Anterior Abdominal Wall.pdf

Gastrointestinal System The Abdominal Walls Welcome to the start of a series of lectures on the Abdomen and Pelvis. We will start by looking at the abdominal walls, most notably the anterior abdominal wall.  Learning Outcomes After this lecture y...

Gastrointestinal System The Abdominal Walls Welcome to the start of a series of lectures on the Abdomen and Pelvis. We will start by looking at the abdominal walls, most notably the anterior abdominal wall.  Learning Outcomes After this lecture you should be able to: Define the boundaries of the abdomen and pelvis and be able to name the four dividing lines and nine subdivisions of the abdomen Differentiate abdominal cavity from peritoneal cavity Describe the fascial layers of the anterior abdominal wall Identify the three flat abdominal muscles and the rectus abdominis and its sheath; list their functions and innervations List the layers of the rectus sheath, and know how these differ above and below the umbilicus Describe the nerve supply of the anterior abdominal wall List the arterial supply and venous and lymphatic drainage of the anterior abdominal wall These are all the learning outcomes for the lecture.  Gastrointestinal System The Abdominal Walls 1. Boundaries and Subdivisions 2. Fascial Layers 3. Muscles of the Anterior Abdominal Wall 4. Neurovasculature The lecture is divided into 4 parts. 1. Boundaries and Subdivisions 2. Fascial Layers 3. Muscles of the Anterior Abdominal Wall 4. Neurovasculature However, we’ll deal with these one by one.  Gastrointestinal System The Abdominal Walls Part 1: Boundaries and Subdivisions In this section, we will discuss the boundaries and subdivisions of the abdomen.  Learning Outcomes After this lecture you should be able to: Define the boundaries of the abdomen and pelvis and be able to name the four dividing lines and nine subdivisions of the abdomen Differentiate abdominal cavity from peritoneal cavity Describe the fascial layers of the anterior abdominal wall Identify the three flat abdominal muscles and the rectus abdominis and its sheath; list their functions and innervations List the layers of the rectus sheath, and know how these differ above and below the umbilicus Describe the nerve supply of the anterior abdominal wall List the arterial supply and venous and lymphatic drainage of the anterior abdominal wall The learning outcomes for this part of the lecture are that afterwards you should be able to Define the boundaries of the abdomen and pelvis and be able to name the four dividing lines and nine subdivisions of the abdomen. The remaining outcomes will be dealt with in subsequent sections of the lecture. Boundaries of the Abdominal Cavity The abdominal cavity is bounded by: Roof Thorax diaphragm Walls anterior and posterior muscles Abdomen Floor Pelvic inlet? Or Pelvis Pelvic floor? Perineum The torso or trunk is divided into the chest or thorax superiorly, the abdomen, the pelvis and finally the perineum inferiorly. The abdomen is the region below the thorax and above the “true” pelvis. It is a space which is bounded by a roof, walls and a floor.  Roof of the Abdominal Cavity The abdominal cavity is bounded by: Roof diaphragm Walls anterior and posterior muscles Floor Pelvic inlet? Or Pelvic floor? The roof is bounded by the diaphragm, which is a bi-domed muscle which arches upwards into the thoracic cavity. This means that part of the abdominal cavity lies behind the ribcage, and is therefore protected by it.  Walls of the Abdominal Cavity The abdominal cavity is bounded by: Roof diaphragm Walls anterior and posterior muscles Floor Pelvic inlet? Or Pelvic floor? The walls are formed by muscle posteriorly, laterally and anteriorly and enclose the cavity. The lateral muscles have flat tendons which run anteriorly, hence they are referred to as ‘anterior’ muscles.  Floor of the Abdominal Cavity The abdominal cavity is bounded by: Roof diaphragm Walls Pelvic inlet anterior and posterior muscles Floor Pelvic floor Pelvic inlet? Or Pelvic floor? There is however ambiguity over whether the floor of the abdomen should classified as the pelvic inlet or the pelvic floor muscles. Since the pelvis lies below the abdomen, technically the abdomen ends at the level of the pelvic inlet. However, there is no physical barrier here, so abdominal content can descend beyond the pelvic inlet into a region known as the ”true” pelvis.  Floor of the Abdominal Cavity Pelvic inlet Pelvic floor Technically, the pelvis ends at the pelvic outlet, which is marked by the lowest point on the bones of the pelvis. However, half way down the pelvis there is another diaphragm of sorts. This time, the diaphragm sags downwards towards the pelvic outlet. It is called the pelvic floor. Since the abdominal content is only limited inferiorly by the pelvic floor, it is better to talk about an abdomino-pelvic cavity, rather than the abdomen in isolation. Beneath the pelvic floor is the region of the perineum. Boundaries of the Abdominal Cavity 11th and 12th rib Inguinal Costal margin ligament Lumbar vertebra Iliac fossa The bony boundaries of the abdomen posteriorly are the 5 lumbar vertebrae and the pair of 12th ribs. The 12th rib gives rise to the attachment of the diaphragm. The diaphragm is also attached to the tip of the 11th rib, and then the lower part of the chest wall anteriorly (indicated by the green line). This is known as the costal margin. In the inferior part of the abdomen laterally are the large plates of the hip (or pelvic) bones. These are called the iliac fossae. Although these are part of the pelvic bones, clearly they are not in the pelvis as they are above the pelvic inlet. Hence, they are sometimes referred to as the ‘false’ pelvis. Attaching between two parts of the hip bones anteriorly is the inguinal ligament. This attaches to the anterior superior iliac spine (or ASIS) laterally, and the pubic tubercle medially. This defines the most inferior part of the anterior abdominal wall, since below this lies the lower limb. The remaining boundaries of the abdomen are bounded by muscle, and we will deal with those in due course.  Surface Anatomy of the Abdomen Linea alba Linea semilunaris The anterior boundaries of the abdomen are clearly visible on most subjects. Above, the inverted V-shape of the costal margin, and below the V-shape of the line of the groin, marking the position of the inguinal ligament. These markings would suggest a relatively small space occupied by the abdomen, but this belittles the true the size of the space since superiorly it is bounded by the diaphragm and inferiorly by the pelvic floor. The arrangement of muscles on the anterior abdominal wall give obvious clues on the surface of lean individuals. In the midline, where the muscles meet, there is a ridge called the linea alba (white line). This line is relatively avascular (hence white), and hence is a good place to make emergency abdominal incisions. In pregnant females, this white line becomes pigmented and is then known as the linea nigra (black line). This is caused by the production of melanocyte-stimulating hormone by the placenta. More laterally, there is a slightly curved line, the linea semilunaris.  Quadrants of the Abdomen Paraumbilical plane Median plane It is useful to divide the abdomen up into sections, both for descriptive purposes of locating the internal organs, and also as a basis of mapping out pain in cases of disease. One simple way of doing this is to draw a horizontal and vertical line through the umbilicus, dividing the abdomen into quadrants. However, this is only of limited use.  Subdivisions of the Abdomen Lateral lines Transpyloric plane Subcostal plane Trans- tubercular plane A better way is to use two horizontal lines and two vertical lines, which provide 9 segments. The vertical are mid-clavicular or mid-inguinal lines (that is they cross the mid-point of the clavicle and inguinal ligament). However, on the abdomen these are rather called the ‘lateral lines’ of the abdomen. For the upper of the two horizontal lines, some choose to use a line which passes horizontally between the lowest aspect of the chest wall, and this is the subcostal plane. However, it is better to use the transpyloric plane as this divides the segments more evenly. The transpyloric plane supposedly passes through the pylorus of the stomach. This organ however is invisible on the patient being examined and thus has to be estimated. This is a hand’s-breadth below the body of the sternum. The lower horizontal line is the trans-tubercular plane, a plane between the two tubercles of the iliac crest.  Regions of the Abdomen RH E LH RL U LL RI SP LI The middle segment is the umbilical region for obvious reasons. Either side of this are the right and left lumbar regions. Above centrally is the epigastric region and to each side of this are the right and left hypochondriac regions. Hypo means below and ‘chondro’ relates to the cartilages of the chest wall. Hence these regions are protected by the ribcage. Centrally below is the suprapubic region as it lies above the pubic bone of the pelvis. This region used to be called the hypogastric region and you may still find that in older textbooks. Either side of this are the left and right inguinal or iliac regions.  Gastrointestinal System The Abdominal Walls Part 2: Fascial Layers In this part of the lecture on the abdominal walls, we will consider the fascial layers of the abdomen.  Learning Outcomes After this lecture you should be able to: Define the boundaries of the abdomen and pelvis and be able to name the four dividing lines and nine subdivisions of the abdomen Differentiate abdominal cavity from peritoneal cavity Describe the fascial layers of the anterior abdominal wall Identify the three flat abdominal muscles and the rectus abdominis and its sheath; list their functions and innervations List the layers of the rectus sheath, and know how these differ above and below the umbilicus Describe the nerve supply of the anterior abdominal wall List the arterial supply and venous and lymphatic drainage of the anterior abdominal wall The learning outcomes for this part of the lecture are that you should be able to; Differentiate abdominal cavity from peritoneal cavity Describe the fascial layers of the anterior abdominal wall  Abdominal Wall Muscles Back muscles Posterior abdominal wall muscles Anterior abdominal wall muscles Rectus abdominis The abdomen is surrounded by muscle. The anterior abdominal wall has a pair of muscles which run vertically - these are the rectus abdominis muscles. Laterally, there are three layers of muscle (external oblique, internal oblique, and transversus abdominis). Posteriorly, there are the pre-vertebral muscles (quadratus lumborum and psoas major). Behind those are the back muscles, most notably erector spinae, but those are not part of the abdomen.  General Plan of the Abdomen Internally, there is a layer of deep fascia inside the layers of muscle and this is known as endo-abdominal fascia, and this lines the entire abdomino-pelvic cavity. Its precise name changes depending upon its location (e.g. infra-diaphragmatic, transversalis or pelvic fasciae). Lining the body wall and endo-abdominal fascia is a layer of serous membrane called parietal peritoneum. This layer evaginates to surround the abdominal organs. This forms the visceral peritoneum and the space between the visceral and parietal layers is filled with fluid. This serves to lubricate the abdominal contents as they are mostly highly mobile. The amount of space shown in this schematic representation is greatly exaggerated, as of course the abdomen is full of organs which fill up this space. The abdominal cavity is narrow due to the inward curvature of the lumbar vertebral column posteriorly, but is a large cavity that extends down into the pelvis below, and runs above under the diaphragm as high as the 4th rib on the right and 5th intercostal space on the left.  Layers of the Abdomen Here is a cross-section through the abdomen. The anterior aspect is at the top of the slide. We can see several key features of the abdomen here. Firstly, you can see how thin the skin over the abdomen is – it is approximately 1-2mm only although it varies between individuals.  Superficial Layer of the Abdomen In contrast, the superficial fascia is thick, though it too is highly variable. Deep fascia is thin if not entirely absent. Deep fascia is inexpansile, and so would hinder the movements of the abdomen during breathing, coughing and defaecation, where the wall of the abdomen has to adjust to perform these functions.  Muscular Layer of the Abdomen The abdomen is surrounded by muscle. The muscle of the posterior part of the abdomen is thick, whilst anteriorly and laterally it is thin. The muscle that is unshaded at the bottom of the cross-section is not abdominal muscle. It is instead muscle of the back. Deep to the muscle lies an inner layer of deep fascia, the endo-abdominal fascia, but internal to that is another layer of loose fascia called extra-peritoneal fascia or extraperitoneal fat.  Abdominal and Peritoneal Cavities The abdominal cavity lies inside the endo-abdominal fasciae. It is narrow due to the inward curvature of the lumbar vertebral column posteriorly but is a large cavity that extends down into the true pelvis below and runs above under the diaphragm. The abdominal contents are highly mobile, and to facilitate this, they are mostly wrapped in a serous membrane, the visceral peritoneum. The visceral peritoneum glides on the parietal peritoneum that lines the inside of the abdominal boundaries. Between the visceral and parietal layers is a cavity called the peritoneal cavity. This cavity lies within the abdominal cavity.  Peritoneal Cavity The peritoneal cavity is in reality a small space that sits around the some of the organs. The space contains peritoneal fluid. The amount of this fluid normally is between 5mL and 20mL normally, but may be much more in pathological conditions, where it is termed ascites.  Fascia of the Abdomen Scarpa’s Camper’s fascia fascia Fascia lata Let’s return to the fascia of the abdomen, as it is rather unusual! It has TWO layers of superficial fascia (at least in the lower abdominal wall), and almost no deep fascia to speak of. The outer fatty layer of superficial fascia is Camper’s fascia. It contains fat and superficial veins, together with cutaneous nerves. It is continuous with the superficial fascia of the lower limb. Here it is shown again on this illustration (on the right). The inner layer of superficial fascia is Scarpa’s fascia. It is membranous in appearance, and is important in limiting the spread of infection, and more importantly limits the spread of fluid in the lower abdominal wall. It binds to the fascia lata of the thigh below the inguinal ligament.  Internal Fascia of the Abdomen Although there is no deep fascia under Scarpa’s fascia, there is a deep fascia inside the abdominal wall, forming its deepest layer. The deep fascia here is called transversalis fascia since it lies deep to the transversus abdominis muscle. But sandwiched between this and the parietal peritoneum, there is a layer of loose connective tissue full of extraperitoneal fat. This layer as well as being a fat store, also serves to bind the peritoneum to the abdominal walls and is known also as endo- abdominal fascia.  Superficial Veins of the Abdomen The superficial veins of the abdomen lie within the Camper’s fascia, and are usually small and unremarkable. The patient shown here has enlarged veins. The veins emanate from the region of the umbilicus (para-umbilical) and drain either upwards towards the chest or downwards towards the top of the thigh. The upwardly-directed veins are called the thoraco-epigastric or thoraco-abdominal veins. These connect to veins around the breast called the lateral thoracic veins. In turn these drain into the axillary veins in the armpit (axilla). The lower veins are the superficial epigastric, which together with the superficial circumflex iliac veins (not labelled) drain to join the femoral vein at the top of the thigh.  Caput Medusae If there is a problem with the deep venous drainage, then these superficial veins may become engorged with blood, and become visible. When this is the case, they are called “caput medusae” (Medusa’s head). For the classical scholars amongst you, you may recall she desecrated Athena's temple by canoodling there with Poseidon. He was probably taken by her beautiful hair. Outraged, Athena turned Medusa's hair into living snakes. The enlargement of the veins is said to resemble this. This often happens for example in liver disease.  Gastrointestinal System The Abdominal Walls Part 3: Muscles of the Anterior Abdominal Wall We shall now consider the muscles of the anterior abdominal wall.  Learning Objectives After this lecture you should be able to: Define the boundaries of the abdomen and pelvis and be able to name the four dividing lines and nine subdivisions of the abdomen Differentiate abdominal cavity from peritoneal cavity Describe the fascial layers of the anterior abdominal wall Identify the three flat abdominal muscles and the rectus abdominis and its sheath; list their functions and innervations List the layers of the rectus sheath, and know how these differ above and below the umbilicus Describe the nerve supply of the anterior abdominal wall List the arterial supply and venous and lymphatic drainage of the anterior abdominal wall The learning outcomes for this part of the lecture are that you should be able to; Identify the three flat abdominal muscles and the rectus abdominis and its sheath; list their functions and innervations List the layers of the rectus sheath, and know how these differ above and below the umbilicus The other outcomes will be dealt with in the final part of the lecture next time.  Rectus Abdominis The anterior abdominal wall has three muscle layers on each side, but also a pair of rectus abdominis muscles. Let’s consider those muscles first. They are attached to the anterior aspect of the rib cage above and the pubic bone below. Each rectus abdominis muscle is a multi-bellied muscle with tendinous intersections. The term ’rectus’ means straight in Latin, so this muscle is running vertically straight down across the anterior abdominal wall. The rectus abdominis is a flexor of the trunk, and a depressor of the ribcage. The region between the muscles is the linea alba and the lateral boundary of each muscle forms the linea semilunaris on each side. These are the muscles that give rise to the 6-pack (at least in some of us!). There are then 3 muscles whose bellies lie laterally and whose tendons cross the rectus abdominis forming a sheath around it attaching medially to the linea alba.  External Oblique Abdominis The outer of these 3 muscles is the external oblique abdominis. The fibres of this muscle layer run forwards and downwards. The external oblique abdominis attaches to the lower ribs (usually ribs 5-12). The posterior part of the muscle attaches inferiorly into the anterior part of the iliac crest, that is the top of the hip bone. Its tendon is an aponeurosis that attaches to the linea alba in the midline and the pubic tubercle and pubic crest inferiorly. At the linea alba, it meets the aponeurosis of the muscle on the opposite side, with which it forms a raphe. The lower part of the muscle folds back on itself (in a U-shape) to form the inguinal ligament. Action of External Oblique Abdominis Each muscle will cause the trunk to rotate to the opposite side, flexing the trunk at the same time. In other words, the right external oblique pulls the right side of the chest downwards towards the left hip. The left external oblique pulls the left trunk down towards the right hip. When both external oblique muscles contract together they pull the trunk forward (flexion of the trunk).  Internal Oblique Abdominis The middle layer is the internal oblique abdominis. The fibres of this layer run backwards and downwards. The internal oblique abdominis attaches to the lateral half of the inguinal ligament, iliac crest, and thoracolumbar fascia, and inserts into the last four ribs (9-12) and the linea alba. The inferior part of the muscle inserts into the pubic crest. One of the numerous functions of this muscle is the stabilisation of the lumbar spine, through its connection with the thoracolumbar fascia. The internal obliques are ipsilateral rotators of the trunk when the pelvis is anchored. To turn the trunk to the left, the left internal oblique contracts with the contralateral (right) external oblique. When both internal obliques and both external obliques contract together, the result is flexion of the trunk.  Transversus Abdominis The deepest layer is the transversus abdominis muscle. This originates from the internal surfaces of the bones and cartilages forming the thoracic outlet and iliac crest. It also arises from the lateral third of inguinal ligament, as well as from the thoracolumbar fascia. It attaches medially along with internal and external oblique to form the linea alba. The aponeurotic tendon of the lower part of the muscle fuses with that of internal oblique abdominis to form the conjoint tendon, and this inserts into the pubic crest. The transversus abdominis is primarily involved in abdominal compression, which occurs during forced expiration, but is also involved in stabilisation of the back via the tension it gives to the thoracolumbar fascia. It may also be used to aid defaecation, micturition (urination) and parturition (child-birth).  Rectus Sheath The aponeurotic muscle tendons, and the deep intra-abdominal fascia (transversalis fascia), form a sheath around the rectus abdominis muscle. The aponeuroses fuse at the lateral border of the rectus abdominis, and this forms the linea semilunaris. The aponeuroses then cross the rectus abdominis to form the rectus sheath, and this has anterior and posterior layers. In the image on the left we can see the external oblique aponeurosis passing anterior to rectus abdominis. The deep muscle, transversus abdominis has its aponeurosis passing behind. You can see that on the illustration on the right by looking through the window created, and what is more in this cadaveric image on the left. However, the rectus sheath is thin in the lower third. Here, it is only formed by the transversalis fascia, and this is because the aponeurotic tendons have shifted to the anterior layer of the rectus sheath. The junction between this part and the tendinous part above, is known as the arcuate line. This is indicated by the pointer. We can see the arcuate line also in this diagram. Some of the aponeurotic tendons and transversalis fascia form the posterior layer above the arcuate line, but below there is only the transversalis fascia.  Rectus Sheath Sections The anterior layer of the rectus sheath above the level of the umbilicus, is comprised of external oblique and half of internal oblique (it splits). The remainder of internal oblique, together with transversus abdominis and transversalis fascia, lies posteriorly. In the lower abdomen, the aponeurotic sheets move anteriorly, leaving only the transversalis fascia posteriorly. This shift of collagen fibres is sometimes seen as a distinct line at the back of the sheath, and is known as the arcuate line. Interestingly, the tendinous intersections adhere to the anterior layer of the rectus sheath, but not to the posterior layer.  Arcuate Line Arcuate line Inferior epigastric artery Here we can see a diagram of the posterior aspect of the rectus abdominis muscles and the arcuate line. One reason for the existence of the arcuate line is to permit a blood vessel to gain access to the rectus abdominus muscle. This is the inferior epigastric artery. Its accompanying veins also travel with it. The vessels only have to pierce the thin transversalis fascia. The artery and vein lie in front of the parietal peritoneum, and their presence creates a fold as viewed from inside the abdomen. This is erroneously called the lateral umbilical fold. Erroneous as it doesn’t connect to the umbilicus. Medial to that is the medial umbilical fold due to the presence of the obliterated umbilical artery. In the fetus, this artery takes blood from pelvis and delivers it to the maternal placenta. The final fold is the median umbilical fold, created by the median umbilical ligament, which is the remnant of the urachus. The urachus is a tube which connects the fetal bladder to the umbilicus. After birth, this fibroses to become a ligament.  Gastrointestinal System The Abdominal Walls Part 4: Neurovasculature So we have now arrived at the final section of this lecture on the abdominal walls. In this part we shall look at the neurovasculature of the anterior abdominal wall.  Learning Outcomes After this lecture you should be able to: Define the boundaries of the abdomen and pelvis and be able to name the four dividing lines and nine subdivisions of the abdomen Differentiate abdominal cavity from peritoneal cavity Describe the fascial layers of the anterior abdominal wall Identify the three flat abdominal muscles and the rectus abdominis and its sheath; list their functions and innervations List the layers of the rectus sheath, and know how these differ above and below the umbilicus Describe the nerve supply of the anterior abdominal wall List the arterial supply and venous and lymphatic drainage of the anterior abdominal wall The outcomes for this section are that you should be able to; Describe the nerve supply of the anterior abdominal wall, and be able to identify its dermatomes List the arterial supply and venous and lymphatic drainage of the anterior abdominal wall  Cutaneous Nerves The cutaneous nerve supply of the abdominal wall is segmental from T7 to L1. At each level there are posterior branches from the posterior ramus of the spinal nerve, whilst the anterior ramus gives lateral and anterior branches. Together these give a continuous band of sensation in a dermatome running obliquely over the abdominal wall. Of particular note is that the umbilicus receives the T10 dermatome. Since the T7 to T12 nerves are derived from the chest (the thorax), on the abdominal wall they should be called thoracoabdominal nerves. T12 is also called the subcostal nerve. The lowest part of the wall towards the groin is supplied by the ilioinguinal and iliohypogastric nerves, which both come from L1. Nerve Supply of Abdominal Muscles The anterior abdominal muscles are also supplied segmentally by the thoraco-abdominal nerves. The rectus abdominis and external oblique abdominis muscle lack a supply from L1. The thoracoabdominal nerves run around the trunk, sandwiched between the internal oblique abdominis and transversus abdominis muscles. They are accompanied by the segmental blood vessels. In dissection, it is often difficult to find the plane between these two muscles, but the presence of the neurovascular bundle is the key. The anterior abdominal muscles may contract in response to tactile stimuli, or as a result of visceral or abdominal cavity disturbance. The nerves that are sensory to the parietal peritoneum are also motor to anterior abdominal wall muscles. This reflex is protective. The contracted abdominal wall provides resistance to pressure, and also reduces the movements that may otherwise permit spread of infection around the abdominal cavity. This is called the "guarding reflex“. The abdominal tactile reflex is obtained by firmly stroking the abdominal skin. The normal result is contraction of the abdominal muscles. Abdominal tenderness spans a spectrum from mild tenderness to severe pain. “Rebound tenderness” occurs when the membrane that lines the abdominal cavity (the peritoneum) is irritated, inflamed, or infected (peritonitis). With peritonitis, the patient will often tense the abdominal- wall muscles when the abdomen is touched by the examiner. Point tenderness is a more general term which defines tenderness in a particular location.  Blood Supply of Abdominal Wall Internal thoracic artery Posterior intercostal arteries Lumbar arteries SE Superior epigastric artery IE Inferior epigastric artery Veins follow the arteries The abdominal walls are supplied by a variety of branches. Firstly, at the anterior wall there is a descending artery which is a continuation of the internal thoracic artery of the chest. As this artery crosses the costal margin, it becomes known as the superior epigastric artery. At the level of the umbilicus (approximately), this artery anastomoses with an ascending artery from the external iliac; this is the inferior epigastric artery. These ascending and descending arteries are the major contribution to the blood supply to the anterior abdominal wall. Secondly there are paired segmental branches; inferior phrenic arteries that supply the diaphragm and 4 pairs of lumbar arteries that supply the posterior musculature. Lastly, at the lateral wall, there is a small contribution from the intercostal arteries of the chest wall. These leave the costal margin to become thoraco-abdominal arteries. The veins essentially follow these arteries, and hence do not need to be committed to memory. Of course, we have previously seen that there is also a superficial set of veins, and we will return to them in a later lecture.  Lymphatics of the Abdomen There are also two sets of lymphatics, a superficial set and a deep set. The superficial lymphatics drain away from the umbilicus. Above the umbilicus they drain upwards towards the armpit. Here they pierce the deep fascia to joint lymph nodes located deeply within the armpit called axillary lymph nodes. The term axilla means armpit in Latin. Below the umbilicus, the lymph vessels drain downwards towards a set of lymph nodes located just below the inguinal ligament. These are the superficial inguinal nodes. In turn the efferent lymphatics from these nodes pierce the deep fascia at the top of the thigh to join the deep inguinal nodes. The lymphatic drainage of the abdomen follows the pattern of the arteries. From the deep inguinal nodes, the lymph vessels reach the aorta, but there are many lymph nodes en-route, including those alongside the aorta, which are the para-aortic nodes. Ultimately, the reach the cysterna chyli situated near the aortic opening in the diaphragm. From here, the lymph travels through the aortic opening via the thoracic duct and onwards to the left lymphovenous portal at the root of the neck.  Gastrointestinal System The Abdominal Walls We have now reached the end of this section on the neurovasculature, and indeed the entire set of lectures on the abdominal walls. We will return to discuss more details of the posterior abdominal wall later, as our focus here has been the anterior one. One aspect of the lower part of the abdominal wall has also been omitted, the inguinal region, and that is where we will turn our attention in the next lecture. I’ll look forward to you joining me there.