Histology of the blood vessels Flashcards
Name and explain the basic 3 layers of blood vessels
- 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
- Tunica media (middle layer) - The thickness of this layer varies massively but it is mainly made up of smooth muscle
- Tunica adventitia (outer layer) - Made up of supporting connective tissue
What it is that separates each of the layers in the structure of blood vessels?
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
Why are some of the largest arteries termed elastic arteries?
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
What is the name given to the vascular supply of large arteries and why do they have their own supply?
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
Explain the structure of arterioles and why they are important
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
Explain the general structure of capillaries
Capillaries are tiny and composed of endothelial cells and a basal lamina. They typically form an anastomatic network
Name and explain the 3 types of capillaries and where they can be found
- Continuous - endothelial cells are continuous. Found in muscle, nerve, lung, skin
- Fenestrated or sinusoidal - Small pores in the endothelial cell. Found in gut mucosa, kidney, endocrine glands
- Discontinuous - Large gaps. Found in places like the liver, spleen, bone marrow
What are pericytes?
Pericytes are cells which surround capillaries outside of the basal lamina
Name some of the vessels which make up the microvasculature
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
What are post-capillary venules?
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)
When does a post-capillary venule become known as a venule?
They are referred to as venules once the vessel has acquired intermittent smooth muscle in a tunica media layer
Explain the structure of veins
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
What is the lymph vascular system?
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
What are the components of the blood and what are the percentages of these?
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
What can you use to separate a sample of blood and how does it separate?
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
What are erythrocytes and what is their average diameter?
Erythrocytes are red blood cells and have a biconcave disc shape and are about 7 micrometres in diameter
Name 4 properties about erythrocytes (red blood cells)
- Mature red blood cells are not true cells because they have no nucleus or organelles
- They have a netwrok of flexible cytoskeletal elements which allow them to deform and slip through spaces which are smaller than themselves
- They last about 4 months and when they have aged they are removed by the spleen and the liver
- 1/3 of their volume is taken up by haemoglobin
What is the alternative name given to white blood cells?
Leukocytes
Name the 5 types of white blood cells and state whether they are granulocytes or agranulocytes
Neutrophils, eosinophils and basophils are all granulocytes.
Monocytes and lymphocytes are agranulocytes
Describe neutrophils
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
Describe eosinophils
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
Describe basophils
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.)
Describe monocytes
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)
Describe lymphocytes
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
Describe platelets
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
What is hemopoiesis?
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.
