H4: Functions of the Liver - PowerPoint Presentation

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H4: Functions of the Liver

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The largest gland in the bodyThe second largest organ (after the skin)About 1.5 kg in massLocated just below the diaphragm and over the upper portion of the stomach

The Liver

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Circulation of Blood and from the Liver

The liver receives blood from 2 major blood vessels and blood leaves the liver by 1 blood vessel

The

HEPATIC ARTERY

is a branch of the aorta

It carries

oxygenated blood

(from the heart) to the liver tissues.

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The

HEPATIC PORTAL VEIN

brings deoxygenated blood from the digestive tract to the liver

This blood is rich in absorbed nutrients from the villi of the small intestine.

The hepatic artery and hepatic portal vein carry blood into the “capillaries” of the liver, called the

sinusoids

.

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All sinusoids are then drained by a central vein which is a branch of the HEPATIC VEIN, which is the sole blood vessel that takes blood away from the liver and delivers it to the vena cavas so it may return to the heart.

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The blood delivered to the liver via the hepatic portal vein is unique (in comparison to the type of blood that is usually delivered to an organ) because:It is low pressure, deoxygenated blood because it has already been through a capillary bed.It has a high quantity of nutrients (particularly glucose) – though this is based on the types of food and the timing of digestion and absorption

HEPATIC PORTAL VEIN

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A major function of the liver is to remove some things from the blood and to add others to it.This is done by hepatocytes (liver cells)O2-rich blood from the hepatic artery, and (sometimes) nutrient-rich blood from the hepatic portal vein, both flow into the sinusoids of the liver.

Sinusoids: The Capillaries of the Liver

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Sinusoids are where the exchange of materials occur between blood and hepatocytes.

Sinusoids

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Kupffer Cells: cells that line the sinusoids.They ingest foreign particles and are involved in the breakdown of old erythrocytes (rbc)The hepatocytes produce bile.Bile will move in the opposite direction of the blood, towards the bile ducts.

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Sinusoids differ from a typical capillary bed in the following ways:Sinusoids have larger lumensSinusoids have Kupffer cells that breakdown rbc for recyclingSinusoids are lined by endothelial cells with gaps between them.These gaps allow large molecules (like proteins) to be exchanged between hepatocytes and the bloodstreamHepatocytes are in direct contact with blood components making all exchanges with the bloodstream more efficient

Sinusoids

vs

Capillary Beds

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Each type of solute dissolved in blood plasma has a normal homeostatic range.Concentrations below or above this range creates physiological problems in the body.The liver helps regulate the levels of nutrients in the blood and maintain homeostatic ranges.

Regulating Nutrients in the Blood

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Ex: after a meal, blood glucose will be converted into glycogen by the hepatocytes.When blood glucose levels are low, the hormone glucagon tells the hepatocyte to release the glycogen so it may be converted back into glucose.

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The liver is the main organ for detoxification.Pesticides, medicines, food additives, alcohol, and other toxins are removed from the blood stream and broken down in the hepatocytes of the liver.The liver does not extract all excess glucose, toxins etc in a single trip through the sinusoids,The chemicals within the blood will be acted on by hepatocytes multiple times as blood continuously makes circuits through the liver.

Detoxification

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After drinking alcohol, each time blood passes through the liver, hepatocytes attempt to remove the alcohol from the bloodstream.The breakdown of alcohol produces free radicals and other reactive molecules that damage proteins, lipids and DNA.

Alcohol & the Liver

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The liver breaks down alcohol in the following way:Alcohol  acetaldehyde  acetic acid  carbon dioxide

Alcohol and the Liver

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Long term alcohol abuse seems to interfere with normal liver metabolism of proteins, fats and carbohydratesLong term alcohol abuse can result in: cirrhosis, fat accumulation, inflammation

Alcohol & the Liver

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The scar tissue left when areas of hepatocytes, blood vessels and ducts have been destroyed by exposure to alcohol.Areas of the liver, showing cirrhosis no longer function

Cirrhosis

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“Fatty liver” Damaged areas of the liver will build fat in place of normal liver tissue thus decreasing function.

Fat

Acummulation

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Inflammation

This is swelling of damaged liver tissue due to alcohol exposure

Sometimes referred to as alcoholic hepatitis

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Hepatitis

Inflammation of the liver

Often leads to jaundice, lack of appetite, and general discomfort

Most cases are cause by a hepatitis virus; can also be caused by the ingestion of toxins (such as alcohol)

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Acute infectious disease of the liver, caused by a hepatitis A virus.Transmission: oral-fecal route from contaminated water or infected individual.Greater risk of contracting virus in a developing country (because of inadequate water treatment)Symptoms: fever, nausea, fatigue, loss of appetite, jaundice

Hepatitis A

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Caused by hepatitis B virusSexually transmitted diseased (transmitted in body fluids: semen, blood, vaginal secretions)Symptoms: liver inflammation, jaundice, vomitting, death in rare cases, chronic cases may result in cirrohosis

Hepatitis B

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Caused by the hepatitis C virusTransmission: blood (transfusions, unsterilized lab equipment)Symptoms: asymptomatic (no symptoms) however, if it becomes chronic, cirrhosis, liver cancer, and liver failure may result.

Hepatitis C

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As mentioned, carbohydrates are stored in the liver in the form of glycogen.The liver also stores iron, vitamin A, and vitamin D

Liver Storage

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Hemoglobin is an important component of rbc and it contains ironIron is present in food, however it is hard for the body to absorb.After red blood cells are broken down, their iron is stored in the liver until it can be used again.

Iron

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The main vitamins stored in the liver are fat soluble vitamins A and DVITAMIN A: found in dairy products; associated with good visionVITAMIN D: often found as an additive in dairy productsmade by the skin in the presence of UV lightImportant in the uptake of calcium

Vitamins

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Plasma Proteins: (blood proteins)ALBUMIN – regulates osmotic pressure of fluids in the bodyFIBRINOGEN – involved in forming blood clots.GLOBULINS – antibodies (defend the body from foreign invaders)

Synthesis of Plasma Proteins

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CholesterolSome cholesterol is ingested and some is made by the liverUsed to produce bileUsed to make cell membranesUsed to make lipid based hormones

Synthesis of Cholesterol

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Erythocytes have a life span of about 120 daysThey do not have a nucleus so, they are destroyed (do not undergo mitosis – remember, new rbc come from bone marrow)When rbc get to 120 days, their cell membranes become weak and eventually rupturesThis usually occurs in the spleen

Recycling of Erythrocytes

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Fist sized organ that regulates and stores red blood cells.

Spleen

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The spleen removes old

rbc

from

circulation

When a

rbc

ruptures, it released millions of

hemoglobin

molecules

that now will circulate in the blood stream and

eventually

pass through the liver

.

As these molecules make their way through the liver, they are absorbed by the

Kupffer

cells via phagocytosis

Hemoglobin is broken down into

heme

group (the iron and non amino acid component) and globin (the amino acid component)

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Hemoglobin

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Contains the iron componentThe iron is stored in the liver before being transported back to the bone marrow to be reused in new erythrocytesThe remainder of the heme group become biliverdin (a green bile pigment), which is then converted into bilirubin (a yellow pigment) that is secreted into the small intestine via bile duct with bile.Bilirubin turns to stercobilin in the colon an is what gives feces its characteristic colour reddish brown colour

HEME

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Gives the reddish brown colour to fecesGives the yellow colour to urineWhen the liver isn’t functioning properly, high amounts will circulate in the blood and give your skin the yellowish appearance known as jaundice.

Bilirubin

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Broken down into amino acidsThese amino acids can then be reused to make other proteinsThey can also be broken down for energy

GLOBIN