Digestion and Absorption (SAS#5)

• Bolus

A swallowed mass of chewed food.

• Chyme

A semiliquid mass formed when the stomach mixes food with gastric juices.

• Epiglottis

Flap that closes off the trachea during swallowing to prevent choking.

• Lower Esophageal Sphincter

Muscle that prevents backflow from stomach to esophagus.

• Pyloric Sphincter

Controls passage of chyme from stomach to small intestine.

• Ileocecal Valve

Sphincter that separates small and large intestines.

• Peristalsis

Wave-like muscular contractions that propel food through the GI tract.

• Segmentation

Circular muscle contractions that mix contents and slowly push them forward.

• Saliva

Contains enzymes like salivary amylase that begin carbohydrate digestion.

• Gastric Juice

Composed of HCl and enzymes; initiates protein breakdown and kills bacteria.

hydrochloric acid

The primary acid in the stomach, produced by parietal cells. It plays a crucial role in digestion by breaking down food, activating enzymes like pepsin, and killing harmful bacteria.

Major digestive event in the stomach

Breakdown of proteins

Pepsin

a proteolytic enzyme, meaning it breaks down proteins, and is a key component of the digestive system in humans and many animals. It is produced in the stomach as an inactive precursor, which is activated by the acidic environment of the stomach.

• Mucus

Protects the stomach lining from acid.

• Pancreatic Juice

Contains digestive enzymes and sodium bicarbonate

Bicarbonate

neutralizes the acidic chyme as it enters the small intestine

Neutral or slightly Alkaline environment

The pH level of the digestive tract contents starting from the small intestine going forward:
As enzymes of the pancreas and intestine work best in this environment

• Bile

Emulsifies fats for digestion; produced in the liver and stored in the gallbladder.

• Villi

Fingerlike projections that increase surface area for nutrient absorption.

Nutrients that goes through the lymph route

Transports fat-soluble nutrients bypassing the liver at first.

Nutrients that goes through the blood route

Transports water-soluble nutrients directly to the liver.

• Chylomicrons

Lipoproteins that transport dietary fats from the intestine.

• VLDL (Very-Low-Density Lipoproteins)

Made by liver to transport triglycerides.

• LDL (Low-Density Lipoproteins)

Deliver cholesterol to cells; high levels increase heart disease risk.

• HDL (High-Density Lipoproteins)

Carry cholesterol back to the liver; protective against heart disease.

Digestion is slower?

Rate of digestion: food rich in fat