Digestive System Lecture Review

Comprehensive vocabulary flashcards detailing the anatomy, histological organization, chemical processes, and physiological regulation of the human digestive system as presented in the lecture notes.

Alimentary Canal

The continuous tube of the digestive system that includes the Oral Cavity, Pharynx, Esophagus, Stomach, Small Intestine ($SI$), and Large Intestine ($LI$).

Accessory Organs

Organs that assist in digestion but are not part of the main canal, including Teeth, Tongue, Salivary Glands ($SG$), Liver ($L$), Gallbladder ($GB$), and Pancreas ($P$).

Propulsion

The movement of food through the $GI$ tract via waves of contraction and relaxation of the wall.

Amylase

A digestive enzyme that breaks down starch into sugars.

Protease

A digestive enzyme that breaks down protein into amino acids.

Lipase

A digestive enzyme that breaks down fat into glycerol and fatty acids.

Absorption

The process where most nutrients enter blood capillaries, while large lipids and lipid-soluble vitamins enter lymphatic capillaries (lacteals).

Saliva

A secretion produced at a rate of $1.5\,L/day$, consisting of $97-99\%$ water, electrolytes, salivary amylase, $IgA$, lysozyme, and mucin.

Extrinsic Salivary Glands

The three pairs of glands located outside the oral cavity: Parotid Gland, Submandibular Gland, and Sublingual Gland.

Salivation Regulation

Triggered by the sight, smell, thought, or taste of food, which stimulates salivary nuclei in the pons to send parasympathetic signals via $CN\,VII$ and $IX$.

Deglutition

The medical term for the process of swallowing.

Mucosa

The innermost layer of the $GI$ tract wall, consisting of epithelium, lamina propria, and muscularis mucosae.

Submucosal (Meissner) plexus

A nerve network located within the submucosa layer of the digestive tract.

Myenteric (Auerbach) plexus

A nerve network located between the longitudinal and circular muscle layers of the muscularis externa.

Esophagus

A food passage located posterior to the trachea and heart that goes through the esophageal hiatus of the diaphragm to link the pharynx to the stomach.

Esophageal Muscularis

A muscular layer composed of $\frac{1}{3}$ skeletal muscle, $\frac{1}{3}$ mixed, and $\frac{1}{3}$ smooth muscle.

Intrinsic Factor

A substance produced by parietal cells in the stomach that is required for the absorption of vitamin $B_{12}$.

Parietal Cells

Stomach cells responsible for secreting hydrochloric acid ($HCl$) and intrinsic factor.

Chief Cells

Stomach cells that secrete pepsinogen, the inactive form of the protease pepsin.

Pepsin

The active form of a protein-digesting enzyme created when $HCl$ converts pepsinogen.

G-cells

Enteroendocrine cells in the stomach that secrete the hormone gastrin into the blood.

Ghrelin

A hormone released by an empty stomach that acts on the hypothalamus to increase appetite.

Rugae

Internal folds of the stomach mucosa that allow for enlargement and expansion.

Stomach Muscularis Externa

Consists of three layers of smooth muscle (longitudinal, circular, and oblique) to allow for mechanical digestion.

Chyme

The mixture of a food bolus and gastric secretions formed by the contractions of the stomach wall.

Retropulsion

The process where the pyloric sphincter closes and stomach contents are forced backward to further mix chyme.

Cephalic Phase

The initial phase of gastric juice release triggered by the taste, smell, or thought of food via the vagus nerves.

Duodenum

The initial segment of the small intestine that receives chyme, bile, and pancreatic juice; it contains alkaline mucous glands.

Jejunum

The second segment of the small intestine, approximately $8\,feet$ long, primary for digestion and absorption.

Ileum

The terminal segment of the small intestine, $12\,feet$ long, which contains Peyer’s patches and is the site of vitamin $B_{12}$ absorption.

Plicae Circulares

Big permanent circular folds of the mucosa and submucosa that increase surface area and act as speed bumps.

Crypts of Lieberkuhn

Intestinal glands located in mucosal invaginations that secrete secretin and cholecystokinin ($CCK$).

Peyer’s patches

Lymphatic nodules specifically located in the submucosa of the ileum.

Liver Lobes

The four anatomical divisions of the liver: Right, Left, Quadrate, and Caudate.

Kupffer cell

Specialized phagocytic cells located within the liver sinusoids.

Bile Salts

Components of bile that emulsify fats into smaller droplets.

Bilirubin

A waste product derived from heme that is found in bile.

Cholecystokinin (CCK)

A hormone secreted by the duodenum that causes gallbladder contraction and hepatopancreatic ($HP$) sphincter relaxation.

Pancreatic Acini

The exocrine part ($99\%$) of the pancreas, containing acinar cells that secrete enzymes and duct cells that secrete $HCO_3^-$.

Islets of Langerhans

The endocrine part ($1\%$) of the pancreas consisting of alpha cells (glucagon) and beta cells (insulin).

Insulin

A hormone that decreases blood glucose by stimulating glucose uptake and glycogenesis.

Glucagon

A hormone that increases blood glucose by stimulating the liver to perform glycogenolysis.

Large Intestine

Extends from the ileocecal junction to the anus; its primary functions are to absorb water and convert chyme into feces.

Bacterial Flora

Trillions of bacteria in the colon that break down indigestibles and produce vitamins $K$, $B_{12}$, riboflavin, and thiamine.

Gastrocolic reflex

The stimulation of mass movements in the colon initiated by the presence of food in the stomach.

Feces Composition

Typically produced at $100\,g/day$, consisting of $75\%$ water and $25\%$ solids (dead bacteria, epithelial cells, fats, proteins, fibers, and bile pigments).

Total Fluid Input

The sum of dietary intake ($2000\,mL$) and digestive secretions ($7000\,mL$), totaling $9000\,mL$ daily.

Intestinal Water Reabsorption

The small intestine reabsorbs $7800\,mL$ of water, while the colon reabsorbs $1250\,mL$, leaving $150\,mL$ lost in feces.