chapter 15 p3

Question 1

The structure of the liver:p1

Answer 1

• Liver cells or hepatocytes have large nuclei, prominent Golgi apparatus, and lots of mitochondria, indicating that they are metabolically active cells
• They divide and replicate - even if around 65% of the liver is lost, it will regenerate in a matter of months.
• The blood from the hepatic artery and the hepatic portal vein is mixed in spaces called sinusoids which are surrounded by hepatocytes.

Question 2

The structure of the liver:p2

Answer 2

• This mixing increases the oxygen content of the blood from the hepatic portal vein, supplying the hepatocytes with enough oxygen for their needs.
• The sinusoids contain Kupffer cells, which act as the resident macrophages of the liver, ingesting foreign particles and helping to protect against disease.
• The hepatocytes secrete bile from the breakdown of the blood into spaces called canaliculi, and from these the bile drains into the bile ductules which take it to the gall bladder.

Question 3

structure of the liver diagram

Answer 3

Question 4

The functions of the liver:

Answer 4

The liver has many functions - around 500 different metabolic pathways are linked to the liver.
Several of these play a major role in homeostasis:

Carbohydrate metabolism:
Deamination of excess amino acids:
Detoxification

Question 5

Carbohydrate metabolism:

Answer 5

• Hepatocytes are closely involved in the homeostatic control of glucose levels in the blood by their interaction with insulin and glucagon.
• When blood glucose levels rise, insulin levels rise and stimulate hepatocytes to convert glucose to the storage carbohydrate glycogen.
• About 100g of glycogen is stored in the liver.
• Similarly, when blood sugar levels start to fall, the hepatocytes convert the glycogen back to glucose under the influence of the hormone glucagon.

Question 6

Deamination of excess amino acids:
p1

Answer 6

• The liver plays a vital role in protein metabolism where hepatocytes synthesise most of the plasma proteins.
• Hepatocytes also carry out transamination - the conversion of one amino acid into another.
• This is important because the diet does not always contain the required balance of amino acids but transamination can overcome the problems this might cause.
• The most important role of the liver in protein metabolism is in deamination - the removal of an amine group from a molecule.
• The body cannot store either proteins or amino acids.
• Any excess ingested protein would be excreted and therefore wasted if it were not for the action of the hepatocytes.

Question 7

Deamination of excess amino acids:
p2

Answer 7

• They deaminate the amino acids, removing the amino group, and converting it first into ammonia which is very toxic and then to urea.
• Urea is toxic in high concentrations but not in the concentrations normally found in the blood.
• Urea is excreted by the kidneys
• The remainder of the amino acid can then be fed into cellular respiration or converted into lipids for storage.
• The ammonia produced in the deamination of proteins is converted into urea in a set of enzyme-controlled reactions known as the ornithine cycle.
• Removing the amino group from amino acids and converting the highly toxic ammonia to the less toxic and more manageable compound urea involves some complex biochemistry.

Question 8

diagram of deamination

Answer 8

Question 9

ornithine cycle diagram

Answer 9

During this cycle, one molecule of urea is produced from one molecule of carbon dioxide and two amino groups (from two amino acids)
The urea diffuses through the phospholipid bilayer of the membranes of the hepatocytes and is then transported to the kidneys dissolved in the blood plasma

Question 10

Detoxification
p1

Answer 10

• The level of toxins in the body always tends to increase.
• Apart from urea, many other metabolic pathways produce potentially poisonous substances.
• We also take in a wide variety of toxins by choice such as alcohol and other drugs.
• The liver is the site where most of these substances are detoxified and made harmless.
• One example is the breakdown of hydrogen peroxide, a by-product of various metabolic pathways in the body.
• Hepatocytes contain the enzyme catalase, one of the most active known enzymes, that splits the hydrogen peroxide into oxygen and water.

Question 11

Detoxification
p2

Answer 11

Another example is the way in which liver detoxifies the ethanol - the active drug in alcoholic drinks.
Hepatocytes contain the enzyme alcohol dehydrogenase that breaks down the ethanol to ethanal.
Ethanal is then converted to ethanoate which may be used to build up fatty acids or used in cellular respiration.

Question 12

liver cells under microscope

Answer 12

Question 13

liver cells under microscope more detail - hepatocytes

Answer 13

Question 14

Cirrhosis of the liver:

Answer 14

Cirrhosis is a disease where the normal liver tissue is replaced by fibrous scar tissue.
There are lots of different causes including genetic conditions and hepatitis C, however, in the UK the most common cause is drinking excessive amounts of alcohol.
There are three stages of alcoholic liver disease - alcoholic fatty liver disease, alcoholic hepatitis, and liver cirrhosis.
In fatty liver, big fat-filled vesicles displace the nuclei of the hepatocytes and the liver gets larger.

Question 15

alcoholic hepatitis,

Answer 15

the patient has fatty liver along with damaged hepatocytes and the sinusoids and hepatic veins become narrowed.
In alcoholic cirrhosis the liver tissue is irreversibly damaged. Many hepatocytes die and are replaced with fibrous tissue.
The hepatocytes can no longer divide and replace themselves so the liver shrinks and its ability to deal with toxins in the body decreases.

Question 16

What are kidneys

Answer 16

Human kidneys are typical of all mammalian kidneys.
They are a pair of reddish-brown organs attached to the back of the abdominal cavity.
They are usually surrounded by a thick, protective layer of fat and a layer of fibrous connective tissue.

Question 17

The kidneys play two important homeostatic roles in the body -

Answer 17

excretion and osmoregulation.

They filter nitrogenous waste products out of the blood, especially urea.
They also help to maintain the water balance and pH of the blood, and hence the tissue fluid that surrounds all the cells.

Question 18

The anatomy of the kidneys:
p1

Answer 18

• The kidneys are supplied with blood at arterial pressure by the renal arteries that branch off from the abdominal aorta.
• Blood that has circulated through the kidneys is removed by the renal vein that drains into the inferior vena cava.
• About 90-120cm’ of blood passes through the kidneys every minute.
• All of the blood in the body passes through the kidneys about once an hour.
• The kidneys filter 180 dm of blood a day, producing 1-2 dm of urine.
• The final volume depends on many different factors.

Question 19

The anatomy of the kidneys:
p2

Answer 19

The kidneys are made up of millions of small structures called nephrons that act as filtering units.
The sterile liquid produced by the kidney tubules is called urine.
The urine passes out of the kidneys down tubes called ureters.
It is collected in the bladder, a muscular sac that can store around 400-600 cm’ of urine.
When the bladder is getting full, the sphincter at the exit to the bladder opens and the urine passes out of the body down the urethra.

Question 20

kidney location diagram

Answer 20

Question 21

Kidney structure:
three main areas

Answer 21

• the cortex, the medulla, and the pelvis

Question 22

The cortex

Answer 22

is the dark outer layer.
This is where the filtering of the blood takes place and it has a very dense capillary network carrying the blood from the renal artery to the nephrons.

Question 23

The medulla

Answer 23

is lighter in colour
it contains the tubules of the nephrons that form the pyramids of the kidney and the collecting ducts.

Question 24

The pelvis

Answer 24

is the central chamber where the urine collects before passing out down the ureter.

Question 25

internal stricture of kidney diagram

Answer 25

Question 26

Nephrons

Answer 26

• the functional units of the kidney
• In the nephrons the blood is filtered and then the majority of the filtered material is returned to the blood, removing nitrogenous wastes and balancing the mineral ions and water.
• Each nephron is around 3 cm long and there are around 1.5 million nephrons in each kidney.
• This provides the body with several kilometres of tubules for the reabsorption of water, glucose, salts, and other substances back into the blood.

Question 27

Structure of the nephron:
The main structures and functions of the nephron are as follows: p1

Answer 27

Bowman’s capsule

Proximal convoluted tubule

Loop of Henle

Distal convoluted tubule

Collecting duct

Question 28

Bowman’s capsule

Answer 28

cup-shaped structure that contains the glomerulus, a tangle of capillaries.
More blood goes into the glomerulus than leaves it due to the ultrafiltration processes that take place.

Question 29

Proximal convoluted tubule

Answer 29

the first, coiled region of the tubule after the Bowman’s capsule, found in the cortex of the kidney.
This is where many of the substances needed by the body are reabsorbed into the blood

Question 30

Loop of Henle

Answer 30

a long loop of tubule that creates a region with a very high solute concentration in the tissue fluid deep in the kidney medulla.
The descending loop runs down from the cortex through the medulla to a hairpin bend at the bottom of the loop.
The ascending limb travels back up through the medulla to the cortex.

Question 31

Distal convoluted tubule

Answer 31

a second twisted tubule where the fine-tuning of the water balance of the body takes place.
The permeability of the walls to water varies in response to the levels of the antidiuretic hormone (ADH) in the blood
Further regulation of the ion balance and pH of the blood also takes place in this tubule.

Question 32

Collecting duct

Answer 32

the urine passes down the collecting duct through the medulla to the pelvis.
More fine-tuning of the water balance takes place - the walls of this part of the tubule are also sensitive to ADH.

Question 33

The nephron has a network of

Answer 33

capillaries around it which finally lead into a venule and then to the renal vein.

Question 34

The blood that leaves the kidney has

Answer 34

greatly reduced levels of urea, but the levels of glucose and other substances such as amino acids needed by the body are almost the same as when the blood entered the kidneys (may be slightly less as some glucose will have been used for selective reabsorption).
The mineral ion concentration in the blood has also been restored to ideal levels.

Question 35

structure of nephron diagram

Answer 35