Abdomen and Pelvic Cavity Outline Week 12

• The abdomen sits between the inferior thorax and superior pelvis.
• The inferior thoracic aperture forms the superior border of the abdomen.
• The pelvic inlet is the inferior border.
• Posteriorly, the lumbar vertebrae define it.
• The abdomen can stretch up to the 4th intercostal space when the diaphragm is relaxed.
• It is continous with the pelvic cavity inferiorly.
• Acts as a chamber that houses and protects major visceral organs, aids in breathing by relaxing during inspiration, and provides trunk support.
• Has two components, the abdominal wall and the abdominal cavity.

Abdominal Wall Layers

• It extends from the thoracic cage to the pelvis.
• The boundaries between anterior and lateral walls lack defined borders.
• The anterolateral wall consists of skin, fascia and muscle.
• From superficial to deep, the layers are: Skin > Camper's Fascia > Scarpa's Fascia > External Oblique > Internal Oblique > Transverse Abdominis > Transversalis Fascia > Extraperitoneal fat > Parietal Peritoneum.
• Superficial fascia includes Camper's Fascia (fatty) and Scarpa's Fascia (membranous).
• Deep fascia, also known as the transversalis fascia, is the lining of the transverse abdominis.
• The parietal peritoneum lies deep to the transversalis fascia, separated by varying amounts of fat.

Abdominal Muscles

• External Oblique (EO) has an inferior end that folds back to form the inguinal ligament.
• Internal Oblique (IO) is another muscle layer.
• Transversus Abdominis (TA) is a transverse muscle.
• Rectus Abdominis runs vertically.
• Rectus Sheath encloses the rectus abdominis.
• EO, IO, and TA muscles continue anteriorly and medially, forming strong aponeuroses.
• The rectus abdominis muscles are surrounded by these aponeuroses, which interweave in the midline to form the linea alba.

Abdominal Wall Functions

• Anterolateral abdominal muscles support the abdominal cavity.
• Protect the abdominal cavity from injury.
• Compress the abdominal cavity to increase intra-abdominal pressure, assisting expiration and relating to the pelvic floor.
• Aid in moving the trunk and maintaining posture.

Inguinal Canal

• A passageway in the inferior anterior abdominal wall.
• In males, it allows passage of the spermatic cord.
• In females, it allows passage of the round ligament.
• It has two openings called superficial and deep inguinal rings.
• In males, the contents include the vas deferens, testicular artery and pampiniform plexus, sympathetic fibers, genitofemoral and ilioinguinal nerves.
• In females, the round ligament of the uterus and the ilioinguinal nerve.

Abdominal Wall Innervation

• Anterior rami innervate the anterolateral wall.
• Thoracoabdominal (intercostal) nerves (T7-T11), subcostal N. (T12), ilioinguinal N. (L1) and iliohypogastric N. (L1) are all anterior rami
• The abdominal wall is innervated segmentally, reflecting overlying dermatome patterns.
• T6 corresponds to the xiphoid process, T10 to the umbilicus, and L1 to the inguinal ligament.

Abdominal Wall Blood Supply

• The superior wall receives blood from branches of the internal thoracic artery.
• The inferior wall is supplied by branches of the femoral and external iliac arteries.
• The lateral wall receives blood from branches of the abdominal aorta.
• Superficial veins drain into the femoral vein below the umbilicus and into the axillary vein above it.
• Superficial lymphatics follow superficial veins to femoral and axillary lymph nodes.
• Deep lymphatics run with deep veins of the abdomen.

Posterior Abdominal Wall

• Superior border: diaphragm.
• Inferior border: pelvic brim.
• Lateral border: anterolateral abdominal wall muscles.
• Medial border: lumbar vertebral bodies.
• Includes the iliacus, psoas major, and quadratus lumborum muscles.
• The nerves consist of the subcostal nerve (T12), anterior rami of lumbar spinal nerves, and lumbar plexus.

Abdominal Cavity Lining

• The peritoneum is the serous membrane lining the abdominal cavity.
• Parietal peritoneum surrounds the abdominal wall.
• Visceral peritoneum surrounds internal organs.
• The peritoneal cavity is the space between parietal and visceral peritoneum, filled with fluid.
• Mesentery is the continuation of visceral and parietal peritoneum that attaches organs to the body wall.
• Retroperitoneal space is posterior to the peritoneum.
• The omentum is an extension of the peritoneum passing from the stomach to adjacent organs.
• The greater omentum hangs like an apron from the greater curvature of the stomach.
• The lesser omentum is smaller, connecting the lesser curvature of the stomach to the liver.

Abdominal Regions and Quadrants

• There are nine regions: right hypochondrium, epigastric, left hypochondrium, right flank, umbilical, left flank, right inguinal, pubic, and left inguinal.
• Four quadrants formed by the intersection of the transumbilical and median planes.
• They include the right upper, left upper, right lower, and left lower quadrants.

Abdominal Viscera - GI Tract

• The GI tract organs include the esophagus, stomach, small intestine, large intestine, and liver.
• The esophagus is a muscular tube transporting food to the stomach through the lower esophageal sphincter.
• The stomach receives, digests, and passes food to the duodenum.
• Includes the cardia (superior opening), fundus (convex superior portion), body (main part), and pylorus (distal portion with pyloric sphincter).
• Also has lesser and greater curvatures.
• The small intestine includes the duodenum, jejunum, and ileum.
• The duodenum is continuous with the stomach and receives ducts from the pancreas, liver, and gallbladder.
• The large intestine absorbs fluids and salts.
• It consists of the cecum (first part), appendix (intestinal diverticulum), colon (ascending, transverse, descending, sigmoid), rectum (fixed, terminal part), and anal canal.
• Bile is produced which emulsifies fat, excretes bile, stores glycogen, and detoxifies.
• The liver has right and left lobes, caudate lobe (between IVC and porta hepatis), quadrate lobe (near gallbladder).
• The porta hepatis is located at the fissure between caudate and quadrate lobes and contains the portal triad (portal vein, hepatic artery, and bile ducts).
• Supported by the coronary ligament (diaphragm to liver) and the round ligament (umbilicus to liver).
• Stores bile produced by the liver
• Releases bile intermittently when fat enters the duodenum to emulsify fat.
• Common hepatic ducts combine with the cystic duct to form the common bile duct.
• Has a body and fundus.

Pancreas and Spleen

• The pancreas is an accessory digestive gland.
• Retroperitoneal, crosses body at L1-L2 vertebra
• Pancreatic duct begins in the tail and passes to the duodenum
• The tail extends toward spleen
• The 3 Parts include the head is in the concavity of the duodenum, the body and the tail
• Exocrine secretion (pancreatic juices, bicarbonate) that enters duodenum via pancreatic duct
• Endocrine secretion (insulin and glucagon) that enters the blood
• The spleen's performs immune function, blood storage and clearance of damaged/old red blood cells.
• Stores RBCs and platelets
• Contains largest lymphatic organ – lymphocyte proliferation and immune system functions

Kidney and Ureter

• Remove excess water, salts and wastes
• Retroperitoneal
• Important landmarks:
  • Cortex – outer region, has nephrons
  • Internal projects between each renal pyramid is called a Renal Column
  • Medulla - middle region, has renal pyramids and columns
  • Renal Pyramids consist of ducts, loops of Henle, and capillaries
  • Calyces collecting ducts for urine exiting the pyramids
  • Renal Pelvis – funnel-shaped expansion of the superior end of ureter
  • Renal hilum – medial margin of the kidney where renal vessels, lymphatics and nerves access the kidney
  • Renal Artery – Branch of the abdominal Aorta
  • Renal Vein – Drains into the IVC
  • Ureters - transports urine to the bladder descending anterior to the psoas major into the pelvis

Adrenal (suprarenal) Glands

• Help regulate metabolism, immune system, blood pressure, and stress responses
• Between superior kidney and inferior diaphragm
• Adrenal Cortex – regulated by endocrine system, produces corticosteroids
• Adrenal Medulla – inner region regulated by the sympathetic nerves, produces catecholamines

Arteries of the Abdomen

• Abdominal Aorta:
  • Begins once the thoracic aorta passes through the aortic hiatus of the diaphragm
  • Bifurcates into R/L Common Iliac A.
  • R/L Common Iliac A. branches into External and Internal Iliac A.
• Anterior Branches of the Abdominal Aorta:
  • Celiac Trunk:
    • Splits into Left Gastric A., Splenic A., and Common Hepatic A.
    • Serves esophagus, stomach, proximal duodenum, liver/gallbladder, pancreas, spleen
  • Superior Mesenteric Artery:
    • Supplies distal duodenum, jejunum, ileum, cecum, ascending colon, proximal 2/3rds of transverse colon
  • Inferior Mesenteric Artery:
    • Supplies distal 1/3rd of transverse colon, descending colon, sigmoid colon, rectum
• Lateral Branches of the Abdominal Aorta:
  • R/L Renal Artery
  • Gonadal A.

Veins of the Abdomen

• Tributaries of the Inferior Vena Cava:
  • Begins at R/L Common Iliac A.
  • Other tributaries correspond with arteries of the same name:
    • Lumbar Vs.
    • Renal Vs.
    • Gonadal Vs.
    • Hepatic V.
  • Caval System (system):
    • External and Internal Iliac V. converge to form the R/L Common Iliac V.
  • R/L Common Iliac V. come together to form the Inferior Vena Cava
    • Renal Vein – drain blood from the kidney
    • Hepatic Veins – drain blood from the liver

Portal System (to liver):

- Hepatic Portal Vein:
    - Main channel of the portal venous system
    - Formed by the union of the superior mesenteric, inferior mesenteric, and splenic veins
        - Drain the stomach, small intestine, large intestine, pancreas, and spleen
        - Carries blood filled with metabolites absorbed in the intestine to the liver

Nerves to the abdominal organs

• Autonomic innervation via splanchnic nerves and vagus nerve (CN X)
  • Sympathetic: fight or flight - decrease GI function and stimulate continence
    • Travel via spinal nerves to sympathetic trunks and continuing as abdominopelvic splanchnic nerves
    • Abdominopelvic splanchnic nerves convey signals to the abdominal aortic plexus where they then cluster around major branches of the aorta
• Parasympathetic: rest and digest - increases GI function and stimulate defecation
  • Vagus N. – parasympathetic fibers for esophagus through transverse colon
  • Pelvic splanchnic nerves (anterior rami S2-S4) – descending colon and rectum
• Visceral afferent innervation accompanies the sympathetic motor fibers
• Peritoneal Innervation:
  • Parietal Peritoneum:
    • Blood, lymphatic, and nerve supply follow the region of the abdominopelvic wall it lines
    • Sensitive to pain, heat and cold, and laceration
      • Pain is well localized
  • Visceral Peritoneum:
    • Blood, lymphatic, and nerve supply follows the visceral nerve supply of the organ it covers
    • Insensitive to touch, heat and cold, and laceration
    • Stimulated by stretch and chemical irritation
      • Poorly localized

Pelvic Regions

• False Pelvis - Above the pelvic inlet
  • Superior part of the pelvic bones and lower lumbar vertebrae
  • Associated with abdomen and generally considered part of the abdominal cavity
• True Pelvis - Area between the pelvic inlet and outlet
  • Encloses pelvic cavity
• Perineal Region (Not within the pelvic cavity itself)
  • Region between the thighs and buttocks from the pubis to the coccyx below
  • Consists of soft tissue below the pelvic diaphragm between the base of the thighs
  • Contains passages to reproductive, urinary, and GI systems
  • Divided into urogenital and anal triangles

Pelvic Cavity

• Pelvic Portion of the abdominopelvic cavity (continuous with abdominal cavity)
  • Enclosed by true pelvis
  • Bounded by:
    • Pelvic Inlet – demarcation between true and false pelvis (pelvic brim)
    • Pelvic Outlet – ischiopubic ramus, ischial tuberosities, sacrotuberous ligament, sacrum/coccyx

Pelvis Walls

• Bones:
  • Inferior portions of the pelvis, Coccyx, Sacrum
• Ligaments:
  • Sacrospinous & Sacrotuberous
• Muscles:
  • Obturator Internus & Piriformis

Anatomical Sexual Differences

• The pelvis is the most sexually dimorphic (two distinct forms) part of the skeleton.
  • Female - shorter and wider for childbearing
  • Male

GI Pelvic Viscera

• Rectum - located superior to the pelvic diaphragm in the pelvic cavity
• Anal Canal – perineal structure within the anal triangle, final passage for feces excretion through the anus
  • Sphincters:
    • Internal Anal Sphincter – Smooth muscle, Involuntary control
    • External Anal Sphincter – Skeletal muscle, Voluntary control
  • Pectinate Line – creates superior and inferior divisions of the anal canal
    • Superior (visceral portion) - Involuntary motor, unconscious sensory innervations
    • Inferior (skeletal portion) - Voluntary motor, and conscious sensory (pain) innervations

Urinary Pelvic Viscera

- Ureters - Muscular tubes caring urine to the bladder from the kidney

• Bladder - Most anterior pelvic viscera
  • Detrusor Muscle - Smooth muscle of the bladder wall
  • Structures:
    • Apex - near pubic symphysis
    • Base - posterior surface
    • Upper corners of the base where the ureters enter the bladder
    • Inferolateral surfaces (2)
    • Cradled by the levator ani and obturator internus muscles
    • Neck - forms attachment for urethra
    • Urethra - Different course between males and females
• Female:
  • Short, straight
  • Opens between labia minora
  • Passes through the pelvic diaphragm, external urethral sphincter, and perineal membrane
• Male:
  • Long, bending
  • 4 parts:
    • Preprostatic Urethra - Surround by internal urethra sphincter
    • Prostatic Urethra - Passes through the prostate, ejaculatory ducts enter here
      • Where urinary and reproductive tracks merge
    • Membranous Urethra- Passes through deep perineal pouch and perineal membrane
      • Surrounded by external urethra sphincter
    • Spongy (penile) Urethra - Courses through the corpus spongiosum of the penis and ends in external urethral orifice
  • Internal Urethral Sphincter - Smooth muscle, involuntary control
  • External Urethra Sphincter - Skeletal muscle, voluntary control

Pelvic Vasculature

• Arteries:
  • R./L External Iliac A. runs in the pelvic cavity, but is the mainly supplier of the lower limb
    • Becomes Femoral A. once it passes the inguinal ligament
  • R/L Internal Iliac A:
    • Branches to pelvic organs (bladder, uterus, vagina, rectum) and wall
  • Branches to perineum
  • Branches to proximal leg
  • Superior and Inferior gluteal As. to gluteal muscles
  • Obturator A. to medial thigh muscles = adductor group

Veins

• R/L External Iliac V. runs in the pelvic cavity, but is the main drainage route for the lower limb
• Transitions from Femoral V. proximal to the inguinal ligament
• Pelvic organs drain via interconnected venous plexuses associated with various organs
• Drain into the Internal Iliac V.

Pelvic Innervation

• Receives somatic and autonomic innervation
• Somatic:
  • Obturator N., Femoral N., Sacral Plexus
  • Innervates skeletal muscle and skin of the pelvic region
• Autonomic:
  • Innervation from Inferior Hypogastric Plexus:
    • Sympathetic fibers from Sacral Splanchnic Nerves
    • Vasoconstriction, inhibits peristalsis, contraction of internal sphincters, ejaculation
  • Parasympathetic – Pelvic Splanchnic Nerves
    • Vasodilation, stimulates peristalsis, relaxation of internal sphincters, erection