THE EXCRETORY SYSTEM

The Excretory System

Excretion

• is a process by which waste materials from the oxidation of food in cell metabolism are removed from the living cell

Other Excretory Organ

1. liver – forms urea and bile
2. skin – excretes water
3. large intestine – removes feces 
   

 

EXCRETORY ORGANS

The excretory system is composed of the following: 2 kidneys, 2 ureters, a urinary bladder, and a urethra.

 

 1. KIDNEY

·      Are bean-shaped organs, dark red in color and have a shape in which one side is convex, or rounded, and the other is concave, or indented.

·       The kidneys of adult humans are about 10 to 13 cm (4 to 5 in) long and about 5 to 7.5 cm (2 to 3 in) wide—about the size of a computer mouse.

·    The kidneys lie against the rear wall of the abdomen, on either side of the spine. They are situated below the middle of the back, beneath the liver on the right and the spleen on the left.

·    The kidneys are the major excretory organs of the body. As the body’s blood flows through the kidneys, microscopic tubules called nephrons remove urea, salts, and other poisonous waste products formed during metabolism. The kidneys produce urine to carry away these waste products.

Functions of the Kidney

·   A primary function of kidneys is the removal of poisonous wastes from the blood. Chief among these wastes are the nitrogen-containing compounds urea and uric acid, which result from the breakdown of proteins and nucleic acids.

·      To dispose waste

·      To maintain an exact proportion of water in the blood

·      To keep the body in exact mineral balance

·      It is also involved in the formation of urine

 

Structure of the Kidney

a.    Cortex

·      The outermost region of the kidney

b.    Medulla

·      The inner 2/3 region containing conical projections called pyramids

·      an area that contains between 8 and 18 cone-shaped sections known as pyramids, which are formed almost entirely of bundles of microscopic tubules.

c.     Pyramids

·      The tips of these pyramids point toward the center of the kidney where urine is secreted

d.    Renal Artery

·      branching from the aorta and carrying the blood into the kidney

e.    Nephrons

·      The task of cleaning, or filtering, the blood is performed by millions of nephrons, remarkable structures that extend between the cortex and the medulla.

·   Under magnification, nephrons look like tangles of tiny vessels or tubules, but each nephron actually has an orderly arrangement that makes possible filtration of wastes from the blood.

·      Are tiny filters that control the chemical composition of blood

·   The primary structure in this filtering system is the glomerulus, a network of extremely thin blood vessels called capillaries. The glomerulus is contained in a cuplike structure called Bowman’s capsule

f.      Bowman’s Capsule

·      A cup-shaped structure that forms one end of the tubule and surrounds a glomerulus in the nephron

g.    glomerulus

·      a mass of capillaries found in the Bowman’s capsule that form a coiled, knoblike end of every arteriole

h.    Renal Vein

·      Carries blood away from the kidney

Urine Formation

·    Urine production begins with the substances that the blood leaves behind during its passage through the kidney—the water, salts, and other substances collected from the glomerulus in Bowman’s capsule.

·      This liquid, called glomerular filtrate, moves from Bowman’s capsule through the renal tubule. As the filtrate flows through the renal tubule, the network of blood vessels surrounding the tubule reabsorbs much of the water, salt, and virtually all of the nutrients, especially glucose and amino acids that were removed in the glomerulus.

·      This important process, called tubular reabsorption, enables the body to selectively keep the substances it needs while ridding itself of wastes. Eventually, about 99 percent of the water, salt, and other nutrients is reabsorbed.

·    At the same time that the kidney reabsorbs valuable nutrients from the glomerular filtrate, it carries out an opposing task, called tubular secretion. In this process, unwanted substances from the capillaries surrounding the nephron are added to the glomerular filtrate. These substances include various charged particles called ions, including ammonium, hydrogen, and potassium ions.

·    glomerular filtration, tubular reabsorption, and tubular secretion produce urine, which flows into collecting ducts, which guide it into the microtubules of the pyramids. The urine is then stored in the renal cavity and eventually drained into the ureters, which are long, narrow tubes leading to the bladder. From the roughly 180 liters (about 50 gallons) of blood that the kidneys filter each day, about 1.5 liters (1.3 qt) of urine are produced.

Composition of Urine

1. water – 95%
2. solid organic wastes such as urea, creatine, ammonia, uric acid and ions

 

2.    URETER

·      a pair of hollow tube that carry urine from the kidneys to the bladder

·      there is one ureter for each kidney

·      are about the size of a macaroni strand

3.    BLADDER

·      organ that stores urine after its formation by the kidneys.

·     urine enters the bladder from the kidneys through two ureters and is discharged through the urethra.

·      average normal capacity of the adult bladder is about half a liter (about 1 pt)

4.    URETHRA

·   The openings of the ureters lie in the basal part of the bladder, each about 3.8 cm (about 1.5 in) from the opening of the urethra

·      located in the midline of the bladder at its lowest point

·      the tube that carries urine from the bladder out of the body

·      the urethra is shorter in females than in males

Diseases or Disorders of the Excretory System

1. Diabetes Mellitus - disease in which the pancreas produces little or no insulin, a hormone that helps the body’s tissues absorb glucose (sugar) so it can be used as a source of energy.
2. Diabetes Insipidus - rare disease caused by deficiency of vasopressin, one of the hormones of the posterior pituitary gland, which controls the amount of urine secreted by the kidneys. The symptoms of diabetes insipidus are marked thirst and the excretion of large quantities of urine, as much as 4 to 10 liters a day.
3. Pyelonephritis - the most common form of kidney disease is an inflammation of the kidney. Most such inflammations are caused by a bacterial infection that starts in the bladder and spreads to the kidney. Sometimes an obstruction that interferes with the flow of urine in the urinary tract can cause the disease.
4. Glomerulonephritis - another common kidney disease, is characterized by inflammation of some of the kidney's glomeruli. This condition may occur when the body’s immune system is impaired. Antibodies and other substances form large particles in the bloodstream that become trapped in the glomeruli. This causes inflammation and prevents the glomeruli from working properly.
5. Kidney stones - which are small, crystallized substances, such as calcium, that form in the kidney or other parts of the urinary tract. Smaller kidney stones can pass out of the body on their own, although this can be painful. Larger stones may require surgery, or they may be broken into smaller pieces with sound waves in a procedure called ultrasonic lithotripsy.

·      Kidney Dialysis, also known as hemodialysis, medical treatment used to remove waste materials from the blood of patients lacking renal function (see Kidney). Blood from an artery is pumped through a dialyzer, or artificial kidney, where it flows past a semipermeable membrane. Dialysis fluid passing on the other side of the membrane removes unwanted elements in the blood by diffusion. The blood is then returned to the body through a vein.