Chapter 21: Vessels Flashcards
What are vessels
A closed system which 5 main vessel types:
- arteries
- arterioles
-capillaries - venules
- veins
Tunica interna
Layer closest to lumen
Made of simple squamous epithelium, basement membrane, and connective tissue
Tunica media
The middle layer
Made of circularly, arranged, smooth muscle fibres which regulates the diameter of the lumen.
Tunica externa
Outermost layer
Made of connective tissue that anchors the blood vessel to its surrounding structures
Blood pressure
The force exerted by the blood against the wall of a blood vessel. Blood pressure differences within vessels keeps the blood moving.
(Blood pressure decrease the further away it is from the left ventricle)
Vasoconstriction
Decreasing the diameter of the lumen which increases blood pressure.
Vasodilation
Increases the diameter of the lumen and decreases the blood pressure.
Hypertension
Constantly high blood pressure
Primary hypertension - no identifiable cause. (90-95%)
Secondary hypertension - does have an identifiable cause such as kidney disease (5-10%)
Systolic pressure
The maximum pressure against the arterial wall during ventricular contraction
Usually 120 mmHg
Diastolic pressure
The minimum pressure against the arterial wall during ventricular relaxation
Usually 80mmHg
Pulse pressure
The differences between systolic pressure and diastolic pressure
SP - DP = PP
Elastic arteries
Arteries which contain many elastic fibres
- tunica media has many smooth muscle layers and many elastic fibres
Includes the pulmonary trunk, and the aorta and its branches.
They are considered conducting arteries.
Muscular arteries
Medium sized and branch to various organs.
- Has the thickest tunica media with more smooth muscle than elastic fibres
Considered distributing arteries since they deliver blood to organs.
Arterioles
Microscopic vessels that contain mostly smooth muscle and very few elastic fibres.
They regulate flow into capillary beds
Known as resistance vessels
Capillaries
Microscopic vessels with a single layer of endothelial cells and a basement membrane.
Have a large surface area in order to function in the exchange of materials between blood and interstitial fluid
How many RBC’s can pass through a capillary at a time? Why?
1
The diameter of a capillary and the diameter of a RNC are the same
Continuous capillaries
In skin and muscles
Allow only LIMITED passage of fluids and small solutes.
Held by tight junctions (very little gaps)
Fenestrated capillaries
In small intestine, kidney
Has a greater permeability (tolerance) to fluids and solutes
Contains fenstrations (pores)
Sinusoid capillaries
In liver, bone marrow, lymph tissue
Allow large molecules to pass between blood and tissues (such as blood cells and proteins)
Have LARGE pores (looks destroyed)
Capillary exchange
Artery end gets net OUTWARD pressure for filtration.
(Fluid exits capillary)
Venous end gets net INWARD pressure for reabsorption
(Fluid enters capillary)
Venules
Receive blood from the capillaries
Veins
Made up of venules joined together.
Function to bring blood back to the heart under low pressure (need for venous return)
How much blood volume can veins hold
Approx. 60% of blood volume
Venous return
Factors that help return blood back to the heart.
- gravity (if above the heart)
- valves in veins
- contraction of skeletal muscles
- respiratory pump
Varicose veins
Veins that are dilated and twisted due to leaky valves
aka hemorrhoids
Cardiac output (CO)
Refers to the volume of blood pumped per minute by each ventricle of the heart.
CO = stroke volume (SV) x heart rate (HR)
End diastolic volume (EDV)
Total volume of blood and ventricle at end of ventricular, relaxation phase (diastolic value)
End systolic volume
Total volume of blood ventricle after the ventricle has contracted and ejected about 60% of the blood from its chambers. (Systolic value)
Stroke volume
The volume of blood pumped by each ventricle during each heartbeat
Stroke volume = EDV - ESV
Affected by 2 things:
1. Stretching of cardiac muscle fibres
2. Contractility of cardiac muscle fibres.
Starlings law
If you increase venous return, you increase the stretch of cardiac muscle fibres, and you increase the force of contraction
Baroreceptors
Pressure sensitive neurons located in the carotid sinus and aortic arch. They will communicate with the medulla oblongata to regulate blood pressure
Is BP increases, baroreceptors stretch more (vice versa)
Peripheral resistance
Refers to the resistance to blood flow due to friction between the blood and vessel wall.
Effected by:
- blood thickness
- vessel radius
Note: first layer of fluid sticks to vessel wall and moves slower.
