Muscle and blood vessels (Dr Campbell) Flashcards
What is meant by the term muscle ?
When referring to a tissue, the term muscle also includes connective tissue elements and services (blood vessels and nerves).
Why does sk muscle look striated ?
Because its contractile proteins are highly organised into an almost crystalline array that refracts light (clearly visible at LM level).
How large are sk myocytes ?
Very large:
- length = 1 mm - 30 cm
- diameter = up to 100 microns
How are sk myocytes connected together ?
Mechanically connected by associated connective tissue.
What does the SR have which is absolutely crucial for contraction ?
Terminal cisternae.
What is a triad made of ?
Triads = 2 terminal cisternae of SR + 1 T-tubule
How many nuclei do sk muscle cells contain ?
Many nuclei (result from fusion of 2 or more sk myoblasts).
How do muscle cells meet the high NRJ demand for contraction ?
By having lots of mitochondria.
What are myofibrils ?
Bundles which contain contractile proteins.
What is the contractile unit of the myofibril ?
The sarcomere.
What are myofibrils made of ?
Myofilaments:
- thin filaments = actin
- thick filaments = myosin
What happens to the contractile proteins during contraction ?
Actin filaments slide over myosin filaments.
What do the striations in sk muscle represent ?
Alternating dark and light bands:
- dark band = overlap of actin and myosin
- light band = actin only
Where are actin filaments anchored ?
At one end of the Z-lines.
What delimitates the sarcomere ?
2 adjacent Z-lines.
What are the three general arrangements cells can form ?
Bundles, sheets or bands.
What is the structure of smooth muscle cells ?
How are they coupled ?
How big are they ?
Are their the same number of organelles as sk myocytes ?
- spindle-shaped
- mononucleate, w/ centrally located nucleus
- ectrically coupled to one another via gap junctions
- contain little connective tissue (compared to sk muscle)
- diameter = 5 microns (2 - 10 microns)
- length 0.2 mm (10 - 600 microns)
- SR = poorly developed –> cells possess plasmalemmal structures = caveolae
- no T-tubule system.
- few mitochondria (compared to sk muscle)
What are intercalated dics ?
Intercalated discs = specialized junctions made of desmosomes (mechanical coupling) and gap junctions (electrical coupling) between cardiomyocytes
How many nuclei do cardiomyocytes posess ?
1-2
How ar T-tubules arranged in cardiomyocytes ?
THERE ARE NO T-TUBULES IN CARDIOMYOCYTES !
How developed is the SR in cardiomyocytes ?
Lack terminal cisternae.
How many mitochondria to cardiomyocytes contain ?
A LARGE number (more than sk myocytes) !
How large are cardiomyocytes ?
- Diameter = 10 - 20 microns
- Length = 50 - 100 microns.
What are the contractile proteins in cardiomyocytes ?
How are these contractile proteins arranged ?
Contractile proteins:
- similar to those in sk muscle
- arranged in a branching myofibrillar network throughout the cytoplasm (the contractile unit of which = sarcomere)
What is the motor endplate ?
Synapse of an motoneuron on the sarcolema of a sk myocyte.
How is sk muscle controlled ?
CNS –> voluntary control
How is smooth muscle controlled ?
Autonomic nerves.
How is cardiac muscle controlled ?
- cardiac muscle cells –> can contract w/o neural stimulation –> automaticity
- timing of contraction –> controlled by specialized cardiac muscle cells w/in nodes
- Purkinje cells = specialized cardiac muscle cells that carry this control to the cardiac muscle cells of the myocardium
What are the different types of bl vessels ?
Venous circuit: large vein > medium vein > venule > fenestrated capillary
Arterial system: large artery > medium artery > arteriole > continuous capillary
What is the main role of arterioles ?
Arterioles = major contributors to peripheral resistance, and therefore blood pressure
What is the role of capillaries + small venules ?
Exchange nutrients, gases + metabolites
What are continuous capillaries ?
- most common type
- adjacent endothelial cells –> connected to each other via junctional complexes
- most impermeable type
What are fenestrated capillaries ?
- endothelial cells –> have small pores = fenestrae
- adjacent cells –> connected via junctional complexes
- quite/very permeable (typically found in kidney –> Bowman’s capsules + in GI tract –> villi of small intestine)
What are endothelial cells ?
- cells lining all components of the circulatory system
- simple squamous epithelium (a single layer of flattened cells)
What are the 3 layers of blood vessels ?
- Tunica intima = inner-endothelial cells + connective tissue (avascular)
- Tunica media = middle layer –> smooth muscle + connective tissue (may be absent from small vessels)
- Tunica adventitia = outer layer –> connective tissue (may be absent from small vessels)
How are the media and adventitia different in larger vessels ?
Media + adventitia of larger vessels –> have their own blood supply from vessels = vasa vasorum (= the vessels of the vessels)
What are the 2 types of large arteries ?
What are their respective characteristics ?
Large elastic arteries (e.g. aorta):
- Intima = endothelial cells + thin layer of connective tissue (collagen and few elastic fibres)
- Media = thick spiral of smooth muscle interleaved w/ sheets of elastic fibres (+collagen fibres)
- Adventitia = thick connective tissue (collagen), vasa vasorum + nerves
Large muscular arteries (most systemic arteries):
- Intima = endothelial cells, prominent layer of CT = inner elastic lamina (IEL) (elastic fibres + some collagen fibres)
- Media: thick spiral of smooth muscle + limited CT (collagen + few elastic fibres)
- Adventitia = thick CT, external elastic lamina (EEL, elastic fibres + collagen) bl vessels + nerves.
What are the different layers of arterioles composed of ?
- Intima = endothelial cells, IEL absent from small arterioles
- Media = smooth muscle (approx. 3 to 6 cells thick)
- Adventitia = merges with surrounding CT, no EEL.
What are the different layers of capillaries composed of ?
Endothelial cells. No media + no adventitia.
What are the different layers of venules and veins composed of ?
- Intima = endothelial cells, no IEL
- Media = smooth muscle (venules 1 - 2, veins 2+ cells thick)
- Adventitia = absent or indistinct, merging with surrounding CT
Veins > 2 mm diameter contain valves: two leaflets of connective tissues (collagen fibres) covered with endothelial cells.
Why do veins > 2mm thick contain valves ?
To prevent back-flow of blood.
