Digestive System: Vitamins, Layers, and Enzymes in Human Digestion

water soluble vitamins

Vitamins that dissolve in water and are not stored in the body, requiring regular intake. Example: Vitamin C is a water-soluble vitamin important for collagen production.

fat soluble vitamins

Vitamins that dissolve in fat and can be stored in the body. Example: Vitamin D is fat-soluble and supports bone health.

mucosa

The innermost layer of the digestive tract that secretes mucus and absorbs nutrients. Example: The mucosa of the small intestine contains villi for nutrient absorption.

submucosa

The layer of connective tissue under the mucosa containing blood vessels, nerves, and glands. Example: Nutrients absorbed in the mucosa pass through the submucosa to the blood.

muscularis

The muscular layer of the digestive tract responsible for peristalsis. Example: The muscularis contracts to push food down the esophagus.

peristalsis

Wave-like muscular contractions that move food through the digestive tract. Example: Peristalsis moves a bolus from the esophagus to the stomach.

serosa

The outermost layer of the digestive tract that protects and lubricates it. Example: The serosa covers the stomach and reduces friction with other organs.

sphincters

Circular muscles that control the passage of food between digestive organs. Example: The pyloric sphincter regulates food leaving the stomach.

mastication (chewing)

The mechanical breakdown of food by teeth. Example: Chewing bread is mastication.

swallowing reflex

Involuntary action that moves food from the mouth into the pharynx. Example: Swallowing prevents food from entering the airway.

gastroesophageal sphincter

Muscle that prevents stomach contents from flowing back into the esophagus. Example: Heartburn occurs if the gastroesophageal sphincter is weak.

epiglottis

Flap of tissue that prevents food from entering the trachea during swallowing. Example: The epiglottis closes over the windpipe when you swallow.

gastric pits

Small depressions in the stomach lining containing gastric glands. Example: Gastric pits release digestive enzymes and acid.

gastric glands

Glands in the stomach that secrete acid, enzymes, and mucus. Example: Gastric glands produce pepsinogen for protein digestion.

gastric juice

Digestive fluid from gastric glands containing acid and enzymes. Example: Gastric juice helps break down proteins in the stomach.

pepsinogen

Inactive precursor of pepsin, secreted by chief cells. Example: Pepsinogen is converted to pepsin in the acidic stomach.

pepsin

Active enzyme that digests proteins into peptides. Example: Pepsin starts breaking down meat proteins in the stomach.

chief cells

Cells in the stomach that secrete pepsinogen. Example: Chief cells produce pepsinogen to digest proteins.

parietal cells

Stomach cells that secrete hydrochloric acid. Example: Parietal cells create the acidic environment needed for pepsin activation.

mucous cells

Cells in the stomach lining that secrete mucus to protect the stomach wall. Example: Mucous cells prevent stomach lining from being damaged by acid.

peptic (stomach) ulcer

A sore in the stomach lining caused by acid or bacterial infection. Example: Helicobacter pylori infection can lead to a peptic ulcer.

pyloric sphincter

Muscle controlling the passage of chyme from the stomach to the duodenum. Example: The pyloric sphincter slowly releases food into the small intestine.

chyme

Partially digested food mixed with digestive enzymes and acid in the stomach. Example: Chyme moves from the stomach to the small intestine for further digestion.

duodenum

The first part of the small intestine where most chemical digestion occurs. Example: Bile and pancreatic enzymes enter the duodenum to aid digestion.

intestinal villi

Small finger-like projections in the small intestine that increase surface area for absorption. Example: Villi help absorb nutrients like glucose and amino acids.

brush border

Microvilli-covered surface of intestinal epithelial cells that further increase absorption. Example: The brush border contains enzymes to digest sugars and proteins.

microvilli

Tiny projections on epithelial cells that maximize nutrient absorption. Example: Microvilli increase the surface area of the small intestine.

pancreas

Organ that secretes digestive enzymes and hormones like insulin. Example: The pancreas releases amylase to digest carbohydrates.

pancreatic enzymes

Enzymes from the pancreas that digest proteins, fats, and carbohydrates. Example: Trypsin and lipase are pancreatic enzymes.

trypsin

Pancreatic enzyme that breaks down proteins into smaller peptides. Example: Trypsin works in the small intestine to digest meat proteins.

chymotrypsin

Pancreatic enzyme that digests proteins into peptides. Example: Chymotrypsin complements trypsin in protein digestion.

carboxypeptidase

Enzyme that removes amino acids from the ends of peptides. Example: Carboxypeptidase completes protein digestion into amino acids.

liver

Organ that produces bile, metabolizes nutrients, and detoxifies chemicals. Example: The liver produces bile to help digest fats.

bile

Fluid containing salts that emulsify fats in the small intestine. Example: Bile breaks large fat droplets into smaller ones for lipase to act.

bile salts

Components of bile that emulsify fats for easier digestion. Example: Bile salts surround fat droplets to aid digestion.

bilirubin

Yellow pigment from the breakdown of hemoglobin, excreted in bile. Example: Bilirubin gives feces its brown color.

lipase

Enzyme that digests fats into fatty acids and glycerol. Example: Pancreatic lipase helps digest butter in the small intestine.

gallbladder

Organ that stores and releases bile into the small intestine. Example: The gallbladder releases bile when fatty foods are eaten. disaccharides - Carbohydrates composed of two monosaccharide molecules. Example: Lactose in milk is a disaccharide broken down by lactase.

aminopeptidase

Enzyme that removes amino acids from the amino end of peptides. Example: Aminopeptidase completes protein digestion in the small intestine.

lactose intolerance

Inability to digest lactose due to low lactase activity. Example: People with lactose intolerance may get stomach cramps after drinking milk.

nucleotidase

Enzyme that breaks nucleotides into nitrogenous bases, sugars, and phosphates. Example: Nucleotidase digests nucleic acids in the small intestine.

nucleosidase

Enzyme that splits nucleosides into a sugar and a base. Example: Nucleosidase works in the intestine to break down RNA and DNA.

phosphates

Enzymes that remove phosphate groups from nucleotides. Example: Phosphates release phosphate ions for absorption.

chylomicrons

Lipoprotein particles that transport absorbed fats through lymph to blood. Example: Chylomicrons carry dietary triglycerides from the intestine to tissues.

hepatic portal vein

Blood vessel that carries nutrient-rich blood from the intestine to the liver. Example: Glucose absorbed in the small intestine travels via the hepatic portal vein.

cecum

Blind-ended pouch at the start of the large intestine. Example: The human cecum contains some gut bacteria for fermentation.

appendix

Small projection from the cecum with immune functions. Example: The appendix contains lymphoid tissue that helps fight infections.

colon

Major part of the large intestine that absorbs water and salts. Example: The colon converts chyme into solid feces.

rectum

Terminal section of the large intestine storing feces. Example: Feces are expelled from the rectum during defecation.

feces

Solid waste consisting of undigested food, bacteria, and dead cells. Example: Fiber adds bulk to feces, aiding digestion.

flatulence

Gas produced in the digestive tract by bacteria or swallowed air. Example: Beans often cause flatulence due to fermentation by gut bacteria.

defecation reflex

Involuntary reflex causing the rectum to expel feces. Example: Stretching of the rectum triggers the defecation reflex.

anal sphincter

Muscle that controls the release of feces from the anus. Example: The external anal sphincter allows voluntary control of defecation.

gastrin

Hormone that stimulates stomach acid secretion and gastric motility. Example: Gastrin increases after a meal to aid protein digestion.

secretin

Hormone that stimulates bicarbonate secretion from the pancreas. Example: Secretin neutralizes acidic chyme entering the duodenum.

cholecystokinin (CCK)

Hormone that stimulates bile release and pancreatic enzyme secretion. Example: CCK helps digest fats in the small intestine.

glucose-dependent insulinotropic peptide (GIP)

Hormone that stimulates insulin release in response to glucose. Example: GIP helps regulate blood sugar after a meal.

α-melanocyte-stimulating hormone (α-MSH)

Hormone that regulates appetite and energy homeostasis. Example: α-MSH suppresses appetite in the hypothalamus.

incisors

Front teeth adapted for cutting food. Example: Humans use incisors to bite apples.

canines

Pointed teeth used for tearing food. Example: Dogs have prominent canines for ripping meat.

premolars

Teeth used for grinding and crushing food. Example: Premolars help chew vegetables.

molars

Large teeth for grinding food into smaller particles. Example: Molars crush grains and seeds.

microbiomes

Communities of microorganisms living in a specific environment. Example: Gut microbiomes help digest fiber.

gut microbiomes

Microbes living in the digestive tract that aid digestion and immunity. Example: Lactobacillus in the gut microbiome helps digest lactose.

ruminants

Herbivorous animals with specialized stomachs for fermenting plant material. Example: Cows are ruminants that digest cellulose in multiple stomach chambers.

rumen

First chamber of ruminant stomach where microbial fermentation occurs. Example: Microbes in the rumen break down cellulose.

reticulum

Second chamber of ruminant stomach that traps foreign objects. Example: Metal objects swallowed by cows are often caught in the reticulum.

omasum

Third chamber of ruminant stomach that absorbs water and nutrients. Example: Omasum reduces particle size before food enters the abomasum. acquired immune deficiency syndrome (AIDS) - Disease caused by HIV that weakens the immune system. Example: AIDS patients are more vulnerable to infections.

human immunodeficiency virus (HIV)

Virus that attacks helper T cells and causes AIDS. Example: HIV reduces CD4+ T cell counts in infected individuals.

vaccination

Introduction of antigens to stimulate adaptive immunity. Example: The flu shot is a vaccination.

immune system

Network of cells, tissues, and organs that defend the body against pathogens. Example: White blood cells are key components of the immune system.

physical barriers

Structural defenses like skin and mucous that block pathogens. Example: Skin acts as a physical barrier against bacteria.

innate immunity

Non-specific defense mechanisms present from birth. Example: Phagocytosis by neutrophils is part of innate immunity.

immune response

Body's defense mechanism triggered by pathogens. Example: Fever and inflammation are signs of an immune response.

acquired immunity

Immunity developed after exposure to a specific pathogen. Example: Recovering from chickenpox provides acquired immunity.

white blood cells (leukocytes)

Cells that defend the body against infections. Example: Neutrophils are a type of white blood cell.

pathogen-associated molecular patterns (PAMPs)

Molecules on pathogens recognized by innate immune cells. Example: LPS on bacteria is a PAMP.

toll-like receptors

Proteins on immune cells that detect PAMPs. Example: Macrophages use TLRs to detect bacterial infections.

defensins

Small antimicrobial peptides that disrupt pathogen membranes. Example: Defensins in the skin prevent bacterial growth.

phagocytes

Cells that engulf and digest pathogens. Example: Macrophages are phagocytes.

phagocytosis

Process of engulfing and destroying pathogens. Example: Neutrophils perform phagocytosis of bacteria.

inflammation

Response to infection or injury that increases blood flow and immune activity. Example: Redness and swelling indicate inflammation.

local inflammation

Inflammation restricted to a specific tissue. Example: A cut finger shows local inflammation.

macrophages

Large phagocytes that engulf pathogens and present antigens. Example: Macrophages activate T cells by presenting antigens.

cytokines

Signaling molecules released by immune cells. Example: Cytokines recruit neutrophils to infection sites.

mast cells

Cells that release histamine during allergic reactions and inflammation. Example: Mast cells contribute to swelling in a bee sting.

histamine

Chemical that increases blood vessel permeability during inflammation. Example: Histamine causes a runny nose in allergies.

neutrophils

Most abundant type of white blood cell that performs phagocytosis. Example: Neutrophils kill bacteria at infection sites.

monocytes

White blood cells that differentiate into macrophages or dendritic cells. Example: Monocytes circulate in blood until they enter tissues.

chemokines

Signaling molecules that direct immune cells to infection sites. Example: Chemokines attract leukocytes to inflamed tissue.

eosinophils

White blood cells that combat multicellular parasites. Example: Eosinophils attack parasitic worms.

systemic inflammation

Widespread inflammation throughout the body. Example: Sepsis causes systemic inflammation.

fever

Elevated body temperature that enhances immune function. Example: Fever helps inhibit bacterial growth.

pyrogens

Molecules that trigger fever. Example: Bacterial toxins act as pyrogens.

complement system

Proteins that aid in pathogen destruction. Example: Complement proteins form membrane attack complexes.

membrane attack complexes

Structures that create pores in pathogen membranes. Example: MACs lyse bacterial cells.

interferons

Proteins released by virus-infected cells to protect neighboring cells. Example: Interferons signal cells to produce antiviral proteins.

natural killer (NK) cells

Lymphocytes that kill virus-infected and cancerous cells. Example: NK cells release perforin to induce apoptosis.

lymphocyte

White blood cell involved in adaptive immunity. Example: B and T cells are lymphocytes.

perforin

Protein that creates pores in target cell membranes. Example: NK cells use perforin to kill infected cells.