The Cardio System 3 Flashcards
The 3 blood vessel wall layere(tunica) are
Tunica intima: contains endothelium(simple squamous epithelium) and basement membranes
Tunica media: contains mostly smooth muscle and some elastic fibres
Tunica externa(tunica adventitia): contains connective tissue for protection and reinforcement
The sympathetic vasomotor nerves adjust blood vessel diameters through
- contraction of smooth muscles(vasoconstriction), narrows the lumen
- relaxation(vasodilation), widens the lumen
Which layer of the blood vessel do vasomotor nerves innervate?
The tunica media
The arterial system
Arteries re divided into 3 groups based on their size and function:
- elastic arteries
- muscular arteries
- arterioles
Elastic arteries
Are the largest arteries in our body which include the pulmonary trunk and aorta
- they have a high proportion of elastic fibres in the tunica intima and media
What is the advantage of large arteries being elastic?
elastic fibres help store some pressure that is released later through elastic recoil
• maintain a continuous and relatively steady flow of blood
Muscular arteries
Medium sized arteries that have a higher proportion of smooth muscles
What is the advantage of medium arteries being muscular?
- propels blood forward
- able to adjust blood flow through vasodilation and vasoconstriction based on regional needs
Arterioles
Are the smallest arteries and are called resistance vessels
- there is a significant drop in pressure
What’s the advantage of small arterioles having high resistance?
- is a protective mechanism
- fine tunes and optimizes local blood flow to respond to immediate tissue needs
Components in the transition to the capillaries
Thoroughfare channels: a vessel that bypasses the capillary network
Metarterioles: a transition vessel between arterioles and capillaries
Precapillary sphincters:
- a ring of smooth muscle that regulates blood flow to the capillaries
- anchors the true capillaries
Anastomoses: when 2 arteries join together when more blood flow is needed
The opening and closing of precapillary sphincters are controlled mainly by
local chemical conditions (low 02, high CO2, and high metabolic waste products such as lactic acid can trigger the relaxation of the precapillary sphincters)
Capillaries
Are the smallest type of blood vessels(also called exchange vessels):
- function in the exchange of gases, nutrients and wastes
- form a capillary bed which are interconnecting vessels that travel between cells
The 3 types:
- continuous(most common)
- fenestrated: small pores
- sinusoid:discontinous
Capillary Exchange
The exchange at the capillary depends on 2 opposing forces:
Hydrostatic pressure(HP): a pushing pressure against the blood vessel wall
(Colloid) osmotic pressure(OP): a pulling pressure by non-diffusible plasma proteins
Hydrostatic pressure
Two pressures are pushing on either side of the capillary wall:
Capillary hydrostatic pressure (HP.) is pressure from inside the capillaries.
Interstitial fluid hydrostatic pressure (HPif) is pressure from the tissues outside the capillary.
• normally insignificant
• interstitial fluid is drained by the lymphatic system
Osmotic pressure
Capillary osmotic pressure (OP.) is pressure inside the capillaries.
• due to plasma proteins
Interstitial fluid osmotic pressure (OPif) is pressure outside the capillary.
• normally insignificant
• interstitial fluid has few proteins
Filtration vs Absorption
Filtration is when blood gets pushed out of the capillary
Absorption is when blood gets pushed back into the capillary
Net filtration process(NTO)
Is the average of all pressures acting on the capillary bed
On the arterial end, the NFO results in filtration
- on the venous end, the NFO results in reabsorotion
The venous system
Capillaries unite to form a venule
Venule unite to form a vein
Veins
Are low pressure vessels
- the movement of blood against gravity requires skeletal muscle contractions
Skeletal muscle pump: when leg muscles contract
Respiratory pump: when the diaphragm contracts
Other special venous system features
Venous valves: prevents back flow of blood and is most abundant in veins of limbs
Venous sinuses: flattened veins with extremely thin walls
- composed of only endothelium
- eg coronary sinus of the heart and dural sinuses in our brain
The difference in walk thickness and linen shape in arteries vs veins
Wall thickness: The artery has thicker walls and more smooth muscles
• Lumen shape: The artery has retained an oval shape, while the vein collapses into an irregular shape
