unit 7 lesson 3 blood vessels and circulation

What is interstitial fluid, what does it consist of

Fluid between the blood vessels and cells, consists of water, nutrients, hormones, enzymes, waste etc. 26% of human overall body fluid. Where blood and cells interactions MUST pass through

Systemic circulation pathway

Oxygenated blood is pumped from left side of heart throughout body via arteries, and further from heart become arterioles.

Arterioles branch out within capillary beds into capillaries. Oxygen leaves the capillaries and CO2 enters the capillaries to be carried back to heart

Deoxygenated blood travels in increasingly larger vessels back towards the right side of the heart. From the capillaries via venues then via the larger veins

Pulmonary circulation pathway

Deoxygenated blood leaves the right side of the heart en route to the lungs to exchange CO2 for oxygen

Oxygenated blood from lungs returns to left side of the heart

Necessary characteristics of all blood vessels

Must be flexible and resilient to withstand pressure and changes to it as well as flexibility to accommodate other tissues around them (organs, etc)

What is anastomosis

The joining of two vessels WITHOUT INTERVENING CAPILLARY BED (arterioles to venule) (connection between peripheral vessels)

What is collateral

More then one artery supplying an area (capillary beds needed), multiple arterioles vessels in one area

What is angiogenesis

Formation of new blood vessels- controlled by endothelial growth factor which tells body to make more

5 types of blood vessels

Artery, arterioles, capillary, venule, vein

What are characteristics and functions of arteries

ALWAYS CARRY BLOOD AWAY FROM THE HEART , initial vessel blood must pass through, highest pressure vessels. Thick walls that contain lots of elastic fibres

What are characteristics and functions of arterioles

Branches of arteries that deliver blood to capillary networks

What are capillary characteristics and functions

Smallest vessels with diameter if only 1 RBC, located between arterioles and venules, whose thin walls allow for the diffusion of gasses, nutrients and waste between plasma and intestinal fluid to cells (blood and tissue interaction)

Characteristics and functions of venules

Thin walled vein with lower pressure than even capillaries to carry blood away from capillaries back towards heart. Unite to form larger veins

Characteristics and functions of veins

Thin walls, Carries blood towards the heart and contains valves

Main differences between arteries and veins

Arteries carry blood away from heart while veins bring blood towards heart

Walls of arteries are thicker than veins

Endothelial lining of arteries have pleated folds (allows for contraction) while veins don’t

What are blood vessel lumens

Inside tube structure of blood vessels

Layers that make up blood vessels (innermost to outermost)

Tunica intima, tunica media, tunica externa or adventitia

What is the tunica intima of the blood vessel

Vessels endothelium (Inner most layer) of blood vessels composed of simple squamous epithelium, thin layer of connective tissue with elastic fibers.

In arteries this layer does not move but instead creates folds (pleated folds)

Tunica media of vessels

Middle layer→thickest layer in arteries, composed of elastic fibers and smooth muscles which causes vasoconstriction and vasodilatation

Adventitia of blood vessels

Tunica externa or outermost layer→ composed of connective tissue with elastic fibres which anchors vessel to surrounding tissues

What is vasa vasorum

Vessels within bigger vessels that supply them with blood flow

Types of arteries to know

Elastic arteries, muscular arteries, aterioles

What are elastic arteries

Largest arteries that transport heart away from heart (pulmonary, aorta). These arteries are rich in elastic fibres with relatively few smooth muscles to enable resiliency and ability to withstand the highest of pressures and decreasing pressures

What are muscular arteries

Most arteries, medium sized with thicker tunica media (more smooth muscles) allowing for vasoconstriction and vasodilatation

What are arterioles

Resistance vessels which are the smallest type. Carries blood from muscular arteries to capillaries. Tunica media has much less smooth muscles and less adventitia. These branch into metarterioles which connect to capillaries

What is vasodilation

An increase in the diameter of arterioles due to relaxation of smooth muscles which in tunica media. (Decreases blood pressure and resistance)

What is vasoconstriction

A reduction in the diameter of arterioles due to the constriction of smooth muscles in the tunica media

What causes vasodilation and vasoconstriction

Occurs in response to local factors, hormones or stimulation of the vasomotor centre in medulla oblongata

What factors will vasodilation and vasoconstriction effect in terms of blood flow

Impacts after load (directly related to resistance), peripheral blood pressure and capillary blood flow

Histology of capillaries

Single layer of simple squamous epithelium (endothelial tube) surrounded by a basement membrane. Known as exchange vessels hence the simple squamous allowing for efficient diffusion

How big are capillary diameters

Only the diameter of one red blood cell

Where are capillaries found

Throughout body, but more extensively in highly active tissues (muscle, brain, kidneys and liver)

Difference between highly vascular vs avascular tissue

Highly vascular tissues have more capillary networking where as avascular tissues have no capillaries

3 types of capillaries

Continuous, fenestrated and sinusoid capillaries

What are continous capillaries

Compared to a typical endothelial tube where there are no gaps in between cells (think blood brain barrier)

What are fenestrated capillaries

Pours capillaries with decent sized holes for rapid exchange of water, solutes, gases. Found in brain ventricles, GI tract

Sinusoid capillaries

Also known as discontinuous endothelium. Capillaries with massive gaps that allow for free movement of plasma proteins. Found in liver, bone marrow, spleen

What is a capillary bed

Network of capillaries connecting metarterioles to venules

What does the opening of each capillary contain

A pre-capillary sphincter→controls amount of arterial blood flow through the capillary by relaxing and contracting several times a minute so that blood flows through in a pulsing fashion

How are pre—capillary sphincters controlled

Through auto regulation (no nervous system or endocrine involvement if working properly and controlled locally)

What is capillary exchange

Term used to describe all chemical and gaseous exchange from blood to body tissues that happens at capillary level. VITAL TO HOMEOSTASIS

How do materials move across capillary walls

Diffusion, filtration and reabsorption

Diffusion in capillaries

Net movement of ions across concentration gradient (higher to lower concentration) via channels (gaps in endothelium in fenestrated and sinusoid capillaries)

Filtration in capillaries

Removal of solutes as a solution flows across a porous membrane due to hydrostatic pressure

Reabsorption in capillaries

Opposite of filtration→As a result of osmosis in which water diffuses to follow solute, pulling extra water back into capillary

What layer of epithelium do venules tend to lack

Lack tunica media (no smooth muscle) except in larger venules

Main purpose of veins

Return blood back to heart

Thickness of layers in veins

Medium sized veins-Tunica media is thin with few smooth muscle, thickest layer is the tunica externa

Large veins (vena cavas)- all three layers are thickest

What type of pressure is found in veins

Very low pressure, has 10% that of arteries

What mechanisms aid blood flow back to heart in venules, medium sized veins

Venous valves and leg muscles

What are venous valves and their purpose, along with leg muscles in blood flow back to heart

Venous valves compartmentalize blood flow to eliminate backflow and blood pooling in the low pressure system. (Working against gravity)

Leg muscle movements push the valves open

Distribution of blood throughout vessels at any given time

30-35% in arteries and capillaries

65-70% found in Veins and venous system

Where and how much venous blood found in what organs

1/3 of venous blood in liver, bone marrow and skin

Vein advantage over arteries

Veins are more distensible due to less muscle with the ability to sustain greater volume without increasing pressure. Allows veins to act as blood reservoirs.

What is tissue perfusion?

Refers to adequate blood flow to the tissues, ensuring that the needs for oxygen and nutrients are being met

What factors influence tissue perfusion

Cardiac output, peripheral resistance and blood pressure (low BP=less tissue perfusion), activity of tissues (circulation and perfusion must increase to meet demands→in not, tissue death)

What mechanisms ensure adequate tissue perfusion

Auto regulation-capillary sphincters ensure perfusion

Vasomotion-changes in vessel diameter (constriction or dialation)

Correlation between blood flow and tissue perfusion

Adequate blood flow is needed to ensure adequate perfusion of tissues (oxygen supply)

What concept does blood flow often mirror

Cardiac output (CO=Heart Rate x Stroke volume) → decrease cardiac output= decreased capillary blood flow

What factors does capillary blood flow highly depend on

Directly proportional to pressure (more pressure=more flow)

Blood flow inversely proportional to resistance (more resistance=less flow)

What is blood pressure

Force exerted by blood against a vessel wall

What is necessary for blood pressure to overcome in order for adequate tissue perfusion

Must be enough to overcome resistance present in blood vessels (vascular resistance (general) and peripheral resistance (in systemic circuit))

Systolic blood pressure, what is it and average

Peak pressure exerted by ejected blood against vessel walls during cardiac systole

Average= 120 mmHg

Diastolic blood pressure

Minimum pressure in arteries when blood is draining off into vessels downstream

Average= 80 mmHg

Common average reading of blood pressure

120/80→ systolic blood pressure/ diastolic blood pressure

What is hypertension

When systolic blood pressure exceeds 140 mmHg (high blood pressure)

What is hypotension

When systolic blood pressure is below 90 mmHg (low blood pressure)

What is pulse pressure

Refers to the difference between systolic blood pressure and diastolic blood pressure and measures the strength of the pulse wave

120-80=40 mmHg

What happens when pulse pressure is too high vs low

If its too high→heart has to work harder to overcome peripheral resistance

If its too low→ heart doesn’t have time to relax (smaller difference)

What is mean arterial pressure

Refers to the average arterial pressure through one cardiac cycle, used to calculate overall blood flow and as a indicator of perfusion of tissues

Minimum mean arterial pressure to properly perfume tissue

In an adult MAP minimum is 65mmHg

Factors that affect blood pressure

Cardiac output and resistance

What is peripheral resistance

Resistance to the flow of blood through small vessels in systemic circuit (after load)

What is peripheral resistance determined by

Blood viscosity, blood vessel length, blood vessel diameter which all cause turbulence

What is total peripheral resistance impacted by

Vascular resistance, viscosity, turbulence

What is vascular resistance and how does it impact peripheral resistance

Determined mainly by FRICTION between blood and vessel wall (more friction, more slow), also impacted by vessel length and diameter (constriction, dilation, obstruction)

How does viscosity effect peripheral resistance

Refers to bloods thickness. The less viscous the blood the less resistance there is. In most cases one has normal blood viscosity except with disease (polycythemia (thick blood))

How does turbulence effect peripheral resistance

Altered blood flow during the swirling of blood, slows down blood and increases resistance.

What is stenosis

Abnormal narrowing of passageways (blood vessels)

Why are arterioles referred to as major resistance vessels

They are able to change diameter of vessels to distribute cardiac output and regulate arterial blood pressure

How do vasoconstriction and vasodilation affect resistance

Vasoconstriction→narrowing of vessel leads to increased resistance

Vasodilation→enlargement of inner diameter of vessel decreases resistance and increases flow through the vessel

Mechanisms to control blood flow and blow pressure classification

Auto-regulation→cause immediate, localized homeostatic adjustments (vasoconstriction and vasodialtion)

Central regulation→ neural and endocrine mechanisms when auto-regulation isn’t sufficient enough

What happens during dilation of pre capillary sphincters (vasomotion)

Local vasidilators that may cause dilation of precapillary sphincters include low O2 or elevated CO2, nitric oxide (NO), inflammatory meditators and increased tissue temperature

What happens during vasoconstriction

Often in response to vessel injury which causes endothelia release which stimulates vascular spasm to restrict blood flow and assemble platelets.

What is central regulation mainly in charge in

Controlling cardiac output and blood pressure through neural and endocrine controls

What type of changes do neural mechanisms detect?

Sense change in arterial pressure (baroreceptors) or blood gas level (chemoreceptors) at specific locations and adjust cardiac output and peripheral resistance to maintain blood flow to vital organs

What part of the brain contains cardiovascular centres? What are the centres referred to

Medulla oblongata;

Cardiac centres (cardioacceleratory, cardio inhibitory)

vasomotor centre

What do the cardiac dentures of the brain do?

Cardioacceleratory centre→sympathetic activation (increases cardiac output and increases blood pressure)

Cardio inhibitory centre→parasympathetic centre (decreases cardiac output and BP)

What does the vasomotor centre of the medulla oblongata do

Directs vasomotor responses in blood vessels; sympathetic input. Responsible for vasomotor tone (vessels never entirely relax). Change diameter and maintain pressure that way

2 groups of neurons tat control vasoconstriction and vasodilation

Vasoconstriction→adrenergic, NE secreted here, lots of neurons always active for tone

Vasodilation→smaller group of neurons, nitric oxide synthesis, chief vasodilator.

Baroreceptors reflex

These receptors are strategically located on carotid sinus, aortic arch and wall of right atrium to detect changes in stretch (related to blood pressure and communicate with CV centres to alter blood pressure

Effects of baroreceptors

1. Decreases cardiac output

2. Causes widespread peripheral vasodilation

Aiming to calm down sympathetic nervous system

STIMULATES VAGUS NURVE →vasovagal response drops blood pressure

VASODILATES TO DECREASE BLOOD PRESSURE

What is the chemoreceptors reflex

Involves a coordinated effort between cardiovascular and respiratory system.

Chemoreceptors respond to changes in the chemical composition/pH of fluid in arteriole blood and cerebrospinal fluid. (O2 level, CO2 level and pH levels) carotid sinuses and aortic bodies.

How do chemoreceptors respond to conditions?

Increased CO2 (decrease in O2 or pH) → stimulates cardioacceleratory and vasomotor centres→increased heart rate and cardiac output, increased blood pressure→stimulation of respiratory centres in medulla to increase BR and O2 intake

Type of changes make by endocrine mechanisms

While neural is immediate and short term, hormones can enhance direct longer term changes

Endocrine mechanisms to know

Adrenal medulla, ADH, aldosterone, angiotensin II, erythropoietin, natriuretic peptides

Adrenal medulla impact on cardiovascular system

Stimulated by the sympathetic nervous system→epinephrine and norepinephrine stimulate increased heart rate, cardiac output and blood pressure stimulate vasoconstriction

ADH or VASOPRESSIN effect on cardiovascular system

Released from Post.Pit in response to decreased blood pressure, increased solute concentration or increased angiotensin II

Stimulates conversation of water by kidneys to elevate blood pressure

Aldosterone effect on cardiovascular system

Released from adrenal cortex in response to low Na+ levels or increased angiotensin II→ stimulates conservation of Na+→water retention→increased blood pressure

Angiotensin II effect on cardiovascular system

In response to decreased blood flow, aims to increase blood pressure

What is renin-angiotensin-aldosterone system

Key regulator where renin released in kidneys causes inactive angiotensin→angiotensin I (still inactive)→angiotensin converting enzyme→angiotensin II (active)→stimulates aldosterone secretion→increases BP

Functions of angiotensin II

Stimulates aldosterone secretion (Na+ conservation)

Stimulates ADH secretion (water conversation)

Stimulates thirst

Stimulates increased cardiac output

Stimulates vasoconstriction (potent vasoconstriction)

Increases blood pressure