Lecture 30 Flashcards
Describe why blood flows through vessels.
Arteries and veins transport blood in two distinct circuits: the systemic circuit and the pulmonary circuit (Figure 20.2). Systemic arteries provide blood rich in oxygen to the body’s tissues. The blood returned to the heart through systemic veins has less oxygen, since much of the oxygen carried by the arteries has been delivered to the cells. In contrast, in the pulmonary circuit, arteries carry blood low in oxygen exclusively to the lungs for gas exchange. Pulmonary veins then return freshly oxygenated blood from the lungs to the heart to be pumped back out into systemic circulation. Although arteries and veins differ structurally and functionally, they share certain features.
List the factors that resist the flow of blood through the vessels.
The three most important factors affecting resistance are blood viscosity, vessel length and vessel diameter and are each considered below
List the factors that assist the return of venous blood to the heart.
- In many body regions, the pressure within the veins can be increased by the contraction of the surrounding skeletal muscle. This mechanism, known as the skeletal muscle pump (Figure 20.15), helps the lower-pressure veins counteract the force of gravity, increasing pressure to move blood back to the heart.
- The respiratory pump aids blood flow through the veins of the thorax and abdomen. During inhalation, the volume of the thorax increases, largely through the contraction of the diaphragm, which moves downward and compresses the abdominal cavity.
Define pulse and identify the arteries where the pulse may be felt.
Since the arteries maintain the pulse throughout their length, even peripheral arteries can be monitored for pulse.
Any place where an artery passes near the surface (usually around a joint) is a pulse point where you can feel the pulse.
The systolic pressure causes the arterial walls to stretch and contract creating the feeling of pulse. The pulse rate slightly lags the heart rate, but is dependent on it.
Discuss the blood velocity and exchange of materials in the capillaries.
The rate, or velocity, of blood flow varies inversely with the total cross-sectional area of the blood vessels. As the total cross-sectional area of the vessels increases, the velocity of flow decreases. Blood flow is slowest in the capillaries, which allows time for exchange of gases and nutrients.
Diffusion, the most widely-used mechanism, allows the flow of small molecules across capillaries such as glucose and oxygen from the blood into the tissues and carbon dioxide from the tissue into the blood.
List hormones that maintain the BP
Several hormones can regulate BP
Aldosterone – secreted from the adrenal cortex increase blood sodium concentration and increase water retention and blood volume.
Angiotensin II –activated in the blood can act as a peripheral vasoconstrictor, increasing peripheral resistance and BP.
Natriuretic peptides – secreted by heart are antagonists to aldosterone, increasing sodium excretion, lowering blood sodium and volume and decreasing BP.
Define blood pressure and discuss the hormonal regulation of blood pressure.
The force of circulating blood on the walls of the arteries. Blood pressure is taken using two measurements: systolic (measured when the heart beats, when blood pressure is at its highest) and diastolic (measured between heart beats, when blood pressure is at its lowest).
Describe the clinical method for recording systolic and diastolic pressure
Measurement of peripheral BP is done by using an external pressure cuff to compress the artery and then monitoring the pulse sound distally as the cuff is deflated. When BP matches cuff pressure, the blood can flow distally into the artery. It is reported as two numbers systolic and diastolic.
List the causes and symptoms of aneurysms, Arteriosclerosis, Hypertension
Aneurysm – a weakening of the muscularis layer, leading to a bulging of the wall and eventual rupture. Related to trauma, alcoholism, and hypertension.
Arteriosclerosis – As we age, the walls of the arteries tend to become less elastic. This is called “hardening” of the arteries. Peripheral pulse and BP are weaker, leading to poor peripheral circulation.
Hypertension – BP in excess of 140/90 and can be caused by several factors. The most common is increased peripheral resistance from atherosclerosis. There is also a genetic form called essential hypertension and also renal hypertension from decreased blood flow to the nephrons.
