CVS

The Cardiovascular System is composed of the [[heart]], blood vessels and blood. Their function is to:

- mediate the continuous movement of all body fluids (also the fluid in the extracellular spaces, due to the differential pressure gradients, which are created due to the pumping of the heart)

- transport of oxygen and nutrients towards the tissues

- transport of carbon dioxide and other metabolic waste away from the tissues

- temperature regulation

- distribution of molecules (e.g. hormones, immune cells)

There are two types of CVS tissues:

- [[Cardiac tissue]] = wall of the heart, which consists of three layers

- Vascular tissue = arteries, veins and capillaries

The [[Cardiovascular System]] has a common basic structure of three tunics (coats):

1. [[tunica adventitia]] (externa)(additional coat)

- supports all the other layers

- [[vasa vasorum]] = blood vessels that supply the tunica and externa and tunica media

2. [[tunica media]] (middle coat)

- intermediate muscular layer, it is comprised of smooth muscle cells. This layer helps to move the blood through the arteries.

- external elastic lamina

3. [[tunica intima]] (inner coat)

- is the inner lining ([[endothelium]])

- supportive basal lamina

- connective tissue (subendothelial connective tissue)

- internal elastic lamina = allows for a certain amount of stretch, that allows for the passage of blood

Pericardium

The pericardial membrane surrounds the heart and consists of three layers and the pericardial cavity. The [[pericardium]] is thus the covering of the heart. It consists of:

- [[fibrous pericardium]] (outer layer)

- composed of collagen bundles - tough and anchors the heart to diaphragm and vessels.

- [[serous pericardium]]

- parietal layer of the serous pericardium

- fused to the fibrous pericardium

- visceral layer of serous pericardium = [[epicardium]]

- [[pericardial cavity]] = lies in-between the parietal and visceral layer and is fluid filled

Thus, the pericardial membrane and heart wall share the [[epicardium]].

The fibrous pericardium limits overfilling of the hearts, as it has no elastic fibres or almost no elastic fibers. The pericardial fluid allows for friction free movement during contraction.

The clinical relevance: [[cardiac tamponade]]: excess fluid builds within the pericardial cavity --> cardiac tamponade (with each contraction more fluid accumulates in the pericardial cavity) --> puts pressure on the heart and prevents full relaxation --> heart contains slightly less blood as they begin each heart cycle --> death.

Layers of the Heart Wall

The heart consists of three layers:

1. [[epicardium]] (outermost layer)(visceral pericardium) = tunica adventitia

- Produces serous fluid

- [[mesothelium]] (squamous cells)

- arteries run through, which supply the underlying myocardium

2. [[myocardium]] (thickest layer) = tunica media

- [[Cardiac muscle tissue]]

- Responsible for the beating of the heart

3. [[endocardium]] (thin inner layer) = tunica intima

- Lines the lumen of the heart, and is thus in direct contact with the blood

- endothelium = special squamous epithelium

- elastic and collagen fibers

[[trabaculae carneae]] = fold within both the myocardium and endocardium, which allows the heart to expand upon the filling of blood

Clinical relevance: [[myocardial infarction]] - results from a lack of blood flow and oxygen to a region of the heart, which results in the death of the cardiac muscle cells.

Blood vessels

Arteries carry blood away from the heart. They branch into smaller vessels, known as [[arterioles]], they further branch into [[capillaries]], which then come together again and form [[venules]], that again join to form veins. Which join a major vein that returns blood to the heart.

Cardiovascular circulation:

- [[pulmonary circuit]] = right side of the heart --> lungs --> left side of the heart

- [[systemic circuit]] = left side of the heart --> head and body --> right side of the heart

| | Arteries | Veins |

| -------------------------------- | -------- | ----- |

| endothelium | x | x |

| subendothelial layer | x | x |

| internal elastic membrane | x | |

| smooth muscle and elastic fibers | x | x |

| external elastic membrane | x | |

| tunica externa | x | x |

| valve | | x |

Arteries/arterioles have thicker walls than veins and venules, but they also have smaller lumens, this allows them to maintain pressure of blood flow. The thicker musculature of arteries tend to give them a characteristic round shape, while veins have a more flattened shape.

Types of blood vessels:

| | Elastic artery | Muscular artery | Arteriole | Continuous capillary (has no pores or fenestrae in walls) |

| ----------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------ | --------------------------------------------------------------------------------------------- | --------------------------------------------------------- |

| Tunica externa | x (fibroelastic CT) | x (thin layer of fibroelastic CT) | (very little, sparse loose CT) | |

| Tunica media | x (40-70 fenestrated elastic membranes, smooth muscle cells in-between the elastic membranes, thin external elastic membrane with vaso varum on outer half) | x (thick, mostly smooth muscle, 40 layers of it.) | x (1-2 layers of smooth muscle cells) | |

| Tunica intima (internal elastic membrane) | x (sub-endothelial layer with incomplete internal elastic lamina) | x (sub-endothelial layer with thick internal elastic lamina) | (sub-endothelial layer not prominent, some elastic fibers instead of internal elastic lamina) | |

| Tunica intima (endothelium) | x | x | x | x |

| | Large vein | Medium-sized vein | Venule | Fenestrated capillary (has pores in their walls that are covered by pore diaphragms7) |

| -------------- | ---------- | ----------------- | ------ | ------------------------------------------------------------------------------------- |

| Tunica externa | x | x | x | |

| Tunica media | x | x | | |

| Tunica intima | x | x | | |

| Endothelium | x | x | x | x |

small and medium veins:

- thin tunica intima, contains valves, as it is a low pressure circulation and protects backflow

- thin tunica media, with thin musculature

- thick tunica adventitia

Large veins:

- tunica intima, contains valves

- thick tunica media, contains elastin

- thick tunica adventitia, contains vasa vasorum