Week 4 - Circulatory system Flashcards
What are the circulatory vessels?
Arterial system - arteries, arterioles
Venous system - Veins, venules
Capilliaries
Describe the arterial system
High pressure system delivering blood away from the heart.
Arteries - carry blood away from heart
Arterioles - Smallest branches of arteries that lead to capillary beds
BP regulation
Capillary Bed
Smallest blood vessels with thin walls
Location of exchange between blood and interstitial fluid.
Venous System
Venules - smallest branches of veins that collect blood from capillaries
Veins - Return blood to heart
Three layers of blood vessels
Tunica intima
Tunica media
Tunica externa
Describe Tunica intima
Encompasses
Endothelial Lining
Connective tissue layer
Internal elastic membrane (Arteries) providing passive elasticity to the tunica intima.
What is the role of Endothelium?
Release vasoactive substances which affect vascular tone, BP and blood flow.
Maintains vasular homeostasis.
Vasodilators (Nitric Oxide)
Vasoconstrictors (Endothelin)
Describe the Tunica Media
Middle layer - contains concentric sheets of smooth muscle in loose connective tissue elastic fibers in arteries, collagen in veins.
Encircles the endothelium that lines the lumen (interior space) of the blood vessel
Binds to inner and outer layers.
External elastic membrane (arteries)
Separates tunica media from tunica externa.
Describe the Tunica externa (outer layer)
Anchors vessel to adjacent tissues
contains - collagen fibers, elastic fibers, smooth muscle cells (in veins)
Vasa vasorum (vessel of vessels)
Small arteries and veins in walls of large arteries and veins, serve cells of tunica media and tunica externa.
Three types of artery
Elastic artery
Muscular artery
Arteriole
What is a capillary?
Endothelial tube, inside thin basement membrane
No tunica media
No tunica externa
Diamater is similar of a RBC
Continuous, fenestrated and sinusoid types.
Describe a continuous capillary
Found in all tissues except epithelia and cartilage
Have complete endothelial lining
Permit diffusion of water, small solutes, and lipid soluble materials
Block blood cells and plasma proteins
Specialised continuous capillaries in CNS and thymus
Have very restricted permeability, for example blood brain barrier.
Describe a fenestrated capillary
Have pores in endothelial lining
Permit rapid exchange of water and larger solutes
Found in: Choroid plexus
Endocrine organs
Kidneys
Intestinal tract
Describe a sinusoid (capillary)
Have gaps between adjacent endothelial cells
Permit free exchange of water and large plasma proteins.
Found in: Liver
Spleen
Bone marrow
Endocrine organs
Phaghocytic cells monitor blood at sinusoids.
Capillary Structure and function
Capillary beds (capillary plexus)
connect one arteriole and one venule
Precapillary sphincter - guards entrance to each capillary, opens and closes, causing capillary blood to flow in pulses
Thoroughfare channels - direct capillary connections between arterioles and venules.
Describe the venous system
Veins - collect blood from capilaries and return it to heart
Compared to arteries, veins have - larger diameters, thinner walls, lower bp
What is the role of venous valves?
Folds of tunica intima
Prevent blood from flowing backward
Compression of veins pushes blood toward heart
When walls of veins near the valves weaken, varicose veins may result.
Why is smooth muscle helpful in veins?
allows autonomic control over blood flow and pressure.
Can vasoconstrict in order to help w the propulsion of blood back to heart.
Also assisted by skeletal muscle pump.
describe total capillary blood flow
TCBF = CO
Determined by pressure and resistance
PRessure genreated by heart to overcome resistance
absolute pressure is less important than pressure gradient.
Pressure gradient is diff in pressure from one end of a vessel to the other.
Flow is proportional to pressure gradient divided by resistance.
Circulatory pressure - must overcome total peripheral resistance.
R of entire cv system
Change in pressure accros systemic circuit is approx 85mmHg
affected by - vascular resistance
blood viscocity
turbulence
What is vascular resistance?
Due to friction between blood and vessel walls
depends on vessel length and vessel diameter
Adult vessel length is constant
Vessel diamater varies by vasodilation and vasoconstriction
R increases exponentially as vessel diamter decreases.
What is Hyper/Hypotension
Normal BP = 120/80
Hypertension - greater than 140/90
Hypotension - Abnormally low
How do we respond to exercise?
Inc HR
Inc CO (Q)
Inc systolic bp
Redistribution blood flow
What is redistribution blood flow?
Blood flows to tissue in proportion to their metabolic demands
Major portion of exercise cardiac output diverts to active muscles
Increase from 7ml per 100g of muscle at rest to 75ml per 100g of muscle during exercise
How is HR regulated?
Parasympathetic Nervous system via vagus nerve slows HR by inhibiting SA and AV node
Sympathetic Nervous system via cardiac accelerator nerves, inc HR by stimulating SA and AV nodes.
Low resting HR due to parasympathetic tone
Inc in HR at onset oof exercise
Initial inc due to parasympathetic withdrawal
Up to 100bpm
Later inc due to inc SNS stimulation.
What causes changes in stroke volume?
Inc forced contraction = inc stroke volume
2 main ways:
1. Inc sympathetic ns activation, effects of circulating adrenaline and noradrenaline, direct stimulation of heart muscle.
2. Inc end diastolic volume, leading to inc stretch of sarcomeres and the inc force of contraction.
Training may improve LV compliance.
What causes changes in CO? (Q)
Inc due to:
Inc HR linear increase to max (Max HR = 220 - age)
Inc SV: Inc then plateu at approx 40% VO2max
No plateu in highly trained subjects
CO can inc to approx 35l/min in highly trained endurance athletes. 20-25l/min in untrained individuals.
HIgher in males: Higher SV lower HR
