Composition and Functions of Blood
1. Composition of blood
scored- Cells
→ 3 types
Red blood cells: erythrocytes (biconcave disk shape)
✓ High surface-area-to-volume ratio so that oxygen and carbon dioxide can diffu rapidly to and from the interior of the cell
✓ Lack nuclei and most organelles
natural is best✓ Cannot reproduce themlves
White blood cells: leukocytes
✓ Polymorphonuclear granulocytes (neutrophils, basophil and eosinophil) have multilo
bed nuclei and abundant membrane-surrounded granules
✓ Monocytes has a single oval or horshoe-shaped nucleus and relatively few cytoplasmic granules
✓ Lymphocytes contains little cytoplasm and a single relatively large nucleus
Platelets
✓ Colourless, nonucleated cell fragments that contains numerous ogranules
- Plasma
→ Liquid in which blood cells are suspended
→ Approximate 55% of whole blood
→ Compod of 90% of water and the remaining are dissolved material
woollyPlasma protein(7 % in blood)
✓ Albumins (55-60%)
✧ Viscosity
✧ Osmotically active which is important for maintaining the volume of blood
✧ Act as buffer to help regulating pH
✧ Act as carrier and regulator to carry hormone (especially lipid hormones) and regulate the amont of free hormone
✓ Globulins (33-38%)
✧ Transport hormones, lipids, metal ions
✧ Act as antibody
✓ Fibrinogen and prothrombin小咬
✧ Types of blood clotting factor
✓ Regulatory proteins (hormones and enyzmes)
Organic and inorganic molecules
✓ Nutrients (gluco, amino acids), ions (Na+, K+,HCO3-, etc.), hormones, enzymes and wastes (e.g. urea, CO2)
2. Class of blood cells
- 3 class
→ Erythrocytes
→ Leukocytes
Polymorphonuclear granulocyte
✓ Neutrophils
✓ Eosinophils
✓ Basonphils
Monocytes
Lymphocytes
→ Platelets
i. Red blood cell
- Main function: carry O2 to the tissue by means of the specialized protein haemoglobin (Hb)
→ Hb
4 haem groups
✓ Protoporphyrin combines with iron in the ferrous (Fe2+) state to form haem
✓ Each haem combines with a globin chain made on ribosome
4 globin chains
✓ Normal adults blood:
✧ The dominant haemoglobin in blood after the age 3-6 month, HbA (α2β2)
✧ Contains small quantity of HbF (α舐犊情深是什么意思2γ2) and HbA2 (α2δ2)
✓ Early fetal life: HbF (α2γ2), highly affinity for O2, and γ chain is largely replaced by β chain after the age 3-6 month
a. Formation of red blood cells (Erythropoiesis)123职称英语网
- Substance needed for erythropoiesis
→ Metal: iron, copper (haem), cobalt (part of vitamin B12)
→ Vitamins: vitamin B12, folate (for DNA synthesis)
→ Amino acids: globin
→ Hormones: 泛滥英文版erythropoietin, androgens and thyroxine
b. Role of erythropoietin (EPO) in stimulate erythropoiesis
- Important physiological regulator of erythropoiesis
- When oxygen(O2) level decrea and is detected by kidney, kidney increas cretion of EPO
→ E.g. anaemia, high altitude (lowered O2014上海中考2 level in atmosphere), lung dias, heart dias
- EPO in bone marrow stimulates myeloid progenitors to commit to erythropoiesis by stimulating the proliferation and differentiation of progenitor
- As a result, haemglobin are produced and thus more red blood cells formed to increas the O2 carry capacity in blood
- This process is a type of negative feedback
c. Normal breakdown of red blood cell
- Destruction occurs after a mean lifespan of 120 days when the cells are removed by the macrophages of the reticuloendothelial (RE) system, particularly in the spleen, liver and bone marrow
- 1st step: haemoglobin breaks down into haem and globin
- 2nd step a: irons in haem group recirculate via plasma transferrin to marrow erythroblasts and the excess iron binds to ferritin to store in liver
- 2nd step b: protoporphyrins in haem break down into bilirubin
- 2nd step c: globin groups break down to amino acids for ferry是什么意思re-utilization of general protein synthesis
- 3rd step: bilirubin circulates to the liver and conjugated to glucuronides
- 4th step a: glucuronides excrete into gut via the bile and convert to stercobilinogen
and stercobilin which are excreted in faeces
- 4th step b: stercobilinogen and stercobilin are partly reabsorbed and excreted in the urine as urobilinogen and urobilin
d. Iron cycle
- Reutilized for haemoglobin synthesis after the red blood cell die
→ Transfer from macrophage to plasma transferrin and so bone marrow erythroblasts
- Absorption is normally just sufficient to make up for iron loss
日射ii. White blood cells (Leukocytes)
- Chemotaxis
- Phagocytes is attracted to bacteria or the site of inflammation by chemotactic substance
s relead from damaged tissues
Cells of the immune system defending the body against infectious dias and foreign materials
