fon 241 chapter 3

FON 241; Digestion: L. Zienkewicz

Digestion, Absorption, and Transport

Chapter 3

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To become part of your body, food must first bedigested and absorbed.


Digestion: The process by which food is broken down into absorbable nutrients

Absorption: The passage of nutrients from the GI tract into either the blood or the lymph


Anatomy of the gastrointestinal (GI)

tract:


The Gastrointestinal Tract

Stomach

Upper esophageal sphincter

Rectum

Pharynx

Small intestine(duodenum, jejunum, ileum)

Esophagus

Pancreatic duct

Anus

Large intestine (colon)Appendix

Liver

Loweresophagealsphincter

Epiglottis

Salivary glands

Trachea (to lungs)

Mouth

PancreasGall bladder

Pyloric sphincter

Bile duct

Ileocecal valve

Liver

Appendix

Rectum

Anus

Loweresophagealsphincter


Start at the beginning…

The mouth- Teeth crush your food; saliva blends with the food.


The TeethIncisors have chiselededges that cut

Canines (cuspids) havepointed crowns that tear

Premolars (bicuspids)and molars have ridgedsurfaces that crushand grind

Tongue


The Teeth

Enamel

Root

Neck

Root canal

Blood vesselsand nervesin pulp

Dentin

Pulp cavity

Gum (gingiva)

Bone

Crown


Digestion:

Pharynx- Tube shared by the digestive and respiratory systems.

Epiglottis- Cartilage that prevents food from entering the lungs during swallowing.


Normal Swallowing and Choking

Larynx rises

Food

Tongue

Esophagus (to stomach)

Trachea (to lungs)Epiglottis closesover larynx


Next… Esophagus- the food pipe; a long tube that

carries a food bolus from the pharynx to the stomach.

Preventive measures: Esophageal sphincters two sphincters on each end of the esophagus.

They function to: 1. Upper ES- allow food into the esophagus2. Lower ES- allow food into the stomach

and prevents backflow of stomach contents.


An Example of a Sphincter Muscle

Esophagus muscles contract,squeezing on the inside.

Esophagus muscles relax,opening the passageway.

Diaphragm muscles relax,opening the passageway.

Longitudinal muscle

Esophagus

Diaphragm muscles contract,squeezing on the outside.

When the circular muscles of a sphincter contract, thepassage closes; when they relax, the passage opens.

Circular muscle

Stomach


What happens in the stomach?

• A bolus enters the stomach via the lower esophageal sphincter.

• The stomach gradually transfers the bolus from the upper portion to the lower portion of the stomach.

• Stomach acids are added and the food is ground by muscular forces

• The bolus is now called chyme.

• The stomach slowly releases chyme through the pyloric sphincter into the small intestine.


Stomach Muscles

Circular

Diagonal

Longitudinal

The stomach has three layers of muscles.


Still going…• Small intestine: Made of three

parts- 1. The duodenum2. The jejunum3. The ileum

In beginning of the small intestine, fluids from the gallbladder and pancreas, flow through the common bile duct and interact with the chyme. The chyme then moves through the 3 parts of the small intestine.


The Small Intestine

Pyloric Sphincter


The surface area of the small intestine is roughly the size of a tennis court.

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And going… through the large intestine• Chyme passes through the Ileocecal valve, the

entrance to the large intestine.

• Chyme bypasses the appendix.

• Chyme travels through the large intestine; water is withdrawn and a semi-solid mass forms.

• The mass moves to the rectum; rectal muscles relax.

• 2 sphincters of the anus relax, thus passing the mass through the anus.


The Colon or Large Intestine

Opening from smallintestine to large intestine

Transverse colon

Ascending colon

Anus

Descendingcolon

End of small intestine

Appendix

Rectum

Sigmoid colon


The whole picture:

Large Intestine

Small Intestine

Esophagus

Stomach


The Digestive Fate of a Sandwich

STOMACH: COLLECTING AND CHURNING, WITH SOME DIGESTION

MOUTH: CHEWING AND SWALLOWING, WITH LITTLE DIGESTION


The Digestive Fate of a Sandwich

LARGE INTESTINE: REABSORBING AND ELIMINATING

SMALL INTESTINE: DIGESTING AND ABSORBING


How does food move through?

• Peristalsis- wavelike muscular contractions that push contents along.

• Segmentation- the circular muscles of the small intestine rhythmically squeeze and contract the contents; chyme is mixed with digestive juices, etc.

• Sphincter contractions- opening and closing of a sphincter to allow contents to enter or exit.


Peristalsis and Segmentation


Digestive Secretions:

Source Secretion

Salivary Glands SalivaStomach Gastric juice

Pancreas Pancreatic

juiceLiver (via gallbladder) BileSmall intestine Intestinal Flora


The Salivary Glands

Salivary glands


The pH Scale

Basic

Acidic

pH neutral

pH’s of common substances:

Oven cleaner

BilePancreatic juice

Concentrated lye

Battery acid

Gastric juiceLemon juice

Vinegar

Orange juice

Urine

BloodWater

Baking soda

Household ammonia

Saliva

Coffee

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0


Absorption

• The small intestine:•Villi- Small intestinal projections•Microvilli- Microscopic hairs on the villi •Crypts- crevices between the villi

All of these components make up the massive absorptive area of the intestine.


Absorption of Nutrients

Cellmembrane

Absorption of nutrients into intestinal cells typicallyoccurs by simple diffusion or active transport.

Carrier loadsnutrient onoutside of cell . . .

Energy

ACTIVETRANSPORT

FACILITATEDDIFFUSION

SIMPLEDIFFUSION

Energy

. . . and thenreleases it oninside of cell.

Outsidecell

Insidecell

Carrier loadsnutrient onoutside of cell . . .

. . . and thenreleases it oninside of cell.


The Small Intestinal Villi

Folds with villi on them

Longitudinal muscles

Circular muscles

Small intestine

Stomach


The Small Intestinal Villi

Goblet cells

Capillaries

Vein

A villus

Artery

Crypts

Lymphaticvessel

Lymphatic vessel (lacteal)

(cont’d next slide)


The Small Intestinal VilliMicrovilli


Nutrient Transport• The nutrient crosses the cell and can…

•1. Enter the blood stream (water soluble)

or•2. Enter the lymphatic system

• Water soluble nutrients and smaller fat products are released into the bloodstream.

• Larger fats, fat-soluble vitamins and turned into chylomicrons and released into the lymphatic system


The Vascular System

Heart

= Arteries= Capillaries= Veins= Lymph vessels

Liver

Leftside

Rightside

Hepatic artery

Digestivetract

Portal vein

Lymph

Entire body

Pulmonary vein

Hepatic vein

Pulmonary artery

Head andupperbody

Lungs

Aorta

Digestivetract

Hepatic artery

Portal vein

Aorta

Leftside

Heart


The Vascular System• Blood delivers Oxygen and

Nutrients to organs and tissues; CO2 and waste products are carried away by the blood.

• The digestive system supplies nutrients to the blood.

• Heart ArteriesCapillaries

Veins


The Vascular System (cont.)

• Blood leaving the digestive system is taken to the liver via a vein.

• The liver is the bodies major metabolic organ.

• It receives nutrients and other products from the digestive system; a gatekeeper.


Route of blood from intestines to heart.

Heart Arteries Capillaries

(in intestines)

Vein Capillaries Veins

(in liver)


The Lymphatic System:

• A route for fluid from tissue to enter the blood.

• Large fats and fat-soluble vitamins use the lymph system

• Ultimately end up in the heart• Once in the blood stream, the

nutrients can be delivered to cells, organs, etc.


Chylomicron: travels via the Lymphatic System

Hydrophilic head

Hydrophobic tail


Common GI Problems…

• Choking- improper closing of the epiglottis, food lodged in the pharynx, etc.

• Vomiting- stomach contents expelled; sometimes the contents of the duodenum are expelled.

• Diarrhea- frequent loose stools, lack of absorption and increased water in the intestine; fast motility

• Constipation- inability to defecate


Common GI Problems (cont.)…

• Gas- excessive gas in the GI tract• Belching-excessive gas in the stomach• Reflux- relaxation of the lower

esophageal sphincter, causing stomach acid to touch the lining of the esophagus

• Ulcers- erosion of the lining of the GI tract• Diseases of the GI tract………


Diverticula in the Colon

Diverticulum (singular)

Diverticula (plural)

Diverticula may develop anywhere along the GI tract,but are most common in the colon.


In-text Figure Page 74

Eat a variety of food to keep your gastrointestinal tract happy.

fon 241 chapter 3

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