Week 1 - Clinically Relevant Gastrointestinal Physiology Flashcards
What are the functional significances of the gastrointestinal tract (3)?
- Nutrient Assimilation
- Excretionelimination
- Immunity
What are the Four Fundamental processes?
- Digestive (Mechanical and chemical breakdown of food)
- Secretion (Delivery of enzymes, mucus, ions into lumen and hormones into blood)
- Absorption (Transport of water, ions, nutrients from the lumen across the epithelium into blood)
- Motility (Contractions of smooth muscle in the wall of the tube that crush, mix, and propel its contents)
Where does the majority of water absorption occur?
Large intestines or Colon
(T/F) Chemical digestion is going to start in the stomach and then go out through the small intestine
True
Digestive systems of different species have evolved certain specifications that allow adaptation to different diets. What digestive system is the following describing?
- Fermentation vats
- Efficiently utilize cellulose
- Symbiotic microbiota extract nutrients from low-quality food
Herbivores
Digestive systems of different species have evolved certain specifications that allow adaptation to different diets. What digestive system is the following describing?
- Small fermentation vats
- No ability to utilize cellulose
Carnivores
Digestive systems of different species have evolved certain specifications that allow adaptation to different diets. What digestive system is the following describing?
- Diet of both plants and animals
Omnivores
What are the Functional Segments of the Gastrointestinal Tract?
- Mouth
- Esophagus
- Stomach
- Liver
- Pancreas
- Small intestine
- Large intestine
Functional Segments of the Gastrointestinal Tract:
Provides bile salts to the small intestine (which are important for digestion and absorption of fats) and bicarbonate secretion to neutralize gastric acid
Liver
Functional Segments of the Gastrointestinal Tract:
Provides digestive enzymes to the small intestine essential for digestion of fats, CHO, and proteins
Pancreas (secretion of bicarbonate, which neutralizes gastric acid in the duodenum)
Which functional segment of the gastrointestinal tract has major species differences?
Large intestine
What part of the esophagus is the following:
- Located between the pharynx and esophageal body
- Skeletal muscle (crycopharyngeal m.) and part of the cricoid cartilage
- Remains closed except during bolus passage
- Prevents reflux of esophageal contents back into the pharynx and minimizes aerophagia
- Increase pressure: Liquid or acid
- Decreased pressure (to allow escape): Air
Upper esophageal sphincter (UES)
What part of the esophagus is the following:
- Muscular tube
- Species variation (smooth versus skeletal muscle)
Esophageal body
What part of the esophagus is the following:
- Located between the esophagus and stomach
- A physiologic sphincter (or high-pressure zone)
- Anatomic contribution to the LES include a thickening of the distal esophageal muscle and the skeletal muscle of th diaphragm
- Remains closed except during bolus passage into stomach
Gastroesophageal sphincter (GES)
(aka lower esophageal sphincter/LES)
(T/F) The normal tone of the gastroesophageal sphincter (aka Les) is important to prevent the reflux of gastric contents into the esophagus, which causes reflux esophagitis
True
(T/F) A hiatal hernia disrupts the normal anatomy of the proximal esophagus and is an important pre-disposing cause of reflux esophagitis
False, distal esophagus
What can contribute to gastroesophageal reflux and reflux esophagitis?
Decreased LES tone (wider)
The following are examples of?
1. Acetylcholine and cholinergic drugs (e.g., bethanecol)*
2. Metoclopramide, cisapride*
3. Gastrin, histamine, motilin
Increased GES tone
What are the Functions of the stomach?
- Motility
- Secretion
(T/F) Most GI promotility drugs (metoclopramide, cisapride) affect skeletal muscle, so they are not effective to treat dogs with decreased esophageal motility (megaesophagus)
False, affect smooth muscle - not skeletal muscle
What stimulates the gastric parietal cell to secrete acid (lowers the pH)?
Gastrin Stimulates
What are the functions of the small intestine (4)?
- Digestion
- Nutrient Absorption
- Extracts Water
- Motility
What are the functions of the colon (3)?
- Recovery of water & electrolytes
- Formation & storage of feces
- Microbial fermentation
What is often recommended in dogs with delayed gastric emptying?
Low-fat diets are often recommended. A liquid or canned food is often better tolerated than a kibble diet in this situation.
What medication binds to and stimulates motilin receptors so it is used therapeutically in dogs to increase GI motility in dogs?
Antibiotic Erythromycin
Fill in the blanks:
The vomiting reflex is a __________ reflex that is integrated into the vomiting (emetic) center, located in the ______________ formation of the brain
CNS, reticular
What is known as the “Hunger Hormone”?
Ghrelin
What was recently released as an appetite stimulant for dogs?
A ghrelin receptor agonist (Capromorelin: Entyce by Aratana)
Chemical Messengers:
- diffuse across synaptic space to act on postsynaptic receptors
Neurocrine transmitters (neurotransmitters)
Chemical Messenger:
- transmission by way of blood
Endocrine transmitters (hormones)
Chemical Messenger:
- diffusion of chemical messenger through intercellular space between the source cell and the target cell
Paracrine transmitters (e.g., histamine, prostaglandins, somatostatin) -
(T/F) The GI tract is the largest endocrine organ
True
- Source: G-cells of the gastric antrum
- Target Organ: stomach - parietal cells
- 1 Effect: increase Gastric acid secretion
- Stimuli: Luminal protein digestion products, gastric distention, vagal stimulation, increase luminal pH
- Feedback control: negative feedback
- Clearance of circulating gastrin: Kidney, liver, small intestinal (variable)
This is……
Gastrin
What inhibits gastrin secretion?
Acid in gastric antrum (via increase release of somatostatin)
Enteric nervous System (Intrinsic Innervation):
What are the two major networks of nerve fibers that form a single functional unit?
- Myenteric plexus (Motor control)
- Submucous plexus (control of intestinal secretion)
(T/F) The submucosal plexus is really important for motor control and controlling overall motility
False, the Myenteric plexus
(T/F) Norepinephrine associated with stress reactions decrease GI motility and secretions
True
(T/F) Acetylcholine and drugs (bethanecol) or toxins (organophosphates or carbamates) that mimic its parasympathetic cholinergic effects increase GI motility and secretion
True
What are the Extrinsic Innervations?
- Parasympathetic cholinergic activity
- Sympathetic noradrenergic activity
What is an important clinical sign that may be due to local oral or pharyngeal disorders or to systemic causes?
Excessive salivation (ptyalism)
Control of gastric acid secretion:
1. Muscarinic type receptor
2. Neural control
3. increase intracellular calcium -> protein kinases -> phosphorylation of cytoskeletal proteins involved in the transport of H+/K+ ATPase from the cytoplasm to the plasma membrane
This is…….
Acetylcholine (stimulates)
Control of gastric acid secretion:
1. From adjacent enterochromaffin-like (ECL) cells
2. Primary modulator of acid secretion
3. Paracrine effect
4. Activates adenylate cyclase -> increase cyclic AMP and activation of protein kinases involved in the transport of H+/K+ ATPase
This is……
Histamine (H2 type receptor) (stimulates)
Control of gastric acid secretion:
1. Secreted by G-cells in gastric mucosa
2. Stimulates histamine release from ECL cell (+/- direct receptor on parietal cell)
This is……
Gastrin (stimulates)
- “in an endocrine fashion”
Peptide hormones (somatostatin, secretin, GIP, glucagon) - _________ gastric secretion
inhibit
Prostaglandin PGE2 (inhibits) – Inhibits __________ ___________
adenylate cyclase
(T/F) Inhibition of gastrin acid secretion is an important target for therapeutic intervention
True
What is also known as “the law of the gut”?
- A contractile ring forms on the orad side of the distended segment moving towards the distended segment and pushing the contents towards the anus. Receptive relaxation occurs downstream and aids this unidirectional movement.
Myenteric Reflex (peristalsis)
(T/F) Normal swallowing requires a series of sequential, well-coordinated events in order to transport food and liquids from the mouth to the stomach
True
Normal Swallowing:
Voluntary initiation but becomes a reflex movement from the -> _____(1)______, through the ____(2)__________, ______(3)______, _______(4)_____ and into the _________(5)____
- pharynx
- upper esophageal sphincter
- body of the esophagus
- gastroesophageal sphincter
- stomach
(T/F) Gastric emptying is the process by which food is delivered to the small intestine at a rate and in a form that optimizes intestinal absorption of nutrients
True
Patterns of SI Motility:
Opioids ___________ (increase/decrease) segmental contractions and _____________ (increase/decrease) intestinal secretions (great for anti-diarrheal activity)
increase, decrease
What are the major ways you can differentiate between regurgitation and vomiting?
- Vomiting is a forceful expulsion of gastric and intestinal contents from the mouth.
- Preceded by nausea, retching, abdominal contractions
(T/F) Vomiting is a common but non-specific clinical sign in dogs and cats that can be caused by primary gastrointestinal disorders, vestibular disease, CNS disease, or systemic disorders (via the CRTZ)
True
What are the drugs of choice for inducing vomiting in dogs?
- Apomorphine
- Ropinirole
(T/F) Dopamine agonists are effective in cats and dogs
It is not effective in cats because they have fewer dopamine receptors in the CRTZ
What is the preferred emetic (stimulate vomiting) for use in cats?
Xylazine
(T/F) Since the feline esophagus has smooth muscle in the distal; third, clinicians can use pro-motility drugs such as cisapride in cats for esophageal hypomotility
True
Is Apomorphine effective for inducing vomiting in cats?
NO, apomorphine is NOT effective to induce vomiting in cats. Cats do not have D2 receptors within chemoreceptor trigger zone (CRTZ)
What is the mechanism of action for xylazine?
Xylazine stimulates alpha2 receptors within the CRTZ in the brain to induce vomiting via stimulation of the vomiting center within the brain
