Week 4: the liver

We started by looking at varices (dilated veins) in the oesophagus and around the umbilicus (caput medusae). We also mentioned hemorrhoids. Read more about these varices with these links:
Patient UK – esophageal varices
New England Journal of Medicine – caput medusae
MedicineNet – hemorrhoids (piles)
Our aim for the session was to use anatomy to explain the occurrence of these varices in patients with liver disease.
Arterial blood is supplied to the liver by the hepatic artery proper, which branches from the common hepatic artery. These vessels arise from the first anterior branch from the aorta: the celiac trunk. Arterial blood has high levels of oxygen.
Venous blood is also supplied to the liver by the hepatic portal vein. This vein receives the splenic vein and the superior mesenteric vein. As the inferior mesenteric vein drains into the splenic vein, almost all the blood from the gastrointestinal (GI) tract is passed to the liver in this way. This venous blood is low in oxygen, but rich in nutrients absorbed across the walls of the GI tract.
How does all this blood get back to the heart? The liver is wrapped around the inferior vena cava (IVC), a very large vein taking blood back to the heart. The IVC is analogous to the aorta in that the aorta carries blood from the heart to the abdomen, pelvis and lower limbs, whereas the IVC carries blood back from the limbs, pelvis and abdomen to the heart. Blood within the liver is passed directly back to the IVC. In this way, blood passes from the portal “circulation” back to the systemic circulation.
How does this help us understand the varices we saw at the beginning? Well, other than the route through the liver there are a number of other links between the portal and systemic circulations. These links between blood vessels are termed anastomoses (singular: anastomosis). Normally a small flow of blood passes through them, but if a normal route becomes blocked or restricted they could pass a greater flow of blood to a tissue that would otherwise receive none.
If the liver becomes progressively more diseased it can develop cirrhosis, where connective tissue replaces healthy tissue. This can restrict the normal flow of blood through it. If a large volume of blood needs to get from the portal circulation back to the systemic circulation but cannot pass through the liver at the normal rate, how else can it get there? Through anastomoses, and in the case of the liver through portosystemic (or portocaval) anastomoses.
There’s a diagram on Instant Anatomy of these portosystemic anastomoses.
So in the oesophagus, portal blood that should go through the liver instead passes to the oesophageal branches of the gastric veins, through anastomoses to the azygos veins of the posterior thoracic wall, and back to the heart. These veins are required to pass a much greater pressure and volume of blood, and being thin walled will stretch, dilate and become varicose.
In the umbilical region remnants of a connection to one’s mother drain blood from a small area of tissue around the umbilicus to the portal vein and the liver. This area also drains blood via epigastric veins to the systemic circulation. If the flow of blood through the liver is impeded, blood may instead pass out to the veins of the umbilical region, across anastomoses to the epigastric veins and back to the heart. Again these normally small vessels become distended, enlarged, and visible.
Parts of the rectum and anal canal are drained by superior, middle and inferior rectal veins. The superior rectal vein drains blood to the inferior mesenteric vein, which passes to the splenic vein, then the portal vein and then the liver. The middle and inferior rectal veins drain blood through pelvic veins to the iliac veins and the inferior vena cava. So, if blood cannot pass easily through the liver it may pass instead through the anasomoses between the superior, middle and inferior rectal veins to get back to the heart. These veins can become distended and form hemorrhoids.
So that’s how liver disease can cause these varices. We’ll also look at the development of these blood vessels in embryology lectures, explaining how and why these anastomoses are formed.

Week 3: Introduction to embryology

The aim of today’s lecture was to talk about what an embryo is, and give a sense of how it forms, what it looks like, and what it will become. I spoke about four principles of growth and development that are really important to the future series of embryology lectures. My underlying aim was to demonstrate why embryology is an important subject for medical students and clinicians. You don’t need to understand all the signaling processes underlying the development of the embryo, but it’s really helpful to have seen how the adult anatomy is formed and what can go wrong.
The embryonic period of development runs from fertilisation to the end of the 8th week. By this point most structures have formed and are functioning to some degree. From then to birth further development is termed the foetal period. Note that clinically the foetus is dated with reference to the last menstrual period, adding 2 weeks to the real gestation time (there’s a gap of about 2 weeks from the start of the menstrual period and ovulation).
We introduced the ideas of growth (through cellular proliferation, cellular hypertophy or accretion of matrix around cells), differentiation (stem cells become specialised), organisation (signalling molecules set up concentration gradients and cells with receptors respond according to their location), and morphogenesis (cells form more complicated structures from simple ones). Look at the lecture on Blackboard or listen to the podcasts for more on these.
We ended with a 5-question quiz about the lecture that the girls’ team won. That starts the girls off 1-0 up with a possible 9 lectures to go. I wonder what we should do for the winning team.

Embryology podcast

14Wk Scan Rhi and I are still chucking out podcasts even though we’re separated by the Bristol Channel. Unfortunately recording over Skype is a bit of a pain in the arse, and Rhi sounds pretty good while I sound like a bee in a jam jar. Skype keeps adjusting my mic levels and I have to tweak them after recording. We’re sending Rhi a Mac so we can switch to iChat & hopefully record separate tracks in Garageband (if it still does that).
The latest recording has just gone up, and is about the development of the eye. (Check the Medicine page for links).

Paracetamol & asthma?

2008-09-19--Annabel On The Swings Beasley et al. are reporting in the Lancet a link between paracetamol use and the onset of asthma after studying 205,487 children aged 6–7. Use of paracetamol for fever in babies was linked to a dose-dependent increase in the risk of developing asthma symptoms by the age of 6-7.
The link doesn’t necessarily mean that paracetamol causes asthma and the BBC reports that, “Researchers do not know if the drug directly increases asthma risk or another underlying factor is to blame.”
“Increasing use of paracetamol in children has coincided with rising cases of asthma over the past 50 years, the researchers said”, however.
“One explanation for the findings is that paracetamol may cause changes in the body that leave a child more vulnerable to inflammation and allergies.
“Another is that the use of paracetamol in children may be a marker for something else which is causing increased rates of asthma, such as lifestyle issues or the underlying infection causing the fever, experts said.
“Study leader Professor Richard Beasley from the University of Auckland said: “We stress the findings do not constitute a reason to stop using paracetamol in childhood.
“However the findings do lend support to the current guidelines of the World Health Organization, which recommend that paracetamol should be reserved for children with a high fever (38.5C or above).”
Interesting stuff.
Lancet abstract (free registration required).
BBC article.

Week 2: Introduction to organs

Today we ran quickly through as many organs as we could to get an idea of where they are (particularly in relation to other organs) and what they do.
The oesophagus is a muscular tube transporting fluid and food to the stomach. The stomach is a muscular bag that churns up the food and mixes it with more enzymes (after saliva) and acid, which activates another enzyme. The mixed up contents are then squirted into the duodenum – the first part of the small intestine. The small intestine (small bowel) is a 6m long coiled tube where about 90% of the absorption of nutrients into the blood occurs. It has a huge surface area, both because of its folded length and its villous surface. The large intestine (large bowel) receives the leftovers into the caecum, and the colon frames the small intestine by running up, across, and down the other side of the abdomen. It ends as the rectum. The large intestine absorbs water, electrolytes and some vitamins from its contents, and forms and stores the faeces. We noted the vermiform appendix, a length of lymphoid tissue extending from the posterior surface of the caecum.
Almost all of the blood from the gastrointestinal (GI) tract passes to the liver, rich in the nutrients from the last meal. The liver is the largest internal organ and has hundreds of functions that could be grouped into “metabolic regulation”, “haematological regulation” and “bile synthesis”. It stores carbohydrates, lipids, amino acids, and fat-soluble vitamins, removing them from or adding them back to the circulation as required, and is involved in the removal of toxins and metabolic waste (aiding the kidneys). It recycles red blood cells, makes plasma proteins, and makes bile that is added to the duodenum to emulsify fats. (A little more here).
The pancreas also adds exocrine secretions to the duodenum. Its pancreatic juice buffers the chyme (duodenal contents) and breaks down the food to component nutrients. Its endocrine secretions are insulin (signals liver cells to take glucose from the blood and store it as glycogen), glucagon (does the opposite of insulin), somatostatin (decreases glucagon and insulin secretion and slows the activity of the GI tract) and pancreatic polypeptide (decreases gallbladder contractions and exocrine pancreatic secretions).
The spleen is a lateral lymphoid organ involved in preparing the body for an immune response and, like the liver, cleans up old or damaged blood cells and other blood components. Because of its superficial location, good bloody supply and weak connective tissue capsule it is at risk of rupturing and causing internal bleeding into the abdomen with trauma.
The thymus gland is a small gland posterior to the sternum that seems to be important in the development of the immune system. It is larger in children.
Almost all of you were familiar with the structures and functions of the heart and lungs, and the differences between the left and right sides of the heart.
We looked at the kidneys, and talked about their function. While many students were aware of their roles of blood filtration, excretion of metabolic waste and regulation of water/blood volume, few made the links to regulation of blood pressure, plasma ion concentration, and pH. The kidneys also have endocrine functions (secreting hormones). More here.
Moving into endocrine glands, we looked at the location of the thyroid gland in the neck and the 4, small parathyroid glands on its posterior surface. Some hormones of the thyroid gland increase the rate of cellular metabolism and respiration, and another (calcitonin) decreases the concentration of calcium ions (Ca2+) in the blood. Parathyroid hormone, in contrast, increases the concentration of calcium ions. Calcium is one of the mineral ions that are vital to cellular function. Calcium is stored in bone and the hormones signal bone cells to store or retrieve calcium.
The adrenal glands sitting atop the kidneys make adrenaline which you’ve all hopefully met in fearful or exciting situations that maybe required a “fight or flight response”. They also make noradrenaline and adrenocorticosteroids that are vital to life, with roles (again) in metabolism.
We skipped the gonads as we didn’t have enough time, but we did talk about the pituitary gland. This pea-sized organ inside the cranium, along with the hypothalamus and other parts of the brain is a controlling centre for many of the other organs that we talked about. It is another endocrine organ, and affects the functions of the kidneys, the thyroid gland, the gonads and other reproductive organs, and it produces growth hormone (more about the hormones and some disorders here).
The session was a very rapid overview of many organs and we’ll meet them all in detail over the next year or two; some in anatomy, some in other lectures.