Kristina C. Erasmo, M.D.. Transport – oxygen, carbon dioxide, nutrients, hormones, waste products...
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Transcript of Kristina C. Erasmo, M.D.. Transport – oxygen, carbon dioxide, nutrients, hormones, waste products...
CIRCULATORY SYSTEM
• Cardiovascular systemo Hearto Two systems of blood vessels:
o Systemic circulationo Pulmonary circulation
• Lymph vascular system
Heart
• Muscular pump that propels blood to the arteries of both systemic and pulmonary circulation
• Systemic circulation – brings blood from the heart to the rest of the body then back to the heart
• Pulmonary circulation – brings blood from the heart to the lungs and then back to the heart
Heart
• Located in the central mediastinum of the thoracic cavity
• Four chambers:o Left ventricle – systemic circulationo Right ventricle – pulmonary o Left atriumo Right atrium
Pericardium
• Connective tissue sac covering the hearto Outer sac (fibrous pericardium)o Inner sac (serous pericardium)
o Parietal pericardiumo Visceral pericardiumo Pericardial cavity – with fluid
Pericardium
• Fibrous and parietal pericardia – dense CT (collagen and elastic fibers, fibroblasts, other CT elements)
• Inner aspect of parietal pericardium – simple squamous epithelium (mesothelium)
• Visceral pericardium a.k.a. epicardium
Epicardium
• a.k.a. visceral pericardium• Outermost layer of heart wall• Lining epithelium of external surface:
mesothelium
Myocardium
• Thickest (thickness varies for different parts)
• Thickest: left ventricle• Thinnest: atria• Mainly cardiac muscle fibers
Purkinje Fibers
• Modified cardiac muscle cells• Initiate and conduct the electrical
impulse that controls the contraction of the heart
• Form the impulse-conducting system of the heart
• Larger, contain more glycogen than ordinary cardiac muscle cells
Myocardium
• Atrial natriuretic peptide (ANP) – polypeptide hormone secreted by cardiac muscle cells in atria and interventricular septumo Causes natriuresis – excretion of
sodium by the kidneys
Endocardium
• Thinnest• Lining epithelium: endothelium• Continuous with innermost layer of
the great blood vessels• Lines all internal surfaces of heart
Endocardium
• Subendothelial layer – loose CT• External to subendothelial layer –
dense CT, thickest portion of endocardium
Blood Vascular System
• Refers to the system of blood vessels within which blood circulates
• 3 types of blood vessels:o Arterieso Veinso Capillaries
Blood Vascular System
• Arteries – carry blood from the heart to the capillaries
• Veins – carry blood from the capillaries to the heart
Endothelium
• Lining of the luminal surface of all blood vessels
• Functions:o Lining blood vessels to facilitate
blood flowo Secretes components of
underlying CT
Endothelium
• Functions:o Secrete prostacyclin – inhibits
platelet aggregation, promotes vasodilation
o Nitric oxide and endothelin I – vasodilator
o Von Willebrand factor – blood coagulation
Vasa Vasorum
• Network of small blood vessels that supply large blood vessels
• Veins: present in the tunica adventitia and media
• Arteries: confined to adventitia
Capillaries
• Smallest blood vessels (5-10 um)• Connect arterioles and venules • Function: Allow exchange of gases
and materials between blood and surrounding tissue
Capillaries
• Wall consists of single layer of endothelial cells and its associated basal lamina
• Surrounding connective tissue elements
Pericytes
• Slender, elongated, perivascular cells that usually accompany capillaries
• Look like fibroblasts• Not part of the endothelium• Contain tropomyosin • Function: contractile cells that
influence the luminal size of capillaries
Continuous Capillary
• Found in muscles, lungs, CNS, skin• The endothelial cell and the basal
lamina do not form openings (which would allow substances to pass the capillary wall without passing through both the endothelial cell and the basal lamina)
Fenestrated Capillary
• Mucous membranes of GIT, renal glomerulus, pancreas, some endocrine glands
• Endothelial cell body forms small openings (fenestrations) which allow components of the blood and interstitial fluid to bypass the endothelial cells
Sinusoids
• a.k.a. discontinuous capillaries or sinusoidal capillaries
• Formed by fenestrated endothelial cells, (which may not even form a complete layer of cells)
• Basal lamina is also incomplete• Found in liver, spleen, red bone marrow
(free exchange of substances or even cells between bloodstream and organ is advantageous)
Tunica Adventitia
• Outermost coat of arteries and veins• Chiefly made up of connective tissue
with cells and fibers arranged longitudinally
Tunica Media
• Middle coat of arteries and veins• Concentrically arranged smooth
muscle fibers• Interspersed between the muscle
cells are connective tissue elements (collagen and elastic fibers)
Tunica Media
• In large arteries: o External elastic lamina/membrane
– outer layer of elastin which demarcates the tunica media from the tunica adventitia
Tunica Intima
• Innermost coat of arteries and veins• Consists of a layer of endothelium
that rest on a basal lamina• Subendothelial layer of loose CT• In arteries:
o Internal elastic lamina/membrane – demarcates tunica intima from tunica media
Arteries
• Classification:o Small (arteriole)o Medium (muscular or distributing)o Large (elastic or conducting)
• Decrease in size but increase in number as they go farther from the heart
Arterioles
• Smallest arteries (40 – 400 um)• Tunica intima: only endothelium, no
IEL or subendothelial CT• Tunica media: no EEL• Tunica adventitia: loose CT
Arterioles
• Relatively thick walls and narrow lumens – offer considerable resistance to blood flow (thus able to deliver blood to the capillary beds under greatly reduced pressure)
Medium Arteries
• Muscular arteries – well-developed tunica media
• Distributing arteries – distribute blood to the different parts of the body
• Biggest: brachial and femoral arteries
Medium Arteries
• Tunica intima: 3 layerso Endothelium, subendothelium,
and IEL• Tunica media: Up to 40 layers of
circularly arranged smooth muscle fibers, EEL present
• Tunica adventitia: loose CT, vasa vasorum
Large Arteries
• Elastic arteries – high elastic tissue content
• Conducting arteries – major conduits in the transport of blood away from the heart
• E.g. aorta• Recoil is responsible for the flow of
blood through the blood vessels during diastole
Large Arteries
• Tunica intima: o Polygonal endothelial cells, o Subendothelial layer – loose CTo Indistinct IEL
Large Arteries
• Tunica media: o 40-60 layers of elastic laminae
arranged concentricallyo Indistinct EEL
• Tunica adventitia: o Thin, merges with surrounding CTo Contains vasa vasorum
Sensory Organs Associated with Arteries
• Carotid bodies and aortic bodies o Sensitive to changes in oxygen and
CO2 tension of blood• Carotid sinus
o Sensitive to changes in arterial blood pressure
Veins
• Carries blood from the capillaries to the heart
• More numerous than arteries• Bigger calibers, more irregular
lumens, thinner and less elastic walls• Increase in caliber and walls become
thicker as they travel toward the heart
Small Veins (Venules)
• The 3 histologic layers of the vessel wall can only be appreciated in venules with a luminal diameter of at least 50 um
• Like capillaries, they are sites for exchanage of gases and substances
Medium Veins
• Tunica intima: o Polygonal endothelial cellso Subendothelial layer
• Tunica media: small bundles of circularly arranged smooth muscle cells
• Tunica adventitia: bulk of the wall
Large Veins
• E.g. inferior and superior vena cava, portal vein
• Tunica intima: thicker• Tunica media: poorly developed, few
smooth muscle fibers
Large Veins
• Tunica adventitia: very thick, consists of 3 poorly-defined zoneso Internal zone – dense CTo Middle zone – longitudinally
arranged muscle fiberso Outer zone – collagenous and
elastic fibers
Arteries vs. VeinsArteries Veins
Lumen Patent, RBC not seen Lumen may be collapsed, RBC usually seen
Endothelial lining Well-defined Not so well-defined
Internal elastic lamina (IEL)
Distinct Poorly defined
Tunica media Forms 2/3 of thickness of wall
1/3
External elastic lamina (EEL)
Distinct Poorly defined
Tunica adventitia Forms 1/3 of thickness 2/3
Lymph Vascular System
• Network of conduits that carry lymph
• Returns the extracellular liquid to the bloodstream (“drainage” system)
• Lymph circulates in one direction
Lymph Vascular System
• Functions:o Return the fluid of the tissue
spaces to the bloodo Upon entering the lymphatic
capillaries, this fluid contributes to the formation of the liquid part of the lymph
Lymph Vascular System
• Functions:o By passing through the lymphoid
organs, contributes to the circulation of lymphocytes and other immunological factors
Lymphatic Vessels
• Lymphatic capillaries – absent in cartilage, bone, thymus, teeth, placenta, CNS
• Lymphatic vessels• Lymphatic ducts (2) – drain into the
veins at the base of neck
Lymphatic Capillaries
• Also lined by endothelium (thin due to incomplete basal lamina)
• Branch and anastomose more freely than blood capillaries
• More variable in shape and caliber• Not associated with pericytes
Lymphatic Vessels
• Large lumen in relation to the thickness of their walls
• Endothelial lining + connective tissue layer (collagenous and elastic fibers, occasional smooth muscle)
• Large vessels: 3 layers (TI, TM, TA)• Have valves
Right Lymphatic Duct
• Smaller, shorter• Right side of body above the
diaphragm• Drains into the right brachiocephalic
vein (junction of internal jugular and subclavian vein)
Thoracic Duct
• Collects lymph from the other parts of the body not served by the right lymphatic duct
• Drains at the junction of left jugular and subclavian veins