Control of Blood Flow (Nursing)

00:01 So now let's take a look at how we control blood flow through our vessels.

00:06 Tissue perfusion refers to our blood flow through the body's tissues, and involves the delivery of oxygen and nutrients to, and the removal of waste from our tissue cells.

00:18 We also have gas exchange at the lungs, absorption of nutrients in our GI tract, and urine formation in the kidneys.

00:28 The rate of flow is precisely just the right amount to provide proper function to a tissue or organ.

00:37 The rate of blood flow is going to be controlled by both extrinsic and intrinsic factors.

00:43 Extrinsic controls include the sympathetic nervous system, and hormones that control the flow of blood through the whole body.

00:52 They also act on arteriolar smooth muscles to reduce the flow to regions that need it the least.

00:59 Our intrinsic controls also referred to as autoregulation is more of a local control of blood flow.

01:07 Where blood flow is adjusted to meet the specific tissues requirements.

01:12 Local arterioles that feed capillaries can undergo modification of their diameters and organs are able to regulate their own blood flow by varying the resistance of their own arterioles.

01:27 Autoregulation or local control is going to regulate blood flow to that local area.

01:35 An example of autoregulation is reactive hyperemia, which increases blood flow to an area due to intrinsic factors.

01:45 There are two main types of intrinsic mechanisms that determine the final autoregulatory response at a tissue.

01:53 We have metabolic controls and myogenic controls.

01:58 With metabolic controls increase in tissue metabolic activities are going to result in a declining level of oxygen, as well as increasing levels of our metabolic products like H+, potassium, adenosine, or prostaglandins.

02:16 The effects of changes on the local level cause a direct relaxation of arterioles and relaxation of our precapillary sphincters.

02:26 This causes the release of nitric oxide as well as powerful vasodilators, our endothelial cells.

02:36 Endothelins also released from the endothelium of our capillaries are going to be potent vasoconstrictors.

02:44 Nitric oxide and endothelins are usually balanced unless blood flow is inadequate.

02:51 In which case, nitric oxide is going to win control and cause vasodilation.

02:57 Also inflammatory chemicals can cause vasodilation.

03:05 Another type of local control are myogenic responses.

03:09 Local vascular smooth muscles are going to respond to changes in the main arterial pressure in order to keep perfusion constant while avoiding damage to our tissues.

03:22 In myogenic control, passive stretch is going to cause our smooth muscles to respond by constricting.

03:30 Here, increase mean arterial pressure stretches the vessel wall more than normal.

03:37 And turn, the smooth muscles respond by constricting and causing a decrease in the blood flow to that tissue.

03:46 Opposite of passive stretch is reduced stretch.

03:50 Here the decreased mean arterial pressure causes less stretch than normal.

03:56 In response, our smooth muscles would dilate causing an increase in the blood flow to that tissue.

04:04 We also have long-term autoregulation as part of our intrinsic controls.

04:10 This occurs when short-term autoregulation cannot meet the tissues nutrient and requirements.

04:17 Long-term autoregulation may take weeks or months to supply an adequate blood supply.

04:25 The number of vessels to a region may increase by way of angiogenesis, and existing vessels may become larger.

04:34 This is common in the heart when our coronary vessels become occluded and also in the body of people who move to high altitude areas.