Flashcards in Cardiovascular System Deck (38):
What is the function of the cardiovascular system?
• Circulates and transports nutrients, oxygen, carbon dioxide, hormones, and blood cells to and from the cells of the body
• Fights disease, stabilizes temperature, pH and helps maintains
What is pulmonary circulation?
A "loop" through the lungs where blood is
What is systemic circulation?
A "loop" through the rest of the body to
provide oxygenated blood and receive deoxygenated blood
What is a closed cardiovascular system?
The blood never leaves the network of arteries, veins and capillaries
How much blood does the average adult have? What is its composition?
2 litres is red blood cells
3 litres is plasma
Where does most of out blood lie?
The peripheral veins
What is bridging?
Bridging is the compression of a segment of a coronary artery during systole, resulting in narrowing that reverses during diastole
What is an end artery?
- A terminal artery supplying all or most of the blood to a body part without significant collateral circulation
- Such arteries undergo progressive branching without the development of channels connecting with other arteries, so that, if occluded, there is insufficient blood supply to the dependant tissue
- Examples of functional end arteries are the coronary arteries, splenic artery, cerebral arteries and renal arteries
- The best example of an absolute end artery (anatomically true end arteries) is the central artery to the retina
What is collateral circulation?
- Partial coronary artery closure or stenosis (narrowing)
- Bypassing of artery to supply the myocardium via alternated circulatory vessels
- Total occlusion of coronary artery
During systole, what happens to the walls of the arteries?
Left ventricle contraction causes the blood pressure in the aorta to rise to approx 120 mm Hg (systolic pressure). The walls of the elastic aorta (and other elastic arteries) stretch
What happens to the aorta during diastole?
The aortic semilunar valve closes. The walls of the aorta recoil, maintaining pressure on the blood and moving it towards the heart and smaller vessels. Aortic pressure drops to 70 – 80 mm Hg (diastolic pressure)
What are the walls of arteries and veins composed of?
- Tunica intima
(next to the lumen)
- Intermediate tunica media
- Outer tunica adventitia/externa
What is an aneurysm?
- Dilation of a blood vessel
Describe the structure of the tunica intima
Thick internal elastic lamina
What is the structure of the tunica media?
- 40 layers of smooth muscle cells
- Connected by gap junctions (coordinated contraction)
- Prominent external elastic lamina
Describe the structure of the tunica adventitia
Think layer of fibroelastic connective tissue containing vasa vasorum (not very prominent, network of small blood vessels), lymphatic vessels and nerve fibres
How is the tunica media depolarised?
Neurotransmitter (noradrenaline) released at the nerve endings diffuses through fenestrations in the external elastic lamina into the external tunica media to depolarise some of the superficial smooth muscle cells. Depolarisation is propagated to all cells of the tunica media via gap junctions.
How many layers of smooth muscle do arterioles have in their tunica media?
What are metarterioles?
Arteries that supply blood to capillary beds are called metarterioles
What is a precapillary sphincter?
- The individual muscle cells are spaced apart and each encircles the endothelium of a capillary arising from the metarteriole.
- This is a precapillary sphincter
- Each smooth muscle cell is believed to function as a sphincter, upon contraction, controlling blood flow into the capillary bed
What is a capillary made up of?
The capillary is made of a single layer of endothelium and its basement membrane
How do pericytes interact with the capillary?
Pericytes form a branching network on the outer surface of the endothelium. These cells are capable of dividing into muscle cells, or fibroblasts, during angiogenesis, tumour growth and wound healing
What are postcapillary venules?
- Postcapillary venules receive blood from capillaries
and are even more permeable than capillaries
- The postcapillary venule wall is similar to that of capillaries (endothelial lining with associated pericytes)
Why does fluid drain into the postcapillary venules?
Because their pressure is lower than that of capillaries or the surrounding tissue, fluid tends to drain into them
When might fluid not drain into the post-capillary venules?
inflammatory response - in which case fluid and leukocytes emigrate. Postcapillary venules are the preferred location for emigration of leukocytes from the blood
How does the diameter and wall thickness of veins compare with other vessels?
- As a general rule, veins have a larger diameter than any accompanying artery
- Thinner wall that has more connective tissue and fewer elastic and muscle fibres
Describe the composition of a vein
- Small- and medium-sized veins have a well developed adventitia.
- The tunica intima is thin, as is the tunica media (2 or 3 layers of smooth muscle)
- Large veins have diameters > 10 mm. The tunica intima is thicker. Most large veins do not have a prominent tunica media, but have a well-developed tunica adventitia.
- An exception are the superficial veins of the legs, which have a well-defined muscular wall, possibly to resist distension caused by gravity
What is capacitance?
Capacitance is defined as the ability of a blood vessel to increase the volume of blood it holds without a large increase in pressure. It is inversely proportional to elasticity
Why are veins called capacitance vessels?
- Veins have thin non-elastic walls so can stretch lots
How does venous blood get from the legs back to the heart in a standing human?
- Calf muscle acts as a pump for deep leg veins
- Valves prevent back flow
- Blood flow upwards caused by muscle contraction
What is cardiac arrest?
- Occurs when the heart malfunctions and stops beating unexpectedly
What is a heart attack?
- Blood flow to the heart is blocked
What causes muscle atrophy?
- Reduction in cell number/ size
• Muscle inactivity
• Congestive cardiac failure, chronic obstructive pulmonary disease (COPD), renal failure
• Neurogenic – e.g motor neurone disease, spinal cord injury
What can be used as an indicator of muscle injury?
• Creatine kinase (all muscle)
• Myoglobin (skeletal muscle) -> myoglobinuria
• Troponin I (cardiac)
How does left ventricular failure lead to pulmonary oedema?
- LV cannot pump enough blood at high pressure to tissues
- Blood pools in ventricle
- Backs up to pulmonary vein
- Into lung
What diseases can be caused by smooth muscle dysfunction?
• Irritable Bowel Syndrome
• Primary hypertension
• Detrusor instability
Why might urine be a dark brown/red colour?
- Myoglobinuria leads to myoglobin in the urine
- Response to rhabdomyolysis
- Rhabdo caused by crash injuries, seizures, falls etc
- Leads to kidney failure