Uterus mbbs nots 10 marks
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Uterus - MBBS Notes (10 Marks)
1. Introduction
The uterus is a thick-walled, hollow, pear-shaped muscular organ situated in the midline of the female pelvis, between the urinary bladder anteriorly and the rectum posteriorly.
Size (non-pregnant adult): ~7.5 cm long, 5 cm wide, 2.5 cm thick
Weight: ~60-80 g
2. Parts of the Uterus
| Part | Description |
|---|---|
| Fundus | Rounded, dome-shaped superior part; above the level of uterine tube openings |
| Body (Corpus) | Main bulk; flattened anteroposteriorly; cavity is triangular when viewed from front |
| Isthmus | Constricted junction between body and cervix (~1 cm); becomes the lower uterine segment in pregnancy |
| Cervix | Cylindrical lower portion, 2.5 cm long; projects into vagina as the portio |
The cervical canal has two openings:
- Internal os - opens into isthmus
- External os - opens into vagina (round in nulliparous, transverse slit after vaginal delivery)
3. Position
- Normally in anteversion + anteflexion
- Anteversion: the uterus as a whole is tilted forward relative to the vagina
- Anteflexion: the body is bent forward on the cervix (angle ~125°)
- Position changes with bladder and rectal fullness
4. Relations
| Surface/Direction | Relation |
|---|---|
| Anterior | Vesicouterine pouch and urinary bladder |
| Posterior | Rectouterine pouch (Pouch of Douglas) and rectum |
| Lateral (broad ligament) | Ureter, uterine artery, ovary |
| Inferior | Vagina |
Important clinical point: During hysterectomy or ligation of uterine artery, the ureter passes close beneath the uterine artery at the base of the broad ligament ("water under the bridge") - risk of ureteric injury.
5. Supports (Ligaments)
The uterus is supported by pelvic floor muscles + ligaments:
Primary/Main Supports:
| Ligament | Origin → Insertion | Key Feature |
|---|---|---|
| Transverse cervical (Mackenrodt's/Cardinal) ligament | Cervix & vaginal vault → lateral pelvic wall | Most important; prevents uterine prolapse |
| Uterosacral ligament | Posterior cervix → sacrum (S2-S4) | Keeps cervix backward and upward; contains autonomic nerves |
| Pubocervical ligament | Cervix → pubis | Prevents forward displacement |
Secondary/Peritoneal Ligaments:
| Ligament | Description |
|---|---|
| Broad ligament | Double peritoneal fold from lateral uterus to lateral pelvic wall; contains mesometrium, mesosalpinx, mesovarium; NOT a true ligament |
| Round ligament | From uterine horn → inguinal canal → labium majus; maintains anteversion; has smooth muscle |
| Infundibulopelvic (suspensory) ligament of ovary | Ovary to pelvic wall; transmits ovarian vessels |
6. Walls (Microscopic Structure)
The uterine wall has 3 layers:
A. Perimetrium (Serosa)
- Outermost layer; peritoneal covering
- Adventitial (no serosa) on anterior and lateral aspects of lower uterus
- Continuous with broad ligament laterally
B. Myometrium
- Thickest layer; composed of interlacing bundles of smooth muscle
- Three indistinct layers (outer longitudinal, middle circular, inner longitudinal)
- Middle circular layer contains large blood vessels
- During pregnancy: undergoes hyperplasia + hypertrophy; contracts forcefully during parturition
- After pregnancy: cells shrink, many undergo apoptosis
C. Endometrium (Mucosa)
- Simple columnar epithelium (ciliated + secretory cells)
- Contains tubular uterine glands penetrating full thickness
- Two zones:
- Basal layer (stratum basalis): Adjacent to myometrium; NOT shed during menstruation; regenerates the functional layer; supplied by straight arteries
- Functional layer (stratum functionalis): Superficial; undergoes cyclic changes; shed during menstruation; supplied by spiral (coiled) arteries
7. Menstrual Cycle - Endometrial Changes
| Phase | Days | Hormone | Endometrial Change |
|---|---|---|---|
| Proliferative (follicular) | 5-14 | Estrogen (from developing follicle) | Glands enlarge & lengthen; stroma proliferates; spiral arteries grow |
| Secretory (luteal) | 15-28 | Progesterone + estrogen (corpus luteum) | Glands become coiled, tortuous, sacculated; stroma becomes edematous; spiral arteries become tortuous |
| Menstrual | 1-4 | Progesterone withdrawal | Vasoconstriction of spiral arteries → ischemia → necrosis → shedding of functional layer |
The basal layer is supplied by straight arteries (not affected by progesterone withdrawal) and is always retained.
8. Blood Supply
| Vessel | Source | Course |
|---|---|---|
| Uterine artery (main) | Internal iliac artery | Runs in broad ligament; crosses over the ureter at the level of the internal os; ascends along lateral uterine wall in a tortuous course; at fundus anastomoses with ovarian artery |
| Ovarian artery | Abdominal aorta (L2) | Supplies fundus via anastomosis with uterine artery |
Venous drainage: Uterine venous plexus (valveless) → uterine veins → internal iliac veins
9. Lymphatic Drainage
| Region | Drains To |
|---|---|
| Fundus & body | Para-aortic nodes (along aorta, via infundibulopelvic ligament) |
| Body | Superficial inguinal nodes (via round ligament) |
| Body (also) | External/internal iliac nodes (via broad ligament) |
| Cervix | Internal iliac + obturator nodes; also sacral nodes |
10. Nerve Supply
- Sympathetic: T12-L1 via hypogastric plexus (→ vasoconstriction, uterine contraction)
- Parasympathetic: S2-S4 via pelvic splanchnic nerves
- Both form the uterovaginal plexus (Frankenhäuser ganglion) lateral to the cervix
- Pain from body/fundus: T11-T12 (referred to lower abdomen)
- Pain from cervix: S2-S4 (referred to back/thighs)
11. Clinical Notes
- Hysterectomy: Removal of uterus; care must be taken to ligate uterine arteries without injuring the ureter beneath them
- Lower uterine segment: Formed from the isthmus during pregnancy; site of lower segment caesarean section (LSCS) - less vascular, heals better
- Implantation: Blastocyst normally implants in the body of the uterus
- Uterine prolapse: Weakening of cardinal and uterosacral ligaments + levator ani; uterus descends into vagina
- Endometriosis: Ectopic endometrial tissue; most common in pouch of Douglas
- Retroversion: ~20% of women; uterus tilted backward; can cause dysmenorrhoea and dyspareunia
Quick Summary Box
UTERUS
├── Parts: Fundus → Body → Isthmus → Cervix
├── Position: Anteverted + Anteflexed (normal)
├── Relations: Bladder (ant.) | Rectum (post.) | Ureter (lat.)
├── Supports: Cardinal lig. (most important) + Uterosacral + Round + Broad
├── Layers: Perimetrium → Myometrium → Endometrium
├── Endometrium: Basalis (retained) + Functionalis (shed)
├── Blood: Uterine a. (from int. iliac) crosses OVER ureter
├── Lymph: Body → Para-aortic; Cervix → Internal iliac/sacral
└── Nerves: Frankenhäuser ganglion (uterovaginal plexus)
Sources: Gray's Anatomy for Students, p. 555 | Color Atlas of Human Anatomy Vol. 2 Internal Organs, pp. 454-460 | Junqueira's Basic Histology 17e, pp. 1129-1134
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