Blood vessels study guide

Arteries

Arteries

•: carry blood away from heart

•Systemic – carry oxygenated blood

•Pulmonary – carry oxygen low blood

Veins

•carry blood toward heart

•Systemic – carry oxygen poor blood

•Pulmonary – carry oxygenated  blood

Capillaries

only vessels to contact tissue cells; directly serve cellular needs

•Tunica intima (intimate contact with blood)

•Endothelium lines lumen of all vessels

•The endothelium is continuous with endocardium

•Forms a slick surface that reduces friction as blood moves via the lumen

Subendothelial layer

•in vessels larger than 1 mm

•Has connective tissue basement membrane supporting the endothelium

Tunica media

•middle tunic

•Composed of smooth muscle cells (SMC) and sheets of elastin

•The activity of the smc is regulated by the sympathetic vasomotor nerve fibers and chemicals

Vasoconstriction

- lumen diameter decreases as the smc contract

Vasodilation

•lumen diameter increases as the smc relaxes

•Influence blood flow and blood pressure

Tunica externa

•(outer layer)

•Made up of collagen fibers protect, reinforce, and anchors the vessel to the surrounding structures

•Contains nerve fibers, lymphatic vessels

•Vasa vasorum

system of smaller blood vessels in larger vessels

•Functions to nourishes external layer

Pericytes

smc that help stabilize their walls and control permeability

Continuous Capillaries

•Most common and are abundant in skin and muscles

•Joined together with tight junctions that connect endothelial cells

intercellular clefts

gaps that are found in continuous capillaries and allow passage of smaller solutes and fluids

Fenestrated Capillaries

•Like continuous but have endothelial cells with pores or  fenestrations

•More permeable than continuous capillaries

•Function in absorption or filtrate formation

•small intestines- nutrients absorption

•endocrine gland- hormones quickly enter the blood stream

•Kidneys- rapid filtration of blood plasma

Sinusoid Capillaries

•Highly modified with slow blood flow

•fewer tight junctions

•usually fenestrated

•larger intercellular clefts

•large irregularly shaped lumens

•Large molecules and blood cells pass between blood and surrounding tissues

•Found only in the liver, bone marrow, spleen, adrenal medulla

•Macrophages in lining to destroy bacteria

Capillary bed

•interwoven network of capillaries between arterioles and venules

Microcirculation

blood flow from between arterioles and venules

Terminal arteriole > ________

metarteriole

Metarteriole continuous with

thoroughfare channel (intermediate between capillary and venule)

thoroughfare channel > _______ that drains bed

postcapillary venue

Vascular shunt

•(metarteriole—thoroughfare channel)

•Directly connects terminal arteriole and postcapillary venule

•True capillaries

•10 to 100 exchange vessels per capillary bed

•Branch off metarteriole or terminal arteriole

Precapillary sphincters

•regulate blood flow into true capillaries

•Surround the root or each true capillary at the metarteriole

•Regulates blood flow into the capillary

Vennules

•- formed when capillary beds unite

•Smallest - postcapillary venules

•Composed endothelium and pericytes

•Very porous; allow fluids and WBCs into tissues

Veins form when _____

venules converge

veins are called ________

capacitance vessels (blood reservoirs); contain up to 65% of blood supply

Venous valves

•prevent backflow of blood

•Most abundant in veins of limbs

Venous sinuses

•flattened veins with extremely thin walls

•Supported by the tissues that surrounds them (e.g., coronary sinus of the heart and dural sinuses of the brain)

______ helps circulation

Exercise (because muscles contract and squeeze blood back to heart)

Varicose veins

- veins that have become enlarged and twisted due to leaky valves

Arterial anastomoses provides alternates pathways (______) to given body region

collateral channels

Venous anastomoses are

Common

Blood flow

Volume of blood flowing through vessel, organ, or entire circulation in given period

•Measured as ml/min

•Equivalent to cardiac output for entire vascular system

•Relatively constant when at rest but can vary widely through individual organs, based on needs

Blood pressure (BP)

Force per unit area exerted on wall of blood vessel by blood

•Expressed in millimeters of Mercury (mm Hg)

•Typically measured as systemic arterial BP in large arteries near heart

•Pressure gradient – Difference in the BP in the entire system

•Provides the force that keeps blood moving from higher to lower pressure areas

Resistance

•opposition of flow 

•Measures of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation

Blood viscosity

- thickness

•Increased viscosity = increased resistance

•Constant but polycythemia (high RBC’s) can increase the viscosity 

Blood vessel length

•Longer vessel = greater resistance encountered

Blood vessel diameter

greatest influence on resistance

Blood pressure near heart is ______

Pulsatile (goes up and down)

Systolic pressure

•pressure exerted in aorta during ventricular contraction

•Averages 120 mm Hg in normal adult

Diastolic pressure (lowest)

lowest level of aortic pressure

Pulse pressure

•difference between systolic and diastolic pressure

•Throbbing of arteries (pulse)

Mean arterial pressure (MAP)

pressure that propels blood to tissues

•MAP = diastolic pressure + 1/3 pulse pressure

•Pulse pressure and MAP both decline with increasing distance from heart

•Ex. BP = 120/80; MAP = 93.3 mm Hg

Low capillary pressure is _____

Desirable

•High BP would rupture fragile, thin-walled capillaries

•Most very permeable, so low pressure forces filtrate into interstitial spaces

Muscular pump

1.contraction of skeletal muscles "milks" blood toward heart; valves prevent backflow

•Long periods of standing can cause edema in ankles 

Respiratory pump

.pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand

•Inhale abdominal pressure increases squeezing the veins and forces blood to the heart

•The pressure in the chest decreases and thoracic veins expand sending blood to the right atrium

______ under sympathetic control pushes blood toward heart

Venoconstriction

maintaining blood pressure

Requires

• Cooperation of heart, blood vessels, and kidneys

• Super vision by brain

Factors influencing BP

• Cardiac output

• peripheral resistance

• blood volume

•Short-term neural and hormonal controls

•Counteract fluctuations in blood pressure by altering peripheral resistance and heart output

•Long-term renal regulation

•Counteracts fluctuations in blood pressure by altering blood volume with the kidneys

•Neural controls of peripheral resistance

•Maintain MAP by altering blood vessel diameter

• if low blood volume all vessels constricted except those to heart and brain

•Alter blood distribution to organs in response to specific demands

•During exercise, blood is diverted from the digestive organs to the skeletal muscles

Neural controls operate via _____

Baroreceptors

Stretch receptors found in the carotid body, aortic body and the wall of all large arteries of the neck

•Vasomotor center sends steady impulses via sympathetic efferents to blood vessels à moderate constriction called _____

vasomotor tone

Monitoring circulatory efficiency Vital signs

•pulse and blood pressure, along with respiratory rate and body temperature

Pulse

•pressure wave caused by expansion and recoil of arteries

•Can detect a pulse from any artery that is close to the surface

Radial pulse

•(taken at the wrist) routinely used

Pressure points

•where arteries close to body surface

•Can be compressed to stop blood flow

sphygmomanometer

measures systemic material BP

•Pressure increased in cuff until it exceeds systolic pressure in brachial artery

•Pressure released slowly and examiner listens for sounds of Korotkoff with a stethoscope

Systolic pressure

normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery

Diastolic pressure

normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely

Hypertension

•high blood pressure

•Sustained elevated arterial pressure of 140/90 or higher

Prehypertension

•if values elevated but not yet in hypertension range

•May be transient adaptations during fever, physical exertion, and emotional upset

Often persistent in obese people

Prolonged high BP is major cause of

•heart failure, vascular disease, renal failure, and stroke

•Heart must work harder à myocardium enlarges, weakens, becomes flabby

Also accelerates atherosclerosis

Secondary hypertension

•less common

•Due to identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushing's syndrome (high cortisol)

Treatment focuses on correcting underlying cause

Hypotension

•low blood pressure

•Blood pressure below 90/60 mm Hg

•Usually not a concern

•Only if leads to inadequate blood flow to tissues

Often associated with long life and lack of cardiovascular illness

Orthostatic hypotension

•temporary low BP and dizziness when suddenly rising from sitting or reclining position

Chronic hypotension

•can be due to severe malnutrition and warning sign for Addison's disease (adrenal cortex) or hypothyroidism

Acute hypotension

important sign of circulatory shock; threat for surgical patients and those in ICU

•Tissue perfusion involved in

•Delivery of O₂ and nutrients to, and removal of wastes from, tissue cells

•Gas exchange (lungs)

•Absorption of nutrients (digestive tract)

•Urine formation (kidneys)

MAP below 60 mm Hg can cause

•syncope (fainting)

MAP above 160 can result in

•cerebral edema

As temperature rises

•Hypothalamic signals reduce vasomotor stimulation of skin vessels à

•Warm blood flushes into capillary beds à

•Heat radiates from skin

Sweat causes vasodilation via ____ in perspiration

bradykinin

•Bradykinin stimulates NO release

Hypovolemic shock

•: results from large-scale blood loss

•Acute hemorrhage, serve vomiting, diarrhea or extensive burns

Vascular shock

results from extreme vasodilation and decreased peripheral resistance

Cardiogenic shock

results when an inefficient heart cannot sustain adequate circulation