Histology of the heart and blood vessels

Question 1

What are the 2 related systems which make up the circulatory system?

Answer 1

The cardiovascular system (blood vascular system) - consisting of the heart, arteries, capillaries and veins
The lymphatic system

Question 2

What are the roles of the CV system?

Answer 2

Transport of oxygen and nutrients to the tissues.
Transport of CO2 and other metabolic waste from the tissues.
Temperature regulation.
Distribution of hormones and immune cells.
Reproductive function in males: penile erection.

Question 3

What are the 3 layers of the blood vessels?

Answer 3

Tunica intima - inner layer of single squamous epithelium called endothelial cells supported by the basal lamina and a thin layer of connective tissue
Tunica media - prodominately smooth muscle , the thickness of this layer is very varied
Tunica adventita- outer layer of supporting connective tissue

Question 4

What separates the tunica intima and tunica media?

Answer 4

a layer of elastic tissue called the internal elastic membrane

Question 5

What separates the tunica media and the tunica adventitia?

Answer 5

a layer of elastic tissue called the external elastic membrane

Question 6

What are the largest arteries collectively termed as?

Answer 6

Elastic arteries as they have many sheets of elastic fibres in the tunica medica in order to provide elastic recoil

Question 7

How does the arterioles structure differ from the general artery structure?

Answer 7

only have one or two layers of smooth muscle in their tunica media and almost no adventitia. Particularly important for controlling blood flow in tissue

Question 8

What is the structure of the wall of a capilliary?

Answer 8

Essentially a endothelial layer and a basal lamina

Question 9

What are pericytes?

Answer 9

connective tissues cells with contractile properties which are just outside the basal lamina of capillaries at intervals

Question 10

3 types of capillary

Answer 10

Continuous - more common in muscle, connective tissue, lung, skin, nerve
Fenestrated capillaries - have 50 nm pores in the wall - in the gut mucosa, endcocrine glands, glomeruli of the kidney
Sinusoidal and discontinuous capillaries - large gaps macromolecules can fit through - basal lamina is either discontinuous or absent - in the liver, spleen and bone marrow

Question 11

What connects small arterioles to a postcapillary venule?

Answer 11

a network made up of metarterioles, thoroughfare channels and capillaries. Precapillary sphincters, composed of smooth muscle, at the beginning of the capillary help control flow through the network.

Question 12

What is a postcapillary venule?

Answer 12

endothelial cell-lined, with a thin layer of connective tissue and occasional pericytes (important when moving cells into the tissue in inflammation)

Question 13

What are venules?

Answer 13

Similar to post-capillary venules but have an intermittent smooth muscle layer in the tunica media

Question 14

What is the structure of veins?

Answer 14

Have a tunica intima, a relatively thin but continuous tunica media with a few layers of smooth muscle - much thinner than in an artery

• largest veins have a tunic adventitia which incorporates bundles of longitudinally orientated smooth muscle
• they have valves - extensions of the tunica intima

Question 15

3 layers of the heart

Answer 15

endocardium - inner layer
myocardium - middle layer
epicardium - outer layer

Question 16

What is the structure of the endocardium?

Answer 16

• inner surface including valves
• Endothelium
• Basal lamina
• Thin layer of collagen fibres
• Layer of denser connective tissue
• Also a subendocardium of loose connective tissue in some areas which contains small blood vessels and nerves and the branches of the impulse conducting system.

Question 17

What is the structure of the myocardium?

Answer 17

• Thick middle layer
• bundles & layers of fibres of contractile cardiac muscle
• individual muscle fibres which are surrounded by delicate, collagenous connective tissue with a rich capillary network

Question 18

What is the role of the intercalated discs?

Answer 18

Attaches cells but also allows the spread of electrical activity

Question 19

What is the structure of the epicardium?

Answer 19

outer layer of the heart

• on the heart surface a single layer of flatttened epithelium called mesothelium
• basal lamina
• fibroelastic connective tissue and in some places adipose tissue

Question 20

What are the 2 parts of the pericardium?

Answer 20

Fibrous pericardium - tough fibrocollagenous sac of connective tissue
Serous pericardium - made up mesotheluim which is backed by a basal lamina and connective tissue

Question 21

Where is the serous pericardium?

Answer 21

It lines the inner surface of the fibrous pericardium - termed the parietal pericardium an covers the heart surface - where it is termed the visceral serous pericardium

Question 22

What is found between the 2 mesothelial layers?

Answer 22

They are apposed to each other and sepataed by a small amount of pericardial fluid which provides the heart with lubrication for movement

Question 23

Describe the heart’s fibrous skeleton

Answer 23

formed by thick bands of fibrous connective tissue around the heart valves, atria and ventricles.
The connective tissue provides support for the valves and an attachment for the cardiac muscle fibres
electrically isolates the atria from the ventricles

Question 24

Histology of the heart valves

Answer 24

• outer endothelial layer with a basal lamina
• layer of collagen and elastin fibres
• dense core of connective tissue called lamina fibrosa - continuous with the fibrous skeleton
• leaflets of the atrioventricular valves anchored to papillary muscles in the wall of the ventricle by collagenous strands called the chordae tendineae, which merge with the lamina fibrosa (continuous with the fibrous skeleton).
• no blood vessels

Question 25

What are the 3 types of cardiac muscle cells?

Answer 25

Contractile cells (99%)
Pacemaker cells
Conducting cells

Question 26

What is the histology of the pacemaker cells?

Answer 26

highly specialised muscle cells - smaller than the cardiac myocytes
embedded in a more extensive connective tissue matrix
few myofibrils and no proper T-tubule system
- appear pale

Question 27

Where are the conducting cells found?

Answer 27

In the bundle of His and in the purkinje fibres

The purkinje fibres are found in the subendocardial layer just deep to the endocardium

Question 28

What is the histology of the purkinje conducting fibres?

Answer 28

abundant glycogen
no T-tubules
no intercalated discs
sparse actin and myosin filaments (tend to be found at the cell periphery)
appear pale - often exhibit a very pale/clear centre.
The Purkinje fibres distribute the excitatory activity such that ventricular contraction generally occurs from inferior to superior.

Question 29

What does the lymphatic vascular system consist of?

Answer 29

relatively thin walled lymphatic vessels that drain interstitual fluid - eventually returning to the veins at the neck base

Question 30

What is the benefit of interstitual fluid being drained by the lymphatic vasculature?

Answer 30

lymph passes through the lymph nodes which provides immunological surveillance

Question 31

What is the structure of the lymphatic vessels?

Answer 31

no central pump
smooth muscle in walls
hydrostatic pressure in the tissue and compression of the vessels by voluntary muscle, combined with valves in the vessels, produces flow.