Lecture 23 - Large intestine and Comments on the Liver

Question 1

Location of the large intestine

Answer 1

Large in diameter but much shorter in length

Consists of
Cecum
Colon
Rectum

Colon is further divided into 
Ascending 
Transverse 
Descending 
Sigmoid 

Ascending and descending colon are reteroperitoneal
Transverse and sigmoidal colon and cecum are intraperitoneal

Question 2

Colon divisions

Answer 2

Colon is further divided into 
Ascending 
Transverse 
Descending 
Sigmoid

Question 3

Diameter of the large intestine

Answer 3

About 7cm in diameter

Question 4

Ileocecal valve

Answer 4

Regulates the passage of material into the cecum

Located between the ileum (small intestine) and the cecum (large intestine) (it is located at the junction between them)

And it will prevent any back flow of faeces and bacteria from the large intestine into the small intestine

Question 5

The appendix

Answer 5

Reserve of large intestine bacteria population - in case the gut needs to be repopulated as bacteria are important for the gut microbiome

Variety of locations, for different people it is different

Inflammation = appendicitis
If it swells up and bursts it is going to burst through the visceral peritoneum and release bacteria and faeces all through the peritoneal cavity which is a problem because it contains fluid and it is very warm which are the kinds of conditions that bacteria thrive in which causes peritonitis

Question 6

Barium enema

Answer 6

Enables xray image to be taken of the large intestine to assess function
Ingest a metallic substance that allows for soft tissue structures to be visualised

Might do a barium enema to see if the valve is working or if there are any holes/blockages in the large intestine

Will hopefully show no back flow into the ileum which means that the illeocecal valve is doing its function by preventing the back flow

Question 7

Gross structure of the large intestine

Answer 7

Teniae coli - bands of longitudinal smooth muscle

Haustra - series of pouches in the wall of the colon

Omental appendices - sacs of fat (dont know the exact function of these)

Question 8

Teniae Coli

Answer 8

Teniae coli - bands of longitudinal smooth muscle

Modification to the muscularis in the large intestine
Puckers the large intestine up into little pockets or pouches which are called haustra

Three bands of longitudinal smooth muscle
Stronger contaction
Condensed regions of longitudinal smooth muscle is needed for creating really strong contractions to propel and move faecal material through the large intestine

Question 9

Haustra

Answer 9

Haustra - series of pouches in the wall of the colon

Separated by semilunar folds

Faecal material is able to move from haustra to haustra and as it moves the faeces will cause distension of the wall which will be a signal that we need to contract in order to keep moving faeces through the colon

Question 10

Omental appendices

Answer 10

Omental appendices - sacs of fat (dont know the exact function of these)

Question 11

Four layers of the gut tube

Answer 11

Lack of villi in the large intestine

Mucosa invaginate to form intestinal glands

Modified muscularis

Question 12

Epithelium of the colon

Answer 12

Mucosa invaginate to form intestinal glands

Remember that the mucosa consists of - epithelium, lamina propria and muscularis mucosae
Note that the muscularis mucosae does not invaginate

Question 13

Mucosa of the colon

Answer 13

Function is for water and salt absorption

Goblet cells produce mucous (protection and lubrication) - allows the easy movement of faecal matter

Question 14

The rectum

Answer 14

Anal columns make boundary where the epitheium changes
Before this point = simple columnar
Epithelium of the anal canal is stratified squamous - close to the exit of the anus, we are going to have an epithelium that is continuous with the epidermis of the skin which will provide us with protection form abrasion

Question 15

Sphincters of the rectum

Answer 15

The internal anal sphincter is smooth muscle (under involuntary control)
The external anal sphincter is skeletal muscle (under voluntary control)

Question 16

Defecation reflex

Answer 16

Movement of faeces into rectum stimulates stretch receptors

Internal anal sphincter relaxes (involuntary)

Conscious decision of defecate - external anal sphincter relaxes

As faeces is moving from the sigmoid colon and into the rectum it is going to cause distension of the rectal wall and this will activate stretch receptors and these will initiate a little reface which will result in stronger contractions of the rectum to propel the faecal material further down and ultimately this will trigger the relaxation of the internal anal sphincter and then the external anal sphincter allows for conscious defecation

Question 17

Summary of the large intestine

Answer 17

Large intestine …
Mucosa invaginated into glands
Significant number of mucus secreting cells
Lack of villi
Longitudinal muscle layer in three bands (teniae coli)

Anal canal…
Sphincters important for control
Stratified squamous epithelium

Question 18

Location of the liver

Answer 18

Location - superior right quadrant of abdominopelvic cavity

Functions (lots) - main one is bile production which is then stored in the gall bladder (bile is important in fat digestion)

Liver is the largest visceral organ we have

Question 19

Blood supply of the liver

Answer 19

Liver receives approximately 25% of the cardiac output

1/3 of the blood supply from hepatic artery - branches off the abdominal aorta to supply the liver with the oxygenated blood

The rest is venous blood from the hepatic portal vein
Nutrient rich, deoxygenated blood from the small intestine
Processed by hepatocytes

The hepatic portal vein, the hepatic artery, and the bile duct travel within the lesser omentum

Question 20

Structure of the liver

Answer 20

Functional units are called lobules

Rows of hepatocytes - produce bile
These rows of hepatocytes in the lobules are orientated around a central vein running through the middle of the lobule

Liver sinusoids between rows, bile canaliculi between cells
Sinusoids are the very leaky capillaries and in between the hepatocytes themselves are bile canaliculi that bile is going to travel in until it reaches the bile duct

Portal triad -
Branch of hepatic artery
Branch of hepatic portal vein
A bile duct

Question 21

The liver

Answer 21

Blood flows towards the central vein
Processed by hepatocytes which produce bile
Bile is secreted into the canaliculi, travels to the bile duct

Blood is going to flow from the branch of the hepatic portal vein and from the branch of the hepatic artery towards the central vein and it will be travelling through the sinusoids which means there will be a mix between oxygenated and deoxygenated blood but the take home message is that this blood is travelling through the sinusoidal capillaries, it is going to be processed by the hepatocytes which will be doing thing like removing toxins from the blood and these hepatocytes also produce bile which travels through the canaliculi to the bile duct

Question 22

Venous drainage of the liver

Answer 22

Central veins drain into the hepatic vein which drains into inferior vena cava

Question 23

Bile and the liver

Answer 23

Bile travels to gall bladder, where it is stored and concentrated

Bile duct ultimately joins pancreatic duct at hepatopancreatic ampulla

When we need bile such as after a fatty meal we can stimulate the gall bladder to contract to squeeze the bile out and into the common bile duct and this bile duct can travel down and meet up with the pancreatic duct at the heptopancreatic ampulla and then the secretions can eventually enter into the duodenal region of intestinal lumen bu the way of the volcano shaped duodenal papilla which means that bile can play it’s important role in fat digestion