LIVER AND BILIARY SYSTEM

D R A N I L C H A U D H A R Y

A S S O C I A T E P R O F E S S O R

P H Y S I O L O G Y

The small intestine receives not only chyme from the stomach but also secretions from the liver and pancreas.

LIVER

LocationR. HypochondriumEpigastric region

4 LobesLeft QuadrateCaudateRight

Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

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LIVER

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The Liver

has tremendous variety of functions, including the secretion of bile for digestive purposes. -Largest Gland of

Body

-Wt.1200-1600gms

STRUCTURE OF LIVER

Liver largest internal organ.Hepatocytes form hepatic plates that are 1–2 cells thick.Arranged into functional units called lobules.each with diameter of 0.5 to 2 mm.

Plates separated by sinusoids.More permeable than other capillaries.

Contains phagocytic Kupffer cells.Secretes bile into bile canaliculi, which are

drained by bile ducts.

MICROSCOPIC ANATOMY

Hepatic lobules – tiny cylinders make up interior of liver; functional units of liver

Lobule – central vein; surrounded by radiating sheets of cuboidal cells – hepatocytes

Between plates of hepatocytes – blood filled channels – hepatic sinusoids

Blood filtering between hepatocytes comes from intestines

Sinusoids – Kupffer cells – hepatic macrophages; removes bacteria & debris from blood

Hepatocytes secret bile into the bile canaliculi and bile ductules.

bile ductule

STRUCTURE OF LIVER (CONTINUED)

Insert fig. 18.20

LIVER HISTOLOGY

Figure 24–20

Liver lobule is the basic functional units of the liverEach lobe is divided:

by connective tissueinto about 100,000 liver lobulesabout 1 mm diameter each

Dual blood supply

Hepatic portal vein Direct input from small

intestineHepatic artery/vein

Direct links to heart

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LIVER

HEPATIC BLOOD SUPPLY

1/3 of blood supply:arterial blood from hepatic artery proper2/3 venous blood from hepatic portal

vein, originating at:esophagusstomachsmall intestinemost of large intestine Hepatocytes are liver cellsAdjust circulating levels of nutrients:through selective absorption and secretion Blood Leaving the Liver returns to

systemic circuitVia hepatic veins:which open into inferior vena cava

MICROSCOPIC ANATOMY OF THE LIVER

THE PATHS OF BLOOD AND BILE IN HEPATIC LOBULE

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HEPATOCYTES

In a liver lobule form a series of irregular plates arranged like wheel spokes

Blood enters liver sinusoids: from small branches of hepatic portal vein from hepatic artery proper

As blood flows through sinusoids:hepatocytes absorb solutes from plasmaand secrete materials such as plasma proteins

Hepatic triad – 3 or more lobules meet ; contains 2 blood vessels and 1 bile duct

After filtering thru sinusoids blood collects in central vein

Flows into L & R hepatic veins and enters inferior vena cava

Bile canaliculi - narrow channels between sheets of hepatocytes ; liver secretes bile here

Bile passes into bile ductules of triads & into R & L hepatic ducts

Hepatic ducts merge Common hepatic duct

Common hepatic duct + Cystic duct from gallbladder join Bile duct

Bile duct joins Pancreatic duct at Hepatopancreatic ampulla and enters duodenum

Hepatopancreatic sphincter regulates passage of bile and pancreatic juices into duodenum

Bile ductules hepatic ducts common hepatic duct

cystic duct

common hepatic duct

gallbladder

common bile duct

hepatopancreatic sphincter

pancreas

duodenum

FUNCTIONS OF THE LIVER

Bile production: 600-1000 mL/day. Bile salts (bilirubin), cholesterol, fats, fat-soluble hormones, lecithin

Neutralizes and dilutes stomach acid Bile salts emulsify fats. Most are reabsorbed in the ileum. Secretin (from the duodenum) stimulates bile secretions, increasing water

and bicarbonate ion content of the bileStorage Glycogen, fat, vitamins, copper and iron. Hepatic portal blood comes to liver

from small intestine.Nutrient interconversion Amino acids to energy producing compounds Hydroxylation of vitamin D. Vitamin D then travels to kidney where it is

hydroxylated again into its active formDetoxification Hepatocytes remove ammonia and convert to ureaPhagocytosis Kupffer cells phagocytize worn-out & dying red & white blood cells, some

bacteriaSynthesis Albumins, fibrinogen, globulins, heparin, clotting factors

Detoxifies/removes Drugs Alcohol

Stores Gycolgen Vitamins (A, D, E, K) Fe and other minerals Cholesterol

Activates vitamin D Fetal RBC production Phagocytosis Metabolizes absorbed food

molecules Carbohydrates Proteins Lipids

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LIVER

DETOXIFICATION OF THE BLOOD

Liver can remove hormones, drugs, and other biologically active molecules from the blood by:

Excretion into the bile.Phagocytosis by Kupffer cells.Chemical alteration of the molecules.

Ammonia is produced by deamination of amino acids in the liver.

Liver converts it into urea. Excreted in urine.

DETOXIFICATION OF THE BLOOD (CONTINUED)

Inactivation of steroid hormones and drugs. Conjugation of steroid hormones and xenobiotics make them anionic.

Can be transported into bile by multispecific organic anion transport carriers.

Steroid and xenobiotic receptors stimulate production of cytochrome P450 enzymes.

SECRETION OF GLUCOSE, TRIGLYCERIDES AND KETONES

Liver helps regulate blood glucose concentration by: Glycogenesis and lipogenesis. Glycogenolysis and gluconeogenesis.

Contains enzymes required to convert free fatty acids into ketone bodies.

PRODUCTION OF PLASMA PROTEINS

Albumin and most of the plasma globulins (except gama globulins) are produced by the liver.

Albumin:Constitutes 70% of the total plasma protein.

Contributes most to the colloidal osmotic pressure in the blood.

Globulins:Transport cholesterol and hormones.

Produce blood clotting factors I, II, III, V, VII, IX, XI.

LIVER FUNCTIONS

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• produces glycogen from glucose• breaks down glycogen into glucose• converts noncarbohydrates to glucose• oxidizes fatty acids• synthesizes lipoproteins, phospholipids, and cholesterol• converts carbohydrates and proteins into fats• deaminates amino acids • forms urea• synthesizes plasma proteins• converts some amino acids to other amino acids• stores glycogen, vitamins A,D, B12, iron, and blood• phagocytosis of worn out RBCs and foreign substances• removes toxins from blood• produces and secretes

CLINICAL APPLICATION

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Hepatitis

• inflammation of the liver• most commonly caused by viral infection• can be caused by reactions to drug, alcoholism or autoimmunity

Signs and Symptoms• headache • low fever• fatigue • vomiting• rash• foamy urine• pale feces• jaundice • pain

Hepatitis A – not washing hands or eating raw shellfishHepatitis B – chronic; serumHepatitis C – serumHepatitis D – very severe; only produces symptoms if infected with B; serumHepatitis E, F, G – more rare