42. Physiology - Regulation of the Alimentary Canal

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Questions and Answers

What primarily stimulates salivary secretion in the alimentary canal?

Sympathetic nervous system activity

Parasympathetic nervous system activity (correct)

Gastric acid ion concentration

Hormonal regulation

Which cranial nerves are responsible for parasympathetic innervation of salivary glands?

Olfactory (I) and Trigeminal (V)

Vagus (X) and Accessory (XI)

Facial (VII) and Glossopharyngeal (IX) (correct)

Optic (II) and Trochlear (IV)

In Zollinger-Ellison syndrome, what substance is predominantly hypersecreted?

Serotonin

Acetylcholine

Gastrin (correct)

Histamine

What is the effect of autonomic stimulation on salivary secretion?

Increased volume of saliva Signup and view all the answers

Which mechanism is NOT involved in the stimulation of saliva production?

Histamine-mediated activation Signup and view all the answers

What physiological change occurs due to the activation of muscarinic receptors in salivary glands?

Increased HCO3 production Signup and view all the answers

Which component of gastrointestinal hormone regulation is NOT classified as a true endocrine hormone?

Histamine Signup and view all the answers

What is the primary role of the autonomic nervous system in saliva production?

It increases salivary gland volume significantly. Signup and view all the answers

Which substance is primarily responsible for stimulating GIIP secretion?

Fatty acids Signup and view all the answers

What role does somatostatin play in the gastrointestinal tract?

Inhibits release of GI hormones Signup and view all the answers

What triggers the secretion of somatostatin in the GI tract?

Presence of H+ in the lumen Signup and view all the answers

Which of the following statements is true regarding the effects of vagal stimulation on somatostatin?

It inhibits somatostatin secretion Signup and view all the answers

Which of the following peptides is characterized as a paracrine in the GI system?

Somatostatin Signup and view all the answers

What is the primary action of histamine in the GI mucosa?

Enhance gastric acid secretion Signup and view all the answers

What mechanism allows paracrines to act on target cells?

Diffuse over short distances Signup and view all the answers

Which factor predominantly inhibits gastric H+ secretion?

Somatostatin Signup and view all the answers

What is the classification of peptides that can act both as hormones and paracrines?

Neural peptides Signup and view all the answers

Under what condition is the secretion of somatostatin inhibited?

Vagal stimulation Signup and view all the answers

What is the primary action of vasoactive intestinal peptide (VIP)?

Relaxes GI smooth muscle Signup and view all the answers

Which neurocrine is known to stimulate the release of gastrin from G cells?

Gastrin-releasing peptide (GRP) Signup and view all the answers

How does histamine affect gastric secretion?

Increases H+ secretion via direct action Signup and view all the answers

Which statement accurately describes the function of enkephalins in the GI tract?

Stimulate contraction of specific sphincters Signup and view all the answers

Which hormone is secreted by fat cells and plays a role in appetite regulation?

Leptin Signup and view all the answers

What is the role of orexigenic neurons in the hypothalamus?

Stimulate appetite Signup and view all the answers

Which part of the hypothalamus is responsible for inhibiting appetite?

Ventromedial nucleus Signup and view all the answers

What effect does VIP have on HCO3- secretion?

Stimulates HCO3- secretion Signup and view all the answers

What is the role of anorexigenic neurons within the hypothalamic centers?

Decrease appetite by releasing POMC Signup and view all the answers

What is a consequence of enkephalins' action in the GI tract?

Inhibits intestinal secretion of fluids and electrolytes Signup and view all the answers

What is the primary mechanism through which gastrin stimulates H+ secretion?

IP3/Ca2+ second messenger system Signup and view all the answers

Which factor does NOT trigger the secretion of gastrin from G cells?

Increased histamine levels Signup and view all the answers

Which of the following statements about CCKB receptors is correct?

They mediate the effects of gastrin on parietal cells. Signup and view all the answers

What is the role of diacylglycerol in H+ secretion by parietal cells?

It activates protein kinases along with Ca2+. Signup and view all the answers

What is a consequence of the phenomenon called potentiation in H+ secretion regulation?

It enhances the overall action of histamine, ACh, and gastrin. Signup and view all the answers

What effect does ghrelin have on appetite?

It increases appetite by stimulating orexigenic neurons. Signup and view all the answers

Which condition is characterized by gastrin hypersecretion?

Zollinger-Ellison syndrome Signup and view all the answers

What is a common symptom in patients with Zollinger-Ellison syndrome?

Worsening diarrhea Signup and view all the answers

What is a key diagnostic tool for Zollinger-Ellison syndrome?

Computed tomography (CT) scan Signup and view all the answers

What typical gastric fluid pH measurement is associated with Zollinger-Ellison syndrome?

Less than 2.0 Signup and view all the answers

In Zollinger-Ellison syndrome, what can endoscopy reveal?

Gastric ulcerations Signup and view all the answers

What challenges are associated with localizing gastrinomas in suspected Zollinger-Ellison syndrome cases?

They are often too small to detect. Signup and view all the answers

What method is currently considered the most sensitive for localizing gastrinomas?

Somatostatin receptor scintigraphy Signup and view all the answers

What role does gastrin play in gastric fluid secretions?

It stimulates H+ secretion. Signup and view all the answers

What might imaging for a patient with Zollinger-Ellison syndrome reveal?

Hyperplasia of gastric mucosa Signup and view all the answers

Study Notes

Regulation of Saliva Production

Saliva production is controlled by the autonomic nervous system.
Both parasympathetic and sympathetic stimulation increase saliva production, with parasympathetic stimulation being more dominant.
Parasympathetic nerves are carried on the facial (cranial nerve VII) and glossopharyngeal (cranial nerve IX) nerves.
Activation of muscarinic receptors leads to increased saliva production, particularly in volume and enzymatic components.
Sympathetic stimulation, carried through the superior cervical ganglion, has a less pronounced effect on saliva production.
Sympathetic stimulation also contributes to salivary secretion by contributing to vasoconstriction, which helps to maintain adequate blood flow.
Myoepithelial cells contraction is also stimulated to help with expulsion of saliva.

GI Hormones and Regulation of Alimentary Canal

GI hormones are involved in the regulation of the digestive system.
They can act as "true" endocrine hormones, paracrines, or neurocrines.

True Endocrine Hormones

They are secreted into the bloodstream and act at distant locations.
Examples include gastrin, secretin, cholecystokinin (CCK), and glucose-dependent insulinotropic peptide (GIP).

Paracrines

Paracrines are released from endocrine cells in the GI mucosa and act on nearby target cells by diffusion.
Examples include somatostatin and histamine.

Neurocrines

Neurocrines are synthesized by neurons in the GI tract and diffuse across the synaptic cleft to target cells.
Examples include vasoactive intestinal peptide (VIP), gastrin-releasing peptide (GRP), and enkephalins.

Satiety Regulation

Satiety and hunger are regulated by two hypothalamic centers: the satiety center (inhibits appetite) and the feeding center (stimulates appetite).
The satiety center is located in the ventromedial nucleus of the hypothalamus, while the feeding center is in the lateral hypothalamic area.
Anorexigenic neurons release proopiomelanocortin (POMC) to decrease appetite, while orexigenic neurons release neuropeptide Y to stimulate appetite.
Leptin, secreted by fat cells, stimulates anorexigenic neurons and inhibits orexigenic neurons, decreasing appetite.
Ghrelin, secreted by the stomach, increases appetite by stimulating orexigenic neurons and inhibiting anorexigenic neurons.

Gastric Secretions

Gastric secretion is a complex process involved in the digestion of food.
The stomach secretes hydrochloric acid (HCl), pepsinogen, mucus, and intrinsic factor.
HCl is crucial for activating pepsinogen into pepsin, which breaks down proteins.

Three Phases of HCl Secretion in the Stomach

Gastric acid secretion is divided into three phases: cephalic, gastric, and intestinal.
Cephalic phase: Initiated by the sight, smell, or taste of food, it involves vagal stimulation of parietal cells and ECL cells.
Gastric phase: Triggered by distention of the stomach and the presence of food, it involves the release of gastrin and histamine.
Intestinal phase: Stimulated by the arrival of chyme in the duodenum, it involves the release of hormones like secretin and CCK.
Gastrin is a key hormone in the regulation of gastric acid secretion.

Inhibition of Gastric H+ Secretion via Negative Feedback

Gastric acid secretion is regulated by negative feedback mechanisms that prevent excessive acid production.
The presence of H+ in the stomach lumen stimulates the release of somatostatin.
Somatostatin inhibits gastrin and histamine release, reducing acid secretion.
This negative feedback loop helps to maintain a balanced pH in the stomach.

Peptic Ulcer Disease

Peptic ulcer disease is a condition characterized by ulcers in the lining of the stomach or duodenum.
Zollinger-Ellison syndrome (ZES) is a rare condition caused by gastrinoma-derived gastrin hypersecretion, which can lead to peptic ulcer disease without the typical risk factors.
Patients with ZES may also present with symptoms such as diarrhea, abdominal pain, and muscle cramping.
Radiologic localization of gastrinomas is challenging but important in determining tumor stage and optimal management.

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Description

This quiz covers the regulation of saliva production by the autonomic nervous system, emphasizing the roles of parasympathetic and sympathetic stimulation. Additionally, it explores the function of GI hormones in regulating the alimentary canal and their impact on digestive processes.