WEEK 15 - Abdominal cavity and GI tract INTRO

Lecture learning objectives- PART 1 AND 2

  • To identify the boundaries of the abdominal cavity and which organs are within this cavity

  • To name the intraperitoneal and retroperitoneal organs

  • To differentiate between parietal and visceral peritoneum and explain what is the peritoneal space

  • To identify and explain the main functions of the mesenteries and, greater and lesser omentum, greater and lesser sacs and pouches/cul-de-sacs

  • To Identify the components of the GI tract and the accessory organs of digestion and their main functions

Abdominal Cavity

Body Cavities

= Body compartments that contain the organs

  • are maintained by = membranes, sheaths and structures

  • abdominopelvic cavity is the largest in the body

ABD Cavity Boundaries

  • Superior = Diaphragm

  • Inferior = Pelvic Inlet

  • Ant/Post/Lat = Abdominal walls (inferior ribs and costal cartilages, lumbar vertebrae L1-L5, abdominal muscles)

Layers of the ABD Wall

  1. Skin

  2. Superficial fascia

    a. Camper’s fascia - Superficial fatty fascia

    b. Scarpa’s fascia – Superficial membranous fascia

  3. Muscles

    a. External obl

    b. Internal obl

    c. Transverse abdominis

    d. rectus abdominis

  4. Transversalis (connective tissue)

  5. Extraperitoneal fascia (fat)

  6. Parietal Peritoneum

ABD Cavity Organs

  • GI tract organs: stomach and intestines (digestive system)

  • Kidneys (adrenal gland) and ureters (urinary system)

  • Liver, gallbladder, pancreas (endocrine and digestive functions)

  • Spleen (immune system)

Peritoneum

= Serous membrane lining the abdominal cavity walls and covering many of the abdominal visceral organs

  • PARIETAL PERITONEUM = lines the walls of the abdominal cavity

  • VISCERAL PERITONEUM = package visceral organs

INTRAPERITONEAL

= Organs ALMOST entirely enclosed by visceral peritoneum

  • e.g. stomach

RETROPERITONEAL

= Organs localized outside of the peritoneum cavity

  • e.g. kidney

MESENTERY

= double layer of peritoneum (continuity of visceral + parietal)

NOTE: Every organ must have an area not covered by visceral peritoneum to
allow the passage of nerves and vessels

Retroperitoneal Space

  • located between the posterior abdominal wall and the parietal peritoneum

  • where organs outside the peritoneal cavity reside

Retroperitoneal Organs

  • S – suprarenal (adrenal gland)

  • A – aorta/IVC

  • D – duodenum (2nd and 3rd parts)

  • P – pancreas (except tail)

  • U – ureters

  • C – colon (asc. and desc.)

  • K – kidneys

  • E – esophagus

  • R – rectum

Peritoneal Cavity

= Potential space between parietal and visceral layers of peritoneum

Peritoneal Fluid

  • produced by = serous peritoneal membrane

  • found within = the peritoneal cavity (thin layer)

  • function = to provide essential lubrication and allows sliding of viscera
    without friction or irritation

  • contains = white blood cells and antibodies (immune function)

  • accumulation of PF = ascites

Mesenteries

= Fold of peritoneal membrane (double layer)

  • contains = blood vessels, lymphatic vessels and nerves supplying intraperitoneal organs

Functions

  • Suspend and anchor intraperitoneal organs to the posterior abdominal wall

  • Provide flexibility of movement in the abdomen for the intraperitoneal organ BUT tethers the organ to the posterior abdominal wall

  • Prevent blood vessels to get tangled

Mesenteries of the ABD cavity

  • MESENTERY OF THE SMALL INTESTINE

    • Suspends the majority of the small intestine from the posterior abdominal wall

  • TRANSVERSE MESOCOLON

    • Connects transverse colon to the posterior abdominal wall

  • SIGMOID MESOCOLON

    • Connects sigmoid colon to the posterior abdominal wall

Stomach

  • shape = J- shape

  • Curvatures

    • Lesser Curvature (medial)

    • Greater Curvature (lateral)

Lesser Omentum

= Mesentery extending between the liver and the lesser curvature of the
stomach and proximal 1st part of duodenum

  • HEPATOGASTRIC LIGAMENT = anchor liver to stomach

  • HEPATODUODENAL LIGAMENT = anchors liver to the initial part of intestine; passageway for the portal triad (hepatic portal vein,
    hepatic artery proper, common bile duct)

Greater Omentum

= generally, location for at storage, passageway for vessels and, physical and immune protection
= Mesentery that form an “apron” draping off the greater curvature of the
stomach

  • GASTROPHRENIC LIGAMENT = Anchors stomach to diaphragm

  • GASTROSPLENIC LIGAMENT = Anchors stomach to spleen

  • GASTROCOLIC LIGAMENT = Anchors stomach to duodenum and covers the intestine and abdominal viscera

Sacs

= omenta subdivide the peritoneal cavity into the greater sac and the lesser sac

Connection Between Sacs

  • OMENTAL FORAMEN (of Winslow) – EPIPLOIC FORAMEN = an opening posterior to the hepatoduodenal ligament

Greater Sac

= accounts for most of the space in the peritoneal cavity

= extends from the diaphragm to the pelvic cavity

Compartments

  • Supracolic Compartment = Superior to the colon and anterior to the greater omentum

    • SUBPHRENIC SPACE ➔between diaphragm and anterior
      surface of liver

    • SUBHEPATIC SPACE ➔between visceral surface of liver and right kidney

  • Infracolic Compartment = Inferior to the colon, posterior to the greater omentum

Lesser Sac / Omental Bursa

= posterior to the lesser omentum and the stomach but anterior to the pancreas

  • Anterior wall = lesser omentum and posterior wall of stomach

  • Left Lateral wall = gastrosplenic ligament and splenorenal ligament

ABD Cavity Floor

= ABD Cav is continuous with pelvic cavity but parietal peritoneum that lines the
abdominal cavity drapes over the organs of the pelvic cavity creating ”pouches” between adjacent pelvic organs

Male Pouches / cul-de-sacs

  • RECTOVESICAL POUCH = between bladder and rectum


Female Pouches / cul-de-sacs

  • VESICO-UTERINE POUCH = (anterior cul-de-sac) - between bladder and
    uterus

  • RECTO-UTERINE POUCH OF DOUGLAS = (posterior cul-de-sac) – between uterus and rectum

GI Tract

= Continuous muscular tube

Composition:

  • mouth

  • pharynx

  • esophagus

  • stomach

  • small intestine

  • large intestine

  • anus

Accessory Organs

  • teeth

  • tongue

  • salivary glands

  • liver

  • gallbladder

  • pancreas

Oral Cavity

  • first step in digestion through the secretion of saliva

  • types of salivary glands:

    • Parotid

    • Sublingual

    • Submandibular

Pharynx

  • Oropharynx

  • laryngopharynx

NOTE: both are shared by respiratory and digestive systems

Esophagus

= collapsible muscular tube extending from laryngopharynx to stomach, posterior to trachea

  • Anterior to thoracic aorta and posterior to trachea

  • Pierces diaphragm at the esophageal hiatus (level → T10)

Layers:

  1. adventitia

    • Fibrous tissue connecting it to neighboring structures

    • small vessels, lymphatic vessels and nerves

  2. muscularis propria

    • Transition from skeletal (upper 1/3) to smooth muscle

    • Inner circularly arranged layer

    • Outer longitudinally arranged layer

  3. submucosa

    • Connective tissue

    • Esophageal mucous glands

  4. mucosa

    • Nonkeratinized stratified squamous epithelium

    • Lamina propria

    • Muscularis mucosae (smooth muscle)

Function:

  • Propulsion of food bolus to stomach by PERISTALSIS (wave-like)

    • UPPER ESOPHAGEAL SPHINCTER (skeletal muscle) = pharynx into Esophagus

    • LOWER ESOPHAGEAL SPHINCTER (smooth muscle) = prevents retrograde movement of stomach contents

Stomach

= stores food and continues the digestion (little) that started in
the mouth

Intestines

small intestine

= where most of digestion occurs (and finishes)

  • duodenum

  • jejunum

  • ileum

large intestine

  • absorption of water and formation of feces

Rectum

= feces exit through the anus

GI Tract Wall Layers

Mucosa Layers (inner - outer)

  1. Surface Epithelium

    • Stratified squamous (ex. pharynx, esophagus)

    • Simple columnar (ex. stomach, small intestine)

    • Secretory cells (especially for mucus and enzymes will be found in here)

    • Continuously being replaced (stem cells)

  2. Lamina Propria

    • loose connective tissue holding epithelium in place

    • Small blood vessels and lymphatics, lymphoid tissue, innervation, immune cells absorbed nutrients enter the blood/ lymph circulation here

  3. Muscularis mucosae

    • Thin layer of smooth muscle

Submucosa Layers

= Regulates release of digestive secretions based on the detected
presence of food in the lumen

  • Loose connective tissue layer with large blood vessels and lymph vessel

  • Submucosal glands - secrete mucus

  • Submucosal (Meissner’s) plexus→ enteric nervous system
    (ENS) → innervates structures of the mucosa and submucosa

Muscularis Externa Mucosa

  • Proximal GI Tract = skeletal muscle

  • Distal GI Tract = smooth muscle

    • inner sheet of circularly arranged fibers (decreases diameter)

    • between muscle layers: Myenteric plexus (Auerbach’s plexus) = innervation that controls GI tract motility - peristalsis and segmentation

    • outer sheet of longitudinally arranged fibers (decreases length)

Serosa Histology

= Serous membrane (visceral peritoneum) covering organs within the abdominal cavity (outer layer)

  • Mesothelium (simple squamous)

  • Loose connective tissue (thin layer)

Functions:

  • Secretes serous fluid

  • Facilitates movement /reduce friction