CARDIAC UNIT: CARDIAC CONTRACTILE ELEMENTS Flashcards
Differentiate between the different circulator system types
systemic: oxygenated arterial blood with multiple parallel paths to supply tissue
Pulmonary: deoxygenated arterial blood
define: mitral valave
located between the upper left heart chamber (left atrium) and the lower left heart chamber (left ventricle)
define and describe the: tricuspid valave
controls the flow of blood from your heart’s right atrium (top chamber) to the right ventricle (bottom chamber
- greater stability for the higher pressure the right side of the heart sees
describe the function of the annulus fibrosus
supports valves preventing prolapse. provides electrical insulation between atria and ventricle
Describe the structure of the ventricles
Left ventricle is thicker - pumps blood to systemic circulation
Right ventricle is 5x lower in blood pressure
Give the function of the chordae tendinae
Chordae tendinae - regulate and support valves (provide tension)
differentiate between the endocarium, myocardium, and epicardium
- Endocardium: inner lining of the ventricular wall
- Myocardium: middle layer of ventricular wall - made up of 95% cardiomyocyte by mass
- Epicardium: outer layer of the ventricular wall
Describe the cellular ultrastructure of the cardiac myocyte
Striated muscle
120-150 μm long
10-20 μm wide
Rectangular shape
In comparison to a skeletal muscle cells, cardiomyocytes are much smaller
What are the physiological adaptions that occur when there is pressure overload in the heart
Can be due to hypertension, weightlifting
High pressure means the heart works harder
- Causes: increased myocyte width 2-3 fold (build more contractile elements to handle load)
- More parallel contractile units
How can volume overload in the heart occur? What are the physiological adaptations when there is volume overload in the heart
- Can be due to valve failure or aerobic exercise
- Valve failure can cause backflow
- Valve failure incident increases with age
- Causes: increased cell length up to 10-20% due to the stretching of contractile units
Describe sarcomere structure
~2.2 um
Made up of thin actin and thick myosin filaments
Define: sarcomere
basic contractile unit of a muscle fiber
Define: Z line
any of the dark thin bands across a striated muscle fiber that mark the junction of actin filaments in adjacent sarcomeres
forms sarcomere boundary
thin filaments run through the Z line
contains α-actinin
~2.2 μm long
Define: I band
The region of a striated muscle fibre that contains only thin (actin) filaments
decreases with contraction
increases with relaxation
contains only actin filaments
Define: A band
The dark band of the muscle sarcomere that corresponds to the thick myosin (protein) filaments
contains thick myosin filaments
doesn’t change with contraction
Define: H zone/band
the central zone of a sarcomere that looks lighter under a microscope. This area of the sarcomere is a lighter portion of the A-band where there is no overlap between the thinner filaments (actin), and the thicker filaments (myosin).
centre of A band (myosin)
Define: M line
thin dark line across the center of the H zone of a striated muscle fiber
attachment for myosin
List and describe the 7 structural elements of the cardiomyocyte cell.
- Contractile elements (sarcomeres) make up 50% of cell volume
Other 50%:
- T-tubules: invagination of the sarcolemma at Z line
- Bring iron right into heart of muscle
- align with Z-lines
3.Mitochondria: energy generation
make up 30-35% cell volume
- Subsarcolemmal mitochondria: to provide energy for ATP driven transport like ATP driven pumps (potassium, calcium, etc.)
- Intermyofibrillar mitochondria: to provide energy for cross bridge cycling
- Sarcoplasmic reticulum: repository for Ca2+ - modified form the endoplasmic reticulum
- Nuclei
- mono or binucleated
-In skeletal cells, they’re polynucleated - Golgi
- Ribosomes
Explain how cardiac myocytes are physically and functionally coupled
- Myocyte branching: myocytes are connected. they are coupled at intercalated disks. allows heart muscle fibers to contract in unison
- provides longitudinal and diagonal coupling - Macula adherens (aka desmosomes):
- cytoskeletal proteins provide physical coupling (“stitches”) between cells - Gap junction (aka nexus): allows muscle fibers to be connected electrically. Connexins provide electrical coupling which creates a functional syncytium
- there are 2 connexons per gap junction.
- a connexon is a hexamer of 6 connexins
- regulated by permeability (e.g. by acidosis)
Define: functional syncytium
Functional syncytium: a unit of contraction comprised of a network of electrically and physically connected cardiac muscle cells (via gap junctions and desmosomes)
able to contract without CNS input
What is the ratio of actin to myosin?
2-1
Define and describe titin
Titin: largest known protein. Exists from M-line to Z-line (half a sarcomere long). Stabilizes position of contractile elements. Acting like a spring, returns stretched muscle to resting length. Protects the heart from being stretched too much.
Define and describe nebulin
- from Z line to thin filament ends
- Runs along thin filament and stabilizes structure
How do thin filaments form? Describe structure of thin filaments.
G-actin twists self to become actin filaments.
Helical in shape. 13 molecules per turn
