This document summarizes the physiology of the digestive system. It describes how digestion breaks down large food molecules into smaller components through mechanical and chemical processes in the mouth, stomach, and small intestine. The small intestine, through villi and microvilli, greatly increases the surface area for absorption of nutrients into the bloodstream or lymphatic system. Nutrients are then transported to the liver via the hepatic portal vein or lymphatic system before entering general circulation to be used by the body's cells. Waste products not absorbed pass through the large intestine and are excreted.

1. PHYSIOLOGY
OF DIGESTIVE
SYSTEM
Presented By
Himanshu Upadhyay

2. DIGESTION
• Digestion is the breakdown of large complex organic
molecules into smaller components that can be used
by the body.
• Molecules need to be small enough to diffuse across
plasma membrane
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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3. Digestion
• Mechanical/Physical digestion:- Breakdown of food
in mouth i.e (chewing).smaller pieces of food
increases surface area for digestion.it takes place in
stomach (churning of food by the muscular stomach
walls)
• Chemical digestion :- uses enzymes to chemically
break down complex food substances into simplest
form .
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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4. Digestion
• Starch digestion :- mouth & small intestine
• Protein digestion:- stomach & small intestine
• Fat digestion :- only small intestine
• Why must be food digested?
large molecules of food are unable to pass through cell
membrane,thus must be broken down into small
molecules so that they can diffuse through cell
membrane into blood stream
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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5. Steps of Digestion
• Ingestion:- consumption/taking food in mouth (eating)
• Digestion:- Both chemical & mechanical process secrets
fluids(enzymes) & breakdown food molecule into smaller
components.
• Absorption :- in this process transportation or delivery of
digested food is done to the body tissue.
• Assimilation :- conversion of absorbed food into the substance
of the body.
• Egestion :- elimination of food waste material from the body.
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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6. Mouth
• Ingestion of food
• Mastication:- before swallowing food the churning
process is called mastication
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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7. Esophagus
• Aprox 10’’ long
• Funtions:-
secrets mucus
movement of food from throat to stomach
(muscle movement is called peristalsis)
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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8. Stomach
• J shaped bag
• Stores food we eat,breaksdown into tiny pieces
• Mixes food with digestive juice (enzyme) & break
down into proteins & lipids.
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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9. Funtions of stomach
• Stores food
• Digest protein
• B12 is absorbed in S.I
• Controlling the proper amount of food leaving the
stomach from S.I
• Producing hormone gasterin helping in pepsin & hcl
production (in stomach) & bile production (in liver)
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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10. Small Intestine
• Roughly 7 meters long
• Major site for digestion & absorption of nutrients
• Lining of intestine has villi (increases surface area)
• Villi is also covered with microvilli which helps in
further increasing the surface area of absorbption
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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11. Large intestine
• About 5ft long
• Glucose, salt & water can be absorbed.
• Accepts what small intestines dont absorb RECTUM
(short term storage which holds feces before it is
expelled).
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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12. Liver
• It is a large accessory organ of D.S that constanly
produces a fluid known as “bile”
• Bile is stored in gall bladder unless and until not
required in the small intestine
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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13. Funtions of liver
• Secrets bile,helps in digestion of food
• Stores glucose in form of glycogen.
• Stores fats.
• Iron storage:- RBC’s are destroyed in spleen & their Hb is sent
to liver to be brokendown further.the iron then released is
stored in liver.bile pigments are also formed from the
breakdown of Hb
• Plasma protein are synthezied here. Ex-
albumin,globulin,fibrinogen.
• Drugs & poisns are detoxicated here.
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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14. ABSORPTION
• This means passage of digested substances through
the mucous membrane of GI tract into the blood or
lymph
In mouth no absorption of food takes place,but some
drugs can be absorbed if allowed to dissolve under
the tounge.
In stomach,the only substances normally absorbed
are h2o,glucose,alcohol & some drugs.
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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15. Carbohydrate
• Carbohydrates having been changed by digestion
into glucose are absorbed
• Glucose, fructose & galactose are absorbed by the
microvilli by active transport,then leave the cell and
enter the capillary.
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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16. Proteins
• Proteins are broken down into aminoacids,and are
absorbed along with glucose.
• Amino acids & glucose then go via the portal vein to
the liver.
• (amino acids crosess the epithelial call membranes by
active transport then enter the capillary)
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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17. Other components
• Water, vitamins,and minerals are absorbed by
diffusion without digestion.
• Fats have been splitted into fatty acid & glycerin they
enter the villi and pass into the lymph capillaries
through lymphatic vessels to the blood stream
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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18. Structure of villus
• Each villus contains a capillary network along with a
lacteal
• End product of carbohydrate & protein digestion
enters the capillary network
• End product of fat digestion are absorbed into the
lacteal. the lacteal is a vessel of the lymphatic system
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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19. What happens to amino acids and
glucose after absorption
 Molecules pass into the epithelial cells
 Through walls of capillaries in the villus & in blood stream
 Capillaries join up with vein
 Vein unites to large vein Hepatic portal vein
 HPV carried blood to liver
 Liver stores product of digestion
 Products released from liver into general blood circulation
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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20. What happens to fatty acid &
glycerol after absorption
Molecules pass into epithelial cells
Recombine into fats in epithelial cells
Fats enter the lacteals
Lymp(fluid in lacteals) + fat = chyle
Lymphatic vessels discharge chyle into blood stream
Himanshu Upadhyay (MSc. Clinical Biochemist.)
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21. Himanshu Upadhyay (MSc. Clinical Biochemist.)
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