Circulatory System

Objectives:

1. to know the anatomy of the heart and its different structures.

2. to be familiar with the main branches of the aorta.

3. to know the main large veins.

4. to learn about the hepatic portal system.

5. to learn about the lymphatic system.

 

The Heart

         The heart is a muscular inverted triangular-shaped organ; the wide base is directed superiorly and the narrow apex is toward the inferior side and slightly shifted to the left. The heart has four chambers; the two atria are superiorly located, while the two ventricles are located inferiorly. The right side of the heart is separated from the left side by two septa: interatrial septum between the two atria and interventricular septum between the two ventricles. The tricuspid valve allows the blood to flow from the right atrium to the right ventricle without returning in the opposite direction. The pulmonary semi lunar valve transfers the blood from the right ventricle to the pulmonary artery,  which will pass then to the right and left lungs to be oxygenated. The bicuspid ( mitral)  valve allows the blood to flow from the left atrium to the left ventricle, then pass to the ascending aorta through the aortic semi lunar valve  to be distributed all over the body. The atrioventricular valves are connected by cordae tendonae to the papillary muscles at the walls of ventricles. The auricles are pockets like structure in the lateral walls of  atria. The heart is supplied with blood by the coronary arteries.

THE MAIN BRANCHES OF AORTA:

         The aorta receives the oxygenated blood from the left ventricle through the aortic semilunar valve, starts as ascending aorta supplies the heart through the coronary arteries which are divided into two divisions: the right coronary artery and the left coronary artery.

         The aortic arch has three branches:

1. the brachiocephalic trunk which divides then to right common carotid artery directed superiorly to the right side of the head and neck. The right subclavian artery which supplies the right upper limb that continues as R.axillary in the axial region, R. brachial at the anterior surface of the arm which will divide into R.ulnar and R.radial in the forearm.

2.  the left common carotid artery supplies the left side of the head and neck.

3.  the left subclavian artery supplies the left upper limb, continues as L.axillary, L.brachial and L.ulnar and L.radial.

         The descending aorta starts to supply the organ in the thoracic cavity and called the thoracic aorta gives the following branches:

1. The intercostal arteries supply the intercostal spaces.

2. The esophageal artery supplies the esophagus.

3. The bronchial arteries supply the bronchioles.

4. The superior phrenic artery supplies the diaphragm superiorly.

         The aorta inters the abdominal cavity to be called abdominal aorta with the following branches:

1.  The inferior phrenic artery supplies the diaphragm inferiorly.

2. The celiac trunk which gives the gastric artery for the stomach, the hepatic artery for the liver and splenic artery for the spleen.

3.  The superior mesenteric artery which supplies the small intestine.

4. The left renal artery and the right renal artery, each one supplies the left kidney and the right kidney respectively.

5.  The right and the left gonadal arteries supply the testes in the male or the ovaries in the female.

6.  The inferior mesenteric artery supplies mainly the large intestine.

         At the level of the iliac crest the abdominal aorta ends and the common iliac arteries start as right common artery and left common iliac artery, each one is divided into internal iliac artery supplies the pelvic organs and the external iliac artery which continues to the anterior aspect of thigh to give the femoral artery then the popliteal artery and the tibial artery in the leg.

THE MAIN VEINS

         The deoxygenated blood is returned to the blood by the veins draining in the right atrium by two main veins: superior vena cava and inferior vena cava. The blood is collected from the heart by the coronary veins which are collected in the coronary sinus which lies at the posterior surface of the right atrium.

         The blood is returned back from the head mainly by the right and the left jugular veins. The upper limbs return back their blood by deep and superficial veins, the ulnar and the radial veins are deep ones unite to form the brachial vein in the arm continues to form axillary vein then the subclavian vein. The cephalic, basilic and median cubital veins are superficial veins drain in the axillary vein, then in the subclavian vein and finally in the brachiocephalic vein before reaching the superior vena cava. The jugular and the subclavian veins unite to form the right and the left brachiocephalic veins. The brachiocephalic veins from both sides drain in the superior vena cava which drains  in the right atrium.

          The azygos vein and hemiazygos vein receive the blood from the intercostal, esophageal and bronchial veins in the thoracic cavity. The two veins drain in the superior vena cava which drain in the right atrium.

         The inferior phrenic, hepatic, right renal, left renal, right gonadal, left gonadal veins drain in the inferior vena cava which drain in the right atrium. The hepatic portal vein collects the blood from the organs that contain blood carrying toxic substances and nutrients due to the metabolic pathways. The splenic, the gastric, the superior mesenteric and the inferior mesenteric veins drain in the hepatic portal vein in the liver for detoxification then in the inferior vena cava through the hepatic vein.

         The blood from the lower limbs collect their blood by the right and left tibial veins then to the popliteal, femoral, external iliac, internal iliac and finally the inferior vena cava.

THE LYMPHATIC SYSTEM

The lymphatic system may be divided into two portions:

                                A*The lymphatic vessels, contain the lymph as circulating fluid which is mainly the excess interstitial fluid must be removed and returned back to the blood stream. The majority of the lymph which is collected from the lower limbs and abdominal organ is drained in the cesterna chyli which lies posterior to the stomach, is then collected in the thoracic duct in the thoracic cavity, continue in the left lymphatic duct with the lymph coming from the left upper limb and from the left side of the head and neck. The lymph descending from the right side of the head and neck and the right upper limb is collected directly in the right lymphatic duct. The two lymphatic ducts drain their contents in the brachiocephalic vein of same side where the lymph will be mixed with the blood.                                                          

                                    B*The lymphatic tissues, referring to the immune system for defense against the microorganisms. The three types of tonsils: palatrine, lingual and the pharyngeal tonsils, the spleen, the thymus gland and the distributed lymph nodes all over the body.  The lymph nodes are concentrated in four major regions of the body; the submandibular, the axillary, the intestinal and the inguinal lymph nodes.