DIGESTIVE SYSTEM · (2) neutralization of acidity of HCL and inactivation of pepsin (3)...
Transcript of DIGESTIVE SYSTEM · (2) neutralization of acidity of HCL and inactivation of pepsin (3)...
DIGESTIVE SYSTEM
DAW SAN DAR TUN
ASSISTANT LECTURER
DEPARTMENT OF ZOOLOGY
UNIVERSITY OF MEDICINE,MAGWAY
Ingestion
• a process by which food is taken in through the mouth
• a reflex action which is involuntary
• it occurs when the food is put at the posterior position of the tongue
A process by which large food molecules
are broken down into smaller pieces
Digestion
Mechanical digestionbiting & chewing
Chemical digestionHydrolysis & enzymes(Simple soluble forms)
Ingestion and digestion of food
Oral cavity
Four kinds of teeth
Incisors – chisel-shaped teeth ( for biting )
canines – pointed teeth ( for tearing )
Premolars & molars – flattened , ridged teeth
( for grinding, pounding,
crushing )
Saliva (pH 6.8)
amylase(ptyalin)mucinwater
starch maltoselubricates
food
helps swallowing
dissolves
soluble food
Chemical Digestion
break down of starch molecules
into maltose molecules by salivary
amylase (from salivary glands)
Starch
maltoses
salivary glands
Peristalsis
Oesophagus
- the peristalsis passes the bolus to stomach
- no digestive enzyme is secreted
Stomach
Cardiac sphincter
(a valve –like ring of muscle )
- relaxes as the bolus
passes through,then
quickly closes
In the stomach,
- food is retained for 4-6 hours in man.
Layer of stomach muscle
contract &churn the bolus of food
with gastric juices to make it a soupy chyme.
Gastric juice
water mucusHCL enzymesalt
mucus cells mucus
oxyntic cells HCL (Hydrochloric acid)
chief cells pepsinogen (proenzyme)
90% 0.2-0.5%
In man
2-3 liters of gastric juice is secreted per day
The stomach and gastric glands
(Oxyntic cell)
Function of hydrochloric acid
(1) change the pH of food from 1 - 3.5
(2) activates
pepsinogen active pepsin
prorennin active rennin
(3) dissolves salts,bones etc. in food
(4) stop salivary enzyme action
(5) kill harmful bacteria
(6) splits nucleoproteins
(7) regulate pyloric sphincter
Hcl
nucleic acid + proteinHcl
Hcl
gastrin gastric juceactivate inhibit
under nervous reflex
Enterogasterone
Action of gastric juice
curd (cal. Paracaseinate)
peptones , proteoses
fatty acid , glycerol
rennin + milk protein(casein)
pepsin + milk curd
Lipase + fats
pepsin + protein proteoses, peptones, large polypeptides
split
split
split
split
To protect the stomach lining from the acid &enzyme
mucous cells secrete mucus
(that lines the stomach cavity)
An over abundance of acid
To protect the stomach lining from the acid &enzyme
mucous cells secrete mucus
(that lines the stomach cavity)
An over abundance of acid
To protect the stomach lining from the acid &enzyme
mucous cells secrete mucus
(that lines the stomach cavity)
An over abundance of acid
due to mucus failure
may lead to an ulcer
The semidigested acidic chyme
in form of small jets to duodenum
Emptying of stomach
- to the rate of processing of chyme into intestine.
Regurgitation of food
- from stomach to oesophagus
- & from duodenum to stomach by pyloric sphincter
is passed
due to rhythmic release of pylorus
is reciprocal
by cardiac sphincter
(which is controlled by hormone gastrin)
Intestinal hormone
Secretin liver and pancreatic cells
Cholecystokinin-pancreo-zymin
- cells of pancreatic acini
- contraction of gallbladder
- relaxation of sphincter Oddi
stimulate
stimulate
c.c.k.p.z
bile juice
• Sodium/potassium chloride
• -------------------- bicarbonates
• -------------------- glycocholates
• -------------------- taurocholates
water
• bilirubin• biliverdin
bile salts bile pigments
Cholesterol, lecithin, fatty acid
Functions of bile juice
(1) intensification of intestinal contraction (peristalsis)
(2) neutralization of acidity of HCL and inactivation of
pepsin
(3) emulsification of fats for easy action of pancreatic juice
(4) easy absorption of fatty acids, cholesterol and other
lipid by forming micelles
(5) absorption vitamin A,D.E & K
(6) excretion of the waste products, toxins etc.
Bile
- contain bile salts which emulsify lipids into smaller droplets without chemical change ( ∴ NOT digest fats)
- provide alkaline medium for enzymes to work
oil
oil droplets
• Fats are emulsified by bile salts.
• Micelles are tiny droplets consisting of fatty acids and monoglycerides complexed with bile salts.
• Micelles diffuse into epithelial cells.
– Resynthesized into triglycerides and pass into the lacteals of the lymphatic system.
pancreatic juice
• Amylase
• Lipase
• Endopeptidases
• Carboxypeptidase
• Nucleases
Water98%
Digestive enzyme
Actions of pancreatic juice
.
1. Amylase + carbohydrates maltosesplits
2. Lipase + fatssplits Fatty acids & glycerol
some into diglycerides
trypsin , chymotrypsin
Peptone, proteosesmall peptides
3. Endopeptidases + protein splits
4. Carboxypeptidase + polypeptides amino acids
5. Nucleases + nucleotidesD.N.A , R.N.A splits
splits
nucleosides
lipase glycerol + 3 fatty acids
lipase
glycerol
fatty acids
lipid
lipid
pancreatic proteases
proteinDipeptides/ polypeptides
protein
dipeptide
protease
disaccharides(eg. maltose)
monosaccharides(eg. glucose)
carbohydrase
disaccharide
intestinal carbohydrase
monosaccharide
intestinal proteases
dipeptides amino acids
proteaseamino acid
Succus entericus(Intestinal juice)
-is released from Crypts of Lieberkuhn
-Is an alkaline fluid – pH 7.5 – 8.0
- (about 2 liters secreted daily in man )
Crypts of Lieberkuhn
succus entericus (intestinal juice)
1. Erepsin
exopeptidases- (aminopeptidases ,carbooxypeptidases)
2 .Carbohydrases maltasesucraselactase
3. Enterokinase -
1.Peptidase + small peptide , dipeptide Amino acids
Maltase + maltose
Sucrase +sucrose
Lactase +lactose
Glucose
Glucose & fructose
Glucose & galactose
split
split
split
3.Enterokinase activates trypsinogenchymotrypsinogen
trypsinchymotrypsin
convert
Action of succus entericus
2.Carbohydrases
Absorption and assimilation
AbsorptionEnd products of digestion
- monosaccharide sugars ( glucose, fructose )
- amino acids
-fatty acids
- glycerol
- nitrogenous bases
- pentose sugars
simple soluble substances
can easily diffuse through cell membranes
About 9 liters of contents
(1 1/2 liter of digested nutrients &
rest water)
are absorbed daily
from gastrointestinal tract in man.
In stomach of man ,absorption
- water,
- glucose,
- alcohol
- some drugs
The intestine alone is well adapted
- whose wall is produced into villi
increasing the area
for absorption about 600 times in man.
lacteal
Epithelial
cell
arteriole
venule
blood
capaillaries
lymph
vessel
villi
Structure of Villi
Villi havedense network capillarieslacteala single lymph vessel
SugarSaltWaterVitaminsNitrogen basesamino acid
digestive juice
- Sugars
-salt,water
-vitamins
-nitrogen bases
-amino acids
-digestive juice etc
are absorbed into blood capillaries
absorbed by mucosal cells forming triglycerides in their smooth endoplasmic reticulum
Fatty acids
Monoglycerides
-the fat molecules are synthesized into
cholesterolWithin the reticulum,
phospholipids
These fat globules encased in a protein coat
chylomicrons
make their way out of absorptive cells
as chyle & enter lacteals.
Lacteals conduct chylomicrons
into larger lymphatics
--- carry them to thoracic lymphatic ducts
--- from they reach venous blood
jugular or subclavian vein
In the large intestine only water is absorbed.
via
Assimilation
The amino acids
monosaccharides
& then go to the heart for circulation in the different parts
of the body where tissues pick up their requirements.
The amino acids are building materials &
constantly needed for formation of
protoplasm.
The excess of amino acids are subjected to the process of
deamination in liver forming ammonia
----which is soon convered into urea
----excreted by the kidneys.
Assimilation
The amino acids
monosaccharides
& then go to the heart for circulation in the different parts
of the body where tissues pick up their requirements.
The amino acids are building materials &
constantly needed
for formation of protoplasm.
First coming into liver through portal circulation after process of absorption
The excess of amino acids
the process of deamination
in liver forming ammonia
----which is soon converted
into urea
----excreted by the kidneys.
The excess of monosaccharides stored
in the form of glycogen-------- in the liver cells.
Whenever glucose level falls down in the blood then
---glycogen is soon converted into--------glucose
( glycogenolysis)
----to maintain its normal level in the blood.
Liver is also concerned with fat metabolism &
---the fatty globules are found filled -------liver cells.
Energr is also released from the fats.
The fats maino acids
carbohydrates
The excess of monosaccharides stored
glycogen--- in the liver cells.
glucose level falls down in the blood then
-glycogen is converted into glucose ( glycogenolysis)
-to maintain its
normal level
in the blood.
Liver is also concerned with fat metabolism &
---the fatty globules are found filled -------in liver cells.
Energy is also released from the fats.
The fats amino acids
carbohydratesby the liver
Egestion ( Defaecation)
After absorption of the digested food,
--remaining contents ,bile pigments ,others
----whatever left ----------- is called faeces.
Vegetable foods form large amount of faeces
Milk forms relatively large amount of faeces
(due to large amount of unabsorbed salt in it.)
Animal proteins are absorbed 98%- 99%
Vegetable proteins to lesser extent.
large intestine
pass into
where water is absorbed from them
Egestion ( Defaecation)
After absorption of the digested food,
--remaining contents ,bile pigments ,others
----whatever left ----------- is called faeces.
Vegetable foods form large amount of faeces
Milk forms relatively large amount of faeces
(due to large amount of unabsorbed salt in it.)
Animal proteins are absorbed 98%- 99%
Vegetable proteins to lesser extent.
animal foodsthan
large intestine
pass into
where water is absorbed from them
The faeces are collected
in distal end of large intestine
the rectum
their removal through anus
defaecation or egestion
Table 1: Enzymes in Digestion
Area Secretion/Enzyme Substrate Product
Mouth Saliva - amylase Starch Maltose
StomachGastric Juice -
pepsin, lipaseProtein, Lipids
Peptides,
fattyacids/gycerol
Duodenum
Pancreatic juice -
amylase, trypsin,
chymotrypsin,
carboxypeptidase,
lipase
Starch, protein,
protein, peptides,
lipids
Maltose, peptides,
peptides, amino
acids,
fattyacids/glycerol
Ileum
None secreted,
remain on villi cells,
Maltase, sucrase,
lactase, peptidase
maltose, sucrose,
lactose, peptides
glucose,
glucose/fructose,
glucose/galactose,
amino acids.