The Large Intestine and Comments on the Liver

Question 1

What are the functions of the large intestine and its basic structural segments?

Answer 1

Functions:
- absorption of water
- storage of faeces until deification

Structure:
Consists of cecum, colon and rectum
Colon is dividd into:
- ascending
- transverse
- descending
- sigmoid (looks like an S)

Question 2

where is the large intestine located?

Answer 2

• ascending and descending colon are retroperitoneal
• transverse and sigmoid colon are intraperitoneal

Question 3

describe the location and some structural features of the cecum

Answer 3

• blind-ended pouch
• location of appendix
• ileocecal valve regulates the passage of material into the large intestine

Question 4

describe the location and features of the appendix

Answer 4

• Called the vermiform appendix
• reserve of large intestine bacteria (good bacteria)
• attached to cecum
• can become inflamed (randomly, no known causal factors or relation): appendicitis

Question 5

what does the large intestine wall need to be modified for and what are some features of the wall that can accomodate these?

Answer 5

• store faeces
• expel aces during defecation
• be lubricated
• allow absorption of water

Teniae coli:
- bands of longitudinal muscle that contract for motility (three of them, discontinuous londitudinal layer but still continues circular muscle layer)
Haustra:
- series of pouches (with folds between them)
Omental appendices:
- sacs of fat

Question 6

describe the large intestine muscularis layer

Answer 6

• inner circular layer
• outer longitudinal layer forms three thick bands called teniae coli
• allows for stronger contraction (to move faeces along)

Question 7

describe the changes to the large intestine mucosa

Answer 7

• no villi
• mucosa invaginates to form intestinal glands which secrete mucous to lubricate large intestine and allow things to slide along smoothly

Cell types:
- absorptive cells for water and salt
- lots of goblet cells produce mucous for protection and lubrication (found in the glands)

Question 8

describe the rectum and the anal canal, including the changes in epithelium

Answer 8

• the rectum is the last part of the large intestine
• stores faeces
• the anal canal connects the rectum to anus
• anal columns mark boundary where epithelium changes
  
  • before: simple columnar
  • after: stratified squamous

Question 9

describe the anal sphincters

Answer 9

• two sphincters work together to control defecation

The internal anal sphincter:
- smooth muscle
- involuntary control
The external anal sphincter (found around and below internal sphincter):
- skeletal muscle
- voluntary control

Note: same idea for urinary system

Question 10

describe the defecation reflex

Answer 10

• movement of faeces into rectum stimulates stretch receptors
• internal anal sphincter relaxes
• conscious decision to dedicate -> external anal sphincter relaxes
• muscular contractions expel faeces from the body

Two reflexes:
- short reflex: triggers a series of contractions in the rectum that move the faeces towards the anus. the internal anal sphincter relaxes
- long reflex: is a spinal reflex that stimulates mass movements that push faeces towards the rectum. it further relaxes the internal anal sphincter

Question 11

describe the function and location of the liver

Answer 11

Function:
- metabolic processes (NO more detail on this in HUBS192)
- detoxifies blood
- produces bile

Location:
- superior right quadrant of abdominopelvic cavity
- wedge shaped organ
- attached to stomach by lesser omentum

Question 12

describe the structure of the gall bladder

Answer 12

• hollow organ below liver
• stores and concentrates bile
• connects via. cystic duct to bile duct
• can become obstructed by gallstones (which form from the bile working too well and becoming calcified)

Question 13

describe the blood supply to the liver

Answer 13

• receives ~25% of the cardiac output (which tells you it is important since it isn’t that bi of an organ)
• 1/3 of blood supply fro hepatic artery
• 2/3 from hepatic portal vein
  - nutrient rich, deoxygenated blood form small intestine
  - processed by hepatocytes

note: the hepatic portal vein, the hepatic portal artery and the bile duct travel within the lesser omentum (just like small structures can travel through the mesentery)

Question 14

describe the smaller level structure of the liver

Answer 14

• Split into lobes which are split into lobules (and these lobules are the functional units) and made up of rows of hepatocytes that produce bile
• liver sinusoids between rows of cells (very leaky capillaries that have open spaces for things like drugs and toxins to get out)
• bile canaliculi between cells
• Portal triad, which is found at every corner of the hexagon like lobules: branch of hepatic artery, branch of hepatic portal vein and bile duct
• central vein in the middle of each lobule

Question 15

describe how the blood and bile travels and is processed in the liver

Answer 15

• blood starts at the corners of the lobules in the triad and then flows towards the central vein
• blood is processed by the hepatocytes as it makes its way towards the central vein, which produce bile
• bile secreted into canaliculi, travels to bile duct
• central veins drain into hepatic vein which drains into inferior vena cava

NOTE: hepatic PORTAL vein goes into the liver, and the hepatic veins drains FROM the liver

Question 16

where does the bile go after it is collected in the bile canaliculi?

Answer 16

• bile travels from canaliculi, into bile duct, up through the cystic duct to the gallbladder to be stored and concentrated
• bile duct joins pancreatic duct at hepatopancreatic ampulla
• when bile needs to go from the gall bladder it travels through the cystic duct, then the bile duct and then into hepatopancreatic ampulla