Blood Vessels and Circulation Flashcards
Arteries
Carry blood away from the heart
Arterioles
Smallest artery branches leading to capillaries
Capillaries
Where diffusion between blood and interstitial fluid takes place
Venules
Unite to form larger veins that return blood to heart
Path of blood
Heart > arteries > arterioles > capillaries > venules > veins > heart
Where does blood leave the heart through?
Pulmonary trunk (right ventricle) > pulmonary arteries > lungs
Aorta (left ventricle) > systemic arteries > all other organs
Vessel wall structure in arteries and veins
- Tunica intima
- Tunica media
- Tunica externa
Tunica intima
- Inner layer
- Endothelial lining and a surrounding layer of connective tissue with a variable number of elastic fibres
- Thick layer of elastic fibres (internal elastic membrane) in arteries
Tunica media
- Middle layer
- Concentric sheets of smooth muscle tissue in a framework of loose connective tissue
- Typically thickest layer
- Smooth muscle cells encircle endothelium that lines the lumen
What separates tunica media and tunica externa?
External elastic membrane
Tunica externa
- Outer layer
- Connective tissue sheath
Vasa vasorum
Blood vessels in the walls of large vessels
Why do large vessels contain vasa vasorum?
Because the vessel walls are too thick for diffusion
Differences between arteries and veins
- Artery walls thicker
- Arteries keep shape in sectional view
- Arteries have folds in sectional view
- Veins have valves
3 main types of arteries
- Elastic
- Muscular
- Arterioles
What gives arteries their elasticity and contractility?
Thick, muscular walls
Vasoconstriction
When stimulated, arterial smooth muscles contract, constricting the arteries
Vasodilation
When arterial smooth muscles relax, the diameter of the lumen increases
What do vasoconstriction and vasodilation affect?
- Afterload on heart
- Peripheral blood flow
- Capillary blood flow
Elastic arteries
Pulmonary trunk and aorta and their major branches
Muscular arteries
Distribute blood to the body’s skeletal muscles and internal organs
Arterioles
Smaller than muscular arteries
Resistance vessels
Arterioles
Aneurysm
Bulge in the weakened wall of an artery
When local blood pressure exceeds the capacity of the elastic component of the arterial walls
Types of capillaries
- Continuous capillaries
- Fenestrated capillaries
- Sinusoids
Continuous capillaries
- The endothelium is a complete lining of the lumen
- Tight junctions and desmosomes connect endothelial cells
Fenestrated capillaries
Contain pores in the wall due to an incomplete or perforated endothelial lining
Sinusoids
Discontinuous endothelium
Capillary bed
Interconnected collective network
Precapillary sphincter
Surrounds the entrance of a capillary and controls arterial blood flow to the tissues
Thoroughfare channel
Central passageway in the arteriole system
What happens when a precapillary sphincter constricts?
Blood is diverted into other branches of the network
Collaterals
Multiple arteries that supply blood to a capillary bed
Arterial anastomosis
The fusion of two collateral arteries that supply an arterial bed
Arteriovenous anastomoses
Direct connections between arterioles and venules
What happens when an arteriovenous anastomosis is dilated?
Blood bypasses the capillary bed and flows directly into venous circulation
Angiogenesis
Formulation of new blood vessels from preexisting vessels
Vascular endothelial growth factor (VEGF)
Directs angiogenesis
Types of veins
- Venules
- Medium sized veins
- Lagre veins
Venules
- Smallest veins
- Collect blood from capillary beds
Medium sized veins
Similar in size to muscular arteries
Large veins
Includes superior and inferior venae cavae and their branches within the abdominopelvic and thoracic cavities
Venous valves
In limbs, in venules and medium sized veins
What makes up valves?
Folds of the tunica intima
Varicose veins
Occurs when valves weaken or become stretched, blood pools in the veins
Which vessels are capacitance?
Veins
Why do veins act as blood resevoirs?
Because they have high capacitance
Venoconstriction
If serious hemorrhaging occurs, sympathetic nerves stimulate smooth muscle cells in the walls of medium sized veins in the systemic system to constrict
This decreases the amount of blood within the venous system, increasing the volume within the arterial system and capillaries
Capillary hydrostatic pressure (CHP)
Pressure of blood within capillary walls
Venous pressure
Pressure of the blood within the venous system
Total peripheral resistance
The resistance of the entire cardiovascular system
Vascular resistance
The forces that oppose blood flow in the blood vessels
What is the most important factor in vascular resistance?
Friction between blood and vessel walls
Two factors affecting amount of friction
- Increasing vessel length increases friction
2. Narrower vessel more resistance to blood flow
Viscosity
Resistance to flow caused by interactions among molecules and suspended materials in a liquid
More viscous = more resistance
Turbulence
Eddies and swirls
Systolic pressure
Peak blood pressure measured during ventricular systole
Diastolic pressure
Minimum blood pressure at the end of the ventricular diastole
Pulse pressure
Difference between systolic and diastolic pressures
Mean arterial pressure (MAP)
Diastolic pressure + (pulse pressure/3)
Hypertension
Abnormally high blood pressure
Hypotension
Abnormally low blood pressure
Is hypertension or hypotension more common?
Hypertension
Stage 1 hypertension
Systolic: 140-159
Diastolic: 90-99
Pre-hypertension
Systolic: 120-139
Diastolic: 80-89
Why is there a risk of fainting when knees are locked?
Leg muscles are immobilised and unable to assist pushing blood against gravity back up to heart
Respiratory pump
Inhale: thoracic cavity expands, reducing pressure, air enters lungs, blood pushed into inferior vena cava and right atrium
Exhale: thoracic cavity decreases, increasing pressure, air forced out of lungs, blood pushed into right atrium
Capillary exchange
Chemical and gaseous exchange between blood and interstitial fluids across capillary walls
Filtration
Removal of solutes as a solution flows across a porous membrane
Reabsorption
Occurs as the result of osmosis
Osmotic pressure (OP)
Pressure that must be applied to prevent osmotic movement across a membrane
Bulk flow
The continuous net movement of water out of the capillaries, through peripheral tissues and back to the bloodstream by way of the lymphatic system
Forces acting across capillary walls
At the arterial end of the capillary, CHP is greater than BCOP do fluid moves out of the capillary (filtration)
Near the venule, CHP is lower than BCOP, so fluid moves into capillary (reabsorption)
Net filtration pressure (NFP)
Difference between net hydrostatic pressure and net osmotic pressure
Tissue perfusion
Blood flow through tissues
Factors affecting tissue perfusion
- Cardiac output
- Peripheral resistance
- Blood pressure
Vasomotion
Changes in vessel diameter
Autoregulation
Causes immediate, localised homeostatic adjustments
Neural mechanisms
Respond to changes in arterial pressure or blood gas levels senses at specific sites
Short term adjustments to cardiac output and peripheral resistance to maintaining BP
Endocrine mechanisms
Hormones that enhance short term adjustments and that direct long term changes in cardiovascular performance
Vasodilators
Factors that promote dilation of precapillary sphincters
Local vasodilators
Cause the capillary sphincters to relax so blood flow increases to the area when dissolved oxygen concentration decreases within a tissue
Cardiovascular (CV) centre
Centre in the medulla oblongata that is responsible for adjusting cardiac output and peripheral resistance to maintain blood flow
Vasomotor centre
- In CV centre
- Group of neurons responsible for controlling vasoconstriction
- Group of neurons responsible for controlling vasodilation
Cardioacceleratory centre
Increases cardiac output through sympathetic innervation
Cardioinhibitory centre
Decreases cardiac output through parasympathetic innervation
Baroreceptor reflexes
Monitor the degree of stretch within expandable organs
Where are baroreceptors located?
Carotid sinuses, aortic sinuses and right atrium
Chemoreceptor reflexes
Respond to changes in oxygen or CO2 levels in blood
What triggers chemoreceptor reflexes?
Sensory neurons located in the carotid bodies and the aortic bodies
Endocrine mechanisms
- Antidiuretic hormone - peripheral vasoconstriction and water conservation
- Angiotensin II - decreases renal BP
- Erythropoietin - causes vasoconstriction
- Natriuretic peptides - reduce blood volume and BP
Light exercise
- Extensive vasodilation
- Venous return increases
- Cardiac output rises
How does exercise lower cholestrol?
By stimulating enzymes that help move LDLs from the blood to the liver where it’s converted to bile and excreted
