

the kidneys

The kidneys are a pair of bean-shaped organs at each side of the body just above the waist. You can see a diagram of a kidney in Figure 19.7. The function of the kidneys is to filter blood and form urine. Tiny structures in the kidneys, called nephrons, perform this function. Each kidney contains more than a million nephrons.

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the urinary system

The urinary system is shown in Figure 19.6. It includes two kidneys, two ureters, the urinary bladder, and the urethra. The main function of the urinary system is to filter waste products and excess water from the blood and excrete them from the body as urine. For a visual presentation on the urinary system and how it works, watch this video: . MEDIA Click image to the left or use the URL below. URL:

excretion

Excretion is any process in which excess water or wastes are removed from the body. Excretion is the job of the excretory system. Besides the kidneys, other organs of excretion include the large intestine, liver, skin and lungs. The large intestine eliminates food wastes that remain after digestion takes place. The liver removes excess amino acids and toxins from the blood. Sweat glands in the skin excrete excess water and salts in sweat. The lungs exhale carbon dioxide and also excess water as water vapor. Each of the above organs of excretion is also part of another body system. For example, the large intestine and liver are part of the digestive system, and the lungs are part of the respiratory system. The kidneys are the main organs of excretion. They are part of the urinary system.

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how the kidneys maintain homeostasis

The kidneys help the body maintain homeostasis in several ways. They filter all the blood in the body many times each day and produce urine. They control the amount of water and dissolved substances in the blood by excreting more or less of them in urine. The kidneys also secrete hormones that help maintain homeostasis. For example, they produce a hormone that stimulates bone marrow to produce red blood cells when more are needed. They also secrete a hormone that regulates blood pressure and keeps it in a normal range.

excretion of urine

From the kidneys, urine enters the ureters. These are two muscular tubes that carry urine to the urinary bladder. Contractions of the muscles of the ureters move the urine along by peristalsis. The urinary bladder is a sac-like organ that stores urine. When the bladder is about half full, a sphincter relaxes to let urine flow out of the bladder and into the urethra. The urethra is a muscular tube that carries urine out of the body through another sphincter. The process of urine leaving the body is called urination. The second sphincter and the process of urination are normally under conscious control.

kidney health and disease

You need only one kidney to live a normal, healthy life. A single kidney can do all the work of filtering the blood and maintaining homeostasis. However, at least one kidney must function properly to maintain life. Diseases that threaten the health and functioning of the kidneys include kidney stones, infections, and diabetes. You can learn more about kidney diseases in this video: . MEDIA Click image to the left or use the URL below. URL: Kidney stones are mineral crystals that form in urine inside a kidney, as shown in Figure 19.8. The stones may be extremely painful. If a kidney stone blocks a ureter, it must be removed so urine can leave the kidney and be excreted. Bacterial infections of urinary organs, especially the urinary bladder, are common. They are called urinary tract infections. Generally, they can be cured with antibiotic drugs. However, if they arent treated, they can lead to more serious infections and damage to the kidneys. Untreated diabetes may damage capillaries in the kidneys so the nephrons can no longer filter blood. This is called kidney failure. The only cure for kidney failure is to receive a healthy transplanted kidney from a donor. Until that happens, a patient with kidney failure can be kept alive by artificially filtering the blood through a machine. This is called hemodialysis. You can see how it works in Figure 19.9.

instructional diagrams

No diagram descriptions associated with this lesson

questions

The lungs are part of the respiratory system and the

a. digestive system.

b. urinary system.

-->  c. excretory system.

d. muscular system.

Organs of excretion include the large intestine and sweat glands in the skin.

-->  a. true

b. false

Blood containing wastes enters each kidney through a ureter.

a. true

-->  b. false

The part of a nephron that filters blood is the

a. urethr

b. tubule.

-->  c. glomerulus.

d. urinary bladder.

Blood containing wastes enters the kidneys through

a. ureters.

b. veins.

-->  c. arteries.

d. sphincters.

All of the water filtered out of the blood in the kidneys is excreted in urine.

a. true

-->  b. false

The process of urination is normally under conscious control.

-->  a. true

b. false

Hormones secreted by the kidneys help regulate

-->  a. blood pressure.

b. the production of white blood cells.

c. blood clotting.

d. two of the above

The kidneys filter all of the blood in the body once a day.

a. true

-->  b. false

What does a hemodialysis machine do?

a. It controls blood sugar in people with diabetes.

b. It treats urinary tract infections.

-->  c. It filters wastes out of the blood.

d. It removes stones from the kidneys.

One function of the kidneys is to help keep blood pressure within a normal range.

-->  a. true

b. false

You need both kidneys to live a normal, healthy life.

a. true

-->  b. false

Excess water is removed from your body when you

a. urinate.

b. exhale.

c. sweat.

-->  d. all of the above

The urinary system includes all of the following organs except the

-->  a. liver.

b. ureters.

c. urethra.

d. urinary bladder.

How many nephrons does each kidney contain?

a. fewer than 10

b. around 100

c. about 1,000

-->  d. more than 1,000,000

Clean blood leaves a kidney through a(n)

a. artery.

b. capillary.

c. urethra.

-->  d. vein.

The liver removes excess water and salts from the blood.

a. true

-->  b. false

Each kidney contains more than a million nephrons.

-->  a. true

b. false

Urine moves through the ureters by

a. gravity.

b. diffusion.

-->  c. peristalsis.

d. none of the above

Some of the water filtered out of the blood by nephrons is reabsorbed.

-->  a. true

b. false

How do the kidneys help maintain homeostasis?

-->  a. They control the amount of water in the body.

b. They secrete a hormone that regulates sweat production.

c. They secrete a hormone that stimulates muscle contractions.

d. all of the above

How does untreated diabetes cause kidney failure?

a. It leads to kidney stones that damage nephrons.

-->  b. It damages capillaries in the kidneys.

c. It causes frequent urinary tract infections.

d. It causes urine to back up in the kidneys.

The bladder is the urinary system organ where urine forms.

a. true

-->  b. false

The only cure for kidney failure is a kidney transplant.

-->  a. true

b. false

__muscular tube that carries urine out of the body

a. ureter

b. kidney stone

c. nephron

-->  d. urethra

e. kidney

f. hemodialysis

g. urinary bladder

__tiny structure in a kidney that filters blood and forms urine

a. ureter

b. kidney stone

-->  c. nephron

d. urethra

e. kidney

f. hemodialysis

g. urinary bladder

__sac-like organ that stores urine

a. ureter

b. kidney stone

c. nephron

d. urethra

e. kidney

f. hemodialysis

-->  g. urinary bladder

__mineral crystal that forms in urine inside a kidney

a. ureter

-->  b. kidney stone

c. nephron

d. urethra

e. kidney

f. hemodialysis

g. urinary bladder

__artificial filtering of blood through a machine

a. ureter

b. kidney stone

c. nephron

d. urethra

e. kidney

-->  f. hemodialysis

g. urinary bladder

__muscular tube that carries urine from a kidney to the urinary bladder

-->  a. ureter

b. kidney stone

c. nephron

d. urethra

e. kidney

f. hemodialysis

g. urinary bladder

__main organ of the urinary system

a. ureter

b. kidney stone

c. nephron

d. urethra

-->  e. kidney

f. hemodialysis

g. urinary bladder

diagram questions

No diagram questions associated with this lesson