Fundamentals of Circulation: Physiology & Pathology of O2 Delivery & Perfusion

Question 1

How does blood flow in the circulatory system?

Answer 1

Blood flows down a pressure gradient, moving from areas of higher pressure to areas of lower pressure.

Question 2

What is the nature of blood flow in the aorta and large arteries?

Answer 2

Blood flow in the aorta and large arteries is pulsatile, meaning it occurs in surges or pulses as the heart contracts and relaxes during each heartbeat.

Question 3

What is the nature of blood flow in the capillaries and veins?

Answer 3

Blood flow in the capillaries and veins is laminar, meaning it occurs in smooth layers or streams without turbulence. This allows for efficient exchange of oxygen, nutrients, and waste products at the capillary level.

Question 4

What is the significance of pulsatile flow in the aorta and large arteries?

Answer 4

Pulsatile flow in the aorta and large arteries helps propel blood forward, ensuring a continuous supply of oxygenated blood to the organs and tissues.

Question 5

Why is laminar flow important in the capillaries and veins?

Answer 5

Laminar flow in the capillaries and veins allows for efficient exchange of gases, nutrients, and waste products between the blood and surrounding tissues. It also helps prevent turbulence and maintains smooth blood flow.

Question 6

Is the rate of blood flow constant throughout the circulation?

Answer 6

Yes, the rate of blood flow remains constant at all levels in the circulation.

Question 7

What is the relationship between velocity, flow, and cross-sectional area?

Answer 7

Velocity (V) is calculated by dividing the flow rate (Q) by the cross-sectional area (A): V = Q / A.

Question 8

What are the units for velocity?

Answer 8

Velocity is typically measured in meters per second (m/s).

Question 9

How does cross-sectional area (CSA) affect blood velocity?

Answer 9

The velocity of blood is inversely proportional to the cross-sectional area. As the cross-sectional area increases, the velocity decreases.

Question 10

Where in the circulation is the cross-sectional area greatest?

Answer 10

The cross-sectional area is greatest in the capillaries, where the numerous small vessels provide a large total area for blood flow.

Question 11

How does the slow velocity in capillaries benefit the body?

Answer 11

The slow velocity in capillaries allows for sufficient time for exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues. It promotes effective diffusion and facilitates nutrient uptake and waste removal.

Question 12

What is the primary function of the circulation regarding oxygen (O2)?

Answer 12

The circulation transports oxygen from the lungs to the tissues.

Question 13

What is the primary function of the circulation regarding carbon dioxide (CO2)?

Answer 13

The circulation transports carbon dioxide from the tissues to the lungs for elimination.

Question 14

What is the role of the circulation in the transport of metabolic waste?

Answer 14

The circulation carries metabolic waste products from the tissues to organs such as the liver and kidneys, where they can be processed and eliminated from the body.

Question 15

How does the circulation contribute to the distribution of nutrients?

Answer 15

The circulation distributes nutrients absorbed from the gut and produced by the liver to various tissues and organs throughout the body.

Question 16

What is the role of the circulation in the distribution of body water and electrolytes?

Answer 16

The circulation helps maintain fluid and electrolyte balance by transporting water and electrolytes between different compartments of the body, such as the intracellular and extracellular spaces.

Question 17

What substances are transported by the circulation besides oxygen, carbon dioxide, and nutrients?

Answer 17

The circulation also transports hormones and immunologically active substances, such as antibodies and immune cells, throughout the body.

Question 18

How does the circulation contribute to thermoregulation?

Answer 18

The circulation plays a role in regulating body temperature by redistributing heat from the core of the body to the skin, where it can be released to the environment.

Question 19

What is the significance of redistributing heat in the body?

Answer 19

By redistributing heat, the circulation helps maintain a stable core body temperature, which is essential for normal physiological functioning.

Question 20

What is the difference in mean pressure between systemic and pulmonary circulations?

Answer 20

The mean pressure in systemic circulation is around 100 mmHg, while in the pulmonary circulation, it is around 15 mmHg.

Question 21

How do the walls of systemic and pulmonary arteries differ?

Answer 21

The walls of systemic arteries are thick and elastic, allowing them to withstand high pressure and maintain blood flow. In contrast, the walls of pulmonary arteries are thinner and more distensible.

Question 22

How do the arterioles in systemic and pulmonary circulations differ in terms of lumen size?

Answer 22

Arterioles in systemic circulation have a smaller lumen, contributing to higher resistance to blood flow. In contrast, pulmonary arterioles have a larger lumen, resulting in lower resistance.

Question 23

What is the typical response of systemic arterioles to hypoxia?

Answer 23

Systemic arterioles respond to hypoxia by vasodilation, allowing increased blood flow to tissues in need of oxygen.

Question 24

What is the typical response of pulmonary arterioles to hypoxia?

Answer 24

Pulmonary arterioles respond to hypoxia by vasoconstriction, redirecting blood flow away from poorly oxygenated areas of the lungs.

Question 25

How does the wall thickness of capillaries in the systemic and pulmonary circulations compare?

Answer 25

The wall thickness of capillaries is thin in both the systemic and pulmonary circulations. This thinness facilitates the exchange of gases and nutrients between the blood and tissues.

Question 26

How does the flow of blood differ in capillaries between systemic and pulmonary circulations?

Answer 26

In systemic capillaries, blood flow is continuous, meaning it occurs without interruption. In pulmonary capillaries, blood flow is pulsatile, coinciding with the rhythmic contraction and relaxation of the right ventricle.

Question 27

How do the pressure levels in systemic and pulmonary veins compare?

Answer 27

The pressure in systemic veins is relatively low, around 2 mmHg, as blood returns to the heart from the body’s tissues. In contrast, the pressure in pulmonary veins is slightly higher, around 5 mmHg, as blood returns from the lungs to the left atrium.

Question 28

How does the capacity or volume of blood in systemic and pulmonary veins differ?

Answer 28

Systemic veins have a high capacity, holding more than 3 liters of blood in the body’s venous system. In contrast, pulmonary veins have a lower capacity, holding less than 500 milliliters of blood, as they primarily receive oxygenated blood from the lungs

Question 29

What is autoregulation?

Answer 29

Autoregulation is the ability of organs and tissues to maintain a relatively constant blood flow despite changes in blood pressure.

Question 30

Why is autoregulation important?

Answer 30

Autoregulation ensures that organs receive a consistent blood supply, even when systemic blood pressure fluctuates. It helps maintain normal organ function and protects tissues from damage due to inadequate or excessive blood flow.

Question 31

How does autoregulation work?

Answer 31

Autoregulation involves multiple mechanisms that can vary between organs. These mechanisms include local vasodilation or vasoconstriction of arterioles, which control the resistance to blood flow and adjust the diameter of blood vessels to maintain optimal flow.

Question 32

How does autoregulation respond to changes in blood pressure?

Answer 32

When blood pressure increases, autoregulation causes arterioles to constrict, reducing blood flow. Conversely, when blood pressure decreases, arterioles dilate to increase blood flow. This helps maintain a relatively constant flow within a specific range of blood pressures.

Question 33

Does autoregulation occur in all organs?

Answer 33

Yes, autoregulation occurs in all organs to some extent. However, the specific mechanisms and effectiveness of autoregulation can vary among organs depending on their metabolic demands and regulatory mechanisms.

Question 34

What are external controls of blood flow?

Answer 34

External controls of blood flow refer to mechanisms that regulate blood flow through the actions of factors outside of the local tissue or organ being supplied with blood.

Question 35

What are the main external controls of blood flow?

Answer 35

The main external controls of blood flow include the autonomic nervous system, hormones, and local vasoactive mediators.

Question 36

How does the autonomic nervous system regulate blood flow?

Answer 36

The autonomic nervous system, specifically the sympathetic division, plays a significant role in regulating blood flow. Sympathetic stimulation causes vasoconstriction, reducing blood flow, while the withdrawal of sympathetic tone leads to vasodilation, increasing blood flow.

Question 37

Which hormones can affect blood flow?

Answer 37

Hormones such as adrenaline (epinephrine) and noradrenaline (norepinephrine) released from the adrenal glands can cause vasoconstriction, increasing blood pressure and reducing blood flow to certain organs. Hormones like angiotensin II can also constrict blood vessels, while others like prostaglandins and bradykinin can promote vasodilation.

Question 38

What are local vasoactive mediators?

Answer 38

Local vasoactive mediators are substances released by cells in the vicinity of blood vessels that can influence blood flow. Vasodilators such as adenosine and nitric oxide (NO) relax smooth muscle, promoting vasodilation. Vasoconstrictors like endothelin constrict blood vessels, reducing blood flow.

Question 39

How do metabolic factors affect blood flow?

Answer 39

Metabolic factors, such as low oxygen levels, high carbon dioxide levels, and low pH (acidosis), can cause vasodilation, increasing blood flow to meet the metabolic demands of tissues.

Question 40

What is the portal system?

Answer 40

The portal system refers to a specialized circulatory pathway that consists of two sets of capillaries connected by a portal vein. It allows for the transport of blood from one set of capillaries to another before returning it to the heart.

Question 41

What is the function of the portal system?

Answer 41

The primary function of the portal system is to transport venous blood containing absorbed nutrients from the gastrointestinal (GI) tract to the liver for processing and metabolic regulation. This allows the liver to extract and process nutrients, detoxify harmful substances, and regulate various metabolic functions.

Question 42

How does the portal system work?

Answer 42

Blood from the capillaries of the GI tract, carrying nutrients from digested food, drains into the hepatic portal vein instead of directly entering the systemic circulation. The hepatic portal vein then delivers this blood to the liver, where it flows through a second set of capillaries called sinusoids. After passing through the liver, blood from the hepatic sinusoids merges with the systemic circulation through the hepatic veins and eventually returns to the heart.

Question 43

Why is the liver an important organ within the portal system?

Answer 43

The liver plays a vital role in processing and regulating substances absorbed from the GI tract. It metabolizes and detoxifies nutrients, drugs, and other substances, synthesizes proteins, stores glycogen, produces bile, and performs various other metabolic functions. By receiving blood through the portal system, the liver can efficiently carry out these processes.

Question 44

How does blood flow through the portal system relate to cardiac output?

Answer 44

At rest, approximately 25% of the cardiac output is directed to the portal system. However, after a large meal, blood flow through the portal system can significantly increase as the digestive system requires more blood for nutrient absorption and processing in the liver.

Question 45

What is the renal circulation?

Answer 45

The renal circulation refers to the blood flow through the kidneys, which is responsible for the filtration of waste products, regulation of fluid and electrolyte balance, and maintenance of blood pressure.

Question 46

What is the significance of renal circulation?

Answer 46

Although the kidneys constitute only about 1% of total body weight, they receive a significant portion of cardiac output, accounting for approximately 20% of the total cardiac output. This high blood flow is necessary for the kidneys to effectively filter and process blood to maintain homeostasis.

Question 47

How does the constriction of arterioles affect renal flow?

Answer 47

Constriction of either the afferent or efferent arterioles within the kidney increases overall resistance in the renal vasculature and reduces renal blood flow.

Question 48

How does constriction of the afferent arteriole affect glomerular filtration rate

Answer 48

Constriction of the afferent arteriole decreases the blood flow into the glomerulus, reducing the hydrostatic pressure and thus decreasing the GFR. This mechanism helps regulate the filtration of blood and prevent excessive fluid loss.

Question 49

How does constriction of the efferent arteriole affect GFR?

Answer 49

Constriction of the efferent arteriole increases the resistance to blood flow, leading to an increase in the glomerular hydrostatic pressure. This increase in pressure enhances the filtration rate, resulting in an increased GFR.

Question 50

What are the mechanisms that control renal blood flow?

Answer 50

Renal blood flow is regulated by several mechanisms, including autoregulation, the renin-angiotensin-aldosterone system, and tubulo-glomerular feedback. Autoregulation helps maintain a relatively constant renal blood flow over a wide range of systemic blood pressures. The renin-angiotensin-aldosterone system regulates renal blood flow and sodium balance in response to changes in blood pressure. Tubulo-glomerular feedback involves feedback mechanisms between the renal tubules and glomerulus to regulate renal blood flow and GFR.

Question 51

How is renal blood flow and glomerular filtration rate (GFR) maintained over a wide range of blood pressures?

Answer 51

Renal blood flow and GFR are maintained within a relatively constant range despite changes in systemic blood pressure. This phenomenon is observed even in denervated and isolated perfused kidneys.

Question 52

What are the mechanisms involved in maintaining renal blood flow and GFR?

Answer 52

Two important mechanisms involved in maintaining renal blood flow and GFR are myogenic autoregulation and metabolic regulation.

Question 53

What is myogenic autoregulation?

Answer 53

Myogenic autoregulation is a mechanism by which the arterioles in the kidneys respond to changes in blood pressure. When systemic blood pressure increases, the arterioles in the kidneys constrict to limit the influx of blood and maintain a constant renal blood flow and GFR. Conversely, when blood pressure decreases, the arterioles dilate to maintain adequate renal perfusion.

Question 54

What is metabolic regulation in the context of renal blood flow and GFR?

Answer 54

Metabolic regulation refers to the local metabolic factors produced within the renal tissue that influence renal blood flow and GFR. For example, a decrease in oxygen or an increase in metabolic byproducts such as adenosine or carbon dioxide can cause vasodilation of the renal arterioles, increasing renal blood flow and GFR. Conversely, increased oxygen or a decrease in metabolic byproducts leads to vasoconstriction and a decrease in renal blood flow and GFR.

Question 55

What are some key characteristics of the brain in relation to its size and blood flow?

Answer 55

The brain represents about 2% of the body weight. However, it receives a disproportionately high amount of blood flow, accounting for approximately 15% of the cardiac output. Additionally, the brain has a high metabolic demand, consuming about 20% of the body’s total oxygen consumption.

Question 56

How is cerebral blood flow regulated?

Answer 56

Cerebral blood flow is tightly regulated to meet the metabolic demands of the brain. Autoregulation mechanisms ensure a relatively constant blood flow to the brain over a range of mean arterial pressures (60-150 mmHg). The primary controls for autoregulation in the brain are tissue pH and tissue partial pressure of carbon dioxide (PaCO2). Low pH and high CO2 levels trigger vasodilation, increasing cerebral blood flow to remove excess carbon dioxide and maintain appropriate pH levels.

Question 57

How does the brain respond to changes in oxygen levels?

Answer 57

Unlike pH and CO2, the brain’s response to changes in oxygen levels (partial pressure of oxygen, PaO2) is relatively weak. Cerebral blood flow only increases significantly when PaO2 levels are very low. The brain relies more on pH and CO2 levels as regulatory factors for maintaining cerebral blood flow.

Question 58

Why is excitability of neurons highly dependent on H+ and CO2 levels?

Answer 58

Neuronal excitability, or the ability of neurons to generate electrical impulses, is highly sensitive to changes in hydrogen ion concentration (H+) and carbon dioxide (CO2) levels. Increased H+ and CO2 levels, which typically occur in conditions such as respiratory acidosis or increased metabolic activity, can lower the pH of the brain tissue. This acidic environment promotes neuronal excitability and can lead to increased neuronal activity.

Question 59

How does the skin act as a heat exchanger?

Answer 59

The skin plays a crucial role in regulating body temperature by acting as a heat exchanger. When the body needs to dissipate heat, the blood flow to the skin increases, allowing heat from the core to be transferred to the skin surface. Conversely, when the body needs to conserve heat, blood flow to the skin decreases, reducing heat loss.

Question 60

How is blood flow controlled in the skin?

Answer 60

Blood flow in the skin is regulated through several mechanisms. Arteriolar constriction can reduce blood flow to the skin, conserving heat. On the other hand, arteriovenous anastomoses, which are direct connections between arterioles and venules bypassing the capillary beds, can dilate to increase blood flow to the skin. These mechanisms are controlled by the sympathetic nervous system, which can constrict or dilate blood vessels in response to temperature regulation signals. Additionally, skin ambient temperature receptors can sense external temperature changes and influence blood flow regulation.

Question 61

What is the role of nitric oxide (NO) in skin blood flow control?

Answer 61

Nitric oxide (NO) is a vasodilator that plays a crucial role in regulating blood flow in the skin. Local metabolic control, such as increased metabolic activity or the presence of certain substances, can stimulate the release of NO, causing vasodilation and increased blood flow to the skin. This helps in dissipating heat from the body’s core to the skin surface.

Question 62

How much can skin blood flow vary?

Answer 62

Skin blood flow can vary significantly depending on the body’s thermoregulatory needs. It can range from near-zero when the body needs to conserve heat in cold conditions, to more than 5 liters per minute when the body needs to dissipate heat in hot conditions or during physical exertion. This flexibility in blood flow allows the skin to adapt to environmental temperature changes and maintain the core body temperature at approximately 37.0°C.

Question 63

What is the blood flow like in skeletal muscle at rest?

Answer 63

At rest, skeletal muscle has relatively low blood flow. This is primarily due to the basal constriction of the alpha-1 adrenergic receptors in the arterioles, which leads to vasoconstriction and reduced blood flow.

Question 64

How does blood flow in skeletal muscle change during extreme exertion?

Answer 64

During extreme exertion, blood flow in skeletal muscle can increase significantly. It can increase up to 50 times compared to the resting state. This is mainly achieved through arteriolar dilation, which allows for greater delivery of oxygen and nutrients to meet the increased metabolic demands of the muscle during intense exercise.

Question 65

What are the main factors that control blood flow in skeletal muscle?

Answer 65

The main control mechanism for regulating blood flow in skeletal muscle is vasodilation due to tissue hypoxia, which occurs when the oxygen levels (PaO2) in the muscle tissue are low. Additionally, other factors such as high carbon dioxide (CO2), low pH (lactic acid accumulation), and high potassium ion (K+) concentrations can also contribute to vasodilation. Local mediators like adenosine and nitric oxide (NO) play a role in vasodilation as well. The sympathetic nervous system can also induce vasodilation through beta-2 adrenergic receptors.

Question 66

What is functional sympatholysis in skeletal muscle?

Answer 66

Functional sympatholysis is when sympathetic vasoconstriction is attenuated or overridden in skeletal muscle during periods of increased metabolic demand. Despite the basal sympathetic tone causing vasoconstriction, the metabolic needs of the muscle during exercise can override this constriction, leading to vasodilation. This allows for increased blood flow and enhanced oxygen and nutrient delivery to meet the demands of the active muscle tissue.

Question 67

What happens to blood flow during ischemia?

Answer 67

During ischemia, blood flow to a specific part of the body is inadequate to meet the metabolic demands of the tissue. This means that the affected tissue is not receiving sufficient oxygen, nutrients, and is unable to effectively remove waste products such as carbon dioxide (CO2).

Question 68

Which areas of the body receive increased blood flow during exercise?

Answer 68

During exercise, blood flow is diverted to the skeletal muscles and the heart. This is achieved through beta-2 adrenergic receptor-mediated vasodilation in these tissues. Increased blood flow to the skeletal muscles and heart is essential to provide them with sufficient oxygen and nutrients to meet the increased metabolic demands during physical activity.

Question 69

Which areas of the body experience decreased blood flow during exercise?

Answer 69

During exercise, blood flow is decreased to certain areas such as the skin, kidneys, and gastrointestinal (GI) system. This is primarily due to alpha-1 adrenergic receptor-mediated vasoconstriction in these tissues. By reducing blood flow to the skin, the body can conserve heat and redirect resources to the active muscles and vital organs.

Question 70

How is blood flow to the brain preserved during changes in blood flow distribution?

Answer 70

Blood flow to the brain is preserved through a process called autoregulation. Autoregulation helps maintain a relatively constant blood flow to the brain despite changes in systemic blood pressure. The cerebral vessels can dilate or constrict to regulate cerebral blood flow and ensure a stable supply of oxygen and nutrients to the brain. This mechanism helps protect the brain from ischemia or excessive perfusion.

Question 71

What are the clinical manifestations of chronic heart failure?

Answer 71

The clinical manifestations of chronic heart failure include peripheral edema, which is the accumulation of fluid in the tissues leading to swelling, and chronic tissue ischemia. Patients may experience muscle fatigue, impaired kidney function, and stagnant hypoxia due to inadequate blood flow and reduced oxygen supply to the tissues.

Question 72

What are the clinical manifestations of acute heart failure?

Answer 72

Acute heart failure presents with pulmonary edema, which is the accumulation of fluid in the alveoli of the lungs, leading to reduced oxygen transfer and acute breathlessness. In severe cases, acute heart failure can result in cardiogenic shock, characterized by low blood pressure (less than 90 mmHg) and a very low cardiac output. Hypoxic hypoxia, resulting from inadequate oxygenation of the blood, may also be observed.

Question 73

What are the clinical manifestations of cardiogenic shock?

Answer 73

Cardiogenic shock is characterized by a severely low cardiac output, leading to inadequate tissue perfusion. Patients may present with cold peripheries and sweating, confusion, low urine output, tissue acidosis, and stagnant hypoxia. The low blood pressure and reduced cardiac output in cardiogenic shock can have widespread effects on organ function and can be life-threatening if not promptly addressed.