GIT HISTOPHYSIOLOGY Flashcards
What are the major functions of the gastrointestinal tract (GIT)?
The GIT’s major functions include motility (movement of food through the digestive tract), secretion (release of enzymes and other substances), digestion (breaking down food into absorbable molecules), and absorption (transfer of nutrients, electrolytes, and water into the bloodstream)
What is the role of parietal cells in the stomach?
Parietal cells are responsible for producing hydrochloric acid (HCl), which creates the stomach’s highly acidic environment. This acid aids in breaking down food, activating enzymes like pepsin, and killing bacteria. Parietal cells have a unique structure, including abundant mitochondria, secretory canaliculi, and tubulovesicles, which support their acid-secreting function
How does the enteric nervous system regulate gut motility?
The enteric nervous system (ENS) regulates motility through two plexuses: the myenteric plexus (controlling muscle contraction strength and frequency) and the submucosal plexus (modulating local secretions and blood flow). The ENS operates largely independently of the CNS but receives input from sympathetic and parasympathetic nerves to modulate gut activity
What are the primary layers of the small intestine wall?
The small intestine wall consists of four layers: mucosa (with villi and microvilli for absorption), submucosa (supporting blood, lymphatic, and nerve supply), muscularis (responsible for peristaltic and mixing movements), and serosa (the outermost protective layer). These layers work together to maximize nutrient absorption and facilitate smooth motility
Describe the role of interstitial cells of Cajal (ICCs) in the gastrointestinal system.
ICCs are pacemaker cells that generate slow-wave electrical activity in the gut, setting a rhythm for smooth muscle contractions. Located near the myenteric plexus, they help regulate gut motility by communicating with enteric neurons to coordinate contractions, ensuring food moves efficiently through the digestive tract
What hormones do enteroendocrine cells in the small intestine release, and what are their functions?
Enteroendocrine cells release several hormones, including:
Secretin: Stimulates pancreatic bicarbonate secretion to neutralize stomach acid.
Cholecystokinin (CCK): Stimulates enzyme secretion from the pancreas and bile release from the gallbladder, and slows gastric emptying.
Gastric inhibitory peptide (GIP): Stimulates insulin release and inhibits gastric secretion and motility. These hormones play crucial roles in digestive coordination by signaling organs to release enzymes or adjust motility based on nutrient content
What are the three structural features of parietal cells that support their function?
Parietal cells contain (1) abundant mitochondria to supply ATP, (2) a secretory canaliculus for H⁺ secretion into the gastric lumen, and (3) tubulovesicles rich in H⁺/K⁺-ATPase for pumping protons into the stomach
What is the function of the Peyer’s patches in the small intestine?
Peyer’s patches are lymphoid follicles found in the ileum that form part of the gut-associated lymphoid tissue (GALT). They play a key role in immune surveillance by trapping and initiating immune responses against antigens from the gut lumen, thereby protecting the body from potential pathogens
How does the secretory canaliculus assist in HCl production?
The secretory canaliculus is an invagination of the apical surface, lined with microvilli, which increases the surface area for active H⁺ secretion, directly contributing to acid production in the stomach
Which enzyme is crucial for HCl production in parietal cells?
Carbonic anhydrase is essential for HCl production as it facilitates the conversion of CO₂ and H₂O into carbonic acid, which dissociates into bicarbonate and hydrogen ions necessary for acid secretion
Describe the process of HCl production in parietal cells.
HCl production involves the active transport of H⁺ ions into the lumen via H⁺/K⁺-ATPase. Cl⁻ ions enter the lumen through a chloride channel, while bicarbonate (HCO₃⁻) exits into the blood, creating an “alkaline tide” after meal
What effect does the alkaline tide have on blood pH?
The alkaline tide temporarily increases blood pH as bicarbonate ions (HCO₃⁻) are released from parietal cells into the bloodstream during gastric acid production
Which transporters and channels are involved in HCl production?
HCl production involves H⁺/K⁺-ATPase (proton pump), Cl⁻ channels, and an anion exchanger that swaps bicarbonate (HCO₃⁻) for Cl⁻, facilitating the passage of these ions into the gastric lumen
Why is carbonic anhydrase important in acid secretion?
Carbonic anhydrase catalyzes the reaction between CO₂ and H₂O to form carbonic acid, which dissociates into H⁺ and HCO₃⁻, providing protons for acid production and bicarbonate for the alkaline tide
What role does Na⁺/K⁺-ATPase play in parietal cells?
Na⁺/K⁺-ATPase maintains the ionic gradient by pumping Na⁺ out and K⁺ into the cell, which supports H⁺/K⁺-ATPase function, essential for active proton transport into the stomach
How do Cl⁻ channels contribute to HCl secretion?
Cl⁻ channels allow chloride ions to move passively from the parietal cell into the gastric lumen, where they combine with H⁺ ions to form HCl
What is the function of HCl in the stomach?
HCl provides an acidic environment for digestive enzymes, particularly pepsin, and offers protection by killing bacteria and pathogens that enter with food
How do bicarbonate ions contribute to mucosal protection?
Bicarbonate ions (HCO₃⁻) enter the mucous layer, creating a neutralizing “mucous blanket” that protects the stomach lining from the highly acidic gastric contents
What are the three main stimulants for HCl secretion?
HCl secretion is stimulated by acetylcholine (ACh), gastrin, and histamine. Each binds to receptors on parietal cells, activating the H⁺/K⁺-ATPase pump and increasing acid secretion
How does histamine affect HCl production?
Histamine, released from enterochromaffin-like (ECL) cells, binds to H₂ receptors on parietal cells, amplifying HCl production by increasing the activity of H⁺/K⁺-ATPase
Which hormone inhibits gastric acid secretion?
Somatostatin, produced by D cells, inhibits gastric acid secretion by reducing gastrin release from G cells and directly inhibiting parietal cell activity
What role does gastrin play in HCl secretion?
Gastrin, secreted by G cells, promotes HCl secretion by stimulating parietal cells and enhancing the release of histamine from ECL cells, creating a coordinated response to food intake
What is the primary function of chief cells in the stomach?
Chief cells produce pepsinogen, an inactive enzyme precursor. In the acidic stomach environment, pepsinogen is converted to pepsin, which begins the digestion of proteins into smaller peptides
Why is pepsinogen secreted in its inactive form?
Pepsinogen is secreted in an inactive form to prevent the digestion of stomach tissues. Activation occurs in the acidic environment of the stomach, where pepsinogen converts to active pepsin
How is the surface area of the small intestine maximized for absorption?
The small intestine’s surface area is amplified by four degrees of folding: circular folds (plicae circulares), villi, microvilli, and crypts of Lieberkühn. These structures increase the contact area for nutrient absorption, enhancing digestive efficiency
What is the primary function of the small intestine?
The small intestine continues digestion and is the main site for nutrient absorption. It mixes chyme with digestive enzymes and pancreatic secretions, exposing nutrients to the intestinal mucosa, and propels unabsorbed chyme toward the large intestine
What are lacteals, and what is their role in the small intestine?
Lacteals are central lymphatic vessels in the villi of the small intestine. They absorb dietary fats in the form of chylomicrons and transport them into the lymphatic system
