C3.6 - Human Digestive Tract

Diagram of Human Digestive Tract

The Mouth and Dentition

Teeth

Mouth, easier to understand

• Digestion begins in mouth

• Food is broken into smaller pieces by teeth

• Teeth

  • 4 incisors
  • 2 canines
  • 4 bicuspids
  • 6 molars on lower jaw

• Tongue covered w/ papillae which house the taste buds

• Taste buds detect

  • sweet
  • sour
  • salty
  • umami
  • bitter

  

• Roof of mouth divided into hard and soft palate

• Uvula hangs from back edge of soft palate and prevents food from entering pharynx when swallowing

• Salivary glands secrete saliva that contains enzymes such as amylase that start chemical digestive process.

• saliva: water liquid that contains digestive enzymes, mucus, and other chemicals to help chemically digest food

• mucus: sticky substance that coats and lubricates food to slide down tube without harming lining tissues

Pharynx

• After leaving mouth, bolus enters pharynx
• bolus: food ball
• pharynx: short tube shared by digestive and respiratory system
• epiglottis: cartilage flap that temporarily seals airway to prevent food from entering airway

Esophagus

• After leaving pharynx, bolus enters esophagus
• esophagus: muscle-lined tube connecting the mouth and stomach
• Lubricant, mucin is secreted to aid in swallowing
• regurgitation: food returning up esophagus

Peristalsis

peristalsis: movement of food through wave-like contractions of muscle in digestive system

Stomach

• stomach: elastic muscular, J-shaped sac that helps digest bolus
• Interior lined w/ 1000s of gastric juice secreting glands contained in gastric pits
• gastric juice: mixture of hydrochloric acid, enzymes like pepsinogen, and mucus
• Gastric juice and muscular movements render food into thick liquid called chyme
• chyme: acidic, nutrient-rich liquid produced by stomach
• Amount of food entering and leaving stomach controlled by 2 sphincters:
  • esophagal -OR-
  • cardiac + pyloric
• Stomach muscles contract, create churning motion to force chyme into small intest.
• pyloric sphincter: junction where stomach connects to duodenum (small intest.)

The Liver

• Large organ, numerous roles
• hepato-: related to liver
• bile: yellow / greenish alkaline liquid produced by liver
• bile duct: passageway for bile to travel through
• Produce bile salts (alkaline organic salts) from cholesterol
• Bile emulsified or breaks up fats and activates lipases in small intestine
• Bile stored in gallbladder
• Breaks down old red blood cells producing bile pigments:
  • biliverdin and bilirubin
• Detoxifies the blood
• Converts monosaccharides (animal starch) into glycogen
• Stores vitamins A, D, E, K

The Pancreas

• Produces pancreatic juice
• pancreatic juice: clear alkaline liquid that neutralizes acidic chyme and contains enzymes to further break down nutrients
• pancreatic duct: passageway for pancreatic juices to pass through
• Produces enzymes such as pancreatic amylase and lipase
• Releases bicarbonate to neutralize acidic chyme in the duodenum
• Frederick Banting found way to preserve pancreatic insulin
  • to treat Type I Diabetes

Diabetes

1. Diabetes – A group of diseases characterized by high blood glucose levels due to issues with insulin secretion, insulin action, or both.

2. Insulin – A hormone produced by the pancreas that controls blood glucose levels; discovered by Frederick Banting and Charles Best in 1921.

3. Type 1 Diabetes – An autoimmune condition where the pancreas cannot produce insulin; cause is not fully understood and currently not preventable.

4. Type 2 Diabetes – A metabolic disorder where body cells do not respond properly to insulin; strongly linked to obesity and lack of physical activity.

5. Effects of Diabetes – Includes fatigue, vision loss, kidney disease, heart problems, and high blood pressure due to persistent high blood glucose.

6. Lifestyle Impact – Sedentary habits and excess body fat hinder insulin effectiveness, increasing the risk of developing Type 2 diabetes.

The Small Intestines

• small intestine: tube w/ folded walls in the body
• villi: folds in the small intestine that increase surface area for absorption of nutrients
• Intestinal glands found within villi
• Villi have finger like projections called microvilli
• Gross cylindrical surface of 0-4 m² (7-8 pgs. of textbook), incl. villi and microvilli
• Surface area is 300 m² (doubles tennis court)
• Each villus has network of microscopic blood vessels and a small lymph vessel
• lymph vessel: structures that carry fluid away from cells
• Subdivided into 3 regions:
  • duodenum: fairly short, U-shaped region connecting stomach to small intestine
    • pancreatic and bile ducts open into duodenum
  • jejunum: 2.5 m long region that contains more folds and intestinal glands than duodenum
  • ileum: 3 m long region that contains fewer and smaller villi which absorbs nutrients broken down in duodenum and jejunum

Large Intestine

• large intestine: 1.5 m long large tube — subdivided into 4 regions:
  • caecum: blind sack, appendix at extreme end
  • colon: the main parts of the large intestine that absorbs water and minerals
    • site of bacterial fermentation
    • Food enters…
      • ascending colon
      • transverse colon
      • descending colon
• Feces passes out of colon to rectum, then anal canal and sphincter
• feces: undigested food material and other waste products

Chemical Digestion

• digestion: chemical breakdown of food by hydrolysis (adding water molecule)
• Hydrolysis sped up by enzymes:
  • carbohydrases (breaks down carbohydrates)
  • lipases (breaks downfats)
  • proteinases (breaks down proteins)
• Excreted from glands into digestive tract
• Major enzymes involved in digestion:
  • salivary amylase (amylose)
  • pepsin (protein)
  • lipase (fats)
  • maltase (maltose)
  • lactase (lactose)
• Digestive secretions regulated by nerves and hormones
• hormones: chemical messengers transported from one part of the body to another through the blood

Diagnosing Digestive Disorders

Diagnostic Tools

• endoscopy: process where narrow tube inserted into throat and passed into esophagus, stomach, and upper intestine
  • small camera in narrow tube allows doctor to see inside and spot problems
• biopsy: cutting of small piece of digestive tissue to view under microscope
• colonoscopy: thin, lighted tube w/ camera inserted through rectum to detect unusual growth
• capsule endoscope: pill with camera swallowed that takes picture of tract before being eliminated

Examples of Digestive Disorders

Condition	Description	Diagnosis and Treatment
Gastroesophageal reflux disease (GERD)	Acid from the stomach frequently flows back into the esophagus.	Avoid smoking, alcohol, and overeating. Use antacids. Surgery may be needed in some cases.
Ulcer	Damage to stomach lining causes irritation by acid.	Tests like blood, stool, X-ray, and endoscopy identify the ulcer and its cause (often H. pylori).
Inflammatory Bowel Disease	Intestines become inflamed and develop ulcers.	Believed to be an allergic reaction to foreign substances in the intestines. Treated with medication or surgery.
Constipation	Stool moves too slowly or becomes too hard due to lack of fiber or other causes.	Eat a high-fiber diet, drink water, and exercise regularly.
Diarrhea	Colon is irritated, reducing water absorption, often due to infection.	Usually resolves with fluids and nutrition. May be a symptom of a more serious condition.

Sources

• https://louis.pressbooks.pub/medicalterminology/chapter/digestive-anatomy/