CHAP 23 digestive system good

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Questions and Answers

What is the primary function of the pyloric sphincter?

To facilitate food mixing within the stomach

To control stomach emptying into the duodenum (correct)

To prevent back flow into the esophagus

To regulate gastric acid production

Which part of the stomach lies directly beneath the diaphragm?

Pyloric part

Cardia

Fundus (correct)

Body

What anatomical feature distinguishes the greater curvature of the stomach?

Convex lateral surface (correct)

Connection to the liver

Uppermost region of the stomach

Concave medial surface

What type of epithelium composes the mucosa of the stomach?

Simple columnar epithelium Signup and view all the answers

Which region of the stomach is primarily responsible for hormone secretion?

Pyloric antrum Signup and view all the answers

The two major omenta associated with the stomach are defined by their location in relation to which curvatures?

Lesser and greater curvatures Signup and view all the answers

What is the role of the muscularis externa in the stomach?

To churn and mix chyme Signup and view all the answers

Which vessels contribute to the blood supply of the stomach?

Celiac trunk and hepatic portal system Signup and view all the answers

What is the primary purpose of enzymatic hydrolysis in digestion?

To break down macromolecules into absorbable monomers Signup and view all the answers

What role do pancreatic enzymes play in digestion?

They break down larger polymers into smaller polymers Signup and view all the answers

How do tight junctions influence the absorption of substances in the intestines?

They force substances to pass through epithelial cells instead of between them Signup and view all the answers

What characterizes the absorption of small nonpolar lipids during digestion?

They passively diffuse through the epithelial cell membranes Signup and view all the answers

What initiates the emulsification of lipids in the small intestine?

The release of bile salts Signup and view all the answers

Which of the following statements about nutrient absorption in the small intestine is true?

Most nutrients are absorbed before the chyme reaches the ileum Signup and view all the answers

What is the primary function of the muscularis externa in the alimentary canal?

To facilitate segmentation and peristalsis Signup and view all the answers

Which layer of the alimentary canal is described as having an abundant supply of blood and lymphatic vessels?

Submucosa Signup and view all the answers

What type of connective tissue replaces the serosa in organs that are outside of the abdominopelvic cavity?

Dense connective tissue (adventitia) Signup and view all the answers

What is the role of the splanchnic circulation in the alimentary canal?

To deliver nutrient-rich venous blood to the liver Signup and view all the answers

The inner circular layer of the muscularis externa thickens to form what important structure?

Sphincters Signup and view all the answers

What is the function of the serosa in the alimentary canal?

Covers the outer surface of intraperitoneal organs Signup and view all the answers

What is the primary function of parietal cells in the stomach?

Secreting intrinsic factor for vitamin B12 absorption Signup and view all the answers

Which type of cell is responsible for secreting pepsinogen?

Chief cells Signup and view all the answers

What is a key characteristic of the gastric mucosal barrier?

It is formed by tight junctions between epithelial cells. Signup and view all the answers

What role do enteroendocrine cells play in the stomach?

They secrete hormones and paracrines. Signup and view all the answers

Which of the following statements about gastritis is true?

It is caused by breaches in the mucosal barrier. Signup and view all the answers

What is the primary cause of most peptic ulcers?

Infections from Helicobacter pylori. Signup and view all the answers

What is the acidity range of hydrochloric acid secreted by the stomach?

pH 1.5–3.5 Signup and view all the answers

Which substance is primarily responsible for protein denaturation in the stomach?

Hydrochloric acid Signup and view all the answers

What happens to damaged epithelial mucosal cells in the stomach?

They are replaced every 3–6 days. Signup and view all the answers

What is the main function of mucous neck cells in the stomach?

To release thin, soluble, acidic mucus Signup and view all the answers

Study Notes

Alimentary Canal Histology

Submucosa contains areolar connective tissue with:
- Blood vessels and lymphatic vessels
- Lymphoid follicles
- Submucosal nerve plexus
- Elastic fibers
Muscularis Externa is responsible for segmentation and peristalsis and contains:
- Inner circular layer of smooth muscle
- Outer longitudinal layer of smooth muscle
- Sphincters that control food movement
Serosa is the visceral peritoneum and is the outermost layer of intraperitoneal organs:
- Areolar connective tissue covered with mesothelium
Adventitia is dense connective tissue found in organs outside the abdominopelvic cavity:
- Binds organ wall to surrounding structures
Retroperitoneal organs have both adventitia (facing body wall) and serosa (facing peritoneal cavity)

Basic Structure of the Alimentary Canal

Four tunics present:
- Mucosa: innermost layer with epithelial lining, lamina propria, and muscularis mucosae responsible for secretion and absorption
- Submucosa: contains connective tissue, blood vessels, lymphatics, and nerves
- Muscularis Externa: smooth muscle layers responsible for movement
- Serosa/Adventitia: outermost layer for protection and attachment

Blood Supply: Splanchnic Circulation

Includes arteries from aorta serving digestive organs:
- Receives 25% of cardiac output, increasing after a meal
- Celiac trunk branches serve spleen, liver, and stomach
- Superior and inferior mesenteric arteries serve intestines
Hepatic portal circulation:
- Delivers nutrient-rich venous blood from digestive organs to the liver

Gross Anatomy of the Stomach

Empty stomach volume: 50 ml, expanding to 4 L when distended
Major regions:
- Cardia: surrounds cardial orifice
- Fundus: dome-shaped region beneath diaphragm
- Body: midportion
- Pyloric part: funnel-shaped region with pyloric antrum and pyloric canal terminating at the pylorus
  - Pyloric sphincter: controls stomach emptying into duodenum
Curvatures:
- Greater curvature: convex lateral surface
- Lesser curvature: concave medial surface
Omenta:
- Lesser omentum: connects lesser curvature to liver
- Greater omentum: drapes inferiorly from greater curvature over intestines, spleen, and transverse colon, containing fat deposits and lymph nodes
ANS Innervation: sympathetic via celiac plexus and parasympathetic via vagus nerve
Blood supply: celiac trunk branches, veins of hepatic portal system

Microscopic Anatomy of the Stomach

Muscularis Externa modified for churning and mixing:
- Contains three smooth muscle layers instead of two
Mucosa modified with:
- Simple columnar epithelium: entirely composed of mucous cells
- Gastric pits: lead into tubular gastric glands that produce gastric juice
  - Pits formed by mucous cells, gland cells vary based on region

Different Types of Gland Cells

Glands in fundus and body:
- Produce most gastric juice
- Secretory cells: mucous neck, parietal, chief, and enteroendocrine
Mucous neck cells:
- Secrete thin, soluble, acidic mucus
Parietal cells:
- Secrete hydrochloric acid (HCl) and intrinsic factor
  - HCl denatures proteins, activates pepsinogen, breaks down plant cell walls, and kills bacteria
  - Intrinsic factor required for vitamin B12 absorption in small intestine
Chief cells:
- Secrete pepsinogen and gastric lipases
  - Pepsinogen activated by HCl
  - Gastric lipases contribute to lipid digestion
Enteroendocrine cells:
- Secrete chemical messengers into lamina propria, including:
  - Paracrines (histamine, serotonin)
  - Hormones (somatostatin, gastrin)

The Mucosal Barrier

Protects stomach lining from acid and proteolytic enzymes
Three factors:
- Thick bicarbonate-rich mucus
- Tight junctions between epithelial cells
- Rapid replacement of damaged epithelial cells (every 3-6 days)

Mechanism of Digestion: Enzymatic Hydrolysis

Digestion breaks down macromolecules into smaller molecules for absorption
Enzymes secreted from glands into the GI tract:
- Pancreatic, salivary, and gastric enzymes break down larger polymers
- Intestinal brush border enzymes further break down polymers into absorbable monomers

Mechanisms of Absorption

Tight junctions force substances to pass through epithelial cells
Substances enter through apical membrane and exit through basolateral membrane
Most substances diffuse into capillaries, except lipids which enter lacteals
Small nonpolar lipids absorbed passively via diffusion
Other substances require membrane transport (mostly active transport)
Most nutrients absorbed before chyme reaches ileum

Carbohydrate Digestion and Absorption

Digested by enzymes:
- Amylase (salivary and pancreatic)
- Brush border enzymes (dextrinase, glucoamylase, lactase, sucrase, maltase)
Absorbed as monosaccharides:
- Glucose, fructose, galactose
Transported across intestinal epithelium:
- Sodium-dependent glucose transporter (SGLT)
- Facilitated diffusion (GLUT)

Protein Digestion and Absorption

Digested by enzymes:
- Pepsin (stomach)
- Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase)
- Brush border enzymes (peptidases)
Absorbed as amino acids:
- Transported across intestinal epithelium by active transport

Lipids

Digested by enzymes:
- Pancreatic lipase
Steps involved:
- Emulsification: bile salts break down large fat globules into smaller droplets
- Digestion: lipase breaks down triglycerides into fatty acids and monoglycerides
- Micelle formation: monoglycerides and fatty acids combine with bile salts to form micelles
- Absorption: micelles transport lipids through the intestinal epithelium
- Chylomicron formation: lipids reassembled into triglycerides and packaged with cholesterol and protein to form chylomicrons, which enter lacteals

Absorption of Vitamins, Electrolytes, and Water

Electrolyte absorption:
- Most ions transported actively throughout small intestine
- Iron and calcium absorbed in duodenum
- Sodium, chloride, and bicarbonate absorbed actively and passively
- Potassium transported by facilitated diffusion
- Iron absorbed actively and bound to ferritin until needed, then transported by transferrin
- Calcium absorption regulated by vitamin D and parathyroid hormone
Water absorption:
- 95% of water absorbed by osmosis
- Concentration gradients established by solute transport drive water absorption

Clinical Considerations

Gastritis: inflammation of stomach lining
Peptic ulcers: erosions in GI tract wall, including gastric ulcers
- Can lead to peritonitis and hemorrhage
H. pylori: common cause of ulcers
Celiac disease: autoimmune disorder caused by gluten intolerance, affecting small intestine

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Description

Test your knowledge on the histological structure of the alimentary canal. This quiz covers the layers such as the submucosa, muscularis externa, serosa, and adventitia, along with their functions and components. Challenge yourself on the intricacies of digestive tract histology!