Histology of Small Intestine.pptx

What is the small intestine?
The small intestine is part of your digestive system. It makes up part of the long pathway that food takes through your body, called the gastrointestinal (GI) tract. When food leaves your stomach, it enters the small intestine, also called the small bowel. The small bowel connects to the large bowel, also called the large intestine or colon. The intestines are responsible for breaking food down, absorbing its nutrients and solidifying the waste. The small intestine is the longest part of the GI tract, and it is where most of your digestion takes place.
What are the different parts of the small intestine?
The small intestine has a beginning section, a middle section and an end section. Although there is no real separation between the parts, they do have slightly different characteristics and roles to play.

Duodenum
The duodenum is the first part of the small intestine that the stomach feeds into. It’s a short, descending chute (about 10 inches long) that curves around the pancreas in a “C” shape before connecting to the rest of the coiled intestines.

Jejunum
The remaining small intestine lays in many coils inside the lower abdominal cavity. Its middle section, called the jejunum, makes up a little less than half of this remaining length. The jejunum is characterized by many blood vessels, which give it a deep red color.

Ileum
The ileum is the last and longest section of the small intestine. Here the walls of the small intestine begin to thin and narrow, and blood supply is reduced. Food spends the most time in the ileum, where the most water and nutrients are absorbed.

FUNCTION
What does the small intestine do?
The small intestine is where most of the long process of digestion takes place. It:

Systematically breaks food down.
Absorbs nutrients.
Extracts water.
Moves food along the gastrointestinal tract.
There’s a lot involved in all this. The process can take up to five hours.

How do the different parts of the small intestine work?
Duodenum
To help break food down, the small intestine receives digestive juices from other organs in your digestive system, including your liver, gallbladder and pancreas. Ducts from these organs feed into the duodenum. Hormone glands in the lining of the duodenum signal these organs to release their chemicals when food is present.

Jejunum
After chemical digestion in the duodenum, food moves into the jejunum, where the muscle work of digestion picks up. Nerves in the intestinal walls trigger its muscles to churn food back and forth (segmentation), mixing it with digestive juices. Other muscle movements (peristalsis) keep the food moving gradually forward.

Mucosa
The walls of the small intestine are lined with a dense mucosa with many glands that both secrete and absorb. In the jejunum and the ileum, the mucosa secretes small amounts of digestive enzymes and lubricating mucus while absorbing nutrients from your food.

1. Histology of Small Intestine Dr Mathew Joseph MBBS, MD(AIIMS), BCC(Palliative Medicine) Assistant Professor Department of Anatomy Amala Institute of Medical Sciences , Thriss ur

2. Basic Histological Layers Mucosa: a. Epithelium b. Lamina Propria c. Muscularis Mucosae Submucosa: Submucosal plexus “Plexus of Meissner” Muscularis: Myenteric plexus “Plexus of Auerbach Serosa

3. Small Intestine It is divided into duodenum, jejunum and ileum. Mucosa: characteristic features- Plicae circularis (valves of Kerkring) Villi & Microvilli Goblet cells (few) Crypts of Lieberkuhn (intestinal glands) Glands are lined by columnar cells, goblet cells, Paneth cells & enteroendocrine cells

4. Types of Cells

5. Layers of Small Intestine Mucosa: E,LP,MM Submucosa: contains blood vessels, lymphatics and Meissner’s plexus. Muscularis externa: Outer longitudinal and inner circular layers of smooth muscle. Serosa/Adventitia

6. Duodenum Presence of Brunner’s glands in submucosa

7. Jejunum Villi are cylindrical shaped. Absence of Brunner’s glands.

8. Ileum Presence of lymphoid aggregations in lamina propria known as Peyer’s patches. Villi are short & finger like.

9. Histology of the Mucosa Organ Epithelium Mouth Nonkeratinized Stratified Squamous Pharynx Nonkeratinized Stratified Squamous Esophagus Nonkeratinized Stratified Squamous Stomach Simple Columnar Small Intestine Simple Columnar Large Intestine Simple Columnar Anus Nonkeratinized Stratified Squamous

10. Histology of the Mucosa Organ Folds of the epithelium Esophagus none Stomach L: Rugae , S: gastric pits Small Intestine L: Plicae circulares, Villi S: Crypts of Lieberkuhn, microvilli Large Intestine L: Haustra S: Intestinal glands

11. Histology of the Submucosa Organ Specialized structures Esophagus Submucosal mucous glands Stomach None Duodenum Brunner’s glands Ileum Peyer’s Patches Large Intestine None

12. Histology of the Muscularis Organ Smooth muscle layers Esophagus 2, circular and longitudinal Stomach 3, oblique, circular, and longitudinal Small Intestine 2, circular and longitudinal Large Intestine 2, circular and longitudinal

13. Histology of the Serosa Organ Serosa Esophagus Adventitia due to the fact that the esophagus is not in a cavity Stomach Visceral Peritoneum Small Intestine Visceral Peritoneum Large Intestine Visceral Peritoneum Anus Adventitia

14. Thank You