Cardiovascular System Flashcards
Diastole
filling
Systole
Contracting
Heart Development - before 3 weeks
Heart forms a straight tube on ventral midline. Relies on oxygenation and nutrient delivery via diffusion.
Heart Development - 3 weeks
Heart tube lengthens and starts to form S shaped tube. Primitive atrium moves dorsally towards head and primitive ventricle swings ventrally and towards the tail = cardiac looping
Heart Development - 3.5 weeks
As atrium moves towards head, it passes behind the bulbus cordis. The sinus venosus is carried with the atrium and disappears from our view. as it moves to the dorsal side of the heart, behind the ventricle
Growth is quicker in regions compared to junction, therefore bulging is pronounced. Sinus venosus is hidden and has horn projects on each side attached to three veins
Common cardinal vein
Drains the embryo
Umbilical vein
Carries oxygenated blood from placenta to embryo
Vitelline vein
Carries nutrient laden blood from the diminishing yolk sac to the SV
Heart Development - 4 weeks
Cardiac looping has finished
Horns of the sinus venosus now enter the atria on cranial and dorsal side. Interatrial septum forms, beginning chamber formation, one on each side of the bulbus cordis. Primitive ventricle forms caudal apex of the heart. Interventricular septum begins to form at old bulboventricular junction, separating LV and RV
Heart Development - 5 weeks
Sinus venosus is no longer recognisable
Blood returning from body drains mostly to the right side.
Right horn enlarges & contributes to the right atrial wall
Left horn diminishes and eventually forms the coronary sinus (draining blood from cardiac veins back to RA.)
Distal part of Bulbus Cordis splits into Conus cordis and Truncus arteriosus
Conus cordis
Forms the outflow tracts of both ventricles
Truncus arteriosus
Form proximal aorta and pulmonary trunk
Heart Development - 6 weeks
SVC & IVC are established
Ridges run lengthwise inside the truncus arteriosus and conus cordis. Ridges run in a spiral and when fusion occurs will form a spiral partition or septum
Heart Development - 7-8 weeks
Aorta (Ao) and Pulmonary trunk (Pt) become separate vessels twisting around another. Caudal part of spiral septum contributes to interventricular septum that separates the two ventricles
Heart Development - Full term fetus
Pulmonary trunks gives rise to left, right pulmonary arteries and ductus arteriosus. Interatrial septum is incomplete allowing blood to pass from RA to LA
Ductus Arteriosus
Transfers most of the blood from he pulmonary into the aorta
Formation of interatrial septum
- Downgrowth of septum primum and formation of L and R endocardial cushion.
- Fusion of inferior and superior endocardial cushion forms septum intermedium
- Cell death creates ostium secundum
- Downgrowth of thick septum secundum. Ostium primum completed sealed
- Septum secundum stops growing and foramen ovale forms allowing blood flow for RH to LH
Fetal circulation: overall pattern
Fetus lungs are fluid filled
Pulmonary capillaries are compressed, resistance to blood flow through lungs is higher than systemic. Blood takes lower resistance path through ductus arteriosus into aorta rather than high resistance path.
Placenta
Drains oxygen rich blood back via the umbilical vein (liver)
Changes at birth
Resistance decreases
- Infant takes first breath, lungs inflate and replaces fluid. Capillaries expand and resistance to blood flow decreases
- Blood leaving right ventricle travels through low resistance lung pathway rather than high resistance ductus arteriosus into the systemic circuit.
- Blood travels through the left side for the first time
- Umbilical vein constricts and is clamped. Venous return to placenta is 0. Inflow to RA from systemic circuit decreases, RA pressure falls
- LA pressure exceeds RA pressure. Septum primum closes, the foramen closes separating the two atria
L ventricle
Pump
95mmHg
Thick muscular walls, inlet & outlet valves
Large arteries
Conduct blood away from pump
Store blood during systole, releasing it during diastole
95mmHg
Elastic walls
Medium-sized arteries
Distribute blood to body
95-85 mmHg
Muscular walls to control diameter, plus CT for strength
Arterioles, metarterioles, precapillary sphincters
Control distribution of blood to capillaries
85-35mmHg
Smooth muscle to control diameter, little CT
Capillaries
Exchange
35-15mmHg
Very thin walls, no muscle or CT
Venules
Collect blood
Thin walled, larger diameter
Veins
Conduct blood to pump
15-0mmHg
Thin walled, variable structure, valves to assist return
R. Atrium
Reservoir & pre-pump
0-2mmHg
Thin, muscular walls
Muscular arteries (size and tunics)
10mm - 0.5mm
Has 3 tunics
Tunica intima
Tunica media
Tunica adventitia
Tunica Intima of muscular arteries
Innermost coat
Endothelium
Basement membrane
Subendothelial CT
Internal elastic lamina - smooth but longitudinal folds after death
Tunica Media of muscular arteries
Middle and thickest coat
SM control diameter
Elastin fibres give resiliency
Collagen fibres limit expansion and prevent rupture
Sometimes has external elastic lamina
Tunica Adventitia of muscular arteries
Outermost coat
Usually only collagen and elastin fibers
Vaso vasorum to service the outer layers of the vessel wall.
Artherosclerosis
Disease of intima
Formation of plaques (atheromas) containing fat and collagen. Caused from damage (shear stress, toxins (smoking), lipid diet) to the endothelium
Atherosclerosis problems
Narrowing of BV
Thrombus (bludclart)
Embolus (stroke)
Aneurism
haemorrhage
Endothelium in Atherosclerosis
Loses ability to regulate whether cholesterol leaves the blood and enters blood vessel wall. Low surface area to volume ratio -> harder to reabsorb it
Macrophages accumulates lipid to form foam cell. Accumulation of hydrophobic lipids
Elastic arteries size and layers
20mm-10mm
Layers:
Tunica Intima
Tunica media
Tunica adventitia
Elastic arteries function and location
Aorta and Pulmonary arteries, downstream of ventricles.
Store blood during systole and recoil during diastole to squeeze blood outwards into arterial tree
Tunica Intima of Elastic arteries
Endothelium
Subendothelial CT
IEL
Is thicker than muscular arteries and contains longitudinal elastin fibres in subendothelial CT
Tunica Media of Elastic arteries
Lamellar units
(Fenestrated sheet of elastin
Smooth muscle
Collagen)
50-60 lamellar units in aorta.
Tunica adventitia of Elastic arteries
EEL
Collagen
Small BV and autonomic nerves
Transition from elastic to muscular
Gradual not abrupt
Aneurysms
Thin, weak section of artery wall which bulge outwards. Weakness may arise from trauma, congenital defect or by atherosclerosis
Berry aneurysms
Occur at branch points of cerebral arteries and rupturing causes bleeding into subarachnoid space or into the brain substance
Dissecting aneurysms
Affect aorta, vessel weakened by atherosclerosis and media is penetrated by blood entering the intima. The split dissects the media over time and if the adventitia fails, death frequently occurs
Arterioles
Smallest of muscular arteries
0.1mm
Wall thickness equal to diameter of lumen
Layers
endothelium
IEL - in larger arterioles
Smooth Muscle Fibre - 3 or fewer
Collagen
For their size have the thickest muscle coat in media.
Greatest pressure drop occurs
Hypertension
Sustained, elevated blood pressure
Arteries constrict to try maintain correct pressure in the capillaries. Arteriole media enlarges and the internal media enlarges and the internal elastic lamina splits and reduplicates. The intima becomes thickened with collagen, thus narrowing the lumen of the vessel
Primary hypertension
No single cause can be found. 90% of cases
Secondary hypertension
Cause can be identified
Can be caused by anything that increases cardiac output ( increases in sympathetic activity from stress)
Microcirculation
The order of blood flow in small arterioles, capillary bed and postcapillary venules.
Distribution is controlled by terminal arterioles (single layer of SM) and metarterioles (incomplete layer of muscle). Precapillary sphincter controls entry into each capillary. Relaxation allows blood to flow through capillaries.
Capillaries
Exchange with tissue fluids
Endothelium with basal lamina
8-10 um
Continuous capillaries
Endothelial cell forms a continuous sheet
Fenestrated capillaries
Endothelial cells are perforated with numerous small fenestrae
Continuous capillaries with closed intercellular clefts
Tight junctions make a complete seal. Occurs in the CNS and is responsible for the blood-brain barrier
Continuous capillaries with open intercellular clefts
6nm clefts permit the passage of water,ions and small molecules NOT plasma proteins
Pericytes wrap around and can differentiate into SM cells
Found in muscle, CT, lungs, most common continuous capillary
Fenestrated capillaries with closed perforations
fenestrae are about 60nm in diameter but are closed by a non-membranous diaphragm. Diaphragm restricts passage of proteins but not water
Most common intestine
Fenestrated capillaries with open perforations
Leaky as fluid exchange is important
Endocrine glands and kidney glomeruli
Sinusoids
Wide-pore capillaries (>9um) between edges of adjacent endothelial cells, allowing easy passage of large molecules and cells.
Sinusoids occur in bone marrow and the spleen where red blood cells leave the bloodstream
Endothelium
Detect changes in blood pressure, blood flow and blood composition
Secrete molecules such as prostacyclin and NO causing SM relaxation and endothelin causes contraction.
Discourage platelets from adhering and do not stimulate blood coagulation. During injury, they can promote thrombosis
Endothelium in atherosclerosis
Hypertension endothelial cells release factors (eg. platelet-derived growth factor PDGF) which cause SM cells to change their form; they proliferate, enlarge and migrate to the intima.
Postcapillary venules
10-25um in diameter drain capillary beds
Lack SM (have pericytes)
During inflammation, respond to histamine and serotonin with increased leakage of blood plasma into tissue fluid, causing swelling (oedema) and migration of neutrophils through vessel wall.
Muscular venules
Larger (20-100 um)
Up to two layer of smooth muscle in media (no IEL)
Characterized by thin wall in relation to their diameter and by endothelial nuclei which bulge into lumen
