Cardiovascular microanatomy Flashcards
Learning outcomes
-List and describe the layers of the heart wall
-Describe the structure of the pericardium
- Describe the structural features of the valves
-Describe the impulse conducting system of the heart
-List and describe the layers of the walls of blood
vessels
-Compare and contrast the structure of arteries and
veins
Heart and circulation- general organisation
- Muscular pump responsible for moving blood around the circulation
- Heart divided into 2 sides, each with an atrium and ventricle separated by a valve
(a) Right Heart – pulmonary circulation – fed by inf. & sup. venae cavae – blood sent to lungs via pulmonary trunk
(b) Left Heart – systemic circulation – fed by pulmonary veins – blood sent to body via the aorta
See slide 4 lecture 9
What is the pericardium/pericardial sac?
Fibrous pericardium – fluid filled sac that limits heart motion and prevents heart from overexpanding
-Attaches to great vessels at base of heart and to the central tendon of the diaphragm
-Serous Pericardium –composed of two layers which
enclose the pericardial cavity
- Parietal pericardium, Visceral pericardium: Secretion of pericardial fluid reduces friction between pericardial membranes
PC attached to diaphragm, sternum and the great vessels, preventing heart moving around too much
Inflammation (pericarditis) can cause a buildup of fluid and as it can’t expand, the volume compresses the epicardium/myocardium
What are the 3 layers of the heart wall?
Epicardium
-Visceral Pericardium- simple squamous
epithelium
-Subepicardium - loose connective tissue and adipose tissue containing coronary vessels and nerves that supply the heart
- Myocardium
- Thickest layer
- Bundles and layers of cardiac muscle cells
- Endocardium
- Smooth inner lining of endothelial cells
- Subendocardium - loose connective tissue containing small blood vessels and branches of the conducting system of the heart
The valves of the heart
Ensure unidirectional blood flow
-Composed of a core of connective tissue (covered with endothelium)
-Atrioventricular (AV) valves
o Right AV valve has 3 cusps (tricuspid)
o Left AV valve has 2 cusps (mitral/bicuspid)
o Chordae tendineae – cords connect AV
valves to papillary muscles (on ventricular
floor)
- Semilunar valves – control flow of blood
into great arteries
o Pulmonary - from right ventricle into
pulmonary trunk
o Aortic - from left ventricle into aorta
Conducting system of the heart
Sinoatrial (SA) Node – Pacemaker
- Located in wall of superior vena cava & right atrium, deep to epicardium
- Specialised cardiac muscle fibres (lots of CT between fibres)
- Possesses its own blood supply
- Causes atrial contraction
Atrioventricular (AV) Node
- Located in septum between atria
- Divides into 2 branches of Purkinje fibers
- Specialised cardiac muscle fibres – larger (x2 approx.)
- Supply papillary muscles first, then apex of heart
- Causes wave of ventricular contraction
Layers of a blood vessel
Above a certain diameter, all blood vessels have some similarities and follow the same general plan
Tunica Intima (Interna) o Endothelium & CT
Tunica Media
o Smooth Muscle collagen and elastic fibres
(relative amounts)
Tunica Adventitia (Externa)
o Loose connective tissue (relative amounts)
o Can have blood vessels and nerves
Arterial system
Carry oxygenated blood (except pulmonary artery- carries blood from RV for oxygenation)
- Takes blood away from the heart
- Wall thick in comparison to lumen diameter
- No valves
Two main types;
- Elastic Arteries (conducting vessels)
- Muscular arteries (distributing vessels)
- Arterioles (small arteries that distribute blood to capillaries)
Elastic artery (aorta) vs Muscular artery vs arterioles
Elastic artery
T. intima – endothelium & underlying CT
T. media – thickest layer with sheets (laminae) of elastic tissue interspersed with smooth muscle and collagen
T. adventitia – CT (lots of collagen to prevent overextension) & blood vessels called vasa vasorum
Muscular artery
Tunica Media predominates in the media
Elastic material mostly reduced to 2 laminae:
-Internal Elastic Lamina (IEL) between intima and media
-External Elastic Lamina (EEL) between media and adventitia
Arterioles
Tunica Media reduced to 2-3 layers of smooth muscle
Tunica Adventitia blends in with surrounding connective tissue
Veins
- Carry deoxygenated blood (except for pulmonary veins)
- Take blood to the heart
- Walls are thin in comparison to lumen diameter
- Tunica media relatively thin compared to arteries
- Tunica adventitia relatively larger compared to arteries
Varicose veins arise when the valves become faulty, leading to twisted, abnormally swollen veins
Large vein (venae cavae) vs medium sized vein
-Tunica intima – endothelium & CT
-Tunica media – smooth muscle, collagen, little elastic
- Tunica adventitia – Thickest layer with lots of smooth muscle, collagen & extensive vasa and nervi vasorum
Collagen fibres
MEDIUM-SIZED VEIN
- Tunica intima – endothelium & underlying CT
- Tunica media – smooth muscle, collagen, little elastic
- Tunica adventitia – elastin and collagen; little smooth muscle
Valves
Found in large and most medium-sized veins but generally absent in small veins
-Inward extensions of tunica intima
- Blood moving toward the heart pushes the cusps of the valves open
-If blood begins to back up in a vein, the cusps are
pushed closed, preventing backward flow
Capillaries
Link arterial and venous circulation - microcirculation
- Site of exchange
-Formed from endothelial cells rolled in a tube
- There are three different types of capillaries:
- Continuous :Found in the skin, muscle
-Fenestrated: Found in the small intestine, kidneys
- Discontinuous: (Sinusoids) Found in the liver, spleen,
bone marrow
The 3 types of capillaries
Continuous capillaries
- Endothelial cells have a complete CONTINUOUS cytoplasm
- Caveolae and other vesicles transport substances
- Basal lamina is continuous
- Pericytes associated with endothelium
Fenestrated Capillary
- Endothelial cells have many fenestrae (80-100nm in diameter) with or without a thin diaphragm
- The basal lamina is continuous
- Found primarily in endocrine glands, intestines, pancreas and glomeruli of the kidney
Sinusoids
- Gaps in endothelial cells are larger (30-40 micrometers) than in fenestrated capillaries
- Basal lamina is discontinuous, fragmented and may be absent
