Chapter 14: The Digestive System

What is the main purpose of the digestive system?

It provides the fuel for bodys cells and also provides the building blocks for cell growth and cell repair

What is the basic/foundational structure of the digestive system?

It is a continuous tube/ digestive tract also known as the gastrointestinal tract.

What is the digestive system divided into

Main organs and acessory organs

What are the main organs of the digestive system

• The oral cavity

• The Pharynx

• Stomach

• Small Intestine

• Large Intestine

• Anus

What are the acessory organs

• Teeth

• Tongue

• Salivary Glands

• Liver

• Pancreas

• Gallbladder

Where is the digestive tract located

In the abdominopelvic cavity covered by a peritoneum which is a serous membrane

What secures and stabilizes the digestive organs in the abdominopelvic cavity?

Mesentries or Mesentry proper

What are the 4 layers of the digestive tract wall

1. Mucosa

2. Submucosa

3. Muscle Layer

4. Serosa

What does the Mucosa layer of the digestive tract wall include

1. Epithelum

2. Connective Tissue or Lamina Propria

3. A Muscle layer that is a narrow sheet of smooth muscle and elastic fibers

What does the Submucosa layer in the digestive tract wall consist of?

A layer of dense irregular connective tissue that binds mucosa to muscle layer. It ahs a network of nerve fibers and neurons known as Submucosal neural plexus

What type of feeling is the submucosal neural plexus responsible for?

The gut brain connection where we get gut feelings about something

What does the muscle layer of the digestive tract wall include

• Inner circular layer

• Outer longitudinal layer

What is Peristalsis and where does it occur

It is the contraction of inner circular layer and outer longitudinal layer that squeezes and pushes contents forward in the muscular layer of the digestive tract

What is a bolus

Soft rounded ball of digestive contents like food

What are the acessory organs of the oral cavity

Teeth, tounge, salivary glands

What are the functions of the oral cavity

1. Sense food before swallowing

2. Mechanical digestion through chewing which touches all the accessory organs in the mouth and allows brain to recognize it is food

3. Mucus and saliva are mixted

4. Limited digestion

What is a Uvula and why is it important

It is a fleshy hanging piece at the back of the throat and it stops entry of food in the nose

What are the 3 major salivary glands

1. Parotid Gland

2. Sublingual gland

3. Submandibular Gland

What is the function of each salivary gland

1. Parotid gland secrets amylase which breaks down starches

2. Sublingual glands produce mucus

3. Submandibular glands sectete buffers and glycoproteins called musins

What are the 3 enzymes of the salivary glands?

1. Salivary amylase

2. Lingial Lipase= breaks down lipids

   1. Lysosome=kills bacteria by destroying cell walls

What does the pharynx do and how does it do it?

It is a major organ and the passageway for food and the food passes down the oropharynx and laryngopharynx into the esophagus

What is the esophagus and what does it do?

Its a tube that the food goes down through and it rests and contracts in order to not let air into the stomach and prevents backflow of content from the stomach

What does deglutition mean

Swallowing

What are the 3 phases of swallowing

1. Buccal Phase

2. Pharyngeal Phase

   1. Esophogeal Phase

What happens during the buccal phase?

It is intiated voluntary an the information is relayed to brain. In this phase the bolus is compressed then goes into oropharynx and seals off nasopharync

What happens in the pharyngeal phase

The bolus goes from the oral cavity to the pharynx where the epiglottis gets folded and food goes past the closed glottis. Uvula keeps blocking nasopharynx

How does the epiglottis work?

It is like a gate and as the bolus comes down it folds down to let the food go down through the esophogus

What happens in the esophageal phase?

While the food is in the esophagus peristasis occurs and bolus is moved toward the stomach

What is the end of the swallowing process

The bolus enters the stomach

Explain what the stomach does and its structure

The stomach is a J shape and it is a food tank that temporarily stores food but it forms chyme which is semifluid food mixed with acidic secretions of stomach.

What are the 4 parts of the stomach

• Fundus

• Body

• Cardia

• Rugae

What is a special part of the mucosa in the stomach wall

The gastric pit which has gastric glands that secrete mucous and enzymes

How is the muscular layer of the stomach wall different?

It has 3 layers of muscle with an additional oblique muscle because it needs enough muscle to mix and churn everything.

What type of lining is in the stomach

Simple columnar epithelium

What are the 3 types of cells in the Gastric Glands

1. Parietal

2. G

3. Chief Cells

What do G cells do?

They are an enteroendocrine cell that produce gastrin that enters the circulation

What do Parietal Cells do

Secrete a glycoprotein that helps absorb vitamin B12 and H+

What do chief cells do?

They secrete pepsinogen which is a proenzyme that is converted to pepsin

What is the only thing that is absorbed by the stomach

Alcohol

What is the cephalic phase

It starts when you smell, taste or think of food and is directed by the central nervous system who prepares stomach to receive food.

What is the gastric phase

This begins when food arrives to the stomach where food secretes gastric juice and mixes food into chyme

What is the intestinal phase

Chyme enters the small intestine but there will be crosstalk between small intestine and stomach. Small intestine needs to neutralize the chyme so it will tell stomach to slow its contractions and it will listen

What happens in the small intestine

Digested food is absorbed

What are the 3 parts of the small intestine

1. Duodenum

2. Jejunum

3. Ileum

What does the duodenum do?

It is the shortest part and it receives chyme and neutralizes chyme

What does the jejunum do

Chemical digestion and nutrient absorption happens here

What does the ileum do

This is the final and longest part where there is a ileocecal valve which is a sphincter that control material into the cecum or the first part of the large intestine

What happens in the large intestine

Stores digestive wastes and reabsorbs water

What are the 3 parts of the large intestine

1. Cecum

2. Colon

3. Rectum

What is the pancreas and what does it do

It is a accessory organ that has an exocrine portion and endocrine portion

Exocrine portion= produces digestive enzymes

Endocrine portion= secretes hormones

What does the liver do

It is an endocrine organ that has hepatocytes and secretes plasma proteins and secrete bile that is stored in the gallbaldder.

What is the hepatic triad

Portal vein, bile duct and hepatic artery

What does the hepatic vein carry

Good blood

What does the portal vein carry

All blood carrying absorbed blood

Central vein

Collects detoxified blood with low oxygen