1- histology of heart vessels

Question 1

what is the tunica intima?

Answer 1

inner layer
- a single layer of squamous epithelial cells termed endothelial cells supported by basal lamina and a thin layer of connective tissue

Question 2

what is tunica media?

Answer 2

middle layer
- made up predominantly of smooth muscle, thickness varies tremendously

Question 3

what is tunica adventitia?

Answer 3

outer layer
- made up of supporting connective tissue

Question 4

what is route from arteries →veins?

Answer 4

arteries →elastic arteries →muscular arteries →arterioles →meta arterioles →capillaries → venules → post capillary venules →veins

Question 5

what is
a) internal elastic membrane?
b) external elastic membrane?

Answer 5

a) layer of elastic tissue that separates tunica intima from the tunica media
b) layer of elastic tissue that separates tunica media from the tunica adventitia

Question 6

what stains elastic fibres?

Answer 6

are not stained using most common stains (including H&E) but can be visualized with special stains like the one shown here – here the elastic fibres stain black.

Question 7

what are elastic arteries?

Answer 7

the very largest arteries e.g. aorta

named this due to many sheets of elastic fibres in their tunica media provide elastic recoil

Question 8

what is vaso vasorum?

Answer 8

vascular supply to large vessels as only the inner part of wall can obtain nutrients from lumen

Question 9

what are arterioles made up of?

Answer 9

only 1 or 2 layers of smooth muscle in tunica media & almost no adventitia
diameter = 30-200 micrometre

• important for controlling blood flow

Question 10

what changes from arteriole →meta arteriole?

Answer 10

smooth muscle replaced by discontinuous non-contractile cells called pericytes (terminates into capillaries)

Question 11

what are capillaries absent in?

Answer 11

• Epithelial cells resting on basement membrane
• Epidermis of skin, hair and nails
• Cornea of the eye
• Hyaline cartilage

Question 12

what are capillaries composed of?

Answer 12

essentially composed of endothelial cells & a basal lamina
- diameter of 4-8 micrometre
- they often have pericytes at intervals just outside basal lamina - these are connective tissue cells that have contractile properties

Question 13

what are precapillary sphincters?

Answer 13

composed of smooth muscle, at the beginning of the capillary to help control flow through the network

Question 14

what are capillaries important for?

Answer 14

These are important sites for exchange e.g. cells moving into the tissue in inflammation

Question 15

when do vessels start to be referred to as venules (after capillaries) ?

Answer 15

Once vessels begins to acquire intermittent smooth muscle cells in a tunica media layer (generally less than 50micrometre)

Question 16

what do capillary networks drain into?

Answer 16

post-capillary venules (10-30 micrometre) which are endothelial cell lined and contain a thin layer of connective tissue & occasional pericytes

Question 17

what is different in vein & artery?

Answer 17

• veins have a relatively thin but continuous tunica media typically consisting of a few layers of smooth muscle (tunica media smooth muscle is thinner than arteries)

in large veins - they have a thick tunica adventitia which incorporates bundles of longitudinally oriented smooth muscle

Question 18

why do veins contain most of blood in the body?

Answer 18

Veins are flexible and can accommodate expansion

Question 19

what are valves made of in most small to medium sized veins?

Answer 19

inward extensions of tunica intima

Question 20

what are the 3 layers of the heart?

Answer 20

1. endocardium = inner layer
2. myocardium = middle layer
3. epicardium = outer layer

(outside epicardium there is visceral serous pericardium then pericardial cavity & then parietal serous pericardium which is covered in adipose tissue)

Question 21

what is endocardium made up of?

Answer 21

endocardium = innermost layer

• endothelium
• basal lamina
• thin layer of collagen fibres
• layer of denser connective tissue

Question 22

what is subendocardium?

Answer 22

in some areas there is also a subendocardium of loose connective tissue containing small blood vessels and nerves and the branches of the impulse conducting system

Question 23

what is myocardium made up of?

Answer 23

myocardium = thick middle layer

• bundles & layers of contractile cardiac muscle fibres
• individual muscle fibres are surrounded by delicate, collagenous connective tissue with a rich network of capillaries

Question 24

what is cardiac muscle cells nucleus like?

Answer 24

they have single central nucleus
= they have intercalated discs passing across fibres at irregular intervals
- they are also connected by cellular junctions like gap junctions, macula adherens/desmosomes and zonula adherens

Question 25

what is epicardium made up of?

Answer 25

= outer layer of heart

• a single layer of flattened epithelium called mesothelium
• basal lamina
• fibroelastic connective tissue and in some places adipose tissue (coronary vessels are typically embedded in this adipose tissue)

Question 26

what is the pericardium made up of?

Answer 26

fibrous pericardium = sac of tough fibrocollagenous connective tissue

serous pericardium = made up of a layer of simple squamous epithelium (mesothelium) back by a basal lamina & connective tissue.

*parietal serous pericardium lines inner surface of fibrous pericardium and visceral serous pericardium covers surface of the heart

Question 27

what are the 2 serous pericardial layers separated by?

Answer 27

thin pericardial cavity which contains a small amount of pericardial fluid that provides lubrication for heart movement

Question 28

what is the hearts fibrous skeleton?

Answer 28

The heart has a fibrous skeleton formed by thick bands on fibrous connective tissue around the heart valves between atria & between ventricles

• this connective tissue supports the valves but also provides the attachment for cardiac muscle fibres

Question 29

what is the valves structure?

Answer 29

• they have outer endothelial layer with basal lamina
• layer of collagen & elastic fibres
• a core of dense connective tissue called the limona fibrosa, that is in continuity with the fibrous skeleton
• the leaflets of the valves separating the atria from the ventricles (the mitral & tricuspid) are anchored to papillary muscles in the wall of the ventricle by collagenous strands called the chordae tendineae which merge with lamina fibrosa

*no blood vessels in valves

Question 30

what is the lamina fibrosa?

Answer 30

the core of the heart valve and is dense irregular connective tissue that is continuous with the fibrous skeleton of the heart (valve is covered on both sides by endothelium)

Question 31

what are the 3 types of cardiac muscle cells?

Answer 31

• Contractile cells (99%)
• Pacemaker cells
• Conducting cells

Question 32

what are pacemaker muscle cells?

Answer 32

highly specialised muscle cells
- they’re considerably smaller (4-8 micrometre) than contractile cardiomyocytes and are embedded more extensively in the matrix of connective tissue

• histologically they appear pale (called P cells) because of the paucity of organelles within them.

They have:
- few myofibrils (and these are irregularly arranged)
- little glycogen
- no proper T-tubule system

Question 33

what is cardiac contractility route? (SA node etc)

Answer 33

at junction of atria & ventricles the depolarisation is picked up by the atrioventricular node and after a delay, conducted rapidly (2-4 m/sec) down interventricular septum via AV bundle that as it descends produces right & left bundle branches.
These fibres reach the inferior tip or apex of the heart and then turn upwards. the conducting system then contacts a complex network of purkinje fibres beneath the endocardium of the ventricles

Question 34

what are purkinje fibres?

Answer 34

• Unlike the small pacemaker and bundle fibres, the Purkinje fibres are larger than normal cardiac muscle cells.
• They are found in the subendocardial layer just deep to the endocardium.

They have:
- abundant glycogen
- no T-tubules
- no intercalated discs
- sparse actin and myosin filaments, which tend to be found at the periphery of the cells.

In histological sections they appear pale, and often exhibit a very pale/clear centre.
- The Purkinje fibres distribute the excitatory activity such that ventricular contraction generally occurs from inferior to superior