Histology of the blood vessels

Question 1

Name and explain the basic 3 layers of blood vessels

Answer 1

1. Tunica intima (inner layer) - single layer of squamous epithelial cells (termed endothelial cells) which is support by a basal lamina and a thin layer of connective tissue
2. Tunica media (middle layer) - The thickness of this layer varies massively but it is mainly made up of smooth muscle
3. Tunica adventitia (outer layer) - Made up of supporting connective tissue

Question 2

What it is that separates each of the layers in the structure of blood vessels?

Answer 2

The inner and middle layers are separated by a layer of elastic tissue called the INTERNAL elastic membrane. The middle and outer layers are also separated by a layer of elastic tissue but this one is called the EXTERNAL elastic membrane

Question 3

Why are some of the largest arteries termed elastic arteries?

Answer 3

This is because some of the largest arteries (e.g aorta) a lot of the smooth muscle in the tunica media is replaced by sheets of elastic to provide elastic recoil

Question 4

What is the name given to the vascular supply of large arteries and why do they have their own supply?

Answer 4

Vasa vasorum. Large arteries have their own blood supply because it is only the inner part of the vessel wall that can obtain nutrients from the lumen

Question 5

Explain the structure of arterioles and why they are important

Answer 5

Arterioles are really small and so only have 1 or 2 layers of smooth muscle in the tunica media and have almost NO tunica adventitia. Arterioles are especially important in controlling the blood flow in tissue

Question 6

Explain the general structure of capillaries

Answer 6

Capillaries are tiny and composed of endothelial cells and a basal lamina. They typically form an anastomatic network

Question 7

Name and explain the 3 types of capillaries and where they can be found

Answer 7

1. Continuous - endothelial cells are continuous. Found in muscle, nerve, lung, skin
2. Fenestrated or sinusoidal - Small pores in the endothelial cell. Found in gut mucosa, kidney, endocrine glands
3. Discontinuous - Large gaps. Found in places like the liver, spleen, bone marrow

Question 8

What are pericytes?

Answer 8

Pericytes are cells which surround capillaries outside of the basal lamina

Question 9

Name some of the vessels which make up the microvasculature

Answer 9

Small ARTERIOLES which is connected to POST CAPILLARY VENULES through a network made up of METARTERIOLES, through THOROUGHFARE CHANNELS and CAPILLARIES. PRE-CAPILLARY SPHINCTORS which are composed of smooth muscle are at the beginning of the capillary and help control flow through the network

Question 10

What are post-capillary venules?

Answer 10

These are endothelial cell-lined and have a thin layer of connective tissue. Capillary networks drain into these and these venules are important sites for exchange (such as cells moving into tissue)

Question 11

When does a post-capillary venule become known as a venule?

Answer 11

They are referred to as venules once the vessel has acquired intermittent smooth muscle in a tunica media layer

Question 12

Explain the structure of veins

Answer 12

Veins have a tunica intima (inner layer), a thin, continuous tunica media which consists of few layers of smooth muscle and an obvious tunica adventitia (outer layer). The largest veins such as the vena cava have a thick tunica adventitia which incorporates bundles of longitudinally orientated smooth muscle

Question 13

What is the lymph vascular system?

Answer 13

This is a system of relatively thin walled vessels which drain lymph (excess tissue fluid) into the blood stream. It transports lymph to lymph nodes for immunological surveillance

Question 14

What are the components of the blood and what are the percentages of these?

Answer 14

Plasma (55%) - Split into water (90%), proteins, nutrients and salts

Formed elements (45%) - made up of red cells, white cells and platelets
Then white cells are divided into:
Granulocytes - includes neutrophils, eosinophils and basophils
Agranulocytes - includes lymphocytes and monocytes

Question 15

What can you use to separate a sample of blood and how does it separate?

Answer 15

To separate blood, use a centrifuge. This causes the red cells to be found at the bottom, white blood cells (known as the buffy coat in this) in the middle and plasma (liquid portion of the blood) is found at the top

Question 16

What are erythrocytes and what is their average diameter?

Answer 16

Erythrocytes are red blood cells and have a biconcave disc shape and are about 7 micrometres in diameter

Question 17

Name 4 properties about erythrocytes (red blood cells)

Answer 17

1. Mature red blood cells are not true cells because they have no nucleus or organelles
2. They have a netwrok of flexible cytoskeletal elements which allow them to deform and slip through spaces which are smaller than themselves
3. They last about 4 months and when they have aged they are removed by the spleen and the liver
4. 1/3 of their volume is taken up by haemoglobin

Question 18

What is the alternative name given to white blood cells?

Answer 18

Leukocytes

Question 19

Name the 5 types of white blood cells and state whether they are granulocytes or agranulocytes

Answer 19

Neutrophils, eosinophils and basophils are all granulocytes.

Monocytes and lymphocytes are agranulocytes

Question 20

Describe neutrophils

Answer 20

These are the most common type of white blood cell. They contain granules and have a prominent multi-lobed nucleus. These cells circulate in an inactive state but once they are activated they enter the tissue where they are highly motile phagocytes. They are also abundant and short-lived so a lot of their time is devoted to the production of bone marrow

Question 21

Describe eosinophils

Answer 21

These are slightly larger than neutrophils and contain a bilobed nucleus. They are released from the marrow and circulate for 8 to 12 hours then move into tissue. They are important in fighting parasitic infection

Question 22

Describe basophils

Answer 22

These are the rarest of the granulocytes. The cells have a bilobed nucleus however this is usually obscured by the prominent granules. They act as effector cells in allergic reaction (e.g hayfever, allergic asthma etc.)

Question 23

Describe monocytes

Answer 23

These are the largest cells circulating in the blood and they have non-lobulated nucleus which look like a kidney bean shape. Monocytes form the backbone of the mononuclear phagocyte system (macrophages are the other thing which makes up this system, macrophages are found all around the body but are particularly in loose connective tissue)

Question 24

Describe lymphocytes

Answer 24

These have a large round nucleus with a thin rim of cytoplasm that has no visible granules. There are 2 general classes of lymphocytes known as B cells and T cells and they both participate in specific immune response. B cells become plasma cells whereas T cells form a complex set of cells that perform many defence functions

Question 25

Describe platelets

Answer 25

These are small cell fragments about 2 micrometres in diameter and are found in large numbers in the blood. They play a key role in hemostasis (the prevention of blood loss - blood clotting). They have no nucleus but have a well developed cytoskeleton

Question 26

What is hemopoiesis?

Answer 26

Hemopoiesis is the production of blood cells and platelets and it occurs in the bone marrow. In the earliest instance of development blood is produced outside of the embryo in a yolk sac. Later, hemopoietic cells move to the liver (sometimes the spleen) and finally into the marrow cavities. As an adult only vertebrae, ribs, skull, pelvis and proximal femurs retain hemopoiesis.