Histology of Blood Vessels & The Blood Film Flashcards
Blood Vessel Layers
Tunica intima - single squamous epithelial cell layer (endothelial cells), supported with basal lamina and thin CT
Tunica media - mostly smooth muscle
Tunica adventitia - supporting CT
Internal Elastic Membrane - in between TI and TM
External Elastic membrane - in between TM and TA
Elastic Arteries
TM contains more elastic fibres than smooth muscle - elastic recoil
Largest arteries
Vasa vasorum - obtain nutrients as inner layer can only receive this
Arteriole
Smallest division of muscular arteries
1-2 layers of smooth muscle
Almost no TA
30-200um diameter
Important in controlling blood flow in a tissue
Terminal Arteriole - no internal lamina, covered by smooth muscle coat
Meta-Arteriole - pericytes instead of smooth muscle, terminates into capillaries
Capillaries
Endothelial cells and basal lamina
4-8um diameter
Absent in specific body regions such as epithelial cells resting on BM, epidermis of skin/hair and nails, cornea of eye, hyaline cartilage
Continuous - no pores, muscle/nerve/lung/skin
Fenestrated - small pores (50nm), continuous basal lamina, found in gut mucosa, endocrine glands, kidney
Discontinuous - large gaps, no continuous basal lamina, found in liver/spleen/bone marrow
Microvasculature
Meta-arteriole - short microvessel that links arterioles and capillaries
Thoroughfare channels - tail end of the metarteriole that connects to the venule, lacks smooth muscle
Capillaries - normally in a network where exchange occurs, endothelial cells and basal lamina
Precapillary sphincters - segments of smooth muscle that help direct blood flow into capillaries
Venules
Capillaries drain into Post-capillary venule (endothelial cells and thin CT)
Once the vessel gains more smooth muscle cells in TM –> Venule
Veins
Thin continuous TM
Few layers of smooth muscle
No obvious TA
Largest veins - thick TA with longitudinally oriented smooth muscle
Small veins - have valves that prevent the backflow of blood
Lymph Vascular System
Thin walled vessels that drain tissue fluid into blood stream
Transports lymph to lymph nodes for immunological surveillance
Smooth muscle in walls, hydrostatic pressure in tissue and compression of vessels by voluntary muscle combined with vessel valves, produces flow
Blood
4.6-6L
Where? - mostly peripheral veins, then the heart/lungs, peripheral arteries and capillaries
Components
- Formed elements –> Red cells, White cells, Platelets –> Granulocytes & Agranulocytes –> Neutrophils, Eosinophils & Basophils, Lymphocytes, Monocytes
- Plasma –> Water, Proteins, Nutrients & Salts
Separating Blood
- RBC are the densest - bottom
- White cells are the next densest
- Plasma is the liquid portion of blood, top
- Serum - remove clotting factors
Erythrocytes
RBCs - Biconcave, 7um diameter
Mature RBCs - no nucleus, 1/3 volume taken up by Hb
Contain cytoskeletal elements - allow to change shape easily
4 months max in circulation - removed by spleen and liver
Hematocrit
Proportion of blood that is RBCs
Hematocrit of 40 –> 40% of blood is cells
Leukocytes
WBCs part of the immune system
Neutrophils
40-75%
Granulocytes
Most common
Cytoplasm contains granules
Multi-lobed nucleus
Inactive in circulation
Stimulated, they enter the tissue
Abundant and short-lived
Bone marrow production
Eosinophils
5%
Bilobed nucleus
Granules - hydrolytic enzymes (inducing/maintaining inflammation)
Fight parasitic infection
Granules have affinity for red acidic eosin
8-12hrs circulate and then move into the tissue
Larger than neutrophils
Basophils
0.5%
Rarest granulocyte
Granules - affinity for basic dyes
Bilobed nucleus - can’t see due to granules
Granules contain histamine, heparin and other inflammatory mediators
Effector cells in allergic reactions
Possess high affinity IgE receptors to specific allergen - release granules
Lymphocytes
20-50%
Round nucleus surrounded by thin-moderate cytoplasm
No visible granules
B cells - give rise to antibody secreting plasma cells
T cells - CD4+ and CD8+, differentiate in thymus, defence functions
Monocytes
1-5%
Precursors of tissue macrophages –> mononuclear phagocyte system
Macrophages are widely distributed in body, especially loose CT
Monocytes have numerous small lysosomal granules in cytoplasm
Largest cell in circulation
Non-lobulated nucleus - kidney shaped
Members of mononuclear phagocytic system are wanderers but some remain resident in specific tissues
Platelets
Small cell fragments
2um diameter
Haemostasis - prevention of blood loss
Developed cytoskeleton - participates in extrusion of granules and clot retraction
Some organelles but no nucleus
Include coagulation factors in granules
Haemopoiesis
Development
- Earliest site for erythrocyte formation is outside the embryo in the yolk sac beginning at about 3 weeks gestation.
- Later, the liver and to some extent the spleen is colonized by hemopoietic stem cells. Thus during the second trimester the liver is the principal site of blood formation.
- Birth - bone marrow is the main site of blood formation
- Bone enlarge - haemopoesis shuts down in many bones
Marrow can revert to blood formation in emergency
Bone Marrow
Megakaryocytes - no nuclear division, nucleus large
Platelets fromed from extensions
Lineage of Blood Cells
In Bone marrow, a very small number of self renewing pluripotent stem cells which are capable of giving rise to all blood cell types, including lymphocytes
The committed progenitor cells are often termed colony-forming units (CFU) of the lineage
Development of granulocytes and monocytes. Haemopoietic stem cells give rise to colony-forming units (CFUs). CFU-GEMMs have the potential to give rise to all blood cells except lymphocytes. These are granulocytes (G), erythrocytes (E), monocytes (M) and megakaryocytes (M), which each develop in response to specific cytokines and hormones. Intermediate CFUs or, for erythrocytes, burst-forming units (BFUs),
