Circulatory system Flashcards
Heart
- muscular organ that contracts to pump blood
- ventricles; pump blood to the body and lungs
- atria; receive blood from the body pulmonary veins
Wall of the heart
- internal endocardium
- inner layer of squamous endothelial cells + subendothelial loose CT
- middle layer of smooth muscle = myoelastic + dense CT, w elastic fibers and collagen fibers
- deep layer of subendocardial loose CT merging w the myocardium
*veins, nerves, branches of impulse-conducting system are in this layer (purkinje fibers) - Myocardium - thickest layer
- cardiac muscle cells (CARDIOMYOCYTES)
~ fibers are arranged spirally around the chambers; thicker in ventricles than atria
- separated by the perimysial loose CT - epicardium - external layer
- simple squamous mesothelium + fibroelastic layer + subepicrdial CT w BLOOD VESSELS AND NERVES
- corresponds to the visceral layer of the pericardium = serousmembrane where heart lies
- Reflects back as a Parietal layer where the vessels enter and exit the heart
*In between the layers there is small lubricant fluid + cushioning adipocytes
~ fluid is produced by the both layers of the serous mesothelium cells
~ facilitate heart movements
Interventricular + interatrial septa
Core of dense fibrous CT of the cardiac skeleton –> attach to the fibrous ring at the fibrous skeleton.
Fibrous skeleton
–> anchors the base of the valves
–> site of origin and insertion of cardiac muscle
Regions of dense irregular CT have diff functions;
- anchoring the heart valves
- insertion of the cardiac muscle
- coordinates heartbeat by acting as electrical insulation between the atria and ventricles
Conducting system of the heart
within the subendocardial layer, modified cardiac muscle cells make it up.
- and spread to the myocardium for contractions
By 2 nodes of specialized myocardial tissue at the right atrium.
sinoatrial node –> atrioventricular node -> AV bundle and subendocardial conducting network
SA node and AV node
1.pacemaker near the superior vena cava
6-7mm3 mass of cardiac muscle with myofibrils and intercalated disks
–> impulse is initiates and moves along the myocardial fibers contracting the atria.
- AV located in the floor of the right atrium next to the AV valve
composed of the SA cells but have the cytoplasmic projections forming an AV bundle to the interventricular spetum (bundle of HIS) into the wall of each ventricle (CONTAINS GAP JUNCTIONS)
–> stimulate depolarization of cells
At the apex bundles divide into the conducting network = Purkinje fibers
- peripheral MYOFIBRILS with 1+ central nuclei
- pale-staining fibers
- high in glycogen
–> trigger conduction to both ventricles
Endothelium (tissue of vascular wall)
Endothelial cell - simple squamous, polygonal and elongated.
–>specialized epithelium that acts as a semipermeable barrier between the blood and the interstitial fluid
Main function; metabolic exchange between molecules of the blood and tissue through diff mechanisms eg. diffusion, receptor-mediated etc.
Other functions;
1. nonthrombogenic surface where blood will not clot and secretes agents controlling clot formation (heparin, plasminogen and von Willebrand factor)
2. regulate vascular tone and blood flow by secreting factors that stimulate smooth muscle contraction or relaxation ; endothelin or nitric oxide
3. inflammation and local immune response …
4. growth factors to promote proliferation of white blood cell lineages and cells of the wall
–> vascular endothelial growth factor (VEGF) stimulate formation of the vascular system form embryonic mesenchyme (vasculogenesis), help maintain vasculature on adults + promote capillary sprouting (angiogenesis)
5. enzymatic function
*Angiopoietins - stimulate endothelial cells to recruit smooth muscle cells and fibroblasts to form the other tissue of wall.
- diapedesis
Sooth muscle
- in walls of the vessels larger than capillaries
–> arranged helically in layer - In arterioles and arteries – connected by gap junctions
- enclosed by a external basal lamina
–> permit vasoconstriction and dilation for regulating the blood pressure
Connective Tissue
Collagen fibers found in the subendothelial layer between the smooth muscle and outer covering.
Elastic fibers - providing ability for the walls to expand under pressure (abundant in large arteries in parallel lamellae).
ground substance - proteoglycans an hyaluronate - physical and metabolic properties
Layers of large blood vessels
1.T intima - endothelium and a thin subendothelial layer of loose CT, w rare smooth muscle cells in longitudinal arrangement
*In arteries; thin layer of internal elastic lamina of elastin between the intima and media
- T media - helically arranged smooth muscle cells, interposed w elastic fibers and lamellae, reticular fibers proteoglycans, collagen type 3, glycoproteins (all produced by the cells).
*+ external elastic lamina at media. - T adventitia - loose CT with type 1 collagen and elastic fibers in longitudinal arrangements
- bound to the stroma
of large vessels; network of unmyelinated autonomic nerve fibers - vasomotor releasing vasoconstrictor norepinephrine (more in arteries than veins).
supplied by the vasa vasorum
- arterioles, capillaries and venules in the adventitia and outer media.
–> provides nutrients + oxygen to the cells of tunica
*luminal blood provides for the intima
Elastic arteries
Aorta, pulmonary artery and their large branches ; conducting arteries to carry blood to smaller arteries.
d= >10mm
same tunica layer
t. intimal - endothelium + subendothelial CT
- internal elastic lamella
tunica media - very thick; elastic lamallae (10um thick) alternate with layer of smooth muscle fibers (circular)
- external elastic memb
t. adventitia - loose CT
(collagen + elastic fibers)
- vasa vasorum + nerves
Staining;
cross section; HE + trichrome
longitudinal section; orcein
Muscular arteries
d= 10-1mm
1. t. intima - endothelium, thin subendothelial layer and a prominent internal elastic lamina
- less elastin and more muscle
- t.media - 40 layers of large smooth muscle cells (circular) interspread with little elastic lamellae
- external elastic lamina only in the larger muscular arteries. - t. adventita - CT (colagen + elastic fiber) w lymphatic capillaries, vasa vasorum and nerves
*microvasculature arteries decrease to 2-3 layer for exchange of blood and tissue fluid
Arterioles
smallest arteries
- less than 0.1 mm in diameter
t. intima- thin subendothelial cells (NO elastic laminae) + endo with round nuclei
t. media - circularly arranged smooth muscle cells (1-3 layer)
t. adventitia - very thin and inconspicuous
*at the end the sphincters for periodic flow into capillaries.
Venules
- transition form the capillaries = postcapillary venule
- 15-20um in diameter.
-t.intima endothelium - t media; smooth m with 1-2
- t adventitita-CT
- converge into larger collecting venules; with a t. media of 2-3 layers of smooth m = muscular venules
- contain pericytes; cells at the intervals of the walls - vessel formation, blood-barrier and immune cell entry.
—> primary site where white blood cells adhere to the endothelium and leave at circulation at affected region.
Veins
- contraction of the smooth m fibers in the media + external compress by surrouning skeletal muscle moves blood back to the heart
- diameters are around 10mm or less
medium vein;
t. intima - thin w valves ( compsed of elastic fibers + covered with endothelium)
t. media - smooth m with network of reticular and elastic fibers (CT) - circular
t. adventitia - thick w collagenous layer + ELASTIC FIBERS + lymphatic capillaries (longitudinal)
LARGE VEINS = MUSCULAR VEIN
thick intima - endothelium, subendothelial CT + sporadic smooth muscle cells (circular)
- thin media - smooth muscle circular with CT
- thicker adventitia - longitudinal bundles of smooth muscle
+ CT (longitudinal)
Capillaries
Capillary beds = network of capillaries
- its density depends on the metabolic activity of tissue
*higher metabolic rate (kidney, liver etc.) have more capillaries. lower MR (smooth muscle, dense CT) have less.
–>supplied by the terminal arteriole branches –> metarterioles - act as precapillary sphincters.
- thoroughfare channels lack muscle.
Capillaries
- composed of single layer of endothelial cells rolled as tube with a basement membrane w junctional complexes holding the cells (tight junctions)
- 4-10um in diameter and 50um long
- transit of blood cells one at a time (5%/300ml of blood traveling through)
- thin alls for gas exchange
