Chapter 10 The Blood Vessels and Blood Pressure

Cardiogenic

("heart produced") shock

Hypovolemic

("low volume") shock

Neurogenic

("nerve produced") shock

Vasogenic

("vessel produced") shock

Mean arterial pressure = cardiac output x total peripheral resistance

(Do not confuse this equation, which indicates the factors that determine the mean arterial pressure, namely, the magnitude of both cardiac output and total peripheral resistance, with the equation used to calculate mean arterial pressure, namely, mean arterial pressure = diastolic pressure + 1/3 pulse pressure.)

The baroreceptors constantly provide information about mean arterial pressure:

-When mean arterial pressure increases, the receptor potential of these baroreceptors increases, thus increasing the rate of firing in the corresponding afferent neurons. -A decrease in the mean arterial pressure slows the rate of firing generated in the afferent neurons by the baroreceptors

Pitting

-caused by constriction (socks, hose, etc. that cause pressure) -small amounts considered normal depending on activity level.

Extrinsic control

Accomplished primarily by sympathetic nerve influence Accomplished to lesser extent by hormonal influence over arteriolar smooth muscle

Secondary hypertension

Accounts for about 10% of hypertension cases Occurs secondary to another known primary problem Examples of secondary hypertension Renal hypertension Endocrine hypertension Neurogenic hypertension

Hormones that influence arteriolar radius

Adrenal medullary hormones Epinephrine and norepinephrine Generally reinforce sympathetic nervous system in most organs Vasopressin and angiotensin II Important in controlling fluid balance by constricting blood vessels.

Lymph

Interstitial fluid that enters a lymphatic vessel

Vein

Large radius offers little resistance to blood flow Also serve as blood reservoir

Lymphatic System Functions

Return of excess filtered fluid Defense against disease Lymph nodes have phagocytes which destroy bacteria filtered from interstitial fluid Transport of absorbed fat Return of filtered protein

Non-Pitting

-usually caused by lymphatic system blockage -tibial myxedema = anterior shin edema

Mean Arterial Pressure

At resting heart rate, about two thirds of the cardiac cycle is spent in diastole and only one third in systole. MAP is the average pressure driving blood forward into tissues throughout cardiac cycle Formula for approximating mean arterial pressure: Mean arterial pressure = diastolic pressure + ⅓ pulse pressure At 120/80, mean arterial pressure = 80 mm Hg + ⅓ (40 mm Hg) = 93 mm Hg

When blood pressure is 120/80, pulse pressure is 40 mm Hg (120 minus 80 mm Hg).

Because the pulse can be felt each time the ventricles pump blood into the arteries, the pulse rate is a measure of the heart rate.

Blood Flow

Blood is "reconditioned" (oxygen, carbon dioxide, and nutrient levels) so composition remains relatively constant Organs that "recondition blood" receive more blood than is needed for metabolic needs Digestive organs, kidneys, skin Adjust extra blood to achieve homeostasis Blood flow to other organs can be adjusted according to metabolic needs Brain can least tolerate disrupted supply

Hypertension

Blood pressure above 130/90 mm Hg 2 broad classes Primary hypertension Secondary hypertension

Hypotension

Blood pressure below 100/60 mm Hg

Mean Arterial Pressure (Part II)

Blood pressure that is monitored and regulated in the body Primary determinants Cardiac output Total peripheral resistance

Resistance Depends on 3 things:

Blood viscosity: Water vs syrup syrup will go slower in tube Vessel length: Longer more surface area Vessel radius: Smaller the radius more resistance, slower the flow R is proportional to 1 r4

Blood Pressure

Can be measured indirectly using sphygmomanometer Korotkoff sounds Sounds heard when determining blood pressure Sounds are distinct (different) from heart sounds associated with valve closure

Hypotension

Circulatory shock Occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained

Vascular Tree

Closed system of vessels Arteries: Carry blood away from heart to tissues Arterioles: Smaller branches of arteries Capillaries: Smaller branches of arterioles Smallest of vessels across which all exchanges are made with surrounding cells Venules: Formed when capillaries rejoin Return blood to heart Veins: Big Formed when venules merge Return blood to heart

Complication of hypertension

Congestive heart failure Stroke Heart attack Spontaneous hemorrhage Renal failure Retinal damage

Mean Arterial Pressure

Constantly monitored by baroreceptors (pressure sensors) within circulatory system Has Short-term control adjustments and Long-term control adjustments

Factors which enhance venous return

Driving pressure from cardiac contraction Sympathetically induced venous vasoconstriction Skeletal muscle activity Effect of venous valves Respiratory activity Effect of cardiac suction

Lymphatic System

Extensive network of one-way vessels Provides accessory route by which fluid can be returned from interstitial space to the blood

Blood Pressure

Force exerted by blood against a vessel wall Depends on Volume of blood contained within vessel Compliance (Distensibility) of vessel walls Systolic pressure Peak pressure exerted by ejected blood against vessel walls during cardiac systole Averages 120 mm Hg Diastolic pressure Minimum pressure in arteries when blood is draining off into vessels downstream Averages 80 mm Hg

Lymph vessels

Formed from convergence of initial lymphatics Eventually empty into venous system near where blood enters right atrium One way valves spaced at intervals direct flow of lymph toward venous outlet in chest

2 Blood Pressure Abnormalities

Hypertension and Hypotension

Other brain regions also influence blood distribution

Hypothalamus Controls blood flow to skin to adjust heat loss to environment

The 4 main Circulatory shocks

Hypovolemic Cardiogenic Vasogenic Neurogenic

Cardiovascular control center

In medulla of brain stem Integrating center for blood pressure regulation

Additional reflexes and responses that influence blood pressure

Left atrial receptors and hypothalamic osmoreceptors affect long-term regulation of blood pressure by controlling plasma volume Chemoreceptors in carotid and aortic arteries are sensitive to low O2 or high acid levels in blood reflexly increase respiratory activity Associated with certain behaviors and emotions mediated through cerebral-hypothalamic pathway Exercise modifies cardiac responses Hypothalamus controls skin arterioles for temperature regulation Vasoactive substances released from endothelial cells play role

Arterioles

Major resistance vessels because they are small enough to have considerable resistance to flow. Radius supplying individual organs can be adjusted independently to Distribute cardiac output among systemic organs, depending on body's momentary needs Help regulate arterial blood pressure Arteriolar walls contain little CT but have a layer of smooth muscle that is reactive to chemical changes.

Arterioles

Mechanisms involved in adjusting arteriolar resistance Vasoconstriction Vasodilation Only blood supply to brain remains steady Changes within other organs alter radius of vessels and adjust blood flow to organ Local chemical influences on arteriolar radius Local metabolic changes Histamine (vasodilator) Local physical influences on arteriolar radius Local application of heat or cold Chemical response to shear stress Myogenic response to stretch Local vasoactive mediators Endothelial cells Release chemical mediators that play key role in locally regulating arteriolar caliber Release locally acting chemical messengers in response to chemical changes in their environment Among best studied local vasoactive mediators is nitric oxide (NO). It is a powerful relaxor of smooth muscle (vasodilator)

Short-term control adjustments

Occur within seconds Adjustments made by alterations in cardiac output and total peripheral resistance Mediated by means of autonomic nervous system influences on heart, veins, and arterioles

Low blood pressure

Occurs when There is too little blood to fill the vessels Heart is too weak to drive the blood

2 Types of Edema

Pitting, Non-Pitting

Blood Pressure

Pressure difference between systolic and diastolic pressure Example If blood pressure is 120/80, pulse pressure is 40 mm Hg (120 mm Hg - 80 mm Hg) Pulse that can be felt in artery lying close to surface of skin is due to pulse pressure

Most common of blood pressure abnormalities

Primary hypertension Catchall category for blood pressure elevated by variety of unknown causes rather than by a single disease entity Potential causes being investigated Defects in salt management by the kidneys Excessive salt intake Diets low in K+ and Ca2+ Plasma membrane abnormalities such as defective Na+-K+ pumps Variation in gene that encodes for angiotensinogen Endogenous digitalis-like substances Abnormalities in NO, endothelin, or other locally acting vasoactive chemicals Excess vasopressin

Vasodilation

Refers to enlargement in circumference and radius of vessel Results from relaxation of smooth muscle layer Leads to decreased resistance and increased flow through that vessel

Vasoconstriction

Refers to narrowing of a vessel

Long-term control adjustments

Require minutes to days Involve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst

Orthostatic (postural) hypotension

Transient hypotensive condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position

Initial lymphatics

Small, blind-ended terminal lymph vessels Permeate almost every tissue of the body

Arteries

Specialized to Serve as rapid-transit passageways for blood from heart to organs Due to large radius, arteries offer little resistance to blood flow Act as pressure reservoir to provide driving force for blood when heart is relaxing Arterial connective tissue contains Collagen fibers Provide tensile strength Elastin fibers Provide elasticity to arterial walls

Edema

Swelling of tissues Occurs when too much interstitial fluid accumulates Causes of edema Reduced concentration of plasma proteins Increased permeability of capillary wall Increased venous pressure Blockage of lymph vessels

Capillaries

Thin-walled, small-radius, extensively branched Sites of exchange between blood and surrounding tissue cells Maximized surface area and minimized diffusion distance Velocity of blood flow through capillaries is relatively slow Provides adequate exchange time 2 types of passive exchanges: Diffusion, bulk flow Narrow, water-filled gaps (pores) lie at junctions between cells Permit passage of water-soluble substances Lipid soluble substances readily pass through endothelial cells by dissolving in lipid bilayer barrier Size of pores varies from organ to organ Under resting conditions many capillaries are not open Capillaries surrounded by precapillary sphincters Contraction of sphincters reduces blood flowing into capillaries in an organ Relaxation of sphincters increases blood flow Metarteriole Runs between an arteriole and a venule

Veins

Venous system transports blood back to heart Capillaries drain into venules Venules converge to form small veins that exit organs Smaller veins merge to form larger vessels

pulse pressure.

What you feel when you "take a pulse" is the difference between systolic and diastolic pressures; you don't feel anything during diastole, but you feel the surge in pressure during systole. This pressure difference is known as the

Resistance of blood vessels

is measure of opposition of blood flow through a vessel

Blood Flow:Pressure gradient

is pressure difference between beginning and end of a vessel Blood flows from area of higher pressure to area of lower pressure