Urinary Tract Anatomy
The lower urinary tract consists of the bladder, urethra, and ureteral orifices. The detrusor muscle (smooth muscle) contracts during micturition under parasympathetic control (S2-S4). The internal urethral sphincter (involuntary) and external urethral sphincter (voluntary) control urine flow.
| Structure | Location | Key Points |
|---|---|---|
| Ureters | Retroperitoneal | 3 narrowing points: UPJ, pelvic brim, UVJ — most common sites for kidney stone impaction |
| Bladder | Pelvic cavity | Trigone = triangle between 2 ureteral orifices + internal urethral orifice; most common site for bladder cancer |
| Female urethra | 4 cm long | Short — higher UTI risk; exits anterior to vagina |
| Male urethra | 20 cm long | Prostatic → membranous → spongy (penile) portions |
⭐ Boards PearlUreteral narrowing: stones commonly get stuck at UPJ (ureteropelvic junction), pelvic brim (crossing iliac vessels), or UVJ (ureterovesical junction). UVJ is the narrowest.
Male Reproductive Anatomy
| Structure | Function | Key Points |
|---|---|---|
| Testes | Spermatogenesis, testosterone production | Seminiferous tubules (sperm); Leydig cells (testosterone); Sertoli cells (FSH-responsive, blood-testis barrier) |
| Epididymis | Sperm maturation and storage | Sperm transit: 12-21 days; most common site for epididymitis |
| Vas deferens | Transport sperm to ejaculatory duct | Vasectomy site; absent bilaterally in cystic fibrosis (CBAVD) |
| Seminal vesicles | 60% of seminal fluid (fructose, prostaglandins) | Posterior to bladder |
| Prostate gland | PSA, proteolytic enzymes; liquefies semen | Surrounds urethra; central zone (BPH), peripheral zone (prostate cancer), transitional zone |
| Cowper's glands | Pre-ejaculatory fluid (lubricant, neutralizes acid) | Bulbourethral glands |
🧐 Mnemonic — Semen ContributionsSeminal vesicles (60%) + Prostate (30%) + Testes/Epididymis (10%) = SPERM. "Some People Think VAs Produce Ejaculate Well."
Female External Genitalia (Vulva)
- Mons pubis — fatty pad over pubic symphysis
- Labia majora — homologous to scrotum; contains Bartholin's glands posteriorly
- Labia minora — inner folds; contain Skene's glands (paraurethral; homologous to prostate)
- Clitoris — homologous to glans penis; erectile tissue; most sensitive structure
- Vestibule — space between labia minora; contains urethral and vaginal openings
- Bartholin's glands — secrete lubrication; can form Bartholin's cyst/abscess
🩹 Clinical NoteBartholin's gland abscess: fluctuant, tender mass at 4-5 o'clock or 7-8 o'clock position in posterior labia majora. Treatment: Word catheter incision and drainage.
Uterus, Fallopian Tubes, and Ovaries
| Structure | Layers / Parts | Clinical Relevance |
|---|---|---|
| Uterus | Perimetrium (outer), myometrium (middle, smooth muscle), endometrium (inner, shed monthly) | Anteflexed and anteverted normally; fundus, body, isthmus, cervix |
| Cervix | Ectocervix (stratified squamous), transformation zone (squamocolumnar junction), endocervix (columnar) | Transformation zone = site of cervical dysplasia and cancer (Pap smear target) |
| Fallopian tubes | Infundibulum, ampulla, isthmus, interstitial | Ampulla = most common site of fertilization AND ectopic pregnancy |
| Ovaries | Cortex (follicles), medulla (vessels) | Not covered by peritoneum — intraperitoneal spread of ovarian cancer |
⭐ Boards PearlEctopic pregnancy most common in ampulla of fallopian tube (~70%). Risk factors: prior PID/STI (especially Chlamydia), tubal surgery, prior ectopic. Beta-hCG + no intrauterine pregnancy on ultrasound = ectopic until proven otherwise.
Reproductive Hormones
| Hormone | Source | Function |
|---|---|---|
| GnRH | Hypothalamus (pulsatile) | Stimulates FSH and LH release |
| FSH | Anterior pituitary | Follicle development (F); Sertoli cells/spermatogenesis (M) |
| LH | Anterior pituitary | Ovulation trigger; Leydig cells/testosterone (M) |
| Estrogen | Granulosa cells, corpus luteum, placenta | Endometrial proliferation, secondary sex characteristics, LH surge feedback |
| Progesterone | Corpus luteum, placenta | Endometrial maintenance (secretory phase); thermogenic; cervical mucus thickening |
| Testosterone | Leydig cells (testes), adrenal cortex, ovarian theca cells | Spermatogenesis, libido, muscle mass, secondary sex characteristics |
| hCG | Syncytiotrophoblast (placenta) | Maintains corpus luteum in early pregnancy; basis of pregnancy test |
| Inhibin B | Granulosa cells / Sertoli cells | Negative feedback on FSH |
Embryology
- Wolffian (mesonephric) duct → male reproductive tract (epididymis, vas deferens, seminal vesicles, ejaculatory duct) — requires testosterone
- Mullerian (paramesonephric) duct → female reproductive tract (fallopian tubes, uterus, upper 1/3 vagina) — develops by default without MIF
- MIF (Mullerian inhibiting factor) — secreted by Sertoli cells; causes Mullerian duct regression in males
- Urogenital sinus → bladder, urethra, lower vagina, prostate, Bartholin's and Skene's glands
- Genital tubercle → glans penis (M) or clitoris (F)
🧐 MnemonicFEMALE has Fallopian tubes, Uterus, and upper vagina from Mullerian ducts. MALE keeps Mesonephric (Wolffian) duct structures. Without hormonal input → default FEMALE anatomy.
Clinical Pearls
⭐ Pelvic Organ ProlapseCystocele = anterior wall prolapse (bladder). Rectocele = posterior wall prolapse (rectum). Uterine prolapse = uterus descends into vaginal canal. Risk factors: multiparity, menopause, chronic straining.
🩹 Lymphatic Drainage (Boards Favorite)Testes drain to para-aortic (lumbar) nodes. Scrotum/vulva drain to superficial inguinal nodes. Ovaries drain to para-aortic nodes. Cervix drains to obturator and internal iliac nodes.
⭐ Micturition ControlSympathetic (T10-L2): bladder filling, internal sphincter contraction (storage). Parasympathetic (S2-S4): detrusor contraction, internal sphincter relaxation (voiding). Somatic (pudendal nerve, S2-S4): external sphincter voluntary control.