LIVER AND BILE SECRETION

25
LIVER AND BILE SECRETION DR. AMEL EASSAWI DR. SHAIKH MUJEEB AHMED 1

description

LIVER AND BILE SECRETION. DR. AMEL EASSAWI Dr. Shaikh Mujeeb Ahmed. objectives. The student should be able to: Enlist the functions of Liver. Know the blood supply to Liver. Describe bile secretion. Discuss bile salts and their Entrohepatic Circulation. - PowerPoint PPT Presentation

Transcript of LIVER AND BILE SECRETION

Page 1: LIVER AND BILE SECRETION

1

LIVER AND BILE SECRETIONDR. AMEL EASSAWI

DR. SHAIKH MUJEEB AHMED

Page 2: LIVER AND BILE SECRETION

2

OBJECTIVESThe student should be able to: Enlist the functions of Liver. Know the blood supply to Liver. Describe bile secretion. Discuss bile salts and their Entrohepatic Circulation. Know the role of bile Salt in lipid emulsification, fat

digestion and absorption. Discuss control of bile secretion. Discuss Jaundice.

Page 3: LIVER AND BILE SECRETION

3

LIVER AND BILE SECRETION

• Bile is formed in the liver, emptied in the duodenum via bile duct.

• Biliary system includes: - Liver - Gallbladder- Ducts

Page 4: LIVER AND BILE SECRETION

4

LIVER FUNCTION• Liver cell is called HEPATOCYTE ‘HEPATO’ means liver,

‘CYTE’ means cell.• Metabolism of carbohydrate, protein, and fat, after their

absorption from the digestive tract.• Detoxification of drugs, hormones, body waste products.• Plasma protein synthesis.• Blood clotting factors synthesis.• Excreting cholesterol and bilirubin [bilirubin is breakdown

product of RBC].

Page 5: LIVER AND BILE SECRETION

5

LIVER FUNCTION• Store glycogen, fat, iron, copper.• Store vitamin A, D, Vit B12.• Activating vitamin D.• Secreting hormones e.g. insulin like growth factor 1

[stimulates growth], thrombopietin [stimulates platelet production].

• Removing bacteria and old red blood cell by macrophages. Hepatocyte does not do Phagocytosis. Phagocytosis is done by macrophages present in the liver called KUPFFER cells.

Page 6: LIVER AND BILE SECRETION

6

LIVER BLOOD FLOWTwo sources: 1. Hepatic Artery – supplies arterial blood. 2. Portal Vein – from GIT.

3. Hepatic Vein – carries blood away from the liver. NOTE – Portal Vein breaks in sinusoids which exchange

with hepatic cells before draining into hepatic vein which joins inferior venaceva.

Page 7: LIVER AND BILE SECRETION

7

LIVER BLOOD FLOW

Page 8: LIVER AND BILE SECRETION

8

LIVER BLOOD FLOW• Liver has functional units called lobules, they are hexagonal

with central vein.• Each lobule has three vessels: - Branch of Hepatic Artery - Branch of Portal Vein - Bile Duct• From Hepatic artery and Portal vein blood goes to expended

capillary space called SINUSOIDS which runs to central vein.• The Kupffer cells line the sinusoids destroy old RBC and

bacteria that pass through them.• Central veins of all liver lobules converge to form hepatic vein,

which carries blood away from the liver.

Page 9: LIVER AND BILE SECRETION

9

Page 10: LIVER AND BILE SECRETION

10

BILE SECRETION• The bile is formed and continuously secreted by liver

cells [Hepatocyte].• Bile goes to bile duct. • Bile ducts from different lobules form right and left

Hepatic duct, it combines with Cystic duct (from Gall bladder) to form Common bile duct.

• Common bile duct transports bile to the duodenum.

Page 11: LIVER AND BILE SECRETION

11

Page 12: LIVER AND BILE SECRETION

12

BILE SECRETION• Bile is continuously secreted by liver and sent to the

gallbladder between meals. • Opening of the bile duct in the duodenum is guarded by

the sphincter of Oddi. It allows the bile to pass in the duodenum during meals.

• When food is not taken sphincter of Oddi is closed , therefore bile secreted by the liver goes to the gallbladder.

• In the gallbladder bile is stored and concentrated between the meals.

Page 13: LIVER AND BILE SECRETION

13

BILE SECRETION• Bile secreted 500 ml per day. • Bile is alkaline fluid pH 8 (has NaHCO3 from bile ducts). • Bile contains: Bile salts, cholesterol, lecithin (phospholipid)

and bilirubin (all derived from Hepatocyte activity).• Bile does not contain any enzyme. • Bile is important for emulsification and helping in digestion

and absorption of fats.

Page 14: LIVER AND BILE SECRETION

14

BILE SECRETIONBILE SALTS AND THEIR ENTROHEPATIC CIRCULATION • Bile salts are derivates of cholesterol. They are actively

secreted in bile.• Most of the bile salts [95%] are reabsorbed from terminal

ileum [small intestine] into the blood by active transport.• Bile salt are returned to liver by hepatic portal system.• Liver re-secretes bile salts into bile. This recycling of bile

salt between small intestine and liver is called ‘ENTROHEPATIC CIRCULATION’ [‘Entro’ means intestine, ‘hepatic’ means liver].

Page 15: LIVER AND BILE SECRETION

15

BILE SECRETIONBILE SALTS AND THEIR ENTROHEPATIC CIRCULATION • On average bile salts cycle between liver and small

intestine twice during one meal.• Only 5% of bile salt are lost in the feces per day.• Lost bile salts are replaced by new bile salts synthesized

by liver.• Bile salts cause lipid emulsification [breaking fat into small

molecules], therefore, increasing the surface area, so that pancreatic lipase can act.

NOTE – If no bile salt, it will take long time for lipase to digest fat.

Page 16: LIVER AND BILE SECRETION

16

Page 17: LIVER AND BILE SECRETION

17

Page 18: LIVER AND BILE SECRETION

18

BILE SALTS AND FAT DIGESTION AND ABSORPTION

Micelle Formation • Micelle is small lipid particle 3-10 nm [emulsified fat

droplet is 1000 nm].• bile salt, cholesterol and lecithin help in Micelle

formation. • Micelle carry Monoglycerides and free fatty acids. Gall Stones - Cholesterol Gall Stone – 75% - Bilirubin Gall Stone – 25%

Page 19: LIVER AND BILE SECRETION

19

BILE SALTS AND FAT DIGESTION AND ABSORPTION

Bilirubin• It is bile pigment, derived from the breakdown of RBC.• It does not play any role in digestion.• Bilirubin is taken from the blood by Hepatocyte and actively

excreted into the bile.• Bilirubin is yellow pigment, therefore, gives yellow color to bile.• In intestine, bilirubin is acted by enzyme and converted to

biliverdin, which gives brown color to feces.• If bile duct is obstructed by stone, color of feces turns to grey

white.• Small amount of bilirubin is reabsorbed in the intestine in the

blood and excreted in the urine and gives yellow color to urine.

Page 20: LIVER AND BILE SECRETION

20

Page 21: LIVER AND BILE SECRETION

21

CONTROL OF BILE SECRETION

Three Mechanism: 1. Chemical 2. Hormonal 3. Neural 1. Chemical Mechanism:• By bile salt, they are most potent stimulus for increasing

bile secretion.• Any substance which increases bile secretion is called

‘CHOLERETIC’.

Page 22: LIVER AND BILE SECRETION

22

CONTROL OF BILE SECRETION

2. Hormonal Mechanism:• Secretin hormone stimulates watery alkaline bile

secretion from the bile ducts.• Food in duodenum [fat] causes release of CCK. This

hormone causes contraction of gallbladder and relaxation of sphincter of Oddi.

3. Neural Mechanism:• Vagal stimulation plays minor role in bile secretion during

cephalic phase of digestion.

Page 23: LIVER AND BILE SECRETION

23

GALL BLADDER• It stores and concentrates bile between meals and

empties bile into the duodenum during meals.• As bile secretion occurs continuously in liver,

therefore, bile secreted between the meals is send to the gall bladder, where it is stored and concentrated.

• In gall bladder, bile is concentrated 5-10 times due to absorption of bile salt and water.

• Gall bladder can hold 50 ml of bile.

Page 24: LIVER AND BILE SECRETION

24

CLINICAL APPLICATIONJaundice:• When bilirubin increases more than 2mg/dL jaundice

occurs.Causes of Jaundice• Pre-hepatic [problem before liver] or Hemolytic Jaundice

– due to increased breakdown of RBC.• Hepatic [problem in liver] e.g. Viral Hepatitis• Post-hepatic [problem after the liver] or Obstructive

Jaundice e.g. stone in the bile duct.

Page 25: LIVER AND BILE SECRETION

25

REFERENCES

• Human Physiology by Lauralee Sherwood, seventh edition.

• Text book Physiology by Guyton &Hall,11th edition.• Text book of Physiology by Linda S. Contanzo, third

edition.