the largest gland in the body the second largest organ (after the skin) about 1.5 kg in mass ...
TRANSCRIPT
H4: Functions of the Liver
The largest gland in the body
The second largest organ (after the skin)
About 1.5 kg in mass
Located just below the diaphragm and over the upper portion of the stomach
The Liver
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.
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.
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.
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:
1) It is low pressure, deoxygenated blood because it has already been through a capillary bed.
2) 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
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
Sinusoids are where the exchange of materials occur between blood and hepatocytes.
Sinusoids
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.
Sinusoids differ from a typical capillary bed in the following ways:
1. Sinusoids have larger lumens2. Sinusoids have Kupffer cells that
breakdown rbc for recycling3. Sinusoids are lined by endothelial cells
with gaps between them. These gaps allow large molecules (like proteins) to
be exchanged between hepatocytes and the bloodstream
Hepatocytes are in direct contact with blood components making all exchanges with the bloodstream more efficient
Sinusoids vs Capillary Beds
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
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.
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
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
The liver breaks down alcohol in the following way:
Alcohol acetaldehyde acetic acid carbon dioxide
Alcohol and the Liver
Long term alcohol abuse seems to interfere with normal liver metabolism of proteins, fats and carbohydrates
Long term alcohol abuse can result in: cirrhosis, fat accumulation, inflammation
Alcohol & the Liver
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
“Fatty liver”
Damaged areas of the liver will build fat in place of normal liver tissue thus decreasing function.
Fat Acummulation
Inflammation This is swelling of damaged liver tissue due
to alcohol exposure
Sometimes referred to as alcoholic hepatitis
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)
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
Caused by hepatitis B virus
Sexually 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
Caused by the hepatitis C virus
Transmission: blood (transfusions, unsterilized lab equipment)
Symptoms: asymptomatic (no symptoms) however, if it becomes chronic, cirrhosis, liver cancer, and liver failure may result.
Hepatitis C
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
Hemoglobin is an important component of rbc and it contains iron
Iron 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
The main vitamins stored in the liver are fat soluble vitamins A and D
VITAMIN A: ◦ found in dairy products; associated with good
vision
VITAMIN D: ◦ often found as an additive in dairy products◦ made by the skin in the presence of UV light◦ Important in the uptake of calcium
Vitamins
Plasma Proteins: (blood proteins)
◦ ALBUMIN – regulates osmotic pressure of fluids in the body
◦ FIBRINOGEN – involved in forming blood clots.
◦ GLOBULINS – antibodies (defend the body from foreign invaders)
Synthesis of Plasma Proteins
Cholesterol◦ Some cholesterol is ingested and some is made
by the liver
◦ Used to produce bile
◦ Used to make cell membranes
◦ Used to make lipid based hormones
Synthesis of Cholesterol
Erythocytes have a life span of about 120 days
They 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 ruptures
This usually occurs in the spleen
Recycling of Erythrocytes
Fist sized organ that regulates and stores red blood cells.
Spleen
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)
Hemoglobin
Contains the iron component
The iron is stored in the liver before being transported back to the bone marrow to be reused in new erythrocytes
The 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
Gives the reddish brown colour to feces
Gives the yellow colour to urine
When the liver isn’t functioning properly, high amounts will circulate in the blood and give your skin the yellowish appearance known as jaundice.
Bilirubin
Broken down into amino acids
These amino acids can then be reused to make other proteins
They can also be broken down for energy
GLOBIN