L1: Functions of cellular elements of blood and regulation of haematopoiesis Flashcards
What is the composition of blood and what is the composition of substances that forms blood?
β Blood is a complex reddish fluid that circulates within the cardiovascular system
β Blood consists of a yellowish fluid (plasma) (55% of blood volume) in which cellular
elements (45% of blood volume) are suspended.
Plasma:- consists of:
- 90% Water
- 0.9% Inorganic substance (Na+, K+, Cl-, HCO3, PO4, SO4)
- 9.1% Organic substances (plasma proteins, lipids, others)
Cellular elements:- Include:
- Red blood cells (RBCs)
- White blood cells (WBCs)
- Platelets
What is the volume of blood in humans?
Its volume is about 8% of the bodyweight i.e. 5600 ml in a 70 kg man. β One litter must be lost to show effectβ
What are the general functions of blood?
1) Major transport medium:
- Blood transports many substances like glucose, O2, CO2, end products of metabolism as urea, and hormones
2) Hemostatic function:
- Stoppage of bleeding from injured blood vessel by platelets and clotting
3) Homeostatic function:
- Keeping the composition (pH, electrolytes, and water) of the internal environment (ECF) constant.
- This is done by continuous exchange of substances between the interstitial fluid (ECF) and blood then between the blood and the external environment through the gastrointestinal tract, lungs, kidneys, and skin.
4) Defensive function:
- WBCs provide the main defense mechanisms against a wide variety of micro-organisms through phagocytosis and the formation of antibodies
What is the size of RBCs?
- Its diameter β 7.5 um.
- Its thickness β at the thickest point is about 2.5 um.
- Its average volume β 90 to 95 u3.
What is the structure of RBCs?
RBCs are not true cells, because they have no nuclei, so called corpuscles.
1) The cell membrane:
- They are surrounded by a plastic semipermeable membrane and has a large surface area, so RBCs are biconcave
2) Its contents:
- Hb is the main constituent of RBCs βcarry o2β (34% of their weight). βThird!β
- K ion is the chief intracellular cation.
- Carbonic anhydrase enzyme, which is important for CO2 transport.
- NO Mitochondria in the RBCs, so they obtain their energy from anaerobic glycolysis. βFor ion balance for exampleβ
What is hemoglobin and what are its levels?
- It is an iron-containing red pigment that is present inside RBCs.
- contents: ο² in adult malesβ 14-18 gm/dl "more RBCs" ο² in adult femalesβ 12-16 gm/dl ο² in newborn β 18 gm/dl ο² in children β 12 gm/dl
What are the functions of RBCs?
1) Functions of cell membrane:
β It has a large surface area than the actual cell volume:
- It gives RBCs its biconcave shape.
- It allows easy diffusion of gases through the cell membrane.
β It is plastic, so it enhances cell flexibility to allow RBCs to be squeezed in small capillaries without rupture of it.
β It keeps Hb inside RBCs, so prevent its loss in urine:
- Filtration of Hb into glomeruli causes its precipitation in
renal tubules and acute renal failure.
2) Functions of Hb:
β It transports CO2 βwith carbonic anhydrase enzymeβ and O2 between lungs and tissues.
β It is an excellent acid-base buffer. βMaintains pHβ
3) Functions of carbonic anhydrase enzyme:
β It helps in the transport of CO2. βIn the form of HCO3β
4) Blood viscosity:
β RBCs share in the production of blood viscosity, which maintains arterial blood pressure (ABP).
What is the lifespan of platelets (thrombocytes)?
8- 12 days βShortβ
What is the function of platelets?
Have a role in hemostasis:
- Release of V.C. substances such as serotonin and thromboxane A2.
- Formation of a primary hemostatic plug.
- Release of platelet phospholipids (PF3) which is essential for blood clotting.
- Stabilization of the blood clot and induction of clot retraction.
- Help repair the damaged vessel wall.
Where are granular leukocytes formed?
Formed in the bone marrow
What percent does each type of granular leukocyte represent?
ο 60-70% (neutrophils) β as they are continuously lostβ
ο 1-5% (eosinophils)
ο 0.0-1.0% (basophils)
What is the lifespan of granular leukocytes?
4 -5 days
What is the function of neutrophils?
The first line of defense against bacterial infection by phagocytosis
What is the function of eosinophils?
- Defense against parasitic infection e.g. schistosomiasis
- Prevent the spread of the local inflammatory during an allergic reaction
What is the function of basophils?
- Synthesize and liberates heparin (anticoagulant) into the blood.
- Releases histamine, serotonin, and bradykinin during allergic reactions.
Where are lymphocytes formed what percent do they represent?
Formed in the lymphoid tissues.
20-30%
Where are monocytes formed and what are their percent?
Formed in bone marrow
3-8%
What is the lifespan of agranular leukocytes?
months or even years βVery longβ
What is the function of lymphocytes?
ο T lymphocytes for cell-mediated immunity
ο B lymphocytes secrete antibodies
What is the function of monocytes?
Phagocytosis β100 and doesnβt dyeβ of bacteria and old cells such as RBCs by forming tissue (fixed) macrophage system or reticuloendothelial system (RES)
What is the definition of hematopoiesis?
It is the process of formation of blood cells
What are the sites of hematopoiesis?
In the early few weeks of embryonic life
ο blood cells are produced in the yolk sac.
In the middle trimester of gestation
ο blood cells are produced in the liver, spleen, and lymph nodes. (RES)
In the last trimester and after birth
ο hematopoiesis is restricted to the red bone marrow (bone marrow of all bones).
After the age of 20 years
ο the bone marrow of all long bones becomes fatty and the RBCs are produced only by the membranous (flat) bones, such as the vertebrae, sternum, ribs, and ilia.
What are the steps of hematopoiesis?
All blood cells originate from pluripotential hematopoietic stem cells (PHSCs), which divide and differentiate into 2 cells lines by hemopoietic growth factors:
1) Lymphoid stem cells: gives rise to lymphocytes, which include the T cells, B cells, and natural killer (NK) cells. These cells quickly migrate from the bone marrow to lymphatic tissues e.g. lymph nodes, spleen, and thymus.
2) Myeloid stem cells: gives rise to all the other formed elements, including the RBCs; megakaryocytes that produce platelets; and a myeloblast lineage that gives rise to monocytes and granular leukocytes: neutrophils, eosinophils, and basophils
What are the factors affecting hematopoiesis?
Hemopoietic growth factors Healthy bone marrow. Healthy liver Hormones Nutritional factors
