Histology of Blood Vessels and Blood Film (Function of Blood Cells) Flashcards
What are the 3 layers of a blood vessel?
- tunica intima (internal)
- tunica media (middle)
- tunica adventitia (external)
What are the features of the tunica intima?
- single squamous epithelium (endothelial cells)
- cells supported by basal lamina and thin layer CT
What are the features of the tunica media?
- made up of predominantly smooth muscle
- variable thickness
Describe the tunica adventitia
outer layer made of supporting CT
What separates the tunica intima and tunica media?
internal elastic membrane
What separates the tunica media and the tunica adventitia?
external elastic membrane
Why are the largest arteries (e.g. aorta) called elastic arteries?
sheets of elastic fibres replacing a significant amount of smooth muscle in the tunica media
What is the vaso vasorum?
vascular supply to large elastic arteries
Why do some elastic arteries have their own vascular supply?
only the inner part of the wall can obtain nutrients from lumen
What is an arteriole?
smallest division of muscular arteries
What happens to the layers of the arteries as they get smaller?
- tunica media loses smooth muscle
- tunica adventitia starts to disappear
What is the function of arterioles?
control blood flow in tissues
What are the 2 types of arteriole?
- terminal arteriole
- meta arteriole
What are the features of terminal arterioles?
- no internal lamina
- covered by continuous coat of smooth muscle cells
What are the features of meta arterioles?
- smooth muscle cells replaced by pericytes
- terminate into capillaries
What is a pericyte?
non-contractile cells in arterioles
What are the components of capillaries?
- endothelial cells
- basal lamina
Where are capillaries absent?
- epithelial cells resting on basement membrane
- epidermis of skin, hair, nails
- cornea
- hyaline cartilage
What are the 3 types of capillaries?
- continuous
- fenestrated
- sinusoidal
Describe the features of continuous capillaries?
- uninterrupted endothelium
- continuous basal lamina
- fine filaments
What are the features of fenestrated capillaries?
- capillaries with small openings/pores
- pores allow large molecules and proteins to move between organs and blood
What are the features of sinusoidal capillaries?
- capillaries with large gaps
- allow blood cells and proteins to pass between blood and tissue
Where would you find continuous capillaries?
- muscles
- nerves
- lungs
- skin
Where would you find fenestrated capillaries?
- gut mucosa
- endocrine glands
- kidney
Where would you find sinusoidal capillaries?
- liver
- spleen
- bone marrow
Where do capillary networks drain into?
post-capillary venules
Describe the structure of post-capillary venules.
- lined by endothelial cells
- thin layer of CT
When do capillaries become referred to as venules?
once the vessel begins to acquire intermittent smooth muscle in the tunica media
Describe the structure of veins
- thin continuous tunica media
- obvious tunica adventitia
- valves (inward extensions of TI)
What is the function of valves in veins?
prevent the back flow of blood
What are the features of large veins?
- thick tunica adventitia
- TA incorporates bundles of longitudinally orientated smooth muscle
What is the distribution of blood in the body (most to least)
- peripheral veins
- heart and lungs
- peripheral arteries
- capillaries
What is the average adult blood volume?
4.5 - 6 litres
What are the components of blood?
- 45% formed elements
- 55% plasma
What are the formed elements of blood?
- red blood cells
- white blood cells
- platelets
What is the composition of plasma?
- 90% water
- proteins (albumin, clotting factors, clotting factors)
- nutrients
- salts
What are the features of erythrocytes?
- biconcave discs
- 7 micrometres
- no nucleus/organelles
- network of flexible cytoskeletal elements that allow them to deform
How long do erythrocytes last in circulation?
~ 4 months
What removes old RBCs from circulation?
- liver
- spleen
Define haematocrit
the proportion of a persons blood that is red blood cells
What is the average haematocrit of an adult male?
~42
What is the average haematocrit of an adult female?
~38
What are the 2 types of white blood cells (leukocytes)?
- granulocytes
- agranulocytes
What leukocytes are granulocytes?
- neutrophils
- eosinophils
- basophils
What leukocytes are agranulocytes?
- lymphocytes
- monocytes
Describe the features of neutrophils.
- most common
- prominent, multi-lobed nucleus
- circulate in an inactive state
- become highly mobile phagocytes when stimulated
- abundant and short-lived
Describe the features of eosinophils
- bilobed nucleus
- granules stain pink
- granules contain hydrolytic enzymes
- induce and maintain inflammation
- respond to allergic reactions and asthma
Describe the features of basophils
- rarest of granulocytes
- granules stain dark (obscure nucleus)
- bilobed nucleus
- granules contain histamine, heparin
- effector cells in allergic reactions
How do basophils cause allergic responses?
- high affinity IgE receptors in cell membrane
- when bound to allergen cell is stimulated to release granules
What are features of monocytes?
- precursors to macrophages
- widely distributed
- found in loose CT
- largest circulating cells
- kidney bean shaped nucleus
- small granules
What are the feature of macrophages
- part of mononuclear phagocytic system
- some wander
- some remain in tissues
What are the features of lymphocytes?
- large round nucleus
- no visible nucleus
- T and B cells
- T cells differentiate in thymus
- B cells give rise to antibody secreting plasma cells
What are the features of platelets?
- small cell fragments
- 2 micrometres
- large numbers in blood
- key role in haemostasis (blood clotting)
- well developed cytoskeleton
What is haemopoiesis?
the formation of new blood cells
Where is the main site of blood formation at birth?
bone marrow
What happens as bones enlarge?
haemapoiesis stops in many bones
What bones produce blood by the time the skeleton reaches maturity?
- vertebrae
- ribs
- skull
- pelvis
- proximal femurs
