Everything about The Urinary System totally explained
The
urinary system (also called
excretory system or the genitourinary system (GUS)) is the
organ system that produces, stores, and eliminates
urine. In humans it includes two
kidneys, two
ureters, the
bladder, and the
urethra. The analogous organ in invertebrates is the
nephridium.
Physiology
Typically, every human has two kidneys. The
kidneys are
bean-shaped organs about the size of a bar of chocolate. The kidneys lie in the
abdomen, rump or
retroperitoneal to the organs of digestion, around or just below the ribcage and close to the
lumbar spine. The kidneys are surrounded by what is called peri-nephric fat, and situated on the superior pole of each kidney is an
adrenal gland. The kidneys receive their blood supply of 1.25 L/min (25% of the
cardiac output) from the renal arteries which are fed by the
Abdominal aorta. This is important because the kidneys' main role is to filter
water soluble waste products from the blood. The other attachment of the kidneys are at their functional endpoints the
ureters, which lies more
medial and runs down to the
trigone of the
bladder.
Functionally the kidney performs a
number of tasks. In its role in the urinary system it concentrates urine, plays a crucial role in regulating
electrolytes, and maintains
acid-base homeostasis. The kidney excretes and re-absorbs
electrolytes (for example
sodium,
potassium and
calcium) under the influence of local and systemic
hormones.
pH balance is regulated by the excretion of
bound acids and
ammonium ions. In addition, they remove
urea, a nitrogenous waste product from the
metabolism of proteins from
amino acids. The end point is a
hyperosmolar solution carrying waste for storage in the bladder prior to
urination.
Humans produce about 1.5
liters of urine over 24 hours, although this amount may vary according to circumstances. Because the rate of filtration at the kidney is
proportional to the
glomerular filtration rate, which is in turn related to the blood flow through the kidney, changes in body fluid status can affect kidney function. Hormones exogenous and endogenous to the kidney alter the amount of blood flowing through the
glomerulus. Some
medications interfere directly or indirectly with urine production.
Diuretics achieve this by altering the amount of absorbed or excreted electrolytes or
osmalites, which causes a
diuresis.
Bladder
The
urinary bladder is a hollow muscular organ shaped like a balloon. It is located in the anterior pelvis. The bladder stores urine. the maximum that it can hold is one litre. It swells into a round shape when it's full and gets smaller when empty. In the absence of bladder disease, it can hold up to 300 ml of urine comfortably for two to five hours. The epithelial tissue associated with the bladder is called
transitional epithelium. Normally the bladder is
sterile.
Sphincters (circular muscles) regulate the flow of urine from the bladder. The bladder itself has a muscular layer (
detrusor muscle) that, when contracted, increases pressure on the bladder and creates urinary flow.
Urination is a conscious process, generally initiated by stretch receptors in the bladder wall which signal to the brain that the bladder is full. This is felt as an urge to urinate. When urination is initiated, the sphincter relaxes and the detrusor muscle contracts, producing urinary flow.
Urethra
The endpoint of the urinary system is the urethra. Typically the urethra in humans is colonised by
commensal bacteria below the external urethral sphincter. The urethra emerges from the end of the
penis in males and between the
clitoris and the
vagina in females.
Role in disease
Kidney diseases are normally investigated and treated by
nephrologists, while the specialty of
urology deals with problems in the other organs.
Gynecologists may deal with problems of incontinence in women.
Diseases of other bodily systems also have a direct effect on urogenital function. For instance it has been shown that
protein released by the kidneys in [[diabetes mellitus sensitises the kidney to the damaging effects of
hypertension
.
Diabetes also can have a direct effect in
micturition due to
peripheral neuropathies which occur in some individuals with poorly controlled diabetics.
Kidney disease
Renal failure is defined by functional impairment of the kidney. Renal failure can be
acute or
chronic, and can be further broken down into categories of pre-renal, intrinsic renal and post-renal.
Pre-renal failure refers to impairment of supply of blood to the functional nephrons including
renal artery stenosis. Intrinsic renal diseases are the classic diseases of the kidney including drug toxicity and
nephritis. Post-renal failure is outlet obstruction after the kidney, such as a
renal stone or
prostatic bladder outlet obstruction.
Renal failure may require
medication, dietary and lifestyle modification and
dialysis.
Primary renal cell carcinomas as well as metastatic cancers can affect the
kidney.
Non-renal urinary tract disease
The causes of diseases of the body are common to the urinary tract. Structural and or traumatic change can lead to
hemorrhage, functional blockage or
inflammation. Colonisation by
bacteria,
protozoa or
fungi can cause infection. Uncontrolled cell growth can cause
neoplasia.
For example:
The term "uropathy" refers to a disease of the urinary tract, while "
nephropathy" refers to a disease of the kidney.
Testing
Biochemical blood tests determine the amount of typical markers of renal function in the blood serum, for instance serum
urea and serum
creatinine. Biochemistry can also be used to determine serum electrolytes. Special biochemical tests (
arterial blood gas) can determine the amount of dissolved gases in the blood, indicating if pH imbalances are acute or chronic.
Urinalysis is a test that studies
urine for abnormal substances such as protein or signs of infection.
A Full Ward Test, also known as dipstick urinalysis, involves the dipping of a biochemically active test strip into the urine specimen to determine levels of tell-tale chemicals in the urine.
Urinalysis can also involve MC&S microscopy, culture and sensitivity
Urodynamic tests evaluate the storage of urine in the bladder and the flow of urine from the bladder through the urethra. It may be performed in cases of incontinence or neurological problems affecting the urinary tract.
Ultrasound is commonly performed to investigate problems of the kidney and/or urinary tract.
Radiology:
KUB is plain radiography of the urinary system, for example to identify kidney stones.
An intravenous pyelogram studies the shape of the urinary system.
CAT scans and MRI can also be useful in localising urinary tract pathology.
A voiding cystogram is a functional study where contrast "dye" is injected through a catheter into the bladder. Under x-ray the radiologist asks the patient to void (usually young children) and will watch the contrast exiting the body on the x-ray monitor. This examines the child's bladder and lower urinary tract. Typically looking for vesicoureteral reflux, involving urine backflow up into the kidneys.Further Information
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