Gross Anatomy Notes
ERS – Gross Anatomy Notes
1. Pituitary Gland
Location:
- Situated in the hypophyseal fossa (Pituitary fossa), a bony depression in the sella turcica of the body of the sphenoid bone.
- Lined by the dura mater and covered by a portion of the dural fold, the diaphragma sella.
Parts:
- Two distinct parts differing embryologically, morphologically, and functionally:
- Adenohypophysis (Anterior Pituitary):
- Pars Distalis (Pars Anterior)
- Pars Intermedia
- Pars Tuberalis
- Neurohypophysis (Posterior Pituitary):
- Median Eminence
- Infundibulum
- Pars Nervosa
Relations:
- Superior:
- Optic chiasma, diaphragma sella, anterior communicating artery, floor of the third ventricle.
- Inferior:
- Hypophyseal fossa, sphenoidal air sinus.
- Anterior:
- Anterior intercavernous sinus.
- Posterior:
- Posterior intercavernous sinus.
- Lateral:
- Cavernous sinus and its related structures.
Blood Supply:
- Arterial Supply:
- Two pairs of hypophyseal arteries arise from the internal carotid artery.
- Superior Hypophyseal Artery:
- Supplies pars tuberalis and infundibulum, forming a primary capillary plexus in the median eminence.
- Inferior Hypophyseal Artery:
- Supplies the posterior lobe.
- Venous Drainage:
- Drains into the cavernous sinus.
Histology:
- Histologically shows pars anterior, pars posterior, and pars intermedia.
- Adenohypophysis / Pars Anterior:
- Composed of clusters of cells separated by sinusoids.
- Two cell types:
- Chromophobes:
- Do not take up stain and appear pale.
- Chromophils:
- Have granules in their cytoplasm.
- Two types based on staining:
- Acidophils:
- Take up acidic stain and appear eosinophilic.
- Basophils:
- Take up basic stain and appear basophilic.
- Pars Intermedia:
- Shows colloid-filled vesicles.
- Neurohypophysis / Pars Posterior:
- Made of unmyelinated nerve fibers, cell bodies located in the paraventricular and supraoptic nuclei of hypothalamus.
- Terminal parts of axons are called Herring Bodies, containing hormones produced by the hypothalamus.
- Supporting cells called Pituicytes are present between the nerve fibers.
Hormones Produced:
- Adenohypophysis / Pars Anterior:
- Acidophils:
- Somatotrophs:
- Produce growth hormone.
- Mammotrophs:
- Produce prolactin.
- Basophils:
- Corticotrophs:
- Produce adrenocorticotropic hormone.
- Thyrotrophs:
- Produce thyroid-stimulating hormone.
- Gonadotrophs:
- Produce follicle-stimulating hormone and luteinizing hormone (female)/interstitial cell-stimulating hormone (male).
- Pars Intermedia:
- Produces melanocyte-stimulating hormone.
- Pars Posterior:
- Stores vasopressin (antidiuretic hormone) and oxytocin.
Embryological Development:
- The pituitary gland develops from two sources:
- A small ectodermal diverticulum (Rathke's pouch), growing superiorly from the roof of the stomodeum, anterior to the buccopharyngeal membrane.
- A small ectodermal diverticulum (infundibulum), growing inferiorly from the floor of the diencephalon of the brain.
- During the second month of development, Rathke's pouch contacts the anterior surface of the infundibulum, with its connection to the oral epithelium elongating, narrowing and finally disappearing.
- Rathke's pouch forms a vesicle that flattens around the anterior and lateral surfaces of the infundibulum.
- The anterior wall of the vesicle proliferates to form the pars anterior of the pituitary.
- The upper part of the vesicle grows around the stalk of the infundibulum, forming the pars tuberalis.
- The cells of the posterior wall form the pars intermedia.
- The infundibulum differentiates into the stalk and pars nervosa of the pituitary gland.
2. Thyroid Gland
Location:
- Lower part of front and sides of neck opposite C5, C6, and C7.
Parts:
- Two lateral lobes (right and left) extending from the middle of the thyroid cartilage to the fourth tracheal ring, connected by an isthmus from the 2nd to the 3rd tracheal rings.
- Sometimes, a third pyramidal lobe may project upward from the isthmus.
Capsules:
- Inner capsule: The true capsule formed by connective tissue condensation.
- Outer capsule: The false capsule derived from pretracheal fascia of the deep cervical fascia.
- Suspensory Ligament of Berry: A thickened false capsule connecting the medial surface of the lateral lobe to the cricoid cartilage, moving thyroid swellings upward during swallowing.
Relations:
- The lobes have conical shapes with apex, base, and three surfaces (lateral, medial, and posterolateral):
- Lateral Surface:
- Sternothyroid, sternohyoid, superior belly of omohyoid, and sternocleidomastoid muscles.
- Medial Surface:
- Contains trachea, esophagus, inferior constrictor, and cricothyroid muscles, as well as external and recurrent laryngeal nerves.
- Posterolateral Surface:
- Carotid sheath and common carotid artery.
- Isthmus Surfaces:
- Anterior: Relates to sternohyoid and sternothyroid muscles.
- Posterior: Relates to 2nd and 3rd tracheal rings.
Blood Supply:
- Arterial Supply:
- Superior thyroid artery, inferior thyroid artery, and sometimes thyroidea ima.
- Arteries anastomose profusely over the surface of the gland.
- Superior Thyroid Artery:
- A branch of the external carotid artery, descends to the upper pole of each lobe, accompanied by the external laryngeal nerve.
- Inferior Thyroid Artery:
- A branch of the thyrocervical trunk, ascends behind the gland to the cricoid cartilage's posterior border.
- Thyroidea Ima: If present, arises from the brachiocephalic artery or the arch of the aorta, ascending in front of the trachea to the isthmus.
- Venous Drainage:
- Superior Thyroid Vein: Drains into the internal jugular vein.
- Middle Thyroid Vein: Drains into the internal jugular vein.
- Inferior Thyroid Veins: Anastomose as they descend in front of the trachea, draining into the left brachiocephalic vein in the thorax.
Histology:
- Covered by a fibrous capsule from which septa extend into the parenchyma, dividing it into lobules and carrying blood vessels, nerves, and lymphatics.
- Parenchyma: Composed of rounded epithelial structures called thyroid follicles.
- Each follicle is lined by simple epithelium and has a central lumen filled with gelatinous colloid (contains glycoprotein thyroglobulin, precursor for active thyroid hormones).
- Follicular cells vary in shape from squamous to low columnar depending on functional activity.
- Active glands show more follicles of low columnar epithelium, while hypoactive glands have mostly squamous follicular cells.
- Parafollicular (C) Cells:
- Larger than follicular cells, stain lightly, and secrete calcitonin (suppressing bone resorption by osteoclasts).
Embryological Development:
- Begins during the third week as an entodermal thickening in the midline of the pharynx's floor between the tuberculum impar and the copula.
- Thickening becomes a diverticulum that grows inferiorly into the underlying mesenchyme, forming the thyroglossal duct.
- The duct elongates, and its distal end becomes bilobed, later forming the thyroid gland.
- The ultimobranchial bodies (from the fifth pharyngeal pouch) and neural crest cells integrate into the thyroid gland as parafollicular cells.
3. Parathyroid Gland
Location & Gross Features:
- Two pairs of small, yellowish-brown, ovoid structures, usually lying between the posterior border of the thyroid gland and its capsule.
- Size: 6 x 4 x 2 mm.
- Weight: 50 mg.
- Identification: Close to the anastomosis of the superior and inferior thyroid arteries.
Hormones Secreted:
- The parathyroid gland secretes parathormone, which controls calcium and phosphorus metabolism alongside calcitonin.
Blood Supply:
- Arterial Supply:
- Both superior and inferior parathyroid glands usually supplied by the inferior thyroid artery.
- Sometimes, the superior parathyroid is supplied by the superior thyroid artery or anastomoses between the superior and inferior thyroid arteries.
- Venous Drainage:
- Drains into plexus of veins on the anterior surface of the thyroid gland.
Lymphatics & Nerve Supply:
- Lymphatics:
- Numerous, associated with those of thyroid and thymus gland.
- Nerves:
- Sympathetic and parasympathetic nerves, believed to be vasomotor, though not secretomotor.
Histology:
- Each parathyroid gland enclosed within a capsule sending septa into the gland, merging with reticular fibers that support elongated cordlike clusters of secretory cells.
- Two types of cells present in parathyroid glands:
- Chief (Principal) Cells:
- Small polygonal cells with round nuclei and pale-staining, slightly acidophilic cytoplasm.
- Filled with secretory granules containing the polypeptide parathyroid hormone (PTH), a major regulator of blood calcium levels.
- Oxyphil Cells:
- Larger than chief cells, characterized by acidophilic cytoplasm filled with atypically shaped mitochondria.
- Some show low levels of PTH synthesis, suggesting these cells are transitional derivatives from chief cells.
Embryological Development:
- Superior parathyroid glands arise from the proliferation of endodermal cells in the fourth pharyngeal pouch on each side.
- Inferior parathyroid glands arise from the proliferation of endodermal cells in the third pharyngeal pouch on each side.
4. Adrenal Gland
Parts:
- Right adrenal is pyramidal in shape, with apex, base, anterior and posterior surfaces, and lateral and medial borders.
- Left adrenal is semilunar in shape, with upper and lower ends and anterior and posterior surfaces, as well as medial and lateral borders.
- Histologically, it consists of two parts: the outer cortex and inner medulla.
Relations:
- The right suprarenal gland is pyramidal.
- The base relates to the upper pole of the right kidney.
- The anterior surface relates to the liver laterally, inferior vena cava medially, and sometimes the duodenum inferiorly.
- The posterior surface relates to the right crus of the diaphragm.
- The left suprarenal gland is semilunar.
- The anterior surface relates to the cardiac end of the stomach, pancreas, and splenic artery.
- The posterior surface relates to the left crus of the diaphragm medially and the kidney laterally.
Blood Supply:
- Arterial Supply:
- Superior suprarenal artery (branch of inferior phrenic artery).
- Middle suprarenal artery (branch of abdominal aorta).
- Inferior suprarenal artery (branch of renal artery).
- Venous Drainage:
- Right suprarenal vein drains into the inferior vena cava.
- Left suprarenal vein drains into the left renal vein.
Histology:
- Covered by a fibrous capsule and divided into outer cortex and inner medulla.
- The adrenal cortex has three concentric zones with cords of epithelial cells arranged differently to produce different steroid hormones:
- Zona Glomerulosa:
- Consists of closely packed, rounded cords of columnar or pyramidal cells surrounded by many capillaries, secreting mineralcorticoids (mainly aldosterone).
- Zona Fasciculata:
- Occupies 65–80% of cortex; consists of long cords of large polyhedral cells, one or two cells thick, separated by fenestrated sinusoidal capillaries.
- Secretes glucocorticoids, especially cortisol.
- Zona Reticularis:
- Comprises about 10% of cortex; consists of smaller cells primarily secreting androgens (dehydroepiandrosterone, DHEA) converted to testosterone in several other tissues.
- Adrenal Medulla:
- Composed of large, polyhedral chromaffin cells arranged in cords or clumps, supported by reticular fibers with sinusoidal capillaries and few parasympathetic ganglion cells.
- Chromaffin cells are considered modified sympathetic postganglionic neurons lacking axons and dendrites but specialized for secretion of epinephrine and norepinephrine.
Embryological Development:
- Suprarenal cortex develops from coelomic mesothelium covering the posterior abdominal wall.
- Initially forms a fetal cortex, later covered by a second final cortex. After birth, the fetal cortex retrogresses, largely completing involution in the first few weeks.
- Suprarenal medulla is formed from sympatho-chromaffin cells of the neural crest that invade the cortex, leading the medulla to occupy a central position arranged in cords and clusters.
- Preganglionic sympathetic nerve fibers grow into the medulla and influence the activity of medullary cells.
5. Scrotum
Introduction:
- The scrotum is the outer covering of the testes, housing the testes, epididymis, and vas deferens.
- Scrotal skin is highly pigmented and hairy.
- Dartos muscle connects the scrotal skin to the deeper layer, contributing to the rugosity of the scrotal skin.
Coverings:
- Composed of five coverings:
- Outer skin (thin, wrinkled, pigmented).
- Dartos muscle (replacing superficial fascia).
- External spermatic fascia (derived from external oblique aponeurosis).
- Cremasteric muscle and fascia (derived from the internal oblique and transversus abdominis muscles).
- Internal spermatic fascia (derived from fascia transversalis).
Blood Supply:
- Arterial Supply:
- Superficial external pudendal artery (branch of the femoral artery).
- Deep external pudendal artery (branch of the femoral artery).
- Cremasteric branch of the inferior epigastric artery.
- Scrotal branch of the internal pudendal artery.
- Venous Drainage:
- Divided into anterior and posterior scrotal veins.
- Anterior scrotal veins drain into external pudendal vein (femoral vein).
- Posterior scrotal veins drain into deep dorsal vein of penis (internal pudendal vein).
Nerve Supply:
- Anterior 1/3:
- Supplied by the ilioinguinal nerve, genital branch of the genitofemoral nerve.
- Posterior 2/3:
- Supplied by scrotal branch of the pudendal nerve, perineal branch of the posterior cutaneous nerve of the thigh.
- Dartos Muscle:
- Involuntary, supplied by sympathetic fibers via the genital branch of the genitofemoral nerve.
Lymphatic Drainage:
- Drain into superficial inguinal lymph nodes.
6. Vas Deferens
Extent:
- The vas deferens is about 45 cm long when straightened.
- A thick-walled muscular duct transmitting spermatozoa, extending from the epididymis to the ejaculatory duct.
Blood Supply:
- Arterial Supply:
- Terminal branches of the superior vesical artery and also from the inferior vesical artery.
- Venous Drainage:
- Drains into the vesical venous plexus, which opens into the internal iliac vein.
Histology:
- Composed of three layers: mucosa, muscularis externa, and adventitia.
- Mucosa:
- Forms low longitudinal folds, lined by a pseudostratified columnar epithelium with long stereocilia.
- Muscularis Externa:
- Well-developed (1.5 mm thick), consists of thick circular layer of smooth muscle between thinner inner and outer longitudinal layers.
- Adventitia:
- Dense, made up of loose connective tissue with blood vessels, nerves, and lymphatics.
Embryological Development:
- The urogenital system develops from the intermediate mesoderm extending along the dorsal body wall of the embryo; nephrogenic cord → mesonephric ridge → mesonephros.
- The mesonephros develops and disappears, with its duct, the mesonephric duct, forming the male reproductive duct system; vas deferens is developed from the middle part of the mesonephric duct (Wolffian duct).
7. Penis
Parts:
- The penis is the male copulatory organ, divided into root (attached part) and body (free part).
- Root:
- Made up of three masses of erectile tissue:
- 2 crura (attached to the margin of the pubic arch, covered by ischiocavernosus).
- 1 bulb (attached to the perineal membrane, covered by bulbospongiosus).
- Body (Shaft):
- Composed of three masses of erectile tissue:
- Two corpora cavernosa (dorsal masses containing deep arteries).
- One corpus spongiosum (a single ventral mass containing the penile urethra and artery of the bulb, expanding terminally as the glans penis).
Structure:
- Skin: Thin, hairless, forming a fold over the glans penis called the prepuce (foreskin).
- Superficial Fascia: Loose areolar tissue, contains the superficial dorsal vein of the penis (no fat).
- Deep Fascia (Buck's Fascia): Surrounds all three masses of erectile tissue but does not extend into the glans.
- Deep Layer: Contains deep dorsal vein, dorsal arteries, and dorsal nerve.
Blood Supply:
- Arterial Supply:
- Internal pudendal artery supplies the deep artery of the corpus spongiosum, dorsal artery, and artery of the bulb in the anterior part of the corpus spongiosum.
- Femoral artery gives rise to the superficial external pudendal artery, supplying the skin and fascia of the penis.
- Venous Drainage:
- Superficial Dorsal Vein: Drains into the superficial external pudendal vein.
- Deep Dorsal Vein: Drains into the prostatic plexus of veins.
Embryological Development:
- Genital Tubercle: Develops ventral to the cloacal membrane during the 4th week, elongating to form a phallus with a urethral groove on its ventral surface.
- Genital swelling becomes the penis (testosterone promotes elongation of the phallus into the penis).
8. Testis
Shape and Measurements:
- Oval/ellipsoid in shape.
- Dimensions: 4.5 cm in length, 2.5 cm breadth, 3 cm in antero-posterior diameter.
- Weight: About 10 to 14 gm.
Coverings:
- Three Coats:
- Tunica Vaginalis: Persistent portion of the processus vaginalis, consists of parietal and visceral layers with a cavity in between (covers the entire testis except the posterior border).
- Tunica Albuginea: Dense, white fibrous coat covering the testis.
- Thickened at the posterior border to form the mediastinum testis.
- Numerous septa extend from the mediastinum to the inner surface of the tunica albuginea, dividing the testis into 200-300 lobules.
- Tunica Vasculosa: Innermost, vascular coat lining its lobules.
Internal Structure of Testis:
- Composed of:
- Septa
- Seminiferous tubule
- Lobule
- Straight tubule
- Efferent ductules
- Rete testis
Descent:
- Develops in lumbar region at levels T10-T12, descending during intrauterine life:
- At 2 months: Descends to the inguinal fossa.
- At 3 months: Rests at the deep inguinal ring (4th to 6th month).
- At 7 months: Passes through the inguinal canal.
- At 8 months: Passes through the superficial inguinal ring.
- By 9 months: Reaches the scrotum.
Applied Anatomy of Testis:
- Cryptorchidism: Undescended testis.
- Anorchism: Absence of both testes.
- Monorchism: Absence of one testis.
Blood Supply:
- Arterial Supply:
- Testicular artery, a branch from abdominal aorta descends to deep inguinal ring, dividing at the posterior border to supply the testis.
- Venous Drainage:
- Pampiniform Plexus: Divides into 4 veins at the superficial inguinal ring and into 2 veins at the deep inguinal ring; drains into IVC (right side) and left renal vein (left side).
Histology:
- Surrounded by tunica albuginea from which fibrous septa penetrate, dividing into lobules, each lobule containing 1-4 seminiferous tubules lined by stratified epithelium with Sertoli cells and spermatogenic lineage.
- Spermatogenic Cells:
- Undergo mitosis to become primary spermatocytes, which then divide to secondary spermatocytes, eventually forming spermatids, which differentiate into sperm cells.
- Leydig Cells:
- Interstitial cells producing testosterone responsible for secondary male sex characteristics.
Embryological Development:
- The Y chromosome induces the genital ridge to secrete testosterone, developing the testis and other reproductive organs.
- Sex cords within genital ridges separate from coelomic epithelium due to mesenchyme proliferation and condense to form the tunica albuginea.
- U-shaped cords form seminiferous tubules, eventually joining to form the rete testis.
9. Prostate
External Features:
- Contains a base, apex, and four surfaces:
- Anterior surface
- Posterior surface
- Right inferolateral surface
- Left inferolateral surface
Lobes:
- Incompletely divided into five lobes:
- Anterior Lobe:
- Lies in front of the urethra, devoid of glandular tissue.
- Median (Middle) Lobe:
- Situated between the urethra and the ejaculatory ducts, rich in glands.
- Posterior Lobe:
- Located behind the urethra and below the ejaculatory ducts, containing glandular tissue.
- Right and Left Lateral Lobes:
- Positioned on either side of the urethra, also rich in glands.
Capsule:
- Inner Capsule:
- True capsule formed by condensation of the peripheral part of the gland, fibromuscular, continuous with the stroma of the gland.
- Contains no venous plexus.
- Outer Capsule:
- Made of pelvic visceral fascia.
- Prostatic venous plexus embedded in it on each side.
Structure:
- Made up of fibromuscular stroma and glandular tissue:
- Composed of 1/4 fibrous tissue, 1/4 muscular tissue, and 1/2 glandular tissue.
- Glandular tissue comprises 30-50 tubuloalvelolar glands arranged in concentric groups:
- Mucosal: Inner layer.
- Submucosal: Intermediate layer.
- Main Prostatic Gland: Peripheral layer around the prostatic urethra.
Relations:
- Superior:
- Base continuously relates to the neck of the bladder; urethra enters the center of the base.
- Inferior:
- Apex lies on the upper surface of the urogenital diaphragm.
- Anterior:
- Related to the symphysis pubis, separated by extraperitoneal fat.
- Posterior:
- Closely related to the anterior surface of the rectum, separated by the rectovesical septum.
- Lateral:
- Side walls of the pelvis, levator ani muscles.
Blood Supply:
- Arterial Supply:
- Supplied by branches from internal pudendal, middle rectal, and inferior vesical arteries.
- Branches form a large outer subcapsular plexus and a small inner periurethral plexus.
- Venous Drainage:
- Rich plexus around the sides and base of the gland forming the prostatic venous plexus outside the capsule.
- Communication exists between prostatic and vertebral venous plexus allowing carcinoma to spread.
Histology:
- Prostate is a fibromuscular glandular organ consisting of 30–50 branched tubulo-alveolar glands surrounded by dense fibro muscular stroma covered by a capsule.
- Each gland has its duct, delivering the secretory product to the prostatic urethra.
- Stroma comprises collagen and smooth muscle fibers.
- Glands are arranged in concentric layers around the urethra: inner mucosal glands, intermediate submucosal glands, and peripheral main glands.
- Tubuloalveolar glands lined by simple or pseudostratified columnar epithelium with wide lumens possibly containing colloid masses (amyloid bodies) and calcified concretions (corpus amylacea).
- Glands secrete prostatic fluid containing glycoproteins and enzymes.
Embryological Development:
- Develops from endodermal buds from the lining of the primitive urethra and adjacent portions of the urogenital sinus within the first three months of intrauterine life.
- Surrounding mesenchyme condenses to form the gland's stroma.
- Prostatic utricle is the remnant of the paramesonephric duct, central zone of glandular tissue derived from mesonephric duct.
10. Ovary
Parts:
- Two poles: upper/tubal pole and lower/uterine pole.
- Two borders: anterior (mesovarian) border and posterior (free) border.
- Two surfaces: lateral and medial surfaces.
Relations:
- Peritoneal Relation:
- Almost entirely covered by peritoneum except for anterior border; two peritoneal layers reflected onto the posterior layer of the broad ligament of the uterus, connected to the posterior layer of the broad ligament by a short fold (mesovarium).
- Lateral part of broad ligament extending from the infundibulum of the uterine tube to the upper pole of the ovary forms the suspensory ligament of the ovary.
- Visceral Relation:
- The upper pole (tubal end) attaches to ovarian fimbria of the infundibulum, the lower pole (uterine end) connects to the upper end of the lateral border of the uterus via the ovarian ligament.
- The lateral surface relates to the floor of ovarian fossa with obturator nerves and vessels, and the medial surface overlaps the uterine tube.
Blood Supply:
- Arterial Supply:
- Ovarian artery arises from the abdominal aorta, descends over the posterior abdominal wall, enters suspensory ligament and branches to the ovary through mesovarium.
- Uterine artery provides some branches reaching the ovary via mesovarium.
- Venous Drainage:
- Pampiniform plexus of veins merges at hilus into single ovarian vein, draining into inferior vena cava (right side) and left renal vein (left side).
Lymphatic Drainage:
- Lymph vessels of the ovary follow the ovarian artery, draining into para-aortic nodes at the level of the first lumbar vertebra.
Histology:
- Covered by simple cuboidal epithelium (germinal epithelium), continuous with the mesothelium; overlaid by dense connective tissue capsule (tunica albuginea).
- Outer cortex filled with cellular connective tissue stroma and many ovarian follicles at various stages of development.
- At puberty, follicle-stimulating hormone (FSH) from the pituitary initiates monthly primordial follicular growth.
- Follicular cells undergo mitosis, forming a simple cuboidal epithelium around growing oocytes (unilaminar primary follicle), proliferating further to form multilayered primary follicles (granulosa).
- zona pellucida develops between oocyte and granulosa cells.
- As follicles develop, follicular fluids accumulate, forming secondary or antral follicles.
- Theca Cells: Surrounding stromal cells differentiate into theca interna (secreting estradiol) and theca externa.
- Each menstrual cycle usually allows one follicle to mature into a Graafian follicle, releasing the oocyte.
- Medulla: Composed of loose connective tissue, blood vessels entering through the hilum from suspending mesenteries.
Embryological Development:
- The female sex chromosome leads the genital ridge on the posterior abdominal wall to secrete estrogens; the presence of estrogen and absence of testosterone promote ovarian and other female genital organ development.
- Primordial germ cells within sex cords become separated by proliferating mesenchyme, forming clusters, eventually differentiating into oogonia.
- Primary oocytes form by mitotic divisions within the cortex by the third month, surrounded by granule cells (forming primordial follicles).
- Many primordial follicles degenerate while mesenchyme forms the ovarian stroma.
11. Uterus
Parts:
- Divided into fundus, body, and cervix:
- Fundus: Part of the uterus lying above the entrance of the uterine tubes.
- Body: The portion below the uterine tube entrance.
- Cervix: Narrow part piercing the anterior wall of the vagina, divided into supravaginal and vaginal parts.
- The cervical canal maintains communication with the body through the internal os and with the vagina through the external os.
Position:
- The non-pregnant uterus resides within the pelvis, positioned in anteversion and anteflexion.
- Anteversion: Long axis of the cervix is bent forward on the vagina, forming an angle of about 90°.
- Anteflexion: Long axis of the body is bent forward on the cervix at the isthmus/internal os, forming an angle of about 170°.
Relations:
- Anterior Relations:
- Body relates to the uterovesical pouch and superior surface of the urinary bladder.
- Supravaginal cervix relates to the posterior surface of the urinary bladder.
- Vaginal portion corresponds to anterior fornix.
- Posterior Relations:
- Fundus, body, and supravaginal cervix covered by peritoneum relate to the rectouterine pouch (pouch of Douglas) separating the uterus from the rectum while containing coils of ileum and sigmoid colon.
- Lateral Relations:
- Body related to broad ligament and uterine artery/vein; supravaginal cervix relates to ureter and uterine artery.
- Vaginal cervix relates to lateral fornices of vagina.
Support:
- The uterus is supported by various structures to prevent sagging:
- Primary Supports:
- Muscular:
- Pelvic diaphragm (Levator ani muscle).
- Perineal body.
- Urogenital diaphragm.
- Fibromuscular:
- Transverse cervical ligaments (Meckendrot’s ligament or cardinal ligament).
- Pubocervical ligaments.
- Uterosacral ligaments.
- Round ligaments.
- Visceral:
- Urinary bladder.
- Vagina.
- Uterine axis.
- Secondary Supports:
- Ligament and peritoneal folds:
- Broad ligaments.
- Uterovesical fold of peritoneum.
- Rectovaginal fold of peritoneum.
Blood Supply:
- Arterial Supply:
- Primarily supplied by the uterine artery (branch of internal iliac artery).
- It runs medially at the broad ligament base, crosses above the ureter, reaching the cervix at the internal os, subsequently ascending along the uterus' lateral margin, anastomosing with the ovarian artery.
- Uterine artery provides a small descending branch for cervix and vagina.
- Venous Drainage:
- Uterine and vaginal veins form a plexus draining into the internal iliac veins.
Lymphatic Drainage:
- Cervix:
- Drains posteriorly to sacral lymph nodes, laterally to internal and external iliac nodes. - Body of Lower Uterus:
- Drains to external iliac nodes. - Fundus & Fallopian Tube:
- Drain along ovarian vessels to lateral aortic nodes, some to external iliac nodes, and along round ligament of uterus to superficial inguinal lymph nodes.
Applied Anatomy of Uterus:
- Intrauterine Contraceptive Device (IUCD).
- Caesarean section.
- Retroverted uterus.
- Prolapse.
Histology:
- The uterine wall consists of three layers:
- Perimetrium: Outer connective tissue layer, largely serosa covered by mesothelium.
- Myometrium: Middle layer consisting of highly vascular smooth muscle.
- Composed of interwoven layers of smooth muscle fibers (longitudinal and circular).
- Thickest layer with larger blood vessels.
- Endometrium: Mucosa with simple columnar epithelium (ciliated and secretory); lamina propria contains collagen fibers, fibroblasts, ground substance, and numerous tubular uterine glands.
- Subdivided into basal layer (remains unchanged during menstrual cycle) and functional layer (undergoes changes).
Embryological Development:
- Derived from fused caudal parts of paramesonephric ducts; their angular junction forms the fundus. - Initially, ducts fuse incompletely, persisting a septum. - Later, the septum disappears, resulting in a single cavity for the body and cervix. - Myometrium is formed from surrounding mesenchyme.
12. Uterine Tube (Fallopian Tube)
Parts:
- Each tube has four parts:
- Infundibulum: funnel-shaped lateral end projecting beyond the broad ligament, with fimbriae over the ovary.
- Ampulla: widest part of the tube.
- Isthmus: narrowest part of the tube, lateral to the uterus.
- Intramural part: segment piercing the uterine wall.
Blood Supply:
- Arterial Supply:
- Uterine artery (internal iliac artery) and ovarian artery (abdominal aorta).
- Venous Drainage:
- Lateral 2/3 drained by pampiniform plexus → ovarian vein → inferior vena cava (right side) and renal vein (left side).
- Medial 1/3 drained by uterine plexus → internal iliac vein.
Lymphatic Drainage:
- Lymph vessels follow veins, draining into internal iliac, pre-aortic, and para-aortic lymph nodes.
Histology:
- Composed of three layers:
- Inner Mucosa: Longitudinal folds lined by simple columnar epithelium (ciliated and non-ciliated peg cells).
- Peg cells provide a nutritive environment for spermatozoa.
- Ciliated cells propel the fertilized ovum and spermatozoa toward the uterus.
- Middle Muscularis: Inner circular and outer longitudinal smooth muscle layers.
- Outer Serosa: Loose connective tissue lined by simple squamous epithelium.
Embryological Development:
- Early in development, the paramesonephric ducts (Müllerian ducts) appear on the lateral side of the mesonephros, forming the uterine tube on both sides from the cranial vertical and middle horizontal segments.
13. Vagina
Extent:
- The vagina is the female copulatory organ and forms the lower part of the birth canal, a distensible fibromuscular tube extending from the vestibule (in the perineum) to the cervix of the uterus located above.
- Lies between the urinary bladder and urethra in front and rectum & anal canal behind.
Dimension:
- Anterior wall: 7.5 cm; Posterior wall: 9 cm.
- Diameter at lower end: 2.5 cm; Diameter at upper end: 5 cm.
- Luminal shape varies: lower end (H-shaped), middle third (transverse slit), and upper third (round/circular).
Relations:
- Anterior Relations:
- Related to bladder above and urethra below.
- Posterior Relations:
- Upper third is related to rectouterine pouch; middle third to ampulla of rectum.
- Lower third related to perineal body, separating it from the anal canal.
- Lateral Relations:
- Upper part relates to ureter; middle part related to anterior fibers of the levator ani and lower part relates to the urogenital diaphragm and bulb of the vestibule.
Blood Supply:
- Arterial Supply:
- Above the levator ani, supplied by uterine and vaginal arteries; below the levator ani by the internal pudendal artery.
- Form anastomosis in the middle of anterior and posterior walls.
- Venous Drainage:
- Plexus of veins forms vaginal vein draining into the internal iliac vein.
Nerve Supply:
- Upper two-thirds supplied by autonomic nerves from the uterovaginal plexus (sympathetic and parasympathetic); sympathetic fibers from L1 and L2, and parasympathetic from pelvic splanchnic nerves (S2, S3).
- Lower one-third is pain-sensitive, supplied by pudendal nerve through inferior rectal and posterior labial branches of perineal nerve.
Lymphatic Drainage:
- Upper third drains to external and internal iliac nodes, middle third to internal iliac nodes, and lower third to superficial inguinal nodes.
Histology:
- Composed of three layers:
- Mucosa: Lined with thick stratified squamous non-keratinized epithelium stimulated by estrogen to synthesize and store glycogen.
- Lamina propria consists of loose fibroelastic connective tissue with a rich vascular supply.
- No glands; vaginal fluid increase during sexual stimulation is from transudate and cervical secretions.
- Muscularis Layer: Composed of smooth muscle cells arranged in outer longitudinal and inner circular layers.
- Adventitia: Composed of fibroelastic connective tissue with blood vessels, nerves, and lymphatics.
Embryological Development:
- Developed from the wall of the urogenital sinus, with fused lower ends of paramesonephric ducts forming the body and cervix, and outgrowths from the urogenital sinus forming the sinovaginal bulbs.
- Sinovaginal bulbs proliferate, forming the vaginal plate, which canalizes to form vaginal fornices.
Notes Diagrammed Information
(Refer to the accompanying diagrams for anatomical contexts)