NRSG 202 - Blood Pressure and Blood Flow

Diffusion (capillaries)

occurs between the endothelial cells of the capillaries, and substances travel down the concentration gradient

5 substances that travel across the capillaries via diffusion

1. O2

2. CO2

3. Glucose

4. Amino acids

5. Hormones

Where does capillary diffusion NOT occur and how?

Diffusion does not occur across the blood-brain barrier because this membrane is very selective - tight junctions seal barrier

Between which two substances does diffusion occur?

Plasma → interstitial fluid

Transcytosis

substances cross through/across the cells

Endocytosis

bring substances into the cell in vesicles

Where is transcytosis used?

blood-brain barrier

Between which two substances does transcytosis occur?

Plasma → interstitial fluid

Bulk flow

Movement of water and dissolved substances

2 components of bulk flow

1. Filtration

2. Reabsorption

Filtration

putting large amounts of solute and putting it into a vesicle (i.e. waste)

Reabsorption

bringing things from the vesicle and absorbing it into the tissue (i.e. water, nutrient

Function of bulk flow

Regulating relative volumes of blood and interstitial fluid

Hydrostatic pressure

Pushing pressure; blood pushing up against the vessel

Hydrostatic pressure entering capillary beds

Higher pressure entering the capillaries, lower pressure exiting the capillaries

Bulk flow through capillary beds

Bulk flow shifts from moving out of the vessels to moving into the vessels in the capillaries

What happens if bulk flow does not shift as necessary throughout the capillary bed?

Edema and other pathologies

Blood flow equation

Blood flow = ∆P/R, where P represents pressure and R represents resistance

What is blood flow equivalent to?

Cardiac output (CO)

What is change in pressure equivalent to?

Blood pressure/pulse pressure

What is resistance equivalent to?

Systemic vascular resistance (SVR)

SVR

total of all vascular resistances by all systemic blood vessels

Cardiac output equation

CO = BP/SVR

Blood pressure equation

BP = CO * SVR

Systolic pressure

Pressure during contraction

Diastolic pressure

Pressure between beats

What measures blood pressure?

Sphygmomanometer

Stroke volume

volume of blood ejected during systole

Heart rate

Rate of systole

Vascular resistance

friction that occurs inside of the blood vessels

Mean arterial pressure (MAP) equation

[2 * (diastolic) + systolic]/3

Pulse pressure equation

Systolic pressure - diastolic pressure

What allows for venous return?

Occurs due to a decreasing pressure gradient

Pressure is about _______ mmHg on the venous side

16

Venous valves function

Prevent backflow

Skeletal muscle pump

pumps flow against gravity to return to the heart

Respiratory pump

uses breathing to pump venous blood up to the heart

Blood flow approaching capillaries (how and why)

- blood slows as it approaches the capillaries so that exchange can occur

- This occurs due to the declining radius of the vessels

How does an increase in cross-sectional area affect blood flow?

leads to a decrease in blood flow

Blood flow control in the brain

Cardiovascular center of the medulla oblongata regulates HR, heart contractility, and blood vessel diameter

Which structures send signals regarding blood flow and blood pressure to the brain?

1. Baroreceptors (stretch)

2. Chemoreceptors (osmolarity/concentration)

Where are baroreceptors located?

Located near the aorta and carotid sinuses

Where are chemoreceptors located?

Near the kidneys

How does the brain control blood pressure?

Activates the autonomic nervous system

Angiotensin II trigger and function

- Responds to low BP

- vasoconstriction

Epinephrine/norepinephrine function

activates sympathetic system to increase HR

ADH/vasopressin 2 functions

- increases blood volume by increasing reabsorption (holding onto water)

- vasoconstriction

Atrial natriuetic protein (ANP)

Responds to high BP

Autoregulation of BP

redirects resources to where they are needed in the moment

What stimulates the autoregulation of BP?

Oxygen availability in body tissues stimulates autoregulation of BP

3 factors that affect resistance and blood flow

1. Lumen diameter

2. Blood viscosity

3. Blood vessel length

How does increased lumen diameter influence resistance?

Decreased resistance

How does increased blood viscosity influence resistance?

Increased resistance

How does increased blood vessel length influence resistance?

Increased resistance

What does RAAS stand for?

Renin Angiotensin Aldosterone System

What triggers RAAS?

Response to low BP

What does Renin activate in the RAAS?

ACE (angiotensin-converting enzyme)

What is angiotensinogen converted to?

Angiotensin

Angiotensin 3 effects

1. Vasoconstriction

2. Increase in resistance

3. Increase in BP

Aldosterone 3 effects

1. Na+ and water reabsorption

2. K+ secretion

3. BP increase

Local signaling effect on BP and blood flow

Can cause vasodilation and vasoconstriction

Myogenic response

kidneys receptors sense stretch of blood entering the kidneys, and increased stretch will lead to vasoconstriction (myogenic contraction)

Effect of myogenic response

1. Decrease in blood flow

2. Decrease in BP downstream