Biology

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Transport of Various Types of Respiratory Gases

Transport of Oxygen

Molecular oxygen is carried in blood in two ways bound to haemoglobin within the red blood cells and dissolved in plasma. Oxygen is poorly soluble in water, so only 3% of the oxygen is transported in the dissolved form. 97% of oxygen binds with haemoglobin in a reversible manner to form oxyhaemoglobin (HbO₂).

The rate at which haemoglobin binds with O₂ is regulated by the partial pressure of O₂. Each haemoglobin
carries maximum of four molecules of oxygen. In the alveoli high pO₂, low pCO₂, low temperature and less H⁺ concentration, favours the formation of oxyhaemoglobin, whereas in the tissues low pO₂, high pCO₂, high H⁺ and high temperature favours the dissociation of oxygen from oxyhaemoglobin.

A sigmoid curve (S-shaped) is obtained when percentage saturation of haemoglobin with oxygen is plotted against pO₂. This curve is called oxygenhaemoglobin dissociation curve (Figure 6.7). This S-shaped curve has a steep slope for pO₂ values between 10 and 50mmHg and then flattens between 70 and 100 mm Hg. Under normal physiological conditions, every 100mL of oxygenated blood can deliver about 5mL of O₂ to the tissues.

Transport of Carbon – Dioxide

Blood transports CO₂ from the tissue cells to the lungs in three ways

(i) Dissolved in Plasma

About 7 – 10% of CO₂ is transported in a dissolved form in the plasma.

(ii) Bound to Haemoglobin

About 20 – 25% of dissolved CO₂ is bound and carried in the RBCs as carbaminohaemoglobin (Hb CO₂)
CO₂ ⇄ Hb Hb CO₂

(iii) As Bicarbonate Ions in Plasma

About 70% of CO₂ is transported as bicarbonate ions. This is influenced by pCO₂ and the degree of haemoglobin oxygenation. RBCs contain a high concentration of the enzyme, carbonic anhydrase, whereas small amounts of carbonic anhydrase is present in the plasma.

At the tissues the pCO₂ is high due to catabolism and diffuses into the blood to form HCO₃^– and H⁺ ions. When CO₂ diffuses into the RBCs, it combines with water forming carbonic acid (H₂CO₃) catalyzed by carbonic anhydrase. Carbonic acid is unstable and dissociates into hydrogen and bicarbonate ions. Carbonic anhydrase facilitates the reaction in both directions.

The HCO₃^– moves quickly from the RBCs into the plasma, where it is carried to the lungs. At the alveolar site where pCO₂ is low, the reaction is reversed leading to the formation of CO₂ and water. Thus CO₂ trapped as HCO₃^– at the tissue level it is transported to the alveoli and released out as CO₂. Every 100mL of deoxygenated blood delivers 4mL of CO₂ to the alveoli for elimination.

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Mechanism of Breathing in Human Beings

The movement of air between the atmosphere and the lungs is known as ventilation or breathing. Inspiration and expiration are the two phases of breathing. Inspiration is the movement of atmospheric air into the lungs and expiration is the movement of alveolar air that diffuse out of the lungs. (Figure 6.4)

Lungs do not contain muscle fires but expands and contracts by the movement of the ribs and diaphragm. The diaphragm is a sheet of tissue which separates the thorax from the abdomen. In a relaxed state, the diaphragm is domed shaped. Ribs are moved by the intercostal muscles.

External and internal intercostal muscles found between the ribs and the diaphragm helps in creating pressure gradients. Inspiration occurs if the pressure inside the lungs (intrapulmonary pressure) is less than the atmospheric pressure.

Inspiraton is initiated by the contraction of the diaphragm muscles and external intercostal muscles, which pulls the ribs and sternum upwards and outwards and increases the volume of the thoracic chamber in the dorso-ventral axis, forcing the lungs to expand the pulmonary volume.

The increase in pulmonary volume and decrease in the intrapulmonary pressure forces the fresh air from outside to enter the air passages into the lungs to equalize the pressure. This process is called inspiration.

Relaxation of the diaphragm allows the diaphragm and sternum to return to its dome shape and the internal intercostal muscles contract, pulling the ribs downward reducing the thoracic volume and pulmonary volume. This results in an increase in the intrapulmonary pressure slightly above the atmospheric pressure causing the expulsion of air from the lungs. This process is called expiration.

On an average, a healthy human breathes 12-16 times/minute. An instrument called Spirometer is used to measure the volume of air involved in breathing movements for clinical assessment of a person’s pulmonary function.

Respiratory Volumes and Capacities

The volume of air present in various phases of respiration is denoted as

Respiratory Volumes: (Figure 6.5)

Tidal Volume (TV)

Tidal volume is the amount of air inspired or expired with each normal breath. It is approximately 500 mL., i.e. a normal human adult can inspire or expire approximately 6000 to 8000mL of air per minute. During vigorous exercise, the tidal volume is about 4-10 times higher.

Inspiratory Reserve Volume (IRV)

Additional volume of air a person can inspire by forceful inspiration is called Inspiratory Reserve Volume. The normal value is 2500-3000 mL.

Expiratory Reserve Volume (ERV)

Additional volume of air a person can forcefully exhale by forceful expiration is called Expiratory Reserve Volume. The normal value is 1000-1100 mL.

Residual Volume (RV)

The volume of air remaining in the lungs after a forceful expiration. It is approximately 1100-1200 mL.

Respiratory Capacities:

Vital capacity (VC) the maximum volume of air that can be moved out during a single breath following a maximal inspiration. A person first inspires maximally then expires maximally. VC = ERV + TV + IRV

Inspiratory Capacity (IC)

The total volume of air a person can inhale after normal expiration. It includes tidal volume and inspiratory reserve volume. IC = TV + IRV

Expiratory Capacity (EC)

The total volume of air a person can exhale after normal inspiration. It includes tidal volume and expiratory reserve volume. EC = TV + ERV

Total Lung Capacity (TLC)

The total volume of air which the lungs can accommodate after forced inspiration is called Total Lung Capacity. This includes the vital capacity and the residual volume. It is approximately 6000mL. TLC = VC + RV

Minute Respiratory Volume

The amount of air that moves into the respiratory passage per minute is called minute respiratory volume.
Normal TV = 500mL; Normal respiratory rate = 12 times/minute Therefore, minute respiratory volume = 6 Litres/minute (for a normal healthy man).

Dead Space

Some of the inspired air never reaches the gas exchange areas but fills the respiratory passages where exchange of gases does not occur. This air space is called dead space. Dead space is not involved in gaseous exchange. It amounts to approximately 150mL.

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Respiratory Function, Facts Organs & Anatomy

The five primary functions of the respiratory system are: –

• To exchange O₂ and CO₂ between the atmosphere and the blood.
• To maintain homeostatic regulation of body pH.
• To protect us from inhaled pathogens and pollutants.
• To maintain the vocal cords for normal communication (vocalization).
• To remove the heat produced during cellular respiration.

Your lungs are part of the respiratory system, a group of organs and tissues that work together to help you breathe. The respiratory system’s main job is to move fresh air into your body while removing waste gases.

There are Five Functions of the Respiratory System

Gas Exchange – oxygen and carbon dioxide.
Breathing – movement of air.
Sound Production.
Oldfactory Assistance – sense of smell.
Protection – from dust and microbes entering body through mucus production, cilia, and coughing.

Allows you to talk and to smell. Brings air to body temperature and moisturizes it to the humidity level your body needs. Delivers oxygen to the cells in your body. Removes waste gases, including carbon dioxide, from the body when you exhale.

Respiratory failure is a serious condition that develops when the lungs can’t get enough oxygen into the blood. Buildup of carbon dioxide can also damage the tissues and organs and further impair oxygenation of blood and, as a result, slow oxygen delivery to the tissues.

Inside the lungs, oxygen is exchanged for carbon dioxide waste through the process called external respiration. This respiratory process takes place through hundreds of millions of microscopic sacs called alveoli. Oxygen from inhaled air diffuses from the alveoli into pulmonary capillaries surrounding them.

The bronchial tubes divide into smaller air passages called bronchi, and then into bronchioles. The bronchioles end in tiny air sacs called alveoli, where oxygen is transferred from the inhaled air to the blood. After absorbing oxygen, the blood leaves the lungs and is carried to the heart.

The oxygen we inhale is used to breakdown glucose into carbon dioxide and water. Energy is released in the process. The breakdown of glucose occurs in the cells of an organism (cellular respiration). If the breakdown occurs without the use of oxygen, the respiration is called anaerobic respiration.

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Nutritional and Digestive Disorders

Intestinal tract is more prone to bacterial, viral and parasitic worm infections. This infection may cause inflammation of the inner lining of colon called colitis. The most common symptoms of colitis are rectal bleeding, abdominal cramps, and diarrhoea.

Protein Energy Malnutrition: (PEM)

Growing children require more amount of protein for their growth and development. Protein deficient diet during early stage of children may lead to protein energy malnutrition such as Marasmus and Kwashiorkor. Symptoms are dry skin, pot-belly, oedema in the legs and face, stunted growth, changes in hair colour, weakness and irritability.

Marasmus is an acute form of protein malnutrition. This condition is due to a diet with inadequate carbohydrate and protein. Such children are suffer from diarrhoea, body becomes lean and weak (emaciated) with reduced fat and muscle tissue with thin and folded skin.

Indigestion:

It is a digestive disorder in which the food is not properly digested leading to a feeling of fullness of stomach. It may be due to inadequate enzyme secretion, anxiety, food poisoning, over eating, and spicy food.

Constipation:

In this condition, the faeces are retained within the rectum because of irregular bowel movement due to poor intake of fire in the diet and lack of physical activities.

Vomiting:

It is reverse peristalsis. Harmful substances and contaminated food from stomach are ejected through the mouth. This action is controlled by the vomit centre located in the medulla oblongata. A feeling of nausea precedes vomiting.

Jaundice:

It is the condition in which liver is affected and the defective liver fails to break down haemoglobin and to remove bile pigments from the blood. Deposition of these pigments changes the colour of eye and skin yellow. Sometimes, jaundice is caused due to hepatitis viral infections.

Liver Cirrhosis:

Chronic disease of liver results in degeneration and destruction of liver cells resulting in abnormal blood vessel and bile duct leading to the formation of fibrosis. It is also called deserted liver or scarred liver. It is caused due to infection, consumption of poison, malnutrition and alcoholism.

Gall Stones:

Any alteration in the composition of the bile can cause the formation of stones in the gall bladder. The stones are mostly formed of crystallized cholesterol in the bile. The gall stone causes obstruction in the cystic duct, hepatic duct and also hepato-pancreatic duct causing pain, jaundice and pancreatitis.

Appendicitis:

It is the inflammation of the vermiform appendix, leading to severe abdominal pain. The treatment involves the removal of appendix by surgery. If treatment is delayed the appendix may rupture and results in infection of the abdomen, called peritonitis.

Hiatus Hernia (Diaphragmatic hernia):

It is a structural abnormality in which superior part of the stomach protrudes slightly above the diaphragm. The exact cause of hiatus hernias is not known. In some people, injury or other damage may weaken muscle tissue, by applying too much pressure (repeatedly) on the muscles around the stomach while coughing, vomiting, and straining during bowel movement and lifting heavy object.

Heart burn is also common in those with a hiatus hernia. In this condition, stomach contents travel back into the oesophagus or even into oral cavity and causes pain in the centre of the chest due to the eroding nature of acidity (Figure 5.10).

Diarrhoea:

It is the most common gastrointestinal disorder worldwide. It is sometimes caused by bacteria or viral infections through food or water. When the colon is infected, the lining of the intestine is damaged by the pathogens, thereby the colon is unable to absorb fluid.

The abnormal frequency of bowel movement and increased liquidity of the faecal discharge is known as diarrhoea. Unless the condition is treated, dehydration can occur. Treatment is known as oral hydration therapy. This involves drinking plenty of fluids – sipping small amounts of water at a time to rehydrate the body.

Peptic Ulcer:

It refers to an eroded area of the tissue lining (mucosa) in the stomach or duodenum. Duodenal ulcer occurs in people in the age group of 25 – 45 years. Gastric ulcer is more common in persons above the age of 50 years.

Ulcer is mostly due to infections caused by the bacterium Helicobacter pylori. It may also be caused due to uncontrolled usage of aspirin or certain antiinflammatory drugs. Ulcer may also be caused due to smoking, alcohol, caffine and psychological stress.

Obesity:

It is caused due to the storage of excess of body fat in adipose tissue. It may induce hypertension, atherosclerotic heart disease and diabetes. Obesity may be genetic or due to excess intake of food, endocrine and metabolic disorders.

Degree of obesity is assessed by body mass index (BMI). A normal BMI range for adult is 19-25 above 25 is considered as obese. BMI is calculated as body weight in Kg, divided by the square of body height in meters. For example, a 50 Kg person with a height of 160 cms would have a BMI of 19.5. That is BMI = 50/(1.6)² = 19.5

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Caloric Value of Carbohydrates, Proteins and Fats

We obtain 50% energy from carbohydrates 35% from fats and 15% from proteins. We require about 400 to 500 gm of carbohydrates, 60 to 70 gm of fats and 65 to 75 gm of proteins per day. Balanced diet of each individual will vary according to their age, gender, level of physical activity and others conditions such as pregnancy and lactation.

Carbohydrates are sugar and starch. These are the major source of cellular fuel which provides energy. The caloric value of carbohydrate is 4.1 Kcal per gram and its physiological fuel value is 4 Kcal per gram.

Lipids are fats and derivatives of fats, are also the best reserved food stored in our body which is used for production of energy. Fat has a caloric value of 9.45 Kcal and a physiological fuel value of 9 Kcal per gram. Proteins are source of amino acids required for growth and repair of body cells.

They are stored in the body only to a certain extent large quantities are excreted as nitrogenous waste. The
caloric value and physiological fuel value of one gram of protein are 5.65 Kcal and 4 Kcal respectively. According to ICMR (Indian Council of Medical Research and WHO (World Health Organization), the daily requirement of protein for an average Indian is 1gm per 1 kg body weight.

Carbohydrates provide 4 calories per gram, protein provides 4 calories per gram, and fat provides 9 calories per gram. You can view this information on the bottom of the Nutrition Facts Panel on food packages.

Ethanol and fats have the highest amount of calorific value per gram i.e. 29 and 37 kilojoules per gram or 6.9 and 8.8kcal/g respectively and proteins and most carbohydrates both have about 17kJ/g or 4kcal/g.

Fat has more than twice as many calories per gram as carbohydrates and proteins. A gram of fat has about 9 calories, while a gram of carbohydrate or protein has about 4 calories. In other words, you could eat twice as much carbohydrates or proteins as fat for the same amount of calories.

Carbohydrates, proteins, and fats are digested in the intestine, where they are broken down into their basic units: Carbohydrates into sugars. Proteins into amino acids. Fats into fatty acids and glycerol. Which hormone regulates carbohydrate, protein and fat metabolism in the body. Thyroxin is the hormone that regulates carbohydrate, protein and fat metabolism in the body.