biology-digestive system enzyms

8/9/2019 Biology-Digestive System Enzyms

1/9

Digestive System

Introduction

Digestion is the chemical breakdown of large food molecules into smallermolecules that can be used by cells. The breakdown occurs when certain specificenzymes are mixed with the food.

Enzymes involved in Digestion

polysaccharides maltose glucose

proteins peptides amino acids

fats fatty acids and monoglycerides

Mouth

Chewing breaks food into smaller particles so that chemical digestion can occurfaster.

Enzymes

Salivary amylase breaks starch (a polysaccharide) down to maltose (adisaccharide).
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Polysaccharideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Polysaccharideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Disaccharideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Monosaccharideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Proteinshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Polypeptideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Amino%20Acidshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Fats%20and%20Oils%20(Triglycerideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Disaccharideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Monosaccharideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Proteinshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Polypeptideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Amino%20Acidshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Fats%20and%20Oils%20(Triglycerideshttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20101/Bio%20101%20Lectures/Biochemistry/biochemi.htm#Polysaccharides


2/9

icarbonate ions in sali!a act as buffers" maintaining a p# between $.% and &.%.

'ucins (mucous) lubricate and help hold chewed food together in a clump called a bolus.

The tongue contains chemical receptors in structures called taste buds. Theses arediscussed in the chapter on sensory systems .

The tongue is muscular and can mo!e food. t pushes food to back where it isswallowed.

Pharynx

The respiratory and digesti!e passages meet in the pharynx. They separate

posterior to the pharynx to form the esophagus (leads to the stomach) and trachea(leads to the lungs).

wallowing is accomplished by reflexes that close the opening to the trachea.

*hen swallowing" the epiglottis co!ers the trachea to pre!ent food from entering.

n the mouth" food is mixed with sali!a and formed into a bolus .

Peristalsis refers to rhythmic contractions that mo!e food in the gut. +eristalsis in

the esophagus mo!es food from the mouth to the stomach.Stomach

The stomach stores up to , liters of food.

-astric glands within the stomach produce secretions called gastric juice .

The muscular walls of the stomach contract !igorously to mix food with gastric uice" producing a mixture called chyme .

Gastric juice

Pepsinogen is con!erted to pepsin" which digests proteins. +epsinogen productionis stimulated by the presence of gastrin in the blood (discussed below).

HCl

#ydrochloric acid (#Cl) con!erts pepsinogen to pepsin which breaks down proteins to peptides. #Cl maintains a p# in the stomach of approximately ,./.

t also dissol!es food and kills microorganisms.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Sensory%20Systems/sensory.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Sensory%20Systems/sensory.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Sensory%20Systems/sensory.htm


3/9

Mucous protects the stomach from #Cl and pepsin.

Secretion of Gastric Juice

eeing" smelling" tasting" or thinking about food can result in the secretion ofgastric uice.

Gastrin is a hormone that stimulates the stomach to secrete gastric uice. ( ee thediscussion of hormones below.)

Ulcer

0n ulcer is an irritation due to gastric uice penetrating the mucous lining of thestomach or duodenum. t is belie!ed that ulcers are caused by the

bacterium Helicobacter pylori " which" can thri!e in the acid en!ironment of thestomach. The presence of the bacteria on portions of the stomach lining pre!ents itfrom secreting mucous" making it susceptible to the digesti!e action of pepsin.

Duodenum

The duodenum is the first part of the small intestine.

Chyme enters through a sphincter .

t enters in tiny spurts.

0t this point" proteins and carbohydrates are only partially digested and lipiddigestion has not begun.

Pancreas

The pancreas acts as an exocrine gland by producing pancreatic juice whichempties into the small intestine !ia a duct.

The pancreas also acts as an endocrine gland to produce insulin. ( ee thediscussion on the slets of 1angerhans or +ancreatic slets in the chapter on theendocrine system .)

Pancreatic Juice

+ancreatic uice contains sodium bicarbonate which neutralizes the acidic materialfrom the stomach.

Pancreatic amylase digests starch to maltose.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Endocrine%20System/endocrin.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Endocrine%20System/endocrin.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Endocrine%20System/endocrin.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/Endocrine%20System/endocrin.htm


4/9

Trypsin and Chymotrypsin digest proteins to peptides. 1ike pepsin (produced inthe stomach)" they are specific for certain amino acids" not all of them. Theytherefore produce peptides.

Lipase digests fats to monoglycerides and fatty acids.

Liver

The li!er produces bile which is stored in gallbladder and sent to the duodenumthrough a duct.

ile emulsifies fats (separates it into small droplets) so they can mix with waterand be acted upon by enzymes.

ther !unctions o" the Liver

The li!er detoxifies blood from intestines that it recei!es !ia the hepatic portal!ein.

The li!er stores glucose as glycogen (animal starch) and breaks down glycogen torelease glucose as needed. This storage2release process maintains a constantglucose concentration in the blood (/.34). f glycogen and glucose run short"

proteins can be con!erted to glucose.

t produces blood proteins.t destroys old red blood cells and con!erts hemoglobin from these cells to

bilirubin and bili!erdin which are components of bile.

0mmonia produced by the digestion of proteins is con!erted to a less toxiccompound (urea) by the li!er.

#ormones Involved in Digestion

The hormones listed below" like all hormones" reach their target cells by thecirculatory system.

Hormone Secretedby:Stimulus forsecretion Effect

-astrin tomach +resence of food inthe stomach timulates the stomach to secrete gastric uice

ecretin Duodenum Chyme from thestomachtimulates the pancreas to produce sodium

bicarbonate and the li!er to secrete bile

CC5 Duodenum +resence of food in

the duodenum

timulates the gallbladder to release bile and the

pancrease to produce pancreatic enzymes- + Duodenum +resence of food in nhibits the gastric glands of the stomach and


5/9

the duodenum inhibits stomach motility

Gastrin

The presence of food in the stomach stimulates stretch receptors which relay thisinformation to the medulla oblongata. The medulla stimulates endocrine cells inthe stomach to secrete the hormone gastrin into the circulatory system. -astrinstimulates the stomach to secrete gastric uice. This pathway of information issummarized below.

stretch receptors medulla oblongata endocrine cells in the stomach gastrin circulatory system stomach secretes gastric uice

Secretin

ecretin is produced by cells of the duodenum.

t6s production is stimulated by acid chyme from stomach.

t stimulates the pancreas to produce sodium bicarbonate" which neutralizes theacidic chyme. t also stimulates the li!er to secrete bile.

$$% &cholecysto'inin(

CC5 production is stimulated by the presence of food in the duodenum.

t stimulates the gallbladder to release bile and the pancreas to produce pancreaticenzymes.


6/9

GIP &Gastric Inhi)itory Pe*tide(

7ood in the duodenum stimulates certain endocrine cells to produce - +.

t has the opposite effects of gastrin8 it inhibits gastric glands in the stomach and itinhibits the mixing and churning mo!ement of stomach muscles. This slows therate of stomach emptying when the duodenum contains food.

Small Intestine

The small intestine is approximately 9 m long.

1ike the stomach" it contains numerous ridges and furrows. n addition" there are

numerous pro ections called villi that function to increase the surface area of theintestine. ndi!idual !illus cells ha!e microvilli which greatly increase absorpti!esurface area.

The total absorpti!e surface area is e:ui!alent to %// or $// s:uare meters.

;ach !illus contains blood !essels and a lacteal (lymph !essel).

+eptidases and maltase are embedded within the plasma membrane of themicro!illi.

Peptidases complete the digestion of peptides to amino acids.

Maltase completes the digestion of disaccharides.

+)sor*tion

0bsorption is an important function of the small intestine.

0cti!e transport mo!es glucose and amino acids into the intestinal cells" then outwhere they are picked up by capillaries.


7/9

'onoglycerides and fatty acids produced by the digestion of fat enter the !illi bydiffusion and are reassembled into fat (triglycerides). They combine with proteinsand are expelled by exocytosis. They mo!e into the lacteals for transport !ia thelymphatic system.

Large Intestine

The large intestine is also called the colon.

t recei!es approximately 3/ liters of water per day. 3.% liters is from food and ne2third of thesolids is intestinal bacteria" ,?96s is undigested materials.

The cecum is a pouch at the unction of the small intestine and large intestine. nherbi!orous mammals" it is large and houses bacteria capable of digestingcellulose. n human ancestors" the cecum was larger but has been reduced bye!olutionary change to form the appendix.

Poly*s

+olyps are small growths in the epithelial lining of the colon.

They can be benign or cancerous and can be remo!ed indi!idually.

0 low2fat" high2fiber diet promotes regularity and is recommended as a protectionagainst colon cancer.

+**endix

The appendix is attached to cecum.

0ppendicitis is an infection. The appendix may swell and burst" leading to peritonitis (infection of the abdominal lining).

Summary o" Digestive Enzymes


8/9


9/9

7ill in the source of each enzyme in the table below and state the product produced by the enzyme.

FOOD TYPE

en ymeSO!"#E P"OD!#TS

#$"%OHYD"$TES

sali!ary amylase

pancreatic amylase

disaccharidases

P"OTE&'S

pepsins

trypsin" chymotrypsin

carboxypeptidase

aminopeptidase

F$TS

lipase

biology-digestive system enzyms

Documents