lecture 20 and 21

Question 1

Identify and describe the gross anatomy of the stomach, including its location relative to other body structures.

Answer 1

• The stomach is a hollow, muscular organ located in the upper left part of the abdominal cavity. It lies beneath the diaphragm, between the esophagus and the small intestine (specifically the duodenum). It is bordered by the diaphragm above, the liver to the right, the pancreas and spleen to the left, and the small intestine below.

Question 2

Describe the general functions of the stomach.

Answer 2

• Mechanical digestion: Churning and mixing food with gastric juices.
• Chemical digestion: Secretion of enzymes like pepsin for protein digestion and hydrochloric acid (HCl) to denature proteins and kill microbes.
• Storage: Temporary storage of food before it enters the small intestine.
• Absorption: Limited absorption, mostly of water, alcohol, and certain drugs.
• Protection: The stomach lining secretes mucus to protect itself from digestive acids.

Question 3

Describe the anatomic specializations of the stomach tunics compared to the tunics of the rest of the GI tract.

Answer 3

The stomach has several distinctive layers in its tunics, which differentiate it from the rest of the GI tract:
* Mucosa: Contains gastric pits and glands that secrete digestive enzymes, acid, and mucus.
* Submucosa: Supports the mucosa with blood vessels and nerves.
* Muscularis externa: Has three layers of muscle (circular, longitudinal, and oblique layers), unlike the two layers in most of the GI tract. This helps with the mechanical digestion and churning of food.
* Serosa: The outermost layer that is continuous with the peritoneum.

Question 4

Relate the anatomic specializations of the stomach tunics (e.g., number of layers of muscle in the muscularis [muscularis externa]) to the organ’s functions.

Answer 4

• The stomach’s three layers of muscle (longitudinal, circular, and oblique) are crucial for its function in mechanical digestion. The oblique layer, unique to the stomach, helps with the vigorous churning and mixing of food, allowing for more effective digestion.

Question 5

Identify and describe the gastric glands, including their cells (e.g., parietal cells, chief cells).

Answer 5

The stomach contains gastric glands in the mucosa that secrete various substances:
* Parietal cells: Secrete hydrochloric acid (HCl) and intrinsic factor (for vitamin B12 absorption).
* Chief cells: Produce pepsinogen, an inactive enzyme that is activated to pepsin by HCl, which begins protein digestion.
* Mucous cells: Secrete mucus to protect the stomach lining from acidic damage.

Question 6

Describe the compositions, locations, and functions of the inferior esophageal (cardiac, lower esophageal) sphincter and the pyloric sphincter.

Answer 6

• Pyloric Sphincter: Located between the stomach and the duodenum, it regulates the passage of partially digested food (chyme) from the stomach into the small intestine.
• Inferior Esophageal (Cardiac) Sphincter: Located at the junction of the esophagus and stomach, it prevents acid reflux from the stomach back into the esophagus.

Question 7

Identify gastric folds (rugae) and discuss their functional significance.

Answer 7

• Rugae are folds in the stomach lining that allow the stomach to expand as it fills with food. These folds help increase surface area and aid in the mechanical digestion of food.

Question 8

Compare and contrast sympathetic and parasympathetic innervation effects on the digestive system.

Answer 8

• Sympathetic: Reduces digestive activity (e.g., decreases gastric motility, constricts sphincters).
• Parasympathetic: Stimulates digestive activity (e.g., increases gastric motility, relaxes sphincters, and promotes gastric secretion).

Question 9

Explain the effects of the cephalic phase, gastric phase, and intestinal phase of digestion on various parts of the gastrointestinal (GI) tract.

Answer 9

• Cephalic phase: Triggered by sensory stimuli (smell, sight, taste of food), leading to gastric secretion and motility before food reaches the stomach.
• Gastric phase: Occurs when food enters the stomach, further stimulating acid secretion and gastric motility.
• Intestinal phase: Occurs when chyme enters the small intestine, inhibiting gastric secretion and motility to slow down digestion.

Question 10

Describe the source, stimuli for release, targets, and actions of gastrointestinal (GI) tract hormones - (e.g., gastrin, cholecystokinin, secretin).

Answer 10

• Cholecystokinin (CCK): Released from the small intestine in response to fats and proteins, stimulates bile release from the gallbladder and pancreatic enzyme secretion.
• Secretin: Released from the small intestine in response to acidic chyme, stimulates the pancreas to release bicarbonate to neutralize stomach acid.
• Gastrin: Released from G-cells in the stomach in response to food, stimulates gastric acid secretion and motility.

Question 11

Describe the general functions of the liver.

Answer 11

• Metabolism: Processes nutrients from the digestive system, including carbohydrates, proteins, and fats.
• Detoxification: Detoxifies harmful substances (e.g., alcohol, drugs).
• Synthesis: Produces proteins like albumin and clotting factors.
• Bile production: Produces bile for digestion and absorption of fats.
• Storage: Stores glycogen, vitamins, and minerals.

Question 12

Identify and describe the structure of the liver, including the individual lobes (right, left, caudate, quadrate), falciform ligament, ligamentum teres (round ligament), and porta hepatis.

Answer 12

The liver consists of four lobes:
o Right lobe: The largest lobe.
o Left lobe: Smaller and located to the left of the right lobe.
o Caudate lobe: Near the inferior vena cava.
o Quadrate lobe: Located near the gallbladder.
 The falciform ligament connects the liver to the anterior abdominal wall, and the ligamentum teres (round ligament) is the remnant of the fetal umbilical vein. The porta hepatis is the area where the hepatic artery, portal vein, and bile ducts enter/leave the liver.

Question 13

Describe the location of the liver relative to other body structures.

Answer 13

• The liver is located just below the diaphragm, mostly in the right upper quadrant of the abdomen.

Question 14

Identify and describe the histological components of the classic hepatic lobule.

Answer 14

• The hepatic lobule is the functional unit of the liver, consisting of hepatocytes arranged in a hexagonal shape around a central vein. It includes the portal triad (hepatic artery, portal vein, and bile duct) at the corners.

Question 15

Identify and describe the structure and functions of the gallbladder.

Answer 15

• The gallbladder is a small, pear-shaped organ located beneath the liver. It stores and concentrates bile produced by the liver until it is needed for digestion, particularly the digestion of fats.

Question 16

Describe the location of the gallbladder relative to other body structures.

Answer 16

• The gallbladder is located on the inferior surface of the liver, in a small fossa between the right lobe and the quadrate lobe.

Question 17

Describe the major functions of the biliary apparatus.

Answer 17

• The biliary apparatus is responsible for the production, storage, and transportation of bile. It ensures that bile is delivered to the duodenum for the emulsification and digestion of fats.

Question 18

Identify and describe the biliary apparatus components (i.e., left and right hepatic ducts, common hepatic duct, cystic duct, common bile duct, main pancreatic duct, hepatopancreatic ampulla, and hepatopancreatic sphincter).

Answer 18

• Left and Right Hepatic Ducts: Carry bile from the liver.
• Common Hepatic Duct: Formed by the union of the left and right hepatic ducts.
• Cystic Duct: Carries bile to and from the gallbladder.
• Common Bile Duct: Formed by the union of the cystic duct and common hepatic duct; delivers bile to the duodenum.
• Main Pancreatic Duct: Carries pancreatic juices to the duodenum.
• Hepatopancreatic Ampulla: The junction where the common bile duct and main pancreatic duct meet.
• Hepatopancreatic Sphincter (Sphincter of Oddi): Controls the release of bile and pancreatic juices into the duodenum.

Question 19

Trace the path of bile and pancreatic juice through the biliary apparatus.

Answer 19

• Bile produced by the liver flows through the left and right hepatic ducts, then into the common hepatic duct. From there, it can either flow into the cystic duct and be stored in the gallbladder or pass through the common bile duct to the duodenum. Pancreatic juice flows through the main pancreatic duct to the hepatopancreatic ampulla, where it joins bile before being released into the duodenum.

Question 20

Identify and describe the structure and functions of the pancreas.

Answer 20

• The pancreas is both an endocrine and exocrine gland. As an endocrine gland, it produces insulin and glucagon to regulate blood sugar levels. As an exocrine gland, it secretes digestive enzymes and bicarbonate to aid in digestion.

Question 21

Describe the location of the pancreas relative to other body structures.

Answer 21

• The pancreas is located behind the stomach, extending from the duodenum on the right to the spleen on the left.

Question 22

Identify and describe the major histological components of the pancreas (pancreatic acini and pancreatic islets [islets of Langerhans]) and discuss their major functions.

Answer 22

• Pancreatic Acini: Clusters of exocrine cells that produce digestive enzymes (amylase, lipase, proteases).
• Pancreatic Islets (Islets of Langerhans): Clusters of endocrine cells that secrete hormones such as insulin and glucagon.

Question 23

Identify and describe the gross anatomy of the small intestine, including its location relative to other body structures.

Answer 23

The small intestine is a long, coiled tube located in the central and lower part of the abdominal cavity. It lies between the stomach and the large intestine and is situated in the middle and lower abdominal regions. It consists of three main sections: the duodenum, jejunum, and ileum. The small intestine is largely surrounded by the large intestine and is also positioned behind the stomach. It is located inferior to the liver and pancreas, and it is in close proximity to the kidney and the transverse colon.

Question 24

Describe the general functions of the small intestine.

Answer 24

o Digestion: The majority of chemical digestion occurs in the small intestine. Enzymes from the pancreas and bile from the liver aid in the breakdown of carbohydrates, proteins, and fats.
o Absorption: The small intestine is the primary site for nutrient absorption. Through its lining, nutrients such as amino acids, fatty acids, vitamins, minerals, and water are absorbed into the bloodstream.
o Secretion: The small intestine secretes digestive enzymes and hormones like secretin and cholecystokinin to regulate digestion.
o Immune function: The small intestine also plays a role in protecting the body from pathogens through its lymphoid tissue (e.g., Peyer’s patches).

Question 25

Identify the specific segments of the small intestine in order (i.e., duodenum, jejunum, ileum).

Answer 25

o Duodenum: The first and shortest part, approximately 25 cm long. It begins at the pylorus of the stomach and is C-shaped, wrapping around the pancreas. This section receives bile from the liver and digestive enzymes from the pancreas to aid in digestion. o Jejunum: The middle portion of the small intestine, about 2.5 meters long. It is primarily responsible for nutrient absorption and contains a thicker wall and more vascular structure compared to the ileum. o Ileum: The final segment, approximately 3.6 meters long. It connects to the large intestine at the cecum and continues nutrient absorption, particularly of bile salts and vitamin B12.

Question 26

Describe the anatomic specializations of the small intestine tunics (e.g., circular folds, villi, microvilli) compared to the tunics of the rest of the GI tract.

Answer 26

The small intestine has several specialized structural features that enhance its function in digestion and absorption:  Circular Folds (Plicae Circulares): These are large folds in the mucosa and submucosa that increase the surface area for absorption and slow down the movement of chyme, allowing more time for digestion and absorption.  Villi: Finger-like projections of the mucosa that increase the surface area for absorption. Each villus contains a network of capillaries and a lymphatic vessel (lacteal) to transport absorbed nutrients.  Microvilli: Tiny projections on the surface of epithelial cells on the villi, forming a "brush border" that further amplifies the surface area for absorption. Microvilli contain enzymes that help digest nutrients. These features are in contrast to the rest of the GI tract, where the surface area is much less specialized for absorption, and the tunics are generally smoother.

Question 27

Relate the anatomic specializations of the small intestine tunics (e.g., circular folds, villi, microvilli) to the organ’s functions.

Answer 27

The anatomical specializations of the small intestine serve to maximize surface area for digestion and absorption:  Circular folds slow the passage of chyme and increase the surface area, ensuring that food stays in the intestine long enough for adequate digestion and absorption.  Villi further increase surface area, allowing a greater number of nutrients to be absorbed. Their vascular network facilitates nutrient uptake into the bloodstream.  Microvilli on the epithelial cells contain enzymes to break down nutrients and also help with the absorption of these nutrients into the cells. These structures work together to ensure efficient absorption of nutrients from the food we consume.

Question 28

Describe the significance of the intestinal crypts

Answer 28

o The intestinal crypts (Crypts of Lieberkühn) are glands located between the villi of the small intestine, extending down into the mucosa. They have several significant functions and are composed of various specialized cells:

Question 29

the major intestinal crypt cells (stem cells, Paneth, enteroendocrine, goblet, and enterocyte)

Answer 29

 Stem cells: Located at the base of the crypts, these cells are responsible for renewing the epithelial lining of the small intestine. They divide rapidly to produce new cells that migrate upwards to replace old or damaged cells.  Paneth cells: These cells are found at the base of the crypts and play a role in immune defense. They secrete antimicrobial enzymes like lysozyme that help protect the intestine from pathogens.  Enteroendocrine cells: These cells secrete various hormones that regulate digestion, such as secretin, which stimulates bicarbonate secretion from the pancreas, and cholecystokinin, which stimulates bile release from the gallbladder.  Goblet cells: These cells secrete mucus, which lubricates the intestinal lining and protects it from digestive enzymes and mechanical damage.  Enterocytes: These are the absorptive cells of the small intestine. They are located on the villi and are responsible for absorbing nutrients such as amino acids, fatty acids, and sugars into the bloodstream.

Question 30

each intestinal crypt cell does what

Answer 30

Each of these cell types contributes to the functionality and homeostasis of the small intestine, enabling it to effectively process food, absorb nutrients, and protect itself from pathogens.