Q.Write a short note on the transport of oxygen in blood. OR Explain the role of RAAS in the regulation of kidney function.
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Formed Elements of Blood
Blood is not just a red liquid — it's a suspension of living cells and cell fragments in a fluid called plasma. If you spin a tube of blood in a centrifuge, the heavier cellular part settles at the bottom, and the lighter plasma stays on top. That bottom layer is the formed elements.
Formed elements = the cellular components of blood: erythrocytes (red blood cells), leucocytes (white blood cells), and platelets (thrombocytes).
Why "formed"? Because they have a definite shape and structure.
Unlike the liquid plasma, these are actual cells or cell fragments that carry out specific jobs. Let's meet each one.
Erythrocytes (Red Blood Cells)
These are the most numerous — about 5 million per microliter of blood. Their job is oxygen transport. They are biconcave discs (like a donut that didn't get a hole punched all the way through), which gives them a huge surface area for gas exchange.
A mature mammalian RBC has no nucleus and no mitochondria. Why? To pack in more haemoglobin — the iron-containing protein that actually binds oxygen. Without a nucleus, the cell can't divide or repair itself, which is why RBCs live only about 120 days before being broken down in the spleen.
The red colour of blood comes from haemoglobin. When oxygenated, it's bright red; deoxygenated, it's darker.
Leucocytes (White Blood Cells)
These are the immune cells. Far fewer than RBCs (about 5000–10,000 per microliter), but they are the army that defends against infection. Unlike RBCs, they have a nucleus and can move independently (amoeboid movement) to squeeze out of blood vessels into tissues.
Leucocytes are classified into two groups:
| Type | Subtypes | Key function |
|---|---|---|
| Granulocytes (have visible granules in cytoplasm) | Neutrophils, Eosinophils, Basophils | Phagocytosis (eating pathogens), allergic responses, inflammation |
| Agranulocytes (no visible granules) | Lymphocytes, Monocytes | Antibody production (B cells), cell-mediated immunity (T cells), macrophage formation (monocytes) |
To remember the granulocytes: Neutrophils, Eosinophils, Basophils → N-E-B (like "neb" — a cloud of granules).
Platelets (Thrombocytes)
These are not whole cells — they are fragments of a large bone marrow cell called a megakaryocyte. Each megakaryocyte breaks into thousands of platelets. Platelets have no nucleus and live only about 7–10 days.
Their job is clotting. When a blood vessel is cut, platelets stick to the exposed collagen, release chemicals that attract more platelets, and form a temporary plug. They also release factors that start the coagulation cascade — a chain reaction that ends with fibrin threads trapping red cells into a stable clot. …
About 97% of the oxygen carried in blood is bound reversibly to haemoglobin inside RBCs, forming oxyhaemoglobin (each haemoglobin molecule can bind up to 4 O2 molecules), while the remaining ~3% is simply dissolved in plasma; the extent of binding/dissociation depends on partial pressure of O2 and CO2, H+ concentration and temp …
Oxygen is transported mainly bound to haemoglobin as oxyhaemoglobin, with only a small fraction dissolved directly in plasma, and its loading/unloading depends on local pO2, pCO2, H+ and temperature.
Transport of oxygen in blood: Oxygen absorbed from the alveoli into pulmonary blood is transported to the tissues in two forms:
- Bound to haemoglobin (~97%): The vast majority of O2 combines reversibly with the iron-containing pigment haemoglobin (Hb) present in RBCs, forming oxyhaemoglobin. Each haemoglobin molecule can bind up to four molecules of O2. This binding is fully reversible: Hb + O2 ⇌ HbO2.
- Dissolved in plasma (~3%): A small amount of O2 remains simply dissolved in the plasma, because O2 has relatively low solubility in water/plasma.
The degree to which O2 binds to or is released from haemoglobin depends on several factors:
- Partial pressure of O2 (pO2): high pO2 (as in the lungs) favours binding/loading; low pO2 (as in tissues) favours dissociation/unloading. …
- CBSE 2026Set ANNUAL1 markMCQQ.Name the blood cells, whose reduction in number can cause clotting disorder, leading to excessive loss of blood from the body.(a) a) Erythrocytes(b) b) Leucocytes(c) c) Neutrophils(d) d) Thrombocytes
›Reveal solutionSolution
[!TLDR]
d) Thrombocytes
Why
Thrombocytes (platelets) are essential for blood clotting; a reduction in their number (thrombocytope …
- CBSE 2024Set ANN1 markQ.Erythro poietin, a peptide hormone produced by __________.
›Reveal solutionSolution
Erythropoietin, the peptide hormone that stimulates RBC (erythrocyte) production, is produced mainly by the kidneys.
Erythropoietin is a glycoprotein hormone that stimulates the process of erythropoiesis (formation of red blood cells) in the bone marrow. It is secreted mainly by specialised cells in the kidney (in response to low oxygen levels/hypoxia), with a small additional contribution from the liver. A fall in RB …
- CBSE 2024Set HALF_YEARLY1 markMCQQ.Members of a family migrate from a high hilly area and started living in the plains. After about 6 months, certain changes start appearing in their body. In this context, which statement will be true regarding the changes in the blood?(a) The number of RBCs increases with the amount of haemoglobin because the air on the mountain is less dense.(b) Along with the decrease in the amount of haemoglobin, the number of RBCs also decreases because the air in the plains is less dense.(c) There is no change in the amount of haemoglobin and the number of RBC.(d) Along with the amount of haemoglobin, the number of RBC may also increase or decrease and there is no change in the density.
›Reveal solutionSolution
Moving from a high-altitude, low-oxygen environment to the oxygen-richer plains reverses the earlier high-altitude acclimatisation, so both haemoglobin content and RBC count fall back towards normal over months.
At high altitude, the atmospheric pressure - and hence the partial pressure of oxygen - is lower than at sea level/plains. The body detects this reduced oxygen availability (hypoxia) and responds by secreting more erythropoietin from the kidneys, which stimulates the bone marrow to produce extra red blood cells; haemoglobin content also rises. This is the well-known high-altitude acclimatisation response, and it is why people who live at high altitude typically have a higher RBC count and haemoglobin level than people living in the plains.
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- CBSE 2024Set HALF_YEARLY1 markQ.State whether True or False: Cu element is found in haemoglobin.
›Reveal solutionSolution
This statement is False: haemoglobin's oxygen-carrying metal is iron, not copper (copper is instead found in a different respiratory pigment, haemocyanin, used by some invertebrates).
Haemoglobin is the red, iron-containing respiratory pigment present inside red blood cells of humans and most vertebrates. Each haemoglobin molecule is made of four polypeptide (globin) chains, each associated with a haem group that holds a central ferrous (Fe2+) ion; it is this iron ion that reversibly binds and releases molecular oxygen, giving blood its red colour and its oxygen-carrying capacity. Copper, by contrast, is the …
- CBSE 2023Set ANNUAL1 markMCQQ.Where are red blood cells made in mammalians :(a) In liver(b) In bone marrow(c) In spleen(d) In kidney
›Reveal solutionSolution
RBCs are made in bone marrow.
In adult mammals, erythrocytes (RBCs) are formed in the red bone marrow (haematopoiesis). The liver and spleen make RBCs mainly during the foetal stage; the spleen later acts as a graveyard of old RBCs. So bone marrow is the …
- CBSE 2022Set ANNUAL1 markMCQQ.Red blood cells are also known by:(a) Erythrocytes(b) Leucocytes(c) Platelets(d) Neutrophil
›Reveal solutionSolution
Red blood cells are also called erythrocytes.
Red blood cells are biconcave, enucleate (in mammals) blood cells packed with the red pigment haemoglobin, which binds and transports oxygen. Their scientific name, erythrocyte, comes from Greek 'erythros' meaning red and 'kytos' meaning cell/vessel. This is distinct from leucocytes (white blood cells, option b — the immune cells), platelets/thrombocytes (option c — cell fragm …
- CBSE 2020Set zoology1 markQ.Name the instrument by which we measure hemoglobin content of Blood.
›Reveal solutionSolution
Haemoglobin content of blood is measured with a haemoglobinometer, commonly Sahli's haemoglobinometer.
Haemoglobin is the iron-containing, oxygen-carrying pigment present in red blood cells. Its concentration in blood (expressed in g/dL) is an important clinical and physiological measurement, since low haemoglobin indicates anaemia.
The classical instrument used for this is Sahli's haemoglobinometer. A small, measured sample of blood is drawn into a graduated tube already containing a reagent (dilute hydrochloric acid), which converts haemoglobin into acid haematin, a brown-coloured compound. Distilled water is then added drop by drop until the colour of the solution matches a fixed brown-coloured standard on the instrument's comparator block. The level reached on the graduated scale directly gives the haemoglobin c …
- CBSE 2020Set ANNUAL1 markQ.Which pigment transports oxygen in blood?
›Reveal solutionSolution
Haemoglobin, the iron-containing respiratory pigment in RBCs, transports oxygen in blood.
Haemoglobin is a conjugated protein made of four polypeptide (globin) chains, each bound to a heme group containing an iron (Fe2+) ion. Oxygen binds reversibly to the iron of the heme group in the lungs (forming oxyhaemoglobin) …
- CBSE 2019Set ANNUAL1 markMCQQ.The Non-Nucleated cell found in blood is(a) RBC(b) WBC(c) Thrombocytes(d) All the above
›Reveal solutionSolution
Mature mammalian RBCs (erythrocytes) are unique among vertebrate blood cells in losing their nucleus, an adaptation that maximises space for haemoglobin.
During erythropoiesis in mammals, the developing red blood cell extrudes its nucleus just before entering the bloodstream, so the mature, circulating RBC is a biconcave, non-nucleated cell filled with haemoglobin. This loss of the nucleus (and most organelles) frees up more room for haemoglobin, improving the cell's oxygen-carrying efficiency, and also gives it its flexible biconcave shape for squeezing through narrow capillaries.
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