THE DIGESTIVE SYSTEM

Question 1

The digestive system is

Answer 1

The main function of the digestive system is to digest and absorb nutrients by a peristalsis – sequential contraction of the gastrointestinal tract (𝐺𝐼𝑇), that moves the bolus forwards. The digestive system is regulated by the endocrine system and the autonomic nervous system (𝐴𝑁𝑆).

Question 2

The Oral Cavity (Stoma)

Answer 2

The oral cavity is the site of mechanical ingestion and initial chemical digestion. The mouth, alongside the
usage of teeth, breaks down ingested food, while it is being broken by the saliva (for instance, salivary
amylase brakes down starch into simple sugars).

• The body produces between 750𝑚𝑙 to 1.5𝑙𝑖𝑡𝑒𝑟 of saliva a day.
• The saliva is produced by the salivary glens.

Question 3

The Pharynx

Answer 3

The Pharynx is a cavity that leads from the mouth to the oesophagus. Its inferior border is the epiglottis.
* The epiglottis is a flap of tissue that covers the larynx while swallowing, preventing entrance of food

to the respiratory tract.

• Swallowing reflex mechanism:
  1. Tongue adheres to the palate.
  2. Upper Oesophageal sphincters relaxes.
  3. Epiglottis covers the trachea.

Question 4

Oesophagus

Answer 4

The oesophagus is a muscular tube that serves as a connection between the oral cavity and the stomach. Its muscular wall is composed of two perpendicular layers of muscle tissue.
All of the 𝐺𝐼𝑇 has these two layers of muscle.

Oesophageal sphincters – two muscles that surround and control the openings of the oesophagus:
1. The upper sphincters – prevents food reflex into the pharynx.

2. The lower sphincters (cardiac sphincter) – prevent reflex of food from the stomach to the oesophagus.

Question 5

Stomach

Answer 5

The stomach is a muscular sack that composed of three layers of smooth muscle, allowing it to dilate and
contract forcefully.
The layers are:
1. Longitudinal layer – the outer most layer.
2. Circular layer – the middle layer.
3. Oblique layer – the inner most layer.

Question 6

The stomach functions are:

Answer 6

• Food storage.
• Sterilization.
• Chemical digestion of proteins.

The stomach can hold up to 1.5𝑙𝑖𝑡𝑒𝑟𝑠 of fluids and nutrients. The 𝑝𝐻 of the stomach is between 1 to 2.

Question 7

Chyme

Answer 7

it is a mixture of food and digestive juices. this is the form of food from that moment and so on.

Question 8

Rugae

Answer 8

fold of the mucosal lining of the stomach allowing it be extremely dilate.

Question 9

Sections of the Stomach.

Answer 9

1. Cardia – where contents of the oesophagus empty into.
2. Fundus – the upper curvature of the stomach. Serves as food storage.
3. Body – the main central region of the stomach.
4. Pyloric antrum (pylorus) – the lower section of the stomach through which contents empty into
   the small intestine.
5. Pyloric sphincter – a muscular ring that can prevent flow of chyme into the small intestine when its contracted.

Question 10

Histology of the Stomach - Types of Cells in the Stomach

Answer 10

1. Mucus cells – produce mucus that protects the stomach from damage that can be caused by
   secreted acid.
2. Chief cells – secrete pepsinogen which becomes active (pepsin) in the acidic environment of the
   stomach’s lumen. Active pepsin is an active enzyme that participates in the breaking down of
   proteins.
3. Parietal cells – secrete hydrochloric acid (𝐻𝐶𝐿) which is a very strong acid. These are responsible for the low 𝑝𝐻 levels in the stomach and they also promotes the production of pepsin (more acid → more pepsin).

Question 11

The low 𝑝𝐻 levels of the stomach has a few roles:

Answer 11

• Killing of bacteria.
• Denaturation of proteins.
• Activation of the enzyme pepsin, which is responsible for protein digestion.
• Proper absorption of many minerals, such as calcium, magnesium, zinc, and manganese.

Question 12

The Small Intestine

Answer 12

The small intestine is six meters long. It is the main site of chemical digestion and absorption of food. It is 
composed of three segments
* Duodenum
* Jejunum
* Ileum

Question 13

Duodenum

Answer 13

main site for digestion of carbohydrates, proteins and lipids by enzymes secreted from the pancreas and bile secreted from the liver.

*Into the duodenum, the pancreas and the gallbladder secrete bile and digestive juices. This is the main site
of vitamin baitwell absorption.

Question 14

Jejunum

Answer 14

main site of absorption with the help of projection that increase surface area

Question 15

Ileum

Answer 15

site of reabsorption of bile and other nutrients such as 𝐵12.

Question 16

The surface of the small intestine

Answer 16

Is covered with projections called villi. Theses villi are lined with epithelial cells that have microscopic projection of their membrane called microvilli. These features greatly enhance the surface through which absorption can occur.

Question 17

The Large Intestine

Answer 17

The colon, also known as the large intestine is 1.5 𝑚𝑒𝑡𝑒𝑟𝑠 long and it has a larger dimeter than the small intestine. Its main function it to reabsorb water and minerals especially vitamin 𝐾.

** The large intestine houses a population of more than seven hundred spices of bacteria that have an
immense impact on physiological processes in the body.

Question 18

Section of the Large Intestine 8 sections

Answer 18

1. Cecum – the first compartment of the colon. Connects the large intestine and the small intestine.
2. Appendix – a tiny closed tube structure that is connected cecum.
3. Ascending colon.
4. Transvers colon.
5. Descending colon.
6. Sigmoid colon.
7. Rectum – storage site of faeces.
8. Anus – a muscular ring opening through which wastes are eliminated.

Question 19

Blood Supply to the 𝑮𝑰𝑻

Answer 19

Mainly from three branches of the abdominal aorta:

• Celiac artery (foregut) – supplies blood to the upper parts.
• Superior mesentery (midgut) - supplies blood to the middle parts.
• Inferior mesentery (hindgut) – supplies blood to the lower parts.

Question 20

Accessory Organs

Answer 20

These organs are not really a part of the 𝐺𝐼𝑇 – meaning no actual food goes in them. But, these organs take part and the digestion and help in the activity of the digestive systems:

• The Liver
• The Gallbladder
• Pancreas

Question 21

The Liver

Answer 21

A large red brown organ located in the upper right abdominal cavity. It produces bile (complex fluid that is made of cholesterol) which is a fluid that is important for lipids digestion by forming micelles (hydrophobic core and hydrophobic exterior). It is also responsiblefor
metabolising absorbed nutrients. All the absorbed nutrients flow through the liver before going
back to the heart (hepatic portal system).

Question 22

The Gallbladder

Answer 22

Bile is stored and secreted into the duodenum through the common bile duct.
* Bile is only stored there; it is created by the liver.

Question 23

Pancreas –

Answer 23

Located behind to stomach. It has endocrine and exocrine functions.

• Endocrine – secretes hormones inside of the pancreas like:
• Insulin – decrease glucose levels in the blood.
• glucagon – increase glucose levels in the blood.
• Exocrine – secretes enzyme outside of the pancreas and into the duodenum like:
• Trypsin – breaks down proteins.
• Lipase – breaks down lipids.
• Amylase – breaks down carbohydrates.
• Ribonuclease and deoxyriboclease – break down nucleic acids.

Question 24

Pathology (16)

Answer 24

• Gastro oesophageal reflex disorder (𝐺𝐸𝑅𝐷) – back flow of acid that causes irritation of the oesophagus
  and mucosal damage.
• Inflammatory bowel disease (𝐼𝐵𝐷) – inflammation of the colon and sometimes lower small intestine.
  Types include:
  * Ulcerative colitis.
  * Crohn’s diseases.
• Colon cancer – third most prevalent in men and women.
• Peptic Ulcer – acid damage in the lining of the stomach or the duodenum. Can be caused by bacterial
  infection (helicobacter pylori) or long term use of non-steroidal anti-inflammatory medicines (𝑁𝐴𝑆𝐼𝐷𝑠) such as aspirin and ibuprofen.
• Hepatitis – inflammation of the liver.
• Enteritis – inflammation of the small intestine.
• Colitis – inflammation of the large intestine.
• Appendicitis – inflammation of the appendix.
• Gastritis – inflammation of the stomach.
• Stomatitis – inflammation of the oral cavity.
• Esophagitis – inflammation of the oesophagus.
• Pancreatitis – inflammation of the pancreas.
• Proctitis – inflammation of the rectum.
• Ileitis – inflammation of the ileum.
• Epiglottitis – inflammation of the epiglottis.
• Gastroenteritis – inflammation of the 𝐺 tract (stomach and small intestine). Can be caused by food
  poisoning.