MCAT Biology Circulatory system Flashcards
The flow of blood through a tissue is known as ___
perfusion
Inadequate blood flow is known as __
ischemia
___have smooth muscle in their walls that can act as a control valve to restrict or increase the flow of blood into the capillaries of tissues
Arterioles
After passing through capillaries, blood collects in small veins called ___
venules
Except for the largest vesssels near the heart, veins lack a __
muscular wall
What are the 4 major roles of endothelial cells lining blood vessels
Vasodilation and vasoconstriction
Inflammation
Angiogenesis
Thrombosis
Why have mammals evolved a separate circulation for lungs?
Blood is pumped away from the heart at high pressure in arteries to pass through the capillaries. If the blood is to pass through one bed of capillaries, and then through another bed of capillaries, the pressure must be very high in the first set of capillaries or blood will not have enough pressure to pass through the second set of capillaries. Having two separate circulations solves this problem
In the ___ blood passes first through capillaries in the intestine, then collects in veins to travel to the liver, where the vessels branch and the blood passes again through capillaries
Hepatic portal system
___is another portal system where blood passes through capillaries in the hypothalamus to the portal veins, then to capillaries in the pituitary
Hypothalamic-hypophysial portal system
The __ evolved as direct transport systems, to transport nutrients directly from the intestine to the liver or hormones from the hypothalamus to the pituitary, without passing through the whole body
Portal systems
The very first branch from the aorta are ___ which branch to supply blood to the wall of the heart
Coronary arteries
Deoxygenated blood from the heart collects in __
coronary veins
Coronary veins merge to form ___ located beneath a layer of fat on the outer wall of the heart
Coronary sinus
Blood in the __ is the only deoxygenated blood that does not end up in the inferior vena cava or superior vena cava, it drains directly into the right atrium
Coronary sinus
Ventricular pressure is very ___ and atrial pressure is __
Ventricular pressure is very high and atrial pressure is lower
During diastole ___
ventricles are relaxed, blood is able to flow into them from the atria
At the end of diastole, ____initiating systole
Ventricles contract
During systole pressure in the atria __
is low and thus the atria fills with blood from the vena cava and pulmonary veins
The equation for cardiac output (L/min) =
Stroke volume (L/beat) X Heart rate (beats/min) CO = SV x HR
Two principle ways to increase venous blood return
- increase total volume of blood in circulatory system (retain more water)
- Contraction of large veins can propel blood towards the heart
- this is why presence of valves throughout the venous system is essential here
Propagation of action potentials requires____
voltage-gated ion channels
Difference between neurons and cardiac muscle cells is that cardiac muscle is a ___ the cytoplasm of different cells can communicate via gap junctions
Functional syncytium
The two voltage-gated ion channels involved in cardiac muscle are
Voltage-gated sodium channels (fast sodium channels)
Slow calcium channels
Why are slow calcium channels in the heart called that?
They stay open longer than the fast sodium channels do, causing the membrane depolarization to last longer in cardiac muscle than in neurons producing a plateau phase
The action potentials of cardiac muscle travel down along ___
T tubules, allow the entry of calcium from the extracellular environment and also induce the sarcoplasmic reticulum to release calcium
The combination of intracellular and extracellular calcium causes the contraction of ___
actin-myosin fibers
Why does the SA node reach threshold faster than any other region of the heart does?
Because it has the most Na+ leak channels
The resting membrane potential of cardiac muscles is about __
-90 mV
The constant level of inhibtiion provided by the vagus nerve releasing acetylcholine that synapse near the SA node bringing the norm heart rate down to 60-80 from its intrinsic 120 bpm is called___
vagal tone
The role of the parasympathetic system in controlling the heart is to __
modulate the rate by inhibiting rapid automaticity
During “fight-or-flight” the sympathetic postganglionic neurons innervate the heart by releasing__
norepinephrine
The second way the sympathetic nervous system influences the heart is by the adrenal medulla__
releasing epinephrine which binds to receptors on cardiac muscle cells
The driving force for blood flow is __
a difference in pressure from arteries to veins
Ohms law summarizes the pressure of blood flow into the formula
P= Q x R Q = blood flow or cardiac output (L/min) R = resistance
How would an increase in stroke volume change blood pressure?
Since CO=SV x HR, an increase in stroke volume would increase cardiac output. Since blood pressure and cardiac output are directly proportional, an increase would increase blood pressure as well
The principle determinant of resistance of blood flow is __
the degree of constriction of arteriolar smooth muscle known as precapillary sphincters
A basa level of pressure privded by constant level of norepinephrine released by millions of sympathetic postganglionic axons innervating precapillary sphincters of arteriolar smooth muscle is termed__
adrenergic tone
The pulse pressure is the difference between __
systolic and diastolic pressure
The hormone ___ made in the kidneys stimulates RBC production in the bone marrow.
Erythropoietin
RBC have no organelles or nucleus and rely on __for ATP synthesis
Glycolysis
When none of the four subunits of hemoglobin have oxygen bound they assume a ___ which has a relatively low affinity for oxygen
tense conformation
The ___of hemoglobin has a higher affinity for oxygen
Relaxed conformation
What three factors stabilize the tense configuration of hemoglobin (low O2 affinity)
- Decreased pH
- Increased pCO2 (level of CO2) in the blood
- Increased temperature
At a given pO2 which has a higher % saturation: tense or relaxed hemoglobin?
Relaxed since it has a higher affinity. This just means that at any O2 level, relaxed hemoglobin will bind more O2 than tense hemoglobin will
What are the three ways that Carbon dioxide is transported in the blood
70% is transported by the conversion of CO2 to Carbonic acid
20% binds to a site on hemoglobin (not the binding site of oxygen) this helps stabilize the tense Hb
3. CO2 is somewhat water-soluble can dissolve in blood, unlike O2 NO O2 can dissolve in blood
Amino acids and glucose are absorbed from the digestive tract and carried by a special vein called ___
hepatic portal vein to the liver
Fats are absorbed from the intestine and packaged into chylomicrons which enter into tiny lymphatic vessles in the intestinal wall called __
lacteals
Lacteals empty into larger lymphatics which eventually drain into a large vein near the neck
Not a card just know this
Two white blood cells can squeeze through the intercellular clefts, the spaces between capillaries, they aere
Neutrophils and macrophages because they are capable of amoeboid motility
Two reasons water has a tendency to flow out of capillaries.
- Hydrostatic pressure created by the heart simply tends to squeeze water out of the capillaries
- High osmolarity of the tissues tends to draw water out of the bloodstream
