Heart Part-2 By Dr. Rabia Inam Gandapore.pptx

Heart part 2

1. Heart Dr. Rabia Inam Gandapore Assistant Professor Head of Department Anatomy (Dentistry-BKCD) B.D.S (SBDC), M.Phil. Anatomy (KMU), Dip. Implant (Sharjah, Bangkok, ACHERS) , CHPE (KMU),CHR (KMU), Dip. Arts (Florence, Italy )

2. Teaching Methodology LGF (Long Group Format) SGF (Short Group Format) LGD (Long Group Discussion, Interactive discussion with the use of models or diagrams) SGD (Short Group) SDL (Self-Directed Learning) DSL (Directed-Self Learning) PBL (Problem- Based Learning) Online Teaching Method Role Play Demonstrations Laboratory Museum Library (Computed Assisted Learning or E-Learning) Assignments Video tutorial method

3. Goal/Aim (Main Objective) Embryology: Describe the physiological changes in circulation after birth . Gross Anatomy: Define pericardium & different reflections of pericardium. Describe the gross structure of the heart and Enlist the Coronary arteries, its branches and major blood vessels Identify chambers of the heart . Identify internal structures of various chambers of the heart. Describe the different components of conduction system of the heart and sympathetic and parasympathetic innervation.

4. Specific Learning Objectives (cognitive) At the end of the lecture the student will able to : Embryology: Describe the physiological changes in circulation after birth . Gross Anatomy: Define pericardium & different reflections of pericardium. Describe the gross structure of the heart and Enlist the Coronary arteries, its branches and major blood vessels Identify chambers of the heart . Identify internal structures of various chambers of the heart. Describe the different components of conduction system of the heart and sympathetic and parasympathetic innervation.

5. Psychomotor Objective: (Guided response) A student to draw labelled diagram of Heart

6. Affective domain To be able to display a good code of conduct and moral values in the class. To cooperate with the teacher and in groups with the colleagues. To demonstrate a responsible behavior in the class and be punctual, regular, attentive and on time in the class. To be able to perform well in the class under the guidance and supervision of the teacher. Study the topic before entering the class. Discuss among colleagues the topic under discussion in SGDs. Participate in group activities and museum classes and follow the rules. Volunteer to participate in psychomotor activities. Listen to the teacher's instructions carefully and follow the guidelines. Ask questions in the class by raising hand and avoid creating a disturbance. To be able to submit all assignments on time and get your sketch logbooks checked.

7. Lesson contents Clinical chair side question: Students will be asked if they know what is the function of Outline: Activity 1 Embryology: Describe the physiological changes in circulation after birth . Activity 2 Gross Anatomy: Define pericardium & different reflections of pericardium. Describe the gross structure of the heart and Enlist the Coronary arteries, its branches and major blood vessels Identify chambers of the heart . Identify internal structures of various chambers of the heart. Describe the different components of conduction system of the heart and sympathetic and parasympathetic innervation .

8. Recommendations Students assessment: MCQs, Flashcards, Diagrams labeling. Learning resources: Langman’s T.W. Sadler, Laiq Hussain Siddiqui, Snell Clinical Anatomy , Netter’s Atlas , BD Chaurasia’s Human anatomy, Internet sources links.

9. Circulation Before and After Birth FETAL CIRCULATION Before Birth: blood from placenta (80 % saturated with oxygen), returns to fetus by way of umbilical vein . On approaching liver, most of this blood flows through ductus venosus directly into inferior vena cava , short-circuiting liver. S maller amount enters liver sinusoids & mixes with blood from portal circulation . S phincter mechanism in ductus venosus , close to entrance of umbilical vein , regulates flow of umbilical blood through liver sinusoids . S phincter closes when a uterine contraction renders venous return too high, preventing a sudden overloading of heart . After a short course in inferior vena cava , where placental blood mixes with deoxygenated blood returning from lower limbs, it enters right atrium . Here it is guided toward oval foramen by valve of inferior vena cava , and most of blood passes directly into left atrium .

10. A small amount is prevented from doing so by lower edge of septum secundum , crista dividens & remains in right atrium . Here it mixes with desaturated blood returning from head & arms by way of superior vena cava . From left atrium , where it mixes with a small amount of desaturated blood returning from the lungs , blood enters left ventricle & ascending aorta. C oronary & Carotid arteries are first branches of ascending aorta , heart musculature & brain are supplied with well oxygenated blood . Desaturated blood from superior vena cava flows by way of right ventricle into pulmonary trunk .

11. During Fetal Life : R esistance in pulmonary vessels is high & blood passes directly through ductus arteriosus into descending aorta , where it mixes with blood from proximal aorta . After coursing through descending aorta , blood flows toward placenta by way of 2 umbilical arteries . O xygen saturation in umbilical arteries 58 %. During its course from placenta to organs of fetus , blood in umbilical vein gradually loses its high oxygen content as it mixes with desaturated blood . Mixing may occur in following places: I n liver ( I): by mixture with small amount of blood returning from portal system I n I nferior vena cava ( II): which carries deoxygenated blood returning from lower extremities , pelvis & kidneys I n right atrium ( III): by mixture with blood returning from head & limbs I n left atrium ( IV): by mixture with blood returning from lungs & at e ntrance of ductus arteriosus into descending aorta (V).

12. CIRCULATORY CHANGES AT BIRTH A t Birth C aused by cessation of placental blood flow & beginning of respiration . Ductus arteriosus closes by muscular contraction of its wall, amount of blood flowing through lung vessels increases rapidly and raises pressure in left atrium . Simultaneously , pressure in right atrium decreases as a result of interruption of placental blood flow. Septum primum is then apposed to septum secundum , & functionally oval foramen closes .

13. After birth Closure of umbilical arteries , accomplished by contraction of smooth musculature in their walls, is probably caused by thermal & mechanical stimuli & a change in oxygen tension. Functionally arteries close a few minutes after birth , although actual obliteration of lumen by fibrous proliferation may take 2 to 3 months . Distal parts of umbilical arteries form medial umbilical ligaments & proximal portions remain open as superior vesical arteries . Closure of umbilical vein & ductus venosus occurs shortly after that of umbilical arteries . Hence blood from placenta may enter the newborn for some time after birth . After obliteration, umbilical vein forms ligamentum teres hepatis in lower margin of falciform ligament . Ductus venosus , which courses from ligamentum teres to inferior vena cava , is also obliterated & forms ligamentum venosum . Closure of ductus arteriosus by contraction of its muscular wall occurs almost immediately after birth ; mediated by bradykinin , a substance released from lungs during initial inflation.

14. Complete anatomical obliteration by proliferation of intima is thought to take 1 to 3 months . In adult obliterated ductus arteriosus forms ligamentum arteriosum . Closure of oval foramen is caused by an increased pressure in left atrium , combined with a decrease in pressure on right side. F irst breath presses septum primum against septum secundum . During First days of life this closure is reversible . Crying by baby creates a shunt from right to left, which accounts for cyanotic periods in newborn . Constant apposition gradually leads to fusion of two septa in about 1year. In 20 % of individuals perfect anatomical closure may never be obtained (probe patent foramen ovale ).

15. Heart Surface anatomy of heart Pericardium H eart wall Chambers of the heart Atria Ventricles Valves of the heart Vasculature of the heart

16. Comparison between heart’s anatomical specimen and 3D volume reconstruction from MRI of heart and coronary vessels

17. Postero -inferior view

18. Surface anatomy of heart H eart is a hollow muscular pump , which lies in middle mediastinum (2-6 costal cartilage , 5-8 Thoracic vertebrae) Orientation and Surfaces The heart does not have a straightforward orientation It is described by many texts as “a pyramid which has fallen over ” The apex of this pyramid pointing in a anterior-inferior direction Heart has 5 surfaces , formed by different internal divisions of the heart: Anterior (or sternocostal ) – Right ventricle Posterior (or base) – Left atrium Inferior (or diaphragmatic) – Left and right ventricles Right pulmonary – Right atrium Left pulmonary – Left ventricle

19. Borders Separating the surfaces of the heart are its borders There are four main borders of the heart : Right border – Right atrium Inferior border – Left ventricle and right ventricle Left border – Left ventricle (and some of the left atrium) Superior border – Right and left atrium and the great vessels

20. Posterior relations of the heart with pericardium removed

21. Sulci of the Heart The divided four chambers of the heart create grooves on the surface of the heart – these are known as sulci C oronary sulcus (or atrioventricular groove ) runs transversely around the heart R epresents the wall dividing the atria from the ventricles S inus contains important vasculature, such as the right coronary artery A nterior and posterior interventricular sulci can be found running vertically on their respective sides of the heart They represent the wall separating the ventricles

22. Pericardial sinus Passages formed the unique way in which the pericardium folds around the great vessels The oblique pericardial sinus is a blind ending passageway (‘ cul de sac’) located on the posterior surface of the heart The transverse pericardial sinus is found superiorly on the heart It can be used in coronary artery bypass grafting

23. Pericardium A fibroserous , fluid filled sack that surrounds the muscular body of the heart and the roots of the great vessels (the aorta, pulmonary artery, pulmonary vein and the superior and inferior vena cava) Functions: Many physiological roles Fixes the heart in the mediastinum and limits its motion Prevents overfilling of the heart Lubrication Protection from infections

24. Anatomical structure of pericardium Made up of two main layers a tough external layer known as the fibrous pericardium , a thin, internal layer known as the serous pericardium Fibrous Pericardium Continuous with the central tendon of the diaphragm , the fibrous pericardium is made of tough connective tissue and is relatively nondistensible This rigidity prevents rapid overfilling of the heart , but can have several serious clinical consequences

25. Pericardium

26. Serous Pericardium Enclosed within the fibrous pericardium, the serous pericardium is itself divided into two layers 1. Outer parietal layer which lines the internal surface of the fibrous pericardium 2. Internal visceral layer which forms the outer layer of the heart (also known as the epicardium ) Each layer is made up of a single sheet of epithelial cells, known as mesothelium . Found between the outer and inner serous layers, is the pericardial cavity , which contains a small amount of lubricating serous fluid This fluid serves to minimize the friction generated by the heart as it contracts and moves about within the thoracic cavity

27. Innervation The phrenic nerve (C3-C5 ) is responsible for the innervation of the pericardium, as well as providing motor and sensory innervation to the diaphragm Originating in the neck and travelling down through the thoracic cavity, the phrenic nerve is a common source of referred pain, with a key example being shoulder pain experienced as a result of pericarditis

28. Mnemonic The order of these layers can be easily remembered using the acronym Fat Politician Sounds Villainous F – Fibrous layer of the pericardium P – Parietal layer of the serous pericardium S – Serous fluid V – Visceral layer of the serous pericardium

29. Clinical Relevance: Transverse Pericardial Sinus . A passage through the pericardial cavity Formed as a result of the embryological folding of the heart tube Its is located Posteriorly to ascending aorta and pulmonary trunk. Anteriorly to superior vena cava. Superior to left atrium Separates the arterial vessels and the venous vessels of the heart This can be used to identify and subsequently ligate the arteries of the heart during coronary artery bypass grafting

30. Clinical relevance cardiac temponade A n accumulation of fluid, known as pericardial effusion , within the pericardial cavity H eart is subject to the resulting increased pressure The chambers can become compressed , thus compromising cardiac output The causes of tamponade are many and varied, and include haemopericardium (blood in the pericardium) and pericarditis

31. Pericardium in relation with the sternum In cardiac compression , the sternum is depressed 4-5cm, forcing the blood out of the heart into the great vessels

32. The heart wall The heart wall itself can be divided into three distinct layers: E ndocardium Myocardium E picardium

33. Endocardium The innermost layer of the cardiac wall is known as the endocardium It lines the cavities and valves in the heart Structurally, the endocardium is made up of loose connective tissue and simple squamous epithelial tissue – it is similar in its composition to the endothelium which lines the inside of blood vessels E ndocardium also regulates contractions and aids cardiac embryological development

34. Clinical Relevance: Endocarditis Endocarditis refers to inflammation of the endocardium C ommonly occurs on the valves of the heart, which the endocardium lines 1. Main form of endocarditis is infective endocarditis – caused by a pathogen Bacteria colonise the heart valve , and cause small clumps of material called vegetations to develop R esulting inflammation can cause permanent damage to the valve D amaged valve is more likely to be colonised in the future, resulting in re- infection 2. Non-infective endocarditis is where the vegetations develop on the valve with a bacterial cause Malignant cancers are the main cause of this condition

35. Subendocardial layer L ies between, and joins, the endocardium and the myocardium It consists of a layer of loose fibrous tissue , containing the vessels and nerves of the conducting system of the heart The purkinje fibres are located in this layer As the subendocardial layer houses the conducting system of the heart, damage to this layer can result in various arrhythmias

36. Myocardium C omprised of cardiac muscle ( striated involuntary muscle) M yocardium is responsible for contractions of the heart Subepicardial layer The subepidcardial layer lies between, and joins, the myocardium and the epicardium Epicardium O utermost layer of the heart , and a layer of the pericardium C omprised of connective tissue and fat The connective tissue secretes a small amount of lubricating fluid into the pericardial cavity L ined by on its outer surface by simple squamous epithelial cells

37. Chambers of the heart Atria Ventricles Atria of the heart receive blood from the great vessels , and pump it into the ventricles In the human heart, there are two atria, one left and one right The ventricles are chambers in the heart They receive blood from the atria, and pump it into the outflow vessels – the aorta and pulmonary artery.

38. Anterior surface of the heart and great vessels in situ

39. Posterior view of the heart

40. Atria of the heart Right Atrium R eceives deoxygenated blood from the superior and inferior vena cava It also receives drainage from the coronary veins via the coronary sinus The atrium pumps this blood the right ventricle The interior surface of the right atrium can be divided into two parts, each with a distinct embryological origin They are divided by a smooth muscular ridge, called the crista terminalis : Posterior to the crista terminalis : This part receives blood from the vena cavae It has smooth walls and is derived from the embryonic sinus venosus

41. Right Atrium

42. Anterior to the crista terminalis : This part is derived from the primitive atrium Internally , it has muscular walls, formed by pectinate muscles It also contains the right auricle The right auricle (also known as the right atrial appendage) is located on the anteromedial portion of the right atrium, overlapping the root of the aorta It acts to increase the capacity of the right atrium

43. Clinical Relevance: Triangle of Koch The triangle of Koch is a triangle in the the right atrium which is an important anatomical landmark to help find the location of the atrioventricular node The borders are : The opening of the coronary sinus . The anterior portion of the tricuspid valve annulus. The tendon of Todaro – a tendinous structure connecting the valve of the inferior vena cava to the central fibrous body posteriorly

44. Interatrial Septum The two atria are separated by a solid muscular wall – the interatrial septum . Within the right atrium, the interatrial septum has a an oval shaped depression, called the fossa ovalis It is the closed form of the foramen ovale , a valve present in the foetal heart

45. Left atrium R eceives oxygenated blood from the pulmonary veins In the anatomical position, it forms the posterior border of the heart Blood is pumped from the left atrium into the left ventricle, via the mitral valve . C an be divided embryologically : Inflow portion – This part receives blood from the pulmonary veins. Its internal surface is smooth It is derived from the pulmonary veins themselves Outflow portion – This part is located anteriorly, where the blood flows into the ventricles It contains the pectinate muscles and the left auricle It is derived from the embryonic atrium

46. Ventricles The right ventricle R eceives deoxygenated blood from the right atrium, and pumps it into the pulmonary artery The ventricle is triangular in shape, and forms the majority of the anterior border of the heart The interior of the inflow part of the right ventricle is covered by irregular muscular structures, called trabeculae carneae They give the ventricle a ‘sponge-like’ appearance

47. Right Ventricle

48. There are three papillary muscles in the right atrium They are attached to chordae tendineae (fibrous cords), which are in turn attached to the tricuspid valve There are three types of trabeculae carneae : Attached to the ventricle wall at both ends (forming a bridge) Attached to the ventricle wall along their length (forming a ridge) Attached to the ventricle wall at their base, and to chordae tedineae at the other end These are known as papillary muscles

49. By contracting, the papillary muscles ‘pull’ on the chordae tendineae , and prevent the valve from regurgitating during ventricular contraction The outflow part (leading to the pulmonary artery) is located in the superior aspect of the ventricle It is called the conus arteriosus , and is derived from the embryonic bulbus cordis It is visibly different from the rest of the ventricle, having smooth walls, with no trabeculae carneae

50. Interventricular septum Externally , the interventricular septum can be located, as it spans between the anterior and posterior interventricular grooves S eparates the two ventricles M ade up of a membranous part (superiorly) and a muscular part (inferiorly) The muscular part forms the majority of the septum It is the same thickness as the left ventricular wall The membranous part is thinner, and part of the fibrous skeleton of the heart

51. Clinical Relevance: Ventricular Septal Defects A ventricular septal defect is a hole in the interventricular septum, allowing blood to pass between the two ventricles Due to the pressure being higher in the left ventricle, blood moves from the left ventricle to the right This has two main effects : Increased output from the right ventricle produces pulmonary hypertension The left ventricle becomes volume overloaded. The main treatment for a septal defect is surgical repair

52. Left Ventricle R eceives oxygenated blood from the left atrium, and expels it into the aorta L ocated anteriorly to the left atrium, contributing to the anterior aspect of the heart, and forming the apex In the left ventricle there are two papillary muscles , which are larger than those found in the right They are attached to the chordae tendinae , which in turn attach to the mitral valve The interior surface of the left ventricle contains trabeculae carnea , in a similar structure to that of the right The outflow part of the left ventricle is known as the aortic vestibule It is smooth-walled, and a derivative of the embryonic bulbus cordis

53. Left side of the heart

54. Left ventricle

55. Blood flow through left ventricle B : Coronal CT angiogram C: Blood flow through left ventricle

56. Valves of the heart Structures which ensure blood flows in only one direction They are made up of connective tissue and endocardium There are four valves of the heart, which are divided into two categories: Atrioventricular valves Located between the atria and the ventricles They close during relaxation of the atria and contraction of the ventricles Semilunar valves Located between the ventricles and the outflow vessels They close during relaxation of the ventricle and elastic recoil of the outflow vessel

57. Valves of the heart

58. Atrioventricular Valves The two atrioventricular valves are Tricuspid valve M itral valves They are closed by contraction of small muscles, known as papillary muscles The papillary muscles are attached to the valves by chordae tendineae (cord-like tendons) . The chordae tendineae can withstand a very high tensile stress, and prevent the valve inverting The closure of the atrioventricular valves are responsible for the first heart sound

59. Atrioventricular valves

60. Tricuspid Valve L ocated between the right atrium and the right ventricle The tricuspid valve has three cusps (cusps are ‘flaps’ which come together to shut the valve ) These cusps are attached to the fibrous ring of the skeleton of the heart The chordae tendinae are attached to the apex of the valves This valve opens during diastole and closes during systole

61. Mitral Valve The mitral valve is located between the left atrium and the left ventricle This valve has two cusps (known as the anterior and posterior cusps), and is occasionally known as the the bicuspid valve because of this The mitral valve opens during diastole and closes during systole

62. Semilunar valves Two semilunar valves are 1. P ulmonary valve 2. Aortic valve They are not closed by papillary muscles Instead , the back-flow of blood collects in the cusps, pushing them together, and closing the valve The closure of the semilunar valves are responsible for the second heart sound

63. Semilunar valves

64. Pulmonary Valve L ocated between the right ventricle and the pulmonary artery H as three cusps attached to a fibrous ring The pulmonary valve opens during systole and closes during diastole When the pulmonary valve closes, it produces the second heart sound The sound has a higher pitch, shorter duration and lower intensity than the first

65. Aortic valve L ocated between the left ventricle and the aorta Around the aortic valve opening is a fibrous ring where the three cusps of the valve attach The three cusps are named the posterior cusp, the right coronary cusp and the left coronary cusp The openings to the coronary arteries are found in the aortic wall just above the right and left coronary cusps During diastole, when the cusps fill, and the valve closes, blood can enter the coronary circulation via the left and right coronary arteries

66. Valves during diastole and systole

67. Vasculature of the heart: Coronary arteries T wo main coronary arteries which branch to supply the entire heart L eft and right coronary arteries Arise from the left and right aortic sinuses within the aorta The aortic sinuses are small openings found within the aorta behind the left and right flaps of the aortic valve When the heart is relaxed, the backflow of blood fills these valve pockets , therefore allowing blood to enter the coronary arteries

68. The left coronary artery (LCA) initially branches to yield the left anterior descending (LAD) or anterior interventricular artery The LCA then progresses to become the left marginal artery (LMA) and the left circumflex artery ( Cx ) The right coronary artery (RCA) branches to form the right marginal artery (RMA) anteriorly and the posterior interventricular artery ( PIv ) posteriorly

69. Distribution of Right coronary artery In general, the area of the heart which an artery passes over will be the area that it perfuses The RCA passes to the right of the pulmonary trunk and runs along the coronary sulcus before branching The right marginal artery arises from the RCA and moves along the right and inferior border of the heart towards the apex The RCA continues to the posterior surface of the heart, still running along the coronary sulcus The posterior interventricular artery then arises from the RCA and follows the posterior interventricular groove towards the apex of the heart

70. Coronary arteries (anterior view)

71. Coronary arteries (posterior view)

72. Left coronary artery The LCA passes between the left side of the pulmonary trunk and the left auricle The LCA divides into the anterior interventricular branch and the circumflex branch The anterior interventricular branch (LAD) follows the anterior interventricular groove towards the apex of the heart where it continues on the posterior surface to anastamose with the posterior interventricular branch The circumflex branch follows the coronary sulcus to the left border and onto the posterior surface of the heart This gives rise to the left marginal branch which follows the left border of the heart

73. Coronary arteriograms with orientation drawings

74. Pattern of coronary circulation

75. Patterns of coronary circulation

76. Cardiac veins The heart is drained by a series of cardiac veins which in turn drain into the coronary sinus The coronary sinus is the main vein of the heart, located on the posterior surface in the coronary sulcus The sinus then drains into the right atrium Within the right atrium, the opening of the coronary sinus is located between the right atrioventricular orifice and the inferior vena cava orifice There are five tributaries which drain into the coronary sinus: The great cardiac vein The small cardiac vein Middle cardiac vein

77. In the centre is the left posterior ventricular vein which runs along the posterior interventricular sulcus to join the coronary sinus The small cardiac vein is also located on the anterior surface of the heart This passes around the right side of the heart to join the coronary sinus Another vein which drains the right side of the heart is the middle cardiac vein It is located on the posterior surface of the heart. The final 2 cardiac veins are also on the posterior surface of the heart :

78. Cardiac veins

79. Diagnosis of Coronary artery disease A blockage in a coronary artery can be rapidly located by a coronary angiogram This involves the insertion of a catheter into the aorta via the femoral artery A contrast dye and imaging is then used to visualise the coronary arteries and any blockage that may be present

80. Immediate treatment of a blockage can be performed by way of a coronary angioplasty This involves the inflation of a balloon within the affected artery This pushes aside the atherosclerotic plaque and restores the blood flow to the myocardium The artery may then be supported by the addition of an intravascular stent Another treatment for coronary artery disease can be through a coronary artery bypass graft ( CABG) This involves redirecting blood, past the blockage, through a new vessel attached by surgeons Common vessels that are used for a CABG are the great saphenous vein or the radial artery

81. Thoracic Esophagus A fibromuscular tube, approximately 25cm in length Transports food from the pharynx to the stomach O riginates at the inferior border of the cricoid cartilage, C6 , extending to the cardiac orifice of the stomach , T11 Anatomically , the oesophagus can be divided into two parts: Thoracic Abdominal

82. Anatomical location Originates in the neck, at the level of the sixth cervical vertebrae C ontinuous with the laryngeal part of the pharynx D escends downward into superior mediastinum of the thorax S ituated between the trachea and the vertebral bodies T1 to T4 It then enters the abdomen by piercing the muscular right crus of the diaphragm, through the oesophageal hiatus at the T10 level The phrenicoesophageal ligament connects the oesophagus to the border of the oesophageal hiatus This permits independent movement of the oesophagus and diaphragm during respiration and swallowing

83. Anatomic relations of thoracic part of esophagus

84. Oesophageal Sphincters There are two sphincters present in the oesophagus , known as the upper and lower oesophageal sphincters They act to prevent the entry of air and the reflux of gastric contents respectively Upper Oesophageal Sphincter A natomical, striated muscle sphincter at the junction between the pharynx and oesophagus P roduced by the cricopharyngeus muscle Normally, it is constricted to prevent the entrance of air into the oesophagus

85. Vasculature of thoracic esophagus Receives its arterial supply from the branches of the thoracic aorta and the inferior thyroid artery (a branch of the thyrocervical trunk) Venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein.

86. Thymus Pink, lobulated lymphoid organ , located in the thoracic cavity and neck In the adolescent, it is involved the development of the immune system After puberty, it decreases in size and is slowly replaced by fat Anatomical Structure and Position The thymus gland has an asymmetrical flat shape, with a lobular structure Lobules are comprised of a series of follicles, which have a medullary and cortical component:

87. Thymus conti … Cortical portion – Located peripherally within each follicle L argely composed of lymphocytes, supported epithelial reticular cells Medullary portion – Located centrally within each follicle C ontains fewer lymphocytes than the cortex, and an increased number of epithelial cells Vasculature Arterial supply is via Anterior intercostal arteries Small branches from the internal thoracic arteries Venous blood drains into the left brachiocephalic and internal thoracic veins

88. Clinical Relevance: DiGeorge Syndrome A genetic syndrome caused by the deletion of part of chromosome 22 Clinical findings vary greatly between individuals The most common features of the syndrome can be memorised using the mnemonic ‘CATCH’ : Congenital heart defects Abnormal facies Thymic aplasia Cleft palate Hypoparathyroidism Individuals with an absent or asplastic thymus are susceptible to recurrent infections due to a underdeveloped immune system .

89. Thank You Any Questions?