Vascular System

Question 1

What defines the tunica intima?

Answer 1

Simple squamous endothelium, also called vascular endothelium, along with its underlying basal lamina. It is a continuous layers in most vessels except some types of capillaries. Larger vessels will have subendothelial connective tissue.

Question 2

What is the internal elastic membrane?

Answer 2

Also called the internal elastic lamella or lamina, it is a structure which is part of the tunica intima. It is the farthest layer, sometimes present

Question 3

What defines the tunica media?

Answer 3

Middle layer of blood vessel wall. It is circumferentially arranged smooth muscle cells or elastic lamellae. Smooth muscle cells produce all the material, including elastic fibers, and types I and III collagen

Question 4

What is the external elastic membrane?

Answer 4

Also called the external elastic lamella or lamina, it is a structure of the tunica media that is not always present.

Question 5

What defines the tunica adventitia?

Answer 5

Outermost layer of connective tissue, consists of longitudinally arranged Type I, Type III collagen fibers, elastic fibers, smooth muscle cells, and fibroblasts. Also is innervated and vasculated in large vessels

Question 6

What is the vasa vasorum?

Answer 6

Small blood vessels that can be found in the walls of the tunica adventitia of large blood vessels, supply nutrients to outer layer and smooth muscle of tunica media

Question 7

What is the nervi vascularis?

Answer 7

Nerves that can be found running through the tunica adventitia that can control the contraction of smooth muscle in the vessel walls

Question 8

How are the endothelial cells of the vascular endothelium normally arranged?

Answer 8

They are flat, elongated, spindle-shape epithelial cells of simple squamous epithelium. The long axis and nuclei aligns itself in the direction of blood flow

Question 9

What is the most important function of capillary vascular endothelium?

Answer 9

controlling transport between blood and tissues (selective permeability barrier)

Question 10

What are the antithrombogenic secretions of vascular endothelium?

Answer 10

Thrombomodulin, prostacyclin, nitric oxide

Question 11

What are the prothrombogenic secretions of vascular endothelium?

Answer 11

von Willebrand factor, tissue factor (tissue thromboplastin, factor III)

Question 12

What is the main thrombolytic agent secreted by the vascular endothelium?

Answer 12

tissue plasminogen activator (TPA)

Question 13

What are two additional functions of the vascular endothelium other than nutrient exchange and clot control?

Answer 13

1. Regulation of leukocyte migration by expressing adhesion molecules (mostly postcapillary venules)
2. Modulation of vascular resistance and blood flow by secreting vasoactive agents (mostly arterioles)

Question 14

Give a vasodilator and vasoconstrictor acting on smooth muscle cells

Answer 14

Endothelin - local vasoconstrictor
Nitric Oxide (NO) - local vasodilator

Both secreted by vascular endothelium

Question 15

What are the three types of arteries?

Answer 15

Elastic arteries, muscular arteries, and arterioles

Question 16

What characterizes the tunica intima of elastic arteries?

Answer 16

Tunica intima - thick with underlying connective tissue and an IEM

Question 17

What makes up the tunica media of elastic arteries?

Answer 17

concentric tubular fenestrated elastic sheets called elastic lamellae. The first and last sheets are IEM (part of intima) and EEM respectively. The fenestrae are holes in the lamellae which allow diffusion of substances within the wall. Ground substance and fibers are secreted by smooth muscle cells

Question 18

What controls the thickness of the elastic lamellae?

Answer 18

Increases with aging, young people have 40-50 lamellae, 70 in older. Can increase due to hypertension

Question 19

What characterizes the tunica adventitia of elastic arteries?

Answer 19

It’s about half the size of t. media. Vasa vasorum supplies it and outer 1/2 of t. media. Nervi vascularis also present.

Question 20

What is the function of an elastic artery?

Answer 20

First vessels to receive blood from the heart and transport blood to the muscular arteries. Conducting vessels. Examples: carotid, subclavian, aorta. Elasticity helps maintain blood pressure and smooth out blood pulses ejected from heart.

Question 21

How can you identify elastic arteries?

Answer 21

Elastic lamellae are often refractile, eosinophilic bands in H&E stained sections. They will be dark parallel lines in the elastic stains

Question 22

What causes Marfan’s syndrome?

Answer 22

Microfibrillar mutation of elastic connective tissue, leading to a weakening of tunica media and subsequent aneurysm or rupture of aortic wall

Question 23

What is distinctive about the layers of muscular arteries?

Answer 23

T. intima has a very prominent, well-defined IEL and minimal connective tissue. T. media consists of 3-40 layers of smooth muscle. EEL often present but not as prominent as IEL. T. adventitia may or may not have nerves and veins in larger arteries.

Question 24

What is the function of muscular arteries?

Answer 24

Distributing vessels, they branch and get smaller to distribute blood all over the body. Examples: brachial, femoral, renal arteries

Question 25

What are the features of the layers of arterioles?

Answer 25

Diameter can change greatly. T. intima may have an IEM, but thin subendothelial layer. T. media have only 1-2 smooth muscle cells layers. T. adventitia is ill-defined connective tissue sheath that blends into surrounding tissue.

Question 26

What is the function of arterioles?

Answer 26

They modulate lots via vasoconstriction. Regulate blood flow to capillary beds. Reduce blood pressure to protect the thin walls of capillaries. They provide the major peripheral resistance to blood flow -> affect systemic arterial pressure

Question 27

What can cause hypertension?

Answer 27

If the overall tonus (contraction) of smooth muscles in arterioles becomes excessive. They are the major source of peripheral resistance

Question 28

What are myoendothelial cell junctions?

Answer 28

Found anywhere, but most prominent in arterioles, they are gap junctions between smooth muscle cells and vascular endothelium. They maintain ionic coupling to autoregulate the size of the vessel lumen

Question 29

What are metarterioles?

Answer 29

They are large vessels between the arteriole and postcapillary venules. They are generally associated with precapillary sphincters. If these are closed, blood can be shunted directly to postcapillary venule.

Question 30

What is the function of precapillary sphincter?

Answer 30

Located on metarterioles, they regulate the blood flow to and within a capillary bed. They are rings of smooth muscle cells at the opening to capillaries

Question 31

Where are capillaries more extensive?

Answer 31

In more metabollically active organs such as the liver, kidney, and skeletal muscles. As opposed to dense connective tissue or mesentery.

Question 32

What are pericytes?

Answer 32

Multipotent cells that wrap around capillary walls of the tunica intima. They can differentiate into smooth muscle during vessel growth periods or following injury. They contribute to tone of small vessels via contractile properties. The basal lamina surrounds the pericyte -> why it is considered part of t. intima.

Question 33

What layers of vessels are absent in capillaries?

Answer 33

T. media and t. adventitia are both absent

Question 34

What are the functions of capillaries?

Answer 34

Site of oxygen, CO2, water, salts, nutrients, and metabolite exchange between blood and surrounding tissues. Transport of molecules across capillary walls is regulated by type of epithelium and charge

Question 35

Where are continuous capillaries prominent? What defines them?

Answer 35

CNS, muscle, and connective tissue. They have a continuous layer of endothelium surrounded by a continuous basal lamina. Pericytes are occasionally found there

Question 36

How does most transport occur for continuous capillaries?

Answer 36

Transcytosis. Thus, endocytotic vesciles are easily seen in endothelial cells of vascular endothelium.

Question 37

Where are fenestrated capillaries prominent?

Answer 37

Prominent where there is a lot of fluid transport, transport of large molecules or hormones. I.e. organs of digestive system, kidney, uvea of eye, and endocrine glands.

Question 38

What is a fenestrae in a fenestrated capillary?

Answer 38

A thin, flattened area of the endothelium. It is a transcellular circular opening. They are usually bridged or closed by a single membrane called a diaphragm. Can be a hole, as in renal glomerulus. Transports water, though transcytosis still occurs in thicker regions of endothelium

Question 39

What capillaries have pericytes vs not?

Answer 39

Continuous and fenestrated have pericytes often, whereas discontinuous do not have them generally, but may have other cells associated (i.e. Kupffer cells in liver or macrophages in lymphoid)

Question 40

Where are discontinuous capillaries found?

Answer 40

vascular channels like bone marrow, liver, spleen, and lymphoid organs

Question 41

What are discontinuous capillaries defined by?

Answer 41

Conform to the shape of the structures in which they are located. They are larger in diameter than continuous or fenestrated, and have huge gaps between endothelial cells. There is a partial or total absence of basal lamina, and no diaphragms.

Question 42

What structurally defines the postcapillary venules?

Answer 42

They arise from the confluence of capillaries. They have a t. intima but no other layers. It includes a basal lamina and prominent pericytes. Endothelial cell junctions are the loosest of all blood vessels

Question 43

What are the blood collection functions of postcapillary venules?

Answer 43

They collect the blood from the capillaries, and also reabsorb blood filtrate that leaks out of the capillaries (with the help of lymphatic vessels). Although fluid will leak from these venules during inflammatory response and allergic reactions

Question 44

What is diapedesis? What mediates it?

Answer 44

Most prominent in postcapillary venules, leukocytes squeeze between adjacent epithelial cells to exit the vessel. Mediated by selectins on endothelium and integrins on leukocytes

Question 45

Where does histamine act and what does it do?

Answer 45

Inflammatory agent acting at the postcapillary venules, vasodilates and increases vessel permeability. It upregulates the expression of P-selectin on endothelial cell surface to induce WBC rolling

Question 46

What are the structure and function of muscular venules?

Answer 46

They have a T. intima with basal lamina, 1-2 layers of smooth muscle, and thin t. adventitia. They function to collect blood from post-capillary venules and deliver them to small veins.

Question 47

How can you identify a muscular venule?

Answer 47

They usually acompany arterioles in tissues. If you identify an arteriole in a section, then the thin-walled, relatively larger vessel nearby is most likely a muscular venule. Also often accompanied by a peripheral nerve.

Question 48

What is a neurovascular bundle?

Answer 48

A collection of three components: venule, arteriole, nerve, or vein, artery, and nerve

Question 49

What are the tunica layers like for small / medium / large veins?

Answer 49

T. intima - endothelial cells with subendothelial layer. Large veins may have IEM that can split with aging.
T. media - Never more than about 4 smooth muscle cell layers, even in largest veins (much thinner than arteries)
T. adventitia - usually predominates over smooth muscle of t. media, especially as veins get larger. Innervation and vasculation may be present in large veins

Question 50

What are vein valves and what are their function?

Answer 50

Found in veins larger than about 2mm, they are flaps made of connective tissue covered by endothelial cells from the tunica intima. They prevent backflow of blood and are most common in arms and legs.

Question 51

What are arteriovenous anastomoses and what is their function?

Answer 51

Also called AV shunts, they are arteriole to venule connections which bypass a capillary bed. Regulated by smooth muscle contraction, when shunt is open, they can conserve heat by not wasting heat in capillaries. They are abundant in skin

Question 52

What is a portal system?

Answer 52

A system in which blood is carried to more than one capillary bed without first returning to the heart

Question 53

What is an arterial portal system and example?

Answer 53

arteriole -> capillary -> arteriole / artery -> capillary -> venule

i.e. renal cortex

Question 54

What is a venule portal system and example?

Answer 54

arteriole -> capillary -> vein / venule -> capillary -> venule

i.e. hepatic portal system of intestines and liver.
or
adenohypophysis (pituitary gland): hypothalamic-hypophyseal portal system

Question 55

What are some possible functions of a portal system?

Answer 55

Second capillary bed recovers material lost from first capillary bed (kidney), second capillary bed serves as a filter for material in first capillary bed (intestines / liver), second capillary bed delivers a hormone produced in first capillary bed (hypothalamus / anterior pituitary)