Exam 4: Blood Vessels Flashcards
Hypertension
blood pressure too high
•can damage blood vessels and lead to cardiovascular disease
Hypotension
blood pressure too low
- body deprived of nutrients
- may cause death if severe
What are the systems that help to maintain blood pressure?
endocrine
nervous
urinary
What are the 5 main types of vessels?
–Arteries
–Arterioles
–Capillaries
–Venules
–Veins
Where do Arteries carry blood?
AWAY from the heart
Where do veins carry the blood?
TO the heart
What are Capillaries?
microscopic, porous site of exchange
What are the 3 layers of vessel walls?
- Tunica intima
- Tunica media
- Tunica externa
how are blood vessels and their functions determined?
5 types of blood vessels and their functions are determined by which tunics they have
All vessels do not have all three tunics
Tunica Intima
–Inner lining in direct contact with blood
–Endothelium continuous with endocardial lining of heart
–Active role in vessel-related activities
Tunica Media
–Muscular and connective tissue layer
–Greatest variation among vessel types
–Smooth muscle regulates diameter of lumen
Tunica Externa
–Elastic and collagen fibers
–Vasa vasorum- tiny vessels that supply blood to other vessels
–Helps anchor vessel to surrounding tissue
Arteries
contain 3 layers (tunics) of typical blood vessel
Thick muscular-to-elastic tunica media
High compliance
Ability to change diameter
What does having a high compliance signify?
walls stretch and expand in response to pressure without tearing
Vasoconstriction
decrease in lumen diameter
Vasodialation
increase in lumen diameter
Elastic Arteries
- Largest arteries
- Largest diameter but walls relatively thin
- Function as pressure reservoir
- Help propel blood forward while ventricles relaxing
- Also known as conducting arteries – conduct blood to medium-sized arteries
Muscular Arteries
–Tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries
–Walls relatively thick
–Capable of great vasoconstriction/ vasodilatation to adjust rate of blood flow
–Also called distributing arteries
Arterioles
- Abundant microscopic vessels
- Metarteriole has precapillary sphincter which monitors blood flow into capillary
- Sympathetic innervation and local chemical mediators can alter diameter and thus blood flow and resistance
- Resistance vessels – resistance is opposition to blood flow
- Vasoconstriction can raise blood pressure
Capillaries
–Smallest blood vessels connect arterial outflow and venous return
–Exchange vessels
–Lack tunica media and tunica externa
–Capillary beds – arise from single metarteriole
What is microcirculation?
flow from metarteriole through capillaries and into postcapillary venule
What is the primary function of a capillary (exchange vessel)
primary function is exchange between blood and interstitial fluid
Due to the lack of a tunica externa in capillaries
Substances pass through just one layer of endothelial cells and basement membrane
Capillary beds: Vasomotion
intermittent contraction and relaxation
Capillary beds:Throughfare channel
bypasses capillary bed
What are the three types of Capillaries?
- Continuous
- Fenestrated
- Sinusoids
Continuous Capillaries
–Endothelial cell membranes from continuous tube
Fenestrated Capillaries
–Have fenestrations or pores
Sinusoid Capillaries
–Wider and more winding
–Unusually large fenestrations
Veins
- Structural changes not as distinct as in arteries
- In general, very thin walls in relation to total diameter
- Same 3 layers
- Not designed to withstand high pressure
- Valves – folds on tunica intima forming cusps
-Aid in venous return by preventing backflow
Capillary Exchange: Diffusion
–Oxygen, hormones, nutrients
–Carbon dioxide and waste products
–Small solutes
–Larger solutes
How do Oxygen, hormones, nutrients diffuse?
•move from higher concentration in blood into interstitial fluid and tissue cells
How do Carbon dioxide and waste products diffuse?
•diffuse from higher concentration in tissue to blood
How do small solutes diffuse?
•diffuse via endothelial cells or intercellular clefts
How do larger solutes diffuse?
•pass through fenestrations or gaps in sinusoids
Capillary Exchange: Vesicular trasport
–Occurs when endothelial cells use pinocytosis
- fuse fluid-filled vesicles with plasma membrane
- transport their contents from blood to interstitial fluid (or reverse)
- certain hormones and fatty acids transported by this method
Capillary Exchange: Bulk Flow
–Movement of large amounts of fluids and dissolved substances
- move in one direction down a pressure gradient
- direction of movement dependent on net pressure of opposing forces
Capillary Exchange: Bulk Flow 2 types
–Filtration
–Reabsorption
Filtration
- movement of fluid out of blood through openings in capillaries
- fluid and small solutes flowing easily
- larger solutes blocked
- occurs on arterial end of capillary
Reabsorption
- movement of fluid back into blood
- on venous end
Capillary Exchange: Bulk Flow Hydrostatic Pressure
–Physical force exerted by fluid on a structure
– E.g., blood hydrostatic pressure (HPb)
- force exerted per unit area by blood on wall
- promotes filtration from capillary
–E.g., interstitial fluid hydrostatic pressure (HPif)
- force of interstitial fluid on external blood vessel
- close to 0 in most tissues
Capillary Exchange: Bulk Flow Colloid osmotic pressure
–Pull of water into tissue by tissue’s protein concentration (colloid)
–E.g., blood colloid osmotic pressure (COPb)
- draws fluid into blood due to blood proteins
- promotes reabsorption, opposing hydrostatic pressure
–E.g., interstitial fluid colloid osmotic pressure (COPif)
- force drawing fluid into interstitial fluid
- few proteins present, so relatively low (0 to 5 mm Hg)
Capillary Eschange: Net Filtration Pressure
–Net hydrostatic pressure
•difference between blood and interstitial fluid hydrostatic pressures
–Net colloid osmotic pressure
•difference between blood and interstitial fluid osmotic pressures
Net Filtration calculation
–Net filtration pressure
•difference between net hydrostatic and net osmotic pressures
–NFP = (HPb - Hpif) - (COPb - COPif)
Net Filtration Pressure Changes: Arterial and Venous ends
Arterial and venous ends of capillary with different pressures
–At arterial end
- HPb = 35 mm Hg, HPif = 0
- COPb = 26 mm Hg, COPif = 5 mm Hg
- NFP = (35 - 0) - (26 - 5) = 14 mm Hg
- net pressure into surrounding tissue
–At venous end
- less amount of blood in vessel
- corresponding decrease in hydrostatic pressure
- osmotic pressures relatively constant through capillary
- HPb = 16 mm Hg, HPif = 0
- COPb = 26 mm Hg, COPif = 5 mm Hg
- NFP = (16 - 0) - (26 - 5) = -5 mm Hg
- net pressure into blood vessel
What generates blood pressure?
Contraction of ventricles
Systolic BP
highest pressure attained in arteries during systole
Diastolic BP
lowest arterial pressure during diastole
What falls progressively with distance from the left ventricle?
Pressure
What does blood pressure also depend on?
Total volume of blood
Interconnected negative feedback systems control blood pressure by adjusting:
heart rate
stroke volume
systemic vascular resistance
blood volume
Negative feedback loops from 2 types of reflexes:
Baroreceptor Reflexes
Chemoreceptor Reflexes
Baroreceptor Reflexes
•Pressure-sensitive receptors in internal carotid arteries and other large arteries in neck and chest
–Carotid sinus reflex helps regulate blood pressure in brain
–Aortic reflex regulates systemic blood pressure
- When blood pressure falls, baroreceptors stretched less, slower rate of impulses to CV (cardiovascular center in medulla)
- CV decreases parasympathetic stimulation and increases sympathetic stimulation
Chemoreceptor Reflexes
- Receptors located close to baroreceptors of carotid sinus (carotid bodies) and aortic arch (aortic bodies)
- Detect hypoxia (low O2), hypercapnia (high CO2), acidosis (high H+) and send signals to CV
- CV increases sympathetic stimulation to arterioles and veins, producing vasoconstriction and an increase in blood pressure
- Receptors also provide input to respiratory center to adjust breathing rate
Hormonal Regulation: (RAA) system
Renin-angiotensin-aldosterone system
•Renin
–released by kidney when blood volume falls or blood flow decreases
• Angiotensin converting enzyme (ACE)
What do Renin and ACE act on to produce active hormone angiotensin II?
Substrates
–Raises BP by vasoconstriction and secretion of aldosterone
»increases water reabsorption in kidneys to raise blood volume and pressure
Hormonal Regulation: Epinephrine and norepinephrine
- Adrenal medulla releases in response to sympathetic stimulation
- Increase cardiac output by increasing rate and force of heart contractions
Hormonal Regulation: Antidiuretic hormone (ADH) or vasopressin
- Produced by hypothalamus, released by posterior pituitary
- Response to dehydration or decreased blood volume
- Causes vasoconstriction which increases blood pressure
Hormonal Regulation: Atrial natriuretic peptide
-Released by cells of atria
–Lowers blood pressure by causing vasodilation and promoting loss of salt and water in urine
–Reduces blood volume
Auto Regulation
–Ability of tissue to automatically adjust its blood flow to match metabolic demands
–Demand of O2 and nutrients can rise tenfold during exercise in heart and skeletal muscles
–Also controls regional blood flow in the brain during different mental and physical activities
–2 general types of stimuli
2 types of auto regulation stimuli
- Physical – temperature changes, myogenic response
- Vasodilating and vasoconstricting chemicals alter blood vessel diameter
Circulation
•Important difference between pulmonary and systemic circulation in autoregulatory response
–Systemic blood vessel walls dilate in response to low O2 to increase O2 delivery
–Walls of pulmonary blood vessels constrict under low O2 to ensure most blood flows to better ventilated areas of lung
