Lecture notes
Cardiovascular System
- Module
- BIOL 1025 (BIOL1025)
- Institution
- University Of Southampton (UOS)
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Cardiovascular PhysiologyWhy do we need CVS
❖ Unicellular organism- Paramecium
o Oxygen, metabolite and waste transfer via diffusion is sufficient
o Surface Area LARGE, movements of extracellular environments- currents/ cilia acid diffusion
❖ Multicellularity
o Allows differentiation and improved efficiency with certain cell types having defined tasks
Multicellularity
Diffusion is SLOW
Over distances greater than few cell diameters- diffusion is too slow to
supply O2 and substrates and remove CO2 and waste products
Bulk Flow/ Diffusion
Methods by which molecules move from one place to another
❖ Bulk flow- movement of fluid down pressure gradient
❖ Diffusion- movement of molecules down concentration gradient
Evolution of CV system
1. Chordate ancestor
a. Open circulatory system with open sinuses
b. Beyond vessels
2. Lancelets- amphioxi
a. Closed system
b. Muscular pumping in aortic regions
c. No heart, no chambers, no valves, NO true gills-
respiratory gas exchange by epidermis
Areas of open circulatory system with sinuses in tissues
- Blood from gills sent directly to rest of body
- Has areas of muscle thickening with pumping activity – Cardinal,
Caudal, Portal Heart
, - Needed as blood travels through two vascular beds
- also has systemic heart….. branchial heart- in effect multiple circuits
3. Hagfish, Myxiniforms
a. Very basic vertebrates- once thought to have been early evolutionary but considered degenerate with
loss of genes
b. Has internal gills/ gill pouches- also have cutaneous respiration and can survive highly hypoxic
Hagfishes Systemic/ Branchial Heart
❖ Single circulatory system in regards to branchial heart
❖ Two chambers
❖ Three layers- endocardium, epicardium and myocardium
o Layers missing in Lancelets
❖ Defined organisation of pumping
o Valves- giving oneway flow of blood
❖ Pacemaker region
❖ Alterations in venous output- response to ANP/ANF and catecholamines and PSNS
Has very low blood pressure
- no need for high oxygen levels- not very refined respiratory system
- no need for separation of systemic and respiratory blood flow
Why two circuits and two ventricles in birds and mammals
1. High metabolic rate- need very efficient O2 transfer
2. Lungs- interaction with air- so lower hydrostatic
pressure
a. Diffusion is slow- so make separation between air and
blood vessel very thin
i. Very thin= very weak
3. General tissue vascular bead is larger and need to
control flows
a. E.g. gut when relaxed, muscle when excited
So needs higher blood pressure in tissues- areas of
increased resistance to control blood flow
so two separate vascular circuits needed high pressure one and low pressure one
Heart generates force- Blood pressure
Systemic Circulatory system controls flow- Resistance
Development of mammalian heart- first organ ~20 days gestation in man
❖ 2 Atria and 2 Ventricle system
❖ Valves between ventricle and associated atria
❖ Valves on outflows of ventricles
Human heart development begins with 2 parallel tubes
❖ Tubes fuse- so does their lumens- gives common space
o With 2 inflows (at bottom) and 2 outflows (at top)
▪ Inflows- enter into one primitive atrium
❖ To give final mature position – differential growth occurs- with
ventricle growing down and pushing atria to one side and above it
❖ Atrium grows out and into 2 inflow vessels
Hence, inflow and outflow is at top of heart and atrium is above ventricle
But things change in heart too
Pinching of central region- separates Atrial and Ventricular region- and ingress occurs- Cushions
, ❖ Two septa grow into cushion in atrium- forming left and right atria neither
septum is complete leaving passage between atria- this should close after
birth
❖ Full septum grows to cushion from lowest part of ventricle wall-
INTRAVENTRICULAR SEPTUM- separating left and right ventricles fully
o This septum continues up spiralling into outflow vessels- so aorta and
pulmonary arteries leave on different sides of heart
❖ At pinching off point between atria and ventricles- A-V valves form and
outflows of ventricles in aorta and pulmonary artery semilunar valves form
Cardiomyocyte
Cardiomyocyte comparison to Skeletal muscle cells Structure of Cardiomyocyte
Energy usage by Cardiomyocytes
❖ Cardiac function has high energy demand, cardiomyocytes contain numerous mitochondria, ~30% of cell
volume
❖ >90% of energy requirements met by oxidative phosphorylation- very large oxygen consumption
o in man, at 60-70bpm- oxygen consumption of myocardium is 20-fold higher than that of skeletal muscle
at rest
❖ Many capillaries and myoglobin
o Capillary density in heart is 2-8 times higher than that in skeletal muscle cf cardiac hypertrophy
❖ Cardiomyocytes maintain very high level of oxygen extraction- from blood- of 70-80% compared with 30-40% in
skeletal muscle
Action Potentials in Cardiac Muscle
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