Digestive



4 Components of Digestion








Mechanical/physical digestion








Chemical Digestion






Mouth










































Esophagus


Stomach










Gastric “Juices”




















Small Intestine





Ingestion

  • Takes in nutrients

Digestion

  • Breaks down complex

Absorption

Egestion



Physically break food into smaller pieces

  • Teeth

  • Tongue

  • Palate

  • Cheeks

  • Gizzard (ex birds, crocodilians, some fish)


Enzymes in saliva, stomach, and small intestine break down larger molecules

  • “Ase” often indicates an enzyme 

  • Ex: lipase, protease, amylase

  • Enzymes = proteins


Site of:

  • Ingestion

  • Physical digestion

    • Mastication (chewing)

  • Chemical digestion

    • Salivary amylases breaks down

Accessory Organs

  • The smell of food or presence of it in your mouth triggers the salivary glands

  • Saliva also contains mucus which acts as a lubricant and helps food stick together in a bolus (food mixed with saliva

Parotid Glands - 2 in cheeks

Sublingual Glands -- 2 under tongue

Submandibular glands -- 2 under jaw

Tongue

  • Positions the food for teeth

  • Taste (detects chemical dissolved in solution/ saliva)

  • Taste buds papillae (rough projections of your tongue) are scattered around the tongue (bitter, salty, sweet)

Teeth

Adult humans (omnivores) have: 

Incisors - specialized for cutting

Canines - dagger - shaped for tearing

Premolar and molars - broader and flattened for crushing

Palate

Hard palate

  • Contains bone, at the top and front of the mouth (helps with chewing)

Soft palate 

  • is at the back of the moth and contains the uvula - prevents food from going up you’re noise

Swallowing

  • Food is pushed to the back of the mouth (voluntary) so that it can be swallowed (involuntary)

  • Bolus of food passed through the pharynx to the esophagus

Pharynx

  • The common path of food and air

Epiglottis 

  • Covers the opening of the trachea during swallowing

Soft palate and uvula 

  • Cover the opening to the nasal passages during swallowing


  • Bolus of food moved through the digestive system



  • J-shaped bag- like structure

  • Food enters through the cardiac sphincter leaves by the pyloric sphincter

  • Muscular walls + Rugae churn the food.

  • Food is mixed with gastric juices (enzymes + acid) in the stomach to form a mile “chyme”

  • Lipids and carbohydrates NOT primarily digested in the stomach (mostly proteins)

  • Cardiac sphincter 


Include: mucus, hydrochloric acid (HCl), enzymes and pepsinogen (turns into pepsin


Mucus

  • Provides a protective coat for the stomach lining

HCl

  • Kills many harmful substances that are ingested with food

Pepsin 

  • protein - digesting enzyme that breaks the long amino acid chains in proteins into shorter chains

Ulcers

  • Mucus lining of the stomach breaks down -- the stomach cells are exposed to the HCl and pepsin leading to a peptic ulcer

  • Increases blood flow and burning of tissue, eventually blood vessels break down

  • Many linked to H. pylori bacteria (although stress, diet and other factors contribute)

  • Lykoudis - infected himself with H. pylori, then treated himself



3 Parts

  • Duodenum, jejunum, ileum

    • D.J.I

  • 3 glands: liver, gallbladder and pancreas

  • Most digestion and most absorption of nutrients occurs here

    • 7m long

(Say surface area)

Properties

  • Peristalsis keep the food moving over the same area for enzyme action and absorption

Duodenum

  • Is the first part of small intestine

  • The liver, gallbladder & pancreas all add secretions to the duodenum


  • Bile duct

  • Pancreas produces many important digestive enzymes

  • Secretions (substances) enter the duodenum by pancreatic duct

  • Secretions include: bicarbonate ions, pancreatic amylase, proteases (trypsin) and lipases

Liver and Gallbladder

  • Liver produces bile and gallbladder stores and secretes bile

  • Bile contains emulsifiers that breaks fat and oil into tiny droplets

Jejunum and I=ileum

  • Chemical digestion is complete in the small intestine

  • Most absorption takes place within the small intestine ( approx 80%, the remaining 20% occurs at the stomach and large intestine)

Glucose and Amino Acids

  • Glucose and amino acids cross the cell layers to the capillaries (smallest blood vessels). Blood goes directly to the liver

  • Liver---removes excess glucose -- what does it store it as?

    • Glycogen

  • Liver modifies some amino acids

Fatty acids and Glycerol

  • Fatty acids and glycerol pass through the intestinal epithelium and into lacteals (part of the lymph system) -- go in the bloodstream


  • Secretes hormones insulin and glucagon into blood to regulate blood glucose levels by transporting into liver cells 

  • Beta cells in the pancreas produces insulin

  • Type 1 diabetes - beta cells are attacked by immune system -- not enough insulin to keep blood glucose down

  • Type 2 diabetes - body builds resistance to insulin -- pancreas tries to produce more insulin -- can lead to beta cells being killed off

  • Treatment: insulin injection

The Liver

  • Jaundice - an obstruction of the bile duct