Take a stand of you hair, snap it in half and check out how thin the end of it is. Pretty thin huh?
And guess what?... Your digestive tract (gut) lining is actually thinner. Consequently, there’s not much separating the inside of you from the outside world.
Here’s what your gut lining is made of…
The passageway from your mouth to anus, aka the gut lumen, contains four main layers that make up its wall lining.
The mucosa (3 sublayers)
The muscularis externa
Layer 1: The Mucosa
Lines the lumen (passageway) of the digestive tract
It’s the first surface that comes in contact with the foods and nutrients you eat
It has a very large surface area, estimated at more than 250 square metres. This in turn maximises your body’s ability to absorb nutrients.
Several structures contribute to it’s huge surface area, including:
Large circular folds that protrude into the lumen
Villi, fingerlike projections that also project out into the lumen
Microvilli, hairlike extensions that sprout out from the villi
Endocrine and exocrine cells are also found among the epithelium
Endocrine cells - secrete various hormones into the blood
Exocrine cells – secrete a variety of substances (e.g. digestive enzymes, mucus & juices) into the digestive tract lumen
The lamina propria
Lies just below the epithelium.
Consists of connective tissues, lymphoid tissues, small blood vessels and lymphatic vessels.
The lymphoid tissue contains a number of different white blood cells (e.g. macrophages and lymphocytes) that help to protect you against ingested microbes, like listeria.
The muscularis mucosa
Layer 2: The Submucosa
The second major layer of the gut is made up connective tissue, more lymphoid tissue and a network of nerves.
This network of nerves is known as the submucosal plexus. It plays a role in:
controlling the release of secretions from the mucosal glands
regulating the mucosal movements
And regulating blood flow to and from the gut
The lymphoid tissue in the submucoa plays a similar role to that in the mucosa; that is it helps to protect the body against foreign materials.
Layer 3: The Muscularis externa
The submucosa connects the first later (mucosa) of the digestive tract to this third layer. This layer contains:
Smooth muscles (both circular and longitudinal) – these muscles contract and relax to move your food through the different sections of the digestive tract. This movement of food is known as peristalsis.
Myenteric plexus - this network of nerves controls the frequency and strength of the muscularis contractions, which in turn affects digestive motility (movement of food through the gut).
Layer 4: The Serosa
The outermost layer of the digestive tract lumen, the serosa, is made up of connective tissue and the visceral peritoneum.
The peritoneum is a membrane that surrounds the organs found in the abdominal and pelvic cavities.
The visceral and parietal peritoneum arrangements create a double-layered membrane within the abdominal space, and it is between these two membranes that the peritoneal cavity is found.
And that's the gut lining... thin but oh so complex and important.