Flashcards · 9700 · AS Topic 8

Transport in mammals (AS Level) flashcards

18 cards on AS Topic 8, subtopics 8.1 to 8.3. Pick a subtopic or study them all.

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Closed double circulation: Closed: blood stays inside vessels. Double: blood passes through the heart twice per complete circuit (pulmonary + systemic).
Which vessels carry blood to and from the lungs, and is it oxygenated?: Pulmonary artery: deoxygenated blood, right ventricle → lungs. Pulmonary vein: oxygenated blood, lungs → left atrium.
Elastic artery vs muscular artery: Elastic artery: many elastic fibres; stretches as blood surges in and recoils between beats, smoothing pressure. Muscular artery: thick smooth muscle; constricts or dilates to control flow to organs.
How are veins and capillaries suited to their functions?: Veins: thin wall, wide lumen, valves to stop backflow at low pressure. Capillaries: wall one endothelial cell thick (short diffusion distance), with gaps that let plasma out to form tissue fluid.
Tissue fluid: Fluid that leaks from capillaries and bathes cells; it supplies oxygen and nutrients and removes carbon dioxide and waste.
How is tissue fluid formed and returned?: Arterial end: high hydrostatic pressure forces plasma out through gaps between endothelial cells; cells and most proteins stay in. Venous end: lower pressure, and plasma proteins keep blood ψ lower, so water returns by osmosis. Excess drains into lymph.

How is carbon dioxide carried from respiring tissues?: Mostly as hydrogencarbonate ions in plasma. CO₂ diffuses into red blood cells; carbonic anhydrase speeds formation of carbonic acid, which dissociates to H⁺ + HCO₃⁻; HCO₃⁻ diffuses out. Some binds haemoglobin (carbaminohaemoglobin); a little dissolves in plasma.
Chloride shift: As HCO₃⁻ diffuses out of the red blood cell into the plasma, Cl⁻ moves in to balance the charges, so HCO₃⁻ removal can continue.
Haemoglobinic acid vs carbaminohaemoglobin: Haemoglobinic acid: haemoglobin + H⁺ (buffers blood pH and makes oxyhaemoglobin release O₂). Carbaminohaemoglobin: haemoglobin + CO₂.
Why is the oxygen dissociation curve S-shaped?: The first O₂ binds with difficulty; haemoglobin then changes shape so the next O₂ molecules bind more easily; the curve flattens near full saturation. In tissues (low pO₂) a small drop in pO₂ releases much O₂.
Bohr shift: High pCO₂ → more H⁺ → haemoglobin's affinity for O₂ falls → the curve shifts right → more O₂ is unloaded in active tissues.
Blood can carry 20.0 cm³ O₂ per 100 cm³. Saturation is 96% in the lungs and 60% in a tissue. How much O₂ is released?: 20.0 × (0.96 − 0.60) = 7.2 cm³ per 100 cm³ of blood.

Atrioventricular and semilunar valves: Atrioventricular: tricuspid (right), bicuspid or mitral (left), held by tendons attached to papillary muscles. Semilunar: at the base of the aorta and pulmonary artery.
Why is the left ventricle wall thicker than the right?: The left ventricle pumps blood around the whole body against greater resistance; the right pumps only to the nearby lungs at lower pressure.
When do the AV valves and the semilunar valves close?: AV valves close when ventricular pressure rises above atrial pressure (stopping backflow into the atria). Semilunar valves close when arterial pressure rises above ventricular pressure.
Initiation and control of the heartbeat: The SAN (pacemaker, wall of the right atrium) sends excitation across both atria, which contract. A non-conducting layer blocks direct spread; the AVN delays it; Purkyne tissue carries it down the septum, so the ventricles contract from the base upwards.
Why does the AVN delay the impulse?: So the atria finish contracting and emptying into the ventricles before the ventricles contract.
Heart rate from a pressure trace: Heart rate = 60 ÷ length of one cardiac cycle in seconds. For example, a cycle of 0.8 s gives 75 beats per minute.