Urinary System Structure and Function

Overview of the Urinary System

The urinary system is responsible for filtering blood, removing waste, and regulating fluid and electrolyte balance. It consists of the kidneys, ureters, bladder, and urethra.

• Kidneys: Produce at least 500 mL of urine daily; filter metabolic waste and regulate blood pressure via electrolyte balance and hormone production (e.g., erythropoietin).

• Ureters: Transport urine from kidneys to bladder using peristaltic action.

• Bladder: Stores urine until excretion; can hold up to 400 mL.

• Urethra: Conducts urine from bladder to exterior; shorter in females, increasing UTI risk.

Urinary Microbiome

The urinary tract harbors a diverse microbiome, which can influence health and disease risk.

• Diversity: Varies by age, sex, and health status.

• Main phyla: Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria, Bacteroidetes, Acidobacteria.

• Shifts in microbiome: Associated with urinary tract infections (UTIs) and other diseases.

Female Reproductive System Structure and Microbiome

Structural Features

The female reproductive system includes the ovaries, fallopian tubes, uterus, cervix, and vagina, each with specialized functions.

• Ovaries: Produce eggs and release hormones (estrogen, progesterone).

• Fallopian tubes: Transport eggs to uterus; site of fertilization.

• Uterus: Muscular organ for fetal development; contracts during labor.

• Endometrium: Lining shed during menstruation.

• Cervix: Opening to uterus; contains folds (rugae) and mucus-secreting glands.

• Vagina: Muscular tube connecting cervix to exterior; site of menstrual fluid exit.

Female Reproductive Microbiome

The vaginal microbiome is crucial for reproductive health, dominated by Lactobacillus species.

• Over 200 bacterial taxa identified in the vagina.

• Dominant bacteria: Lactobacillus (produce lactic acid, maintain low pH).

• Functions: Inhibit pathogen growth, support immune defenses, and maintain healthy pregnancy.

Male Reproductive System Structure and Microbiome

Structural Features

The male reproductive system includes the scrotum, testes, epididymis, vas deferens, and accessory glands.

• Scrotum: Pouch containing testes.

• Testes: Produce sperm and hormones.

• Epididymis: Stores sperm for maturation.

• Vas deferens: Transports sperm during ejaculation.

Semen Microbiome

Semen contains a diverse microbiome, mainly from the following phyla:

TORCH Agents and Pregnancy

Placental Barrier and TORCH Pathogens

The placenta protects the fetus but some pathogens (TORCH agents) can cross and cause serious complications.

• TORCH: Toxoplasma, Other (syphilis, HIV, varicella-zoster, parvovirus B19, Zika), Rubella, Cytomegalovirus, Herpes simplex virus.

• Complications: Stillbirth, birth defects, developmental delays.

Urinary Tract Infections (UTIs) and Catheter-Associated UTIs (CAUTIs)

Types and Risk Factors

UTIs are classified by location and complexity. Catheter use greatly increases risk.

• Lower UTI: Urethritis (urethra), Cystitis (bladder), Prostatitis (prostate).

• Upper UTI: Pyelonephritis (kidneys).

• Complicated UTI: Associated with catheters, urinary tract malformations, or underlying conditions.

• Uncomplicated UTI: Occurs in healthy people with normal urinary tracts.

Catheter-Associated UTIs (CAUTIs)

• Urinary catheters drain urine from bladder to a bag.

• Greatly increase UTI risk; cause 70–80% of complicated UTIs.

Microbial Causes of UTIs

Bacterial UTIs

Most UTIs are caused by bacteria, especially Escherichia coli (UPEC).

• Uropathogenic E. coli (UPEC): Flagellated, Gram-negative rod; adheres to urinary tract, forms biofilms.

• Other bacteria: Pseudomonas aeruginosa, Staphylococcus saprophyticus, Group B Streptococcus.

Fungal and Viral UTIs

• Candidiasis: Candida albicans causes yeast infections; can complicate UTIs, especially in immunocompromised patients.

• Symptomatic viral UTIs: Rare, usually in immunocompromised individuals.

Diagnosis of UTIs

Urine Dipstick and Culture

UTIs are diagnosed using urine dipstick tests and cultures.

• Dipstick test: Detects nitrites (bacterial metabolism) and leukocyte esterase (WBCs).

• Urine culture: Confirms infection and identifies causative agent.

Sexually Transmitted Infections (STIs)

Chlamydia

• Agent: Chlamydia trachomatis, Gram-negative, intracellular.

• Prevalence: 1.5 million cases in the U.S. (2015); most common STI.

• Symptoms: Often asymptomatic; can cause pelvic inflammatory disease, infertility.

Gonorrhea

• Agent: Neisseria gonorrhoeae, Gram-negative diplococcus.

• Prevalence: 400,000 cases in the U.S. (2015); incidence rising.

• Symptoms: Urethritis, discharge, pelvic pain; can cause neonatal infections.

Syphilis

• Agent: Treponema pallidum, spirochete bacterium.

• Stages:

  • Primary: Chancre at infection site.

  • Secondary: Disseminated rash.

  • Tertiary: Gumma lesions on skin and bones.

• Curable: With antibiotics if detected early.

Herpes Simplex Virus (HSV)

• HSV-1: Causes oral herpes; transmitted by direct contact.

• HSV-2: Causes genital herpes; can be transmitted during birth.

• Symptoms: Painful ulcers, "dewdrop on a rose petal" lesions, recurrent outbreaks.

Comparisons and Epidemiology

Age and Sex Distribution of STIs

STIs such as chlamydia and gonorrhea are most prevalent in young adults (15–24 years).

• Women: Higher risk for UTIs due to shorter urethra.

• Men: Prostate and urinary tract conditions can increase UTI risk.

Summary Table: Common Urinary and Reproductive Pathogens

Key Equations and Diagnostic Principles

• Urine Output Equation:

• Dipstick Nitrite Reaction:

Additional info:

• Notes include inferred details about the role of the microbiome in health and disease, and the importance of anatomical differences in infection risk.

• Tables and pie charts were interpreted and recreated in text and HTML format for clarity.