Urinary System 1

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Urinary System 1...

Urinary System 1:

The first successful human organ transplant was a kidney transplant performed in 1953. Because the donor and the recipient were identical twins, rejection was not a problem. Thousands of kidney transplants have been done since then. Although a person has two kidneys, it is clear that one kidney can carry out the complex work required to maintain homeostasis of the body fluids.

The urinary system consists of:

two kidneys

two ureters

urinary bladder

urethra

The formation of the urine is the function of the kidney, the rest of the system is responsible for eliminating the urine. The kidneys produce the urine. Urine leaving the kidneys travels along the paired ureters to the urinary bladder for temporary storage until the muscular contraction of the bladder forces the urine through the urethra and out of the body.

Body cells produce waste products such as urea, creatinine, and ammonia, which must be removed from the blood before they accumulate to toxic levels. Toxic wastes accumulating in the cells cause them to suffocate and literally poison themselves.

FUNCTIONS OF THE URINARY SYSTEM

1. Regulation o blood volume and blood pressure by adjusting the volume of water lost in the urine and releasing hormones such as renin and erythropoietin.

2. Regulating blood concentrations of sodium, potassium, chloride and other ions by controlling the quantities lost in the urine.

3. Stabilizing the blood pH by controlling the loss of ions in the urine.

4. Conserving valuable nutrients by selectively preventing losses while eliminating waste products.

KIDNEYS

LOCATION: The kidneys lie just above the waistline on the posterior aspect of your body. Usually the right kidney is a little lower than the left due to slight displacement because of the liver. The upper portions of the kidneys rest on the lower surface of the diaphragm and are enclosed and protected by the lower margins of the rib cage. The left kidney is slightly longer than the right and is closer to the midline. The kidneys assume slightly different positions with changes in body positions.

The kidney is the primary organ of the urinary system. The kidneys are embedded in adipose or fat tissue that acts as a cushion and is in turn covered by a fibrous connective tissue membrane called the fibrous capsule, which helps to hold the kidneys in place.

Each kidney has a hilus or an indentation on the medial aspect. At the hilus, the renal artery enters the kidney, while the renal vein and the ureters emerge. The renal artery is a branch of the abdominal aorta, and the renal vein returns blood to the inferior vena cava. The ureter carries the urine from the kidney to the urinary bladder.

INTERNAL STRUCTURE OF THE KIDNEY- The outermost area of the kidney is the renal cortex. The cortex contains parts of the renal corpuscle of the glomeruli and portions of the convoluted tubule, which are parts of the millions of microscopic structures called nephrons, which are in the renal pyramids.

The middle area is the renal medulla, which is made up of other nephron structures such as the loops of Henle and the renal pyramids with parts of the tubular system.

The third area of the kidney is the renal pelvis; this is not a layer of tissue but simply a cavity formed by the expansion of the ureter at the hilus. Funnel shaped extensions of the renal pelvis called the calyces enclose the papillae at the ends of the renal pyramids. Urine flows from the renal pyramids to the papillae into the calyces then to the renal pelvis and out into the ureter.

OK…let’s take another look at the parts of the kidney:

· fibrous capsule

· adipose capsule

· hilus

· renal cortex

· renal medulla

· renal pyramid

· renal papillae

· minor calyx

· major calyx

· renal pelvis

NEPHRON

The nephron is the structural and functional unit of the kidney. Although each kidney looks like a separate entity, it consists of more than a million micro-organs called nephrons. Interestingly enough, the number of nephrons does not increase after birth. Growth of the kidney is due to the enlargement of existing nephrons not due to an increase in their number. When nephrons are damaged they are not replaced or regenerated. About one third of the nephrons in a kidney must be functional to ensure survival of the organ. It is in the nephrons with their associated blood vessels that urine is formed. Each nephron has two major portions; a renal corpuscle and a renal tubule.

Let us look at the nephron as a whole.

The parts of a nephron include the saclike Bowman’s capsule that surrounds the glomerulus, which makes up a renal corpuscle, and then there are the proximal and distal convoluted tubules, the loop of Henle, and the collecting tubule, as well as the afferent and efferent arterioles.

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