A&P Chapter 24 - Digestive System - Part 1

Where are Digestive System Organs Located?

Gastrointestinals (GI) Tract

Function of Digestive System

Subunit Molecules

Monosaccharides

Amino acids

Fatty acids

Glycerol

How do Subunit Molecules Cross Plasma Membranes?

Using facilitated and active transport

How are Nutrients Made Available?

By being transported by blood to our cells

Ingestion

Intake of food via mouth

Digestion

Mechanically or chemically breaking down foods into their subunits

*Begins in the mouth, continues in the stomach, and is completed in the small intestine

Mechanical Digestion

Chewing in the mouth and contractions of smooth muscles in the stomach

Chemical Digestion

Digestive enzymes hydrolyze macromolecules into subunits

Stages of Digestion

Movement

Absorption

Elimination

Movement - Digestion

Food is passed from one organ to the next, normally by contractions of smooth muscle called peristalsis

Indigestible must be expelled

Absorption - Digestion

Movement of nutrients across the GI tract wall into the blood; they are then delivered to cells

Elimination - Digestion

Removal of indigestible wastes

*Defecation

Lumen

Open area of a hollow organ or vessel

In the GI tract, it contains food or feces

4 Layers of Lumen

Mucosa

Submucosa

Muscularis

Serosa

Mucosa

Innermost layer of lumen

Produces mucus for protection

Produces digestive enzymes

Submucosa

Loose connective tissue

Contains blood vessels, lymphatic vessels, and nerves

Muscularis

Made of 2 layers of smooth muscle (inner, circular layer, and an outer, longitudinal layer) that move food along the GI tract

Serosa

Outer lining of lumen

Part of the peritoneum

Diverticulosis

A condition in which the mucosa of any part of the GI tract (usually the large intestine) pushes through the other layers and forms pouches where food collects

Diverticulitis

When the pouches become infected

*happens in 10-25% of people with diverticulosis

Inflammatory Bowel Disease (IBD)

Chronic diarrhea, abdominal pain, fever, and weight loss

Irritable Bowel Syndrome (IBS)

Contractions of the muscularis cause abdominal pain, constipation, and diarrhea

*underlying cause is not known

Mouth (Oral Cavity)

Receives food and begins mechanical and chemical digestion

What does the Roof of the Mouth Separate?

The Nasal Cavity from the Oral Cavity

2 Parts of Roof of Mouth

Bony Hard Palate

Soft Palate

Soft Palate

Made of muscle

Uvula

End of the soft palate

Tonsils

In back of mouth on either side of tongue

Lymphatic tissue

Help protect from disease

Adenoids - Pharyngeal Tonsil

Single tonsil in the nasopharynx

How Many Pairs of Salivary Glands?

3 pairs

Salivary Glands

Secrete saliva

Contain Salivary Amylase and Lysozyme

Salivary Amylase

Begins carbohydrate digestion

Lysozyme

Antibacterial enzyme

Tongue

Covered in taste buds

Assists in mechanical breakdown and movement of food

Forms a bolus and moves it toward the pharynx

Bolus

Mass of chewed food

Teeth

Mechanically digest food

How Many Teeth in Adult?

32 teeth

How Many Teeth in Baby?

20 teeth

-small deciduous teeth

2 Main Divisions of Tooth

Crown

Root

Crown

Part of tooth above the gum line

Root

Portion of tooth below the gum line

Enamel

Extremely hard outer layer of tooth

Dentin

Thick layer of bonelike material on tooth

Pulp

Nerves and blood vessels of tooth

Periodontal Membranes

Anchor tooth to jawbone

Dental Caries

Tooth decay, cavities

How do Dental Caries Occur?

Occur when bacteria metabolize sugar and produce acids, which erode the teeth

Can be painful when it reaches the nerves of the pulp

Gingivitis

Inflammation of the gums; can spread to the periodontal membrane, causing loosening of the teeth

Periodontitis

Loss of bone and loosening of the teeth

Pharynx

Throat

Passageway after the mouth and nasal passages that lead to the esophagus and trachea

Trachea

Windpipe; air passage

In front of and Parallel to the esophagus

Esophagus

Food passage

Behind and Parallel to the trachea

Muscular tube that leads to the stomach

Swallowing - Reflex

Starts off voluntary, but once food or drink is pushed back into the pharynx, it becomes an involuntary reflex

Swallowing Process

Food normally enters the esophagus because other possible avenues are blocked

Soft palate moves back to close off the nasal passage, and the trachea moves up under the epiglottis to cover the glottis, the opening to the larynx

Peristalsis

Contractions that push food through the digestive tract

Sphincter

A ring of muscle that acts as a valve

When it contracts, it stops food from moving through

When it relaxes, it allows food through

Lower Esophageal Sphincter

Between the esophagus and stomach

Heartburn

Failure of Lower Esophageal Sphincter

Stomach contents move from stomach into esophagus

Vomiting

When strong contractions of the abdominal muscles and the diaphragm force the contents of the stomach into the esophagus and oral cavity

Diaphragm

The muscle separating the thoracic and abdominal cavities

Stomach Functions

Stores food, starts digestion of proteins, and controls movement of food into the small intestine

Does not absorb nutrients

Does absorb alcohol, because alcohol is fat-soluble and can pass through membranes easily

3 Layers of Muscle in Muscularis Layer of Stomach

Circular

Longitudinal

Oblique

*help in mechanical digestion

Heartburn (GERD)

Lining of the esophagus is thinner than the lining of the stomach

If chyme enters esophagus, it produces a burning sensation

Can be caused by pregnancy and excess fat pushing on the stomach

Gastroesophageal Reflux Disease (GERD)

Chronic heartburn

Rugae

Deep folds in mucosa of stomach

Gastric Pits

Located in mucosa

Contain Gastric Glands

Gastric Glands

Product Gastric Juice

What does Gastric Juice Contain?

Pepsin—digests proteins

Hydrochloric acid (HCl)—pH of 2 to kill bacteria and activate pepsin

Mucus

How Long for the Stomach to Empty?

2-6 hours

Chyme

Mixture of food and gastric juice

Pyloric Sphincter

Allows only a small amount of chyme to enter the small intestine at a time

Small Intestine Structure

Small diameter compared to large intestine's

Longer than the large intestine

Averaging about 6 m (18 ft) in length, whereas the large

intestine is about 1.5 m (4.5 ft

3 Regions of Small Intestine

Duodenum

Jejunum

Ileum

What is the Main Digestive Organ?

Small Intestine

*absorbs nutrients as well

Pancreas

Secretes digestive enzymes through a duct into the duodenum

Duodenum

First portion of small intestine

*Another duct brings bile from the liver and gallbladder here

Bile Function

Emulsifies fat

Mechanical digestion; causes fat droplets to disperse in water to expose more of it to lipase

Produced by pancreas

Hydrolyzes fats into glycerol and fatty acids

Pancreatic Amylase

Produced by the pancreas

Secreted into duodenum

Digests carbohydrates

Trypsin

Produced by the pancreas

Secreted into duodenum

Digests proteins, so is a protease

Protease

A class of enzymes that digest proteins

What does Pancreatic Juice Contain to Neutralize Acidic Chyme?

Sodium bicarbonate

Villi

Fingerlike projections in mucosa

Microvilli

Within the cells that cover villi

Give the villi a fuzzy "brush border"

Contain brush border enzymes that complete digestion

Villi and Microvilli Function

Greatly increase the surface area of the small intestine for absorption of nutrients

Lacteal

Small lymphatic capillary within villi

Blood Capillaries and Lacteal of Small Intestine

Monosaccharides and amino acids enter blood capillaries of a villus

Glycerol and fatty acids form chylomicrons, which then enter a lacteal

*After nutrients are absorbed, they are eventually carried to all cells of body by blood

Chylomicrons

Lipoprotein droplets formed from glycerol and fatty acids