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Describe the steps in excitation contraction coupling.
- Ca2+ enters cell during depolarization and triggers release of Ca2+ from terminal cisternae
- Ca2+ binds to troponin-C inducing conformational change in troponin complex
- Myosin binds actin – cross bridge cycling occurs
- Ca2+ is sequestered by SR via SERCA pumps
- Ca2+ leaves troponin-C, myosin cannot bind actin
- Sarcomere returns to original relaxed length
There are seven 'phases' that occur during the cardiac cycle. What are they?
Atrial systole;
- Atria contract, topping up mostly filled ventricles
Isovolumetric contraction;
- Ventricles contract, but all valves are closed
Rapid ejection;
- Semilunar valves open, ventricles expel blood
Reduced ejection;
- Semilunar valves open, end of ventricular contraction
Isovolumetric relaxation;
- Ventricles relax, all valves remain closed
Rapid ventricular filling;
- AV valves open, blood begins to fill the ventricles
Diastasis;
- Ventricles fill slowly as venous pressure>ventricular pressure
What are the functions of the lungs and respiratory tract?
- Gas exchange of 02-C02
- Metabolism (ACE)
- Acid-Base balance
- Thermoregulation
- Immune defence
What are the non-respiratory functions of the lung?
Immune function and defence against infection;
- Mucociliary escalator
- Many lymph nodes
- lgA secretion
- Alveolar macrophages and neutrophils
Cardiovascular / Volume regulation;
- Conversion of angiotensin I to angiotensin Il via angiotensin converting enzyme (ACE)
- Inactivation of bradykinin, 5-HT (serotonin), prostaglandin
- Uptake of norepinephrine, histamine (by lung slice)
- Metabolism and release of arachadonic acid metabolites
- lipoxygenases >leukotrienes cyclooxygenases > prostaglandins/thromboxane A2
- Clotting — mast cells contain heparin
What is 'Vital capacity'?
- The maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume
- A normal adult has a vital capacity between 3 and 5 litres.
Explain the conductive airways.
- Airways consist of series of branching tubes
- Trachea to terminal bronchioles
- No gas exchange = Anatomic dead space
Explain the respiratory zone.
- Where gas exchange occurs
- Functional unit distal to terminal bronchiole is called the acinus
Explain the structure of the Trachea.
- The trachea is composed of about 20 rings of tough cartilage. The back part of each ring is made of muscle and connective tissue. Moist, smooth tissue called mucosa lines the inside of the trachea. The trachea widens and lengthens slightly with each breath in, returning to its resting size with each breath out. Cilliated epithelium lines the trachea, with goblet cells amongst as well.
Explain the structure of the bronchiole.
- No longer contain cartilage, cilliated epithelium or goblet cells.
- Clara cells prevent collapsing
- Contains smooth muscle (can prevent air from exchanging from alveoli)
- Lots of lymph nodes
Explain the structure of the Alveolar duct.
- Alveoli on all sides
- Openings guarded by rings of smooth muscle, continuous with spiral smc
- Contraction allows redistribution of gas
- Calibre is much greater than respiratory bronchiole Alveolar sac
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