Circulatory System (Extended Response)

Question 1

Explain the control mechanism of the heart rate. (7 marks)

Answer 1

-sinoatrial node/SAN is a specialized group of muscle cells located in the right atrium
-acts as a pacemaker/controls the heart rate
-sends out electrical signal/impulses/
depolarisations
-electrical signal stimulates contraction «of heart muscle»
-signal passes through walls of atria/passes to AV node
-then through walls of the ventricles
-medulla «oblongata of brain» can change/increase/decrease the rate
-through nerves/named example of nerve/autonomic/sympathetic/ parasympathetic nervous system
-one nerve increases the rate and the other decreases it
-epinephrine/adrenaline increases heart rate/force of contraction
-epinephrine/adrenaline prepares the body for vigorous activity/is part of fight or flight response

Question 2

Describe the functions of valves in the mammalian heart. (4 marks)

Answer 2

-prevents backflow/ensures one-way flow/controls direction of flow
-opening and closing of valves controls timing of blood flow «during cardiac cycle»
c. closed «semilunar» valves allow ventricles/chambers to fill with blood or allow pressure in ventricles to rise «rapidly»
-valves open when pressure is higher upstream/ converse for closed valves
-AV/bicuspid/tricuspid/mitral valves prevent backflow from ventricle to atrium
OR
AV/bicuspid/tricuspid/mitral valves open when pressure in atrium is higher «than in the ventricle»/when atrium is pumping/contracting
-semilunar/aortic/pulmonary valves prevent backflow from artery to ventricle
OR
semilunar/aortic/pulmonary valves open when pressure in ventricle is higher «than in the artery»/when ventricle is pumping/contracting

Question 3

The human circulatory system is structured to serve the organs and tissues of the body efficiently.
Outline the exchange of materials between capillaries and tissues. (3 marks)

Answer 3

-molecules move by diffusion / move down a concentration gradient
-nutrients move into tissues
-gas exchange / Oxygen and carbon dioxide exchange between tissues and blood/capillaries
-(nitrogenous) wastes/excess water move from cells/tissues into blood/capillaries
-hormones leave capillaries in target tissues/to attach to receptors on cells / (endocrine) organs/gland tissues release hormones into the bloodstream

Question 4

Explain the structures and functions of arteries and veins. (8 marks)

Answer 4

-arteries and veins have three layers in their walls
-pressure is high in arteries/pressure is low in veins
-arteries receive blood from ventricles/heart / carry blood away from heart
-lumen of artery is small to keep pressure high
-arteries have thick (muscular) walls (with elastic fibres) to withstand pressure
-elastic fibres recoil in response to ventricle/heart contraction
-muscle / elastic fibres help maintain pressure between heartbeats
OR
muscle / elastic fibres help propel blood toward capillary beds
-veins receive blood from capillaries/capillary beds / carry blood to heart
-large lumen of veins so there is less resistance to blood flow
-valves in veins keep blood flowing toward heart/prevent backflow

Question 5

Explain how circulation of the blood to the lungs and to other systems is separated in humans and what the advantages of this separation are. (8 marks)

Answer 5

-double circulation / pulmonary and systemic circulations
-heart is a double pump / heart has separate pumps for lungs and other systems / left and right sides of heart are separate / no hole in heart (after birth)
-deoxygenated blood pumped to the lungs and oxygenated to other organs/tissues/whole body (apart from lungs)
-each side of the heart has an atrium and a ventricle
-left ventricle/side pumps blood to the systems/tissues and right ventricle/side pumps blood to the lungs
-left atrium receives blood from the lungs and right atrium receives blood from systems/tissues
-left ventricle pumps blood via the aorta and right ventricle pumps blood via the pulmonary artery
-left atrium receives blood via the pulmonary vein and right atrium receives blood via the vena cava
-lungs require lower pressure blood / high pressure blood would damage lungs
-high pressure required to pump blood to all systems/tissues apart from lungs
-pressure of blood returning from lungs not high enough to continue to tissues / blood has to be pumped again after returning from lungs
-oxygenated blood and deoxygenated blood kept separate / all tissues receive blood with high oxygen content/saturation