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By going through these CBSE Class 11 Biology Notes Chapter 22 Chemical Coordination and Integration, students can recall all the concepts quickly.

Chemical Coordination and Integration Notes Class 11 Biology Chapter 22

→ There are special chemicals that act as hormones and provide chemical coordination, integration, and regulation in the human body.

→ These hormones regulate the metabolism, growth, and development of our organs, the endocrine glands, or certain cells.

→ The endocrine system is composed of the hypothalamus, pituitary and pineal, thyroid, adrenal, pancreas, parathyroid, thymus, and gonads (testis and ovary).

→ In addition to these, some other organs, e.g., gastrointestinal tract, kidney, heart, etc., also produce hormones.

→ The pituitary gland is divided into three major parts, which are called pars distalis, pars intermedia, and pars nervosa. Pars distalis produces six tropic hormones. Pars intermedia secretes only one hormone, while pars nervosa (neurohypophysis) secretes two hormones.

→ The pituitary hormones regulate the growth and development of somatic tissues and activities of peripheral endocrine glands.

→ The pineal gland secretes melatonin, which plays a very important role in the regulation of 24-hour (diurnal) rhythms of our body (e.g., rhythms of sleep and state of being awake, body temperature, etc).

→ The thyroid gland hormones play an important role in the regulation of the basal metabolic rate, development, and maturation of the central neural system, erythropoiesis, metabolism of carbohydrates, proteins and fats, menstrual cycle.

→ Another thyroid hormone i.e., thyrocalcitonin regulates calcium levels in our blood by decreasing them.

→ The parathyroid glands secrete parathyroid hormone (PTH) which increases the blood Ca²⁺ levels and plays a major role in calcium homeostasis.

→ The thymus gland recreates thymosins which play a major role in the differentiation of T-lymphocytes, which provide cell-mediated immunity In addition, thymosins also increase the production of antibodies to provide humoral immunity.

→ The adrenal gland is composed of the centrally located adrenal medulla and the outer adrenal cortex. The adrenal medulla secretes epinephrine and norepinephrine. These hormones increase lateness, pupillary dilation, piloerection, sweating, heartbeat, the strength of heart contraction, rate of respiration, glycogenolysis, lipolysis, proteolysis.

→ The adrenal cortex secretes glucocorticoids and mineralocorticoids.

→ Glucocorticoids stimulate gluconeogenesis, lipolysis, proteolysis, erythropoiesis, cardio-vascular system, blood pressure, and glomerular filtration rate and inhibit inflammatory reactions by suppressing the immune response.

→ Mineralocorticoids regulate the water and electrolyte content of the body.

→ The endocrine pancreas secretes glucagon and insulin.

→ Glucagon stimulates glycogenolysis and gluconeogenesis resulting in hyperglycemia. Insulin stimulates cellular glucose uptake and utilization, and glycogenesis resulting in hypoglycemia.

→ Insulin deficiency and/ or insulin resistance results in a disease called diabetes mellitus.

→ The testis secretes androgens, which stimulate the development, maturation, and functions of the male accessory sex organs, appearance of the male secondary sex characters, spermatogenesis, male sexual behavior, anabolic pathways, and erythropoiesis.

→ The ovary secretes estrogen and progesterone. Estrogen stimulates the growth and development of female accessory sex organs and secondary sex characters.

→ Progesterone plays a major role in the maintenance of pregnancy as well as in mammary gland development and lactation.

→ The atrial wall of the heart produces an atrial natriuretic factor that decreases blood pressure.

→ The kidney produces erythropoietin which stimulates erythropoiesis.

→ The gastrointestinal tract secretes gastrin, secretin, cholecystokinin, and gastric inhibitory peptide. These hormones regulate the secretion of digestive juices and help indigestion.

→ Hormones: Hormones are non-nutrient chemicals that act as intercellular messengers and are produced in trace amounts.

→ Anterior pituitary: The pars distalis region of the pituitary, commonly called the anterior pituitary, produce growth hormone (GH)

→ Gonadotrophins: FSH stimulates gonadal activity and hence are called gonadotrophins.

→ Androgens: In males, LH stimulates the synthesis and secretion of hormones called androgens from the testis.

→ Melatonin: Pineal secretes a hormone called Melatonin.

→ Corticoids s The adrenal cortex secretes many hormones, commonly called corticoids.

→ Mineralocorticoids: Corticoids, which regulate the balance of water and electrolytes in our body are called mineralocorticoids.

→ Hormone receptors: Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.

By going through these CBSE Class 11 Biology Notes Chapter 21 Neural Control and Coordination, students can recall all the concepts quickly.

Neural Control and Coordination Notes Class 11 Biology Chapter 21

→ The neural system coordinates and integrates functions as well as metabolic and homeostatic activities of all the organs.

→ Neurons, the functional units of the neural system are excitable cells due to a differential concentration gradient of ions across the membrane.

→ The electrical potential difference across the resting neural membrane is called the ‘resting potential’.

→ The nerve impulse is conducted along the axon membrane in the form of a wave of depolarisation and repolarisation. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron which may or may not be separated by a gap called the synaptic cleft. Chemicals involved in the transmission of impulses at chemical synapses are called neurotransmitters.

→ The human neural system consists of two parts

1. Central neural system (CNS) and
2. the Peripheral neural system.

→ The CNS consists of the brain and spinal cord. The brain can be divided into three major parts:

1. Forebrain,
2. Midbrain and
3. Hindbrain.

→ The forebrain consists of the cerebrum, thalamus, and hypothalamus. The cerebrum is longitudinally divided into two halves that are connected by the corpus callosum. A very important part of the forebrain called the hypothalamus control the body temperature, eating, and drinking.

→ Inner parts of cerebral hemispheres and a group of associated deep structures form a complex structure called the limbic system which is concerned with olfaction, autonomic responses, regulation of sexual behavior, expression of emotional reactions, and motivation.

→ The midbrain receives and integrates visual, tactile, and auditory inputs.

→ The hindbrain comprises the pons, cerebellum, and medulla. The cerebellum integrates information received from the semicircular canals of the ear and the auditory system.

→ The medulla contains centers, which control respiration, cardiovascular reflexes, and gastric secretions.

→ The pons consists of fiber tracts that interconnect different regions of the brain. The entire process of involuntary response to peripheral nerve stimulation is called reflex action.

→ Information regarding changes in the environment is received by the CNS through the sensory organs which are processed and analyzed. Signals are then sent for necessary adjustments. The wall of the human eyeball is composed of three layers.

→ The external layer except the cornea is called the sclera. The inside the sclera is the middle layer, which is called the choroid.

→ Retina, the innermost layer, contains two types of photoreceptor cells, namely rods and cones.

→ The daylight (photopic) vision and color vision are functions of cones and twilight (scotopic) vision is the function of the rods. The light enters through the cornea, the lens, and the images of objects are formed on the retina.

→ The ear can be divided into the outer ear, the middle ear, and the inner ear. The middle ear contains three ossicles called malleus, incus, and stapes.

→ The fluid-filled inner ear is called the labyrinth and the coiled portion of the labyrinth is called the cochlea. The organ of Corti is a structure that contains hair cells that act as auditory receptors and is located on the basilar membrane.

→ The vibrations produced in the eardrum are transmitted through the ear ossicles and oval window to the fluid-filled inner ear.

→ Nerve impulses are generated and transmitted by the afferent fibers to the auditory cortex of the brain.

→ The inner ear also contains a complex system located above the cochlea called the vestibular apparatus. It is influenced by gravity and movements and helps us in maintaining a balance of the body and posture.

→ Coordination is the process through which two or more organs interact and complement the functions of one another.

→ Neurons: The neural system of all animals is composed of highly specialized cells called ‘neurons.

→ Somatic neural system and autonomic neural system: The PNS is divided into two divisions called somatic neural system and autonomic neural system.

→ Synaptic knob: Each branch terminates as a bulb-like structure called a synaptic knob.

→ Nissl’s granules: The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s granules.

→ Nodes of Ranvier: The gaps between two adjacent myelin sheaths are called ‘nodes of Ranvier.

→ Synaptic cleft: At a chemical synapse, the membranes of the pre and post-synaptic neurons are separated by a fluid-filled space called the synaptic cleft.

→ Arachnoid: A very thin middle layer is called arachnoid.

→ Corpora quadrigemina: The dorsal portion of the midbrain consists mainly of four round swellings (lobes) called corpora quadrigemina.

→ Labyrinth: The fluid-filled inner ear called labyrinth consists of two parts, the bony and the membranous labyrinths.

By going through these CBSE Class 11 Biology Notes Chapter 20 Locomotion and Movement, students can recall all the concepts quickly.

Locomotion and Movement Notes Class 11 Biology Chapter 20

→ Movement is an essential feature of all living beings.

→ Protoplasmic streaming, ciliary movements, movements of fin, limbs, wings, etc., are some forms exhibited by animals,

→ A voluntary movement that causes the animal to change its place is called locomotion.

→ Animals move generally in search of food, shelter, mate, breeding ground, a better climate or to protect themselves.

→ The cell of the human body exhibit amoeboid, ciliary, and muscular movements.

→ Locomotion and many other movements require coordinated muscular activities.

→ Three types of muscles are present in our body.

→ Skeletal muscles are attached to skeletal elements. They appear united and are voluntary in nature.

→ Visceral muscles, present in the inner walls of visceral organs are nonstriated and involuntary.

→ Cardiac muscles are the muscles of the heart. They are striated, branched, and involuntary.

→ Muscles possess excitability, contractility, extensibility, and elasticity.

→ A muscle fiber is the anatomical unit of muscle. Each muscle fiber has many parallelly arranged myofibrils. Each myofibril .contain many serially arranged units called sarcomere which is the functional unit.

→ Each sarcomere has a central A-bond made of thick myosin filaments, and two half I-bands made of thin actin filaments on either side of it marked by Z lines.

→ Actin and myosin are polymerized proteins with contractility, the active sites for myosin on resting actin filament are masked by a protein- troponin.

→ Myosin head contains ATP phase and has ATP binding sites and active sites for actin.

→ A motor neuron carries the signal to the muscle fiber which generates action potential in it. This causes the release of Ca⁺⁺ from the sarcoplasmic reticulum.

→ Ca⁺⁺ activates actin which binds to the myosin head to form a cross bridge. These cross bridges pull the actin filaments causing them to slide over the myosin filaments and thereby causing contraction.

→ Ca are then returned to the sarcoplasmic reticulum which inactivates the actin. Cross bridges are broken and the muscles relax.

→ Repeated stimulation of muscle leads to fatigue. Muscles are classified as Red and White fibers based primarily on the amount of red-colored myoglobin pigment in them.

→ Bones and cartilages constitute our skeletal system. The skeletal system is divisible into axial and appendicular.

→ Skull, vertebral column, ribs, and sternum constitute the axial skeleton. Limb bones and girdles form the appendicular skeleton.

→ Three types of joints are formed between bones or between bone and cartilage:

1. Fibrous,
2. cartilaginous, and
3. synovial.

→ Synovial joints allow considerable movements and therefore, play a significant role in locomotion.

→ Locomotion: Such voluntary movements i.e., limbs, jaws, eyelids, tongue, etc. are called locomotion.

→ Striated muscles: Skeletal muscles have a striped appearance under the microscope and hence are called striated muscles.

→ Voluntary muscles: As striated muscle activities are under the voluntary control of the nervous system, they are known as voluntary muscles too.

→ Smooth muscles (nonstriated muscle): Visceral muscles do not exhibit any striation and are smooth in appearance. Hence, they are called smooth muscles (non-striated muscles).

→ Involuntary muscles: Smooth muscle activities are not under the voluntary control of the nervous system and are therefore known as in-voluntary muscles.

→ Fascia: Each organized skeletal muscle in our body is made of a number of muscle bundles or fascicles held together by a common collagenous connective tissue layer called fascia.

→ Myofilaments or myofibrils: A characteristic feature of the muscle fiber is the presence of a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils.

→ ‘I’ band and ‘A’ band: The light bands contain actin and are called T band or Isotropic band whereas the dark band called ‘A’ or Anisotropic band contain myosin.

→ Thin and thick filaments: Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively.

→ ‘M’ Line: The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called the ‘M’ line.

→ Sarcomere: The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere.

→ ‘H’ Zone: Central part of thick filament, not overlapped by thin filaments is called the ‘H’ zone.

→ Meromyosins: Each myosin (thick) filament is also a polymerized protein. Many monomeric proteins called meromyosins constitute one thick filament.

→ Myoglobin: Muscle contains a red-colored oxygen storing pigment called myoglobin.

→ Red muscles: Myoglobin content is high in some of the muscles which give a reddish appearance. Such muscles are called the Red muscles.

→ Aerobic muscles: Red muscles also contain plenty of mitochondria that can utilize a large amount of oxygen stored in them for ATP production. These muscles, therefore, can also be called aerobic muscles.

→ Hyoid: A single ‘U’ shaped bone called hyoid is present at the base of the buccal cavity and it is also included in the skull.

→ Spine and Acromion: The posterior, flat, triangular body of the scapula has a slightly elevated ridge called the spine which projects as a flat, expanded process called the acromion.

→ Glenoid Cavity: Below the acromion is a depression called the glenoid cavity which articulates with the head of the humerus to form the shoulder joint.

→ Collar bone: Each clavicle is a long slender bone with two curvatures. This bone is commonly called the collar bone.

By going through these CBSE Class 11 Biology Notes Chapter 19 Excretory Products and their Elimination, students can recall all the concepts quickly.

Excretory Products and their Elimination Notes Class 11 Biology Chapter 19

→ Many nitrogen-containing substances, ions, CO₂, water, etc, accumulate in the body by various means, most of which have to be eliminated to keep the body in homeostasis.

→ The nature of nitrogenous wastes formed and their excretion vary among animals, mainly depending on the habitat (availability of water).

→ Ammonia, urea, and uric acid are the major nitrogenous wastes excreted.

→ Protonephridia, nephridia, malpighian tubules, green glands, and the kidneys are the common excretory organs in animals. They not only eliminate nitrogenous wastes but also help in the maintenance of the ionic and acid-base balance of body fluids.

→ In humans, the excretory system consists of one pair of kidneys, a pair of ureters, a urinary bladder, and a urethra. Each kidney has over a million tubular structures called nephrons.

→ The nephron is the functional unit of the kidney and has two portions glomerulus and renal tubule.

→ The glomerulus is a tuft of capillaries formed from afferent arterioles, fine branches of the renal artery.

→ The renal tubule starts with a double-walled Bowman’s capsule and is further differentiated into a proximal convoluted tubule (PCT), Henle’s loop (HL), and distal convoluted tubule (DCT).

→ The DCTs of many nephrons join to a common collecting duct, many of which ultimately open into the renal pelvis through the medullary pyramids.

→ The Bowman’s capsule encloses the glomerulus to form Malpighian or renal corpuscle.

→ Urine formation involves three main processes, i.e, filtration, reabsorption, and secretion.

→ Filtration is a non-selective process performed by the glomerulus using the glomerular capillary blood pressure.

→ About 1200ml of blood is filtered by the glomerulus per minute to form 125ml of filtrate in the Bowman’s capsule per minute (GFR).

→ JGA, a specialized portion of the nephrons plays a significant role in the regulation of GFR. Nearly 99 percent reabsorption of the filtrate takes place through different parts of the nephrons.

→ PCT is the major site of reabsorption and selective secretion. HI. primarily helps to maintain osmolar gradient (300m Osm/ 1 – 1200m Osm/1) within the kidney interstitium.

→ DCT and collecting duct allow extensive reabsorption of water and certain electrolytes, which help in osmoregulation: FT, K^+, and NH could be secreted into the filtrate by the tubules to maintain the ionic balance and pH of body fluids.

→ A counter current mechanism operates between the two limbs of the loop of Henle and those of the vasa recta (capillary parallel to Henle’s loop). The filtrate gets concentrated as it moves down the descending limb but is diluted by the ascending limb.

→ Electrolytes and urea are retained in the interstitium by this arrangement.

→ DCT and collecting duct concentrate the filtrate about four times i.e, from 300 mOsmoiL^-1 to 1200 mO smolL^-1, an excellent mechanism of conservation of water.

→ Urine is stored in the urinary bladder till a voluntary signal from CNS carries out its release through the urethra i.e. micturition.

→ Skin, lungs, and liver also assist in excretion.

→ Ureotelic: Mammals, many terrestrial amphibians, and marine fishes mainly excrete urea and are called ureotelic animals.

→ Uricotelic: Reptiles, birds, land snails, and insects excrete nitrog¬enous waste as uric acid in the form of a pellet or paste with a minimum loss of water and are called uricotelic animals.

→ Kidney: In most invertebrates, these structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys.

→ Renal pelvis: Inner to the hilum is a broad funnel-shaped space called the renal pelvis.

→ Calyces: The renal pelvis with projections called calyces.

→ Columns of Bertini: The cortex extends in between the medullary pyramids as a renal column. called columns of Bertini.

→ Nephrons: Each kidney has nearly one million complex tubular structures called nephrons, which are the functional units.

→ Distal convoluted tubule: The ascending limb continues as another highly coiled tubular region called the distal convoluted tubule.

→ Collecting duct: The DCTs of many nephrons open into a straight tube called a collecting duct.

→ Pertitubular capillaries: The efferent arteriole emerging from the glomerulus forms a fine capillary network around the renal tubule called the peritubular capillaries.

→ Glomerular Filtration: The first step in urine formation is the filtration of blood, which is carried out by the glomerulus and is called glomerular filtration.

→ Reabsorption: A comparison of the volume of the filtrate formed per day (180 liters/day) with that of the urine released (1.5 liters), suggests that nearly 99 percent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption.

→ Micturition reflex: The process of release of urine is called micturition and the neural mechanisms causing it is called the micturition reflex.

→ Uremia: Malfunctioning of kidneys can lead to accumulation of urea in blood, a condition called uremia, which is highly harmful and may lead to kidney failure.

→ Hemodialysis: In such patients, urea can be removed by a process called hemodialysis.

By going through these CBSE Class 11 Biology Notes Chapter 18 Body Fluids and Circulation, students can recall all the concepts quickly.

Body Fluids and Circulation Notes Class 11 Biology Chapter 18

→ Vertebrates circulate blood, a fluid connective tissue in their body, to transport essential substances to the cells and to carry waste substances from there. Another fluid, lymph (tissue fluid) is also used for the transport of certain substances.

→ Blood comprises a fluid matrix, plasma and the formed elements.

→ Red blood cells (RBCs, erythrocytes), White blood cells (WBCs, leucocytes) and platelets (thrombocytes) constitute the formed elements.

→ Blood of humans is grouped into A, B, AB and O systems based on the presence or absence of 2 surface antigens, A, B on the RBCs. Another blood grouping is also done based on the presence or absence of another antigen called Rhesus factor (Rh) on the surface of RBCs.

→ The spaces between cells in the tissues contain a fluid derived from the blood called tissue fluid. This fluid called lymph is almost similar to blood except for the protein content and the formed elements.

→ All vertebrates and a few invertebrates have a closed circulatory system. Our circulatory system consists of the muscular pumping organ, heart, a network of vessels and the fluid, blood.

→ The heart has two atria and two ventricles.

→ Cardiac musculature is auto-excitable.

→ Sino-atrial node (SAN) generates a maximum number of action potentials per minute (70-75/min) and therefore it sets the pace of the activities of the heart. Hence it is called the pacemaker.

→ The action potential causes the atria and then the ventricles to undergo contraction (systole) followed by their relaxation (diastole).

→ The systole forces the blood to move from the atria to the ventricles and to the pulmonary artery and aorta.

→ The sequential event in the heart which is cyclically respected is called the cardiac cycle.

→ A healthy person shows 72 such cycles per minute.

→ About 70ml of blood is pumped out by each ventricle during a cardiac cycle and it is called the stroke or beat volume.

→ The volume of blood pumped out by each ventricle of the heart per minute is called the cardiac output and it is equal to the product of stroke volume and heart rate (approx 5 litres).

→ The electrical activity of the heart can be recorded from the body surface by using an electrocardiograph and the recording is called an electrocardiogram (ECG) which is of clinical importance.

→ We have a complete double circulation i.e., two circulatory pathways namely pulmonary and systemic are present.

→ The pulmonary circulation starts by the pumping of deoxygenated blood by the right ventricle which is carried to the lungs where it is oxygenated and returned to the left atrium. The systematic circulation starts with the pumping of oxygenated blood by the left ventricle to the aorta which is carried to all the body tissues and the deoxygenated blood from there is collected by the veins and returned to the right atrium.

→ Though the heart is auto-excitable, its functions can be moderated by neural and hormonal mechanisms.

→ Serum: Plasma without the clotting factors is called serum.

→ Haemoglobin: They have a red coloured, iron-containing complex protein called haemoglobin.

→ Thrombocytes: Platelets also called thrombocytes, are cell fragments produced from megakaryocytes.

→ Universal donors: Group ‘O’ blood can be donated to a person with any other blood group and hence ‘O’ group individuals are called ‘Universal donors’.

→ Universal recipients: A person with an ‘AB’ group can accept blood from persons with AB as well as the other group of blood. Therefore such persons are called ‘Universal recipients’.

→ Rh-positive and Rh-negative: Such individuals are called Rh-positive (Rh+ve) and those in whom this antigen is absent are called Rh negative (Rh-ve).

→ Erythroblastosis Foetalis: In the case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-ve) can leak into the foetus or could cause severe anaemia and jaundice to the baby. This condition is called erythroblastosis foetal.

→ Prothrombin: Thrombins, in turn, are formed from another inactive substance present in the plasma called prothrombin.

→ Lymphatic system: An elaborate network of vessels called the lymphatic system collect this fluid and drains it back to the major veins.

→ Sinuses: Open circulatory system is present in arthropods and molluscs in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses.

→ Atria and ventricles: Our heart has four chambers, two relatively small upper chambers called atria and two larger lower chambers called ventricles.

→ Nodal tissue: A specialised cardiac musculature called the nodal tissue is also distributed in the heart.

→ Sino-atrial node: A patch of nodal tissue is present in the right upper comer of the right atrium called the sino-atrial node.

→ Atrio ventricular node: Another mass of this tissue is seen in the lower left comer of the right atrium close to the atrioventricular septum called the atrioventricular node.

→ Purkinje fibres: These branches give rise to minute fibres throughout the ventricular musculature of the respective sides and are called Purkinje fibres.

→ Pacemaker: The SAN can generate a maximum number of action potentials.e., 70-75 per minute and is responsible for initiating and maintaining the rhythmic contractile activity of the heart. Therefore, it is called the Pacemaker.

→ Stroke volume: During a cardiac cycle, each ventricle pumps out approximately 70ml of blood which is called the stroke volume.

→ Hepatic portal system: A unique vascular connection exists between the digestive tract and liver called the hepatic portal system.

→ Myogenic: Normal activities of the heart are regulated intrinsically, i.e., auto regulated by specialised muscles (nodal tissue), hence the heart is called myogenic.

→ Congestive heart failure: Congestion of the lungs is one of the main symptoms of this disease.

By going through these CBSE Class 11 Biology Notes Chapter 17 Breathing and Exchange of Gases, students can recall all the concepts quickly.

Breathing and Exchange of Gases Notes Class 11 Biology Chapter 17

→ Cells utilise oxygen for metabolism and produce energy along with substances like carbon dioxide which is harmful.

→ Animals have evolved different mechanisms for the transport of oxygen to the cells and for the removal of carbon dioxide from there. We have a well developed respiratory’ system comprising two lungs and as-sociated air passages to perform this function.

→ The first step in respiration is breathing by which atmospheric air is taken in (inspiration) and the alveolar air is released out (expiration).

→ Exchange of O₂ and CO₂ between deoxygenated blood and alveoli, transport of these gases throughout the body by blood, exchange of O₂ and CO₂ between the oxygenated blood and tissues and utilisation of O₂ by the cells (cellular respiration) are the other steps involved.

→ Inspiration and expiration are carried out by creating pressure gradients between the atmosphere and the alveoli with the help of specialised muscles intercostals and diaphragm. Volumes of air involved in these activities can be estimated with the help of a spirometer and are of clinical significance.

→ Exchange of O₂ and CO₂ at the alveoli and tissues occurs by diffusion.

→ The rate of diffusion is dependent on the partial pressure gradients of O₂ (pO₂) and CO₂ (pCO₂), their solubility as well as the thickness of the diffusion surface. These factors in our body facilitate the diffusion of O₂ from the alveoli to the (deoxygenated blood as well as from the oxygenated blood to the tissues.

→ The factors are favourable for the diffusion of CO₂ in the opposite direction i.e. from tissues to alveoli.

→ Oxygen is transported mainly as oxyhaemoglobin. In the alveoli where pO₂ is higher, O₂ gets bound to haemoglobin which is easily dissociated at the tissues where pO₂ is low and pCO₂ and H+ concentration are high.

→ Nearly 70 per cent of carbon dioxide is transported as bicarbonate (HCO₂) with the help of the enzyme carbonic anhydrase. 20-25 per cent of carbon dioxide is carried by haemoglobin as carbamino-haemoglobin.

→ In the tissues where pCO₂ is high, it gets bound to blood whereas, in the alveoli where pCO₂ is low and pO₂ is high, it gets removed from the blood.

→ Respiratory rhythm is maintained by the respiratory centre in the medulla region of the brain.

→ A pneumatic centre in the pons regions of the brain and a chemosensitive area in the medulla can alter the respiratory mechanism

→ Breathing/ Respiration: O₂ has to be continuously provided to the cells and CO₂ produced by the cells have to be released out. This process of exchange of O₂ from the atmosphere with CO₂ produced by the cells is called breathing, commonly known as respiration.

→ Gills/Lungs: Special vascularised structures called gills are used for respiration by most of the aquatic arthropods and molluscs whereas vascularised bags called lungs are used by the terrestrial forms.

→ Alveoli: Each terminal bronchiole gives rise to a number of very thin, irregular-walled and vascularised bag-like structures called alveoli.

→ Partial Pressure: Pressure contributed by an individual gas in a mixture of gases is called partial pressure.

→ Respiratory rhythm centre: A specialised centre present in the medulla region of the brain called the respiratory rhythm centre is primarily responsible for this regulation.