Abdominal Muscles: Anatomy Overview

• Surface anatomy requires knowledge of the nine regions of the abdomen.
• Locations and innervations for lateral and medial muscle groups must be known.

Lateral Abdominal Muscles

• Consists of the external abdominal oblique, internal abdominal oblique, and transversus abdominis, from outermost to innermost.

Medial Abdominal Muscles

• Consists of the rectus abdominis and pyramidalis, near the pubic symphysis.
• Innervation for all muscles in the lateral and medial groups comes from the lower 6 intercostal nerves and L1.
• The inguinal ligament originates from the external abdominal oblique muscle.
• The lowest portion of its aponeurosis rolls in on itself.
• Travels from the anterior superior iliac spine to the pubic tubercle.
• Serves as a landmark structure.

Cremaster Muscle

• Originates from the caudal part of the internal abdominal oblique muscle.
• Innervated by the genital branch of the genitofemoral nerve.
• Cremasteric reflex is not a pathology.
• Palpating the upper thigh in cases of trauma or masses to the testes causes the cremaster muscle to contract, indicating the genitofemoral nerve is functioning.
• The rectus sheath's location includes the aponeurosis of the external and internal oblique muscles, with the internal oblique dividing into two layers that wrap around the rectus sheath.
• The aponeurosis of the transversus abdominis lies posteriorly.
• Contents include the rectus abdominis muscle, inferior and superior epigastric vessels, and the lower 5 intercostal nerves, including the subcostal nerve.

Inguinal Canal

• Deep Inguinal Ring constitutes the internal opening and a gap in the fascia transversalis.
• Superficial Inguinal Ring forms as a gap in the aponeurosis of the external abdominal oblique muscle.
• Male contents include the spermatic cord.
• Female contents include the round ligament of the uterus and lymphatics.

Cryptorchidism

• Testes fail to descend and must be removed before they turn cancerous.

Hydrocele of the Cord

• The process vaginalis fails to close; fluid forms around the spermatic cord, which should be removed and sutured.
• The spermatic cord contains the ductus deferens, testicular artery, artery of the ductus deferens, cremaster artery, pampiniform plexus (testicular veins), autonomic nerve fibers, the genital branch of the genitofemoral nerve, lymphatics, and the cremaster muscle.

Inguinal Hernia

• Direct inguinal hernia runs parallel to the inguinal canal, medial to the epigastric vessels, with a low risk of strangulation and is always acquired, mostly in middle-aged men.
• Indirect inguinal hernia is lateral to the epigastric vessels.
• Passes through the inguinal canal.
• Has a high risk of strangulation, congenital or acquired, more common in younger people, larger, and requires surgery.

Intraperitoneal Organs

• Organs inside the peritoneum with mesenteries: stomach, spleen, liver, gallbladder, small intestine (superior part of the duodenum), large intestine (transverse and sigmoid colons), and cecum with the vermiform appendix.

Retroperitoneal Organs

• Organs with no mesentery: kidneys, suprarenal glands, uterine cervix, ascending and descending colon, duodenum (excluding the superior part), pancreas, and the upper ⅔ of the rectum.
• The lesser sac is posterior to the stomach.
• Can be accessed through the epiploic foramen.

Clinical Significance of Lesser Sac and Epiploic Foramen

• Site of herniation.
• Surgery should be done from the other side, avoiding the porta hepatis.
• Cystic gallbladder can be reached through this foramen.
• The greater omentum is a fatty curtain that prevents the visceral and parietal peritoneum from adhering to each other.
• Includes immune cells that respond to inflammatory mediators and moves toward infected or inflamed areas and protects abdominal organs against injury and acts as an insulator against heat loss.

Peritoneal Spaces and Compartments

• Postoperatively, fluid accumulation in the subphrenic space can occur due to inhaled anesthetics.
• The rectouterine pouch in females is deep in the pelvic cavity and can be a site of fluid accumulation in pelvic inflammatory disease.
• The rectovesical pouch is in males.

Peritonitis

• Inflammation of the peritoneum from injury.

Ascites

• Fluid accumulation in the abdominal cavity due to liver failure and increased blood pressure in the portal vein, causing other organs to squeeze out fluid, cirrhosis of the liver.
• The foregut includes the esophagus, stomach down to the 2nd part of the duodenum, liver, biliary system, gallbladder, and pancreas.
• The midgut starts from the lower half of the 2nd part of the duodenum and jejunum, ileum, colon (ascending and the right ½ of the transverse colon), and cecum.
• The hindgut includes the left ⅓ of the transverse colon, descending colon, sigmoid colon, and rectum.
• The blood supply to the foregut comes from the celiac trunk, to the midgut from the superior mesenteric artery and to the hindgut from the inferior mesenteric artery.
• The foregut and midgut are innervated parasympathetically by the vagus nerve and sympathetically by T5-L2.
• The hindgut is innervated parasympathetically by S2-S3-S4 and sympathetically by T5-L2.
• Blood supply to the upper esophagus is via the inferior thyroid artery(cervical portion), to the middle esophagus is the thoracic aorta (4-5 arteries) and bronchial arteries (thoracic version), and to the lower esophagus, via the left gastric artery (from the celiac artery) and the inferior phrenic artery (from the abdominal aorta).
• Venous drainage is via the inferior thyroid vein, azygos, hemiazygos, and gastric veins, with the gastric veins draining into the portal veins.

Esophageal Varices

• The dilated submucosal veins in the lower esophagus is due to portal hypertension.

Histology of the Esophagus

• Four layers/tunics form the walls of tubal structures in the body.
• Epithelial cells line all tubes.
• The mucosa is stratified squamous non-keratinized epithelium that protects against friction from swallowed food.
• Thin layer of smooth muscle drives local movement.
• The submucosa contains blood vessels, lymphatics, and nerves.
• The tunica muscularis pushes food downwards.
• The outermost layer is the adventitia/serosa.
• The GI tract from mouth to anus is lined with stratified squamous non-keratinized epithelium
• Simple columnar lines the rest of the tract.

Clinical Significance of Zenker's Diverticulum

• Upper esophagus pouches forming (mucosa and submucosa herniation) lead to dysphagia and halitosis.

Achalasia

• A motility disorder leading to the relaxation failure of the lower esophageal sphincter (LES) due to the loss of inhibitory neurons.

Barrett's Esophagus

• GERD causes epithelium cells begin to modify and can cause cancer.
• Stomach rugae and the oblique muscle layer of stomach allow the stomach to expand.
• Oblique muscle churns the food.

Gastric Pits vs Gastric Glands

• Gastric pits are shallow and contain mucus cells.
• Gastric glands are deeper and contain specialized cells.
• The body and fundus of the stomach contain the Mucoid cells which protect stomach lining from strong acids, Chief cells which make pepsinogen (activated by HCI), and Parietal cells that produce HCI and intrinsic factor for B-12 absorption in the ileum.
• G cells in the pyloric antrum of the stomach produce gastrin.
• Gastrin stimulate parietal cells and break down food.

Blood Supply of the Stomach

• Supplied by branches of the Celiac Trunk: Left gastric, common hepatic (right gastric), common hepatic (gastroduodenal which forms right gastroepiploic and splenic artery which forms short gastric arteries (left gastroepiploic artery).
• Venous drainage is via the portal vein.
• Parasympathetic and vagus nerve innovation.
• Sympathetic innovation.

Gastric Ulcers

• Defective mucus barrier in the lining of the stomach.
• The same causes as gastritis.

Vagotomy

• Cutting the vagus nerve when medication does not work, which causes stimulatory response to the parietal cells.
• Complicates gastric emptying.

Hemigastrectomy

• Removal of the pylorus and antrum, the location where gastrin is produced.
• ALI is done to treat gastric ulcers and reduce stomach acids.

Hiatal Hernias

• Sliding occurs when the esophagus and fundus slide up through the hiatus, causing regurgitation, heartburn, and pressure on the lower esophageal sphincter.
• Paraesophageal occurs when the cardia does not move and peritoneum pass through the esophageal hiatus with no regurgitation.
• Fundoplication treatment.
• Thickened pyloric muscle of spyloric causes blocked stomach emptying.
• Nonbilious vomiting.
• The first segment location is L1, anterior to the portal vein and common bile duct, and a site of ulcers.
• The second descending segment which L1-L3, the major dueodenum pappili that leads to the shincter, reaches the ampula of vator and connects the main pancreatic duct and common bile duct, and the minor dueodenum papila as an accessory pancreatic duct.
• Neutralizes chyne and releases pancreatic enzymes.
• The third horizontal segment location is the L3, crosses the IVC and abdominal aorta, and the Superior mesentaric artery runs above it
• The 4th Ascending segment location is L1-L2 that goes across midline to the duedejenual.
• Receives chyme, bile, and pancreatic enzymes for digestion and absorption.
• The submucosal Plexus (Meissner's) secretion, blood flow, and absorption is dysfunctional with Hirschsprung's disease.
• The Myenteric Plexus (Auerbach's) controls motility & peristalsis with dysfunction in Achalasia and Hirschsprung's disease.
• Sympathetic inhibits digestion.

Jejunum

• A main site of nutrient absorption.
• Absorbs most water & electrolytes.
• Has long, dense villi and many plicae circulares for maximum absorption.

Ileum

• Absorbs vitamin B12 & bile salts.
• Contains Peyer's patches.
• Fewer folds & villi than the jejunum.

Blood Supply of Intestine

• SMA supplies blood.
• Superior mesentaric vein drains blood into the portal vein.
• Sypmathetic splanchnic nerve and Parasympathetic Vagus Nerve innovation

Meckel's Diverticulum

• Located in the ileum.
• A congenital anomaly, omphalomesenteric duct, fails to close, is more common in males and from a ilococular valve.
• A gastric and pancreatic ectopic mucosa.
• The vermiform appendix is attached to the cecum and at McBurney's point.
• The appendix is a reservoir for gut bacteria (e-coli)
• An appendicitis is a inflamation due to a foreign body blockage.
• Foreign body blockage require appendix removal.

Colon Blood Supply and Venous Drainage

• Branches of superior and inferior mesentaric arteries supplies blood.
• Marginal artery of drummond
• Anastemosis of inferior and superior necentaric arteries.
• Colic veins drains into the superior mesentaric veins and portal vein

Pectinate Line

• Seperates sections of anal canal.
• Visceral nevers are above and feel no pain.
• Somatic nerves are below and hurt.

Rectum and Anus Blood Supply and Venous Drainage

• Superior rectal artery with the Inferior mesenteric artery (IMA)
• Middle rectal artery with the Internal iliac artery.
• Inferiorrectal artery with the Internal pudendal artery.
• Above Pectante line with the Superior rectal vein draining into the inferior mesintary and then portal vein.
• Below Pectinate Line with Inferior and rectal veins draining into the internal iliac vein

Portocaval Anastomosis

• A back up plan when the portal vein is blocked or compromised due to cirrhosis of the liver.
• Results in Caput medusa, Internal hemorrhoids, and Esophageal varices.

Hemorrhoids

• Internal hemorrhoids are located above the pectinate line, connected to the visceral autonomic nerves, bleed, and is associated with portal hypertension.
• External hemorrhoids are located below the pectinate line, connected to the painful somatic pudendal nerve, caused by intra abdominal pressure, and are less likely to bleed.
• Hirschsprung's disease is a congenital condition with absent ganglion cells in the myenteric (Auerbach) and submucosal (Meissner) plexuses.
• Causes lack of peristalsis in the affected segment and constipation.
• Symptoms include abdominal distension and failure to pass meconium in newborns.

Liver Functions

• Metabolism of carbs, fats, and proteins.
• Detoxification of drugs, toxins, and ammonia.
• Bile Production.
• Storage of glycogen, vitamins (A, D, B12), and iron.
• Plasma Protein production of Albumin, clotting factors, and lipoproteins.

Glisson's Triad

• Found at each portal lobule corner
• Contains Hepatic artery (oxygenated blood), Portal vein (nutrient-rich blood), Bile duct

Liver Cells

• Disse's Space between hepatocytes and sinusoids for material exchange.
• Ito Cells store Vitamin A and become fibroblasts in liver cirrhosis.
• Hepatocytes perform detoxification, bile production, and metabolism.
• Cirrhosis of the liver is a disease where normal liver tissue replaced by fibrous scar tissue.
• Alcoholism, hepatitis, and fatty liver disease causes it.
• Cirrhosis symptoms are Jaundice, ascites, and esophageal varices, which are treated with liver transplants.

Gallstones

• Gallstones (Cholelithiasis): Hardened deposits of cholesterol, bilirubin, or calcium in the gallbladder.
• RUQ pain, nausea, jaundice symptoms are caused by it.
• Murphy's sign (pain on palpation).
• Cholecystectomy is the treatment.
• Secondary condition is Pancreatitis (if a gallstone blocks the pancreatic duct).

Pancreas

• Produces hormones (Insulin, Glucagon, Somatostatin) to the Islets of Langerhans with endocrine function.
• Exocrine function secretes digestive enzymes and neutralizes stomach acid by bicarbonate secretion.

Pancreatitis

• Causes inflammation of pancreas due from gallstones, alcohol, and trauma.
• High amylase/lipase symptoms
• Cystic FIbrosis is a genetic disorder (CFTR mutation) which causes fatty stools.

Spleen

• Filters old/damaged blood cells.
• Stores platelets & blood.
• Provide immune function.
• Kidney filtration: removes waste, excess water, toxins
• Kidney function to regulate blood pressure & electrolyte balance.

Erythropoietin (EPO)

• Hormone that stimulates RBC production and maintains calcium balance.
• Nephron filters blood, reabsorbs water, and excretes waste.
• Juxtaglomerular Complex regulates blood pressure by secreting renin.

Renin-Angiotensin-Aldosterone System (RAAS)

• Renin → Converts Angiotensinogen to Angiotensin.
• ACE converts Angiotensin I to Angiotensin II (vasoconstrictor).
• Aldosterone increases BP.

Kidney Blood Supply

• Arterial Supply: Renal arteries (from the abdominal aorta).
• Venous Drainage: Renal veins → Inferior Vena Cava.

Adrenal Cortex Layers

• Glomerulosa: Aldosterone (Salt).
• Fasciculata Cortisol: Sugar.
• Reticularis Adrogens: Sex hormones.
• Epinephrine & Norepinephrine product Medulla to allow Sympathetic control.

Nerves of Lumbar Plexus

• Iliohypogastric & Ilioinguinal (L1).
• Genitofemoral L1-L2.
• Lateral Femoral L1-L4 Sensory.
• Femoral Quadriceps Extension.
• Obturator L2-L4 Thigh.

Pelvis

• Male narrow pelvis.
• Female short and wide pelvis.
• Piriformis are pelvic walls.
• Coccygeus pelvic floors.
• fibroids, endometriosis: uterus, endometriali tissue: fertility.
• Follicular and Leutal, egg released with LH surge.

Male Urethra

• Internal to prevent ejaculation.
• Passed on to the seminal production.
• External and spongy.
• Epididimis is sperm.
• Prostatic stores the semen.
• Seminal vesicle: energy.

Fluid

• Alkaline
• Erection: Vasodilation: Parasympathetic nitric oxide
• Sympathetic urethra fluid.
• Pudendal ejaculation and Contractions.