Gi Phiso

What is the chemical composition of saliva?

Saliva primarily consists of water (about 99.5%), with other components including electrolytes, mucus, antibacterial compounds, and enzymes such as amylase and lipase, which aid in digestion.

What are the physiological stimuli of salivary secretion?

Physiological stimuli of salivary secretion include the sight, smell, or thought of food, as well as mechanical stimulation of the oral cavity. These stimuli activate the autonomic nervous system, leading to increased saliva production.

Describe the voluntary component of swallowing.

The voluntary component of swallowing involves the conscious act of pushing food or liquid from the mouth into the pharynx, where it then initiates the involuntary swallowing reflex.

What is the reflex component of swallowing?

The reflex component of swallowing is an involuntary process triggered once food reaches the pharynx, leading to a series of coordinated muscular contractions that propel the food down the esophagus towards the stomach.

Distinguish the wall layers of the esophagus.

The wall layers of the esophagus include the mucosa, submucosa, muscularis externa, and adventitia. These layers contribute to the structural and functional properties of the esophagus, facilitating the movement of food.

How does the small intestine wall differ from the esophagus?

The small intestine wall has additional adaptations such as villi and microvilli, which increase the surface area for nutrient absorption, and a more complex structure including circular and longitudinal muscle layers for enhanced peristalsis. It also has a more developed seorsa.

What are local peristaltic reflexes in the esophagus?

Local peristaltic reflexes in the esophagus are localized contractions of the muscularis externa that occur in response to the presence of food. These reflexes help to move the bolus through the esophagus by coordinating sequential waves of contraction and relaxation.

How does positive abdominal pressure affect the lower esophageal sphincter (LES)?

Positive abdominal pressure can increase the tension of the lower esophageal sphincter (LES), which may help prevent gastroesophageal reflux by enhancing the closure of the sphincter during activities like coughing or lifting.

What are the exocrine functions of the pancreas?

The exocrine functions of the pancreas involve the secretion of digestive enzymes, including amylase, lipase, and proteases, into the small intestine to aid in the digestion of carbohydrates, fats, and proteins.

How is secretin related to pancreatic function?

Secretin stimulates bicarbonate secretion in response to acidic chyme in the small intestine; its release is inhibited as pH increases.

How is cholecystokinin (CCK) involved in pancreatic regulation?

CCK stimulates enzyme secretion from the pancreas and gallbladder contraction in response to fatty acids and amino acids, with its release inhibited by increased enzyme levels.

What are the layers of the gut wall?

• Mucosa: Absorption and secretion.

• Submucosa: Contains blood vessels, nerves, and connective tissue.

• Myenteric Plexus: Regulates gastrointestinal motility.

• Muscularis: Composed of inner circular and outer longitudinal muscle layers that facilitate peristalsis.

• Serosa: Outermost layer, provides protection and support.

Describe the effects of sympathetic and parasympathetic stimulation on intrinsic gut activity.

Sympathetic stimulation generally inhibits gut motility and secretion, while parasympathetic stimulation enhances peristalsis and digestive secretions.

How does the enteric nervous system function as a control center for short reflexes?

The enteric nervous system can regulate gut function independently, mediating short reflexes in response to local stimuli without needing input from the central nervous system.

What is the basal electrical rhythm (BER) in gut smooth muscle?

The BER establishes a rhythmic pattern of electrical impulses that dictate the basic pace of contraction. Additional stimuli can superimpose on this rhythm to produce action potentials that can translate into muscle tension.

What are the effects of stretch, Ach, epinephrine, atropine, elevated extracellular K+, and BaCl on GI smooth muscle?

Definition: - Stretch: Triggers myogenic reflexes that induce contraction.

• Ach: Increases contractility by depolarizing the membrane potential.

• Epinephrine: Inhibits motility and causes relaxation.

• Atropine: Blocks parasympathetic effects, reducing contraction.

• Elevated extracellular K+: Can depolarize cells, affecting muscle activity.

• BaCl: Blocks potassium channels, causing depolarization and increased contractility.

Describe the gastric mucosa and its secretions.

The gastric mucosa contains gastric pits that secrete gastric juices (HCl and pepsinogen). These secretions aid in digestion by breaking down proteins and maintaining an acidic environment.

What is the mechanism and regulation of HCl and pepsin secretion?

HCl is secreted by parietal cells in response to histamine, gastrin, and Ach, while pepsinogen is converted to pepsin in the presence of acid, initiating protein digestion.

How does the gastric muscularis compare to that of the esophagus or small intestine?

The gastric muscularis has three layers (inner oblique, middle circular, outer longitudinal) for mixing and churning food, contrasting with the two-layer muscularis of the esophagus and small intestine.

Explain the relationship between the intrinsic BER and extrinsic stimulators of motility in the stomach.

The intrinsic BER sets the basic rhythm of contractions, while extrinsic factors (neural and hormonal signals) can modulate this activity to increase or decrease motility.

What are the layers of the small intestine wall?

Similar to the general gut wall, the small intestine has the mucosa, submucosa, muscularis (inner circular, outer longitudinal), and serosa, with additional structures like villi for increased absorption surface area.

Describe the countercurrent mechanism in the intestinal villus.

The countercurrent mechanism in the villus allows for efficient nutrient absorption and turnover of epithelial cells by facilitating the exchange of materials between blood vessels.

How are carbohydrates, proteins, and fats digested and absorbed in the small intestine?

Definition: - Carbohydrates: Broken down into monosaccharides by amylase and absorbed via active transport.

• Proteins: Hydrolyzed by proteases to amino acids and absorbed through specialized transporters.

• Fats: Emulsified by bile, digested by lipases, and absorbed into lymphatic vessels as chylomicrons.

What are the intrinsic, neural, and hormonal regulators of small intestine motility?

ntrinsically, gut hormones (like CCK and secretin) and the enteric nervous system regulate motility, while extrinsically, the autonomic nervous system influences motility.

Briefly describe the microstructure of the liver.

The liver consists of lobules with hepatocytes, bile ducts, and sinusoids that facilitate blood flow and processing of nutrients.

What is the hepatic portal system?

The hepatic portal system transports blood from the gastrointestinal tract and spleen to the liver, allowing for the processing of absorbed nutrients.

Describe the production and secretion of bile.

Bile is produced by hepatocytes and stored in the gallbladder; it serves as both a secretory product (aiding digestion) and excretory product (removing waste).

What is the importance of bile in lipid digestion and absorption?

Bile emulsifies fats, increasing the surface area for lipase action, and facilitates the absorption of fatty acids and monoglycerides in the small intestine.