Histology - Blood and Blood Vessels Flashcards
3 layers of blood vessles
Tunica intima, tunica media and tunica adventitia
Tunica intima
Single layer, squamous epithelium with a basal lamina and and a thin connective tissue layer
Tunica Media
Mostly smooth muscle, varying level of tissue thickness
Tunica Adventitia
Supporting connective tissue
Separation of tunica intima and tunica media
Internal elastic membrane - layer of elastic tissue
Separation of tunica media and tunica adventitia
External elastic membrane - layer of elastic tissue
Staining elastic fibres
Not using common stains eg H&E but special ones (not named)
Variation in blood vessel structure
In large arteries (eg Aorta) a significant amount of smooth muscle in tunica media is replaced by sheets of elastic fibres - elastic arteries
What is the purpose of ‘Elastic Arteries’
To provide elastic recoil
Vascular supply in elastic arteries
They have their own vascular supply - ‘vaso vasorum’ as only the inner part of the wall can get nutrients from the lumen
Tissue layers in Arterioles
Only one or two layers of smooth muscle in tunica media and miniscule amounts of adventitia
How are arterioles formed?
Arteries become smaller losing smooth muscle from tunica media. (they are around 30-200µm)
Why are arterioles important?
Help to control blood flow in tissues
Capillaries
Composed of endothelial cells and a basal lamina and have diameters of 4-8µm, they also form networks
3 types of capillaries
Continuous, fenestrated and discontinuous/sinusoidal
Continuous capillaries
An uninterrupted lining which only allows small molecules (eg water to pass)
Location of continuous capillaries
Muscle, nerve, lung, skin
Fenestrated capillaries
Have small pores (50nm) to allow extensive molecular exchange. more permeable than continuous
Location of fenestrated capillaries
Gut mucosa, endocrine glands, kidney
Discontinuous capillaries
Have much larger gaps (remember also sinusoids)
Location of discontinuous capillaries
Liver, spleen, bone marrow and lymph nodes
Microvasculature
(Basically) a small arteriole connected to a postcapillary venule through a network of metarterioles, thoroughfare channels and capillaries.
What is a metarteriole?
A short microvessel that links arterioles and capillaries. No continuous tunica media instead spaced smooth muscle that forms a precapillary sphincter.
What is a thoroughfare channel?
Links metarterioles to venules. Form arteriovenous anastomoses
Precapillary sphincters and their function
(a band of) smooth muscle at the beginning of the capillary to help blood flow
What are post-capillary venules?
endothelial lined vessels, containing a thin layer of connective tissue that capillary networks drain into. diameter of 10-30µm.
Why are post-capillary venules important?
Sites for exchange eg cells moving into the tissue in inflamation
What are venules?
When a vessel begins to acquire intermittent smooth muscle cells in the tunica media (>50µm) - in basic terms a small vein
Composition of veins
tunica intima, a thin, continuous tunica media (a few smooth muscle layers) and a large tunica adventitia
Special features of large veins
a thick tunica adventitia with bundles of longitudinally oriented smooth muscle
Special features of many small veins
valves (formed by an inward extension of tunica intima) to prevent backflow of blood
Structure of the lymph vascular system
thin walled vessels. no central pump but smooth muscle in walls, hydrostatic pressure in tissue and compression of tissues by voluntary muscle & valves = flow
Function of lymph vascular system
drains excess tissue fluid (lymph) into the . blood stream. transports lymph to lymph nodes for immune surveillance
Where in the body is your blood?
The majority is in peripheral veins (around 65%), then heart and lungs (around 20%), peripheral arteries (around 10%) and capillaries (around 5%)
How much of blood is formed elements?
45%
How much of blood is plasma?
55%
What 3 types of cells make up formed elements?
Red cells, white cells and platelets
What are the 2 types of white cells in blood?
Granulocytes and Agranulocytes
3 types of granulocytes?
neutrophils, eosinophils and basophils
2 types of agranulocytes?
lymphocytes and monocytes
What is plasma composed of?
water (roughly 90%), proteins, nutrients and salts
What are the main proteins in plasma?
Albumin, immunoglobulins and clotting factors
What is the average adult blood volume?
4.5-6 litres
What technique is used to separate blood?
Centrifugation (in a centrifuge)
What factor determines layers in blood separation?
Density of components
Which is the densest blood component?
Red blood cells and are found at the bottom of the tube.
Which is the 2nd densest blood component?
White blood cells
Which is the least dense blood component?
Plasma (the liquid portion of blood)
What is serum?
Blood with its clotting factors removed
How is serum obtained?
Allow blood to clot and then remove the clot before centrifugation
What are erythrocytes?
(red blood cells) biconcave discs about 7µm in diameter.
Are erythrocytes true cells? reason
No as they don’t have a nucleus or any organelles.
How much of erythrocytes’ volume is haemoglobin?
1/3
Structural feature of erythrocytes
Flexible cytoskeleton network which allow them to deform and get through spaces smaller than themselves
Lifespan of erythrocytes
Last approx 4 months and then are removed (usually) by the spleen and liver.
What is a leukocyte?
White blood cell
Proportion of leukocyte cell types
neutrophils (40-75%) eosinphils (5%) basophils (0.5%) lymphocytes (20-50%) monocytes (1-5%)
Neutrophils structure
many granules in the cytoplasm but they don’t stain well with acidic or basic dyes = neutro. multi lobed nucleus
Role of neutrophils
are inactive in circulation until stimulated (eg by presence of bacteria or inflammation) when they enter tissue with high motile phagocytes
Life of neutrophils
They are abundant and short lived so lots of bone marrow is dedicated to their production.
Eosinophils structure
Prominent granules with an affinity for red acidic dye (eosin), slightly larger that neutrophils and have a bilobed nucleus.
Life of eosinophils
released from marrow, circulate for 8-12 hours then move into tissue (usually spleen, lymph nodes and GI tract) to live.
Role of eosinophils
induce and maintain inflammation (especially in allergic reaction and asthma) as their granules contain a variety of hydrolytic enzymes. they also help fight parasitic infection.
Structure of Basophils
prominent granules have a high affinity for basic dyes (eg methylene blue) so stain blue/purple. bilobed nucleus (often obscured by granules)
What components are in basophils’ granules?
histamine, heparin and other inflammatory mediators
Function of basophils
Effector cells in allergic reactions. high affinity IgE receptors in the membrane are directed against a specific antigen so when it binds to that antigen the cell is stimulated to degranulate. this causes hayfever, allergic asthma, allergic dermatitis etc
Structure of monocytes
many small lysosomal granules in their cytoplasm. largest cells in blood circulation and have a non-lobulated nucleus (looks like a kidney bean)
Function of monocytes
precursors of macrophages and together they form the mononuclear phagocyte system. macrophages are all over the body but mainly in loose connective tissue.
Distribution of the mononuclear phagocyte system
Many move all around the body but some stay resident in a specific tissue eg Kupffer cells in the liver, microglia in the brain and Langerhan’s cells in the skin
Structure of lymphocytes
Round nucleus with a thin/moderate rim of cytoplasm. no visible granules.
How many classes of lymphocyte are there?
2 - B cells and T cells
How do you differentiate between T and B cells in routine staining?
You can’t.
Where are B and T cells made?
Bone marrow
Where do T cells differentiate?
Thymus (lymphoid organ in the immune system)
What is B cells function?
Specific immune response - give rise to antibody secreting plasma cells
What is the function of T cells?
Specific immune response - form a complex set of cells to perform defence functions (aid other immune cells, kill defective cells etc)
Structure of platelets
small cell fragments, about 2µm in length with a well developed cytoskeleton which is important in extruding granules and retracting clots. they have visible granules that contain (alongside others) coagulation factors. they have some organells but no nucleus
Function of platelets
have a key role in preventing blood loss ( hemostatis)
What is hemopoiesis?
The process of making blood from stem cells in bone marrow
Where does hemopoiesis happen during fetal development?
(Principally) the liver and occasionally the spleen
Where does hemopoiesis happen at birth?
The bone marrow, all bones participate. as bones grow there is excess capacity so hemopoiesis is shut down in many bones.
Where does hemopoiesis happen at skeletal maturity?
The vertebrae, ribs, skull, pelvis and proximal femurs.
What is the marrow not being used for hemopoiesis used for?
Mainly adipose (fatty) tissue however in emergencies it can revert to blood formation
Megakaryocytes’ function
Large (30-100µm) cells of bone marrow that produce platelets.
Duplication of megakaryocytes
its nuclear material is duplicated but it doesn’t actually undergo nuclear or cell division - ie very large nucleus. Platelets are essentially the extensions at the cells outer margin which fragments as it grows larger.
