- Skeletal system
- Blood vessels
- Respiratory system
- Digestive system
- Endocrine glands
- Nervous system
- Lymphatic system
- Female reproductive system
Cecum and vermiform appendix
The cecum (Latin: caecum) is the first and most proximal part of the large intestine connecting the ileum with the ascending colon. It is a sac-like or pouch-shaped organ located in the abdominal cavity. Cecum starts the absorption of remaining water and salts. From the posteromedial surface of the cecum goes the cylindric-shaped vermiform appendix (Latin: appendix vermiformis), mostly providing the immunologic function.
The cecum is located in the right iliac fossa, which is found in the right inguinal region. The organ is approximately 5 - 7 centimeters long with a diameter of 7-7.5 centimeters, so it is usually wider than its length. The ileum, the terminal part of the small intestine, connects with the cecum on its medial surface in the ileocecal junction site. The junction place has an ileocecal orifice. The orifice contains the ileocecal valve (also known as the Bauhin’s valve).
The ileocecal valve demarcates the transition zone between small and large intestines. It is more a functional valve, preventing the intestinal content backflow from the large intestine into the small intestine. But it can not control the movement from the ileum to the cecum. The valve is made up of the circular muscle fibers of the cecum and ileum.
The visceral layer of the peritoneum covers the cecum from all sides. The cecum is an intraperitoneal organ. The cecum does not have mesentery, and that is why it is very mobile.
- Posterior to the cecum is situated iliacus and psoas major muscles, lateral cutaneous nerve, femoral nerve and genitofemoral nerve.
- The anterior surface has a connection with the wall of the abdominal cavity. Sometimes it can also connect with the greater omentum and the loops of the small intestine.
- In the superior direction, the cecum continues as ascending colon, but inferior is the part of the inguinal ligament.
- Medial to the cecum is the ileocecal valve and the terminal part of the ileum.
Characteristics of large intestine
Almost all parts of the large intestine have typical characteristics. Therefore also, the cecum has haustra, teniae and epiploic appendages.
The wall of the cecum is formed into pocket-like sacs or small segmented pouches caused by sacculation. The sacs are called the haustra, and it gives the segmented appearance of the intestine.
The longitudinal muscle layer does not go throughout all the intestine. But instead, it forms three flat muscle bands or ribbons called the teniae. The free teniae are located on the anterior side of the intestine. The mesocolic teniae are situated posteromedially. The omental teniae are located posterolaterally, and to it attaches the greater omentum. Contractions of muscle fibers in the teniae provide the intestine segmentation (haustra) as the teniae are shorter than the length of the intestine.
The visceral peritoneum contains tiny fat-filled droplets or pouches hanging down mainly along the free and omental teniae and attached to them. These droplets are called the epiploic appendages. However, epiploic appendages rarely are present in the cecum.
Anatomy of vermiform appendix
Approximately 1-2 centimeters below the ileocecal orifice from the cecum’s posteromedial surface hangs down the vermiform appendix. Its shape, location, and size can vary in individuals. Usually, it is around 7 - 9 centimeters long, but the length can vary from only two up to 20 centimeters. The diameter usually is around 0.5 to 1 centimeter.
The vermiform appendix has an opening called the vermiform appendix orifice at the site where it connects with the cecum. Usually, the anterior surface of the vermiform appendix is covered by the small intestine. But sometimes, it has a connection with the abdominal wall.
The visceral layer of the peritoneum covers the appendix from all sides. The vermiform appendix is an intraperitoneal organ. It is attached to the lower end of the mesentery of the small intestine by a triangular-shaped mesoappendix. Sometimes it also is attached to the posterior abdominal wall. Connection takes place in the ileocecal junction area.
The vermiform appendix doesn not have teniae, haustra, and epiploic appendages. The vermiform appendix is a vestigial organ. It means that one can live everyday life without it as it does not provide vital functions.
Position variations of vermiform appendix
The vermiform appendix can have different position variations among the individuals.
- Posterior location or the retrocecal position (11 o’clock) is the most common one. The appendix goes posterior to the cecum. In this case, it can turn up and reach the right kidney or the liver. If this location is present, the appendix can also fuse with the wall of the cecum.
- Caudal or pelvic position (5 o’clock) is also visible relatively often. The vermiform appendix goes down in the direction of the lesser pelvis. It crosses the terminal line, and below it has a connection with the rectum, bladder, and right ovary and right uterine tube in females.
- When the pre-iliac position (1 or 2 o’clock) is present, the appendix is located anterior to the terminal part of the ileum. But in the post-ileal (1-2 o’clock) position, it finds behind or posterior to the terminal part of the ileum.
- The sub-ileal location is present when the appendix goes parallel to the terminal ileum (3 o’clock). The sub-cecal position is current when the appendix goes below the cecum (6 o’clock).
- The para-cecal location happens when the appendix goes along the cecum’s lateral surface (10 o’clock). The rarest location is when the appendix is located on the anterior surface of the caecum.
Cecum and vermiform appendix histology
The wall of the cecum and vermiform appendix consists of four histological layers:
- Muscular layer
The mucosa is covered by simple columnar epithelium. Underneath the epithelium are located the lamina propria containing connective tissue and so-called sub-epithelial collagen table with collagen fibers. Mucosa also has prominent muscular lamina with smooth muscle fibers forming the outer longitudinal and inner circular layers.
The mucosal part is very thick, and together with the submucosa, it creates semilunar mucosal folds at the sites where two haustra meet. The cecum contains slight folds compared to other parts. The vermiform appendix does not have mentioned folds, and its mucosa is smooth.
Opposite to the small intestine, the cecum does not contain villi and circular folds. The large intestine contains more crypts than the small intestine does. They are deeper and placed more densely. The cecum contains the lowest crypts in height compared to other parts of the large intestine.
The epithelial cells of the large intestine are called colonocytes. Besides colonocytes, the epithelium also contains a significant amount of the goblet cells producing mucus. The crypt base contains simple tubular glands, also known as the Lieberkuhn crypts. The crypts contain various cells:
- Epithelium stem cells - provide the regeneration of epithelium;
- Colonocytes - secrete and absorb multiple substances
- Goblet cells - produce mucus;
- Paneth cells - produce antibacterial substances;
- Endocrine cells - provide the secretion of hormones.
Compared to the small intestine, the large intestine rarely contains the Paneth cells. But the large intestine contains significant amounts of goblet cells and stem cells as they often differentiate into goblet cells. The ratio between colonocytes and goblet cells in the cecum is 4:1.
Mucosa contains solitary lymphoreticular intestinal tissue. Solitary tissue often forms larger follicles in the mucosa with a continuation in the submucosa. The mucosa of the vermiform appendix contains a significant amount of lymphoid tissue grouped in lymphoreticular tissue aggregates. Because of the massive lymphoid tissue amount, the appendix was formerly called the abdominal tonsil. Aggregates can be found not only in mucosa but also in submucosa .
The submucosa is very well developed and contains irregular connective and adipose tissue. It has a strong connection with the mucosa and muscular layers. The tissue includes lymphatic and blood vessels, ganglion cells, and nerve fibers forming two submucosal nerve plexuses - the Meissner’s and Henle’s plexuses.
The muscular layer consists of two parts - the inner is circular layer, but the outer is the longitudinal layer. As mentioned before, the longitudinal layer forms three flat bands or ribbons called the teniae. Between tenia, the longitudinal layer is half of the thickness of the circular layer.
Between the circular and longitudinal layers are located nerve fibers forming the Auerbach’s nerve plexus. The nerve plexus contains thick nerve fiber bundles participating in the reflex realization. When the chyme goes into the cecum from the ileum, the colon gets signals to activate its motor function.
The vermiform appendix does not contain teniae. It has a regular composition of the muscular layer. It includes the muscular layer only at the sites where there are no lymphoreticular aggregates. That is the reason why it looks like the submucosa merges with the muscular layer.
As mentioned before, the visceral layer of the peritoneum covers the cecum and the vermiform appendix from all sides. Both are intraperitoneal organs. Cecum does not have mesentery, but the appendix has a mesoappendix.
Cecum and vermiform appendix functions
Like the rest of the large intestine, the cecum provides the absorption of remaining water and salts. The cecum also works as a reservoir for the chyme that is received from the ileum. The cecum participates in cellulose digestion. In the cecum, the ingredients of food rich in plants are decomposed by bacteria. The cecum provides the fermentation of carbohydrates. As the cecum contains mucus-producing cells, it participates in the lubrication of the intestinal lining for a better waste product movement.
The vermiform appendix contains a massive amount of lymphoreticular tissue. Therefore it primarily provides the immunological function.
Neurovascular supply of cecum and vermiform appendix
Arterial blood supply
The arterial blood supply to the cecum is provided by the anterior and posterior cecal branches of the ileocolic artery. The ileocolic artery is a branch of the superior mesenteric artery. The vermiform appendix is perfused by the appendicular branch arising from the ileocolic artery.
The venous drainage is provided by the cecal veins draining to the ileocolic vein and next to the superior mesenteric vein. From the superior mesenteric vein blood is carried next to the portal vein.
Lymphatic drainage from the cecum happens via the superior mesenteric nodes.
Parasympathetic innervation is provided by the vagus nerve (CN X). But the sympathetic innervation comes from the superior mesenteric plexus.
Appendicitis is an inflammation of the vermiform appendix. It is one of the most common causes of abdominal pain leading to surgery. Everyone is at the risk of developing the condition, but most often, it affects men between the age of 10 to 30 years. Appendicitis can develop suddenly, and then it is called acute appendicitis. The symptoms can come and go over some time, and in that case, it is chronic appendicitis. Acute appendicitis usually presents with more severe symptoms than chronic.
Appendicitis happens because of the blockage or obstruction in the appendix that results in an infection and inflammation, as the bacteria accumulate and grow, leading to tissue swelling. There are various causes, but usually, the blockage happens because of the buildup of stool. Sometimes the exact cause of appendicitis stays unknown. Other causes include the following:
- Intestinal worms
- Enlarged lymphoid aggregates
Appendicitis usually starts slowly with mild cramping and pain around the navel or more in the upper abdominal region. The pain can begin already in the right side of the lower abdomen. As the process continues, the pain becomes more severe and moves to the lower right abdominal region. Pain gets worse when walking or coughing. Low-grade fever and chills, nausea and vomiting, loss of appetite, abdominal bloating, diarrhea, or constipation can be present.
When the pain starts, usually it is dull and cramp-like and located more around the navel. But when the process continues, the pain gets sharper and find more in the right lower part of the abdomen. Pain becomes more severe and constant. The low-grade fever usually is between 37.2 to 38 degrees Celsius. The temperature can go higher in the case of a ruptured appendix. It is crucial to seek medical help as soon as the symptoms start.
The diagnosis usually is made by the following:
- Physical examination
- Blood and urine tests
- Abdominal ultrasound
Appendicitis is characterized by pain worsening when the pressure is put on the site and suddenly released. Typically in appendicitis, the tenderness is present in the lower right quadrant in McBurney’s point. The point is located at one-third the distance between the anterior superior iliac spine and the navel.
Usually, appendicitis needs treatment, and it gets better without proper treatment in extremely rare cases. Appendicitis usually is treated with medication and surgery. In very mild cases, the treatment can only include antibiotics. If the condition gets better during the first few hours after the antibiotic treatment, there might not be a need for surgery.
Appendix removal surgery is called an appendectomy. There are two ways for an appendectomy. Depending on the severeness of the condition, open or laparoscopic surgery can be performed. The recovery after the surgery usually is speedy, but recovery time can depend on the surgery type, overall health, and complications.
The most common complication is a ruptured appendix, and it is a life-threatening condition. The risk of rupture is minimal during the first 24 hours, but it increases within the next 24 hours. The burst usually happens 48 to 72 hours after the first symptoms appeared. If the bursting happens, the infection can quickly spread in the abdomen, causing more severe condition - peritonitis. Sometimes after the rupture of the appendix, it forms an abscess.
Although a person can reduce the risk of obstruction by having a fiber-rich diet (fruits, vegetables, beans, lentils, oats), there are no specific prevention methods. Increased fiber amount can prevent constipation and stool buildup.