Lecture 8.1: Internal Surfaces of the Body Flashcards
Membrane Types
• Mucous membranes (mucosae singular, mucosa)
• Serous membranes (serosae singular, serosa)
Mucous Membranes: Where?
Mucous membranes line internal tubes that open to the exterior:
• Alimentary tract
• Respiratory tract
• Urinary tract
• Reproductive tract
The layers of a mucous membrane (3)
1) An epithelium lining the lumen of a tube, the type depends on the site
2) An adjacent layer of connective tissue often referred to as the lamina propria
3) In the alimentary tract, a 3rd layer of smooth muscle cells is present: the muscularis mucosae
What are Serous Membranes?
Serous membranes are thin, two-part membranes that line certain closed body cavities (spaces that do not open to the exterior)
Development of Serous Membranes
During embryonic development, the heart, lungs, and digestive tract develop next to a bag-like cavity, into which they invaginate (turned inside out or folded back on itself to form a cavity or pouch)
This way, they become enveloped by serous membranes
What do Serous Membranes Envelop?
• The Peritoneum, which envelops many abdominal organs
• The Pleural Sacs, which envelop the lungs
• The Pericardial sac, which envelops the heart
What do serous membranes secrete?
These serous membranes (or serosae) secrete a lubricating fluid that promotes relatively friction-free movement of the structures that they surround
The Pericardial Sac: Outwards to Inwards
Parietal Pericardium
Pericardial Cavity
Visceral Pericardium
Pleurae of Lungs: Outwards to Inwards
Parietal Pleura
Pleural Cavity
Visceral Pleura
Where do most digestive organs lie?
Abdominopelvic Cavity
The Peritoneum
Most digestive organs lie within the abdominopelvic cavity, which is covered by the visceral layer of the peritoneum
The cavity wall is lined by the parietal peritoneum
Serous fluid allows movement of the organs during digestion
What is the Mesentery?
A double layer of peritoneum extending from the posterior body wall
Supplying blood vessels, lymphatics and nerves to the intestines
It is also a site of fat storage
Retroperitoneal Organs
Include (most of) the pancreas and oesophagus, the kidneys, ureters, and ascending and descending colon
The Gastrointestinal Tract
Oesophagus
Stomach
Small Intestine (Duodenum, Jejunum, Ileum)
Colon
Rectum
The 4 Layers of the Gut Tube
1) A mucosa surrounding the lumen (epithelium, lamina propria, muscularis mucosae), the epithelium is simple columnar throughout, bookended by stratified squamous non-keratinised epithelium
2) A submucosa (loose irregular CT)
3) External layers of circular and longitudinal smooth muscle (muscularis externae)
4) An outer serosa (or adventitia at either end)
Layers of the Mucosa of the Gut Wall: Outwards to Inwards
Muscularis mucosae
Lamina propria
Epithelium
Peyer’s Patches (Mucosa of Gut Wall)
Aggregations of lymphocytes are often present in the lamina propria, particularly distal ileum where they form Peyer’s patches
The Submucosa of the Gut Wall
A layer of loose irregular connective tissue bearing glands, arteries, veins, lymphatics and nerves
Glands within the submucosa
External Muscle of the Gut Wall
Two layers of smooth muscle comprise the muscularis externa:
• Outer longitudinal smooth muscle layer
• Inner circular smooth muscle layer
The muscularis externa creates successive peristaltic waves to move luminal contents along the gut under the control of the enteric nervous system
The Serosa of the Gut Wall
Simple Squamous Epithelium (Mesothelium)
Connective Tissue
Mesentery (double layer of visceral peritoneum) containing arteries, veins and nerves
Layers of the the Oesophagus: Outwards to Inwards
Muscularis externa (comprised of skeletal muscle only in the upper 1/3 of the oesophagus)
Submucosa
Mucosa (Muscularis mucosae, Lamina propria, Epithelium)
Oesophageal Mucosa (3 Layers)
Muscularis mucosae: thin layer of smooth muscle
Lamina propria: loose connective tissue bearing blood and lymph vessels, some smooth muscle cells and many cells of immune system
Epithelium: stratified squamous non-keratinized (withstands abrasion)
Outer Layers of the Oesophagus
Submucosa: subtending layer of connective tissue containing mucus secreting glands
Muscularis externa: a mix of smooth and skeletal muscle layers (inner– circular; outer– longitudinal) that move food by peristalsis
Adventitia: thin outermost layer of connective tissue to anchor organ
Regions of the Stomach (4)
The stomach has four distinct regions:
• Cardia
• Fundus
• Body
• Pylorus