Biology 20IBiology 20IDigestive System

OR

From Food to Feces in a couple hundred steps!

DIGESTIVE SYSTEMDIGESTIVE SYSTEMHETEROTROPHIC NUTRITIONHETEROTROPHIC NUTRITION

Unable to manufacture food from inorganic molecules.

Depend on autotrophs.

AUTOTROPHIC NUTRITIONAUTOTROPHIC NUTRITION Organisms capable of synthesizing

organic molecules from simple inorganic material.

Types: photosynthesizers and chemosynthesizers.

Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition

1) Ingestion• eating or drinking• Putting organic molecules into the

system. • Heterotrophs need:

– Sugars– Amino Acids– Fatty Acids– Glycerol– Minerals– Vitamins

Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition

2) Digestion• Breakdown of macromolecules into smaller

ones that can be absorbed by the cells– Mechanical -- chewing– Chemical -- digestive enzymes

Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition

3) Absorption• Nutrients are absorbed into the blood

– Digested monomers– Water– Minerals– Vitamins

4) Egestion• Elimination of undigested material• Poop but because this is a Biology class

we will call it FECES

Steps of Heterotrophic NutritionSteps of Heterotrophic Nutrition

5) Assimilation• The conversion of nutrients into fluid or solid

parts of the organism. Assimilation can only occur after absorption has taken place.

• “You will be assimilated. Resistance is futile. ” Locutus of Borg

Digestion TermsDigestion Terms

• Mastication• To chew food

• Increases surface area for digestion

• Peristalsis • The wavelike muscular contractions of the

alimentary canal by which contents are forced onward

88

Digestion TermsDigestion Terms

• Sphincter• A ring-like muscle that normally maintains

constriction of a body passage or orifice and that relaxes as required by normal physiological functioning.

DigestionDigestion

Lipase(Pancreatic lipase)

Protease(pepsin)

Amylase (Salivary amylase)

Optimum

pHProductSubstrateSourceEnzyme

DigestionDigestion

6.1.1 - Macromolecules must be digested into their respective monomers so that our bodies can absorb them.

6.1.2 – Enzymes are needed by our body to increase the rate of digestion at our body temperature

Digestion H.2.1Digestion H.2.1

Digestive juices are secreted into the alimentary canal by glands• salivary glands

• gastric glands in the stomach wall

• pancreas

• wall of the small intestine.

Digestion H.2.2Digestion H.2.2 Exocrine glands – have secretory cells

around hollow spaces (acini) (lt. berries) which are grouped around ducts into which they secrete their products

Digestion H.2.2Digestion H.2.2

Sweat Gland Exocrine Gland

PartsParts

Organs•Mouth•Pharynx•Esophagus•Stomach•Small Intestine•Large Intestine•Anus

Glands• Salivary Glands

• Pancreas

• Liver

• Gall Bladder

Order of EventsOrder of Events

MouthMouth Hard Palate

• hard part of roof of mouth Soft Palate

• back of roof of mouth Pharynx

• chamber in throat where – nasal cavity and mouth meet

– esophagus and trachea meet

Mucus Membranes• lubricates walls of mouth for easy passage of

food

MouthMouthPurpose

• Mechanical digestion by teeth and tongue–increases surface area for action by enzymes–Mixes food thoroughly with teeth and tongue

• Chemical digestion by enzymes in salivaValue

• food easily swallowed• increases SURFACE AREA exposed for

action by digestive enzymes• thoroughly mixes the food with the TEETH

AND TONGUE

Salivary GlandsSalivary Glands•Secretions

•Saliva

•1 to 2 liters per day

•from 3 pairs of glands in the mouth

•Sub-lingual

•parotid

•Sub-mandibular

MouthMouth

Composition of Saliva

• Water

– moistens food

• Amylase (ptyalin)

– begins STARCH digestion

• Mucin

– lubricant

– binds food together for easier swallow

33 salivary glands salivary glands

• Parotid salivary gland – secrete amylase• Sublingual salivary gland – mucous

secretion that acts as a buffer and lubricant• Submandibular salivary gland – secrete

mixture of buffer, mucins and salivary amylase

• Buffers in saliva keep pH of mouth near 7.0• Prevent build up of acids produced by bacterial

action• Increase saliva when feel sick• These are exocrine glands - secretion goes

outside of body and not into the circulatory system.

MouthMouth

Control of Salivary Secretions

• Mechanical pressure

– food in the mouth

• Nervous system - glands

– Brain thinking of food in the mouth

– Signal sent to salivary glands from the brain

– Pavlov’s Dog anyone? “ring a bell and I’ll salivate”

PharynxPharynx

PharynxPharynx

Throat• Common tube through which both air and food

pass Four openings

• Nasal Cavity Mouth Cavity• Trachea Esophagus

Contains a flap of tissue called the EPIGLOTTIS to prevent food from entering the trachea

EsophagusEsophagus

Hollow muscular tube Connects pharynxpharynx to the stomachstomach

What makes the food go to the stomach? Movement of food by peristalsis

• rhythmic waves of contraction and relaxation of muscular walls

• food is squeezed through esophagus into stomach

Epiglottis and uvula shunt food into esophagus during swallowing

PeristalsisPeristalsis

PeristalsisPeristalsis

EsophagusEsophagus

Structure

• thick walled and muscular

• from pharynx to stomach

• walls contain mucus glands which

secrete mucin to lubricates food for

easy passage

StomachStomachStructurea hollow muscular pouch J shaped – shape and volume

changes from meal to meal.located high in the abdominal

cavity, just under the diaphragm where your ribs come up together – not at your waist/belt.

Structure of Stomach (con’t)Structure of Stomach (con’t) Connection between esophagus and the

stomach is regulated by cardiac sphincter.• muscular ring surround esophagus at this point• acts like a valve to open and close the tube• keeps the food from falling out of your stomach

when standing on your head. Water demo!!!! Connection between the small intestine and the

bottom end of the stomach is regulated by the pyloric sphincter.• Regulate the release of chyme into small intestine

when food is liquefied it is called chyme.

StomachStomachFUNCTIONS

• temporary storage of ingested food

• mechanical breakdown of ingested food–churning of the stomach mixes juice with food

• liquefaction of food

• beginning of protein digestion (disruption of chemical bonds in food through action of acids and enzymes)

Secretions -- Gastric JuiceSecretions -- Gastric Juice

pH plays an essential role in gastric activity• Regulated by amount of gastric

juice secretionGastric juice is secreted into

the stomach cavity by stomach cells

Secretions -- Gastric JuiceSecretions -- Gastric Juice Contains

1. Hydrochloric Acid – HCl(aq)

–pH of 1-2 –H+ and Cl- are secreted separately, becomes

HCl in stomach–Acidity:

• destroys bacteria present in food • Denatures proteins and inactivates enzymes in food• Break down plant cell walls and connective tissues

in meat• Activates Pepsin!!!!

Secretions -- Gastric JuiceSecretions -- Gastric Juice

Contains

2. Pepsin –an enzyme which begins protein

digestion

–Pepsin is produced and secreted in an inactive form called pepsinogen

• Pepsinogen convert to pepsin when pH gets to 2

Secretions -- Gastric JuiceSecretions -- Gastric Juice Why is pepsin secreted as pepsinogen, an

inactive form? Pepsin is secreted as pepsinogen first is to

protect the stomach lining.

stomach lined with a mucus coating

• prevents acid and protein digesting enzymes

from damaging wall

• Hence, stomach only digests food, and does

not have any food absorption

Digestion in StomachDigestion in Stomach pH of stomach is decreased by gastric juice When food just arrives in the stomach, pH of

stomach is still high• When pH is still above 4.5 – salivary amylase

is still active – break down carbohydrates

• When HCl in gastric juice lowers pH to 1-2, pepsin is activated – breaks down protein

– Complex proteins are broken into smaller peptide and polypeptide chain

Regulation of Gastric ActivityRegulation of Gastric Activity

1. Central Nervous System• See, smell, taste, or think of food will stimulate

increase production of gastric juice in stomach• Nervous system prepares stomach to receive

food• Production of gastric juice accelerates 500mL per

hour• Emotional states can also affect

– e.g. Anxiety – decrease stimulation & slows digestion

Regulation of Gastric ActivityRegulation of Gastric Activity

2. Hormones• Gastrin

– Produced by stomach cells– Enters blood stream– Increase secretion of HCl and Pepsinogen by

stomach cells• pH decrease

– Increase gastric motility

• When chyme enters small intestine, stomach cells secrete other hormones to temporarily inhibit gastric juice secretion

Small IntestineSmall Intestine

FUNCTION

• complete the digestion of food

– important secretions from the pancreas and

the liver.

• absorb the nutrients into the circulatory

system (blood)

Small IntestineSmall Intestine

STRUCTURE + FUNCTION About 6 meters long

• Three sections1) Duodenum

• first 25 cm • Digestion• Neutralize acids in chyme• Receives and mixes pancreatic and liver secretions

2) Jejunum • next 2 meters • Bulk of chemical digestions and nutrient absorption

3) Ileum • next 4 or 5 meters • absorption

Small IntestineSmall Intestine

STRUCTURE (con’t) the inside of the S.I. is covered with millions

of tiny finger-like projections called villi• each villus is actually covered with millions of

microvilli• the villi and microvilli increase surface area for

absorbing food molecules into blood.• 600 times more surface area

Surface of small intestine contains membrane-bound digestive enzymes

Secretions -- Pancreatic FluidSecretions -- Pancreatic Fluid

Contains1. NaHCO3 – sodium bicarbonate

– raises pH to 8 (important for enzymes to function)

2. Pancreatic Amylase – an enzyme which continues the digestion of

starch into maltose units

3. Lipase – enzyme digesting lipids into fatty acids & glycerol

Secretions -- Pancreatic FluidSecretions -- Pancreatic Fluid

4. Proteolytic Enzymes

-enzymes which continue protein digestion

-2 types:

1. protease – break down large protein complexes

2. peptidases – break down small peptide chains into individual amino acids

Example:

Trypsin (protease)– Secreted as trypsinogen in pancreas (similar to pepsinogen)– Activated into trypsin by an enzyme in membrane surface of

small intestine

Liver and Gallbladder SecretionLiver and Gallbladder Secretion

The liver produces bile– brown fluid

Bile is stored in the gallbladder when fats enter the small intestine,

the gallbladder contracts and squirts bile into the duodenum

Small IntestineSmall Intestine

• Lipase is water-soluble, only contact fat droplets on the outside surface

– Cannot break down the fat on the inside of the droplet

• bile emulsifies fats– physically prevents fats to coalesce with each

other – Fats are in smaller droplets

–greater surface area for action by lipase

• bile is NOT an enzyme because it does not cause a chemical change in fat.

Small Intestine Small Intestine H.2.9H.2.9• Explain the problem of lipid digestion in a

hydrophilic medium and the role of bile in overcoming this. –Lipid molecules tend to coalesce and are only

accessible to lipase at the lipid–water interface. Bile molecules have a hydrophilic end and a hydrophobic end, and thus prevent lipid droplets coalescing. The maximum surface is exposed to lipases. Lipase needs to be water-soluble and to have an active site to which a hydrophobic substrate binds.

Small IntestineSmall Intestine

All types of foods are acted upon.

Small Intestine H.2.5Small Intestine H.2.5 digestion of disaccharides and dipeptides is

completed by enzymes on surface membrane of intestinal villi in small intestine• sucrase

– digests sucrose

• maltase – digests maltose

• lactase – digests lactose

• aminopeptidase – breaks down dipeptides into amino acids

Small IntestineSmall Intestine

once all food molecules are at monomer stage, they are ready to be absorbed into the circulatory system through the villus on small intestine surfaces

Assignment H.3.1 Assignment H.3.1

Draw and label a Draw and label a diagram showing a diagram showing a transverse section of transverse section of the ileum as seen the ileum as seen under a light under a light microscope. Include microscope. Include mucosa and layers mucosa and layers of longitudinal and of longitudinal and circular muscle.circular muscle.

Absorption in the Small Intestine H.3.3Absorption in the Small Intestine H.3.3

Digested Nutrient

Product Method of Absorption

Site of Absorption

Small IntestineSmall Intestine

notice that glycerol recombines with 3 fatty acids to form a fat molecule which enters the lacteal instead of the capillary

Why is fat completely digested and then recombined to form a fat molecule again?

H.3.2H.3.2 Explain the structural features of an epithelial

cell of a villus as seen in electron micrographs.• Microvilli – folds of the cell membrane that increase

the surface area of the epithelial cell.• Mitochondria – provide energy for the cell to

transport nutrients.• Pinocytotic vesicles – assist with endocytosis of

nutrients.• Tight junctions – connections between epithelial

cells that maintain structure integrity of the tissue.

Large IntestineLarge Intestine

Large IntestineLarge Intestine

Material NOT absorbed by this point will enter the large intestine through another sphincter – the ilial-caecal sphincter

The caecum is a small pouch at the beginning of the large intestine.• contains a small projection called the

appendix– this is a vestigial organ which functions in

cellulose digestion in some herbivorous mammals

Functions of the Large IntestineFunctions of the Large Intestine

absorb water into blood

absorb vitamins and minerals into blood

eliminate undigested material from digestive

tract (cellulose, lignin, bile pigments, bacteria

and intestinal cells.)

Large IntestineLarge Intestine

Some bacteria live in the large

intestine of mammals

• they digest material that we are not able

to digest

a byproduct of this activity results in

the synthesis of vitamins

• Vitamin K

Rectum & AnusRectum & Anus

last section of digestive tract rectum is a holding pouch for feces feces exits the digestive tract through

a sphincter muscle called the anus. rectal veins are found near opening

• if they get inflamed…– the inside diameter of anus decreases – passage of feces is difficult and painful – called hemorrhoids or piles.

What About Fiber???What About Fiber???

fiber in the diet serves to retain water throughout the digestive

tract resulting in soft feces.

H.2.6 Outline the reasons for cellulose not being digested in

the alimentary canal. See above.

H.3.4 The materials that are not absorbed but are egested are

cellulose, lignin, bile pigments, bacteria and intestinal cells.

Biology 20Biology 20

Control of Digestive Secretions

SalivaSaliva

Nervous

• Pavlov

• Sight, smell, presence, or even thought of Sight, smell, presence, or even thought of

food stimulatesfood stimulates vagus nerve

• results in the production of saliva

Gastric JuiceGastric Juice

Nervous

• Stimulation of vagus nerve also

stimulates cells of stomach to begin

producing gastrin

Gastric JuiceGastric Juice Hormonal

• Gastrin (a hormone) is released from certain upper stomach cells into the bloodstream.

• gastrin circulates until it reaches the lower stomach cells resulting in the release of gastric juices.

• Once pH falls below 2, gastrin stops being secreted.

• If pH rises above 2.5 gastrin secretion begins again.

Pancreatic JuicePancreatic Juice Nervous

• presence ofpresence of food food in mouthin mouth and stomach stimulates pancreatic secretions

Hormonal• presence of chyme in the S.I.presence of chyme in the S.I. causes the cells of the

duodenum to secrete the hormone secretin into the blood• Secretin (a hormone) causes the pancreas to begin

producing pancreatic juice • Pancreatic Juice will enter the duodenum through the

pancreatic duct. • when acidic chyme becomes alkaline, production of

secretin stops

Liver & Gall BladderLiver & Gall Bladder

BileBile Hormonal

• presence of chyme in the S.Ipresence of chyme in the S.I. causes the cells

of the duodenum to secrete the hormone

cholesystekinin into the blood.

• This causes the gall bladder to contract,

propelling bile into the duodenum through the

bile duct

DISORDERSDISORDERS

H.2.8 Discuss the roles of gastric acid and Helicobacter pylori in the

development of stomach ulcers and stomach cancers.

•Burrows into mucus layer in stomach and produces toxins and enzymes that destroy gastric lining

•One enzyme breaks down the mucus, exposing the stomach cells to gastric juices

•Can get it from contaminated food or water. Can pass from human-to-human contact.

•Treated with combination of antibiotic and antacid.

How did they figure this out??How did they figure this out??

Barry Marshall – scientist in Australia No one would believe him that ulcers

could be due to a bacteria – the stomach is too acidic!

To prove his suspicion he drank a mixture of H. pylori himself and gave himself ulcers!

Won the Nobel prize in Medicine or Physiology, 2005 for this research

DisordersDisorders

Tapeworms are a group of parasitic worms that live in the intestinal tracts of some animals. Several different species of tapeworms can infect humans. Tapeworm disease or cestodiasis occurs most commonly after eating raw or undercooked meat or fish that contains the immature form of the tapeworm.

TapewormTapeworm

TapewormTapeworm

IntestinalDisordersIntestinalDisorders Appendicitis  Cancer  Celiac Disease Constipation  Diarrhea  Diverticulitis  Hernias  Inflammatory Bowel Disease  Irritable Bowel Syndrome  Lactose Intolerance  Short Bowel Syndrome 

Anorectal DisordersAnorectal Disorders

Anal Fissures  Cancer  Constipation  Hemorrhoids  Imperforate Anus 

Stomach DisordersStomach Disorders

Cancer  Cyclic Vomiting Syndrome  Indigestion  Peptic Ulcer  Reflux Disease 

Gallbladder DisordersGallbladder Disorders

•Gallstones 

Liver DisordersLiver Disorders

Alagille Syndrome  Alpha1-Antitrypsin Deficiency 

Associations Cancer Children 

Crigler-Najjar Syndrome Hepatic Encephalopathy Hepatitis Support Groups Transplant Wilson's Disease Zellweger Syndrome 

Pancreatic DisordersPancreatic Disorders

Cancer 

Cystic Fibrosis 

Pancreatitis 

Oral DisordersOral DisordersDrooling Dysphagia Mouth Ulcers