9 Cardiovascular_1

1. Nutrition/Metabolic: nutrient transport, gas exchange (lungs), waste removal (kidneys), hormone distribution (everywhere)

2. Protective: mechanism by which immune cells are distributed throughout the body; also provides cells/mechanisms needed for clotting

3. Homeostasis: keeps organs functioning the way they should - regulates body temperature (dilation/constriction of peripheral BVs), as well as pH & blood pressure

• LAYERS, called ‘tunics’
• Tunica Intima: innermost layer
• Tunica Media: middle layer of smooth muscle
• Tunica Adventitia: outermost connective tissue layer
• most vessels have all 3 although thickness will vary (smallest vessels, eg. capillaries, really only have intima)

• lined by endothelial cells ALWAYS if talking about blood or lymph
• then there’s a little bit of underlying CT
• may or may not be an inner elastic lamina

• usually but not always the thickest part
• made of smooth muscle
• may also have an internal elastic lamina, elastic fibers, & an external elastic lamina

• outermost layer made up of connective tissue that blends with other CT in the body
• it can itself contain things like blood vessels & nerves

Smooth Muscle (not fibroblasts, which usually makes elastic components)

• artery is lined by an endothelium
• surrounding that is some some sub-endothelial CT which may or may not contain elastin
• then comes the tunica media which here contains elastic fibers
• the outermost layer = the tunica adventitia (mostly collagen + fibroblasts)
• in a corresponding vein the wall tends to be a lot thinner - there’s less smooth muscle, see very few elastic fibers (really the only place they’re seen is in a very large vein)

• artery:
• dots next to lumen: endothelial cell nuclei
• dark line: inner elastic lamina
• pink: tunica media
• outside peach: tunica adventitia
• corresponding vein:
• see dots ~ endothelial cells
• very little SM muscle/tunica media
• looks like you go from endothelia cells → tunica adventitia

• tunica intima is lined by endothelial cells + a certain amount of sub-endothelial CT
• then there’s a VERY thick tunica media with lots of elastic lamina
• larger vessels have their OWN nerve + blood supply (are so large they’re organs in their own right)

• systole: when blood is ejected from heart
• elastic compartment of tunica media expands

• diastole: heart is not ejecting blood
• contraction of the vessels elastic layers maintains a continuous flow

• wavy sheets that allow the vessels to expand during systole when the heart contracts & then contract during diastole to propel the blood forward/through the vessel system
• *reduces the pulsatile flow
• the elastic sheets do have pores in them so there’s communication between 1 layer & the next

a blood vessel WITHIN a blood vessel (vessel of a vessel)

• will have inner elastic lamina (wavy dark line - IEL) just deep to the endothelial cells
• tunica media = all SM muscle with some interspersed elastic fibers
• there are typically 10-40 layers of SM muscle
• then there’s an external elastic lamina (EEL) - wavy continuous sheet
• outermost layer = the tunica adventitia

• Muscular Arteries
• because they are also elastic to some extent, they’ll expand during systole

• contain ~3-10 layers of SM muscle
• may or may not contain an IEL (the one in the picture does)

• IEL or EEL (internal or external elastic lamina)
• venous flow is never pulsatile because it’s ‘post-capillary bed’
• might see elastic fibers in the media or adventitia of large veins (usually), but never elastic laminae

consists of Arterioles & Capillaries

• part of the ”microcirculation"
• contain ~< 3 layers of smooth muscle
• there’s no elastic laminae whatsoever
• almost always associated with accompanying veins
• can differentiate between arteriole & venule because arteriole will be much more round & have a more eosinophilic (pink) layer of smooth muscle

• Cross-Sectional: tunica media (smooth muscle) nuclei are long/flat, tunica intima (endothelial) are dots
• Longitudinal: smooth muscle nuclei are dots (because SM muscle cells wrap around the vessel) & endothelial nuclei are long/flat

• part of the ”microcirculation"
• made up of endothelial cells + a basal lamina
• do NOT have tunica media OR adventitia
• usually are quite small: 4-10 microns, just large enough for RBCs to pass through

• 1. Continuous: endothelial cell wraps around vessel & forms a tight junction with itself; not leaky; most of the capillaries in the body

• 2. Fenestrated: found in endocrine glands & kidney; have little holes that allow small molecules to escape

• 3. Discontinuous: found in lymphoid organs & liver; large gaps that allow cells to squeeze through

• they live in the basal lamina & accompany endothelial cells
• they can be found in all blood vessels
• they regulate capillary permeability, are contractile (can regulate vessel lumen size), & can help control endothelial cell proliferation (there are gap junctional connections between pericytes & endothelial cells)

• lined by an endothelial cell wall
• small venules have NO Tunica Media or Adventitia (arterioles have media but he doesn’t mention adventitia…)
• are quite leaky - this is where most cells exit the blood to interstitial CT or lymph
• these are histamine sensitive, which makes them even leakier - lots of fluid + cells can escape out to tissue

• again lined by endothelial cells, but this time they DO have a Tunica Media & Tunica Adventitia
• can be between 0.1-10mm in diameter
• from this point on, especially in the extremities, enlarged veins have VALVES

• in order to direct blood flow in one direction, back to heart & prevent reflux

because there's high pressure in them & lots of smooth muscle

• when valves fail, blood won’t travel back to the heart as efficiently as it should
• as these veins dilate because of the additional pressure, they get enlarged & tortuous
• typically happens in superficial veins, so this can be visualized

• really thick structures
• have Tunica Intima lined by endothelial cells
• a Tunica Media
• what’s characteristic of Large Veins is that the Tunica Adventitia has lots of SM muscle (+ elastic fibers)
• eg. vena cava, brachiocephalic veins

• the Tunica Adventitia - which is where the SM muscle is in Large Veins
• it’s much thicker than the Tunica Media

• the SM muscle runs longitudinally in Large Veins, so in a cross-sectional view you’ll see smooth muscle bundles

• Elastic (Large/Aorta) → Muscular → arteriole → capillary
• Large Vein (inferior vena cava) → medium vein → venule

• where you have a capillary bed separating 2 other vessels
• eg. arteries turn into a capillary bed → a portal vein → another capillary bed → then back to the heart
• usually you’d go from a capillary bed → a vein → heart
• there are several in the body, the biggest is the hepatic portal vein

• has 3 layers, outer → inner:
• epicardium → myocardium → endocardium
• these are equivalent to the tunicas of the major blood vessels: adventitia → media → intima
• the heart is sitting in a sack called the Pericardium
• the space in between the heart wall & the Pericardium is the pericardial sack (has a small amount of fluid)

• surface of the Pericardium that FACES the heart (inside of the Pericardium)
• made up of squamous cells

• mesothelium of the epicardium that faces the Pericardial space

• surface directly next to the blood
• lined by endothelial cells + a small amount of CT just below

separate from the Endocardium, contains Purkinje Fibers

• specialized cardiac myocytes (muscle cells)
• are contractile, contain myfibrils & cytoplasm + lots of glycogen
• have specializations for CONDUCTION (enable the heart to contract in a coordinated fashion)
• if you see them you know you're looking at the Subendocardial CT in the ventricles of the heart

• heart’s ‘tunica media’
• contains all the heart’s cardiac myocytes
• can see intercalated discs (end-to-end junctions between intercalated cells)
• nucleus is found in the central part of the cell

• outside the epicardium is a space where you have a small amount of fluid
• that outside layer (facing the pericardial space) consists of mesothelial cells; this is the Visceral Pericardium
• just below that = CT
• below that = adipose tissue

• in the Epicardium (itself contains blood vessels)