What is the anatomy of the stomach, its histological features, and its roles in digestion and absorp

1
What is the anatomy of the stomach, its
histological features, and its roles in digestion
and absorption?
2
Functions of the Stomach

• Storage of ingested food
• Mechanical breakdown of ingested food
• Chemical digestion of ingested food
• Production of intrinsic factor

3
4 Regions of the Stomach

• Cardia
• Fundus
• Body
• Pylorus

4

• Chyme
• Mixture of secretions and food in the stomach
• Rugae
• folds in stomach, allow for expansion when filling

5
Smooth Muscle

• Muscularis mucosae and muscularis externa
• contain extra layers of smooth muscle cells
• in addition to circular and longitudinal layers

6
The Stomach
Figure 2412b
7
Histology of the Stomach

• Simple columnar epithelium lines all portions of
  stomach
• Epithelium is a secretory sheet
• produces mucus that covers interior surface of
  stomach

8

• Gastric Glands
• In fundus and body
• extend deep into underlying lamina propria
• Gastric Pits
• shallow depressions that open onto the gastric
  surface

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2 Types of Secretory Cells

• In gastric glands
• parietal cells
• Secrete hydrochloric acid (HCl) and intrinsic
  factor
• chief cells
• secrete pepsinogen (inactive proenzyme) and HCl
• converted by HCl to pepsin (active proteolytic
  enzyme)

10
Pyloric Glands

• In the pylorus
• produce mucous secretion
• some produce hormones, such as gastrin,
  stimulates secretion of the gastric glands

11
The Stomach Lining
Figure 2413
12

• Stomach performs preliminary digestion of
  proteins by pepsin
• some digestion of carbohydrates (by salivary
  amylase) and lipids (by lingual lipase) continues
• Although digestion occurs in the stomach,
  nutrients are not absorbed there

13
What are the anatomical and histological
characteristics of the small intestine?
14
The Small Intestine

• Plays key role in digestion and absorption of
  nutrients
• 90 of nutrient absorption occurs in the small
  intestine

15
3 subdivisions of Small Intestine

• Duodenum
• closest to stomach
• Receives chyme from stomach and digestive
  secretions from pancreas and liver
• Jejunum
• middle segment
• location of most chemical digestion and nutrient
  absorption
• Ileum
• final segment

16

• Plicae
• Transverse folds in intestinal lining
• Villi
• fingerlike projections in mucosa of small
  intestine
• Covered by simple columnar epithelium which are
  covered with microvilli
• Lacteals
• Lymphatic capillaries for fat absorption

17
Segments of the Intestine
Figure 2416
18
The Intestinal Wall
Figure 2417
19
Regional Specialization

• Duodenum
• Few plicae, many villi
• Jejunum
• Many plicae and villi
• Ileum
• Lack plicae, few villi, Pyers patches

20
What are the structure, functions, and regulation
of the accessory digestive organs?
21
Associated Glandular Organs

• Pancreas
• digestive enzymes
• buffers
• Liver
• bile

22
The Pancreas

• Lies posterior to stomach
• Retroperitoneal organ
• wrapped in thin, connective-tissue capsule
• Large pancreatic duct
• Delivers digestive enzymes and buffers to duodenum

23

• Common Bile Duct
• From the liver and gallbladder
• Meets pancreatic duct near duodenum
• Duodenal Ampulla
• receives secretions from both common bile duct
  and pancreatic duct

24
Functions of the Pancreas

• Endocrine cells
• secrete insulin and glucagon into bloodstream
• Exocrine cells
• secretion of pancreatic juices mixture of
  digestive enzymes, water and ions

25
Pancreatic Secretions

• 1000 ml pancreatic juice per day
• Controlled by hormones from duodenum
• Contain pancreatic enzymes
• pancreatic amylase
• pancreatic lipase
• nucleases
• proteases
• peptidases

26
The Pancreas
Figure 2418
27
The Liver

• largest visceral organ
• Involved in metabolic regulation, hematological
  regulation and bile production
• wrapped in tough fibrous capsule
• divided into lobes

28

• Hepatocytes
• liver cells
• Liver lobules
• basic functional units of the liver
• Each lobe is divided
• by connective tissue into about 100,000 liver
  lobules

29

• Bile
• Produced in liver
• Contains buffers and bile salts
• Bile salts break lipid droplets apart
  (emulsification)
• Stored in gallbladder
• Discharge into duodenum

30

• The Right and Left Hepatic Ducts
• Collect bile from all bile ducts of liver lobes
• Unite to form common hepatic duct which leaves
  the liver
• Bile flows from common hepatic duct to either
• the common bile duct, which empties into duodenal
  ampulla
• the cystic duct, which leads to gallbladder

31
The Gallbladder

• Is a pear-shaped, muscular sac
• located on posterior surface of right lobe
• Stores and concentrates bile
• Releases bile into duodenum
• only under stimulation of hormone cholecystokinin
  (CCK)
• Amount secreted depends on lipid content of chyme

32
Anatomy of the Liver
Figure 2419
33
Gallbladder and Bile Ducts
Figure 2421
34
Metabolic Regulation

• The liver regulates
• composition of circulating blood
• nutrient metabolism
• waste product removal
• nutrient storage
• drug inactivation

35
Hematological Regulation

• largest blood reservoir in body
• removes old or damaged RBC
• site of plasma protein synthesis
• absorption of circulating hormones
• removal of toxins
• absorption of antibodies

36
What is the gross and histological structure of
the large intestine?
37
The Large Intestine

• Extends from end of ileum to anus
• Lies inferior to stomach and liver
• Frames the small intestine

38
Functions of the Large Intestine

• Reabsorption of water
• Compaction of intestinal contents into feces
• Absorption of important vitamins produced by
  bacteria
• Storage of fecal material prior to defecation

39
3 Parts of the Large Intestine

• Cecum
• the pouchlike first portion
• Colon
• the largest portion
• series of pouches (haustra)
• permit expansion and elongation of colon
• Rectum
• the last 15 cm of digestive tract

40
4 Regions of the Colon

• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon

41
The Appendix

• Also called vermiform appendix
• Is a slender, hollow appendage
• dominated by lymphoid nodules (a lymphoid organ)
• attached to posteromedial surface of cecum

42
The Large Intestine
Figure 2423
43
Absorption in the Large Intestine

• Reabsorption of water
• Reabsorption of bile salts
• in the cecum
• transported in blood to liver
• Absorption of vitamins produced by bacteria
• Absorption of organic wastes