Lecture 7: Cardiac Histology Flashcards
What are some hallmarks of smooth muscle cells?
- Non-striated (very smooth)
- Smooth muscle cells occur as sheets/bundles of elongated fusiform cells
- Centrally located nucleus
How are smooth muscle cells interconnected?
Gap junctions
What types of contractions do smooth muscle produce?
- Continuous contractions of low force
- Rhythmic contraction responsive to ANS stimulation
- Sustain long contractions
What do smooth muscles anchor to during contractions?
Cytoplasmic Densities/Dense Bodies
Smooth muscles lack T-tubules. How does calcium enter the cell to initiate movement?
Caveolae: very similar to T-tubules
What are some of the key histological features of cardiac muscle?
- Cells short, branched, Y shaped
- Extensive capillaries
- Intercalated discs/transverse junctions
- Purkinje cells (may or may not be able to see depending on magnification)
- Lipofuscin granules
What is present in cardiac cells that allows the passage of electrical current?
Intercalated discs/transverse junctions
Specialized gap junctions only found in cardiac cells
What type of cells are present in cardiac muscle that act as the “pacemaker” cells?
Purkinje Cells
What are the two layers of pericardium?
- Fibrous Pericardium: outer covering of dense CT
- Serous Pericardium: provides fluid to reduce friction
What are the two layers of serous pericardium?
- Parietal Serous Pericardium: lines inner surface of fibrous pericardium
- Visceral Serous Pericardium (aka Epidcardium): covers outer surface of heart
Where is the pericardial cavity located?
Between parietal and visceral layers of serous pericardium
What are the key features of the epicardium/visceral serous pericardium?
- Outermost layer of the heart wall (can be thick)
- Lined with mesothelium (simple squamous)
- Dense fibrocollagenous CT with elastic fibers
- Branches of coronary arteries are embedded in adipose tissue
- Can find nerves
What are some key features of the myocardium?
- Thickest layer of the heart
- Contains
- Striation
- Intercalated discs
- Dyad T tubule system
- Lot of mitochondria
- Lipofuscin granules
- Atrial granules (myoendocrine cells)
What are the key features of the endocardium?
- Simple squamous endothelium
- Areolar CT
- Reduce friction with blood vessles and valves
Where are intercalated discs located?
- At sites where cells meet end to end
- Perpendicular to length of cell
- Always coincide with Z lines
What are the three types of membrane-membrane contact in cardiac muscle cells?
- Fascia adherens (Transverse/perpendicular region)
- Desmosomes (Transverse/perpendicular region)
- Gap junctions (Longitudinal/parallel region)
What are the features of the fascia adherens?
- Actin filaments at end of terminal sarcomeres
- Transmit contractile forces between cells
What are the features of desmosomes?
- Provide anchorage for intermediate filaments of the cytoskeleton: structural support
- Prevent tearing depending on the force of contraction
What are the features of gap junctions?
- Sites of low electrical resistance
- Allow excitation and communication to pass between cells
What makes up a Dyad T-tubule?
Where is it found
- 1 T-tubule + 1 SR cisterna
- Found at Z lines
What is the function of Dyad T-tubules?
Permits uniform contraction of myofibrils within a single cardiomyocyte
What are nodal cardiomyocytes?
- Modified cells in SA/AV node that initiate and relay electrical signals
- Lack interlacated disc
- Only modify rate of intrinsic cardiac muscle contraction
What are Purkinje fibers?
What are some of their histological features?
- Conducting fibers that generate and transmit impulse
- Located at periphery of myocardium/ adjacent to to endocardium
- Lack T tubules
- Cells larger and have larger nucleus
- Few intercalated discs
- Nuclei are more round in appearance
What are lipofuscin granules?
- Small bodies that accumulate with age in stable non-dividing cells
- Contain material from residual bodies after lysosomal digestion
- Pretty close to the nucleus on histology slide (if staining permits you to see them)
- gold-ish color
Describe atrial granules.
- Atrial cardiomyocytes with membrane bound granules
- Mostly in right atrium
- Contain ANF
- Increases GFR
- Decrease Na+ and H2O retention in kidneys
How does the endocardium differ between ventricles and atria?
Ventricles
- Subendocardial layer which contains Purkinje Fibers
- Thin layer of CT and smooth muscles
Atria
- Purkinje Fibers are closer to endothelium and intermixed with myocardium
What are the histological features of the cardiac/fibrous skeleton?
- Dense irregular CT located in endocardium
- Anchors valves and surrounds AV valves to maintain shape, acting like a ligament
What is function of the cardiac/fibrous skeleton?
- Electrical insulator between atria and ventricles
- Insertion of cardiac muscle
What are the histological features of heart valves?
- Core of fibroelastic CT (lamina fibrosa)
- Covered by endothelium
- Fibroelastic layer condenses to form valve ring (makes central portion of valve)
Identify the tissue type.
Smooth muscle
Identify the tissue types.
Top: longitudinal section of smooth muscle
Bottom: cross section of smooth muscle
Identify the tissue type.
Cardiac muscle
Identify the three arrows.
Top arrow: endocardium
Middle arrow: myocardium
Bottom arrow: epicardium
Identify the tissue type shown.
Epicardium
Identify the arrows.
Intercalated discs
Identify features of this picture.
Top to bottom:
- Desmosome
- Desmosome
- Fascia adherens
- Gap junction
- Fascia adherens
Identify features of this picture.
Left (top to bottom)
- Intercalated disc
- Gap junction
Right
- Terminal cisterna of SR
Identify the tissue feature.
Lipofuscin granules
Identify the circled structure.
Atrial granules
Identify the features on the histological slides.
- Ventricular endocardium (with subendocardium)
- Atrial endocardium
- M: myocardium
- P: Purkinje Fibers
Identify the cell type.
Purkinje Fibers
Identify.
Left to Right (Top to Bottom)
- Left atrium
- Endocardium
- Endothelium
- Valve ring
- Left ventricle
- Endocardium
- Endothelium
- Lamina fibrosa
