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IMS: Microanatomy > Cardiovascular System > Flashcards

Cardiovascular System Flashcards

1
Q

Tunica Intima Layers

A
  • Endothelium
  • Basal Lamina
  • Subendothelial CT
  • Internal elastic lamina
    • Composed of elastin
    • Fenestrated
    • Seperates intima from media in arteries
    • Most prominant in muscular arteries
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2
Q

Tunica Media

A
  • Usually the thickest layer in arteries
  • Contains circularly arranged smooth muscle
    • Contraction narrows lumen
  • Contains elastic fibers, reticular fibers, & proteoglycans
    • All produced by smooth muscle cells
  • In capillaries and post-capillary venules, layer is replaced by pericytes
  • External elastic lamina
    • Seperates media from adventitia
    • Most prominent in muscular arteries
    • Fenestrated
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3
Q

Tunica Adventitia

A
  • Longitudinally oriented collagen and elastic fibers
    • Primarily type I collagen
  • Blends into surrounding CT
  • Contains autonomic nerves that enter tunia media and innervate smooth muscle
  • In thick vessels, contains small blood vessels called vasa vasorum
    • Nourish adventitia & media of vessels too thick for diffusion
    • More frequent in veins than arteries
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4
Q

Vasculature Innervation

A
  • Smooth muscle in tunica media of most organs innervated by sympathetic fibers that release norepinephrine
    • Causes sympathetic vasoconstriction response
    • More prevalent in arteries than veins
    • Most common in skin and kidneys
  • Skeletal muscle blood vessels innervated by sympathetic fibers that release acetylcholine
    • Causes sympathetic vasodilator response
  • Parasympathetic fibers innervate very few organs
    • Salivary glands
    • Erectile tissue of penis
    • Release acetylcholine, nitric oxide, and other co-transmitters
    • Causes parasympathetic vasodilator response
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5
Q

Endothelial Cell

Functions

A
  • Permeability barrier
  • Secrete type IV collagen and laminin for basement membrane
  • Synthesize clotting molecules
    • von Willebrand factor
  • Secrete vasoactive factors that control blood flow
    • Endothelin - vasoconstriction
    • Nitric oxide - vasodilation
  • Produce growth factors
    • Fibroblasts growth factor (FGF
    • Platelet-derived growth factor (PDGF)
  • Produce cell adhesion molecules that mediate acute inflammatory response
    • Selectins
    • Integrins
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6
Q

Weibel-Palade Bodies

A

Rod-shaped membrane-bound organelles within endothelial cells used for storage.

E.g. von Willebrand factor, P-selectins.

Derived from Golgi.

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7
Q

Pericytes

A
  • Undifferentiated mesenchymal cells which surrounds capillaries and post-capillary venules.
    • Differentiates into endothelial cells, smooth muscle, or fibroblasts.
  • May be contractile.
  • Branched cytoplasmic processes wrap around vessels.
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8
Q

Arteries

A
  • High pressure vessels transporting blood away from heart
  • Tunica media is dominant layer
  • Narrow lumen with thicker wall
  • Two basic types of arteries:
    • Elastic arteries
      • Aorta & pulmonary trunk
      • Helps convert pulsatile blood flow to steadier flow via elastic recoil
    • Muscular arteries
      • Distributing arteries
      • Includes most of the named arteries of the body
      • Distribute blood to specific organs as needed
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9
Q

Arterioles

A
  • Regulate blood pressure
  • Regulate blood distribution to various organs & capillary beds
  • Less than 5 layers of smooth muscle
  • Metarterioles
    • smallest arterioles
    • discontinuous layer of smooth muscle
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10
Q

Capillaries

A
  • Location of metabolic exchange
  • Can be smaller than diameter of RBC
  • Consist of a single layer of endothelium and a basal lamina
  • Discontinuous layer of pericytes may be present
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11
Q

Venules

A
  • Smallest vessels of venous system
  • Two types of venules:
    • Post-capillary venules
      • Receive blood from capillaries
      • Major site of WBC egress into extravascular tissues
    • Muscular venules
      • ​Contains at least one complete layer of smooth muscle
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12
Q

Elastic Artery Structure

A

Aorta, pulmonary artery, etc.

  1. Tunica intima
    • Endothelium
    • Subendothelial connective tissue
    • Internal elastic lamina
  2. Tunica media
    • Layers of smooth muscle cells alternating with and attached to 40-60 fenestrated elastic laminae
      • Vessels expand with systole and recoil with diastole
      • Elasticity decreases with age
    • Reticular fibers and ground substance
    • No distinct external elastic lamina
  3. Tunica Adventitia
    • Loose network of collagen and elastic fibers
    • Fibroblasts and macrophages predominant
    • Contain vasa vasorum
    • poorly defined outer boundary
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13
Q

Muscular Artery Structure

A
  1. Tunica Intima
    • Endothelium
    • Thinner subendothelial layer
    • Prominent internal elastic lamina
      • Appears scalloped if smooth muscle of media contracted
  2. Tunica Media
    • Up to 40 layers of circularly arranged smooth muscle cells
    • Few elastic fibers
    • External elastric lamina often fragmented into several thin layers that extend into adventitia
  3. Tunica Adventitia
    • Collagen and adipose
    • Larger vessels have vasa vasorum
    • Blends in with surrounding CT
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14
Q

Arteriole Structure

A
  • Endothelium
  • +/- internal elastic lamina
  • Tunica media only a few layers thick (call it less than 5)
  • External elastic lamina typically absent
  • Contains pre-capillary sphincters
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15
Q

Metarterioles

A
  • Smallest arterioles
  • Discontinuous layers of smooth muscle
  • Form preferential channels through capillary beds
  • Arise from ordinary capillaries and drain into venules
  • Contains precapillary sphincters
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16
Q

Arteriosclerosis

A

Any thickening and hardening of arterial walls.

Atherosclerosis most common form:

  • Hardening of arterial wall caused by fatty plaque (atheroma)
  • Foam cells accumulate
  • Smooth muscle cells proliferate in intima and produce ECM components contributing to fibrosis
  • Weakens vessel & reduces luminal diameter
  • Platelet aggregation & thrombus formation can cause sudden blockage
17
Q

Classes of Capillaries

A

Continuous

  • found in most tissues
  • tight junctions between endothelial cells
  • no fenestrations
  • pinocytotic vesicles transport substances across endothelium

Fenestrated

  • Found in GI tract, kidney, endocrine organs
  • Fenestrations or pores occur in thin areas of cytoplasm
    • Have diaphragms in most organs
    • Glomerular capillaries lack diaphragms
  • More permeable than continuous

Sinusoidal

  • Found in liver, bone marrow, spleen, adrenal cortex
  • Leakiest capillary
  • Wider diameter
  • Irregular shape
  • Large gaps between endothelial cells
  • Basal lamina discontinuous or absent
18
Q

Venous Circulation

A
  • Low pressure vessels returning blood to heart
  • Larger lumens with thinner walls
  • Valves prevent backflow
    • Formed by a fold of the tunica intima
    • Most common in large veins below level of heart
19
Q

Postcapillary Venules (PCVs)

Structure

A
  • Consists mainly of endothelium, basal lamina, and discontinuous pericytes
  • Reabsorb filtrate which leaked from capillaries
  • Major site for vasoactive mediators
    • Ex. Histamine and serotonin
  • Main site of leukocyte diapedesis
    • Via selectins, integrins, and ligands
20
Q

Diapedesis

A
  • Lymphocytes leave PCV’s of lymph nodes
    • Requires L-selectins on lymphocyte to bind ligand on endothelial surface
  • In inflammation, all types of leukocytes leave PCVs at site
    • Requires P-selectins and E-selectins on endothelial surface to bind ligands on leukocytes
    • Expression of selectins induced by products of inflammatory process
  • Binding causes cell to slow and roll
  • Integrins then strengthen binding and cause cell to stop
  • Leukocyte inserts pseudopod into endothelial intercellular junction
    • Widened by histamine and leukotrienes from mast cells and basophils
21
Q

Muscular Venules

A
  • Receives blood from postcapillary venules
  • Differ from PCV in that they have true tunica media with 1-2 complete layers of smooth muscle
  • Have thin tunica adventitia
22
Q

Medium & Large Vein

Structure

A

In artery-vein companion pairs, vein usually larger diameter and appears collapsed/irregular in shape.

  1. Tunica Intima
    • Endothelium
    • Thin subendothelial CT layer
    • Occasional internal elastric lamina
    • valves present in veins with >2mm diameter
      • paired folds of intima
  2. Tunica Media
    • Much thinner smooth muscle layer
  3. Tunica Adventitia
    • Typically thickest layer of vessel wall
    • Collagen and elastic fibers
    • Fibroblasts
    • Large veins like IVC may also contain bundles of longitudinally arranged smooth muscle
23
Q

Lymphatic Vessels

Characteristics

A
  • Low pressure
  • More permeable than capillaries
  • Picks up excess interstitial fluid and returns it to circulation
  • Found in most tissues except nervous system and bone marrow
  • Major metastatic pathway
24
Q

Lymphatic Capillaries

A
  • Begin as open ended endothelial tubes located near capillary beds
  • Single layer of thin endothelial cells
  • Basal lamina discontinuous or missing
  • Often have valves
  • Achoring filaments connect basal lamina to perivascular CT
    • Prevents collapse
  • Irregularly shaped
  • May contain many lymphocytes
25
Q

Lacteals

A

Specialized lymphatic capillaries located in the intestinal villi.

Absorbs dietary lipids in the form of chylomicrons.

26
Q

Large Lymphatic Vessels

A
  • Similar in structure to small veins
    • Larger lumen
    • Thinner walls
    • Have valves
  • Right lymphatic duct and thoracic duct return lymph to blood
    • Have 3 tunics similar to large veins
27
Q

Interstitial Pressure

A

Movement of fluid between capillaries and interstitium controlled by fluid forces:

  1. Osmotic Pressure
    • Created by concentration of albumin and other plasma proteins
    • Draws fluid into venules from interstitium
  2. Hydrostatic Pressure
    1. Created by blood flow against capillary walls
    2. Forces fluid out of capillaries into the interstitium

Arterial side: hydrostatic > osmotic = fluid leaves vessels

Venous side: osmotic > hydrostatic = fluid returns

Excess interstitial fluid causes edema

28
Q

Causes of Edema

A
  1. Increased venous hydrostatic pressure
    • Left heart failure → pulmonary edema
    • Right heart failure → peripheral edema
    • Pregnant uterus compressing common iliac veins
  2. Lymphatic obstruction preventing return
    • Axillary lymph node remvoal
    • Radiation damage
    • Parasitic infection of lymphatic vessels (elephantiasis)
  3. Capillary damage or increased permeability causing excessive leakage
    • Burns
    • Acute inflammation
      • Histamine increases post capillary venule permeability
  4. Decreased blood osmotic pressure causing decreased reabsorption
    • Hepatic cirrhosis
    • Nephritic syndrome
      • Kidneys loss excessive proteins
    • Malnutrition
29
Q

Heart Chambers

A
  • Right atria
    • Receives blood from superior & inferior vena cava
  • Right ventricle
    • Pumps blood to pulmonary circulation
  • Left atria
    • Receives blood from pulmonary veins
  • Left ventricle
    • Pumps blood via aorta to systemic circulation
30
Q

Endocardium

A

Continuous with tunica intima of blood vessels.

  • Endothelium
  • Subendothelial connective tissue
    • Elastic fibers
    • Collagen fibers
    • No adipose
  • More complex in ventricles where there is:
    • Middle layer of CT and few smooth muscle cells
      • Subendocardial layer of collagen and elastic fibers
      • Contains Purkinje fibers
31
Q

Myocardium

A

Continuous with tunica media of blood vessels.

  • Consists mainly of cardiac muscle
    • Involuntary striated muscle
    • Ventricular myocytes slightly larger than atrial myocytes
  • Myocardium much thicker in ventricles and on left side
  • Dense capillary beds
32
Q

Epicardium

A

Continuous with tunica adventitia of blood vessels.

  • outermost layer is visceral pericardium
    • mesothelium plus fibrous connective tissue
  • subserosal connective tissue
    • abundant adipocytes
    • contains large vessels of coronary circulation
    • contains large nerve bundles from ANS
33
Q

Cardiac Conduction System

A

Composed of modified cardiac myocytes

Rate modified by ANS

  • Sinoatrial (SA) node
    • Pacemaker
    • Located deep in epicardium of right atrium
  • Atrioventricular (AV) node
    • Receives impulse from SA node
    • Located in the interatrial septu near tricuspid valve
  • Atrioventricular bundle (bundle of His)
    • Continuous with AV node
    • Only direct connection between atrial & ventricular myocardium
    • Extends into interventricular septum
      • Branches into right and left bundle branches
      • Bundle branches end in Purkinje fibers
34
Q

Cardiac Innervation

A
  • Innervated by ANS
  • Nerves end near SA node, AV node, and coronary arteries
  • Parasympathetic → ACH → decreases HR & force of contractions, constricts coronary arteries
  • Sympathetic → NorEpi → Increases HR & force of contraction, dilates coronary arteries
35
Q

Nodal Cells

A
  • Smaller in diameter than regular myocytes
  • Paler due to fewer myofilaments
  • Seperated by more CT
  • Less interconnected
    • Some gap junctions
    • No intercalated disks
36
Q

Purkinje Fibers

A
  • Larger than ordinary cardiac myocytes
  • Pale due to large amounts of glycogen
  • Few myofilaments located at periphery of cell
  • No T-tubles
  • Irregular Z-lines
  • Located in the layer of endocardium called subendocardium
  • Ends first on papillary muscles
    • causes them to contract before remainder of ventricle
    • this “sets” AV valve leaflets preventing eversion back into atria during ventricular contraction
  • Continues to rest of ventricular myocardium
37
Q

Atrioventricular (AV) Valves

A

Tricuspid valve seperates right atrium from right ventricle.

Bicuspid (mitral) valve seperates left atrium from left ventricle.

  • Leaflets (cusps) are folds of endocardium covering fibrous core.
  • Base of each leaflet anchored to an annulus fibrosus of cardiac skeleton.
  • Free edges of leaflets anchored to papillary muscles by many chordae tendinae
    • Chordae tendinae have CT cores covered by endocardium
38
Q

Semilunar Valves

A

Pulmonic valve seperates right ventricle from pulmonary trunk.

Atrial valve seperates left ventricle from aorta.

  • Consists of 3 pocket-shaped cusps
  • Not associated with chordae tendinae or papillary muscles
39
Q

Cardiac Skeleton

A
  • Composed of dense collagenous tissue
    • Not cartilage or bone
  • Serves as anchoring point for myocytes
  • Seperates ordinary atrial and ventricular myocytes from one another
  • Heart valves are continuous with the skeleton

Has 3 main components:

  1. Four annuli fibrosi
    • Lies in the plane between atria and ventricles
    • Surrounds the openings of the aorta, pulmonary artery, and atrioventricular orifices
    • Provides attachment sites for leaflets of heart valves
  2. Two fibrous trigones (right and left)
    • Join the annuli fibrosi together
    • AV bundle pierces right fibrous trigone to reach interventricular septum
  3. Septum membranaceum
    1. Extends downward from right fibrous trigone
    2. Is the upper non-muscular part of interventricular septum

IMS: Microanatomy (16 decks)

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