Large Intestine

Question 1

What is a large intestine ?

Answer 1

The large intestine is where the absorption of water and salts occurs, where chyme is turned into feces until defecation
It consists of cecum, colon and rectum
Colon divided into ascending, transverse, descending and sigmoid

Question 2

Where is the colon located?

Answer 2

Ascending and descending colon are retroperitoneal
Transverse and sigmoid colon are intraperitoneal as well as the cecum

Question 3

What is the cecum?

Answer 3

The cecum is a blind ended-pouch located at the appendix. The ileocecal valve regulates the passage of material into the large intestine
Once waste is separated from nutrients in the small intestine it is moved through the ileocecal valve into the cecum

Question 4

What is the appendix?

Answer 4

The appendix/vermiform appendix is the reserve of large intestine bacteria and is attached to the cecum. If it becomes inflamed appendicitis occurs (bacteria goes into intraperitoneal cavity and damages organs)
Important as need bacteria throughout your gut for normal function however can live without it

Question 5

Why does the large intestine wall need to be modified?

Answer 5

To store feces, expel feces during defecation, be lubricated and allow absorption of water

Question 6

What are the three parts of the large intestine wall?

Answer 6

Teniae coli - bands of longitudinal muscle
Haustra - series of pouches allows more room for storage
Omental appendices - sacs of fat allows for fat storage, attached to outermost wall of intestine

Question 7

Muscularis modifications

Answer 7

Inner circular layer
Muscularis discontinuous - broken up into three clumps
Outer longitudinal layer forms three thick bands - teniae coli - when we contract the muscle we want strong contractions hence teniae coli allows for stronger contraction

Question 8

Mucosa modifications

Answer 8

Villi are absent in the large intestine - smooth outer most surface
Some enterocytes along surface absorb water and salt
Mucosa invaginates to form intestinal glands which are packed with goblet cells which produce mucus allowing for lubrication and protection

Question 9

Rectum to the anal canal pathway

Answer 9

The rectum is the last part of the large intestine which stores feces
The anal canal connects the rectum to the anus
Anal columns mark boundary where epithelium changes, before it is simple columnar and after it is stratified squamous - protection from abrasion as feces pass

Question 10

What are anal sphincters?

Answer 10

Two sphincters work together to control defection, when they constrict the tube is closed, when relaxed tube open
The internal anal sphincter is smooth muscle under involuntary control
The external anal sphincter is skeletal muscle under voluntary control

Question 11

Defecation reflex process

Answer 11

Feces pass along large intestine into rectum, as this happens rectum distends/stretches, in the muscularis there are strength receptors which send signals causing the internal anal sphincter to relax, more feces will start to move into the anal canal and send more signals to the brain which causes the external anal sphincter to open/relax, muscular contractions occur to push out the feces and abdominal muscle contracts to help expel feces from body

Question 12

Functions and location of the liver

Answer 12

Metabolic processes, detoxifies blood and produces bile (needed for digestion of fats)
Superior right quadrant of abdominopelvic cavity, wedge shaped organ, attached to stomach by lesser omentum, below liver is the gall bladder

Question 13

What is the gall bladder?

Answer 13

Gall bladder is a hollow organ below the liver which stores and concentrates bile. Connected via cystic duct to bile duct
Can become obstructed by gallstones if calcifies bile too much

Question 14

Where is the blood supply for the liver from?

Answer 14

Receives ~25% of cardiac output, needs to detoxify blood (get rid of toxins, drugs, alcohol)
1/3 of blood supply to liver from hepatic artery - oxygenated blood
2/3 from hepatic portal vein - nutrient rich, deoxygenated blood from small intestine, processed by hepatocytes

Question 15

How does blood get supplied to the liver?

Answer 15

The hepatic portal vein, the hepatic artery and the bile duct travel within the lesser omentum
Allows bile duct to get to duodenum to release bile
Portal triad is made up of a branch of hepatic artery, branch of hepatic portal vein and branch bile duct, found on the corners of the lobules and connected via sinusoids

Question 16

What is the structure of the liver?

Answer 16

Liver is broken up into lobes which are broken into lobules (functional units). In the middle of each lobule is a big open space called the central vein. Packed into each lobule are rows of hepatocytes that produce bile. Liver sinusoids sit between the rows of cells and bile canaliculi are found between cells

Question 17

Blood flow and drainage pathway

Answer 17

Blood flows towards central vein and is detoxified, processed by hepatocytes which produce bile which is secreted into canaliculi and empty into the bile duct
Central vein drains detoxified blood into hepatic vein which drains into inferior vena cava and is pumped around the heart

Question 18

What is bile?

Answer 18

Bile travels to gallbladder to be stored and concentrated. Bile duct joins pancreatic duct at hepatopancreatic ampulla which is where the bile mixes from secretions from the pancreas and there is a sphincter which controls ampulla. When relaxed secretions travel through to small intestine and it is mixed with acidic chyme