Histology

Question 1

What are 3 characteristics of purkinje fibres?

Answer 1

Specialised conducting fibres (not neurons)
1) Central nucleus
2) Few myofibrils
3) Numerous mitochondria
4) No T-tubule system
5) Numerous glycogen particles in cytoplasm

Question 2

How does the heart ensure electrical impulses from the atria enter the ventricles only through the AV node?

Answer 2

Fibrous skeleton: electrical insulator → isolated atria from ventricles
- only AV node passes through fibrous skeleton

Question 3

Why is conduction through the AV bundle slow?

Answer 3

very few gap junctions?

Question 4

Why is conduction through the purkinje fibres faster then the other parts of the heart?

Answer 4

1) lots of gap junctions
2) RMP is lower than rest of ventricular myocardium (70mV<90mV)

Question 5

What is the fibrous skeleton of the atria made of?

Answer 5

Mostly fibrocytes and few cardiac myocytes

Question 6

How is the SAN able to initial APs on their own?

Answer 6

1) Less -ve RMP (60-70 compared to 90mV)

2) Voltage-gated Ca2+ channels rather than voltage gated Na+ channels in other cardiac cells

3) Funny channels

Question 7

SNS innervated the whole heart include the SA and AV nodes but the PNS does not innervate _____________.

Answer 7

Ventricular muscles

Question 8

What are the 3 main layers of arteries?

Answer 8

1) Tunica intima
- endothelium and connective tissue

2) Tunica media
- smooth muscle and elastic/collagen fibres

3) Tunica adventitia
- connective tissue

Question 9

How can large lymphatic vessels be differentiated from venules?

Answer 9

Large lymphatic vessels:
1) Large lumen
2) Very thin and irregular wall
3) No RBCs

Question 10

What are 3 characteristics of elastic arteries?

Answer 10

1) Tunica intima internally lined by endothelial cells and thicker than muscular arteries

2) Endothelial cells:
- microvilli, pinocytotic vesicles, microfilaments, lysosomes, cell junctions

3) Tunica media
- concentrically arranged fenestrated laminae, collagen and smooth muscle fibres

4) Tunica adventitia
- fairly well-developed and no external limiting membrane

Question 11

What are 4 characteristics of muscular arteries?

Answer 11

1) Medium sized vessels
2) Tunica media (<40 layers of smooth muscle cells)
3) Collagen fibres, smooth muscles, and proteoglycans
4) Round lumen
5) Internal elastic limiting membrane
6) External elastic limiting membrane
7) Adventitia:
- collagen and elastic fibers
- blood vessels (vasa vasorum) and nerves

Question 12

What are 4 characteristics of arterioles?

Answer 12

1) Small vessels (<0.5mm)
2) Narrow lumen
3) Tunica intima:
- no subendothelial layer
4) No internal elastic limiting membrane
5) Tunica media (1-5 layers of circular smooth muscle fibers)
6) Poorly developed adventitia

Question 13

What are 3 characteristics of large veins?

Answer 13

1) Large
2) Well developed tunica intima
3) Tunica media:
- smooth muscles (but less than large arteries)
- abundant collagen and elastic fibres
4) Tunica adventitia:
- thickest
- contains neuro-vascular bundles

Question 14

What are 3 characteristics of medium veins?

Answer 14

1) Lined by endothelium
2) 1-9mm
3) Tunica intima:
- subendothelial layer present
4) Tunica media:
- several layers of smooth muscle cells mixed with collagen fibres
5) Tunica adventitia:
- well developed
- mainly collagen fibres
6) Valves

Question 15

What are 3 characteristics of venules?

Answer 15

1) Small (0.2-1mm)
2) Tunica intima:
- 1 layer of endothelial cells only
3) Tunica media:
- 0-a few laters of smooth mucles
4) Tunica adventitia:
- least developed
- rich in collagen fibres

Question 16

What are 4 characteristics of capillaries

Answer 16

1) Thin walled: Single layer endothelium
2) Basal lamina present
3) Allows RBC to pass 1 at a time
4) Endothelial cells held together by tight junctions
5) Pericytes usually present
6) Either continuous or fenestrated