मराठी

Overview of Respiration and Circulation

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Maharashtra State Board: Class 12

Key Points: Mechanism of Respiration

Process Meaning Site Major Events Outcome
Breathing Physical process of intake and release of air Lungs & thoracic cavity Inspiration and expiration by diaphragm and intercostal muscles Exchange of air
External Respiration Exchange of O₂ and CO₂ between alveoli and blood Alveoli & pulmonary capillaries O₂ diffuses into blood, CO₂ diffuses into alveoli Oxygenated blood
Internal Respiration Transport of respiratory gases by blood Blood (RBCs & plasma) O₂ transported mainly by haemoglobin; CO₂ by plasma, bicarbonates, and Hb Gas transport
Transport of Gases Movement of O₂ and CO₂ in blood RBCs & plasma O₂ as oxyhaemoglobin; CO₂ mainly as bicarbonate ions Delivery to tissues
Cellular Respiration Oxidation of food to release energy Cells (mitochondria) Oxidation and phosphorylation reactions ATP production
Maharashtra State Board: Class 12

Key Points: Regulation of Breathing

  1. Control of Breathing
    Respiration is under dual control—nervous and chemical, and normal breathing is an involuntary process regulated by respiratory centres.
  2. Respiratory Centres
    The respiratory centres are located in the medulla and pons and include the dorsal group (inspiration), ventrolateral group (inspiration and expiration), and pneumotaxic centre (limits inspiration).
  3. Hering–Breuer Reflex
    Inflation of lungs stimulates stretch receptors which send impulses via vagus nerve to inhibit inspiration, initiating expiration; this reflex controls depth and rhythm of breathing.
  4. Voluntary Control
    Respiratory centres are connected to the cerebral cortex, allowing voluntary control of breathing, but this is limited by rise in carbon dioxide levels in blood.
Maharashtra State Board: Class 12

Key Points: Circulation in Animals

Type of Circulation Meaning Key Features Examples
Open Circulation Circulation in which blood flows through body cavities (haemocoel) and directly bathes tissues Low pressure, no respiratory pigment, slow flow Arthropods (cockroach), Molluscs
Closed Circulation Circulation in which blood flows only through blood vessels and does not directly contact tissues High pressure, haemoglobin present, efficient transport Annelids, Vertebrates
Single Circulation Blood passes through the heart once in one complete cycle Heart → gills → body → heart; heart pumps deoxygenated blood Fishes
Double Circulation Blood passes through the heart twice in one complete cycle Pulmonary + systemic circulation; complete separation of blood Birds, Mammals, Humans
Maharashtra State Board: Class 12

Key Points: Phase of Cardiac Cycle

Phase of Cardiac Cycle Duration Chambers Involved Major Events Valves & Heart Sounds
Atrial Systole (AS) 0.1 sec Atria Atria contract and push blood into ventricles AV valves open; no heart sound
Ventricular Systole (VS) 0.3 sec Ventricles Ventricles contract; blood pumped into aorta and pulmonary artery AV valves close (lubb); semilunar valves open
Ventricular Diastole (VD) 0.5 sec Ventricles Ventricles relax and begin to fill with blood Semilunar valves close (dupp)
Joint Diastole 0.4 sec Atria & Ventricles All chambers relaxed; passive filling occurs AV valves open; no heart sound
Maharashtra State Board: Class 12

Definition: Electrocardiogram (ECG)

The graphical recording of electrical variations detected at the surface of the body during their propagation through the heart wall is called electrocardiogram.

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