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DIGESTIVE SYSTEM

DRAFT

Overview

Defn

Parts: Top to bottom

Diagram everything !the easy way"

Hormones & Enzymes

Defn

the physicaland/or chemicalbreakdown of food

physical/mechanical!rending

chemical!hydrolytic

foods "polymer#

into small molecules "monomer#for absorption

a simplified...

Physical digestion

involves physically breaking the food into smallerpieces without chemically changing it into di#erentmolecules

which increases the exposed SAfor chemicaldigestion

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e.g.,

Mouth$teeth!chew, masticate"

Stomach$muscle, rugal folds/ridges!churn"

Liver$bile!emulsifies lipids"

Lipid + Bile

increasedSA...

droplet droplets

Lipid

Chemical digestion

the breaking down of the large molecules!polymers"into smaller soluble molecules!monomers"for easy absorption

via hydrolysis

Lipid + water glycerol + fatty acidslipase

!enzyme"

THE PARTSTop to Bottom

Teeth

physical digestion

Mouth

incisors

canines

premolars

molars

carnivore

herbivore

omnivore

$cut

$hold, tear

$grind

$grind

+%

%

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Carnivore

Herbivore

Omnivore

incisors

canines premolarsmolars

Saliva

mostly water and mucus

lubricant

rich in salivary amylase

Amylose + water MaltoseAmylase

!enzyme""Starch# "disaccharide#

Swallowing: Steps

1. Bolus!chewed food ball"contacts the pharynx!back of the throat"and stimulates an autonomic!involuntary"gulp response:

boluspharynx

palate

trachea$ind pipe

larynx%oice box

esophagus!sophagus"

food pipe

epiglottis

nasal cavity

2. The palate seals o"the nasal cavity,preventing food from entering it.

3. This response stops breathingand theepiglottis seals o"the trachea,

4. the esophageal sphincter relaxes...

epiglottisclosing over the glottis

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step$by$step

Movement

gravity fed

via Peristalsiswave$like, rhythmicalcontractions of circular,smooth !involuntary"muscle

stomach, small and largeintestines too...

Esophagus

Stomachesophagus

cardiacsphincter

pyloricsphincter

small intestine

stomach

rugae

pH 1$3

Sphincters

Cardiac Sphincter

limits the back flow of gastric juices up theesophagus

failure: acid reflux !heart burn"

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Sphincters

Pyloric Sphincter

limits the flow of gastric juices !pH 1"into the smallintestine !pH 6$6.5,duodenu&"

which would normally denaturethe intestinal juices !critical fordigestion"

Source: gastric pits of the cardia,fundus, &pylorus

fundus

cardia

pylorus

Gastric Juices

Goblet cells

pits body

source: Parietal cells!w/in gastric pits"

Fcn:

breaks up connective tissues...

increasing SA for enzyme !e.g., pepsin"activity

kills surface bacteria

reacts with pepsinogen...

Hydrochloric Acid (HCl)

Gastric Juices

pH 1$3

source: Chief cells!w/in gastric pits"

pepsin precursor

pepsinogen + HCl ! pepsin

Pepsinogen

Gastric Juices

"protein# "enzyme#

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protein + water a.a strands

Pepsin (protease)

Gastric Juices

"polypeptide'agments#

a.a.a.a.

"peptide'agments#

# a.a.

pepsi(

source: Goblet cells!w/in the gastric pits"

protects stomach lining

from autodigestion

from abrasion

lubricant for food passage

Mucus (aka Mucin)

failure: ulcer

Common causes:

bacterial !Helicobacter pylori"infection

!: antibiotic regime

excessive NSAIDs use, e.g., aspirin, ibuprofen,naproxen

Mucus

Mucus is also found in the:

salivary glands, esophagus, small intestine, colon

duodenum:Brunners gland$alkaline mucus toneutralize acid chyme from the stomach

respiratory tract: bronchi, nose...

reproductive tract: cervix, cowpers gland...

Mucus

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Chyme

semi$fluid, partially digested mass that exits thestomach

pH 2...

in three parts

1. Duodenum !twelve fingers

~ 30cm, pH 6$6.5

site of digestion

produces and receives numerous digestiveenzymes and hormones, and bile

Small Intestines

2. & 3. Jejunum & Ileum

~ 6m, pH 7$8

site of absorption

Jejunum & Ileum

increase SA for absorption...

villi

microvilli!brush border"

folds

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Increasing SA

villi

folds

Villi

capillaries

lacteals

blood

lymph

microvilli!brush border cells"glycerol &

fatty acids

glucose &a.a.

Carbohydrates

as monosaccharides, e.g., glucose

via capillaries!hepatic portal vein !liver

excess glucose is stored as glycogen &insuli(

and released as needed to maintain homeostasis!4$6 mmol/L"&glucago(

a diet high in processed carbohydrates, i.e., with aglycemic index !GI"> 70 may lead to

type II diabetes !insulin resistance"

heart disease !excess glycogen forms triglycerides"

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Proteins

as a.a.

via capillaries!hepatic portal vein !liver

liver:

a.a. !plasma!blood"proteins

e.g., albumin, prothrombin, fibrinogen...

deamination of proteins!a.a. !amino group !ammoniaNH3 !v. toxic"

is converted by the liver tourea!less toxic"forexcretion via the kidneys

NH3 + CO2 !urea !excreted w/ urine"

Bu"er:NH3 + H+ !NH4+!ammonium ion"

Lipids

as glycerol!monoglycerides

"and free fatty acids

via lacteals !lymph"!to the body... !subclavian vein!superior vena cava !heart...

to muscle and adipose tissues that take up thetriglycerides for storage !and energy use"

and back to the liver for:

cholesterol synthesis !VLDL !LDL, HDL"

lipid synthesis !e.g., triglycerides"

for storage !and energy use"

triglycerides

fatty acidsmonoglycerides

triglycerides

proteins+phospholipids +

cholesterol coatingchylomicrons

"lipoprotein#

lacteal

simplified...

microvi)i"mice)es#

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Ileum

Duodenum

Jejunum

Colon

Pancreas

Liver lymph

blood

Chylomicron

muscle, adipose

remnant CM

blood

VLDL

bil*

lipas*

LDL

HDL

&

Ileum

Duodenum

Jejunum

Colon

Pancreas

Liver lymph

blood

Chylomicron

muscle, adipose

remnant CM

blood

VLDL

bil*

lipas*

LDL

HDL

&

HDLHigh Density Lipoprotein source: Liver and small intestine travels around the body picking up

excess cholesterolLDLLow DensityLipoprotein delivers fat

!triglyceride"andcholesterol tobody

before returningto the liver

VLDLVery Low Density Lipoprotein. delivers fat !triglyceride"and cholesterol to

body once its done,VLDL goes back to the liver

and the remainder gets made into LDL

to tissues

But if too much,or damaged...

plaquebuild up

LDLHDL

In an artery...

=atheroma

HDL scrubsthe excess...

returningexcess to theliver orto LDL andVLDL

Large Intestine

aka colon, bowel

~1.5m, pH 7$5.5ascending

appendix

sma)intestin*

cecum

rectum

transverse

descending

sigmoid

anus

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Fcn:

Water reabsorption

Excretion of excess:

Iron salts

Calcium salt

Large Intestin*

Site ofE. coli

generally mutualistic !beneficial"symbiont that

inhibits colonization by harmful bacteria

synthesizes vitamins, esp. vit. K, and B vitamins!e.g., folic acid"

produce a.a, and other growth factors

Large Intestin*

functions to compact the undigested wastes that isleft over from digestion for easier elimination/defecation

Large Intestin*

SUMMARY: THE PARTS

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salivary glands

esophagus

stomach

pancreasgall bladder

small intestinelarge intestine

rectum

anus

liver

appendix

cecum

epiglottismouth...

+ Plus...

mouth

salivary glands

esophagus

stomachcardiac sphincter

pyloric sphincterpancreas

gall bladder

liversmall intestine

!DJ &I"

large intestine

hepatic portal vein

hepatic veinrectum

anus

inferiorvenacava

HORMONES

bolus passes thru thecardiac sphincter

stimulates gastrin

which stimulatesHClproduction

and increasesstomach motility!churning"

Gastrin

stomach

Gastrin

duodenu&

esophagus

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acid!rich chyme

stimulates secretin

which stimulates therelease of sodiumbicarbonate !bu#er"

and...

Secretin

Secretin

pancreas

duodenum"sma)intestine#

Secreti!

bil"

stimulates the release ofalkaline bilefrom the

gall bladder

counteracting anyexcess stomach acidbefore it enters theileum

Secretin

gall bladder

duodenum"sma)intestine#

liver

bile duc+

chole = bile, cyst = sac,kinin = movement

lipid$rich and protein$richchyme

stimulates gall bladdertoreleasebile!emulsifier"

stimulates pancreas torelease digestive enzymes

Cholecystokinin (CCK)

CCK

bil"

Bile: Emulsification

source: liver

stored in the gall bladder

a surfactant,increases SA for enzyme !lipase"activity

Fat Fat droplets

bile incr.SA

"#$

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together inhibit peristalsisand HCl production

slowing digestion

CCK & Secretin

Insulin & Glucagonantagonistic hormones

Homeostatic:4$6 mmol/L

Low bloodglucose

High bloodglucose

Insulinlowers blood glucoseconverts and stores

glucose as glycogen

Glucagonraises blood glucose

converts storedglycogen to glucose

body cells!esp. muscle"

LIVERA quick overview of key functions

Liver Functions

Bile synthesis

a surfactant, emulsifierof lipids

alkaline, neutralizes gastric acids in the smallintestine

excretionof bilirubin, biliverdin !RBC pigment"

Quick Review...

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Protein synthesis

plasma %blood&proteins:

albumin$bu#er, osmotic regulator

prothrombin$blood clotting

fibrinogen$blood clotting

...

Quick Review...

Lipid synthesis

cholesterols !HDL, LDL..."

triglycerides

Quick Review...

Glucose Homeostasis

glucose!glycogen %insuli!&

glycogenesis

glycogen!glucose %glucago!&

gluconeogenesis!glucose from other sources..."

site of insulin breakdown

Quick Review...

Storage

iron, copper

vitamins !A, B, D..."

glycogen

Quick Review...

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Deamination

breakdown of excess proteins !formation ofammonia

Quick Review...

Detoxification

ammonia!urea !excretory"

breaks down insulin and other hormones

breaks down hemoglobin !bile

general detoxificationof toxic substances

Quick Review...

ENZYMESSELE

CT

Source Enzyme SubstrateDigestionProduct

Salivaryglands

salivaryamylase

amylose!starch"

maltose

Stomach pepsin"protease#

protein a.a. strands"peptide'agments#

pH 7

pH 1

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Source Enzyme SubstrateDigestionProduct

peptidase peptides a.a.

nuclease nucleic acids"DNA, RNA#

nucleotides

uo enum!small maltase

"disaccharidase#maltose

"disaccharide#glucose

"monosaccharide#

sucrase sucroseglucose +'uctos*

lactase lactoseglucose +galactos*pH 8

Source Enzyme SubstrateDigestionProduct

pancreaticamylase amylose

maltose

Pancreas"these enzymes

trypsin

"protease# protein a.a. strandsoperate w/in th*sma)intestine# nuclease nucleic acids nucleotides

lipase lipidsglycerol &fatty acidspH 8

nucleotidesNucleic Acids

Polysaccharides

Proteins

Lipids

salivary amylase $salivary glands "pH 7#

pancreatic amylase $pancreas"pH 8#

maltose

maltase $small intestine

glucose

peptides

glycerol & fatty acids

lipase $pancreas

pepsin $stomach "pH 1#

trypsin $pancreas "pH 8#peptidase $small intestine

a.a.

nucleosides +phosphate

sugar +base

nuclease $pancreas

nuclease $intestinal nucleosidas*nucleotidas*

"monoglycerides &'ee fatty acids#

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