DIGESTIVE SYSTEM : ACCESSORY STRUCTURES

LIVER

GALL

BLADDER PANCREAS

• Largest internal organ.

• Comprised of hexagonally shaped functional units called hepatic lobules separated to each other by a septum.

THE LIVER OVERVIEW

• Liver cells comprising these lobules are called hepatocytes.

• Although the digestive function of the liver is only to produce

bile, it is also involved in many metabolic and regulatory roles.

THE LIVER STRUCTURE

HEPATIC LOBULE

• Hepatocyte form hepatic plates that

radiate outward from a central vein

running in the longitudinal axis of the

lobule.

• Sinusoids form the space in between

hepatic plates

• Bile canaliculi collects the bile

produced by hepatocytes and drains into

the bile duct.

Portal triad:

• Branch of Hepatic Artery

• Supply oxygen-rich arterial blood

to the liver

• Branch of Hepatic Portal Vein

• Carry blood laden with nutrients

from the digestive viscera (3/4

deoxygenated)

• Bile Duct

THE LIVER STRUCTURE

BLOOD ENTERS(1/4 Hepatic Artery, 3/4 Portal Vein)

BLOOD EXITS

BILE

Actions

DigestiveSynthesis of bile saltsConjugation and excretion of bile pigment(bilirubin).

Metabolicand Synthetic

Glucose Metabolism (regulation of blood sugar)- Conversion of blood glucose to glycogen and fat.- Production of glucose from glycogen and other molecules by gluconeogenesis- Secretion of glucose into blood

Fat Metabolism- Synthesis of triglycerides and cholesterol, excretion of cholesterol in bile, and

production of ketone bodies from fatty acids.

Protein Metabolism- Production of albumin, plasma transport proteins, clotting factors (fibrinogen, prothrombin, and others)

Detoxification

Phagocytosis by Kupffer cellsChemical alteration of biologically active molecules (hormones and drugs)Production of urea, uric acid and other compounds that are less toxic than the parent compound.

THE LIVER FUNCTIONS

THE LIVERDIGESTIVEFUNCTION

- Production of bile- Yellow-green alkaline solution containing bile salts, bile pigment,

cholesterol, triglycerides, phospholipids, and a variety of electrolytes.

- Bile salts (cholic and chenodeoxycholic acid) emulsify fats.

- Break them down into smaller pieces and distribute them throughout

the intestine to facilitate fat digestion and absorption.

- Only bile salts are recycled (through the enterohepatic circulation.)

(1) reabsorbed into the blood by the ileum,(2) returned to the liver via the hepatic portal blood,

and then(3) resecreted in newly formed bile.

THE LIVERDIGESTIVEFUNCTION

- Production of bile

- Bilirubin is the chief pigment in bile.

- Waste product of the heme of the hemoglobin formed during the

breakdown of worn-out erythrocytes.(by Kupffer cells)

(hemoglobin = heme + globin + iron)

*Over production,

impaired transportation,

blocked excretion, and

over re-absorption of

bilirubin in the intestine

may result in Jaundice.

THE LIVER

• Contents of blood coming from the portal veins are

monitored by the hepatocytes in the liver and

potentially toxic substances are removed from it.

– Organic substances such as alcohol and drugs are

metabolized into their inactive form.

– Hormones are metabolized and removed to keep within

homeostatic level.

– Converts ammonia to urea as part of urea cycle.

– Excreted through bile.

DETOXIFICATION

THE LIVERGLUCOSE, LIPID, PROTEIN METABOLISM

• Carbohydrate metabolism

– Glucose converted to glycogen/fat (glycogenesis/lipogenesis)

– Glucose produced from glycogen(gluconeogenesis)

• Lipid metabolism

– Synthesis and release of lipid

– Decomposition of fatty acid

– Synthesis and transport of cholesterol

• Protein

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

GALL BLADDER

FUNCTION

• Thin-walled green muscular

sac about 10 cm long, about

the size of a kiwi fruit.

• Stores bile that is not

immediately needed for

digestion.

• When gall bladder fills with bile, it expands.

– Contraction of muscularis layer ejects bile into the common bile duct.

• When small intestine is empty, sphincter of Oddi closes.

*Gallstones are cholesterol that havecrystallized within the gall bladder.

PANCREAS STRUCTURE

• Soft, tadpole-shaped gland

that extends along the

abdomen and encircled by the

C-shaped duodenum.

• Has endocrine and exocrine

component:

– Exocrine

• Acini cells are raspberry

like clusters surrounding

tiny ducts responsible for

secreting digestive enzymes

– Endocrine

• Pacreatic islets responsible

for glucose metabolism.

PANCREAS PANCREATIC JUICE

- Contains H20, HC03- and digestive

enzymes.

- HC03- neutralizes the acidic chyme

entering the duodenum and provides an

optimal environment for pancreatic

enzymes.

- Most pancreatic enzymes are produced

as zymogens, which are inactivated

form of the digestive enzymes.

PANCREAS PANCREATIC JUICE

• Trypsin, chymotrypsin, elastase, carboxypeptidase and phopholipaseare released in their zymogenic form when released in the duodenum.

PANCREAS PANCREATIC JUICE

• Trypsinogen when activated by the enterokinase in the lining of the duodenum is converted to Trypsin.

• Trypsin triggers the activation of other pancreatic enzymes (chymotrypsin, elastase, carboxypeptidase and phopholipase)