Cardiovascular System Anatomy & Embryology

Transcription

1 بسم رلاهللا Cardiovascular System Anatomy & Embryology Portal circulation: Portal vessel: a vessel or a vein running between two sets of capillaries, the portal vein of the liver starts from a set of capillaries in the wall of intestine and ends within the capillary sinus of capillaries. Each minute the liver receives 1/4 the cardiac output, approximately 1200 ml, 80% of the cardiac output enters the liver through the portal vein and 20% through the hepatic artery. Both types of the blood will mix inside the sinusoids of the liver. How the blood leaves the liver? Through 3 hepatic veins. The hepatic veins do not have a route outside the liver, they open directly into the inferior vena cava. The portal vein collects blood from the stomach, small & large intestines, pancreas, spleen and gallbladder then the blood enters the liver for detoxification and metabolism of products of digestion then the blood returns through the inferior vena cava to the systemic circulation. The portal vein begins behind the neck of pancreas by the union of splenic vein and the superior mesenteric vein. The superior mesenteric vein brings blood from the midgut. The inferior mesenteric vein brings blood from the hindgut.

2 The inferior mesenteric joins the splenic artery at its end. The portal vein receives blood from the stomach; right & left gastric veins, it also receives superior pancreatic rudimentary. The portal vein collects blood from most of the GI. The route of the portal vein is divided into: 1. Infraduodenal part: behind the neck of pancreas (the beginning of the vein), the IVC lies behind it. 2. Retroduodenal part: behind the first part of duodenum. 3. Supraduodenal part: runs through a fold of peritonium ( the lesser omentum). Between the portal vein and the first part of duodenum, there are the bile duct and the gastroduodenal artery ( a branch from hepatic artery). The lesser omentum: is a fold of peritoneum that extends from the liver to the stomach and the first part of duodenum, its free margin contains: the portal vein (posteriorly), the bile duct lies anterior to the portal vein and to the right (dextral) and the hepatic artery lies anterior to the portal vein and to the left. The IVC lies behind the epiploic foramen that lies behind the free margin of lesser omentum.

3 The portal vein is near the IVC, in other words the portal circulation is near the systemic circulation. Sometimes we need to connect the portal vein with the IVC "portosystemic anastomosis", we undergo this operation to patients with "portal hypertension" due to a liver disease which causes hypertension in the portal circulation and leads to hemorrhage for example "esophageal varices". Carcinoma of head of pancreas may lead to: 1. Obstructive jaundice: due to the closure of the bile duct that lies behind the head of pancreas. 2. Ascitis: accumulation of fluids in the abdomen due to the closure of portal vein which increases the pressure in the superior & inferior mesenteric veins. The portal vein begins as a vein (from capillaries) and ends as an artery porta hepatis; right & left branches. The right branch is shorter & wider than left branch. The cystic vein- if present- drains into the right branch of porta hepatis(portal vein). The left branch receives drainage from wrapped veins around ligamentum teres. In cholycystectomy, 1. ligation of cystic artery (in carotid triangle). 2. ligation of cystic vein. Commonly the cystic vein is absent because in most cases the gallbladder is attached to the liver so the venous drainage goes directly into it.

4 Caudate and quadrate lobes are considered functionally as a part of the left lobe so they are supplied by the left branch of portal vein and left branch of hepatic artery and also the bile goes into the left bile duct. Before the entrance of the left branch to the liver, it receives two ligaments: 1. Ligamentum teres which was the left umbilical vein that brings highly oxygenated blood from the placenta (in the free margin of falciform ligament). Falciform ligament extends from the abdominal wall to the liver. 2. Ligamentum venosum which was ductus venosus (a tube inside the liver). Around ligamentum teres there are paraumbilical veins that extend from the capillaries in the abdominal wall to the liver (connect the systemic circulation to the left branch of portal vein). Occlusion of the portal vein : increase the pressure in the portal vein and its tributaries in the liver as in liver cirrhosis (the soft parenchyma becomes hard fibrous tissue) which presses the veins running in the liver as a result it decreases the blood flow in it. The blood runs into alternative route to drain into IVC. This is called portosystemic anastomosis: collateral circulation which returns to the heart directly outside the liver. It is a dangerous situation, because the liver removes toxic substances and in this case they stay in the circulation.

5 Please refer to the sites of portosystemic anastomosis in the handout. Notes : Celiac trunk gives 3 branches: 1) Splenic artery. 2) Common hepatic artery. 3) Left gastric artery. In portal hypertension... the anastomosis in the submucosa of the lower end of esophagus enlarges to form a route -outside the liver- for blood return from portal vein to the left gastric vein then to the azygous vein which drains into SVC. The veins of anastomosis become tortuous and dilated "esophageal varieces" rupture bleeding the blood reaches the stomach then the patient vomits "light red blood". Rarely bleeding peptic ulcer causes vomiting of blood, because bleeding peptic ulcer occurs in the body of stomach then this blood reaches the intestine " black stool". Portal hypertension vomiting of light red blood (hematemesis) Portal hypertension is due to liver cirrhosis: alcoholic cirrhosis (common in Jordan) and bilharzia/ schistosomiasis (rare in Jordan). Treatment of portal hypertension is conservative and not treated surgically except in some cases.

6 Superior rectal vein as they ascend they become inferior mesenteric vein which joins splenic vein drains into portal vein. Middle and inferior rectal veins drain into internal iliac vein. If the anastomosis increases varicose veins in the submucosa of rectum and anal canal are called "piles or hemorrhoids" light red blood with feces. Hemorrhoids: are dilated tortuous veins that develop within the anus or develop outside the anus. Piles may be due to underlying genetic factors and not necessarily due to portal hypertension (50% of the cases not due to portal hypertension). We should examine the patient with proctoscope to exclude carcinoma of the rectum which presses the veins and they become dilated. Asking for liver function test to check if there is portal hypertension,should not be the first step to examine the piles. Caput medusae : in Greek mythology was a monster, generally described as having the face of hideous human female with living venomous snakes in place of hair{wikipedia}.europe countries have many cases of caput medusae as a result of alcoholic cirrhosis. Bare area of the liver: is in direct contact with the diaphragm, absent of peritoneum.

7 The anastomosis at the bare area of liver is between the capillaries of the liver (portal) and veins of the diaphragm (systemic). The ascending colon and descending colon are retroperitoneal (attached directly to the posterior abdominal wall). The anastomosis is between the colic veins that drains into the inferior mesentric vein and the lumbar veins of posterior abdominal wall (systemic). Extensive anastomosis on the posterior abdominal wall in bilharzia cases. The spleen is intraperitoneal and the evidence on this, when the spleen is enlarged, it descends and moves from the left to the right. The surface markening/ anatomy of the cardiac valves: To draw lines on the chest of the patient in order to determine the site of a valve depending on its anatomical position. The auscultation area: the area where we hear the sound of the valve, not necessarily to be at the anatomical position of the valve. Tricuspid is the widest valve but it is not the strongest valve. Mitral is the strongest valve because it has a large papillary muscle (due to the high pressure in left ventricle).

8 In pulmonary stenosis we can hear the murmur in the second left intercostal space near the sternum. In arterial hypertension the sound of the aortic valve is strong so we can hear it in the second right costal cartilage near the sternum (sternal angle). We can hear the sound of mitral stenosis (murmur) in the cardiac apex. Surface marking of the heart: Draw the 4 borders of the heart depending on its anatomical position. In normal sized heart, the upper border is oblique but is hidden by ascending aorta and pulmonary trunk. The line of the lower border of the heart is horizontal. To determine the left and right borders of the heart: On the right side; draw a slightly convex line to the right between the two points (3rd and 6th right costal cartilages), large convexity at the 4th costal cartilage. On the left side; draw a slightly convex line to the left between the two points (2nd left costal cartilage and the apex of the heart). If the left border is far away from the sternum 12cm rather than 9cm, there is enlargement of the left ventricle or the heart is devoted to the left due to tumor or other reasons. How to determine the fundus of the inflamed gallbladder (polycystitis)?

9 Put your finger on the tip of 9th costal cartilage and press it, then the patient will have pain "positive Murphy's sign". How we feel the tip of the 5th costal cartilage? At the site of convergence of two lines: transpyloric plane passes through L1 (handbreadth under xyphoid process) and the midclavicular line ( the outer border of rectus abdominis, when the patient bends towards forward, it becomes obvious). Embryology: The embryo in the first weeks is formed by the embryonic disc and two spaces: amniotic cavity (above) and yolk sac (below). The embryo in the second week is formed by bilaminar disc then it becomes trilaminar disc because the intraembryonic mesoderm is formed. So the three layers are ectoderm, endoderm and intraembryonic mesoderm between them. The superior view of the embryonic disc is formed by ectoderm(above), endoderm (below) and mesoderm in between except two sites that lack mesoderm: the buccopharyngeal membrane (cranial end) the future mouth and the cloacal membrane (caudal end) the future anus, at a certain stage these membranes break down and become openings. The ectoderm forms the neural tube: the future nervous system.the intraembryonic mesoderm has three parts: The paraxial mesoderm will form the somites : form the muscles of the body especially the vertebral muscles.

10 Intermediate mesoderm : form parts of the urogenital system, example the kidneys. The lateral plate mesoderm : has cavities that are united to form a space inside the embryonic disc called " intraembryonic coelom" which is the future pericardium,pleural cavity and the peritoneal cavity. We have two peritoneal cavities, two pleural cavities and pericardial cavity but due to "lateral folding" the cavities become closer to each other then they unite to form one plural cavity and one peritoneal cavity. Note: foldings are longitudinal (cephalocaudal) and lateral. Lateral folding and cephalocaudal folding lead to the formation of cylindered tube rather than a disc. The cranium of pericardium cavity: is a mass of mesoderm in the cranial end "septum transversum". The septum transversum forms the liver bud (the capsule and stroma of the liver) but the liver is endodermal in origin. The formation of cardiovascular system begins by blood islands. In the beginning, small capillaries are formed then layers are added from the surrounding mesoderm to form venules, arteriols, arteries and veins. Note:- body stalk becomes umbilical cord. -Yolk sac becomes the gut, it is pulled inside the embryo by cephalocaudal folding.

11 Three main vessels are formed: a. Vitelline vessels in the wall of yolk sac. b. Umbilical vessels in the chorion. c. Common cardial vessels from the body wall. In the beginning, the heart was formed of 2 primitive vessels then they join together as a result of lateral folding and form single primitive heart tube. Sinus venosus has two horns,each horn receives blood from three directions: the umbilical vein, common cardial vein and vitelline vein. Between the primitive atrium and the primitive ventricle there is single A-V canal. Bulbus cordis has two parts: conus (near the ventricle) and truncus arteriosus (the farthest). In the earliest stages, the atrium and sinus venosus lie outside the pericardial cavity but within septum transversus. At a certain time the heart tube grows faster than the pericardium then it pulls the atrium and sinus venosus inside it. Vitelline and umbilical veins must run through the liver to enter the percardium. Bulbo-ventricular chamber gives rise to both ventricles. It grows faster than the pericardium and fold on itself. The primitive ventricle only forms the rough part of the left ventricle (trabeculated part).

12 Smooth &rough parts of right ventricle and smooth part of the left ventricle are formed by bulbus cordis. The atrium is divided into left and right by a septum. The posterior smooth part of the right is from right horn of sinus venosus and called "sinus venerum". The anterior rough part of the right atrium is from primitive atrium. The rough part of the left atrium (the auricle) is from the primitive atrium. According to the smooth part of the left atrium, pulmonary vein develops from its wall then the pulmonary vein gives branches. After the growth of pulmonary vein, it is reabsorbed again to the wall forming the smooth part of left atrium. Before the cephalocaudal folding: the most cranial is septum transversum, superior to the prochordal plate (buccopharyngeal membrane) is the pericardium cavity from intraembryonic coelom and the primitive heart tube is ventral to the pericardium cavity. The neural tube develops quickly and forms the brain vesicles. After the cephalocaudal folding: the most caudal/posterior is septum transversum, the heart tube becomes above the pericardium and invaginates in it. The most anterior is the buccopharyngeal membrane "reversal". The primitive heart tube and the pericardium lie under the foregut. The evidence on this : the esophagus (foregut) lies behind the heart.

13 Done by Sarah AL-Najafi Sorry for any mistakes.