Principles of Biology BIOL 100C: Introductory Biology III The Digestive System Dr. P. Narguizian Fall 2012

Principles of Biology

BIOL 100C:BIOL 100C:Introductory Biology IIIIntroductory Biology IIIThe Digestive SystemThe Digestive System

Dr. P. NarguizianFall 2012

Copyright © 2009 Pearson Education, Inc.

OBTAINING AND PROCESSING

FOOD


Animals ingest their food in a variety of ways

Most animals have one of three kinds of diets

– Herbivores, plant-eaters—cattle, snails, sea urchins

– Carnivores, meat-eaters—lions, hawks, spiders

– Omnivores, eating both plants and other animals—humans, roaches, raccoons, crows


Animals obtain and ingest their food in different ways

– Suspension feeding

– Substrate feeding

– Fluid feeding

– Bulk feeding

Animals ingest their food in a variety of ways

Caterpillar Feces


Overview: Food processing occurs in four stages

Food is processed in four stages

– Ingestion

– Digestion

– Absorption

– Elimination

Mechanicaldigestion

Piecesof food

Food

Chemical digestion(hydrolysis)

Nutrientmoleculesenter bodycells

Smallmolecules

Undigestedmaterial

DigestionIngestion 21 Absorption3 Elimination4


Mechanical digestion breaks food down into smaller pieces

– Smaller pieces are easier to swallow

– Smaller pieces have more surface area exposed to digestive fluids



Chemical digestion breaks down large organic molecules into their components

– Proteins split into amino acids

– Polysaccharides and disaccharides into monosaccharides

– Nucleic acids into nucleotides


Protein-digestingenzymes

Polysaccharide

Macromolecule

Protein

Carbohydrate-digestingenzymes

Components

Amino acids

MonosaccharidesDisaccharide

Nucleic acid-digestingenzymes

NucleotidesNucleic acid

Fat-digestingenzymes

Fat Glycerol Fatty acids


Digestion occurs in specialized compartments

Sponges digest food in vacuoles

Most animals digest food in compartments

– Enzymes break down the food

– Food particles move into cells lining the compartment

– Undigested materials are expelled


Cnidarians and flatworms have a gastrovascular cavity with a single opening, the mouth

– Food enters the mouth

– Undigested food is expelled back out the mouth


Food(Daphnia,a waterflea)

Gastrovascularcavity

Food particleengulfed

Soft tissuesdigested

Tentacle

Mouth

Digestiveenzymesreleased froma gland cell

Food particledigested infood vacuole

4

3

2

1


Most animals have an alimentary canal with

– Mouth

– Anus

– Specialized regions


Mouth

Pharynx

Esophagus

Crop

Gizzard Anus

Intestine

Earthworm

Dorsal fold

Interior of intestine

Wall of intestine

EsophagusMidgut

Mouth

Crop

Grasshopper

Anus

HindgutGastric pouches

Mouth

Esophagus

Crop

Gizzard

Anus

Intestine

Bird

Stomach


HUMAN DIGESTIVE SYSTEM

Digestive System I: The Upper Gastrointestinal Tract

http://education-portal.com/academy/lesson/digestive-system-i-the-upper-gastrointestinal-tract.html





The human digestive system consists of an alimentary canal and accessory glands

Alternating waves of contraction and relaxation by smooth muscle in the walls of the canal move food along in a process called peristalsis

Sphincters control the movement of food into and out of digestive chambers


The pyloric sphincter

– Regulates the passage of food from the stomach to the small intestine

– Limits the upward movement of acids into the esophagus

The human digestive system consists of an alimentary canal and accessory glands

Mouth Salivaryglands

Esophagus

Gall-bladder

Liver

Pancreas

Smallintestine

Stomach

RectumAnus

Largeintestine

A schematic diagram of thehuman digestive system

Pharynx

Esophagus

Oralcavity

Tongue

Mouth

Salivaryglands

Gall-bladder

Liver

Pancreas

Smallintestine

Rectum

Anus

Largeintestine

Esophagus

Stomach

Smallintestine

Sphincter

Sphincter


Digestion begins in the oral cavity

Teeth break up food, saliva moistens it

– Salivary enzymes begin the hydrolysis of starch

– Buffers neutralize acids

– Antibacterial agents kills some bacteria ingested with food

The tongue tastes, shapes the bolus of food, and moves it toward the pharynx

Opening of asalivary gland duct

Salivaryglands

Tongue

Incisors

Premolars

Molars

“Wisdom”tooth

Teeth

Canine


After swallowing, peristalsis moves food through the esophagus to the stomach

The trachea conducts air to the lungs

The esophagus conducts food from the pharynx to the stomach

Epiglottisup

Pharynx

Esophagealsphincter

Bolus offoodTongue

Esophagus

Larynx

Trachea

Sphincter contracted

Epiglottisdown

Esophagus

Larynxup

Sphincter relaxed

Epiglottisup

Sphincter contracted

Larynxdown


The swallowing reflex

– Food moves from the pharynx into the esophagus

– The swallowing reflex prevents food from entering the trachea

– A coughing reflex helps expel materials that accidentally enter the trachea

After swallowing, peristalsis moves food through the esophagus to the stomach

Esophageal sphincter(contracted)

Bolus offood

Muscles contract,constricting passagewayand pushing bolus down

Stomach

Bolus offood

Muscles relax,allowing passagewayto open


The stomach stores food and breaks it down with acid and enzymes

Acid

– pH 2

– Parietal cells secrete hydrogen and chloride ions, which combine to make HCl

– Acid kills bacteria and breaks apart cells in food

Pepsinogen and HCl produce pepsin

– Pepsin production activates more pepsinogen production—positive feedback

– Pepsin begins the chemical digestion of proteins

– Acidic gastric juices mix with food to produce acid chyme


What prevents the gastric juices from digesting the walls of the stomach?

– Mucus helps protect against HCl and pepsin

– New cells lining the stomach are produced about every 3 days

The stomach stores food and breaks it down with acid and enzymes

Interior surfaceof stomach

Lumen (cavity)of stomach

Stomach Gastrin

Esophagus

Sphincter

Sphincter

Smallintestine

Interior surfaceof stomach

Pits

Release of gastric juice(mucus, HCl, and pepsinogen)

Epithelium

Gastricgland

Mucouscells

Chief cells

Parietal cells

Pepsin(activeenzyme)

Pepsinogen

H+

Cl–

HCl2

3

1


The small intestine is the major organ of chemical digestion and nutrient absorption

Small intestine is named for its smaller diameter—it is about 6 meters long

Alkaline pancreatic juice neutralizes acid chyme and its enzymes digest food

Bile, made in the liver and stored in the gall bladder, emulsifies fat for attack by pancreatic enzymes

Gall-bladder

Pancreatic juice

Liver Bile

Acid chyme

Pancreas

Stomach

Intestinalenzymes

Duodenum ofsmall intestine

Digestive System II: The Lower Gastrointestinal Tract

http://education-portal.com/academy/lesson/digestive-system-ii-the-lower-gastrointestinal-tract.html


Enzymes from cells of the intestine continue digestion



Surface area for absorption is increased by

– Folds of the intestinal lining

– Fingerlike villi


Musclelayers

Largecircular folds

Villi

Lumen

Nutrientabsorption

Intestinal wall

Veinwith blooden route tothe liver


Nutrients pass across the epithelium and into blood

Blood flows to the liver where nutrients are processed and stored


Lymphvessel

Bloodcapillaries

Villi

Nutrientabsorption

Epithelialcells

Lumen of intestine Lumen of intestine

Nutrient absorptioninto epithelial cells

Microvilli

Aminoacidsand

sugars

Fats

Blood

Fattyacidsand

glycerol

Epithelial cellslining villus

Lymph


One of the liver’s many functions is processing nutrient-laden blood from the intestines

Blood from the digestive tract drains to the liver

The liver performs many functions

– Glucose in blood is converted to glycogen and stored in the liver

– Liver synthesizes many proteins including blood clotting proteins and lipoproteins that transport fats and cholesterol

– Liver changes toxins to less toxic forms

– Liver produces bile

Heart

Hepaticportalvein

Kidneys

Liver

Intestines


The large intestine reclaims water and compacts the feces

Diarrhea occurs when too little water is reclaimed

Constipation occurs when too much water is reclaimed

Feces are stored in the rectum

Colon bacteria produce vitamins—biotin, vitamin K, B vitamins


Appendix

– Located near the junction of the small intestine and colon

– Makes a minor contribution to immunity

The large intestine reclaims water and compacts the feces

Largeintestine(colon)

Endof smallintestine

Appendix

Cecum

Sphincter

Unabsorbedfood material

Anus

Rectum

Smallintestine


EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems often relate to diet

The length of the digestive tract often correlates with diet

– Herbivores and omnivores have relatively longer digestive tracts than carnivores

Small intestine

Cecum

Stomach

Colon(large intestine)

Carnivore Herbivore


Many herbivores have specializations of the gut that promote the growth of cellulose-digesting microbes

– Rumen

– Reticulum

– Omasum

– Abomasum

EVOLUTION CONNECTION: Evolutionary adaptations of vertebrate digestive systems often relate to diet

Intestine Omasum Rumen

Esophagus

ReticulumAbomasumRumen

a. g.

h.

i.

j.

k.

l.

m.

b.

c.

d.e.

f.


You should now be able to

1. Describe the four stages of food processing

2. Describe the main components of the human digestive tract and their functions

3. Explain how teeth and saliva help us swallow

4. Explain why the stomach does not digest itself5. Compare the structures and functions of

the small and large intestines

6. Compare the digestive tracts of carnivores and herbivores

Documents

Principles of Biology BIOL 100C: Introductory Biology III The Digestive System Dr. P. Narguizian Fall 2012