The Common Vein Copyright 2007
Throughout the last few chapters I have introduced you to the rather difficult job of relating abstract concepts, such as time, independence, and uniqueness, to medicine, one of the most practical fields around. While these chapters were not particularly challenging to read you may be wondering why I continue to elaborate upon such basic topics. After all, even grade school children understand the passage of time and what it means to be independent. However, I do not intend to patronize you by emphasizing these topics, rather only to introduce you to the art of relating the abstract to the concrete, the intangible to the practical. In today’s Western world, the study of medicine is full of facts and figures whose complexity makes medical science seem far removed from “everyday” concepts like time and space. By relating simple yet abstract concepts to medicine I hope to convince my readers that even the most intricate and challenging of sciences can be reduced to a several basic principles.
Space is a fundamental part of the universe. There are both scientific and philosophical concepts making a single definition difficult, but in the context of the Common Vein Project it relates to the position in which matter exists, both as an absolute but usually in relation to other structures.
In the context of everyday conversation space is usually a reference to the universe at large or to one’s “personal space.” In the world of machinery the precise positioning cogs of a wheel for example, is essential to function. With respect to biologic units, space refers to how cells, tissues, and organs are positioned within the body. While these frameworks for understanding space may seem quite different they are actually very easily relatable. For instance, it is commonly understood that violation of one’s personal space is a source of considerable discomfort and tension, which one usually attempts to escape. If the cogs of the wheel are not in correct position the wheels will not turn on each other and function will be lost. Organs, too, are negatively affected by encroachments upon their space by other factors – be they tumors, external pressure, or other abnormalities. Additionally if the cells or organs are not positioned correctly in relation to the blood vessels for example they too will not function optimally. A heart under increased pressure from fluid occupying space in the pericardial sac cannot pump as well and similalrly lungs under pressure from fluid in the pleural space makes breathing more difficult. Through this and countless other examples it is clear that the positioning of structures relative to each other is critical to optimizing their functions.
In biology and the world within which we live, the positioning in space of one structure in relation to others is critical in the function of biological units. We also see the impotrance of positioning in non biological systems as demonstrated in the example below of cogs in the wheels of a mechanical tool. The positioning of the cogs of one wheel have to coincide with the cogs of the other in order for the turning of one to effect the turning of the other, and in the end for the functioning of that unit to occur.
Positioning of the Cogs is Essential to The Workings of the Whole System
|In this instance the cogs of the wheel in space are perfectly aligned with the cogs of the second wheel and so theoretically this machine as far as positioning, is ready to function.86627.8 cogs in a wheel precise position Davidoff art Davidoff photography Lowell Massachusetts Remnants of days gone by copyright 2008|
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Cogs in Disorder –
|In this instance the cogs of these wheels are malpositioned as they lie in disarray on the ground and are thertefore far from being a functional unit.89051p 89049p cactus gears junk discarded not functioning disorder Disney World Magic Kingdom Davidoff photography|
In the context of everyday living, space is usually a reference to the universe at large or to one’s “personal space.” With respect to biologic units, however, space refers to how cells, tissues, and organs are positioned within the body. While these two frameworks for understanding space may seem quite different they are actually very easily relatable. For instance, it is commonly understood that violation of one’s personal space is a source of considerable discomfort and tension, which one usually attempts to escape.
Did the Photographer Impinge on Her Space?
|This little girl was playing in the park and the approach of the photographer was sufficient for her to react with this expression which in effect says “Get out of my face and my space!”02716p.8 girl in a park with doll anger protection space impingement Boston Massachusetts Davidoff photography Courtesy Ashley Davidoff MD Davidoff photography people copyright 2008|
Organs, too, are negatively affected by encroachments upon their space by other factors – be they tumors, external pressure, or other abnormalities. One of the reasons that cancer is such a devastating disease, is that it takes over the space occupied by normal functioning tissue. The liver is known as the metabolic warehouse of the body, and it is involved in many metabolic activities of the body. In the example shown below, a normal liver and a liver overwhelmed with cancer is shown. The cancerous components, not only occupy space, but they distort, and compress and destroy normal tissue and thus the liver is prevented from performing its metabolic functions.
Normal and Diffuse Metastases
|The left image is a anatomical specimen of a normal liver, though the gallbladder does contain 4 stones. In the specimen on the right the liver is overwhelmed with yellow cancer deposits that originated from a cancer in the duodenum. The cancer is only concerned about its survival and plays no part in contributing positively to the normal required processes of the body. By occupying the space of the normal liver it inhibits the function of the liver and also destroys the tissue.13456 liver normal anatomy gallbladder stones cholelithiasis grosspathology 02635 metatstases to the liver from primary duodenal carcinoma|
A heart under increased pressure cannot pump as well. Pericardial tamponade is a life threatening condition in which the pericardium fills rapidly with a mere 100ccs of fluid . Tension pneumothorax is another life threatening condition in which air rapidly accumulates in the pleural space and encroaches on the the lungs and cardiovascular system. The examples of life threatening space occupation by disease are countless. It is clear that the positioning of structures relative to each other is critical to optimizing their functions, and maintaining viability.
Normal above and Tension Pneumothorax below
|The above example represents a normal chest X-ray (a & b) and a tension pneumothorax (c and d) Note that in a lung markings are seen on either side of the heart, whereas in c, the left chestcavity is black (c) since it is filled with air, represented by the green overlay in d. Air has leaked into the chest cavity from the lung into the pleural space. As the air builds up in the cavity it starts to push on the other structures including the heart and vessels. In b, the arrows represent the normal position of the aorta and pulmonary artery. Note how they have been pushed to the right by the pneumothoraxin c and d and are barely visible. As the pressure pushes on the vessels they become obstructed so that blood cannot enter or leave the heart and total circulatory collapse occurs and death can ensue. This is an example of space occupation by air under pressure of the thorax with devastating result. The treatment is quite simple if the diagnosis is rapidly made. A small needle placed in the right place allows the air to be removed and the lung can return to its rightful position. 42106c04|
Positioning of the Liver Cell Around the Sinusoids
|The liver cells (purple with central pink nucleus) are arranged in cords along the sinusoid (maroon) which is the smallest blood vessel of the liver. The portal vein brings metabolic products from the gastrointestinal tract and combines with the hepatic artery which brings oxygen to the liver cell, to form the sinusoid. The liver cell imports the raw products and oxygen (light orange arrow) from the sinusoid, processes them and exports the product (red arrow) back into the sinusoid. The sinusoids eventually deliver the metabolic products into the central vein which connects with inferior vena cava and the heart.13062b05b04.8 liver hepatocyte sinusoid Kupffer cell space of Disse bile canaliculus import export excrete transport portal blood hepatic arterial blood Davidoff MD Davidoff art|
Within the cell, the receiving, processing, and exporting functions occur between spatially oriented and connected organelles.
Receiving Processing Exporting
Optimal Spatial Relationships Necessary
|When the metabolic products enter the cell (orange arrow) they also have to enter a factory line that has a different arrangement than liver cord/sinusoid arrangement of the liver lobule. The organelles in the cell have to be spatially positioned and connected for the metabolic and biochemical processes to take place. The exact mechanisms and organelles responsible for the processwill be discused in detail in future modules and are represented here as organelles with cogs situated within the cell cytoplasm. The metabolic substrates enter the cell (light orange arrow) and are processed by the dark blue organelle, then exported to the light green organelle and so on, until the final step where a by product called bile (lime green arrow) is transported to the bile canaliculus ( green sphere between two cells) and the primary product is exported (red arrow) into the portal circulation (maroon).Untitled Document13062b.4k08.8 Davidoff MD D avidoff art|
The physical location of structures described above allows the component parts to hand off metabolic products from one to the other, as one might imagine happens in the factory line typified for example in production of a motor car. This was one of Henry Fords contributions to our factory industry – the factory line where each worker performed his or her repetitive function and then passed on the product to the next in line, who, in turn adds another component, screws, and tightens. As the product is passed on in the line, it evolves in an efficient manner mostly because of the spatial arrangement of the workers. It is almost as if Henry Ford understood liver structure and function when he came up with the idea. Biology has perfected these processes over thousands of years and has a lot more to teach us if we could only look, comprehend, and apply them to our macroscopic world.
When a chemical message needs to be communicated, the spatial relationship between the giver and receiver has to be optimised . Examples include messages between two nerves, or between a nerve and a muscle, between a hormone and a receptor, or between a drug and a receptor. The diagram of the synapse below, shows the spatial relationship between the afferent (presynaptic) nerve and the efferent (postsynaptic) nerve. In this instance the two cells at the site of the synapse are quite different in their configuration. The presynaptic nerve is designed to optimise the release of the chemical message, the postsynaptic is designed and positioned to receive the chemical and its message. The space between them has to be appropriately sized and positioned to enable the message to pass through.
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Synaptic Cleft Requiring Chemical Transmitters eg Acetylcholine to Transmit Impulse Across Nerve Junctions
|72046.800 mitochondria transmitter vesicles presynaptic terminal post synaptic terminal soma of neuron synaptic cleft acetyl choline norepinephrine dopamine serotonin forces chemical energy function principles Davidoff art Davidoff drawing Davidoff MD|
At a macroscpic level the body houses the organs in cavities and spaces
Cavities of the body
The cranial cavity, is the space formed inside the bony skull that houses the brain. The capacity of an adult human cranial cavity is 1,200-1,700ccs. The cranial cavity in the adult is a non compliant vault – that fits the brain prerfectly with little wiggle room. Aside from the small cushion effect of the meninges and surrounding cerebrospinal fluid the brain comes into close physical contact with the vault. As a relatively soft structure the brain requires this spatial arrangement to protect it.
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Cranial Cavity Housing the Brain
|The cranial cavity in the adult is a non compliant vault – that fits the brain prerfectly with little wiggle room. The MRI above is a sagittal projection, and shows the small space between the brain and the skull that is filled with memninges and cerebrospinal fluid.71053.800 brain normal skull cranial cavity spinal cord cerebellum MRI T1 weighted normal anatomy Courtesy Ashley Davidoff MD copyright 2008|
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Spaces in the Cranial Cavity
The cranial cavity is divided into smaller spaces called the anterior, middle and posterior fossa each housing separate parts of the brain.
|48720c01 brain cerebrum cerebral skull anterior cranial fossa middle cranial fossa posterior cranial fossa space position protection bone skull anatomy applied biology TCV|
Since space is limited in the brain space occupation by tumors, blood or edema can affect the patient significantly, sometimes even when small. In the following example a large benign mass called a meningioma is demonstrated. The tumor is characteristically grows slowwly over a number of years, progressively taking up the space of normal brain. As it grows it will also start to push on the brain and may if left untreated push the brain down into the foramen magnum which represents the largest hole in the skull and therefore the line of least resistance. The shift can cause pressure on vital centres of the brain and consequently may result in death if left untreated. This complication in which the brain is pushed downward into the foramen magnum as a result of space occupation is called coning.
423078c meningioma Courtes James Donnelly MD
In the following example, a small metastasis from a renal cell carcinoma occupies little space, but it does cause significant edema in the brain, and it is the edema, rather than the tumor itself that does harm by occupying space.
77300c bilateral RCC mets to lung hemorrhagic mets to brain mass edema mass effect midline shift edema MRI T2 weighted Courtesy Ashley DAvidoff MD copyright 2008
77300c01 bilateral RCC mets to lung hemorrhagic mets to brain mass edema mass effect midline shift edema MRI T2 weighted Courtesy Ashley DAvidoff MD copyright 2008
Non Critical Space Occupation
In the following example a benign bony tumor on the outside of the skull. occupies space but does no harm.
29107c 44F one occiput occipital bone fx mass ossified dx osteoma neoplasm benign CTscan Davidoff MD
The Chest Cavity
The chest cavity or thoracic cavity, is the space formed inside the rib cage that houses the heart, lungs and mediastinum. It is connected to the neck at the thoracic inlet, and separated from the abdominal cavity by the diaphragm. The major organs that lie within the chest cavity include the heart with great vessels, lungs with airways, and the esophagus. The spinal cord lies posteriorly in its own chamber within the vertebral column and is not traditionally considered part of the thoracic cavity.
The lungs with pleura and airways take up the largest space. The lung at full inspiration can take up to 6 litres of air.
45770b02c.jpg chest lungs fx normal chest CT anatomy Courtesy Ashley Davidoff MD Davidoff
The lungs surround the heart and are surrounded by by two layers of pleura that are adhered together by a thin layer of fluid.
|32634b10 32634b11b01 The surface of the lung is magnified in the following two images. Fig 1a shows the pink visceral pleura, the yellow pleural space, and the green parietal pleura. Fig 1b shows the costophrenic sulcus where the visceral pleura is absent and two layers of parietal pleura face each other. Courtesy Ashley Davidoff MD . 32634b11b01 32634b11b|
When we inspire, the muscles of the rib cage move out, pull on the outside layer of the pleura, (parietal pleura) which in turn pulls on the inner layer of visceral pleura, which in turn pulls on the lungs, which then expand and pull in fresh air. The fluid layer in between the two layers of pleura enable the two smooth layers of pleura to adhere together by capillary force in the same way that two wet pieces of smooth glass are inseparable by virtue of the same capillary forces.
When excessive fluid accumulates in the pleural space it pushes on the lung and causes compression of the normal lung since there is only a limited amount of space in the thoracic cavity. At some stage, the area that is compressed collapese and becomes airless, and therefore non functional. Although this is not a life threatening situation it may cause the patient to become short of breath. In the case of the tension pneumothorax described above, the pressure that accumulates in the pleural space is higher, and for this reason tension pneumothorax can be lethal. In both instances however the underlying concept is the same – ie space occupation.
|74238c01 88 year old male bilateral complex effusions pleura pleural space atelecactasis space occupation normal 3D volume rendering CTscan Courtey Ashley DAvidoff MD|
pleural effusions 74243b01 74242 74242b01 88 year old male complex effusions pleura pleural space thickened pleura thickening unilateral atelecactasis pleural calcification calcified CTscan Courtey Ashley DAvidoff MD
There are many instances of disease and destruction caused by space occupation but another one that comes to mind in the chest is acute coronary thrombosis. The coronary arteries are basically tubes that deliver blood with life sustaining oxygen to the heart muscle. If these become blocked with thrombus, the space normally occupied by flowing blood is obstructed with thrombus and flow threfore cannot occur commonly resulting in death of the myocardium, and sometimes death of the patient.
78387c breast skin heart pericardium invasion space occupation prosthesis CTscan Courtesy Ashley Davidoff MD
The abdominal cavity, is the space formed by a diaphragm of muscle above and a diaphragm of pelvic muscle below, and usually includes the pelvic cavity. It mostly houses organs of the gastrointestinal system, genitourinary system, but components of the cardiovascular system, nervous system, endocrine system, reticuloendothelial system, and musculoskeletal system are present to enable the abdominal cavity to connect with the thorax and all the other parts of ther body.
The major organs that lie within the abdominal cavity include the liver, spleen, adrenals, kidneys, pancreas, gastrointestinal tract, uterus ovaries and prostate and bladder.
Unlike the cranial cavity and the thoracic cavity, there is little bony protection. Most of the protection comes from more elastic and pliable abdominal musculature.
The spinal cord lies posteriorly in its own chamber within the vertebral column and is not traditionally considered part of the abdominal cavity.
The distinction and border between the abdominal cavity proper and the pelvic cavity is ill defined and vague, and for the sake of discussion it is considered in this text as both part of the abdominal cavity, though a specific subsection of this text will discuss the pelvic cavity separately as well.
Spaces in the Abdomen
The abdominal cavity is divided into the peritoneal cavity and the retroperitoneal cavity. Each of these is further divided and the detail will be expanded in later modules. The peritoneal cavity is the larger of the two and it contains almost all the abdominal organs. The reroperitoneal space contains only the kidneys, ureters, the larger tributaries of the neurovascular system like the aorta, inferior vena cava, nerves and lymphatic duct.
The accumulation of fluid or disease processes in the peritoneal cavity is not as life threatening as space occupation described in the chest. Accumulation of fluid in the abdomen is called ascites and is seen in many conditions. In the patient shown below the fluid accumulation is due cancer deposits on the peritoneum which is the abdominal lining.
77370c01 abdomen abdominal cavity ascites ovarian cancer omentum omental cake granulomatous liver disease mass malignant ascites Courtesy Ashley Davidoff MD copyright 2008
The pelvic cavity, is the space formed by a diaphragm of pelvic muscle below and an open roof above where the distinction between the pelvic cavity and abdominal cavity is vague but best defined by the region of the bony pelvis, including the iliac crests and lumbosacral joint and sacral promontory and the pubic symphisis. It houses the uterus, ovaries and Fallopian tubes, the bladder and distal ureters, prostate vasa deferentia, sigmoid colon and rectum. Components of the cardiovascular system, nervous system, endocrine system, reticuloendothelial system, and musculoskeletal system are present to enable the pelvic cavity to connect with all the other parts of ther body.
Similar to the cranial cavity and the thoracic cavity, there is prominent bony protection by the pelvic bones.
71198b01 pelvis bone iliac crest pubic symphisis hip ischial tuberosity pubic bone normal anatomy CTscan 3D Courtesy Ashley Davidoff MD copyright 2008
Spaces in the Pelvis
Most of the pelvic cavity is part of the peritoneal cavity but the retroperitoneum does extend down into the pelvic cavity and thre is also a space called the extraperitoneal space.
Diseases and fluid accumulation can occupy space in the pelvis in the same way as they may in the abdominal cavity. Similarly the space occupation is not uually immedietely and emergently life threatening. The cul de sac is a space that in the female lies between the rectum and uterus, and in the male lies between the bladder and the rectum. It is the most posterior space in the abdominal-pelvic cavity, and therefore by default is the the first space to accumulate fluid when the patient is imaged in the supine projection.
Space occupation is sometimes (though rarely) a welcoming event. In the case of the pelvis, the gravid uterus occupies space in the pelvis and although progressively uncomfortable, the final result is not only desirable but also restoresthe space to its usual owners.
46704 abdomen pregnancy fetus baby head brain lungs amniotic cavity amniotic fluid normal anatomy physiology MRI T2 weighted Davidoff MD
There are other spaces and compartments in the body that do not fit in to the confines of the larger spaces described above. These include the space of the spinal column, prevertebral spaces, compartments of the muscles bones and joints, the oral cavity, spaces of the neck, the vagina, the external space occupied by the penis and testes, and of course all the microscopic spaces of the tissues, cells and molecules that have a world of their own.
of 57927.800 houses town organization position efficiency Muizenberg Cape South Africa Davidoff photography
When one extends the concept of space beyond the body and into homes and towns, cities and countries and then of course planets and the universe – the universality of the principles unfold. When all is in order – and space is well used, and apportioned then peace and harmony exist. When on the other hand aggressive space occupation occurs the stories of disorder, disease, death, and misery are told in our history.