Animal Physiology: Biological Molecules and the Digestive System

Comprehensive vocabulary flashcards covering macromolecules, micromolecules, anatomy and physiology of the human digestive tract, and common gastrointestinal disorders.

Monomer

A small molecule that can be bonded to other identical or similar molecules to form a polymer ("a link in the chain").

Polymer

A large molecule composed of repeating monomer units bonded together in a chain.

Carbohydrates

Biological macromolecules composed of carbon, hydrogen, and oxygen in a $1:2:1$ ratio; used as an energy source, for short-term energy storage, and to build cell membranes.

Monosaccharide

A simple sugar monomer consisting of a single sugar ring that breaks down quickly in the body, such as glucose, fructose, and galactose ($C_6H_{12}O_6$).

Condensation Reaction

A chemical reaction in which two molecules join together by the removal of a water molecule.

Disaccharide

A sugar formed when two monosaccharides bond together via a condensation reaction, including maltose, lactose, and sucrose.

Polysaccharide

A complex carbohydrate composed of long chains of bonded monosaccharides, used for energy storage or cellular structures.

Glycogen

A polysaccharide used by animals for storing energy in tissues.

Cellulose

An indigestible structural polysaccharide found in plant cell walls.

Lipids

Insoluble macromolecules composed of carbon, hydrogen, and oxygen that store $2.25$ times more energy per gram than any other biological macromolecule; used for long-term energy storage, insulation, cushioning, hormone synthesis, and cell membranes.

Triglyceride

A lipid molecule composed of one glycerol backbone bonded to three fatty acid chain monomers.

Saturated Fats

Lipids whose fatty acid chains contain only single carbon-carbon bonds, causing them to be solid at room temperature.

Polyunsaturated Fats

Lipids whose fatty acid chains contain multiple carbon-carbon double bonds, causing them to remain liquid at room temperature.

Phospholipids

Lipids that comprise the primary structural component of cell membranes, consisting of a glycerol backbone, two fatty acid chains, and a phosphate group.

Steroids

Lipids characterized by a four-ring carbon skeleton that act as chemical messengers in the body, such as cholesterol, estrogen, and testosterone.

Proteins

Macromolecular polymers composed of amino acid monomers containing carbon, hydrogen, oxygen, and nitrogen; essential for muscle building and repair, tissue maintenance, defense, and enzymatic catalysis.

Essential Amino Acids

The $8$ amino acids that the human body cannot synthesize internally and must obtain through the diet.

Enzymes

Specialized protein catalysts that speed up chemical reactions without being consumed, functioning optimally at body temperature ($37^\circ\text{C}$) and susceptible to denaturing from excessive heat or acidity.

Nucleic Acids

Molecules ($DNA$ and $RNA$) that store genetic information and direct the growth and development of an organism.

Minerals

Inorganic substances required by the body in trace amounts to assist with chemical reactions, tissue development, growth, and immunity.

Water-Soluble Vitamins

Vitamins (such as vitamins $B$ and $C$) that cannot be stored in bodily fat, requiring daily ingestion and being excreted in urine if unused.

Fat-Soluble Vitamins

Vitamins (such as vitamins $A$, $D$, $E$, and $K$) that are capable of being stored within body fat tissues.

Vitamin D

A fat-soluble vitamin synthesized by the skin upon ultraviolet ($UV$) exposure, essential for absorbing calcium and building bones.

Ingestion

The primary digestive stage of taking in nutrients, chemical energy, vitamins, and minerals into the body.

Mechanical Digestion

The physical breakdown of food matter into smaller pieces through mechanical processes like chewing or stomach churning.

Chemical Digestion

The molecular breakdown of food particles into absorbable nutrients through enzymatic chemical reactions.

Bolus

A moist, rounded mass of chewed food formed by the tongue before swallowing.

Amylase

An enzyme present in saliva that breaks down starch (amylose) into simpler carbohydrates during chewing.

Epiglottis

A flap of tissue that folds over the entrance of the trachea during swallowing to prevent food from entering the respiratory tract.

Peristalsis

Rhythmic, wave-like contractions of smooth muscle that propel food downwards through the esophagus and along the digestive tract.

Lower Esophageal Sphincter

A muscular ring at the junction between the esophagus and stomach that relaxes to allow bolus entry and contracts to prevent gastric reflux.

Rugae

Internal folds lining the stomach wall that enable it to expand as it fills with food.

Pepsin

A protein-digesting enzyme contained in gastric juice that cleaves proteins within the bolus inside the stomach.

Chyme

A thick, acidic semifluid mass of partially digested food and gastric juices produced in the stomach.

Pyloric Sphincter

A muscular valve situated at the distal outlet of the stomach that regulates the gradual release of chyme into the small intestine.

Duodenum

The initial, shortest segment of the small intestine that receives secretions from the pancreas and liver/gallbladder, where the majority of chemical digestion takes place.

Bile

A greenish-yellow fluid generated by the liver and stored in the gallbladder, containing waste bile pigments from dead red blood cells and fat-emulsifying bile salts.

Bile Salts

Compounds in bile that act like detergents, breaking down large insoluble fat masses into smaller suspended droplets to assist enzymatic digestion.

Pancreatic Fluid

A secretion delivering approximately $1\,\text{L}$ of fluid daily to the duodenum, containing bicarbonate ions to elevate the $\text{pH to } 8$ as well as carbohydrases, proteases, peptidases, and lipases.

Villi

Tiny, finger-like mucosal projections along the small intestine wall that, along with microvilli, amplify the surface area for nutrient absorption over $600\times$.

Jejunum

The middle section of the small intestine (approximately $2.5\,\text{m}$ long) characterized by numerous folds where most nutrient absorption occurs.

Ileum

The final segment of the small intestine with fewer folds and villi, completing nutrient uptake and pushing unabsorbed contents into the cecum.

Cecum

The initial pouch-like region of the large intestine that receives undigested matter from the ileum and attaches to the appendix.

Peptic Ulcers

Open sores that develop in the protective lining of the stomach or duodenum when mucus barriers weaken against gastric juices and pepsin, often triggered by Helicobacter pylori.

Crohn's Disease

A chronic inflammatory bowel disease ($\text{IBD}$) capable of causing inflammation across any portion of the digestive tract, most frequently affecting the ileum and colon.

Ulcerative Colitis

An inflammatory bowel disease ($\text{IBD}$) specifically targeting the mucosal lining of the colon, producing ulcers and symptoms such as loose, bloody stools.

Hepatitis

A liver condition marked by inflammation resulting from a viral infection, existing in types $A$, $B$, $C$, $D$, and $E$.

Cirrhosis

A severe, irreversible liver disorder wherein functional hepatic tissue is replaced by non-functional scar tissue, commonly caused by chronic alcoholism or hepatitis $C$.

Gallstones

Hard crystalline deposits formed inside the gallbladder when cholesterol precipitates out of bile.

Diabetes

A chronic metabolic disorder in which cells cannot absorb glucose for energy due to absent or deficient insulin production by the pancreas or impaired insulin sensitivity.

Endoscope

A flexible diagnostic medical device fitted with a light and miniature camera, inserted via the mouth or anus to inspect the interior of the alimentary tract.