unit 5, pt 1a: peritoneal cavity, mesenteries & layers of digestive tract

Digestive System Anatomy

  • Overview of digestive system anatomy, histology, and gross anatomy

  • Focus on how organs work together to extract nutrients

  • Reinforcement of concepts from unit one with extra details

  • Kidney anatomy, waste extraction, and urine excretion

  • Comparison of male and female reproductive anatomy

  • Brief mention of lymphatic and endocrine systems

Body Cavities

  • Major body cavities:

    • Pleural cavities: surround the lungs.

    • Pericardial cavity: surrounds the heart.

    • Peritoneal (abdominal) cavity.

Serous Membranes

  • Serous membranes or serosal membranes are associated with cavities.

  • Pleural cavities: Pleura.

  • Pericardial cavities: Pericardium.

  • Peritoneal cavity: Peritoneum.

  • Parietal peritoneum: outside border (red).

  • Visceral peritoneum: covers the organs themselves (blue), e.g., liver, transverse colon, small intestine (jejunum, ileum).

Mesenteries

  • Double layer of peritoneum.

  • Extension of the peritoneum that keeps organs in place and provides a pathway for blood vessels.

Peritoneal Cavity

  • Visceral peritoneum:

    • Covers much of the digestive system organs in the abdominal cavity.

    • A serous membrane that secretes fluid (serum) for lubrication.

    • Reduces friction between organs.

  • Visceral peritoneum is continuous with the parietal peritoneum.

  • Abdominal organs can be within or outside the peritoneal cavity.

  • Examples:

    • Pancreas is outside the cavity.

    • Sigmoid colon is outside the cavity.

    • Urinary bladder and uterus (in females) are also outside.

Organ Relationships to the Peritoneal Cavity

  • Terms to describe organ relationships:

    • Intraperitoneal.

    • Retroperitoneal.

    • Secondarily retroperitoneal.

Intraperitoneal Organs

  • Lie within the peritoneal cavity.

  • Completely covered with visceral peritoneum.

  • Examples:

    • Stomach.

    • Liver.

    • Jejunum and ileum (parts of the small intestine).

    • Transverse and sigmoid colon.

Retroperitoneal Organs

  • Located behind or posterior to the peritoneal cavity.

  • Covered with parietal peritoneum only on their anterior surface.

  • Examples:

    • Kidneys.

    • Ureters.

    • Abdominal aorta (after passing through the diaphragm).

    • Ascending and descending colon.

    • Rectum.

    • Pancreas and duodenum* Secondarily retroperitoneal- start inside then move out.

Sagittal View

  • Intraperitoneal:

    • Liver.

    • Stomach.

    • Transverse colon.

    • Most of the small intestine (jejunum and ileum).

    • Sigmoid colon.

  • Retroperitoneal:

    • Pancreas (only anterior surface covered).

    • Duodenum.

    • Rectum.

    • Urinary bladder.

    • Uterus.

  • Food Pathway:

    • Esophagus to stomach (into the peritoneal cavity).

    • From the stomach to the duodenum (outside peritoneal cavity).

    • Back into the peritoneal cavity through the small intestine and then in and out of the large intestine.

Transverse Section

  • Looking down into a sliced torso.

  • Features: vertebra, spinal cord.

  • Intraperitoneal:

    • Liver.

    • Stomach.

    • Portions of the large and small intestines.

  • Retroperitoneal:

    • Pancreas.

    • Duodenum.

    • Abdominal aorta.

    • Kidneys.

  • Greenish color shows peritoneum (visceral and parietal).

Mesenteries Explained

  • Peritoneal membrane (visceral).

  • Peritoneum sandwiched together to form sheets.

  • Functions to keep organs in place and allow passage of blood vessels.

  • Examples:

    • Falciform ligament: holds the liver in place.

    • Lesser omentum: connects stomach to liver.

    • Greater omentum: connects stomach and transverse colon, drapes over organs.

    • Transverse mesocolon: supports the transverse colon.

    • Mesentery proper: supports the small intestine.

    • Sigmoid mesocolon: supports the sigmoid colon.

  • Parietal peritoneum transitions into mesentery, then into visceral peritoneum around organs.

Mesentery Attachments

  • Greater omentum drapes off the stomach.

  • Lesser omentum attaches stomach to the liver.

  • The large intestine attaches to the back of the body wall via the transverse mesocolon.

  • Fusion fascia and mesentery proper help hold everything in place.

  • Mesenteries ensure food passes through the digestive system properly.

Layers of the Digestive Tract

  • Focus from esophagus to stomach, small intestine, and large intestine.

  • Four main layers (deepest to superficial):

    • Mucosa.

    • Submucosa.

    • Muscularis externa.

    • Serosa.

    • Serosa = Visceral peritoneum

Mucosa

  • Deepest layer, closest to the lumen.

  • A mucous membrane, often makes mucus.

  • Components:

    • Epithelium (stratified or simple).

    • Basal lamina (lamina propria): areolar connective tissue.

    • Muscularis mucosa: smooth muscle.

  • Epithelial cells vary:

    • Oral cavity, esophagus, and pharynx: stratified squamous cells (non-keratinized).

    • Stomach, small intestine, and large intestine: simple columnar epithelium.

  • Tongue example: stratified squamous epithelium with connective tissue underneath.

  • Simple columnar cells feature microvilli.

Submucosa

  • Dense irregular connective tissue (like the dermis).

  • Contains blood vessels and lymphatics.

  • Submucosal plexa: specialized nerves.

  • Sensory neurons and parasympathetic/sympathetic nerves.

  • Arteries, veins, lymphatic vessels, and submucosal plexus.

Muscularis Externa

  • Surrounds the submucosa.

  • Smooth muscle.

  • Forms sphincters and valves.

  • Myenteric plexus: nerves present (parasympathetic and sympathetic).

  • Multiple layers of muscle: longitudinal and circular.

  • Myenteric plexus: nerves in between the muscles.

  • Muscle contractions generate specific movements.

  • Muscle contractions: peristalsis (movement) and segmentation (breaking up food).

Special Terms

  • Mesenteric: Bands of peritoneum (Meso = middle) (Enter = intestine)

  • Myenteric: Muscles inside the intestines (Myo = muscle)

Muscle Contractions

  • Digestive tract consists of smooth muscle.

  • Muscularis mucosa and muscularis externa have pacemaker cells.

  • Two types of muscle contractions:

    • Peristalsis: moves food through the digestive tract through coordinated muscle contractions.

    • Segmentation: breaks up food into smaller pieces through squeezing and contractions.

Serosa

  • Most superficial layer.

  • Visceral peritoneum.

  • A serosal membrane able to make serum fluid.