33.3 Introduction to the Urinary System
3 min read•june 18, 2024
Your urinary system is like a sophisticated plumbing network in your body. It filters waste, balances fluids, and keeps you healthy. From the bean-shaped to the and , each part plays a crucial role in processing and eliminating urine.
Understanding how your urinary system works helps you spot potential issues. Common problems like UTIs, incontinence, and prostate enlargement can disrupt this delicate system. Knowing the signs and risk factors empowers you to take better care of your urinary health.
Anatomy and Physiology of the Urinary System
Urinary system components
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Urine Transport, Storage, and Elimination | Boundless Anatomy and Physiology View original
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- Kidneys
- Bean-shaped organs located in the retroperitoneal space behind the peritoneum
- Primary functions include filtering blood to remove waste products and excess fluids, regulating electrolytes (sodium, potassium) and acid-base balance, and producing urine
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- Thin, muscular tubes that connect the kidneys to the bladder, typically 10-12 inches long
- Transport urine from the to the bladder via peristaltic contractions, which are rhythmic muscle contractions that propel urine forward
- Bladder
- Hollow, muscular organ located in the pelvic cavity that stores urine until it is ready to be expelled from the body
- Composed of the , which contracts during (urination) to expel urine
- is a triangular area where the ureters and urethra connect to the bladder, forming a smooth triangle
- Urethra
- Thin tube that carries urine from the bladder to the external urethral orifice for elimination from the body
- Longer in males (8-10 inches) than in females (1.5 inches) due to the passage through the penis
Micturition process
- Micturition (urination) is the process of emptying the bladder of urine
- Involves both voluntary control from the brain and involuntary control through a reflex arc
- Reflex arc
- Stretching of the bladder wall stimulates stretch receptors, which send sensory signals via neurons to the sacral spinal cord
- Motor neurons then stimulate the detrusor muscle to contract and the internal urethral sphincter to relax, allowing urine to flow out
- Voluntary control
- Pontine micturition center in the brainstem coordinates voluntary control of urination
- External urethral sphincter is under voluntary control and can be consciously contracted to delay urination when it is not socially appropriate
- Stages of micturition
- Filling stage occurs as the bladder fills with urine from the ureters; the detrusor muscle relaxes to accommodate the increasing volume of urine
- Storage stage maintains urine in the bladder as the external urethral sphincter remains contracted to prevent leakage
- Emptying stage occurs when the bladder reaches its threshold volume (about 300-400 mL), triggering the micturition reflex, which causes the detrusor muscle to contract and the internal urethral sphincter to relax, allowing urine to flow out through the urethra
Common Urinary System Disorders
Urinary disorders
- Urinary incontinence
- involves leakage of urine during physical activity or increased abdominal pressure (coughing, sneezing, lifting heavy objects)
- is a sudden, intense urge to urinate followed by involuntary loss of urine, often associated with overactive bladder
- occurs when the bladder becomes overfilled, leading to leakage of urine, often caused by bladder outlet obstruction or weak detrusor muscle
- is a combination of stress and urge incontinence symptoms
- Urinary tract infections (UTIs)
- Cystitis is an infection of the bladder, commonly caused by bacteria like Escherichia coli (E. coli) ascending from the urethra
- Symptoms include dysuria (painful urination), frequency, urgency, suprapubic pain, and hematuria (blood in urine)
- Pyelonephritis is an infection of the kidney that can result from untreated cystitis
- Symptoms include fever, chills, flank pain, nausea, and vomiting
- Risk factors for UTIs include female gender, sexual activity, poor hygiene, and urinary stasis (incomplete emptying of the bladder)
- Cystitis is an infection of the bladder, commonly caused by bacteria like Escherichia coli (E. coli) ascending from the urethra
- Benign prostatic hyperplasia (BPH)
- Noncancerous enlargement of the prostate gland that commonly occurs in older men
- Can cause urinary symptoms such as frequency, urgency, weak stream, and incomplete emptying of the bladder
Key Terms to Review (31)
Bladder: The bladder is a hollow, muscular organ located in the pelvis that serves as a storage and collection vessel for urine produced by the kidneys. It plays a crucial role in the urinary system, responsible for temporarily holding urine until it can be voluntarily expelled from the body.
Bowman's Capsule: Bowman's capsule is a cup-shaped structure that surrounds the glomerulus, the primary filtration unit of the nephron in the kidney. It is a crucial component of the renal system and the urinary system, playing a vital role in the filtration of blood to form urine.
Collecting Duct: The collecting duct is a key structure within the kidney's nephron, responsible for the final stages of urine formation and concentration. It serves as the final pathway for the transport and excretion of waste products and excess water from the body.
Creatinine: Creatinine is a waste product generated from the breakdown of creatine, a molecule found in muscle tissue. It is primarily filtered out of the bloodstream by the kidneys and excreted in urine, making it an important biomarker for evaluating kidney function.
Detrusor Muscle: The detrusor muscle is a smooth muscle layer in the wall of the urinary bladder that is responsible for the contraction and relaxation of the bladder, allowing it to store and expel urine. It is a key component of the urinary system and plays a crucial role in the regulation of bladder function.
Distal Convoluted Tubule: The distal convoluted tubule is a segment of the nephron in the kidney, located between the loop of Henle and the collecting duct. It plays a crucial role in the regulation of fluid and electrolyte balance within the body, and is a key site of action for various diuretic medications.
Filtration: Filtration is the process by which the kidneys selectively remove waste, toxins, and excess substances from the bloodstream while retaining essential molecules and nutrients. It is a crucial component of the renal and urinary systems, responsible for maintaining homeostasis and ensuring the body's overall health and well-being.
Functional Incontinence: Functional incontinence is a type of urinary incontinence where the inability to reach the toilet in time is the primary cause, rather than a physical or neurological problem with the bladder or urinary sphincter. It is often associated with impairments in mobility, cognition, or physical dexterity that prevent a person from getting to the bathroom quickly enough.
Glomerulus: The glomerulus is a cluster of small blood vessels (capillaries) located within the nephrons of the kidneys. It is the primary filtration unit responsible for removing waste, excess water, and other substances from the bloodstream to be excreted as urine.
Homeostasis: Homeostasis is the process by which the body maintains a stable and balanced internal environment, despite changes in external conditions. It is a fundamental principle that allows the body to function optimally and adapt to various stressors.
Kidneys: The kidneys are a pair of bean-shaped organs located in the lower back, just above the waist. They are a vital part of the renal system, responsible for filtering waste and excess water from the blood, regulating fluid balance, and maintaining overall homeostasis in the body.
Loop of Henle: The loop of Henle is a U-shaped structure within the nephron of the kidney that plays a crucial role in the reabsorption and concentration of urine. It is a key component in the kidney's ability to regulate fluid and electrolyte balance in the body, which is essential for maintaining homeostasis.
Micturition: Micturition is the process of expelling urine from the urinary bladder through the urethra. It involves both voluntary and involuntary muscle contractions.
Mixed Incontinence: Mixed incontinence is a type of urinary incontinence characterized by the presence of both stress incontinence and urge incontinence. It involves the involuntary leakage of urine during physical activity or exertion, as well as a sudden, strong urge to urinate that is difficult to control.
Nephrons: Nephrons are the functional units of the kidneys, responsible for the filtration, reabsorption, and secretion of substances in the body to maintain fluid and electrolyte balance, as well as remove waste products from the bloodstream.
Nocturia: Nocturia is the medical term for the need to wake up and urinate one or more times during the night. It is a common condition that can have various underlying causes, including diabetes, diuretic medication use, and age-related changes in the urinary system.
Overflow Incontinence: Overflow incontinence is a type of urinary incontinence characterized by the involuntary leakage of urine due to an overfull bladder. It occurs when the bladder becomes too full and unable to empty completely, leading to urine spilling out. This condition is often associated with an underlying obstruction or impaired bladder function, and can be related to both the Introduction to the Urinary System and Urinary Stimulants topics.
Proximal Convoluted Tubule: The proximal convoluted tubule is a section of the renal tubule located in the cortex of the kidney. It is responsible for the reabsorption of the majority of filtered substances, playing a crucial role in maintaining fluid and electrolyte balance in the body.
Reabsorption: Reabsorption is the process by which certain substances filtered from the blood by the kidneys are returned to the bloodstream, allowing the body to conserve valuable nutrients, water, and electrolytes. This process is a crucial aspect of the renal system and the urinary system's function in maintaining homeostasis within the body.
Renal Pelvis: The renal pelvis is the funnel-shaped expansion of the ureter within the kidney. It serves as the collecting area for urine produced by the kidney before it drains into the ureter and down to the bladder.
Serum creatinine: Serum creatinine is a waste product found in the blood that comes from muscle metabolism. It is commonly used as an indicator of kidney function.
Stress Incontinence: Stress incontinence is a type of urinary incontinence characterized by the involuntary leakage of urine during physical activity, exertion, sneezing, or coughing. It occurs when the muscles that support the bladder and urethra are weakened, leading to an inability to maintain control over urine flow during increased abdominal pressure.
Trigone: The trigone is a triangular-shaped region located at the base of the bladder, formed by the two ureteral orifices and the internal urethral orifice. It is an important anatomical landmark in the urinary system that plays a crucial role in the proper functioning of the bladder and urinary tract.
Urea: Urea is a waste product that is formed in the liver as the end-product of protein metabolism. It is a small, water-soluble molecule that is filtered out of the blood by the kidneys and excreted in the urine, playing a crucial role in the urinary system's function of removing waste and maintaining fluid balance in the body.
Ureters: The ureters are a pair of muscular tubes that connect the kidneys to the bladder. They are responsible for transporting urine from the kidneys to the bladder for storage and eventual elimination from the body.
Urethra: The urethra is a tube that carries urine from the bladder out of the body. It is an essential part of both the urinary and reproductive systems, playing a crucial role in eliminating waste and facilitating sexual function.
Urge Incontinence: Urge incontinence is a type of bladder control problem characterized by a sudden, intense urge to urinate that is difficult to control, often leading to involuntary urine leakage. It is closely related to the functioning of the urinary system and the use of certain medications that affect bladder and urinary tract function.
Urinary incontinence (UI): Urinary incontinence (UI) is the involuntary leakage of urine due to loss of bladder control. It can result from various underlying conditions affecting the urinary system.
Urinary tract infection (UTI): A urinary tract infection (UTI) is an infection in any part of the urinary system, including the kidneys, ureters, bladder, and urethra. It is commonly caused by bacteria such as Escherichia coli.
Vesicoureteral reflux: Vesicoureteral reflux (VUR) is a condition where urine flows backward from the bladder into the ureters or kidneys. This can lead to urinary tract infections and kidney damage.
Voiding: Voiding refers to the process of emptying the bladder, which is an essential function of the urinary system. It involves the coordinated contraction of the bladder muscle and the relaxation of the urethral sphincter, allowing urine to be expelled from the body.