Monthly Archives: November 2013

falling over and liquorice

We admit a lot of elderly patients who have fallen over. There are a whole range of problems which cause falls, one of which is postural, or orthostatic hypotension.  Emily is 78 and lives alone in a bungalow. Her husband died three years ago, but her daughter calls in to help most days. She was fairly well until she went to her family doctor’s surgery last week and had her blood pressure measured.  The result was not good – 186/88mmHg.

She first developed high blood pressure when she was in her fifties, and it had crept up since. She was already taking ramipril (an ACE inhibitor) and indapamide (a thiazide diuretic). She had tried amlodipine, but that gave her swollen ankles, which she hated. Her GP decided to try her on doxazosin. This is an alpha-blocker that lowers blood pressure by opening up small arteries. The morning of the day of admission she got up and took her tablets. Then she had a bath, but when she got out felt awful, and faint, and fell to the floor. She lay on the floor for a few minutes and tried to get up, but felt very dizzy and had to lie down again. She phoned her next-door neighbour on her mobile phone. The neighbour came round and helped Emily to her feet, but she went wobbly and could not stand, ending up on the floor again. Her neighbour became really worried and called for the ambulance. When the ambulance paramedics arrived they found that when they tried to stand Emily up, her blood pressure dropped from 160mmHg systolic to 90mmHg. They brought her in to see us.

There is a popular notion that all antihypertensive drugs cause postural hypotension, but this is not the case. As we will see, beta-blockers can even be used to treat this condition.

What is happening with the circulation to cause Emily’s blood pressure to drop when she stands up?

standard clinical rubber glove
standard clinical rubber glove

The whole explanation is made much easier with a standard hospital rubber glove (the stretchier the better) and a sink, and a supply of water. First we fill the glove up with the right amount of water.

glove about half filled with water - laid flat - notice the thumb is filled with water - this represents cardiac filling pressure
glove about half filled with water – laid flat – notice the thumb is filled with water – this represents cardiac filling pressure

The water in the glove represents blood in the venous side of the circulation. The arterial side is much lower volume, and is very little affected by changes in pressure due to posture.

When we stand up the amount of fluid in the veins of the legs and abdomen increases, due to increase in hydrostatic pressure stretching the rubbery material. Veins are thin-walled and rubbery, and will naturally distend if the pressure inside is increased.  If this happens, the thumb empties, this represents the filling pressure to the heart. If cardiac filling pressure drops,  cardiac output drops and blood pressure falls.

no venous squeeze due to failure of the autonomic system, due to brain stem or peripheral problems means no cardiac filling pressure - the thumb is empty
no venous squeeze due to failure of the autonomic system, due to brain stem or peripheral sympathetic nerve action means no cardiac filling pressure – the thumb is empty

This will result in a fall in systemic arterial blood pressure – postural hypotension.

But this does not happen in healthy, young people. We have autonomic reflexes which cause constriction of veins before we stand up, so that filling pressure to the heart is maintained.  In the glove model this is represented by my hand squeezing the fingers and main hand of the glove.

in healthy individuals the autonomic nervous system provides a squeeze of abdominal and leg veins to maintain filling pressure of the heart - notice the thumb is now full of water
in healthy individuals the autonomic nervous system provides a squeeze of abdominal and leg veins to maintain filling pressure of the heart – notice the thumb is now full of water

There are two main causes for postural hypotension – failure of autonomic squeeze of the veins, and insufficient filling of the venous compartment.

Let’s take the first of these – not enough squeeze.  When we move from lying down to standing up, our brain knows what is about to happen. As we move our limbs the proprioceptors in our joints tell our brain what is about to happen and our conscious mind probably also has a role. Messages are sent to the control centre (Houston – prepare for lift-off) in the medulla. Sympathetic nerves send messages down to the veins to tell them to constrict. It is interesting that human intra-abdominal mesenteric veins are particularly richly supplied with sympathetic nerve endings – presumably because we are one of the few animals where standing is such a problem. In animals such as horses and dogs, moving from lying to standing does not involve a capacious venous network to be subjected to large pressure changes – their legs have very little venous blood and their abdomen and contents is on the same level as the heart.

It is also not surprising that if you take a healthy, young person and strap them to a tilt-table, and suddenly move them from horizontal to vertical, they will experience an impressive drop in blood pressure. If they are lying on a bed and stand up – blood pressure hardly changes because the brain-stem prepares us for the change in posture with messages to our abdominal and leg veins to constrict.

As we get older, everything starts to go wrong (see last week’s post). Autonomic reflexes become impaired. Patients with Parkinson’s disease are particularly prone to develop postural hypotension because of impaired brain stem autonomic reflexes – this used to be called Shy-Drager syndrome when I was young – it is now know as multi-system atrophy. Some drugs such as antidepressants and methydopa inhibit brain stem sympathetic output and predispose to this condition.

The sympathetic nerves end up on the outside (adventitia) of veins and release noradrenaline which causes constriction of venous smooth muscle by stimulating alpha receptors. Emily had been given an alpha-blocker to reduce constriction of her arterioles and thereby reduce blood pressure. In her it reduced the ability of veins to constrict when standing up by blocking venous alpha receptors.

Some patients have problems with the autonomic nerves. Diabetics and alcoholics are prone to develop autonomic neuropathy which may result in postural hypotension due to inability of veins to constrict.

Temperature also plays a part in venous constriction. Most of us have noticed occasionally when getting out of a hot bath or sauna feeling dizzy for a few seconds, we hold onto the edge of the bath then things improve. What has happened is that the hot bath water has caused venous dilatation and the normal reflexes have not been enough to maintain cardiac filling pressure. Cardiac output drops, baroreceptors panic (Houston, we have a problem). Houston responds quickly by sending a stronger sympathetic signal to the veins and to the heart to increase cardiac output and the problem is soon sorted. But of course preventing the problem is much better than reacting when it has happened.

The second main cause of postural hypotension is insufficient fluid in the circulation.

to represent fluid loss - some water is poured out of the glove
to represent fluid loss – some water is poured out of the glove

In Emily’s case this may have been partly due to the thiazide diuretic she was taking for her blood pressure. Patients on loop diuretics such as furosemide are even more prone to fluid depletion. Sepsis causes problems with a postural blood pressure drop because of fluid shifts out of the circulation into interstitial spaces, and because fever causes venous dilatation as in the hot bath above. Jonathan, who had a lobar pneumonia a few weeks ago, may well have collapsed in his GP’s surgery because of a postural blood pressure problem.

even with reduced volume - when lying flat the thumb is still filled with water and blood pressure is maintained
even with reduced volume – when lying flat the thumb is still filled with water and blood pressure is maintained

Blood loss from trauma or intestinal bleeding may often not result in blood pressure drop until the patient stands up – it is far easier to maintain filling pressure when lying down and not having to squeeze the veins hard.

with reduced volume, squeezing the legs and abdomen no longer maintains filling of the thumb - cardiac filling reduces and blood pressure drops
with reduced volume, squeezing the legs and abdomen no longer maintains filling of the thumb – cardiac filling reduces and blood pressure drops

Sorting out Emily’s postural hypotension was straightforward. We gave her two litres of intravenous saline and stopped her doxazosin, and diuretics. We had a plan to start her on verapamil or diltiazem when she could stand up without her blood pressure dropping – which it did the next day.

Do ACE inhibitors/ARBs, beta blockers or calcium channel blockers cause postural hypotension?

The answer is to begin with, no and no.

ACE inhibitors can cause a postural drop when they are first started. This is because angiotensin does have an effect on venous constriction, but only transiently when it is increased or decreased. If angiotensin II is infused into a hand vein it will constrict, but only for a few hours at most. Similarly if angiotensin II is withdrawn, the vein will dilate, but only briefly. This means that it is prudent to warn patients that they may develop postural symptoms following the first dose – and it is a good idea to take it when lying down before going to bed. The effect of angiotensin II on arterioles is long-lasting, which is why these drugs are useful in treating arterial hypertension.

Beta blockers reduce blood pressure by mechanisms which are not completely understood, but is likely to be a combination of reduced cardiac output and inhibition of renin release from the kidney. There are beta2 receptors in arteries and veins, but these cause vascular dilatation. Beta blockers can help veins constrict, which is why they are sometimes used to treat postural hypotension. Having said that, if there is a postural drop in blood pressure, the reflex mechanisms set in train by baroreceptors involve increased sympathetic stimulation to the heart via beta1 receptors, increasing force and rate of contraction. Beta blockers will block this response and may therefore impair the recovery from an episode of postural hypotension, but they will not cause it.

Calcium channel blockers have an effect on arterioles, not on veins. Calcium channels are important in maintaining arterial tone, but not venous tone. Venous tone depends almost entirely on sympathetic stimulation. Therefore, at least in theory, drugs such as verapamil, diltiazem and amlodipine will not cause a postural drop. But of course if there is a postural drop, lower initial blood pressure caused by these agents may make the episode worse.

Sorting out Emily’s orthostatic hypotension was fairly straightforward. What about when it is caused by age-related impairment of brain stem function, or by irreversible peripheral autonomic neuropathy? It can be a real problem.

overfilling the glove means that even with no squeeze to the veins the thumb remains full of water when the glove is upright - overfilling the circulation with fludrocortisone can help prevent postural hypotension
overfilling the glove means that even with no squeeze to the veins the thumb remains full of water when the glove is upright – overfilling the circulation with fludrocortisone can help prevent postural hypotension

One approach is to use fludrocortisone. This is a synthetic analogue of aldosterone. Made from cholesterol (again!) this hormone is made in the adrenal cortex, in different cells which make cortisol from cholesterol. The function of aldosterone is to regulate how much salt and water is excreted from our kidneys. Aldosterone helps the reabsorption of more salt from the distal convoluted tubule and will therefore increase circulating volume of blood. This will have the opposite effect to diuretics and overfill the circulation and help keep filling pressure at heart level adequate on standing up. Another drug which is sometimes used is midodrine, an alpha receptor agonist, helping constrict veins and maintain cardiac filling when upright. The drug does not have a licence for this indication in the UK.

We have made a not very good video showing how postural hypotension works – my first attempt at youtube – thanks for your help Steph. We will try to make a better one soon and update this post. The video is at:

The food link this week was not obvious when I started, but of course it has to be liquorice.

liquorice has been popular for a long time - it is made from the root of the liquorice plant
liquorice has been popular for a long time – it is made from the root of the liquorice plant

Liquorice contains glycyrrhizin which has a chemical structure similar to steroids such as cholesterol and aldosterone (made from cholesterol – again!). It has long been known to have a mineralocorticoid effect. This is not because it acts directly in the kidney to stimulate aldosterone receptors. Instead it prevents the conversion of cortisol to cortisone. Cortisone, synthesized by the adrenal glands, is converted to cortisol in the kidney, then back to cortisone, cortisol has more mineralocorticosteroid effects than cortisone – full details are in the NEJM paper:

http://www.nejm.org/doi/full/10.1056/NEJM199110243251706

Eating too much liquorice can cause high blood pressure and low plasma potassium levels –  similar to primary hyperaldosteronism.

old age and malbec

Dorothy was born in 1911. She is 102. When someone over 100 is admitted to our ward there is always a lot of interest – but it is happening more and more. Dorothy, or Dot, as she is known by her friends, has been living on her own in sheltered housing. She has her own ground floor flat, but eats meals with the other elderly residents and has help with washing and dressing in the morning, and there is always a manager on hand if there are problems. Slide1She can make herself simple meals and cups of tea, and her 78 year-old son, David, usually visits every Sunday.  I saw her in our ward last week. She had fallen over on Sunday night and bashed her head on the edge of a table, resulting in a huge bruise over her right eye. She has atrial fibrillation and is on warfarin – the ambulance crew brought her in to hospital as she was a bit confused and they were worried she might have a blood clot on her brain.

The CT head scan on the left of a healthy 96 year old woman, the one on the right is of a 23 year old woman. The dark portion in the middle of the old brain is fluid, not brain. The younger person's head is completely full of brain.
The CT head scan on the left is that of a healthy 96 year old woman, the one on the right is that of a 23 year old woman. The dark portion in the middle of the old brain is fluid, not brain. The younger person’s head is completely full of brain.

Luckily the CT scan of her head showed no evidence of serious bleeding, although her brain was considerably shrunken compared to a young person. She was quite deaf, but clearly had most of her marbles. She recounted how her father had fought, and was wounded, in the Battle of the Somme in the first world war, and her husband Rodney, who died in 1980 had fought in the second. She worked in a munitions factory during the war and had three children – all boys. It’s strange calling elderly people children, but offspring or any other word does not seem quite right. Only the youngest was still alive. She could remember the names of all 5 grandchildren and 7 great-grandchildren, but did struggle with the name of the Prime Minister and what year it was. Her brain was old as well as her skin and her ears, and all the rest of her.

How much longer will Dot live? There was an entertaining paper in the Christmas BMJ in 2011. http://www.bmj.com/content/343/bmj.d7679

It has been shown that for any cohort of elderly people, the main determinant of longevity is how old you are – as we get older the more likely we are to die sooner. The second most important factor is gender – women live longer than men. The third, somewhat surprisingly, is how fast you can walk. This is probably because being able to walk fast requires a lot of things to be working well – good lungs, good cardiac function, good muscles, good joints, good brain function, good eyesight, good peripheral nerve function etc. The paper suggests another alternative explanation – that if you walk slowly the grim reaper will catch up with you.

One explanation of why elderly people die soon if they cannot walk fast. Illustration by Belle Mellor - http://bellemellor.com (with permission - thanks Belle)
One explanation of why elderly people die soon if they cannot walk fast. Illustration by Belle Mellor – http://bellemellor.com
(with permission – thanks Belle)

Why do people get old? This is a difficult question, and I cannot give you a definite answer, but will give you my thoughts.  Ageing (aging in the US) seems inevitable.  We can guess how old someone is by their skin, which becomes wrinkled – their hair becomes thin and grey, and their posture becomes bent. The cells in our skin, bones, brain and just about everywhere else continually become older, but some of our cells do not age in the same way. Think about a sixty year old man who becomes a new father.  His sperm have contributed to make a baby that is not old, but brand new. The cells in his testes which have made the sperm are old, but they must have in them the information about how to make a cell which is not old. This, to me, very much suggests that old cells have not lost the information in the form of DNA sequence that they had when they were new. The creation of Dolly the sheep confirms this. Dolly was made from the nucleus of  her “mother’s” mammary gland cell (she was called Dolly after Dolly Parton, who has very impressive mammary glands). In a test-tube this nucleus was inserted into an egg cell of another sheep (also her mother?) and processed to de-differentiate it.

Dolly Parton - from Wikimedia commons
Dolly Parton – from Wikimedia commons

This means the nucleus of the mammary gland cell was changed so that instead of only being able to make more, old, mammary gland cells, it could make all the new and different cells of baby Dolly the sheep. So, I’ll ask the question again, why do cells get old? It’s not that they have lost the information about how to be new cells, but nature has determined that after a certain period of time they change into old cells. What is happening in the cells to make them old? – clearly they are not so damaged that the DNA sequence is irreparably altered. There must be a clock inside cells that tells them how old they are – this is suggested by the classic studies of Leonard Hayflick, who showed that cells from human babies only divide about 50 times, and then stop.

cells must have some sort of clock inside them - it may well be the amount of methylation of DNA in the nucleus
cells must have some sort of clock inside them – it may well be the amount of methylation of DNA in the nucleus

Cells from older people divide far fewer times. It was thought for many years that the reason cells could only divide a certain number of times was because each time division took place, the teleomeres at the end of each chromosome become shorter. When they become too short, the cell can no longer divide. Teleomeres have been likened to like the plastic bits at the end of shoelaces – they stop the lace from fraying and are necessary in chromosomes to keep the DNA strands from coming apart.

It may well be that short teleomeres contribute to the cellular clock, but it seems they are not the only answer.

teleomeres are on the end of chromosomes like the bits of plastic on the end of shoelaces - to stop them fraying
teleomeres are on the end of chromosomes like the bits of plastic on the end of shoelaces – to stop them fraying

More recent research suggests that epigenetic changes in DNA may be responsible. Epigenetics is a very fashionable science. Once a cell is differentiated in the growing embryo – say into a skin cell – its DNA becomes progressively altered. In particular methyl groups (CH3) become attached to a cytosine nucleotide when a cytosine and guanine are next to each other in the nucleic acid chain (CpG). This methyl group attached to the cytosine is copied when the cell divides. Recent research suggests that the age of cells is closely related to the number of methyl groups attached to CpG sequences in DNA.

http://genomebiology.com/2013/14/10/r115

What to me is really interesting, is that when sperm cells meet egg cells and their nuclei fuse to make the start of a new baby, all the methyl groups are stripped from the CpG sequences in DNA.  This looks like a definite candidate for the cellular clock.

But why do we need to age? What if cells stayed “new”? What if we could stop the cellular clock? If we could inject a substance into Dot which reversed the epigenetic changes would she suddenly get lovely wrinkle-free baby-like skin and a fully functioning brain, ears and eyes? I don’t know, but I suspect not – answers please.

Why did evolution invent a clock in our cells to stop them dividing as we get older? One explanation for this is that cells become damaged with time, and dividing may not be a good thing for damaged cells as it is more likely that they will become malignant. We now know that most malignant cells develop a sequence of gene defects over time, which when added together cause the cell to become cancerous. Maybe the clock, which limits the number of divisions, is a way of preventing further DNA damage and malignancy. Certainly it seems that reactive oxygen compounds that can cause damage to DNA also cause CpG methylation – in a way causing premature ageing of cells.

I used to think that the reason our cells got older was so that we would die and no longer be competition for our children, who, through evolution, had become more fit than us.  It seems this is not the explanation because there is very good evidence that early humans did not die from age-related causes, but from infections and trauma.  The average life-span in prehistoric times was much lower than in modern times, most people dying before 30 and nearly all before 40 years of age.  This means that it is not possible for evolution to select for, or against, those people who lived longer, because there were so few of them. Instead it seems that evolution only cares about keeping us alive until we have produced and reared babies – after that it has no interest or influence one way or the other. If there was a new gene that made a prehistoric human live longer, it would be extremely unlikely that the owner would survive longer and there would be no positive or negative pressure to keep it. This does not mean that our genes cannot influence how long we live. An important factor in determining how long we live is how long our parents lived. Another is where we live and our lifestyle.

Roger Corder, scientist and author of The Red Wine Diet
Roger Corder, scientist and author of The Red Wine Diet

There is a wonderful book by an erstwhile colleague of mine, Roger Corder, called The Red Wine Diet, which suggests that eating foods with certain polyphenols can make us live longer.

polyphenols are large molecules made up of lots of phenols - they are useful antioxidants which trap oxygen radicals
polyphenols such as tannins are large molecules made up of lots of phenols – they are useful antioxidants which trap oxygen radicals

Polyphenols are found in plants and are often brightly coloured. Tannins are polyphenols, and cause a characteristic “furry” taste in the mouth because they react with the protein molecules on the surface of our tongue. These molecules are powerful antioxidants. What does that mean, and why do plants make them? In the case of a grape, one of its main concerns is DNA damage by ultraviolet light. Although short wavelength UV light can directly damage DNA, it seems that less powerful, longer wavelength rays can generate very reactive oxygen radicals such as singlet oxygen and hydroxyl, which then combine with, and damage DNA. Polyphenols can rapidly “mop up” or detoxify these oxygen radicals and protect DNA.  If you live in the mountains of SW France, Sardinia, Crete or Sicily, the plants, and especially grapes, are subjected to large amounts of UV irradiation and produce lots of polyphenols. The people who live eat and drink lots of these polyphenols live to an unexpected old age. It might be a coincidence, but, for me, the inconvenience, expense and sheer tedium of drinking three glasses of red wine a day seems worth a try. But don’t overdo it and do remember Kevin (vodka and sweetbreads) below. The food link this week is a drink – Malbec.

Argentinian Malbec is full of tannins
Argentinian Malbec is full of tannins

This is a grape variety, which, according to Roger Corder, contains very high levels of procyanidins – tannins which he thinks helps protect us from heart disease and cancer, and makes us live longer.  Antioxidants prevent the oxidation of LDL cholesterol (see previous post on chest pain and horsemeat lasagne) and reduce DNA damage that can make normal cells malignant and age more quickly. It is grown in the mountains of SW France and is the main variety in Cahors wine – a particularly dark and astringent glassful. Argentinian Malbec is more available in the UK and is also grown high up in the mountains where it gets plenty of ultraviolet light.

gallstones and mayonnaise

A few weeks ago we admitted Sylvia. She had been feeling unwell for a some days, with fever and episodes of uncontrollable shaking. What really alarmed her was when she turned yellow, and then developed abdominal pain and vomited a couple of times. Sylvia is forty eight, and had always been healthy. She rowed with the local club twice a week and kept her weight under control. For the past year or so she noticed that she got pains in her abdomen after eating fatty foods such as fish and chips, and now avoided foods like that. It was her son who noticed she was yellow – he then phoned Sylvia’s GP. The duty doctor came and confirmed that she was indeed jaundiced, feverish and unwell, and persuaded her that she needed to go to hospital.

these people look jaundiced - in fact they are not - the whites of their eyes are white - this image is copyrighted but Wiki thinks its ok to use it so I'm hoping its ok for me to do so
these people look jaundiced – in fact they are not – the whites of their eyes are white – this image is copyrighted but Wiki thinks its ok to use it so I’m hoping its ok for me to do so

We did all the usual things for someone with suspected biliary sepsis. Took blood cultures and routine blood tests. These tests confirmed she had elevated bilirubin and transaminases, increased alkaline phosphatase, as well as a high neutrophil count and CRP.  We gave her intravenous fluids, anti-emetics and antibiotics. We were able to get an ultrasound within a couple of hours. Ultrasound is really good at looking at the liver and biliary system in jaundiced patients – better than CT.

The ultrasound showed that Sylvia had a gallbladder full of gallstones and her common bile duct was dilated. It seemed likely that she had a stone blocking the flow of bile from the liver to the duodenum, and that the stagnant bile had become infected with bacteria causing ascending cholangitis and liver inflammation.

bile is made in the liver - it is stored in the gallbladder and squirted into the small intestine after a fatty meal, along with pancreatic secretions - Sylvia's gallstone was impacted in the sphincter of Oddi
bile is made in the liver – it is stored in the gallbladder and squirted into the small intestine after a fatty meal, along with pancreatic secretions – Sylvia’s gallstone was impacted in the sphincter of Oddi

The questions I want to answer this week are:

Why did Sylvia turn yellow?

What are gallstones made of and why do they form?

Why is there an increase in alkaline phosphatase in the bloodstream when the biliary system is obstructed?

The last of those questions is the hardest, but I will make some conjectures, and  hope that others who know more about it will correct me.

Jaundice is fairly straightforward. It is caused by the accumulation of bilirubin, which is a greenish-yellow colour. Bilirubin is made from haem, the central working part of myoglobin, but most bilirubin comes from the breakdown of haem in the haemoglobin from red blood cells.

So why is haemoglobin red? It is not only – or even mainly – the iron that makes haem red, but the porphorin ring that surrounds the iron. This large ring is made of four smaller pyrrole rings.

Pyrroles are often coloured – the dye indigo has two pyrrole rings and red acrylic paint often contains the dye pyrrole-red. Melanin, the pigment that gives skin and hair its colour is brown or black or red because it has a related structure – indole – a pyrrole stuck to a benzene ring. Without this pyrrole ring we would be like albinos, but without pink skin and eyes.  As we shall see, we would also produce beige poo and colourless urine.

this is a pyrrole - all pyrroles are highly coloured, and are in most of the things which make people the colour they are
this is a pyrrole – all pyrroles are highly coloured, and are in most of the things which make people the colour they are

Red blood cells last on average 120 days before they wear out and have to be recycled.  As we have five litres of blood and in each litre there is at least 120 grammes of haemoglobin, it means we have to make, and break down, five grammes a day.  About a teaspoonful.  This all happens inside macrophages in the spleen and liver, as they try to salvage useful parts of the red cells to make new things.

Macrophages are similar to neutrophils but slightly smarter.  Some are good at host defence: they come to the scene after the neutrophils have done their job, do the forensics, and find out what the germs are made of. They then tell the lymphocytes how to make antibodies to protect us in the future.

Other macrophages are good at clearing up the mess, breaking down dead tissue and making things neat and clean.  The spleen and liver macrophages that deal with old red cells are the latter kind. When they take red cells apart, they separate haem from globin, and then take the iron out of the haem.  Next, the porphorin ring is broken to form bilirubin – its molecule of linked pyrrole rings looks like four beach huts in a row.

haem is broken down by the enzyme haem oxygenase to form bilirubin
haem is broken down by the enzyme haem oxygenase to form bilirubin

The bilirubin is then thrown away (I don’t know why it can’t be re-used).  It attaches to albumin and becomes water soluble after conjugating in the liver with a sugary molecule called glucuronate.  The conjugated bilirubin is then transported into the biliary system, stored in the gallbladder, and squirted into the duodenum when we eat fatty food.  In the bowel, it is converted to urobilinogen, which makes poo brown.  Some is reabsorbed and excreted in urine, which makes urine yellow.Slide2

Sylvia had noticed that her poo had changed colour – it had become putty-coloured – and her urine had become much darker. That is because conjugated bilirubin was not getting into her intestines and instead some had leaked into her bloodstream and was appearing in her urine. The whites of her eyes and skin had become yellow because of the very high level of conjugated bilirubin in her blood.

Now to the gallstones.  In Western countries they are most commonly made of cholesterol.  I have already talked about the importance of cholesterol in keeping cell membranes rigid and non-leaky.  Cholesterol is made in large amounts by the liver and transported to other cells gift-wrapped as LDL cholesterol.  It is also used to make bile salts.  It only needs a minor modification of the basic chemical structure of cholesterol to make bile salts – the main component in bile which makes it work – the main function of bile salts is to help us digest dietary fat.

structure of cholesterol
structure of cholesterol

Bile salts are detergents.  Just like washing-up liquid, they emulsify fats, breaking large fat globules into smaller micelles which do not stick to each other, or anything else. Cholesterol is essentially very insoluble in water, or hydrophobic.  When an organic acid group is added – to make bile salts – it gains a hydrophilic or water-attracting group. This is just like soap – a long lipid chain with an organic acid group at the end.  The hydrophobic lipid part is embedded in the tiny fat globule and the hydrophilic groups stick outside in the watery medium of the intestinal contents.

bile acids are a minor modification of cholesterol - hydrophilic OH  and COOH  groups are added to make it into a detergent
bile acids are a minor modification of cholesterol – hydrophilic OH and COOH groups are added to make it into a detergent

As well as bile salts, the liver secretes phospholipids into bile – principally phosphatidylcholine. This, with cholesterol, is the main stuff cell membranes are made of.  It is also an emulsifying agent, and is used extensively in the food industry to keep fats in suspension.

So, when we eat fat, the small intestine detects it and releases the hormone cholecystokinin (CCK).  This causes the gallbladder to contract to send bile into the duodenum, and also makes the pancreas release enzymes, including lipase.  CCK also has some very interesting effects on our brains, making us feel less hungry, and curiously, opposing the effects of opiate drugs.  The bile and pancreatic secretions are both delivered into the duodenum through the same tube – see diagram. The detergent bile salts, emulsifying phospholipid and pancreatic lipase are designed to work together to digest fat.

the hydrophilic parts of cholesterol are all on one side of the molecule - this allow it to act as a detergent - it works well to disperse fat into small globules so that pancreatic lipase can work on it and break it down to fatty acids and monoglyceride
the hydrophilic parts of cholesterol are all on one side of the molecule – this allow it to act as a detergent – it works well to disperse fat into small globules so that pancreatic lipase can work on it and break it down to fatty acids and monoglyceride

The bile breaks it up into tiny globules and the lipase breaks triglyceride into fatty acids and monoglyceride. These are transported across the intestinal mucosal cell membrane and then the triglyceride is put back together again. Seems a daft system, but it clearly works. The triglyceride is taken away from the intestine not in the portal blood, like most other substances absorbed by the gut, but in the lymphatic system in the form of chylomicrons – small fatty globules covered by a layer of phospholipid. The chylomicrons travel up the lymphatic vessels to emerge into the circulation just below our left clavicle. This means that it avoids passing straight away through the liver. If blood is taken soon after a fatty meal and centrifuged, it will have a milky appearance because of the large amount of chylomicrons.

So why do gallstones form? As well as bile salts, unmodified cholesterol is also secreted into bile. It is only kept soluble by the bile salts and phospholipid – the ratio of cholesterol to bile salts and phospholipid is therefore important. When it goes wrong, cholesterol precipitates out and forms solid stones like those that caused all Sylvia’s recent problems – a bit like when I try to make mayonnaise and it curdles – the fat becomes un-emulsified and separates out.

In some parts of the world, gallstones are made from bile pigment – bilirubin. This can be due to increased red blood cell breakdown resulting from abnormalities such as sickle cell disease, but it’s also common in East Asia, for reasons which are not clear.  A good, comprehensive analysis of why gallstones of all types form can be found at:

http://gastro.ucsd.edu/fellowship/materials/Documents/Gallstones/pathogenesis%20gallstones.pdf

Now the alkaline phosphatase. Bile is alkaline.  Alkaline phosphatase is an enzyme that removes phosphate groups in alkaline conditions.  When bile flow is blocked – by stones, as in Sylvia’s case, or for any other reason – the liver makes much more alkaline phosphatase, some of which appears in the blood.  Bones use a similar alkaline phosphatase to rearrange phosphate groups to make hydroxyapatite – the hard stuff bone is made from.  Most of the alkaline phosphatase normally in our blood is the bone sort.

There is plenty of information about whether alkaline phosphatase is from bone or liver, but very little I can find that suggests why the liver should make this enzyme when the biliary system is blocked.  I think a clue here is that neutrophils also have alkaline phosphatase in their granules, which help kill bacteria.  This is in addition to the myeloperoxidase and esterase mentioned in earlier posts.  Why should a phosphatase be damaging to bacteria?  The answer may well involve techoic acid, an important reinforcing molecule in some gram-positive bacteria.

cartoon of gram positive bacterial cell wall - techoic acid is thought to inhibit the action of lysozyme and protect the peptidoglycan from being broken down - techoic acid contains phosphate groups which may be removed by alkaline phosphatase
cartoon of gram positive bacterial cell wall – techoic acid is thought to inhibit the action of lysozyme and protect the peptidoglycan from being broken down – techoic acid contains phosphate groups which may be removed by alkaline phosphatase

In these microbes, techoic acid strengthens the peptidoglycan cell wall and inhibits the action of lysozyme, yet another enzyme made by neutrophils.  Lysozyme is designed to break some of the sugar-sugar bonds in peptidoglycan – so getting rid of the techoic acid would surely be helpful.  We know that alkaline phosphatase is effective in breaking up techoic acid – see, for instance:

http://jb.asm.org/content/102/3/747.short

Maybe the liver is producing this anti-bacterial enzyme to help prevent infection when the flow of bile slows down.  Unfortunately, this won’t work with gram negative organisms such as E.coli because they don’t make techoic acid – and it was a gram negative bacterium we grew from Sylvia’s blood culture – the germ that was causing her ascending cholangitis.

Soon after she came in, Sylvia had an ERCP – an endoscopic retrograde cholangio-pancreatoscopy.  The endoscopist managed to remove the impacted gallstone from her ampulla of Vater, and she quickly recovered.  A week later she had her gallbladder removed, including the stones, and now is quite well – she can even eat fish and chips.

Now to the food link: mayonnaise.

French mayonnaise - made with olive oil and mustard
French mayonnaise – made with olive oil and mustard

This is an emulsion of lipid, such as olive oil, in an aqueous (watery) medium – vinegar or lemon juice.  The emulsifying agent is raw egg yolk, which – just like bile – contains lots of phospholipid – phophatidylcholine and is also rich in cholesterol.  In France, mustard is also added.  Mustard seed contains mucilage, a gooey stuff that some plants produce made of sugar polymers. (Thanks again to Harold McGee). These also act as emulsifiers and further thicken the mayonnaise, and give it a better taste. When I make cheese sauce, I use a sugar polymer (flour) to achieve a stable emulsion between butter and milk – no doubt the phospholipid in the milk helps too.  It seems likely that in the small intestine, the mucus from the stomach, a similar gloopy sugar polymer, probably has a similar effect to mustard seed mucilage to help with fat emulsification.