Lecture 1 – Mouth to Stomach UNIT 4

 What are the two types of digestion? Which one uses enzymes?

The two types of digestion are mechanical digestion and chemical digestion.

 Chemical digestion uses enzymes to break chemical bonds and make smaller molecules for absorption.

   Which cranial nerves are used by the parasympathetic division to promote GI activity? How does the sympathetic division affect GI activity?

The parasympathetic division promotes GI activity through the facial, glossopharyngeal, and vagus nerves.

The sympathetic division inhibits GI activity by decreasing motility and secretions and contracting inner sphincters, while also reducing blood flow to digestive organs.

The enteric nervous system includes what two plexuses? These plexuses are used to reflexively control all GI activity and are called the short reflexes because they originate within ……

The enteric nervous system includes the submucosal plexus and the myenteric plexus. These plexuses reflexively control all GI activity and are called short reflexes because they originate within the tunics of the GI tract.

Which layer of the muscularis is responsible for peristalsis? Which layer is responsible for mixing?

The outer longitudinal layer of the muscularis is responsible for peristalsis.

Inner circular layer is responsible for mixing.

  How do segmentation and gastric mixing differ? (should be able to list two differences)

Segmentation occurs in the small intestine and involves kneading motions without directional movement for mechanical digestion and mixing.

Gastric mixing, however, occurs in the stomach, involving stronger contractions from multiple muscular layers that produce a more thorough mixing of food and secretions.

 Saliva contains both salivary amylase and lingual lipase enzymes. Which one participates in chemical digestion within the oral cavity? Which one functions once it reaches the stomach?

Salivary amylase participates in chemical digestion within the oral cavity, while lingual lipase functions in the stomach, where the low pH activates it.

   How does saliva inhibit bacterial growth in the oral cavity?

Saliva inhibits bacterial growth by containing lysozyme and IgA, which both have antibacterial properties.

 Before we sit down to eat, what can cause us to salivate? Which cranial nerves stimulate the salivary glands?

Salivation before eating can be triggered by the thought, smell, or sight of food.

The facial nerve stimulates the submandibular and sublingual glands, and the glossopharyngeal nerve stimulates the parotid gland.

What type of digestion are the teeth a part of?

The teeth are part of mechanical digestion, as they physically break down food through mastication.

What type of molecules can be absorbed directly through the mucus membrane of the oral cavity and into the blood?

Small, nonpolar molecules, such as nitroglycerin, can be absorbed directly through the mucous membrane of the oral cavity into the blood.

What is another name for swallowing? What are the three phases?

Another name for swallowing is deglutition, and the three phases are the voluntary phase, the pharyngeal phase, and the esophageal phase.

Before the bolus can move from the oral cavity into the esophagus, what must occur? (what 3 things happen during the pharyngeal phase)

During the pharyngeal phase, the soft palate and uvula elevate to block the nasopharynx, the larynx elevates causing the epiglottis to cover the laryngeal opening, and the superior esophageal sphincter relaxes to allow the bolus to enter the esophagus.

  Why does the superior portion of the esophagus have skeletal muscle fibers instead of smooth muscle?

The superior portion of the esophagus has skeletal muscle fibers to allow for rapid contraction, which helps quickly move swallowed material out of the pharynx so breathing can resume.

   Once the bolus from the mouth mixes with the juices in the stomach, what is the semifluid mass called?

Once the bolus mixes with gastric juices in the stomach, it forms a semifluid mass called chyme

What type of chemical digestion can occur in the stomach? (what is not chemically digested by the stomach)

The stomach performs chemical digestion of proteins and fats but does not chemically digest carbohydrates, though salivary amylase may still act briefly.

   What does the stomach secrete that is needed for vitamin B₁₂ absorption?

The stomach secretes intrinsic factor, which is necessary for vitamin B12 absorption in the ileum.

 How does the mucus differ between the surface mucous cells and the mucous neck cells?  Why is there a difference?

Surface mucous cells produce an alkaline mucus that protects the stomach lining from acid, while mucous neck cells produce an acidic mucus to maintain acidic conditions for HCl formation. The difference ensures both protection and proper acidity.

What two enzymes are released by the chief cells? What do they each digest (be specific)?

Chief cells release gastric lipase, which digests 10–15% of triglycerides, and pepsinogen, which is activated into pepsin to chemically digest denatured proteins into smaller peptides.

What do G-cells secrete?

G-cells secrete the hormone gastrin.

Why is vitamin B₁₂ so important?

Vitamin B12 is important because it is required for the production of erythrocytes (red blood cells); a deficiency can lead to pernicious anemia.

Besides intrinsic factor, parietal cells release hydrochloric acid. But how do they release such a strong acid without becoming damaged from it? (how is it released)

Parietal cells release H⁺ and Cl⁻ ions separately into the lumen of the gastric glands, where HCl forms outside the cell, preventing damage from the strong acid.

Because HCl is so strong it is highly regulated. What hormone can inhibit the release of HCl and where is this hormone being release from?

The hormone somatostatin inhibits HCl release and is secreted by enteroendocrine cells within the mucosa when the stomach pH gets too low.

Nervous and hormonal control of the stomach can alter what two things? (what cannot be altered)?

Nervous and hormonal control of the stomach can alter the force of contraction and secretory activity of the gastric glands, but not the rate of contractions.

  During the cephalic phase of gastric regulation, the Vagus nerve stimulates the stomach to do what?

During the cephalic phase, the vagus nerve stimulates the stomach to increase the force of contraction and enhance gastric gland secretion.

 What stimulates the cephalic reflex?

The cephalic reflex is stimulated by the thought, smell, sight, or taste of food.

 The gastric reflex functions the same as the cephalic reflex but what stimulates the gastric reflex?

The gastric reflex is stimulated when food enters the stomach, activating baroreceptors (stretch) and chemoreceptors (proteins and pH change).

What hormone is also released during the gastric phase? How does this hormone affect the pyloric sphincter?

During the gastric phase, gastrin is released. This hormone stimulates stomach motility and secretions and causes tightening of the pyloric sphincter to slow emptying.

   The pyloric sphincter is never stimulated to ‘open’. So how does chyme from the stomach empty into the small intestines?

Chyme empties into the small intestine when pressure from peristaltic waves in the pylorus becomes greater than the pressure of the pyloric sphincter, allowing 3 mL of chyme to pass through before the sphincter tightens again.

What is the purpose of the intestinal phase?

The purpose of the intestinal phase is to slow stomach emptying to allow adequate time for digestion and absorption in the small intestine.

   How is the intestinal reflex different than the cephalic and gastric reflexes?

The intestinal reflex differs from the cephalic and gastric reflexes because it opposes them, sending decreased signals to the medulla and vagus nerve, which reduces gastric activity.

What two hormones are released during the intestinal phase?

The two hormones released during the intestinal phase are cholecystokinin (CCK), in response to fat, and secretin, in response to acidic chyme. Both inhibit gastric secretions and contractions.