HUBS192 Lecture 25: Chemical Digestion, Mouth, Esophagus & Stomach

Flashcards testing concepts of luminal and contact digestion, salivary glands, gastrointestinal motility patterns, and gastric secretions based on HUBS192 Lecture 25 notes.

What are the three pairs of salivary glands and what type of secretion does each produce?

Sublingual glands produce mucus only, submandibular glands produce mixed secretions, and parotid glands produce serous fluid with amylase.

What are the four stages of chemical digestion for lipids (fats)?

1. Emulsification: Mixing (via motility/segmentation), 2. Emulsification: Stabilisation (via bile salts), 3. Digestion/Hydrolysis (via pancreatic lipase and colipase), and 4. Formation of micelles.

What products are formed when triglycerides undergo hydrolysis by pancreatic lipase and colipase?

One monoglyceride and two free fatty acids.

How do autonomic nervous system pathways regulate salivary secretion in the mouth?

Parasympathetic nervous system (PNS) stimulation produces large amounts of dilute (watery) fluid, while sympathetic nervous system (SNS) stimulation produces small volumes of viscous (thick) fluid.

What are the three time phases that make up one cycle of the migrating motor complex (MMC)?

A $1\,\text{hour}$ period of inactivity, a $30\,\text{min}$ period of medium intermittent uncoordinated activity, and a $15\,\text{min}$ period of intense coordinated peristaltic contractions.

How is hydrogen ion ($H^+$) generated and secreted into the stomach lumen by parietal cells?

$H^+$ and $\text{HCO}_3^-$ are generated from $\text{CO}_2$ and $\text{H}_2\text{O}$ by the enzyme carbonic anhydrase; $H^+$ is then pumped into the stomach lumen by an $H^+\text{-ATPase}$ in the apical membrane.

What mechanism transports chloride ($\text{Cl}^-$) into parietal cells across the basolateral membrane?

An $\text{HCO}_3^-/\text{Cl}^-$ exchanger on the basolateral membrane moves $\text{Cl}^-$ into the cell in exchange for $\text{HCO}_3^-$ leaving the cell.

What is retropulsion in the stomach, and what contraction frequency does it feature?

Retropulsion is the motility process where peristaltic waves grind food against the closed pyloric sphincter and squeeze it backwards toward the stomach body, occurring at a rate of $3\,\text{contractions per min}$.

What are the functions of hydrochloric acid (HCl) secreted by parietal cells during gastric digestion?

HCl produces an electrolyte fluid with a $\text{pH} = 1.0$ that denatures proteins, converts pepsinogen to active pepsin, provides an optimal pH for pepsin, protects against microbes, and dilutes food for mechanical digestion.

Which hormones released by duodenal enteroendocrine cells act to decrease stomach secretion?

Cholecystokinin (CCK) and secretin.