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Example Question #31 : Circulatory System
Which of the following areas in the general circulation has the lowest blood pressure?
Vena cavae
Venules
Capillaries
Arteries
All of these have the same average blood pressure
Vena cavae
In the general circulation, the highest blood pressure is found in the aorta and the lowest blood pressure is in the vena cava. As this suggests, blood pressure drops in the general circulation as it goes from the aorta to the rest of the body. Pressure drops form the aorta to the arteries, the arteries to the arterioles, and the arterioles to the capillaries. Flow rate reaches a minimum in the capillaries before blood begins to pool in the venules. Pressure continues to drop from the venules to the veins to the vena cavae.
Example Question #1 : Blood Vessels And Vasculature
Which of the following best describes the cause of diastolic blood pressure?
The viscosity of blood
Venous pressure
Elastic recoil of the aorta
Right ventricular contraction
Elastic recoil of the aorta
Systolic blood pressure is generated by the contraction of the left ventricle and the ejection of blood into the aorta. As blood is ejected into the aorta, the aorta expands to accommodate the large volume of blood. The wall of the aorta then begins to recoil and pushes blood through the arteries. This is how blood pressure continues to stay elevated even when the heart is not contracted.
Right ventricular contraction causes blood to go into the pulmonary circulation, which is not measured with blood pressure testing. The viscosity of blood does not impact the pressure that is exerted on the wall of a blood vessel. Venous pressure is not typically measured, as it is much lower than arterial pressure and is relatively unaffected by heart contractions due to the narrowness of the preceding capillaries.
Example Question #1 : Blood Vessels And Vasculature
Where is blood pressure the greatest?
The aorta
Arterioles
Pulmonary veins
Capillaries
The aorta
Blood pressure tends to be the greatest near the heart, and decreases as blood flows to the capillaries. The pressure is greatest at the aorta and gradually decreases as blood moves from the aorta to large arteries, smaller arteries, and capillaries. The pressure is lowest in the venous system, which is why blood can pool in the veins and act as a "blood reservoir". Veins contain valves that allow them to pump blood back to the heart.
Example Question #861 : Biology
The sympathetic nervous system is responsible for the "fight or flight" responses in the body. When innervated, the sympathetic nervous system will redirect blood from the digestive and excretory organs, and send the blood to the muscles of the body.
How is blood "redirected" to other areas of the body?
Sympathetic innervation of venule shunts
Sympathetic vasoconstriction of arterioles
Blood is redirected to the muscles by the heart
Parasympathetic innervation of venule shunts
Sympathetic vasodilation of arteries
Sympathetic vasoconstriction of arterioles
The heart is incapable of selectively pumping blood to certain areas, nor can it manipulate the speed of blood flow through certain areas. Instead, the sympathetic nervous system can stimulate the smooth muscle surrounding arterioles to constrict. This constriction of arterioles allows blood to be redirected to other areas of the body where blood is needed. Venule shunts are important for counteracting gravity, but the lack of thick smooth muscle lining these vessels makes them ineffective at redirecting blood flow.
Example Question #33 : Circulatory System
Which of the following statements about capillaries is FALSE?
I. The blood flow to a capillary bed can be interrupted by constriction of pre-capillary sphincters.
II. There is a continuous, slow exudation of intravascular fluid into all capillary beds.
III. Together with small arteries, capillaries constitute the "resistance bed" of an organ.
IV. The blood in the distal capillaries of many tissues has a higher osmotic pressure than the blood in the same proximal capillaries.
V. In the pituitary vascular portal system, capillaries take up releasing hormones from the hypothalamus.
II
V
I
III
IV
II
Some—but not all—capillary beds experience transudation of fluid from the vessels. Recall that capillaries can be discontinuous (spaces between adjacent cells), completely closed with tight junctions between cells (as in the brain), or fenestrated (pores through their cytoplasmic membranes (as in the kidney). Closure of arteriolar pre-capillary sphincters can reduce or eliminate the blood flow to a region of tissue. This is why your fingers blanche in very cold weather. Although the arterioles are the major resistance vessels in a circuit, the capillary beds have some contribution. Transudation of fluids, but not large molecules such as protein, from inside to outside a capillary indeed raises the osmotic pressure of the remaining blood; this is Starling's Law, not to be confused with the Frank-Starling law of the heart.
Choice V is a true statement regarding the hypothalmo-hypophyseal portal system.
Example Question #34 : Circulatory System
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
The hemoglobin gene can be the site of catastrophic genetic changes, one of which is the change seen in sickle cell anemia. In this disorder, hemoglobin mutations cause red blood cells to take on a sickled appearance. These cells are less able to flow freely in the blood through tight spaces. Which of the following vessels is most likely to be the site of accumulation of these misshapen cells?
Veins
Capillaries
Arteries
Venules
Arterioles
Capillaries
With morphological changes, cells are most likely to be caught in regions with the smallest cross sectional area. Though capiallary beds have the highest TOTAL cross sectional area of any vessel bed in the body, individual capillaries are smaller than any other type of blood vessel. The result is that misshapen red blood cells, such as those in sickle cell anemia, can easily get stuck in capillaries.
Example Question #11 : Blood Vessels And Vasculature
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
During exercise the flow of blood is changed, and blood flow is preferentially directed toward working muscles. These muscles are then able to utilize the oxygen carried by hemoglobin. What vessels are most likely to be directly mediating changes in blood flow?
Venules
Arteries
Arterioles
Veins
Capillaries
Arterioles
Arterioles serve an important sphincter function at the entry point to capillary beds. During exercise, capillary beds that are not in need of perfusion at a given moment may enlist the use of arterioles to constrict and divert blood where it is more needed.
Example Question #12 : Blood Vessels And Vasculature
Hemoglobin is the principal oxygen-carrying protein in humans. It exists within erythrocytes, and binds up to four diatomic oxygen molecules simultaneously. Hemoglobin functions to maximize oxygen delivery to tissues, while simultaneously maximizing oxygen absorption in the lungs. Hemoglobin thus has a fundamentally contradictory set of goals. It must at once be opitimized to absorb oxygen, and to offload oxygen. Natural selection has overcome this apparent contradiction by making hemoglobin exquisitely sensitive to conditions in its microenvironment.
One way in which hemoglobin accomplishes its goals is through the phenomenon of cooperativity. Cooperativity refers to the ability of hemoglobin to change its oxygen binding behavior as a function of how many other oxygen atoms are bound to the molecule.
Fetal hemoglobin shows a similar pattern of cooperativity, but has unique binding characteristics relative to adult hemoglobin. Fetal hemoglobin reaches higher saturation at lower oxygen partial pressure.
Because of cooperativity, adult and fetal oxygen-hemoglobin dissociation curves appear as follows.
Beyond its ability to carry oxygen, hemoglobin is also effective as a blood buffer. The general reaction for the blood buffer system of hemoglobin is given below.
H+ + HbO2 ←→ H+Hb + O2
Hemoglobin takes time to unload oxygen at tissues that need it, as well as time to pick up carbon dioxide from working cells. Blood flow must slow down during the most active periods when hemoglobin is absorbing and releasing atoms. Since cross-sectional area is inversely proportional to flow velocity, which of the following vessel beds has the greatest total cross sectional area?
Venules
Arterioles
Veins
Capillaries
Arteries
Capillaries
Capillary beds have the greatest TOTAL cross-sectional area, but are composed of individual vessels that are smaller than any other type in the body. Because velocity is dependent on overall cross sectional area, capillary blood velocity is the lowest.
Example Question #37 : Circulatory System
One component of the immune system is the neutrophil, a professional phagocyte that consumes invading cells. The neutrophil is ferried to the site of infection via the blood as pre-neutrophils, or monocytes, ready to differentiate as needed to defend their host.
In order to leave the blood and migrate to the tissues, where infection is active, the monocyte undergoes a process called diapedesis. Diapedesis is a process of extravasation, where the monocyte leaves the circulation by moving in between endothelial cells, enters the tissue, and matures into a neutrophil.
Diapedesis is mediated by a class of proteins called selectins, present on the monocyte membrane and the endothelium. These selectins interact, attract the monocyte to the endothelium, and allow the monocytes to roll along the endothelium until they are able to complete diapedesis by leaving the vasculature and entering the tissues.
The image below shows monocytes moving in the blood vessel, "rolling" along the vessel wall, and eventually leaving the vessel to migrate to the site of infection.
Capillaries, such as the one depicted in the passage, not only exchange immune cells, but also gas and nutrients with neighboring tissues. Which of the following is true of capillaries?
I. Hydrostatic pressure is greater at the arteriolar end.
II. Osmotic pressure is greater at the arteriolar end.
III. There is a net loss of fluid to the extravascular tissue from the arteriolar to the venule end of the capillary.
I and II
III, only
I and III
I, only
II and III
I and III
There is greater hydrostatic pressure pushing fluid out of the capillary at the arteriolar end, and greater osmotic pressure pulling fluid back in at the venule end. Despite this balance, it is not exact, and there is a net loss of fluid to the extravascular compartment over the length of the capillary. This extra fluid is captured by lymphatics and recycled via lymph vessels.
Example Question #41 : Circulatory System
All of the following are examples of human capillary classifications except __________.
hypodermic
fenestrated
sinusoidal
continuous
hypodermic
Capillary beds can be broken down into three types: continuous, fenestrated, and sinusoidal.
Continuous capillaries have no pores, fenestrated have small pores, and sinusoidal have large, leaky pores. Hypodermic describes the region just beneath the skin; while this is the location of many capillaries, it is not a classification.
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