Lecture 15 - Blood Flow

Question 1

What is tissue perfusion involved in?

Answer 1

Delivery of oxygen and nutrients to, and removal of wastes from:

Tissue cells
Gas exchange in the lungs
Absorption of nutrients from the digestive tract
Urine formation isn’t he kidneys

Question 2

What does extrinsic control of blood flow involve?

Answer 2

The sympathetic nervous system and hormones to control blood flow through the whole body

Question 3

Intrinsic control of blood flow

Answer 3

Automatic adjustments of blood flow to each tissue are made in proportion to its need by modifying T diameter of local arterioles

Question 4

What are Metabolic controls strongly stimulated by?

Answer 4

Shortage of oxygen at the tissues

Question 5

What do cells lacking oxygen release?

Answer 5

Nitric oxide

A powerful vasodilator, to increase local blood flow.

normally balanced by endothelins

If nitric oxide levels rise, they overcome the effects of the endothelins and blood vessels dilate.

Question 6

Endothelins

Answer 6

vasoconstrictors released by endothelium that are also present in the bloodstream.

Question 7

What does Myogenic control involve?

Answer 7

localized response of vascular smooth muscle to passive stretch

Increased arterial pressure stretches vessel walls more than normal, so smooth muscle responds by constricting, causing decreased blood flow to the tissue to avoid damage from elevated pressure.

Question 8

Long term autoregulation

Answer 8

develops over weeks or months involves an increase in diameter of blood vessels and an increase in number of vessels in a specific area, called angiogenesis

Question 9

Why does Muscular auto regulation occur

Answer 9

almost entirely in response to decreased oxygen concentrations

Question 10

What happens in active or exercise hyperemia?

Answer 10

blood flow increases in direct proportion to muscle or metabolic activity. Local controls override sympathetic vasoconstriction and blood flow can increase tenfold compared to when at rest.

Question 11

Blood flow to brain

Answer 11

Cerebral blood flow is tightly regulated to meet neuronal needs, because neurons cannot tolerate periods of ischemia (inadequate blood supply), and increased blood carbon dioxide causes marked vasodilation.

Brain is vulnerable to extreme systemic pressure changes; mean arterial pressure below 60 mmHg can cause syncope (fainting) while mean arterial pressure above 160 mmHg can result in cerebral edema.

Question 12

What does low pulmonary oxygen cause?

Answer 12

Vasoconstriction

Question 13

What does high pulmonary oxygen cause?

Answer 13

Vasodilation

Question 14

Local vasoconstriction

Answer 14

Tightening blood vessels in one area

Decreases local blood pressure

Question 15

Systemic vasoconstriction

Answer 15

Tightening blood vessels everywhere

Increases blood pressure

Question 16

What does slow blood flow through capillaries promote?

Answer 16

Diffusion of nutrients and gases and bulk flow of fluids

Question 17

Bulk flow

Answer 17

Fluid forced out through intercellular clefts int he capillaries at the arterial end and most of the fluid returns to the blood at venous end

Causes continuous mixing between plasma and interstitial or extracellular fluid.

Question 18

Hydrostatic pressure

Answer 18

Force of a fluid against a membrane

Question 19

Capillary hydrostatic pressure

Answer 19

capillary blood pressure that tends to force fluids through capillary walls.

pressure is greater at arterial end of the capillary bed than at the venule end.

Question 20

Interstitial fluid hydrostatic pressure

Answer 20

the pressure pushing fluid back into the blood vessel.

usually assumed to be zero because lymphatic vessels drain interstitial fluid.

Question 21

Colloid osmotic pressure

Answer 21

the force opposing hydrostatic pressure

created by the presence of large, non-diffusible molecules that are prevented from moving through the capillary membrane.

Question 22

Capillary colloid osmotic pressure

Answer 22

the “sucking” pressure created by non-diffusible plasma proteins pulling water back into the capillary.

Question 23

Interstitial fluid colloid osmotic pressure

Answer 23

is inconsequential because interstitial fluid has a very
low protein content.

Question 24

When do fluids leave capillaries?

Answer 24

if net hydrostatic exceeds net colloid osmotic pressure.

This occurs at the arterial end of the capillary bed.

Question 25

When do fluids enter the capillaries?

Answer 25

if net colloid osmotic pressure exceeds net hydrostatic pressure.

This occurs at the venous end of the capillary bed.

Question 26

Edema

Answer 26

an abnormal increase in the amount of interstitial fluid.

caused by either an increase in outward pressure (driving fluid out of the capillaries) or a decrease in inward pressure (failure to return fluid back to the capillaries or to drain into the lymphatic system).

Question 27

What can cause an increase in interstitial fluid colloids osmotic pressure?

Answer 27

Inflammatory response

Inflammation increases capillary permeability and allows proteins to leak into interstitial fluid, which causes fluid to be pulled into the interstitial space.