The Digestive SystemFrom Intake to Output

The body cannot use food in its original form◦ The pieces are too large ◦ Some foods, such as fats, cannot be absorbed by

the bloodstream◦ Overall foods are too complex for the body to use

without being broken down first The process of digestion is:

◦ Physical or mechanical – teeth, chewing, peristalsis

◦ Chemical – enzymes

Digestion

Alimentary canal◦ An approximately 30-foot long tube running from

the mouth to the anus◦ Includes the mouth, throat, esophagus, stomach,

small intestine, large intestine, and anus Accessory organs

◦ Aid the digestive process by reducing food mechanically and chemically to a simple form that the body can use

◦ Includes the teeth, tongue, salivary glands, pancreas, liver, and gallbladder

Digestive System – 2 Parts

Digestive Pathway Mouth → Pharynx → Esophagus → Stomach → Small intestine → Large intestine → Rectum → Anus

Digestive Pathway - Mouth Primary role – to help digest food by

reducing its size through chewing (physical digestion)

Also aids in chemical digestion by mixing food with saliva, which contains enzymes

The mouth moves food to the back of the throat; called the pharynx

At this point a cartilaginous lid called the epiglottis closes over the larynx to keep food out of the trachea

Food passes through the pharynx into the esophagus

A food delivery tube that descends through the mediastinum and the diaphragm into the stomach

Swallowing moves the food down the esophagus to the stomach

A sphincter muscle is located where the esophagus joins the stomach◦ This muscle opens to allow food to enter the

stomach◦ It then closes to prevent the food and stomach

acid from flowing back up the esophagus

Digestive Pathway - Esophagus

Primary role – Storage and to continue reducing the size of the food◦ The stomach goes through contractions of its

smooth muscles in order to grind food into smaller and smaller particles

◦ Acid, mucous, and enzymes are introduced in the stomach

The stomach moves the finer food particles to the pyloric region of the stomach, which pushes it to the small intestine

Digestive Pathway - Stomach

A coiled tube about 22 feet long where a majority of the digestion takes place◦ Broken into 3 sections

Duodenum Jejunum Ileum

◦ Coiled in order to increase its surface area Provides more surface for glands to secrete enzymes

for digestion Lined with 4-5 million villi

◦ Finger-like projections that help to mix food with enzymes and to move it along to the large intestine

Digestive Pathway – Small Intestine

Primary role – to absorb water and electrolytes or salts

A 5-foot tube similar to the small intestine◦ Differs in that it has no villi and absorbs no

nutrients Has sections

◦ Ascending colon – goes up right side◦ Transverse colon – goes across abdomen◦ Descending colon – goes down the left side◦ Sigmoid colon – end of large intestine; delivers

leftovers to the rectum

Digestive Pathway – Large Intestine

Last stop in the digestive pathway Where all undigested food, known as feces,

goes to be eliminated The rectum contains 2 sphincter valves,

known as the anus, that remain tightly closed except during defecation

Digestive Pathway - Rectum

Body’s largest gland Secretes bile to help the body digest fats Also helps to filter toxic chemicals from the

venous blood as it travels back to the heart

Spleen◦ assists the liver by removing damaged blood cells

Accessory Organs – Liver/Spleen

Produces a fluid with 3 enzymes that breaks down food

Also secretes insulin◦ Without insulin, sugar collects in the blood instead

of reaching tissues, which causes diabetes

Accessory Organs - Pancreas

Pear-shaped sac located on the underside of the liver (green)

Receives most of the liver’s bile and stores it until needed

Sends bile to the small intestine when needed to break down fatty foods

Accessory Organs - Gallbladder

Teeth – Grinds food into smaller, more manageable particles for digestion

Tongue – Contains glands that secrete enzymes and helps to move the food to the pharynx

Salivary glands – Secrete salivary amylase, the first enzyme involved in digestion◦ Can’t taste food without this enzyme

Accessory Organs – Teeth, Tongue, and Salivary Glands

Fluids that come through the body must also be digested and filtered

The urinary system is responsible for filtering fluids and eliminating excess acids and salts

The body’s cells discharge all waste into the bloodstream

The blood carries the acids and salts to the kidneys for filtration

The kidneys filter the blood, then return the filtered fluid back to the bloodstream

Liquid Wastes

The kidneys continue to filter the leftover fluid and send it along to the ureter

The ureter is a long tube that descends to the urinary bladder

The bladder is a hollow muscular organ with a sphincter muscle on its lower section

Once the bladder fills, the body triggers the sphincter to relax and the liquid waste is eliminated as urine

Urinary System

1. What is the pathway of digestion? 2. What are the organs of the alimentary

canal? 3. What are the accessory organs of

digestion? 4. What is physical digestion? 5. What is chemical digestion? 6. Why does the body need to go through

digestion of food?

Study Guide Questions

7. Be able to define the following:◦ Epiglottis◦ Peristalsis◦ Pyloric region◦ Duodenum◦ Jejunum◦ Ileum◦ Enzyme◦ Gland◦ Villi◦ Pharynx

Study Guide Questions

8. Know the role of the following in digestion:◦ Mouth, teeth, tongue◦ Esophagus◦ Stomach◦ Small intestine◦ Large intestine, including the 4 regions◦ Rectum◦ Liver◦ Pancreas◦ Gallbladder◦ Kidneys

Study Guide Questions