histology of blood Flashcards
histology:
study of tissues.
functions of blood:
body heat- the bodys central heating system, circulating a fluid at a constant temperature. coagulation- seals the body to external environment by clotting at the site of cuts.
defence- provides a network for immune cells to move around the body.
export- removes the waste products made during cellular metabolism.
food- ensures cells have all the nutrients they need to function.
gas exchange- supply of o2 and removal of co2.
hormones- moves hormones and other signalling molecules around the body to allow tissues to communicate with 1 another.
3 main groups of cell in blood:
red cells- erythrocytes. carry o2 around the body.
white cells- leukocytes. make up our immune system.
platelets- thrombocytes. assist blood clotting.
bone marrow:
in adult mammals, blood cells are made in the bone marrow. this process of making new blood is called haematopoiesis.
bone marrow is an important stem cell niche as it houses the stem cells responsible for blood cell differentiation. stem cells which form blood cells are called haematopoietic stem cells (HSC).
HSC:
haematopoietic stem cells can differentiate into lots of different blood cells- it is multipotent.
they can not differentiate into non blood cells like fat, bone and cartilage, therefore they are not pluripotent.
sites of haematopoiesis change as we age:
at birth almost all of our marrow spaces are occupied by haematopoietically active tissue. as we age this is gradually replaced by adipose (fat) tissue. only around 1/4 of marrow space is actively performing haematopoiesis by 60. fatty marrow is dynamic and may convert back to haematopoietic marrow in disease or severe blood loss.
haematopoiesis:
haematopoiesis is a tightly controlled process involving a complex network of cell signalling. need to ensure basal level of cells in blood. but also monitor and shift the populations of cells such as an increase in white cells in response to injury or infection.
haematopoietic regulation:
erythropoietin (EPO). EPO is produced in the kidney and liver in response to hypoxic stress (low o2 concentration). EPO stimulates the survival of the red blood cell precursor/ progenitor cells in the bone marrow. increase in RBCs means more cells available to carry o2 and to hopefully counteract the hypoxia.
red blood cells:
erythrocytes are the major cellular constituent of blood. they make up 95% of all blood cells. there is around 5,000,000,000 rbcs in 1ml of blood. the lifespan of a rbcs is around 100 days. every second bone marrow is making around 2 million new rbcs.
the arm of haematopoiesis in which specifically rbcs are formed from a haematopoietic stem cell is called erythropoiesis.
rbcs are atypical mammalian cells as they do not contain DNA, they are also atypically small for a mammalian cell (less than 10um). they are easily deformed which means they can squeeze into tiny capillaries. it takes a rbc about 20 seconds to complete a full lap of a circulatory system.
white blood cells:
wbcs defend us from attack by bacteria, fungi and viruses. they ensure the body heals correctly when it is damaged and recovers after surgery. about 1-10 in every circulating blood cell is a leukocyte. this equates to approx 5,000,000 per ml of blood. there are lots of different leukocyte families, each with their own function during infection and inflammation.
some wbcs act non selectively to destroy any materials deemed as foreign to the body, they are called innate immune cells. others target specific foreign bodies to minimise collateral damage to other cells in the body, these are called adaptive immune cells.
classes of wbcs:
- lymphoid: B lymphocyte, T lymphocyte. myeloid: monocyre, basophil, eosinophil, neutrophil.
-agranulocytes: monocyte, T lymphocyte, B lymphocyte.
granulocytes: neutrophil, basophil, eosinophil.
-mononuclear: monocyte, T lymphocyte, B lymphocyte.
polymorphonuclear: neutrophil, basophil, eosinophil.
WBCs can also be grouped on whether their role involves eating foreign material, this process is called phagocytosis, giving these leukocytes the name professional phagocytes: monocyte and neutrophil.
polymorphonuclear cells: neutrophils
neutrophils are the first line of defence. most common leukocyte in circulation- 3,000,000-8,000,000 neutrophils per ml of blood.
60% of all WBCs are neutrophils. they are short lived, and last about 4-7 days. they contain a range of membrane bound organelles in their cytoplasm. these granules contain enzymes and biochemicals capable of degrading bacteria and other foreign substances.
neutrophils:
a pathogen may be internalised into the cell where it comes into contact with these granules or they can be released into the extracellular environment. this process is called degranulation.
they are granulocyte. there are different types of neutrophil granule, with each type containing a different variety of cytotoxic substances. in total there are around 300 proteins spread over the neutrophil granules. they also have lobed nuclei polymorphonuclear.
professional phagocytes
eosinophils:
like neutrophils eosinophils are also a granulocyte. their granules react with the die eosin which gives them a red colour. 30,000-300,000 eosinophils per ml of blood. although not considered a professional phagocyte, they do have phagocytic capability. their specific function is less characterised than the neutrophil. eosinophils are particularly common at the mucus membrane/tissue interface of the gut. eosinophils contribute to protecting the body from large invading organisms such as worms, these are called helminthic infections.
also involved in the pathology of allergy and asthma, numbers increase at sites of allergic reaction.
WBCs- eosinophils:
like neutrophils eosinophil granules contain an abundance of cytotoxic enzymes and biochemicals, large proportion of eosinophil granules have a crystalloid structure. these granules are termed secondary granules.
basophils:
like neutrophils and eosinophils, basophils are granulocyte. they react with the basic dye haematoxylin. they are relatively rare- 10,000-30,000 per ml blood. implicated in the bodys response to large invading microorganisms and allergic reactions. they also play a role in the bodys response to exoparasites like mites and ticks. along with eosinophils and other immune cells they have a receptor for a type of antibody called immunoglobin E. this particular type of antibody is produced in response to parasitic infection and also plays a role in causing allergic responses.
basophil granules contain a number of important molecules- histamine, heparin, serotonin, enzymes.
mononuclear cells: monocytes
very important immune cell. they are a unipotent progenitor cell- they migrate into tissues where they become a lineage committed leukocyte called macrophage. macrophages are the most important/active phagocytes in the immune system. 200,000-900,000 monocytes per ml of blood. mononuclear leukocyte and characterised histologically by the presence of a kidney or horseshoe shaped nucleus, although they are a dynamic cell and this morphology is not always clear.
macrophages are antigen presenting leukocyte.
wbc- T lymphocytes:
important cell in the adaptive immune system. between 1,000,000-1,500,000 T cells per ml blood. they have a group of molecules on their surface called the T cell receptor (TCR) complex. they are made in the bone marrow and mature in the thymus. TCR allows T cells to recognise and act upon infections by interacting with proteins expressed using MHC complexes. there are several different types of T cell with different roles in mounting, executing and terminating an immune response.
wbcs B lymphocytes:
also involved in the adaptive immune system. B cells make antibodies. antibodies recognise molecules on the surface of pathogens and provide a signal for other more aggressive immune cells to destroy them using a system called fc receptor. B cells can also present antigen in a similar manner to macrophages via MHCII so can also activate T cells. when B cells are activated they migrate into tissues and form large antibody producing cells called plasma cells.
blood cells- platelets:
thrombocyte. like red cells they do not have a nucleus, although their poesis occurs via a different mechanism. platelets are formed from cytoplasmic budding from a much larger cell called a megakaryocyte. the function of platelets is to plug holes to stop bleeding. the they secrete play an important role in mediating blood clotting and inflammation.
megakaryocytes:
produces 4000 thrombocytes during its lifetime. arent typically found in blood. they produce their thrombocytes in bone marrow which subsequently migrates into the blood. their presence in blood may be indicative of disease. these can tell the difference between a blood sample and a bone marrow sample. megakaryocytes are still rare in bone marrow.
endothelial cells:
cells which line the inside of blood vessels. they grow in sheets and line the entire vascular system from the heart to the capillaries. endothelial cells are monolayer- one cell thick. they provide a semipermeable barrier controlling the passage of water and substances from the blood into the surrounding tissues. they also let cells in and out in a process called extravasation. this allows leukocytes to reach the site of infection or injury. they can also sense tissue stress and send new blood vessels to damaged areas to provide cellular and nutritional support. they help to prevent blood clotting by expressing anti coagulant markers on their surface.
