Introduction

The term "uria" is derived from the Greek word "-ouria," which means to urinate. It is used as a suffix in combination with other words to indicate abnormal conditions related to urine. For example, dysuria (painful urination) and pyuria (presence of pus in the urine). This article will explore the details of the abnormal condition known as nocturia and explain the role of the urinary system in this condition.

What is nocturia?

The term nocturia refers to the need to wake up more than once at night to urinate. The key components of the term nocturia are "noct" meaning night and "-uria" meaning to urinate. Occasionally waking up to urinate is common and not a problem. However, waking up two or more times per night can significantly impact your quality of life and overall health.¹ 

Nocturia affects both males and females and generally becomes more frequent as they age.^1,2

Overview of the urinary system

Anatomy of the urinary system

The urinary system in both males and females consists of the following:

Two kidneys

The kidneys are a paired set of solid organs, generally measuring 11 cm long, 6 cm wide, and 3 cm thick, on each side of the spine within the retroperitoneum. The hilum, located on the inner side of each kidney, is a depression that opens into the renal sinus, a central area surrounded by the kidney's functional tissue (renal parenchyma). Within this space are the structures responsible for collecting urine (such as the renal pelvis) and the blood vessels (renal vessels) that enter and exit the kidney through the hilum.³

Two ureters

The ureter emerges from the hilum of the kidney and descends vertically downward as a 25- to 30-cm muscular tube that connects the renal pelvis to the urinary bladder in adults.⁴

A bladder

The urinary bladder is a flexible and hollow internal organ that temporarily stores urine, continuously transported to it by the two ureters.⁵

A urethra

The urethra is a passage that links the urinary bladder to the outside of the body. The urethra varies in length between males and females, with males typically having a longer urethra measuring 18-20 cm, whereas females have a shorter urethra measuring approximately 4 cm. 

In females, the external opening of the urethra is situated near the vaginal opening, and its function is solely to expel urine. In males, the urethral opening is located at the tip of the glans penis, serving as a passage for both urine and seminal fluid.⁵

The diagram below illustrates the anatomical structure of the urinary system. 

Function of the urinary system

The main functions of the urinary system include:

Filtration and excretion

The urinary system filters approximately 200 litres of fluid daily from renal blood flow, facilitating the elimination of toxins, metabolic waste products, and excess ions in the form of urine.⁶

Regulation of fluid and electrolyte balance

The urinary system plays an important role in fluid balance in the body and the maintenance of electrolyte levels in the blood.

Causes and pathophysiology of nocturia

The causes of nocturia are diverse and influenced by both urological and non-urological disorders. 

Physiological causes

• These include ageing, excess weight and obesity

Medical conditions

• Urinary tract infections ( UTI)
• Diabetes: Diabetes mellitus (DM) has been linked to a 1.3 to 1.4 times greater likelihood of experiencing nocturia⁷
• Hypertension 
• Bladder disorders: Overactive bladders 
• Others include: Pregnancy, menopause

Lifestyle factors

• Fluid intake: The water from our food constitutes a significant but smaller portion of our total dietary fluid intake. Most of the body's water comes from drinks consumed throughout the day. Consequently, the more fluid one drinks, the more urine is produced. Increased fluid intake, particularly in the evenings close to bedtime, leads to higher urine production at night and can result in frequent nighttime urination⁸
• High salt intake: Consuming a high amount of dietary sodium causes increased thirst and, consequently, higher fluid intake⁸

Medications 

• Diuretics e.g. furosemide, angiotensin-converting enzyme inhibitors ( ACEI) e.g. lisinopril increase osmotic clearance ( diuresis)

Alcohol and caffeine consumption

• Caffeine causes increased urine production (diuresis), stimulates the central nervous system, and enhances the contractility of smooth muscles in the lower urinary tract⁹

The pathophysiology typically involves multiple factors and may result from a complex interplay between age-related changes in bladder function and common pathophysiologic processes in the population.¹⁰ It can be attributed to at least three distinct mechanisms:

• Reduced or nocturnal decrease in bladder capacity, leading to low-volume voiding
• An overall increase in urine production (24-hour polyuria)
• An increase in urine production specifically at night (nocturnal polyuria which refers to passing a large volume of urine at night)
• Sleep disorders such as obstructive sleep apnea¹⁰

A common mechanism of nocturia involves a mismatch between the amount of urine produced at night and the bladder's capacity to hold an adequate volume of urine during sleep. This means that either too much urine is being produced, overwhelming the bladder's storage capacity or the bladder's capacity is reduced, necessitating more frequent trips to the bathroom during the night.¹¹

As people age, the bladder's structure and function deteriorate. Research has shown that the bladder's ability to hold urine overnight and its muscle contraction strength decreases with age, due to a higher proportion of collagen compared to smooth muscle.¹¹ Bladder capacity reductions can also arise from neurogenic causes, bladder wall fibrosis, or bladder cancer.¹²

In older men, conditions like benign prostatic hyperplasia (BPH) can cause the prostate to enlarge, obstructing urine flow and reducing bladder capacity, causing incomplete bladder emptying which leads to frequent urination at night.¹³

Arginine vasopressin (AVP), also known as antidiuretic hormone, is the primary regulator of water excretion by the kidneys promoting water reabsorption in the distal renal tubules and collecting ducts. It is released into the bloodstream in response to changes in osmotic pressure and blood volume. An increase in osmolality is the primary trigger for AVP secretion to help retain water. Insufficient AVP activity in the kidneys can result from either reduced hormone secretion or renal resistance to AVP. Significant reductions or absence of AVP secretion can cause nocturnal polyuria.¹²

Diagnostic approaches

Patient history 

The general practitioner (GP) asks various relevant questions for the patients to gather information. Some of the questions might include: 

• How many times do you wake up at night to pass urine?
• How much does the nocturia bother you?
• What medications are you taking?
• Do you have any underlying health conditions?
• Have you checked your hormone levels recently?¹⁴
• How much caffeine or alcohol do you consume each day?

Physical examination

• A distended bladder (your bladder may stretch if it does not empty completely)
• Swelling in the ankles and legs (known as peripheral oedema)
• Genital skin damage (a sign of urinary incontinence)
• Discharge from the urethra (a sign of infection)
• Abnormalities in the genitals
• Prostate (digital rectal) examination in men 
• Measurement of body mass index and/or waist circumference to determine if the person is obese 

Laboratory tests

Laboratory tests are conducted based on the patient's age, other medical conditions, and the severity of symptoms they are experiencing.

• Urinalysis: Includes urine culture if urinary tract infection is present¹⁵ 
• Blood tests: To evaluate kidney function ( e.g. creatinine level), determine levels of serum electrolytes¹⁵
• Specialised tests:
  • Ultrasound of the urogenital system 
  • Cystoscopy
  • Prostrate specific antigen (PSA) to screen for prostate cancer 

Bladder diary or frequency volume chart (FVC)

A bladder diary or FVC records fluid intake and the amount of urine passed over 2 to 3 days. It also records the number of urination episodes, along with specific times of each visit. Although this task can be tedious for the patient, it provides valuable insights into bladder capacity and helps in diagnosis.¹⁴

Management and treatment

The most suitable treatment for each individual with nocturia depends on its underlying cause. Behavioural modifications or addressing medical conditions are preferred treatments in some cases, while medication may be necessary in others.¹⁶

Lifestyle and behavioural modifications

• Fluid management: Reduce fluid intake, especially caffeine and alcohol, at least 2 hours before bedtime¹⁵ 
• Bladder training: The practice of emptying the bladder before bedtime
• Weight management
• Reduced salt intake
• Timing of medications: The timing of medications is important. For instance, medications like diuretics, which can cause nocturia, should be taken in the morning or mid-afternoon to minimise their impact on nighttime urine frequency

Pharmacological treatments

• Muscarinic receptor antagonists in the treatment of cases of overactive bladder. Examples are oxybutynin and tolterodine
• Desmopressin is a vasopressin analogue and it is also effective in treating nocturia resulting from nocturnal polyuria

Surgical interventions

Surgical interventions like prostate surgery may be required in certain cases.

Treatment of underlying conditions

• Heart failure management
• Treatment of sleep disorders
• Control sugar levels in cases of diabetes 
• Treating urinary tract infection

Summary 

Nocturia simply refers to the need to wake up more than once at night to urinate. It can significantly impact your quality of life and overall health. Nocturia becomes more frequent as people age.

Overall, the causes of nocturia can be attributed to either increased urine production due to medical conditions affecting the urinary system, increased fluid intake, or decreased bladder capacity due to ageing or other medical issues.

To identify the cause of nocturia, a focused patient history is crucial. This should include maintaining a 3-day bladder and sleep diary. A physical examination along with laboratory tests would aid the diagnosis.

Managing conditions that affect the urinary system can help reduce nocturia. Medications, lifestyle changes, or behavioural therapies aim to modify urinary system function to reduce episodes of nocturia. In conclusion, understanding the urinary system can significantly improve symptoms of nocturia.