Non-ruminant Digestion

These flashcards cover key terminology and concepts from the Non-ruminant Digestion lecture, aiding in the understanding of gastrointestinal anatomy and digestive processes.

Gastrointestinal Tract (GIT)

The multi-organ system comprising the mouth, esophagus, stomach, small intestine, and large intestine. Its primary role is to coordinate ingestion, the mechanical and chemical breakdown of food, the absorption of essential nutrients into the bloodstream, and the egestion of undigested waste.

Peristalsis

A series of wave-like, involuntary muscle contractions and relaxations involving both the circular and longitudinal muscles of the muscularis externa. This process, regulated by the enteric nervous system, propels a bolus of food or chyme through the digestive tract in a unidirectional manner.

Zymogens (Proenzymes)

Inactive enzyme precursors that must undergo a biochemical change (such as the cleavage of a peptide bond by an activator like $HCl$ or another enzyme) to become catalytically active. This latency prevents autolysis, or the digestion of the cells that produce the enzymes.

Villi and Microvilli

Villi are finger-like projections of the intestinal mucosa, while microvilli are microscopic folds on the apical surface of individual enterocytes (the brush border). Together, they dramatically increase the surface area available for nutrient absorption. Villi contain blood capillaries and lacteals for transport.

Emulsification

The physical process of breaking down large lipid globules into smaller, stable droplets known as micelles. This is facilitated by bile salts, which act as detergents to increase the surface-area-to-volume ratio ($SA:V$), allowing the enzyme lipase to efficiently hydrolyze triglycerides.

Active Transport

The movement of substances across a cell membrane from a region of lower concentration to a region of higher concentration (against the concentration gradient). This process requires specific transmembrane carrier proteins and the expenditure of metabolic energy in the form of Adenosine Triphosphate ($ATP$).

Volatile Fatty Acids (VFA)

Short-chain fatty acids, specifically Acetate ($C<em>{2}$), Propionate ($C</em>{3}$), and Butyrate ($C_{4}$), which are end-products of anaerobic microbial fermentation. They serve as the primary energy source for ruminants and hindgut fermenters, absorbed directly through the gut wall.

Cecum

A large, blind-ended pouch located at the junction of the small and large intestines (the ileocecal junction). In hindgut fermenters such as horses, it houses a vast population of microbes that produce cellulase to ferment complex plant fibers into VFAs.

Mechanical Digestion

The physical disintegration of food into smaller pieces to increase surface area for enzymatic attack. Key processes include:

1. Mastication: Chewing in the oral cavity.
2. Segmentation: Mixing movements in the small intestine.
3. Churning: Muscular contractions of the gastric wall.

Chemical Digestion

The catabolic process of breaking down complex macromolecules (polymers like starch or proteins) into their basic building blocks (monomers like glucose or amino acids) through the action of water and specific digestive enzymes, a process known as hydrolysis.

Chyme

The semi-fluid, acidic mass of partially digested food, water, and gastric secretions ($HCl$ and pepsin) that passes from the stomach through the pyloric sphincter into the duodenum.

Hydrolysis

The fundamental chemical reaction in digestion where a water molecule ($H_{2}O$) is used to break the covalent bonds within a nutrient molecule (e.g., peptide bonds in proteins or glycosidic bonds in carbohydrates).

Rumen

The massive first compartment of the ruminant stomach which acts as a fermentation vat. It contains billions of bacteria, protozoa, and fungi that break down cellulose and hemicellulose, producing microbial protein and VFAs.

Abomasum

The fourth compartment of the ruminant stomach, referred to as the 'true stomach.' It functions analogously to the monogastric stomach by secreting hydrochloric acid ($HCl$) and pepsinogen to begin the chemical digestion of proteins.

Enterocytes

Specialized epithelial cells that line the inner surface of the small and large intestines. They are responsible for the final stages of digestion via brush border enzymes and the subsequent uptake of nutrients into the body.

Facilitated Diffusion

A passive transport mechanism that moves solutes (such as glucose or fructose) across cell membranes down their concentration gradient using specific carrier proteins, without requiring energy ($ATP$).

Bile

An alkaline fluid produced by hepatocytes in the liver and stored in the gallbladder. It contains bile salts, cholesterol, and bilirubin, and is essential for the neutralization of stomach acid and the emulsification of dietary fats.

Pancreas (Exocrine Function)

The glandular organ that secretes 'pancreatic juice' into the duodenum. This juice contains bicarbonate to neutralize chyme and a suite of enzymes including trypsinogen, pancreatic lipase, and amylase for macromolecule breakdown.

Rugae

The internal longitudinal folds of the stomach mucosa and submucosa. These folds allow the stomach to increase its volume (expand) significantly when food is ingested without a corresponding increase in internal pressure.

Mastication

The mechanical process of 'chewing' food, which involves the rhythmic movement of the jaw and teeth. It facilitates the formation of a bolus and increases the surface-area-to-volume ratio ($SA:V$) for more efficient enzyme action.