Heart Histology Flashcards
Heart Structure
Left heart to all body except \_\_\_\_ (systemic) Right heart to \_\_\_\_ (pulmonary) Systemic arteries: \_\_\_\_ blood Pulmonary arteries: \_\_\_\_ blood Systemic veins: \_\_\_\_ blood Pulmonary veins: \_\_\_\_ blood Atria: receive blood from veins Ventricles: pump blood to arteries
lungs lungs oxygenated deoxygenated deoxygenated oxygenated
Layers of the heart wall
1. Pericardium (external layer): • Homologous to the \_\_\_\_ of blood vessels. • Smooth, slippery texture to outermost surface. 2. Myocardium: • Continuous with the \_\_\_\_ of blood vessels. • 95% of heart is \_\_\_\_ muscle 3. Endocardium (inner layer) • Homologous to the \_\_\_\_ of blood vessels. • \_\_\_\_ lining.
• Heart wall > three layers ○ Pericardium § Tissues at level of tunica adventitia: \_\_\_\_, adipose, nerves, other blood vessels □ Likely that pericardium is composed of the same type of tissues as the blood vessels, specifically connective tissue ○ Myocardium (bulk) § Tunica media of large arteries □ Important difference: tunica media has \_\_\_\_ muscle, and myocardium is composed of \_\_\_\_ muscle ○ Endocardium (thin lining the interior of the myocardium) § Tunica intima > an endothelium that may be contain other tissues (\_\_\_\_ connective tissues)
tunica adventitia tunica media cardiac tunica intima endothelial
connective
smooth
cardiac
subendothelial
Pericardium
- Membrane surrounding and protecting the heart.
- Confines while still allowing ____.
- 3 layers:
- Fibrous pericardium:
- Inelastic, dense ____ CT.
- Prevents ____, overfilling. • Anchors the heart.
- Serous pericardium:
- Thinner, more delicate CT.
- Double layer:
- ____ layer: fused to fibrous pericardium.
- ____ layer: also called epicardium.
• Pericardial cavity: Between parietal and visceral layers: contains pericardial fluid which reduces ____.
• Prevents the heart from overextending • Three components of pericardium is formed primarily of \_\_\_\_ tissue > allows it to have its function ○ Fibrous § Rich in collagen and poor in \_\_\_\_ (elastin allows contraction and elongation easily) ○ Serous (between the two layers > pericardial cavity) § Parietal § Visceral (epicardium) ○ Pericardial cavity § Allows movement of heart and prevents friction
free movement irregular overstretching parietal visceral friction
connective
elastin
Pericardial cavity
- Serous pericardium:
- Thinner, more delicate CT. • Double layer:
- Parietal layer: fused to fibrous pericardium.
- Visceral layer: also called epicardium.
• Pericardial cavity: Between parietal and visceral layers: contains pericardial fluid which reduces friction.
• Fluid in pericardial cavity composed of \_\_\_\_ and polysaccharides ○ Same role that is played in \_\_\_\_ cartilage > gives the fluid ability to reduce friction • Also a a lot of \_\_\_\_
proteoglycans
articular
water
Myocardium
• Thickest layer of the heart: • Thickest in \_\_\_\_ - to overcome high pressure of systemic circulation. • Thinnest in \_\_\_\_ - low resistance to back flow.
- Myocardial cell types:
- Contractile cardiocytes (a.k.a. cardiomyocytes):
- Specialized ____ cells.
- Myoendocrine cardiocytes:
- Secrete ____ – regulates diuresis and sodium excretion to control blood volume.
- Nodal cardiocytes:
- Control the ____ of heart contraction.• Amount of muscle correlates with ____ of blood
• Contractile cardiocytes
○ Closely related to ____ muscle cells (more than smooth), but behave like smooth muscle cells
• Myoendocrine cardiocytes
○ ANF - regulates production of ____
• Nodal cardiocytes
○ Present in cardiac ____
○ Heart contracts based on signals by NC, which are modified by ____ system that is influenced by other factors
§ Changes in relative charge of the membrane of these cells
left ventricle right atrium muscle atrial natriuretic factor rhythm pressure skeletal urine nodes autonomic
The Cardiac Muscle Cell or Cardiomyocyte
Striated, branched cylinders, with a single, ____- located nucleus.
Wrapped around the ____ walls, increasing efficiency of blood ejection.
• Left ○ Section of cardiac muscle - \_\_\_\_ (looks like skeletal) § But the cells are histologically different > because of single centrally located nucleus • Right ○ Wrap around ventricular walls > by their contraction > pumping of blood
centrally
ventricular
striated
Comparison of Skeletal, Cardiac and Smooth Muscle
TABLE!
• Cardiac cells are only present in the \_\_\_\_ ○ Similar in morphology to skeletal muscle cells due to striations § Striations depend on the contractile mechanisms of organization into \_\_\_\_ ○ Presence of densities (vertical bands) > \_\_\_\_ § Place where two different cardiac cells touch each other and fuse ○ Cardiac cells are \_\_\_\_ (skeletal is NOT) ○ Nuclei are \_\_\_\_ located (unlike peripherally like in skeletal) ○ Do not fuse into \_\_\_\_ cell (sinctitiam), like skeletal cells do ○ Cardiac looks very different from smooth cell, but the \_\_\_\_ is similar between the two § Contraction of cardiac cells is \_\_\_\_ which is controlled by the ANS (like the smooth muscle cell)
heart sarcomeres intercalated disks branched centrally multi-nucleated behavior involuntary
Histology of the Cardiac Muscle
• Left ○ Intercalated disk § Two cells meet and fuse ○ Nucleus located \_\_\_\_ • Right ○ \_\_\_\_ § Thin CT that surrounds every cardiac fiber • Myocardium has same three levels of connective tissue that’s in \_\_\_\_ muscle ○ \_\_\_\_ - surrounds fibers ○ \_\_\_\_ - surrounds bundles ○ \_\_\_\_ - surrounds whole organ
centrally
endomysium
skeletal
endomysium
epimysium
perimysium
Histology of the Cardiac Muscle
* Longitudinal section stained on the left, the blue arrows indicate the intercalated disks that are the limits between cells * Yellowish tissue with lots of nuclei is \_\_\_\_, it is connective tissue so those nuclei belong to \_\_\_\_ * On the right you have cross section of cardiac muscle cells
endomysium
fibroblasts
Structure of the cardiomyocyte cell
- Organization of myofibrils similar to ____ muscle.
- Differences in the membrane system:
- Larger ____, found at the level of Z disk.
- ____ not as extensive.
- ____ (not triads): one T tubule interacting with one SR cisterna.
- More abundant ____.• Sarcomere made of thick and thin fibrils
○ Identical
• Cisternae of the SR
• Larger T tubules at level of Z disk
○ Allows a more efficient trafficking of ions, and during transmission of excitation signal > allows quicker liberation of ____ from SR
○ Contracting all the time, unlike skeletal which is only contracting some of the time
• In skeletal > triads > two cisternae and one T tubule; but in cardiac it’s a diad > one and one
skeletal t tubules SR diads mitochondria Ca++
The Sarcomere
- Myofibrils are repeats of sarcomere units.
- I band:
- ____ – major component; two protein strands twisted around each other, contain “active sites”.
- Other proteins – ____, Troponins, ____.
• A band:
• ____ - flexible “heads” with ATPase activity protrude outward (except at ____), attach to “active” sites on actin (thin) filament.
• H band – contains ____; forms ____.
• M line – located in midline of the H band;
provides ____ support to myosin filaments.
• Z-disk (Z-line, Z-band)–where thin filaments attach; mostly ____.
• Everything at this level is identical between skeletal and cardiac ○ Even the Z disks are identical (where actin and filaments attach) • Question about this!
actin
tropomyosin
nebulin
myosin filament center creatine kinase ATP structural support
alpha-actinin
Structure of the Cardiomyocyte Cell
• Organization of myofibrils similar to skeletal muscle.
• Differences in the membrane system: • Larger T tubules found at the level of Z
disk.
• Sarcoplasmic reticulum not as extensive.
• Diads (not triads): one T tubule interacting with one SR cisterna.
• More abundant mitochondria.
* In skeletal > T tubule is at junction of \_\_\_\_, but in cardiac cell they're at the \_\_\_\_ * Only one SR cisternae located > diad, instead of triad (one and one)
I-A band
Z disk
Structure of the cardiomyocyte cell
• Cells are joined at the end by intercalated disks in a step-like arrangement:
• Transverse component: ____ link, transmission of contractile force.
• Desmosomes.
• Fasciae adherens (α-actinin and vinculin):
insertion site for ____.
- Longitudinal components: ionic (____) link, contraction coordination.
- ____, ion channels.
- Membrane receptors.• Reasons for joining of intercalated disk > heart must contract in coordinated manner > links cells mechanically and physiologically
• Mechanical link of ID > transverse component
○ Desmosomes
§ Serve to tightly bind to cells > common in ____
○ Fasciae adherens
§ ____ and vinculin > form the Z disks (myotendinous junction, junction between skeletal muscle and tendons)
• Mechanical contraction only works somewhat, the whole muscle organ contraction must be coordinated; in order to ensure that all cells in one seciton of heart contract (LV, for example) > functional link > longitudinal component
○ Ionic link; ions traffic from one cell to the next very rapidly
mechanical actin thin filaments functional gap junctions epithelia actinin
Structure of the cardiomyocyte cell
• Blue arrows > electron dense regions > rich in proteins > \_\_\_\_ component
transverse
Structure of the cardiomyocyte cell
• Longitudinal components DOES NOT mean that gap/ion channels are on side of cells > there are some in regions where transverse component is less \_\_\_\_ ○ More easily for \_\_\_\_ to travel through the cells ○ Enriched in the \_\_\_\_, most logical place for them to be located
dense
ions
intercalated disks
Endocardium
- ____ cardiac layer.
- Similar to the vascular ____.
- Composed of:
- Endothelium - ____.
- Subendothelial connective tissue:
- Fibroblasts – ____ and elastic fibers.
- ____, nerves, ____.• Equivalent to endothelium of a BV
• Similar to tunica intima
○ Single layer of endothelial cells, in addition, also find other tissues: subendothelial CT (subendocardial CT), purkinje fibers, adipose, and capillaries
innermost tunica intima simple squamous epithelium collagen capillaries purkinje fibers
Conduction system of the heart
- Sinoatrial node:
• Node of small, typical cardiomyocytes at wall of ____ - ____, sets basic heart rate. - Atrioventricular node:
• Small cardiomyocytes.
• Located in inferior part of ____.
• Impulses travel from SA node via ____. - Atrioventricular bundle:
• Enters ____ and divides into right and left bundle branches.
• Midway down the interventricular septum, bundle branches split into ____ - Purkinje fibers:
• Approach the ____ of the heart and then turn superiorly.
right atrium
pacemaker
interatrial septum
internodal pathway fibers
interventricular septum
purkinje fibers
apex
• SAN
○ Not to ____ - only to generate changes in membrane potential
• AVN
○ Between atrium and ventriculum
• AVB
○ Ends up in PF
Located in the subendothelial CT > end of the conducting mechanism, and when receives electrical impulse it transmits it to the myocardial wall
• Ends up in PF
○ Located in the ____ > end of the conducting mechanism, and when receives electrical impulse it transmits it to the myocardial wall
• All cells have in common: instead of being required for heart contraction, they’re specialized in conducting ____
○ Derived from the cardiac myocytes > but they do not contract, either to generate ____, or to ____ impulse from one end of heart to another
contract
subendothelial CT
electrical impulses
electrical impulse
transmit
Purkinje Fibers
- Long rows of large diameter, barrel shaped cardiac muscle cells, specialized for ____ more than contraction.
- Large modified ____:
- ____ in groups.
- ____ nuclei and stain pale due to high ____ content and fewer myofibrils.
- Pale compared to myocardium and subendothelial CT
- IDENTIFY PURKINJE FIBER CELLS, no? > then be able to tell it’s a section of the HEART WELL
conduction cardiomyocytes cluster 1-2 glycogen
Cardiac muscle: purkinje fibers
- Larger than regular ____ fibers.
- ____-rich.
- ____-stained.
- Fewer ____.
- Pale > rich in glycogen (storage of glucose molecules) > require a lot of ____ bc they’re transmitting electrical impulses
- Myocardial cells > rich in mitochondria > red
cardaic
glycogen
pale
myofibrils
energy
Purkinje fiber cells
• Still some \_\_\_\_ fibers, but there are VERY FEW > do not form functional \_\_\_\_
contractile
sarcomeres
Cardiac valves
• 4 valves:
• 2 ____ - mitral and
tricuspid; in the chambers.
• 2 ____ - aortic and pulmonary.
atriovntricular
semilunar
Cardiac valves
• Histology:
• Endothelium – ____
lining.
- Connective tissue:
- Spongiosa – ____ CT; loose collagen.
- Fibrosa - ____ of connective tissue.
- Ventricularis: - dense connective tissue with many ____ and collagen fibers.• Valves are made of connective tissue
• AV valve shown, but the histological structure is the same bwteen then two different valves, just different sides
• Very rich in ____ - secreted by fibroblasts
○ Endothelium (simple squamous, a single layer)
○ Bulk of valve > connective tissue: (distringuished by morph and composition)
§ Spongiosa
□ Present on ____ side
□ Rich in collagen deposited in bundles in random/irregular form (dense irregular)
§ Fibrosa
□ EVEN MORE RICH OF COLLAGEN
§ Ventricularis
□ Very rich in collagen, but also rich in elastic fibers
□ Elastic on this side because the valves ____ (elastin makes it open and close, while collagen prevents breaking of valve where there is high resistance on one side - resistant to ____)
simple squamous epithelium
dense irregular
dense core
elastic
collagen
atrial
open and close
stretching
Fibrous “skeleton” of the heart
• ____ connective tissue within atrioventricular septum.
- Surrounds all 4 valves.
- ____ valve cusps
- Prevents ____ of valve openings
- Serves as an ____ for bundles of cardiac muscle
- Blocks direct spread of ____ from atria to ventricles• Fibrous skeleton anchors the valves to the cardiac organ
○ Similar action to ____ (prevents overstretching of heart)
○ Similar to ____ at end of skeletal muscle (allows insertion of cardiac muscle)
○ Since it’s CT > acts as an ____ > different parts of heart contract independently > electrically isolate one part of heart from another > the impulses can be restricted to atria, ventricle, etc. > so entire heart is not contracting at same time
dense anchors over-dilation insertion electrical impulses
pericardium
tendon
electrical insulator
