CGIER 14 - Intestinal enzymes; Liver, hepatitis, cirrhosis; Large intestine

Question 1

List intestinal enzymes and their secretions.

Answer 1

1. Aminopeptidase
2. Dipeptidase
3. Sucrase
4. Maltase
5. Lactase
6. Enterokinase
7. Mucus
8. Succus Entericus

Question 2

What effect does bile have on fat droplets?

Answer 2

Bile contains large amounts of bile salts that have a detergent effect on fat droplets, turning them into minute bile salt micelles. This allows pancreatic lipase to break triglycerides into glycerol and fatty acids.

Question 3

What are the five functions of the liver?

Answer 3

1. production of bile
2. metabolism and storage of food
3. blood consumption activities (blood sugar)
4. detoxification activities (alcohol & drugs)
5. destruction of old red blood cells (after 120 days)

Question 4

Where do nutrients from the gut go?

Answer 4

Nutrients from the gut go directly to liver cells, in which they may be broken down further, stored, or redistributed.

Question 5

Describe the entire structure of the liver, and explain how the pancreas works.

Answer 5

The liver is divided into a large right lobe and a smaller left lobe, and two smaller lobes on the ventral side. Each lobe is composed of many hexagonal lobules that are made of hepatocytes. A two cell thick wall of hepatocytes separates each sinusoid. At the 6 corners of the hexagonal lobules, there is the hepatic artery, hepatic portal vein, and hepatic bile duct called the portal area. From the portal area, blood flows from the hepatic portal vein to the sinusoids and then to the central vein. Bile flow is the reverse. Bile is carried from the hepatocytes that secrete it, through the bile canaliculi to the hepatic bile duct. From there, bile either goes directly into the duodenum or to the gallbladder via the cystic duct.

Question 6

How does the gallbladder secrete bile?

Answer 6

The secretion of bile is stimulated by the hormones secretin and cholecystokinin which are produced in the duodenal crypts of Liberkuhn when chyme enters the duodenum. Secretin stimulates the bile duct to produce sodium bicarbonate which expands the volume of bile and increases the flow out into the intestine to compact the acidity of chyme. Cholecystokinin stimulates the secretion of bile by the hepatocytes.

Question 7

What is bilirubin?

Answer 7

Bilirubin is the byproduct of haemoglobin breakdown from the destruction of erythrocytes. Bacteria convert in the large intestine convert bilirubin into stercobilin which gives the faeces its characteristic colour.

Question 8

Explain the formation of gallstones.

Answer 8

Bile is responsible for the secretion of cholesterol in the body. Bile salts keep the cholesterol dissolved within the bile, but high concentrations of cholesterol can lead to the formation of gallstones that can obstruct the flow of bile through the cystic duct to the gallbladder, leading to obstructive jaundice causing intense pain. Gallstones can be removed surgically, but now they can be treated with drugs, ultrasound, and lasers.

Question 9

What is hepatitis?

Answer 9

Hepatitis is the inflammation of the liver, caused by alcohol, drugs, and toxins which results in damage to the hepatocytes and eventually cell death. Prolonged inflammation can lead to cirrhosis which leads to the widespread and progressive death of hepatocytes.

Question 10

What is the function of the large intestine?

Answer 10

The reabsorption of water and ions secreted earlier by the GIT. Bacteria also produce vitamins K and B12.

Question 11

What are the sections of the large intestine called?

Answer 11

There are anatomical sections:

1. Ileocaecal Valve
2. Caecum (Appendix)
3. Accending Colon
4. Transverse Colon
5. Descending Colon
6. Sigmoid Colon
7. Rectum
8. Anus

Question 12

What is Appendicitis?

Answer 12

The inflammation of the appendix.

Question 13

Describe the structure of the large intestine (4).

Answer 13

• 1.5m in length and divided into 4 sections
• has pockets called haustra
• lacks villi, but has goblet cells in mucosa layer
• muscularis externa has circular muscle, but the longitudinal muscle is arranged in three bands called tenia coli

Question 14

Describe the structure of the rectum.

Answer 14

• 12cm in length
• rectum has more goblet cells than the colon
• thicker longitudinal muscle in muscularis externa

Question 15

Describe the structure of the anus.

Answer 15

• 4cm in length

- guarded by internal sphincters (smooth muscle) and external sphincters (striated muscle)

Question 16

How does chyme flow through the large intestine?

Answer 16

1. When chyme enters through the ileocaecal valve and into the caecum, only 100-200ml of it is lost to faeces.
2. Reabsorption of water, ions, bacteria, undigested cellulose, and fat
3. Faeces are propelled through the colon to the rectum via persistaltic waves.
4. Faeces enter the rectum and causes is to distend, stimulating stretch receptors.
5. A process of defaeceation is under the control of the parasympathetic nervous system (internal sphincter) and somatic motor nerves (external sphincter)
6. Defeaceation only occurs when the internal and external sphincter relax, which controlled consciously.