The Excretory Function of the Kidney
There are two bean-shaped kidneys in the body of a mammal. These kidneys lie asymmetrically on the dorsal body wall of the lumbar (upper) region of the abdomen, the right kidney being more anterior than the left. They are held in place by masses of fatty tissue. Lying above each kidney is a conical adrenal gland, which is an endocrine gland.
The kidneys remove unwanted nitrogenous substances, e.g. urea and ammonium compounds, as well as dissolved carbon dioxide, from the blood. They also get rid of excess water and salts and kept the osmotic concentration of the blood constant.
Each kidney is reddish-brown in color and is covered by a tough, transparent membrane, called the capsule. The outer edge of the kidney is convex while the inner edge is concave. At the concave edge of the kidney lies a depression, from which a narrow tube, the urethra, arises. The depression is also the point at which the renal artery enters the kidney and the renal vein leaves it. The renal artery, which arises from the dorsal aorta, brings blood containing excretory products to the kidney, while the renal vein drains filtered blood from the kidney to the posterior vena cava.
The urethra connects the kidney with any oval, transparent sac-like chamber called the urinary bladder situated at the base of the abdomen. The walls of the bladder are elastic. From the bladder, a narrow, muscular tube, the urethra, continues downwards and opens to the outside as a small aperture. For the rabbit for an example; In both the male and female rabbit, the urethra is urinal genital in function and the aperture by which it opens is known as thee urinal genital opening. The urethra of the male is longer than that of the female as the former traverses a long, erect organ, the penis. There is no penis in the female, this being replaced by a rudimentary rod like structure, the clitoris. The urethra does not traverse this structure but opens behind it. In the female human being, the urethra is a urinary tract only. The genital tract is separate and lies slightly dorsal to it.
A longitudinal section of a kidney shows that it consists of two distinct regions, an outer cortex and an inner medulla. Several thousands of fine narrow tubules, the urinary tubules, traverse both these regions and open at the tips, or papillae (singular-papilla), of triangular-shaped masses of tissue called pyramids. These pyramids open into a funnel-shaped cavity called the pelvis. This cavity is continuous with the urethra. The kidney tissue also consists of a vast number of blood capillaries, which are branches of the renal artery and vein.
HOW THE KIDNEY FUNCTIONS:
Each urinary tubule consists of a corpuscle, which is situated in the cortex, and a convoluted, ciliated tube. The corpuscle body consists of a thin-walled cup-like chamber, the Bowman's capsule, into which fits a knot of blood capillaries, the glomeruli. The cilia in the tubule help to maintain the flow of urine in one direction. Beyond the corpuscle body, each tubule makes a characteristic U-shaped loop known as Henley's loop. All along its course, the tubule is closely associated with several networks of blood capillaries.
The tubule widens as it approaches the pelvis. Together with many other tubules, it pours its contents into wider, main collecting tubes, which eventually join up and open into the pelvis at the apices of the pyramids. Each pyramid is traversed by a number of main collecting tubes: it follows, therefore, that there are many contents into wider, main collecting tubes which eventually join up and open into the pelvis at the apices of the pyramids. Each pyramid is traversed by a number of main collecting tubes: it follows therefore, that there are many such collecting tubes.
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Blood brought to the kidneys by the renal arteries flows through all the renal capillaries. As it circulates through the capillaries of each Bowman's capsule, substances such as water, urea and other nitrogenous compounds, mineral salts, sugar and plasma solutes are filtered into the capsule by a process known as ultra-filtration. Blood corpuscle and other colloidal substances like the plasma proteins cannot filter through and, therefore, remain in the blood stream. In fact, the filtered fluid is identical in composition with plasma from which proteins have been removed.
The fluid in the capsule, known as the glomerulus's filtrate, then flows down the tubule. As it passes through the proximal portion of the tubule and then through Henley's loop, some water, sugar, amino acids and salts (e.g. sodium chloride) which are useful to the body, are reabsorbed into the blood capillaries. This is known as selective re-absorption. Consequently, the fluid becomes more concentrated. It then flows into the distal portion of the tubule, which is also surrounded by a network of blood capillaries. More water is reabsorbed into these capillaries and the resulting fluid, urine, is even more concentrated than before. Urine is composed mainly of water, urea, uric acid, ammonium compounds, cretonne and mineral salts. The quantities of the various substances found in 24 hours urine produced by a resting man of average weight and on a standard diet, is shown below:
SUBSTANCE URINE g/24 hrs.
There are two bean-shaped kidneys in the body of a mammal. These kidneys lie asymmetrically on the dorsal body wall of the lumbar (upper) region of the abdomen, the right kidney being more anterior than the left. They are held in place by masses of fatty tissue. Lying above each kidney is a conical adrenal gland, which is an endocrine gland.
The kidneys remove unwanted nitrogenous substances, e.g. urea and ammonium compounds, as well as dissolved carbon dioxide, from the blood. They also get rid of excess water and salts and kept the osmotic concentration of the blood constant.
Each kidney is reddish-brown in color and is covered by a tough, transparent membrane, called the capsule. The outer edge of the kidney is convex while the inner edge is concave. At the concave edge of the kidney lies a depression, from which a narrow tube, the urethra, arises. The depression is also the point at which the renal artery enters the kidney and the renal vein leaves it. The renal artery, which arises from the dorsal aorta, brings blood containing excretory products to the kidney, while the renal vein drains filtered blood from the kidney to the posterior vena cava.
The urethra connects the kidney with any oval, transparent sac-like chamber called the urinary bladder situated at the base of the abdomen. The walls of the bladder are elastic. From the bladder, a narrow, muscular tube, the urethra, continues downwards and opens to the outside as a small aperture. For the rabbit for an example; In both the male and female rabbit, the urethra is urinal genital in function and the aperture by which it opens is known as thee urinal genital opening. The urethra of the male is longer than that of the female as the former traverses a long, erect organ, the penis. There is no penis in the female, this being replaced by a rudimentary rod like structure, the clitoris. The urethra does not traverse this structure but opens behind it. In the female human being, the urethra is a urinary tract only. The genital tract is separate and lies slightly dorsal to it.
A longitudinal section of a kidney shows that it consists of two distinct regions, an outer cortex and an inner medulla. Several thousands of fine narrow tubules, the urinary tubules, traverse both these regions and open at the tips, or papillae (singular-papilla), of triangular-shaped masses of tissue called pyramids. These pyramids open into a funnel-shaped cavity called the pelvis. This cavity is continuous with the urethra. The kidney tissue also consists of a vast number of blood capillaries, which are branches of the renal artery and vein.
HOW THE KIDNEY FUNCTIONS:
Each urinary tubule consists of a corpuscle, which is situated in the cortex, and a convoluted, ciliated tube. The corpuscle body consists of a thin-walled cup-like chamber, the Bowman's capsule, into which fits a knot of blood capillaries, the glomeruli. The cilia in the tubule help to maintain the flow of urine in one direction. Beyond the corpuscle body, each tubule makes a characteristic U-shaped loop known as Henley's loop. All along its course, the tubule is closely associated with several networks of blood capillaries.
The tubule widens as it approaches the pelvis. Together with many other tubules, it pours its contents into wider, main collecting tubes, which eventually join up and open into the pelvis at the apices of the pyramids. Each pyramid is traversed by a number of main collecting tubes: it follows, therefore, that there are many contents into wider, main collecting tubes which eventually join up and open into the pelvis at the apices of the pyramids. Each pyramid is traversed by a number of main collecting tubes: it follows therefore, that there are many such collecting tubes.
Blood brought to the kidneys by the renal arteries flows through all the renal capillaries. As it circulates through the capillaries of each Bowman's capsule, substances such as water, urea and other nitrogenous compounds, mineral salts, sugar and plasma solutes are filtered into the capsule by a process known as ultra-filtration. Blood corpuscle and other colloidal substances like the plasma proteins cannot filter through and, therefore, remain in the blood stream. In fact, the filtered fluid is identical in composition with plasma from which proteins have been removed.
The fluid in the capsule, known as the glomerulus's filtrate, then flows down the tubule. As it passes through the proximal portion of the tubule and then through Henley's loop, some water, sugar, amino acids and salts (e.g. sodium chloride) which are useful to the body, are reabsorbed into the blood capillaries. This is known as selective re-absorption. Consequently, the fluid becomes more concentrated. It then flows into the distal portion of the tubule, which is also surrounded by a network of blood capillaries. More water is reabsorbed into these capillaries and the resulting fluid, urine, is even more concentrated than before. Urine is composed mainly of water, urea, uric acid, ammonium compounds, cretonne and mineral salts. The quantities of the various substances found in 24 hours urine produced by a resting man of average weight and on a standard diet, is shown below:
SUBSTANCE URINE g/24 hrs.