Blood and Blood Vessels

Blood

• Can be separated by spinning in a centrifuge

• Components: erythrocytes ~45%, buffy coat (leukocytes and platelets) <1%, plasma ~55%
• Plasma has clotting factors
• Clotting factors removed → serum

Erythrocytes (RBCs)

• Biconcave discs around 7µm in diameter

• No nucleus or organelles (when mature)

• Network of flexible cytoskeletal elements

White blood cells

Granulocytes

• 40-75% of WBCs

• Phagocytes (when activated)

• Single, multi-lobed nucleus

• 5% of WBCs

• Acidic granules that stain red, and a bi-lobed nucleus

• Granules contain hydrolytic enzymes - inflammation

• 5% of WBCs

• Basic granules that stain purple/blue, and a bi-lobed nucleus

• Effector cells in allergic reactions

Agranulocytes

• 1-5% of WBCs

• Precursors of tissue macrophages (phagocytes)

• Large, kidney bean-shaped nucleus

• 20-50% of WBCs

• Small spherical nucleus and basophilic (blue) cytoplasm

• B cells: give rise to antibody secreting plasma cells

• T cells: differentiate in thymus, many defensive functions

Platelets

• Cell fragments that have a key role in haemostasis

Blood vessels

Structure of arteries

• Tunica intima: single layer of squamous epithelial cells (endothelium) supported by a basal lamina and a thin layer of connective tissue

• Tunica media: predominantly made up of smooth muscle

• Tunica adventitia: made up of supporting connective tissue

Arteriole

• 1 or 2 layers of smooth muscle in tunica media, almost no adventitia

Capillaries

• Endothelial cells and a basal lamina

• 3 types:
• Continuous: no pores
• Fenestrated: small pores
• Discontinuous: large gaps

Venules

• Postcapillary venules: endothelium and thin layer of connective tissue

• Venules: intermittent smooth muscle in tunica media

Veins

• Tunica intima, a thin, continuous tunica media and a tunica adventitia