Veterinary Histology: Cardiovascular System

Front 1

Cardiovascular system function

Back 1

- flow of blood and lymph

Front 2

Cardiovascular system components

Back 2

- heart (pump)
- blood vessels and lymphatics (plumbing)
- includes pulmonary and systemic circulations

Front 3

Heart

Back 3

- consists of striated cardiac muscle
- has a conducting system that allows for coordinated electrical "ignition" of the heart and this is made of nerves and Purkinje fibers
- there may be an os cordis

Front 4

Purkinje fibers

Back 4

- modified cells that are derived from cardiac muscle

Front 5

Layers of the heart wall

Back 5

- Epicardium: outer layer
- Myocardium: thick, middle layer
- Endocardium: thin, inner layer

Front 6

Epicardium

Back 6

- outer layer of heart wall
- single layer of mesothelial cells
- scant underlying connective tissue
- along the outer surface are the epicardial adipose tissue, nerves and blood vessels

Front 7

Myocardium

Back 7

- thickest heart wall layer
-composed of striated skeletal myocytes, blood vessels and conduction system

Front 8

Endocardium

Back 8

- inner layer of heart wall
- single layer of endothelial cells with their underlying connective tissue

Front 9

Flow of conduction

Back 9

- Signals are initiated at the SA node which is located at the junction of the right atrium and caudal vena cava (cristae terminalis)
- Signal extends to the AV node and through the AV bundle (bundle of His)
- then it goes to the right and left bundle branches and then to the subendothelial branches (Purkinje fibers)

Front 10

Layers of the cardiac valves

Back 10

- Fibrosa
- Spongiosa
- Ventricularis

Front 11

Fibrosa

Back 11

- core of the cardiac valve
- consists of dense fibrous extensions from the os cordis

Front 12

Spongiosa

Back 12

- loose connective tissue on the "upper" side of the valve
- contains abundant elastic fibers and proteoglycans in addition to collagen making it flexible and compressible
- acts as a shock absorber for the valves

Front 13

Ventricularis

Back 13

- layer of dense connective tissue and elastin fibers on the underside of the valve

Front 14

Regulation of Heart Rate

Back 14

- accomplished by the sympathetics (raise rate) and parasympathetics (lower rate)
- it can also be influenced by circulating substances such as epinephrine, norepinephrine, calcium, thyroid hormone, caffeine, etc

Front 15

How cardiovascular system is monitored

Back 15

- Baroreceptors
- Volume receptors
- Chemoreceptors

Front 16

Baroreceptors

Back 16

- located in the carotid sinus and aortic arch

Front 17

Volume Receptors

Back 17

- located within the walls of the cardiac atria and ventricles and measure cardiac distention
- incite secretion of atrial natriuretic factor which stimulates diuresis and natriuresis by increasing GFR

Front 18

Chemoreceptors

Back 18

- carotid and aortic bodies provide information about O2 and CO2 concentrations and pH

Front 19

Layers of blood vessels

Back 19

- Tunica intima
- Tunica media
- Tunica adventitia

Front 20

Tunica intima

Back 20

- innermost layer
- includes endothelium, its basal lamina and sparse loose subendothelial CT
- in arteries the outer edge of the intima is defined by the internal elastic lamina

Front 21

Internal elastic lamina

Back 21

- defines outer edge of the tunica intima
- it is a thick, wiggly, eosinophilic band of elastin

Front 22

Tunica media

Back 22

- consists of smooth muscle with associated CT and sometimes elastic fibers
- much larger in the arteries than in the veins

Front 23

Tunica adventitia

Back 23

- loosest, outermost coat
- mostly fibrous tissue
- boundary between the media and adventitia is defined by the external elastic lamina
- adventitia of very large arteries and veins have the vasa vasorum

Front 24

External elastic lamina

Back 24

- boundary between the tunica media and tunica adventitia

Front 25

Vasa vasorum

Back 25

- present in thick arteries and veins
- it is a network of small blood vessels that supplies oxygen and nutrients and vascular drainage to the outer portions of the vessel

Front 26

Endothelium

Back 26

- line all vascular spaces in the body
- following activation they have many roles in inflammation and thrombosis including:
1. maintaining a selectively permeability barrier (caveolae, pinocytotic vesicles, intercellular junctions, basement membranes)
2. preventing unwanted thrombosis
3. moderating blood flow and blood pressure (influences vascular constriction or dilation)
4. regulating immune response
5. producing growth factors and metabolizing a large number of inflammatory substance, hormones

- in some species, endothelium also plays an important role in indicentally modifying lipoproteins via oxidation, which enhances their phagocytosis by macrophages and leads to atherosclerosis

Front 27

Large arteries

Back 27

- elastic
- include the aorta and its large branches
- known as conducting arteries
- function is to "smooth out" blood flow, and so they expand to receive a large bolus of blood during systole and they contract and expel this blood during diastole

Front 28

Medium arteries

Back 28

- muscular
- distributing arteries

Front 29

Small arteries

Back 29

- resistance vessels
- final branches of arterial circulation
- distribute blood to capillary beds
- tunica media is small

Front 30

Capillaries

Back 30

- extremely thin-walled and narrow
- precapillary sphinctors are present where the capillaries arise from arterioles

Front 31

Continuous capillaries

Back 31

- present in most tissues
- surrounded by a continuous basement membrane
- endothelial cells are not fenestrated and are joined by tight junctions
- substances are transported across endothelial cells by caveolae and pinocytotic vesicles
- along the capillaries there are spindle/mesenchymal cells between the endothelium and the basement membrane called pericytes and they have functions of both fibroblasts and smooth muscle cells

Front 32

Fenestrated capillaries

Back 32

- present in kidney, intestinal villi, choroid plexus, ciliary process (basically any tissue where there is a lot of fluid flow)
- continuous basement membrane but the endothelial cells have holes (fenestrae)
- the holes are covered by a thin membrane and they allow for easy diffusion of substances between the circulation and body tissues

Front 33

Discontinuous (sinusoidal) capillaries

Back 33

- present in liver and spleen
- allow for maximal exchange of cells and large macromolecules
- basement membrane is present but is discontinuous
- endothelial gaps are even larger than those in fenestrated capillaries

Front 34

Venules

Back 34

- small vessels that immediately follow the capillary bed
- postcapillary venules are the most important site at which blood cells migrate into body tissues via diapedesis (important in inflammatory processes)

Front 35

Veins

Back 35

- thin-walled and very compliant in comparison to arterial vessels of the same diameter
- contain the same 3 vascular tunics as arteries but there is no inner elastic lamina, the tunica media is thinner and blends into the adventitia
- there are valves that are extension of the intima that prevent back-flow of blood

Front 36

Lymphatics

Back 36

- begin as blind-ended sacs in proximity to capillary beds
- they are extremely thin-walled and lack tight junctions
- lymph flows on account of intrinsic contractions of their mural smooth muscle, and by extrinsic contraction of surrounding muscles