Digestive System

Question 1

Mouth, Esophagus

Answer 1

• The smell of food is a result of your parasympethetic system at work as one of its functions is “rest and digest”
• The anticipation of eating activates your salivary glands to secrete saliva, which helps
  
  1. moisten the food to help it move down the esophagus
  2. Breakdown nutrients
• Ptyalin is an amylase enzyme in our saliva that breaks down sugars
• Lingual Lipase helps begin lipid breakdown
• Our mouths are mechanically breaking down large chunks and mixing it with saliva to form a softer, moderatley sized food wad, called a bolus with the help of a tounge.
• Once the food is swallowed, systemic contraction and relaxation of esophageal muscles known as peristalsis transports each bolus to the stomach
  *

Question 2

Stomach

Answer 2

• The stomach blends and curns the food up using its ridges of muscles that lie in the stomach, these are called ruage
  
  • It churns the food and drink, and to make sure the food is getting broken down, the stomach added hydrochloric acid or HCL into the mix, which is secreted by gastric glands.
  • This creates an incredibly harsh acidic environment at a pH of 2
  • These acid condition helps breakdown the bolous of food even further, by activating special enzymes that can help us split up proteins, with the added benefit of killing some harmful bacteria that you might have consumed.
    
    • One enzyme is pepsin.
      
      • The acidic conditions in our stomach creates the right pH in the environment to convert inactive pepsinogen to active pepsin
        *

Question 3

GERD: Gastroesophageal reflux disease

Answer 3

• Is a disease when harsh gastric juices make their way up into their esophagi.

Question 4

Surface Mucous cells

Answer 4

• In the stomach that prevent the gastric acidic juices from going back up into the esophagus.
• These cells covering the inside of our stomach secrete mucus, which acts as a protective barrier against the corrosive nature of the gastric acid.

Question 5

Chyme

Question 6

Chyme

Answer 6

• The semifluid acid mixture containing food particles and gastric juices in the stomach
• This is the end stage of mechanical digestion

Question 7

Duodenum

Answer 7

• Chyme leaves the stomach via the pyloric sphincter and enters the first part of the small intestines, the duodenum
• As chyme enters the duodenum, the lining of the duodenum gets stimulated and secretes a bunch of enzymes called brush border enzymes
  
  • These enzymes include peptidases, which break down peptides into amino acids and disaccharidases which break down diaccharides into monosaccharides which are more absorbable
  • It also secretes enteropeptidase, which is involved in activating other digestive enzymes from accessory organs, particularly turning on trypsinogen, a protease from the pancrease into trypsin.
• At this point chyme is still acidic, which may inactivate different enzymes, so a peptide hormone secrtin, gets released, stimulating pancreatic enzymes to make their way into the duodenum while also regulating the pH of the digestive tract, reducing HCl, and increasing bicarbonate secretion in the process.
  
  • Note that the pancreatic juices that enter the duodenum through the pancreatic duct include a variety of enzymes that can digest carbohydrates, fats, and proteins, but we could only use them after adjusting the pH to 8.5 with that bicarbonate.
  • tHe bicarbonate from the pancreatic juices neutralizes the acid chyme to enable the other digestive enzymes to keep breaking down peptides and polysaccharides.

Question 8

Bile

Answer 8

• Collection of bile salts, pigments and cholesterol.
• The bile salts breakdown fat molecules by emulsifying them in the cyme into micelles, which is just how molecules can get aggregated together due to the hydrophobic and hydrophilic regions on the bile salts.
• Importance of Bile emulsification:
  
  • prevents fats from separating out
  • Increasing the surface area of the fats
• This is important because it allows the water-soluble enzyme, pancreatic lipase, which is involved in chemically breaking down fats by hydrolyzing their ester bonds, to come in and interact with the emulsified fat mixture
• Bile also makes chyme alkaline, or less acidic and contains pigments like bilirubin which are responsible for making stool brown

Question 9

Jejunum and Ileum

Answer 9

• maximized the surface are of food that passes through the small intestines and allows for maximum absorption of nutrients.
• Finger-like projections called villi are present in the inner lining of the intestine that also allow for maximizing surface area.
  
  • Each villi also has micro villus which further increases the surface area available for absorption.
    
    • These increase the exposed surface area of the gastrointestinal tract
  • Villi need channels to transport the absorbed nutrients, so each villus has a capillary bed to absorb water-soluble nutrients.
    
    • It also has a lymphatic channel, lacteal to absorb fats
  • Constant circulation of the blood and lymph through these channels keep concentrations of nutrients lower in the channels than in the lumen of the intestines
    
    • This facilitates the absorption of nutrients
  • The actual transport of nutrients is possible due to carrier proteins present in the membrane of the intestinal epithelial cells.
  • These carrier proteins transport water-soluble nutrients like sugars and amino acids inside the epithelial cells
    
    • From the epithelial cells, these nutrients then enter the blood and finally reach the liver via hepatic portal circulation.
  • Small fatty acids simply diffuse across the lipid membrane of the intestinal epithelial cells, but a mechanism is needed to transport larger fats and cholesterol
  • Triglycerides and cholesterol get packages into chylomicrons and are transported away via lymphatics circulation.
  • Absorption of water facilitates the absorption of salts and minerals. This maintains the pH in the bowels.

Question 10

Liver

Answer 10

• It processes the nutrient-rich blood received by the hepatic portal vein for storage
• The liver converts glucose to glycogen and fats to triglycerides for later use.
• When our bodies need to use stored nutrients, like during fasting, the liver steps in
• It uses stored forms of nutrients via processes like gluconeogenesis to generate simple monomers for energy production.

Question 11

Large Intestines and Rectum

Answer 11

• Undigested material from the small intestines passes to the large intestines, which is primarily involved in water absorption
• As the mixture enters the large intestines into the cecum through the ileocecal valve.
  
  • from there this mixture continues through the largest part of the large intestines → the colon
  • The colon absorbs any leftover water and salts from the undigested material. In the process, it concentrates the undigested food to from stool, which is ready for excretion in the last part of the large intestine, the rectum
  • Stool is stored in the rectum and excreted through the anus by the opening of sphincters.
• The colon is home for several anaerobic and a few aerobic bacteria.
• The bacteria get a location to colonize and feast, and we get beneficial bacterial byproducts such as vitamin K.