digestivo fisio

What are the four main functions of the digestive system?

Motility, absorption, digestion, and metabolism.

What are the main layers of the intestinal wall, from outermost to innermost?

Serosa, muscularis externa (circular + longitudinal muscle), submucosa (with muscularis mucosae), mucosa, and mucosal glands.

What is the role of the mesentery in the digestive system?

It is fibrous connective tissue that holds all the intestines together.

Which two major neural plexuses are found in the intestinal wall?

Myenteric plexus (Auerbach) and submucosal plexus (Meissner).

Where is the submucosal plexus located and what does it innervate?

In the submucosa; it innervates the muscularis mucosae.

Where is the myenteric plexus located and what does it innervate?

In the muscularis externa, between the circular and longitudinal muscle layers; it innervates both layers.

Which receptors modulate the activity of the myenteric plexus?

Mechanoreceptors, via the autonomic nervous system.

What type of muscle is modulated by the myenteric plexus?

Smooth muscle.

How are the two muscle layers of the muscularis externa connected?

By fibers that form a functional syncytium.

What is the approximate diameter and length of the myenteric plexus fibers?

Diameter: 2-10 microns; Length: 200-500 microns.

How does the action potential reach the myenteric plexus?

Through neurons from the central nervous system (CNS).

What are the three types of electrical behaviors in GI smooth muscle cells?

Spike depolarizations, plateau depolarizations, and slow waves.

What does the dotted line represent in GI smooth muscle electrical activity graphs?

The threshold of contraction.

What type of electrical activity occurs in GI smooth muscle at rest?

Slow waves.

What ion influx is responsible for the depolarization phase of slow waves?

Calcium (Ca²⁺) influx.

What ion efflux is responsible for the hyperpolarization phase of slow waves?

Potassium (K⁺) efflux.

What maintains basal muscle tone in the GI tract?

Slow waves.

What triggers stronger GI contractions beyond the basal tone?

Induced depolarization.

What are the main causes of depolarization in GI smooth muscle?

Mechanical distension, acetylcholine (PS nervous system), and hormones.

What is one of the main stimuli for GI muscle contraction?

Mechanical distension.

What is the main neurotransmitter of the parasympathetic nervous system in the GI tract?

Acetylcholine (Ach).

Which two substances cause hyperpolarization of GI smooth muscle?

Noradrenaline and the combination of adrenaline + noradrenaline.

What type of nervous system input causes hyperpolarization in GI smooth muscle?

Sympathetic nervous system.

What type of contractions do slow waves produce at rest?

Rhythmic contractions.

What are tonic contractions in the GI tract?

Sustained, non-rhythmic, segmental contractions.

What is the effect of parasympathetic innervation on the GI tract?

Stimulates muscle function and peristalsis.

What is the effect of sympathetic innervation on the GI tract?

Inhibits peristalsis and muscle contraction.

What are the main neurotransmitters of the parasympathetic and sympathetic systems in the GI tract?

Parasympathetic: Acetylcholine (Ach); Sympathetic: Adrenaline (A) and Noradrenaline (NA).

How do sympathetic fibers arrive at the GI plexuses?

As postganglionic neurons.

How do parasympathetic fibers arrive at the GI plexuses?

As preganglionic neurons that synapse at the walls of the organ.

Besides sympathetic and parasympathetic fibers, what other type of fibers are present in the GI plexuses?

Afferent fibers.

Where is the myenteric plexus located?

Between the circular and longitudinal muscle layers of the muscularis externa.

Where is the submucosal plexus located?

In the submucosa.

What is the main function of the myenteric plexus?

To regulate motility of the GI tract.

What is the main function of the submucosal plexus?

To regulate glandular secretion and local blood flow.

What are the excitatory effects of the myenteric plexus?

Increases tone, intensity, frequency, and velocity of contractions in the muscularis externa via acetylcholine (Ach).

What are the inhibitory effects of the myenteric plexus?

Relaxes sphincters (e.g., pyloric sphincter, ileocecal valve) via vasoactive intestinal peptide (VIP).

What are the local effects of the submucosal plexus?

Local contractions of the submucosal muscle, secretion, and absorption.

How does the submucosal plexus contribute to absorption?

By altering the surface area through submucosal muscle contraction and controlling local secretions and absorptive processes.

What are mixing contractions (segmentation) in the GI tract?

Low-efficiency propulsive contractions that mix chyme and spread it along the epithelial surface to enhance absorption.

What is the main purpose of segmentation in the intestine?

To mix the chyme, divide it into subchymes, and increase contact with the absorptive surface.

What are propulsive contractions and which nervous system mediates them?

Coordinated contractions that move chyme or bolus forward, mediated by the parasympathetic nerves via the myenteric plexus.

What is the pattern of contraction and relaxation in propulsive contractions?

Upstream contraction and downstream relaxation.

How fast does the bolus move in the proximal GI tube during propulsion?

0.5-2 cm/second.

How fast does the bolus move in the distal GI tube during propulsion?

About 1 cm/minute.

How long does it take for the bolus to move from the pylorus to the ileocecal valve?

3 to 5 hours.

Which muscles are responsible for elevating the jaw during chewing?

Temporal and masseter muscles.

Which muscles are responsible for depressing the jaw during chewing?

Lateral and medial pterygoideus, digastric, mylohyoid, and geniohyoid.

What innervates most jaw muscles involved in chewing?

The mandibular nerve (V3), the third branch of the trigeminal nerve.

What innervates the geniohyoid muscle?

C1 spinal nerve.

What is the role of salivary glands in chewing?

They aid in chemical homogenization by secreting enzymes like salivary amylase.

Which cranial nerve innervates the sublingual and submandibular glands?

The facial nerve (CN VII).

Which cranial nerve innervates the parotid gland?

The glossopharyngeal nerve (CN IX).

Does the facial nerve innervate the parotid gland?

No, it courses through the parotid gland but does not innervate it.

What is the function of tongue muscles during chewing?

Mechanical homogenization of food.

What are the four intrinsic lingual muscles?

Superior longitudinal, vertical, transverse, and inferior longitudinal.

What nerve innervates the intrinsic tongue muscles?

The hypoglossal nerve (CN XII).

What are the four extrinsic lingual muscles?

Genioglossus, hyoglossus, styloglossus, and geniohyoid.

What types of sensory inputs is the tongue responsible for?

General sensory (touch) and special sensory (taste).

What nerve provides general sensation to the posterior 1/3 of the tongue?

Glossopharyngeal nerve (CN IX).

What nerve provides general sensation to the anterior 2/3 of the tongue?

Lingual nerve, a branch of the mandibular nerve (V3) from the trigeminal.

What nerve provides taste sensation from the beginning of the pharynx?

Vagal branch (internal laryngeal nerve) of the vagus nerve (CN X).

What nerve provides taste sensation to the posterior 1/3 of the tongue?

Glossopharyngeal nerve (CN IX).

What nerve provides taste sensation to the anterior 2/3 of the tongue?

Chorda tympani branch of the facial nerve (CN VII).

Is the pharyngeal phase voluntary or involuntary?

Involuntary.

What are the three main functions of the pharyngeal phase?

Coordination of bolus passage, prevention of food entering the nasopharynx, and prevention of food entering the lungs.

What seals the nasopharynx from the oropharynx and laryngopharynx during swallowing?

Elevation of the soft palate and uvula.

Which two muscles are responsible for elevating and tensing the palate during swallowing?

Levator veli palatini and tensor veli palatini.

Which cranial nerve senses the presence of food in the pharynx to initiate the swallowing reflex?

Glossopharyngeal nerve (CN IX).

Which cranial nerves provide motor innervation to the palate elevator and tensor muscles during swallowing?

Vagus nerve (CN X) and mandibular nerve (V3, branch of CN V).

What two structures are elevated in pharyngeal phase II?

The pharynx and the larynx.

Why does the larynx move anteriorly during swallowing?

To aid the closing of the epiglottis.

What is the purpose of elevating and widening the pharynx during swallowing?

To receive the bolus more easily.

Which cranial nerve innervates the superior, middle, and inferior pharyngeal constrictors?

Vagus nerve (CN X).

Which cranial nerve innervates the stylopharyngeus muscle?

Glossopharyngeal nerve (CN IX).

Which cranial nerve innervates the salpingopharyngeus and palatopharyngeus muscles?

Vagus nerve (CN X).

What causes the elevation of the pharynx and larynx during phase II?

Contraction of the inner longitudinal pharyngeal muscles.

Do pharyngeal constrictors participate in bolus propulsion during phase II?

No, their role begins in the next phase.

What happens during pharyngeal phase III to protect the airway?

Adduction of vocal cords, deglutition apnea, and closure of the epiglottis.

What reflex is triggered if food enters the airway?

The coughing reflex.

What is the main event of pharyngeal phase IV?

Pharyngeal peristalsis: the propulsion of the bolus.

Which muscles contract to push the bolus into the esophagus?

Outer circular pharyngeal constrictors: superior, middle, and inferior.

What muscle must relax to allow food to enter the esophagus?

Cricopharyngeal muscle (upper esophageal sphincter).

Is the esophageal phase voluntary or involuntary?

Involuntary.

What pushes the food bolus from the pharynx into the esophagus during the esophageal phase?

Sequential contraction of the three pharyngeal constrictor muscles (pharyngeal peristalsis).

What happens to the upper esophageal sphincter once the bolus enters the esophagus?

It closes again.

What is primary esophageal peristalsis?

It's a continuation of the pharyngeal peristalsis, initiated by swallowing, moving the bolus through the esophagus in 5-10 seconds.

What is secondary esophageal peristalsis?

It is triggered by esophageal distention when the bolus is not cleared by primary peristalsis.

What type of muscle is found in the upper third of the esophagus, and how is it innervated?

Striated muscle, innervated by CN IX and CN X via vagal motor fibers from the nucleus ambiguus.

What type of muscle is found in the lower third of the esophagus, and how is it controlled?

Smooth muscle, controlled by the myenteric plexus and vagal efferents from the dorsal motor nucleus of the vagus nerve (CN X).

Is the CNS required for esophageal peristalsis in smooth muscle segments?

CNS is required for primary peristalsis, but secondary peristalsis can occur independently via intrinsic neuromuscular mechanisms.

How can secondary peristalsis be triggered without CNS input?

Through local distention and electrical stimulation, even in the absence of extrinsic innervation.

What triggers secondary esophageal peristalsis?

Local mechanoreceptors detecting bolus-induced distention.

What happens above the bolus during secondary peristalsis?

Circular muscle contracts; longitudinal muscle relaxes.

What happens below the bolus during secondary peristalsis?

Circular muscle relaxes; longitudinal muscle contracts.

Which neurotransmitters cause relaxation in secondary peristalsis?

VIP (vasoactive intestinal polypeptide) and nitric oxide (NO).

Which neurotransmitters stimulate contraction in secondary peristalsis?

Acetylcholine and substance P.

Where are neurotransmitters released during peristalsis?

To either the circular or longitudinal muscle layers, depending on the bolus position.

What occurs during esophageal phase II?

Relaxation and opening of the lower esophageal sphincter (cardias).

Where does the esophagus pierce the diaphragm?

At the level of the lower esophageal sphincter.