Structures and Functions of the Digestive System

Comprehensive vocabulary flashcards covering the anatomy, enzymatic reactions, and physiological processes of the human digestive system based on lecture notes.

Alimentary Canal

A long muscular open tube, also known as the digestive or Gastrointestinal (GI) tract, which consists of a mouth at one end and an anus at the other.

Herbivore Digestive Tract

A longer digestive tract required because the cellulose in their plant-based diet is more difficult to digest and takes more time.

Accessory Glands

Organs that secrete digestive juices through ducts into the alimentary canal, including the salivary glands, pancreas, liver, and gallbladder.

Peristalsis

Alternating waves of contraction and relaxation in the smooth muscles lining the canal that push food along the digestive tract.

Sphincters

Ring-like valves formed by smooth muscle that close off the tract to regulate the passage of materials between compartments and prevent backflow.

Mechanical Digestion (Mouth)

The process where teeth cut (incisors, canines) and grind (molars) food to increase surface area, while saliva softens it.

Salivary Amylase

An enzyme in saliva that helps breakdown starch (Amylose), a polysaccharide, into the disaccharide maltose by adding $H_2O$.

Bolus

The softened mass of food that is moved by the tongue to the back of the mouth for swallowing.

Uvula

The part of the soft palate that moves up and pushes against the back wall of the pharynx to seal off the nasal cavity during swallowing.

Epiglottis

A valve that closes the opening of the trachea (windpipe) during swallowing to prevent food from entering the lungs.

Lower Esophageal (Cardiac) Sphincter

A ring of muscle at the entrance to the stomach that remains closed to prevent acidic stomach contents from backing up, but relaxes to let the bolus enter.

Rugae

Folds in the walls of the stomach that allow it to expand after a meal.

Gastric Juice

A secretion from gastric glands containing hydrochloric acid ($HCl$), salts, enzymes, water, and mucus.

Chyme

A liquid mixture created in the stomach by the mechanical churning of food with gastric juices.

Pyloric Sphincter

A valve at the end of the stomach that controls the release of chyme into the small intestine.

Pepsin

The active protein-digesting enzyme in the stomach that hydrolyzes proteins into smaller polypeptide chains.

Pepsinogen

The inactive form of pepsin secreted by Chief cells which requires Hydrochloric acid ($HCl$) to become activated.

Parietal Cells

Cells lining the stomach that are responsible for secreting Hydrochloric Acid ($HCl$).

Chief Cells

Cells lining the stomach that are responsible for secreting pepsinogen.

Duodenum

The first region of the small intestine after the stomach which receives secretions from the pancreas and the gallbladder.

Jejunum

The second region of the small intestine, approximately $2.5\,m$ long, which contains the most folds for chemical breakdown and nutrient absorption.

Ileum

The third region of the small intestine, $3\,m$ long, which absorbs nutrients and pushes undigested material into the large intestine.

Villi/Microvilli

Finger-like projections and brush-like fibers on the folds of the small intestine that greatly increase surface area to speed up absorption.

Pancreatic Fluid

A fluid containing enzymes for digesting carbohydrates, lipids, and proteins, as well as bicarbonate to change chyme pH from $1$ to $8$.

Bile

A greenish-yellow fluid produced by the liver containing bile pigments (waste) and bile salts (essential for fat digestion).

Bile Salts

Substances that act like detergent to physically break up fat droplets into smaller droplets, increasing surface area for chemical digestion.

Hepatic Portal Vein

The blood vessel that transports absorbed monosaccharides and amino acids from the small intestine to the liver.

Glycogen Storage

An anabolic process where the liver converts excess glucose into glycogen for temporary storage in the liver and muscles.

Urea

A nitrogen-rich waste product formed in the liver from metabolic reactions involving amino acids, later filtered by the excretory system.

Lacteals

Tiny lymphatic vessels within the villi that absorb protein-coated triglycerides (fats) and transfer them into the bloodstream.

Ileocecal Sphincter

The muscular valve that connects the small intestine to the large intestine.

Large Intestine (Colon)

The structure responsible for absorbing approximately $90\%$ of water from indigestible matter and housing anaerobic bacteria that produce vitamins B and K.

Bilirubin

A by-product of hemoglobin breakdown found in bile that gives feces its brown color after bacterial breakdown.

Enzyme Conditions

Most digestive enzymes work best at a body temperature of $37\,^\circ C$; their bonds can weaken if temperature or pH deviate too much.