Digestive System functions

Mouth function

Ingestion, mechanical digestion (chewing/mastication), and chemical digestion

Salivary glands function

Three pairs (parotid, submandibular, sublingual) that secrete saliva to lubricate food.

What is Amylase

An enzyme in saliva that begins the chemical breakdown of starches (complex carbohydrates) into maltose

What is Lysozyme

An enzyme in saliva with antimicrobial properties that destroys bacterial cell walls to prevent infection

What is Bolus

The soft, lubricated mass of chewed food mixed with saliva that is swallowed

Esophagus function

Transports the bolus from the mouth to the stomach via involuntary muscular movements

What is Peristalsis

Waves of coordinated, involuntary smooth muscle contractions and relaxations that push food down the digestive tract

What is acid reflux (heartburn)

Occurs when the lower esophageal sphincter fails to close tightly, allowing acidic stomach contents to escape upward into the esophagus, irritating its lining

What is lower esophageal (cardiac) sphincter

A muscular ring at the junction of the esophagus and stomach. It relaxes to let food enter the stomach and constricts to prevent stomach contents from backing up

Stomach Function

Mechanical churning of food, temporary storage, and initiation of protein digestion

Stomach secretions

HCL, (pepsinogen converted to pepsin with HCL), mucus

What is HCL

Lowers stomach pH to kill microbes and denature proteins.

Pepsinogen to Pepsin: Gastric chief cells secrete inactive pepsinogen. In the presence of highly acidic HCl, it cleaves into active pepsin, an enzyme that digests proteins into smaller peptides.

What is mucus

Secreted by mucous cells to form a thick, protective barrier that prevents HCl and pepsin from digesting the stomach wall itself.

What is chyme

The semi-liquid, highly acidic mixture of partially digested food and gastric juices formed by the stomach's churning action.

What is Ulcers

Painful sores in the stomach lining

What causes Ulcers

Primarily caused by infection with the bacterium Helicobacter pylori (H. pylori) or regular, long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen.

Liver function

filtering toxins from the blood, aiding digestion by producing bile, and regulating metabolism by storing energy and producing essential proteins

Gallbladder function

Stores and concentrates bile, releasing it into the duodenum via the common bile duct when fatty foods enter the small intestine.

What makes and stores bile and function

Produced by the liver, stored by the gallbladder. Is an emulsifier (not an enzyme). It breaks large fat globules down into tiny droplets, vastly increasing the surface area for pancreatic lipase to work.

What is gallstones

Hardened deposits of cholesterol or bilirubin that form in the gallbladder. They can block bile ducts, causing severe pain and inflammation.

Pancreas function

Secretes pancreatic juice (an alkaline mixture of bicarbonate and digestive enzymes) into the duodenum.

What is bicarbonate

An alkaline secretion that neutralizes the highly acidic chyme entering from the stomach, raising the pH to an optimal level for intestinal enzymes to function

Digestive enzymes

amylase, lipase, nuclease, trypsin

Amylase function

Continues the breakdown of starches into disaccharides.

Lipase function

Breaks down emulsified lipids (fats) into fatty acids and glycerol.

Nuclease function

Breaks down nucleic acids (DNA and RNA) into nucleotides.

Trypsin function

A protease secreted as inactive trypsinogen; once activated in the duodenum, it digests proteins into shorter peptides.

Small intestine function

The primary site of final chemical digestion and nutrient absorption.

Duodenum function

The first, shortest section. It is the primary site of chemical digestion, mixing chyme with bile, pancreatic juice, and its own brush border enzymes (peptidase for peptides, sucrase/maltase/lactase for sugars, and intestinal lipase for fats)

Jejunum function

The middle section. Highly specialized for the absorption of major nutrients like carbohydrates, amino acids, and fatty acids.

Ilium function

The final section. Absorbs remaining nutrients, vitamin B12, and bile salts before emptying into the large intestine

What is villi

Finger-like projections lining the inner wall of the small intestine. They are covered in microscopic microvilli (the "brush border").

Villi function

They drastically increase the internal surface area of the small intestine to maximize nutrient absorption into the bloodstream and lacteals (lymph vessels)

Celiac’s disease cause

An autoimmune disorder triggered by ingesting gluten (a protein found in wheat, barley, and rye). The immune system mistakes gluten for a threat and attacks the small intestine lining, flattening and destroying the villi.

Celiac’s disease result

Drastically reduces surface area, leading to severe malabsorption of nutrients, malnutrition, and chronic GI distress

Large Intestine function

Reabsorption of water and electrolytes, compaction and storage of feces, and housing a massive microbiome that synthesizes vitamins (like Vitamin K).

Appendix function

A small, worm-like pouch hanging off the cecum. It acts as a reservoir for beneficial gut bacteria

Cecum function

The blind pouch at the start of the large intestine, receiving waste from the ileum

Colon function

process indigestible food material, absorb remaining water and electrolytes, and compact waste into solid stool for elimination

Ascending colon function

Travels up the right side of the abdomen

Transverse colon function

Crosses horizontally from right to left below the stomach.

Descending colon function

Travels down the left side of the abdomen.

Sigmoid colon function

An S-shaped curve leading into the pelvis.

Rectum function

The final straight portion of the large intestine where feces is temporarily stored before elimination

Anus function

The terminal opening of the digestive tract, controlled by internal (involuntary) and external (voluntary) sphincters to regulate defecation

Large intestine diseases

Appendicitis, Diarrhea, Constipation, Hemorrhoids, Polyps/colon cancer

What is appendicitis

Acute inflammation of the appendix, usually caused by a blockage (like trapped stool). It requires emergency surgical removal to prevent rupture, which can cause life-threatening peritonitis (abdominal infection).

What is diarrhea

Occurs when waste moves through the large intestine too rapidly, preventing adequate water reabsorption. Results in loose, watery stools; can cause dehydration.

What is constipation

Occurs when waste moves through the large intestine too slowly, causing excess water to be reabsorbed. Stools become hard, dry, and difficult to pass.

What is hemorrhoids

Swollen, inflamed veins in the lower rectum or anus. They can be caused by straining during bowel movements, pregnancy, or chronic constipation, leading to pain and bleeding.

What is polyps

Small, benign growths on the inner lining of the colon.

What is colon cancer

Over time, certain types of polyps can undergo genetic mutations and transform into malignant tumors (colon cancer). Regular screenings like colonoscopies aim to find and remove polyps before they become cancerous.