Ch 21 Vessel Structure Thru Venous Return Flashcards
Blood vessels
Are organs- made of tissues working together to allow organ to complete basic functions
General systemic circulatory pathway for flow of blood
Aorta- arteries- arterioles- capillaries- venules- veins- vena cavaae (large veins)
3 main types of blood vessels
Artery
Vein
Capillaries
Walls of an artery or vein contain 3 layers
Tunica intima- internal
Tunica media- middle
Tunica adventitia - externa
The thickness of the walls and amounts of connective tissue and smooth muscle depend on …
The amount of pressure the vessel must endure
Arteries, veins and capillaries all have spaces for blood to travel through called a
Lumen
Covering of lumen (all 3)
Endothelium- assists in blood flow
All 3 also have a
Basement membrane
Capillaries structural aspect
Lumen
Endothelium
Basement membrane ur
Artery internal tunic
Internal elastic layer (Swiss cheese)- elastic fibers (elastin) - reinforces wall of artery
Main tissue component of middle tunic
Smooth muscle, allows vessels to respond to signals from endocrine and nervous system
Middle tissue layer only in artery
Second layer of elastic connective tissue
Tunica externa
Semi dense- outer casing
Artery thicker than vein
Arteries carry blood ____ the heart, veins carry blood ___\
From, back to
Arteries have ____ walls than veins
Thicker
Blood pressure in arteries is _____ whereas it’s ______ in veins
High, low
Diameter of lumen- arteries have _____ lumen whereas veins have____ lumen
Small, large
Elastic fibers- arteries have ____ elastic fibers where as veins have _____ elastic fibers
More, less
Veins have valves arteries
Do not, allowing one way flow
Arteries- resistance vessels- carry away from heart
Relatively strong, resistant tissue structure that resists high BP
Conducting arteries aka elastic
Elastic/large
Aorta, common carotid, subclavian, pulmonary trunk, common iliac arteries
Distributing arteries
Muscular or medium
Distributed to specific organs
Brachial, femoral, renal, splenic arteries
Smooth muscle layers constitute 3/4 of wall thickness
Elastic artery aka conducting
Thick walls
Located close to heart- aorta and
branches of aorta (2.5- 1 cm diameter)
Tunica media made up of elastic fibers
Stretched as blood is ejected from heart during systole accommodating the surge of blood ( pressure reservoirs)
Recoil during diastole- help propel blood
Conducting arteries aka elastic
Elastin
Arteriosclerosis
Deal with highest pressures
Biggest, thickest
Muscular arteries
Distributing arteries which move blood into organs- diameter 1.0-.3 cm
Thickest - tunica media
Elastic arteries
Move blood forward even during rest
Elastic vesselsStretch under____ and re
Stretch under systole, recoil under diastole
Atherosclerosis
Artery hardened, elastic tissue cannot recoil , less effect on forward moving blood
Leads to CHF/heart disease
Muscular arteries
Lie distal to elastic
Include most named arteries
Vasoconstriction and dilating- help with distribution of blood to organs
Thickest media of all vessels
More smooth muscle and less elastic tissue
Thick sheets of elastin on each side of tunica media
External elastic lamina lies between the tunica media tunica externa
Metabolic needs
Dictate constriction and dilation
Arterioles
Positioned just before capillary bed
Control blood flow/pressure entering capillaries
Thin muscular walls- 1-2 layers of smooth muscle
Smallest arteries
Resistance arteries
Diameter controlled by local factors (intrinsic) and sympathetic division (extrinsic) and long term factors ( hormones)
Capillaries
Micro circulation
Metarterioles
Just upstream from capillary beds
Precapillary sphincters
Controls blood reaching capillary beds
Arterioles regulate blood flow from arteries to
Capillaries
Peripheral resistance
Arterioles are most significant point of control over peripheral resistance and flow
On proximal side of capillary beds and best positioned to regulate flow into capillaries
Outnumber any other type of artery - most control points
More muscular in proportion to diameter- highly capable of vasomotion
Arterioles produce half of the total
Peripheral resistance
Arterioles control
Peripheral pressures in extremities ( peripheral BP)
Micro circulation
Where nutrient waste exchange takes place
Made up primarily of capillaries
Capillaries are the only vessels that allow
Nutrient waste exchange
Capillaries are referred to as the functional unit of circulatory system
Smallest blood vessels
Capillary network
Exchange of gases nutrients and waste
Walls one cell thick
Great length of capillaries throughout body
Immense surface area for exchange of material
Exchange between blood in capillary and surrounding tissue/ interstitial fluid
Capillaries come in form of___ and___\
Network and beds
Micro circulation
Transport of nutrients to the tissues and removal of cell waste
Micro circulation of each organ is organized specifically to meet
That organs needs
Continuous capillaries
Gaps between neighboring cells
Muscle and lung
Small pores
Most common- skin, muscle
Fenestrated capillaries
Plasma membrane have many holes
Kidney, small intestine, endocrine
Medium size pores
Sinusoids
Very large fenestrations
Incomplete basement membrane
Liver, bone marrow, spleen
Large size pores
Pores in the walls of capillaries aloe for
Nutrient waste exchange
Closed fluid system
No leaks, maintain pressure possible ( brakes in car)
If we’re a closed circuit how do we get nutrients out of blood
Small holes in capillaries
Capillary exchange
Most important blood in the body is in capillaries
Two way movement of fluid across capillary walls -
Water, oxygen, glucose, amino acids lipids, minerals, antibodies, hormones, waste, carbon dioxide, ammonia
Through capillary walls are exchanges made between blood and
Surrounding tissues
Chemical pass through the capillary walls by 3 routes
Endothelial cell cytoplasm
Intercellular clefts between endothelial cells
Filtration pores (fenestrations) of fenestrated capillaries
Mechanisms involved in capillary exchange
Diffusion
Transytosis, filtration, reabsorption
Starling law of capillaries
Net movement out of capillary into interstitium
Movement is governed by hydrostatic
pressure - protein (oncotic) pressure
Volume of fluid and solutes reabsorbed normally is almost as large as volume filter.
Every day 20L of fluid filter out of capillaries in tissue throughout the body . Of this, 17 liters are reabsorbed and 3L enter lymphatic capillaries
Filtration requires
Pressure
Blood enters capillaries from areteioes
At arterioles end- pressure is higher
Where they dump into veins (capillary)
Venule end- pressure is low
Arterial end result
Net filtration
Venous end result
Net reabsorption
Capillary filtration and reabsorption
Variations- glomeruli- devoted to filtration
Alveolar capillary - devoted to absorption
Activity or trauma- increases filtration
Starling
Movement of fluid in and out of arterioles, capillaries and venules is regulated by the balance between
Intravascular hydrostatic pressure-
Tends to force fluid out of vessels
Osmotic pressure of plasma protein
Tends to retain fluid within vessel
Venous return mechanism-
Veins returning blood to heart
Pressure of blood in veins is too low to push blood back to the heart. Over come a few ways
Hydrostatic pressure
Action of the heart
Inspiration
Pocket valves
Skeletal pumps
Normal venous return
Blood flow to heart help-Valves utilized- skeletal muscle of extremities- skeletal muscle pump, breathing action- respiratory pump
Respiratory pump- how does this help with blood flow back to heart
Enhances venous return- up and down of diaphragm creates a volume- low pressure in chest, high pressure lower/abdomen-
fluid goes high pressure to low pressure
Skeletal muscle pump
Squeeze when skeletal muscle contracts (tooth paste tube),into vein- contraction, squeezes blood up towards heart, muscle relaxes- pulls new blood in
Why is venous return important
Cardiac output is controlled by venous return
Heart is not primary controller of CO, venous return is
Heart can only pump volume of blood given
Usually- Venus return (5l/min)will equal
Cardiac output
Venous return is dependent on
Blood volume and venous pressure
Vasoconstriction caused by symp
Skeletal muscle pumps
Pressure drop during inhalation
End diastolic volume is
Preload
Venous return controls
End diastolic volume and stoke volume, cardiac output
Starling
Increase preload, heart fills efficiently, stronger force of contraction
Venous return and physical activity
Exercise increases return by: beating faster- increasing CO and BP
Vessel of skeletal muscle lungs and heart dilate and increase flow
Increase respiratory rate increase action of thoracic pump
Venous pooling happens with
Inactivity
Venous pressure not enough force blood upward
Prolonged standing, CO may be low enough to cause dizziness
Prevented by tending leg muscles, activating skeletal muscle pump
