THE DIGESTIVE SYSTEM Flashcards
The digestive system is
The main function of the digestive system is to digest and absorb nutrients by a peristalsis โ sequential contraction of the gastrointestinal tract (๐บ๐ผ๐), that moves the bolus forwards. The digestive system is regulated by the endocrine system and the autonomic nervous system (๐ด๐๐).
The Oral Cavity (Stoma)
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 750๐๐ to 1.5๐๐๐ก๐๐ of saliva a day.
- The saliva is produced by the salivary glens.
The Pharynx
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.
Oesophagus
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 ๐บ๐ผ๐ has these two layers of muscle.
Oesophageal sphincters โ two muscles that surround and control the openings of the oesophagus:
1. The upper sphincters โ prevents food reflex into the pharynx.
- The lower sphincters (cardiac sphincter) โ prevent reflex of food from the stomach to the oesophagus.
Stomach
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 โ the outer most layer.
2. Circular layer โ the middle layer.
3. Oblique layer โ the inner most layer.
The stomach functions are:
- Food storage.
- Sterilization.
- Chemical digestion of proteins.
The stomach can hold up to 1.5๐๐๐ก๐๐๐ of fluids and nutrients. The ๐๐ป of the stomach is between 1 to 2.
Chyme
it is a mixture of food and digestive juices. this is the form of food from that moment and so on.
Rugae
fold of the mucosal lining of the stomach allowing it be extremely dilate.
Sections of the Stomach.
- Cardia โ where contents of the oesophagus empty into.
- Fundus โ the upper curvature of the stomach. Serves as food storage.
- Body โ the main central region of the stomach.
- Pyloric antrum (pylorus) โ the lower section of the stomach through which contents empty into
the small intestine. - Pyloric sphincter โ a muscular ring that can prevent flow of chyme into the small intestine when its contracted.
Histology of the Stomach - Types of Cells in the Stomach
- Mucus cells โ produce mucus that protects the stomach from damage that can be caused by
secreted acid. - Chief cells โ secrete pepsinogen which becomes active (pepsin) in the acidic environment of the
stomachโs lumen. Active pepsin is an active enzyme that participates in the breaking down of
proteins. - Parietal cells โ secrete hydrochloric acid (๐ป๐ถ๐ฟ) which is a very strong acid. These are responsible for the low ๐๐ป levels in the stomach and they also promotes the production of pepsin (more acid โ more pepsin).
The low ๐๐ป levels of the stomach has a few roles:
- 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.
The Small Intestine
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
Duodenum
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.
Jejunum
main site of absorption with the help of projection that increase surface area
Ileum
site of reabsorption of bile and other nutrients such as ๐ต12.
The surface of the small intestine
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.
The Large Intestine
The colon, also known as the large intestine is 1.5 ๐๐๐ก๐๐๐ long and it has a larger dimeter than the small intestine. Its main function it to reabsorb water and minerals especially vitamin ๐พ.
** 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.
Section of the Large Intestine 8 sections
- Cecum โ the first compartment of the colon. Connects the large intestine and the small intestine.
- Appendix โ a tiny closed tube structure that is connected cecum.
- Ascending colon.
- Transvers colon.
- Descending colon.
- Sigmoid colon.
- Rectum โ storage site of faeces.
- Anus โ a muscular ring opening through which wastes are eliminated.
Blood Supply to the ๐ฎ๐ฐ๐ป
Mainly from three branches of the abdominal aorta:
- Celiac artery (foregut) โ supplies blood to the upper parts.
- Superior mesentery (midgut) - supplies blood to the middle parts.
- Inferior mesentery (hindgut) โ supplies blood to the lower parts.
Accessory Organs
These organs are not really a part of the ๐บ๐ผ๐ โ 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
The Liver
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).
The Gallbladder
Bile is stored and secreted into the duodenum through the common bile duct.
* Bile is only stored there; it is created by the liver.
Pancreas โ
Located behind to stomach. It has endocrine and exocrine functions.
- Endocrine โ secretes hormones inside of the pancreas like:
- Insulin โ decrease glucose levels in the blood.
- glucagon โ increase glucose levels in the blood.
- Exocrine โ secretes enzyme outside of the pancreas and into the duodenum like:
- Trypsin โ breaks down proteins.
- Lipase โ breaks down lipids.
- Amylase โ breaks down carbohydrates.
- Ribonuclease and deoxyriboclease โ break down nucleic acids.
Pathology (16)
- Gastro oesophageal reflex disorder (๐บ๐ธ๐
๐ท) โ back flow of acid that causes irritation of the oesophagus
and mucosal damage. - Inflammatory bowel disease (๐ผ๐ต๐ท) โ inflammation of the colon and sometimes lower small intestine.
Types include:
* Ulcerative colitis.
* Crohnโs diseases. - Colon cancer โ third most prevalent in men and women.
- Peptic Ulcer โ 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 (๐๐ด๐๐ผ๐ท๐ ) such as aspirin and ibuprofen. - Hepatitis โ inflammation of the liver.
- Enteritis โ inflammation of the small intestine.
- Colitis โ inflammation of the large intestine.
- Appendicitis โ inflammation of the appendix.
- Gastritis โ inflammation of the stomach.
- Stomatitis โ inflammation of the oral cavity.
- Esophagitis โ inflammation of the oesophagus.
- Pancreatitis โ inflammation of the pancreas.
- Proctitis โ inflammation of the rectum.
- Ileitis โ inflammation of the ileum.
- Epiglottitis โ inflammation of the epiglottis.
- Gastroenteritis โ inflammation of the ๐บ tract (stomach and small intestine). Can be caused by food
poisoning.
