Human Physiology | Module 2 Unit 1 | Calicut University First Semester BSc. Zoology Notes PDF |

 Physiology of Respiration and Circulation: Calicut University Free Study Material 

Hello everyone! In this study material i have included topics from Module 2 Respiration from the Unit 1 of First Semester BSc. Zoology of Calicut University 

Summary of what's covered in this study material

🌬️ External and Internal Respiration

External respiration refers to the exchange of gases between the atmosphere and the blood through the lungs. During inspiration, oxygen enters the alveoli, diffuses across the alveolar membrane, and binds to haemoglobin in red blood cells. During expiration, carbon dioxide diffuses from blood into the alveoli and is expelled.

Internal respiration occurs at the tissue level. Oxygen diffuses from blood into cells, where it participates in oxidative metabolism, while carbon dioxide produced by cellular respiration diffuses into the blood to be transported back to the lungs.

📏 Lung Volumes and Capacities

Tidal volume (TV) is the amount of air inhaled or exhaled during normal breathing, approximately 500 ml in adults. A portion of this air remains in the conducting airways as dead space.

Inspiratory reserve volume (IRV) represents the additional air that can be inhaled after a normal inspiration, while expiratory reserve volume (ERV) refers to the extra air expelled after normal expiration.

Residual volume (RV) is the air that remains in the lungs even after maximal expiration. This prevents lung collapse and ensures continuous gas exchange.

Vital capacity (VC) is the maximum volume of air expelled after maximal inspiration and equals TV + IRV + ERV. Total lung capacity (TLC) includes residual volume and represents the total air present after maximal inspiration.

Functional residual capacity (FRC) refers to the air remaining in the lungs after normal expiration and is important for maintaining stable alveolar oxygen levels.

🩸 Respiratory Pigments

Respiratory pigments are coloured, metal-containing proteins that transport oxygen. The respiratory pigments in vertebrates are haemoglobin. It is an iron containing conjugated protein present in red blood cells. 

Structure and Function of Haemoglobin

Haemoglobin is a tetrameric protein composed of four polypeptide chains and four haeme groups. In adults (HbA), it consists of two alpha and two beta chains, while fetal haemoglobin (HbF) contains two alpha and two gamma chains.

 Each haeme group contains a ferrous (Fe²⁺) ion capable of reversibly binding one oxygen molecule. Thus, one haemoglobin molecule can transport four oxygen molecules. 

Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, facilitating oxygen transfer across the placenta.

 Haemoglobin transports oxygen in the lungs as oxyhaemoglobin and releases it in tissues. It also participates in carbon dioxide transport and acts as a buffer, helping maintain blood pH.

📈 Oxygen Transport and Dissociation Curve

Approximately 97% of oxygen is transported bound to haemoglobin, while a small fraction remains dissolved in plasma. Oxygen binding to haemoglobin exhibits positive cooperativity. The binding of one oxygen molecule increases the affinity for subsequent molecules.

The oxygen–haemoglobin dissociation curve is sigmoid-shaped, reflecting this cooperative binding. At high partial pressure of oxygen (in lungs), haemoglobin becomes saturated. At lower partial pressures (in tissues), oxygen is released.

A rightward shift of the curve occurs under conditions of increased temperature, elevated CO₂, low pH, and increased 2,3-DPG levels. This phenomenon, known as the Bohr effect, enhances oxygen delivery to tissues.

🌫️ Transport of Carbon Dioxide

Carbon dioxide is transported in three forms: dissolved in plasma, bound to hemoglobin as carbaminohemoglobin, and primarily as bicarbonate ions.

Inside red blood cells, carbon dioxide reacts with water to form carbonic acid under the influence of carbonic anhydrase. Carbonic acid dissociates into hydrogen and bicarbonate ions. Bicarbonate diffuses into plasma in exchange for chloride ions this process known as the chloride shift or Hamburger phenomenon.

⚠️ Carbon Monoxide Poisoning

Carbon monoxide binds to haemoglobin with an affinity 200–250 times greater than oxygen, forming carboxyhaemoglobin. This drastically reduces oxygen-carrying capacity and leads to tissue hypoxia.

Symptoms include headache, dizziness, confusion, and in severe cases, unconsciousness and death. Treatment involves administration of 100% oxygen or hyperbaric oxygen therapy.

🧠 Nervous and Chemical Regulation of Respiration

Respiratory rhythm is controlled by centers in the medulla oblongata and pons. The medullary centers generate basic respiratory rhythm, while pontine centers regulate its pattern.

Chemical regulation depends primarily on carbon dioxide concentration and blood pH. Increased CO₂ lowers pH, stimulating central chemoreceptors to increase ventilation. Peripheral chemoreceptors respond mainly to low oxygen levels.

👶 Respiratory Disorders in Newborns

Infant Respiratory Distress Syndrome (IRDS) occurs due to deficiency of pulmonary surfactant, which normally reduces alveolar surface tension. Premature infants often lack adequate surfactant, leading to alveolar collapse and breathing difficulty.

Other conditions include Sudden Infant Death Syndrome (SIDS) and asphyxia neonatorum.

👴 Respiratory Problems in Old Age

With aging, lung elasticity decreases and respiratory muscles weaken. Older individuals are more susceptible to infections and chronic respiratory disorders.

Chronic Obstructive Pulmonary Disease (COPD) is a progressive disorder characterised by airflow limitation. It includes chronic bronchitis and emphysema and is strongly associated with smoking and environmental pollutants.

🦠 COVID-19 and Respiratory Impact

COVID-19, caused by SARS-CoV-2, primarily affects the respiratory tract. The virus binds to ACE2 receptors on alveolar cells, causing inflammation and impaired gas exchange. Severe cases may lead to pneumonia and acute respiratory distress syndrome.

🏔️ High Altitude Adaptations

At high altitudes, reduced atmospheric pressure causes hypobaric hypoxia. The body responds by increasing ventilation and heart rate.

Long-term adaptation includes increased red blood cell production due to elevated erythropoietin levels, enhancing oxygen-carrying capacity.

📝 Important Exam Questions

• Define external and internal respiration.
• What is tidal volume?
• Define vital capacity.
• State the Bohr effect.
• What is the chloride shift?Structure of hemoglobin
• Oxygen–hemoglobin dissociation curve
• Transport of carbon dioxide
• Carbon monoxide poisoning
• COPD

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