The Urinary System

Urinary System FunctionsRegulation of the volume of blood by

excretion or conservation of waterRegulation of the electrolyte content of the

blood by the excretion or conservation of minerals

Regulation of the acid-base balance of the blood by the excretion or conservation of ions such as hydrogen (H+) and bicarbonate (HCO3)

Regulation of all of the above in tissue fluid

Urinary System FunctionsIn summary, the process of urine formation

helps maintain the normal composition, volume and pH of both blood and tissue fluid by removing those substances that would upset the normal constancy and balance of these extracellular fluids

Urinary System StructureConsists of:

KidneysUretersUrinary BladderUrethraWorks in conjunction with the circulatory

system

KidneysEmbedded in adipose tissue that acts as a

cushion and is in turn covered by a fibrous connective tissue membrane called the renal fascia, which helps hold the kidneys in place.

Each kidney has an indentation called the hilus on its medial side. At the hilus, the renal artery enters the kidney, and the renal vein and ureter emerge.

Function of the kidney is the formation of urine.

Structure of the KidneyOuter tissue layer is called the renal cortex. Inner tissue layer is called the renal

medulla.The third area is called the renal pelvis, this

is not a layer of tissue, but rather a cavity formed by the expansion of the ureter within the kidney at the hilus

The Kidney

The NephronIs the structural and functional unit of the

kidneyEach kidney contains approx 1 million

nephrons.It is in the nephrons, with their associated

blood vessels, that urine is formed.

The Nephron

Elimination of UrineIs performed by the rest of the structures

within the Urinary System:UretersUrinary BladderUrethra

UretersEach ureter extends from the hilus of the

kidney to the lower, posterior end of the urinary bladder.

Smooth muscle in the wall of the ureter contracts in peristaltic waves to propel urine toward the urinary bladder

As the bladder fills, it expands and compresses the lower ends of the ureters to prevent backflow of urine

Ureters

Urinary BladderIs a muscular sac that acts as a reservoir for

accumulating urine, and it contracts to eliminate urine.

The mucosa of the bladder is transitional epithelium, which permits expansion without tearing the lining.

The smooth muscle layer in the wall of the bladder is called the detrusor muscle. It is a muscle in the form or a sphere; when it contracts it becomes a smaller sphere and the volume diminishes.

The opening of the urethra is the internal urethral sphincter (muscle), which is involuntary

Urinary Bladder

UrethraCarries urine from the bladder to the exteriorExternal urethral sphincter is made of the

surrounding skeletal muscle of the pelvic floor, and is under voluntary control.

In females, the urethra is anterior to the vagina

In males, the first part just outside the bladder is called the prostatic urethra because it is surrounded by the prostate gland. The rest of the urethra passes through penile tissue.

In males, the urethra carries sperm as well as urine.

Urethra

Urination ReflexUrination is also called micturition or voidingThis reflex is a spinal cord reflex over which

voluntary control may be exerted.The stimulus for the reflex is stretching of the

detrusor muscle of the bladder.