Digestive System Flashcards

Summer Course Petitioning

• If a class is full, students can petition to join by attending lectures and labs.

• Around week two or three, the professor decides based on available space.

• Waitlisted students are prioritized first, followed by petitioners.

• In the fall, Professor Krupa and Doctor Sapira will teach anatomy instead.

  • Both are described as excellent professors, with Professor Krupa being nicer and Doctor Sapira being smarter.

General Structure of the GI Tract

• The gastrointestinal (GI) tract is a tube-like structure made of many organs that allow food to pass through the digestive system.

• General structure that will be specialized later when specific organs are discussed.

Layers of the GI Tract

Mucosa

• Innermost layer.

• Contains an epithelium (type varies between organs).

• Underneath the epithelium is areolar connective tissue called lamina propria.

  • Lamina propria's function is already known as it is made of areolar conn’ective tissue.

• Muscularis mucosae: a smooth muscle layer underneath the lamina propria.

  • Function: Twitches involuntarily to dislodge anything stuck in the lumen of the GI tract.

Submucosa

• Underneath the mucosa.

• Made of moderately dense connective tissue (a type of areolar connective tissue) with elastic fibers.

• Contains lymph nodes, blood vessels, and submucosal glands.

  • Submucosal glands secrete seromucous secretions (a mixture of mucus and water).

• Most mucosal epithelia contain goblet cells, which secrete mucus.

Muscularis Externa

• Contains two layers:

  • Inner circular la yer: Smooth muscles oriented around the circumference of the GI tract.

  • Outer longitudinal layer: Smooth muscles run along the longitudinal tracts (coming out of the board in a 3D perspective).

• Both layers are responsible for peristalsis and segmentation (movements of the GI tract).

Serosa or Adventitia (Outermost Layer)

Serosa

• Made up of two layers with a space in between:

  • Visceral peritoneum: Layer touching the muscularis externa.

  • Parietal peritoneum

  • Peritoneal cavity: Space between the visceral and parietal peritoneum, containing serous fluid (peritoneal fluid).

    • Function: Lubricates the movement of the gastrointestinal tract.

  • Similar to the pericardium and pleural cavity.

• Visceral and parietal peritoneum are made up of two layers itself:

  • Areolar connective tissue (fibrous layer)

  • Simple squamous epithelium (serous layer).

Adventitia

• Made up of dense irregular connective tissue, similar to the tunica adventitia of blood vessels.

• Functions include:

  • Protecting the organ from abrasion.

  • Keeping the organ together.

  • Attaching the organ to surrounding structures.

• Only three organs are made up of adventitia:

  • Esophagus

  • Duodenum

  • Rectum

• All other GI tract organs are made of serosa.

Peristalsis and Segmentation

Peristalsis

• Wave of contraction that pushes material in one direction.

• Allows eating even when doing a handstand (against gravity).

• The distal portions of the esophagus relax, and the wall of muscle pushes food in a specific direction.

• Reverse peristalsis is possible (vomiting).

Segmentation

• Primarily for mixing and mechanical digestion, not for the movement of food.

• Involves squishing and mixing the contents of the GI tract.

• Does not occur in the esophagus (prevents constant gagging while eating).

• Occurs in the stomach and small intestine.

• Less prevalent towards the end of the small intestine and not much in the large intestine.

Organs of the GI Tract

Esophagus

• Has the adventitia layer.

• The mucosa is made of non-keratinized stratified squamous epithelium.

  • Same type of epithelium that lines the nasal and oral cavities.

• Muscularis externa layer:

  • Superior third: Made up of skeletal muscle (voluntary control over swallowing).

  • Inferior third: Made up of smooth muscle (involuntary control).

  • Middle third: Combination of skeletal and smooth muscle.

• Swallowing has voluntary and involuntary portions; digestion is mostly involuntary.

• Food sometimes gets stuck in the chest when eating too fast because the autonomic nervous system hasn't kicked in yet.

• No segmentation occurs, but reverse peristalsis does (vomiting).

Stomach

• Not the MVP of the digestive system; performs surprisingly little digestion.

• Most important function: Stores food and slowly releases it to the small intestine over 4-6 hours for proper digestion.

• Varies in size depending on food intake (can increase up to three times its original size due to rugae).

Rugae

• Bumps on the walls of the mucosal epithelium.

• Increase surface area of the stomach and allow for stretching.

• Assist in mechanical digestion through churning (vigorous segmentation).

• The stomach can do a much more vigorous and effective action of segmentation called churning.

• The reason why the stomach is capable of it is because it has more muscles for it to do it.

Functions of the Stomach

• Store food

• Mechanical digestion.

  • Churning.

• Some chemical digestion.

  • Hydrochloric acid doesn't break covalent bonds; it breaks apart the individual amino acids.

• Kills bacteria on food.

  • Hydrochloric acid is very acidic (almost as acidic as a car battery).

  • Stomach acid is only secreted and released when eating to avoid burning the stomach.

• To avoid food poisoning, chew food slowly to allow the stomach to produce hydrochloric acid.

Stomach Epithelium Composition

• Simple columnar epithelium

• 100% goblet cells

  • Secrete large amounts of mucus to protect against acid.

  • If not protected from acid, it will expose the underlying connective tissue causing gastric ulcer

  • Gastric ulcers are mostly caused from bacterial infections; h pylori.

• Lamina Propria

• Gastric Pits

  • Where cells are made; hydrochloric acid.

  • Replication rate is high.

Layers of the Stomach

• Muscularis mucosae

• Muscularis Externa

  • Contains three Layers:

    • Oblique layer

    • Inner Circular Layer

    • Outer Longitudinal Layer

• Serosa

  • Contains peritoneal Cavity

• Submucosa - remember to draw (oops).

Other Important Features

• This is the organ that receives food from the esophagus

• Passes from the diaphragm through to get there.

  • The diaphragm is important for things other than just breathing. It helps with mechanical digestion.

  • Overeating affects breathing because of the position of the diaphragm.

• Cardiac Sphincter

  • Is a fake sphincter. It does not close.

  • Allows the removal of air (burping) and vomiting.

  • Throwing up a lot can cause enamel to break down.

    • Those diagnosed with Bulimia are at risk.

  • Rats have cardiac sphincters that can close.

    • This is why rat poison is not affective on humans

  • Rodent traps instead rat poison.

  • The diaphragm assists the cardiac sphincter to close.

Acid Reflux/Heartburn

• Occurs when acid from the stomach goes up into the esophagus.

• Causes a burning sensation.

• Can lead to esophageal cancer as goblet cells from the stomach migrate into the esophagus and proliferate.

  • Not all liquid in the stomach is hydrochloric fluid, but has more liquid that acid sometimes. Depends on when the reflux happens.

Gastric Ulcers

• Occur when the mucosal epithelium of the stomach burns away, exposing the underlying connective tissue (lamina propria).

• Can be fatal if large, as hydrochloric acid spreads throughout the abdominal cavity.

• Mostly due to infections, not loss of mucus.

Esophageal Hiatus

• Esophagus passes through it in order to get to the stomach

• The diaphragm assists in the closing of the cardiac sphincter.

Hiatal Hernia

• Organ or piece of organ sticking out in a place where it does not belong.

• Occurs when the diaphragm loses elasticity (common in people 50+).

• Allows the stomach to go through the esophageal hiatus and peaks up through the thoracic cavity.

• Increases the likelihood of heartburn.

• Treatment: Surgery and advise them to stop overeating.

Gastric Bypass Surgery

• Bypasses the stomach, sending food directly to the small intestine.

• Done for weight loss reasons.

• Reduces the amount of food that can be eaten because the stomach's storage function is bypassed.

• Personal opinion: should be a last resort. Eat less instead by controlling the amount of food eaten by the individual.

• Gastric Sleeve: is another form of gastric bypass.

  • However, this procedure is caused mostly because of medical reasonings that is not just about weight: medical conditions like cancer.

• Gastric Band: Wraps around the stomach.

  • Limits food intake

  • Can break if overeaten.

Small Intestine

• Also known as the small bowel

• it is the longest parts of our gastrointestinal tract (20 feet long)

• its metric measurements is about (3 meters long)

• Called "small" due to its small diameter (about 1 inch).

Functions

• Digestion:

  • Almost all chemical digestion.

  • Mechanical digestion (segmentation).

• Absorption:

  • Almost all absorption.

    • Once food is chemically digested into glucose, amino acids, and fatty acids, this process allows nutrients to enter the blood and lymphatic vessels.

Sections of the Small Intestine

1. Duodenum

   • First part of the small intestine.

   • About 12 fingers long.

   • Receives secretions from the pancreas, liver, and gallbladder to assist in digestion.

   • The Duodenum is not capable of handling the acidity from the stomach

     • Pancreas releases bicarbonates mixed with mucus to neutralize acidity from the stomach.

     • Gallbladder/Liver sends Bile. Bile is used to Emulsify matter.

       • Used as a detergent to separate globs of fats into smaller globs for efficiency as a result of surface area.

2. Jejunum

   • Middle section of the small intestine.

   • Where most digestion occurs which is a result of its secretions

   • Called "jejunum" because it means "empty" (always empty during cadaver dissections).

3. Ileum

   • Last part of the small intestine

   • Where most absorption of the small intestine occurs. Most Longest Section

   • Contains many lymph nodes (to break down bacteria absorbed accidentally).

Small Intestine Structure

• Plaques Circulars: folds in the small intestine that increase surface area in the orientation of a circular motion, Just Like Muscularis Externa. It can also be referred to its skirt version: pleated

• Villus: Extensions coming out from the Plaquets Circulars.

  • Increase surface area

• Microvilli: Smaller versions of villi found on the columnar cells.

  • Increase surface area

• All of these structures dramatically increase surface area.

Drawing of Small Intestine

• Mucosal epithelium

  • Villus, and intestinal crypts

  • Simple columnar epithelium with goblet cells (secrete mucus for lubrication only)

    • Because too much mucus that it inhibits the purposes of absoprtion

    • The pancreatic released digestive enzyes that make the mucosal epithelial cells die very fast.

      • Thus Intestinal Crypts is used to make those mucosal epithelial cells

      • Very rapid, every 12 hrs will those cells are replaced.

      • Your epidermis turns over every two weeks.

• Lamina Propria

• Muscularis Mucosae

• Submucosa

  • A regular Connective Tissue, has blood and lymphatic vessels to absorb nutrients

    • Artery with capillary bed

      • Lymphatic and Veins are in the submucosa

        • Capillaries are used for carbohydrates and protein absorbsion.

        • Non Processed fats needs to go to the liver first!

          • It sends it to a lymph vessel that comes up to the Villus

            • Lacteal

              • This vessel if capable of Fat Absorbsion!

• Muscularis externa

• serosa
  Duodenum has adventitia, jejunum and ileum has serosa

Submusocal Gland

• These ceramus fluids can b found in the submucosa.

Large Intestine

• Named after its wider diameter, not its length which is shorter than small.

Functions

1. Store feces:

   • By the time food reaches here, there is nothing left.

2. Reabsorbs or absorbs Water.

3. Stores beneficial bacteria:

   • Has a symbiotic relationship with us:

     • We give things to them that they want; they give us things that we want.

       • We give them a warm environment. food, nutrients, etc.

       • In turn they will give us Vitamins B12 and Vitamin K.

       • 3 lb of bacteria is found in our large intestines and help us from diseases. Those bacteria protect us from foreign invaders.

       • They will cause Inflammation.

• Having the strongest versions of antibiotics, if those cells die; will cause treatment for the loss of bacteria called the biotic transplants

  • Take their poop and wash the poop away to have bacteria and send it back to the patient

    • Can be given as a suppository or as an oral measurement.

Functions of the Small Intestine

• Digestion:

  • Almost all chemical digestion occurs here.

  • Mechanical digestion via segmentation.

• Absorption:

  • Nearly all nutrient absorption happens in the small intestine.

  • Once food is chemically digested into glucose, amino acids, and fatty acids, nutrients enter the blood and lymphatic vessels.