Small Intestine: Anatomy – Digestive System Organs (Nursing)

00:01 The next major organ of the digestive system after the stomach is going to be our small intestine.

00:09 This is going to be responsible for both digestion and absorption.

00:14 And is really our first absorptive organ outside of the small amount of absorption that happens in the stomach.

00:24 The small intestine is 2 to 4 meters long or about 7 to 13 feet.

00:30 So like to very tall people.

00:34 From the pyloric sphincter to the ileocecal valve, which is where it's going to come in contact or join with the large intestine.

00:45 It also has a pretty small diameter of 2.5 to 4 centimeters, but don't let that small diameter fool you.

00:54 There is a lot of space for absorption and digestion to occur even in this very small area.

01:02 Looking at the growth anatomy of the small intestine, we start with the duodenum.

01:08 The duodenum is the first section of the small intestine.

01:12 It is mostly retroperitoneal and it is about 25 centimeters long.

01:18 It curves around the head of the pancreas and has most of the features of our small intestine.

01:25 After the duodenum we have the jejunum, which is about 2.5 meters long and is attached to the posterior by the mesentery.

01:36 Lastly, we have the ileum, which is about 3.6 meters long and attached posteriorly by the mesentery it joins the large intestine at a valve known as the ileocecal valve.

01:52 The small intestines length and other structural modifications provide for a huge surface area for nutrient absorption.

02:01 Recall that the diameter is actually quite small, but the surface area is increased by 600 times to about 200 meters squared or the size of a tennis court.

02:16 These modifications such as circular folds, Villi, and microvilli within the small intestines are what allow for this increase or huge surface area compared to its diameter.

02:32 Looking closely at these modifications.

02:35 We find the circular folds which are permanent folds that force the chyme to slowly spiral through the lumen, which is allows them more time for nutrient absorption.

02:48 Within these folds we have Villi are finger-like projections of the mucosa with a core that contains a dense capillary bed and lymphatic capillary called the lacteal for absorption.

03:03 This is going to be important when we're trying to absorb nutrients either into the blood or the length.

03:10 And then on the microscopic level we have microvilli.

03:15 These are cytoplasmic extensions of these mucosal cells that give a fuzzy appearance called a brush border that contains membrane-bound enzymes known as brush border enzymes.

03:28 These brush border enzymes are going to play a key role and the digestion of carbohydrates and proteins.

03:37 So looking at an image of the small intestines and these modifications again, you find you have the circular folds followed by the Villi, followed by the microvilli of the cells of the Villi.

03:55 So looking at these modifications of the mucosa, we find that it reflects its function in digestion.

04:03 Within these modifications, we find intestinal crypts, which are tubular glands that are going to be scattered between the Villi.

04:13 These are also going to be very important for the function of digestion.

04:20 Within our Villi and in the crypts, we have different types of cells.

04:26 First we have enterocytes, which are going to make up the bulk of this epithelial layer.

04:32 These are simple columnar absorptive cells that are bound by tight junctions and contain many microvilli.

04:40 The Villi are going to absorb nutrients and electrolytes while the crypts are going to produce intestinal juices, which is a watery mixture of mucus that acts as a carrier fluid for the chyme.

04:55 Also within these Villi we have goblet cells.

04:59 These are going to be mucus secreting cells that are found in the epithelia of the Villi as well as the crypts.

05:07 And lastly we have our enteroendocrine cells, which are going to be the source of our enterogatrones such as CCK and secretin.

05:17 These are also found scattered in the Villi with a little bit of them found within these intestinal crypts.

05:25 Next we have the paneth cells which are found deep in the crypts and specialized secretory cells that are going to fortify the small intestines defences by secreting antimicrobial agents, like defensins and lysozymes that are able to destroy bacteria.

05:45 And finally we have the stem cells of the intestines that are going to continuously divide to produce other cell types.

05:54 And the villus of our epithelium is renewed every two to four days.

05:59 So within a week the entire Villi and epithelium of your intestine is going to change twice.

06:07 So also found in our small intestines.

06:10 We have some lymphoid tissue, which is going to be important for protecting us against microorganisms.

06:17 This involves mucus associated lymphoid tissue also known as MALT and is going to be individual lymphoid follicles.

06:27 These are found in structures known as peyer's patches which are located in the lamina propria and are found in great numbers and the distal part of the small intestines where bacterial numbers begin to increase.

06:43 The lamina propria also contains large amounts of plasma cells that secrete IGA which has an immune function as well.

06:53 The submucosa is going to consist of areolar tissue and within that tissue duodenal glands of the duodenum are going to secrete an alkaline mucus that is able to naturalize acidic chyme.