Lecture 26 Flashcards
Where does the large intestine start and travel through?
The large intestine starts at the cecum (coming from the small intestines ilium and controlled by a barrier known as the ileio-caecal valve), comes up to the bottom of the liver and turns (hepatic flexure, or right colic flexure), travels across the body and turns (splenic flexure or left colic flexure) down (descending colon) and then turning to the midline (zigmoid colon) and to the anal canal (anus). It is retroperitoneal (behind the peritoneum) and is held in place by connective tissue.
What are some extra features of the large intestine?
The vermiform apendix has a lumen which is quite closed in adults and open in children (to let more bacteria out) and is still part of the tube, it acts as a storage site for non pathogenic bacteria which live in the gut. The large intestine is contructed of pouches seperated by wall like structures, this occurs because the longitudinal muscle has been changed into three bands which are still longitudinal in direction, this is possibly to increase local force. Epiploic apendiges are storages of fat.
What specialisations does the large intestine have?
The large intestine has all four normal layers but has the loniitudinal muscle changed into the Taenia coli (3 muscle bands), semilunar folds are between the haustra (the pouches of the large intestine).
The mucosa has folded epithelium but not as much as in the small intestine, there are no villi. Simple tubular glands are formed into the connective tissue with the muscularis mucosae behind it to push secreted fluid out of the gland. The fibrous connective tissue contains more cells than normal (the extras are immune cells to protect against pathogenic bacteria).
What do the simple tubular glands of the large intestine function to do?
The simple tubular glands of the large intestine contain absorptive cells to absorb water and salts as well as mucous cells to secrete mucus.
What are the main parts of the rectum?
The rectum contains shelf like structure rectal valves to slow the movement of waste material. There is still an epithelial layer to secrete mucus (lots of mucus secreted from the anal sinus within the anal canal). The internal hemorroidal plexus is a series of blood vessels near the start of the anal canal. The anal canal changes to stratified cells rather than normal epithelial cells. The internal sphincter is smooth muscle and relaxes upon pressure, we have the external sphincter which is skeletal muscle which can be controlled bbby the brain to prevent release of poo.
What nerves control the internal sphincter?
parasympathetic and sympathetic.
How does the liver blood supply work?
The liver recieves blood from the hepatic portal vein and the hepatic artery. The hepatic portal vein provides nutrient rich oxygen poor blood and the hepatic artery provides oxygen rich blood, they branch into interlobular portal vein and interlobular arterys which then mix in sinusoidal capillaries and bile flows in the opposite direction via the interlobular bile duct.
How is the liver arranged at a cellular level?
The livers cells are arranged in rows of hepatocytes with sinusoidal capillaries between the rows and bile canniliculi between the cells (not next to the sinusoids).
