Chapter 19- Blood vessels Flashcards
“Vaso-“
Vessels
“Vasa-“
Vessels
3 layers of the vessel wall
- Tunica intima
- Tunica media
- Tunica externa
Tunica intima
Innermost layer of the vessel wall. Contains endothelium of simple squamous cells, continuous with the lining of the inside of the heart. It provides slick surface to reduce friction as the blood moves, and helps to increase flow of blood
Tunica media
Middle layer. Contains smooth muscle, and is thicker in arteries than in veins. Function- maintaining blood pressure and circulation
Vasodilation
Dilates blood vessels (lumen becomes larger), which decreases pressure in the blood vessel. Carried out by the tunica media in the blood vessel wall.
Vasoconstriction
Constricts blood vessels (lumen becomes smaller). Less blood can move through, increases blood pressure. Carried out by the tunica media in the blood vessel wall.
Tunica externa
Outermost layer of the blood vessel wall. Contains collagen fibers- protects the blood vessel, anchors blood vessels to surrounding structures. This prevents the blood vessel from twisting.
Vasa vasorum
Found in large blood vessels like the pulmonary artery, pulmonary vein, and aorta. It consists of small blood vessels on the outside of the large blood vessels so the tissue doesn’t die- too much distance for nutrients from the blood to diffuse through.
Arteries
Blood vessels that carry blood away from the heart. They branch several times to form smaller blood vessels (ex- arterioles). Systemic arteries carry oxygenated blood, pulmonary arteries carry oxygen poor blood.
Types of arteries (3)
- Elastic arteries
- Muscular arteries
- Arterioles
Elastic arteries
Conducting arteries, including the aorta and its largest branches. Three walls contain large amounts of elastin, and expand and recoil as heart pumps blood- blood flows continuously (rather than start-stop start-stop). Importance- maintains blood flow during diastole
How does a large lumen in the blood vessels affect resistance?
A large lumen decreases resistance
Muscular arteries
Distributing arteries that are derived from elastic arteries and have a thicker tunica media. They don’t have much elastic quality, but are very good for vasoconstriction- influences blood pressure
Arterioles
Resistance arteries- these are the smallest arteries. The body can constrict/dilate the arterioles to affect resistance to blood flow into the capillaries. Arterioles flow directly into capillary beds.
Capillaries definition
Exchange vessels. No tunica media or externa, need a thin wall to diffuse materials through. They have an extremely small diameter- RBCs have to pass through single file.
Capillaries function
Contact tissue cells, allow for gas exchange, waste removal, etc. Capillaries are structurally suited for exchange across a thin wall. Cells joined by tight junctions, but have intercellular clefts- allows passage of fluids and small solutes
Types of capillaries (3)
- Continuous capillaries
- Fenestrated capillaries
- Sinusoid capillaries
Continuous capillaries
Most common, but least permeable. Found in the skin and skeletal muscle tissue
Fenestrated capillaries
Large pores, more permeable. Found mostly in places of the body where absorption and filtration is frequent, ex- small intestine and kidneys
Sinusoid capillaries
Least common, but most permeable. They have large intercellular clefts between cells with an incomplete basement membrane and a larger lumen than other capillary types. Found in the liver, spleen, red bone marrow- want blood cells to be able to get out of the red bone marrow through the capillaries
Microcirculation definition
The flow of blood from an arteriole to a venule through a capillary bed.
How does arteriole diameter affect flow into the capillary bed?
Dilation- blood enters capillary bed
Constricted- blood is diverted past the capillary bed. Decreases the amount of blood, but it’s never completely reduced.
How does microcirculation occur?
The terminal arteriole branches several times to form a network of capillaries. Pressure from arterioles controls how much blood flows through the capillary bed, and the capillary bed empties into a postcapillary venule. If blood is provided to capillary beds via arterioles- gas exchange, metabolic waste removal, etc. will occur here
Venules
The smallest veins that lead from capillary bed to larger veins. Tend to be very porous, allow easy passage from bloodstream.
Veins
Carry blood toward the heart, systemic veins carry oxygen poor blood, pulmonary veins carry oxygenated blood. Have thinner tunics and larger lumen than arteries of comparable size. Large lumen allows for large amounts of blood to stored- blood reservoirs
How do the thin vessel walls of veins affect the pressure inside the vessels?
Thin tunics= low pressure within veins. Problem- low pressure in veins (with thin tunica media) dampens ability to return blood to the heart
Adaptations of veins to increase return flow to heart (2)
- Large diameter lumen
2. Venous valves
How does the large diameter of the lumen in veins help to return blood to the heart?
Causes little resistance to blood flow. Benefit- doesn’t take a lot of work to move blood through veins
How do venous valves help to return blood to the heart?
Prevents backward flow of blood through veins. Greater number of valves in appendages, because the appendages are very long and have a greater chance of backflow of blood.
Varicose veins
A homeostatic imbalance where leaky valves cause backflow of blood, causing blood to pool and walls of veins to stretch.
3 important factors of circulation
- Blood flow
- Blood pressure
- Resistance
Blood flow
The volume of blood flowing through a vessel, an organ, or the entire circulation in a given period. Blood flows from high pressure to low pressure- arteries have high pressure due to thicker tunica media, veins have low blood pressure
Hydrostatic pressure difference
Refers to different pressures in arteries vs veins. This must exist or the blood would stop moving.
Blood pressure (circulation factor)
The force exerted on a blood vessel wall by the contained blood. Blood always “pushes against” the vessel it is flowing through, and blood pressure is highest in the aorta since the aorta receives blood directly from the heart. As you travel from arteries- capillaries- veins, blood pressure decreases. We are usually only concerned with arterial blood pressure
Resistance
Opposition of blood flow through a vessel due to the friction between the vessel wall and the flowing blood. Peripheral resistance- resistance is highest in systemic circulation. As resistance decreases, flow increases, and as resistance increases, flow decreases.
Sources of resistance (3)
- Blood viscosity, more viscous= greater the resistance
- Vessel length, longer blood vessels= greater resistance
- Vessel diameter, smaller diameter vessels= greater resistance
Relationship between resistance, blood pressure, and blood flow
ΔP/R= F
As change in blood pressure (ΔP) increases, blood flow (F) increases
As peripheral resistance (R) increases, blood flow decreases
General rule of systemic blood pressure
The pumping action of the heart generates blood flow. Blood pressure results when blood flow is opposed by resistance. Blood pressure is a general indicator of cardiovascular health.
Pulsatile
Rises and falls in a regular fashion. Describes blood pressure in the arteries near the heart.
Arterial blood pressure is affected by (2)
- Distensibility of blood vessel walls- degree of stretch of blood vessels. Less elasticity= higher pressure
- Volume of blood being pumped into arteries. Higher blood volume= higher blood pressure
Systolic blood pressure
Pressure peak generated by contraction of the left ventricle (during heart beat). Ventricle contracts, forcing blood into the aorta and stretching its walls. In healthy adults, it’s about 120 mm Hg
Diastolic blood pressure
Pressure when heart is relaxed (between heart beats). Walls of aorta relax and recoil, but still maintain enough pressure to move blood. In healthy adults, it’s about 70-80 mm Hg
Pulse pressure
The difference between systolic and diastolic blood pressure (subtracting). Represents the force the heart generates with each contraction. Ex- for an individual with a blood pressure of 120/80, the pulse pressure is 40
What is pulse pressure used to diagnose?
Can be used to diagnose cardiovascular system conditions that are asymptomatic. Anything over 60 can indicate risk for certain diseases (heart attack, etc.). However, 180/140 blood pressure gives a pulse pressure of 40 but is still very dangerous
Where can pulse pressure be felt?
Can be felt (palpated) at several points in the body as a pulse. Ex- wrist and neck
Capillary blood pressure
Low blood pressure is typical in capillary beds. Importance- thin walls of capillaries could burst under high pressure, low pressure allows for maximal trade of respiratory gasses at tissues
Venous blood pressure
Much more steady than arterial blood pressure, blood pressure is generally low. Problem- low pressure in veins would prevent efficient blood return
Solutions to low venous blood pressure (3)
- Use of skeletal muscle- contracting muscles “squeeze” veins- push blood forward
- Respiratory pump
- Sympathetic vasoconstriction
How does the respiratory pump work?
Inhaling- increases pressure in the abdomen, pushes blood in veins towards the heart
Exhaling- pressure in chest drops, allowing vessels to expand- blood flows into the right atrium
Sympathetic vasoconstriction
Vessel walls constrict, reducing venous volume and pushing blood toward the heart
Maintenance of blood pressure involves (3)
Regulation of cardiac output (CO), peripheral resistance (R), and blood volume
Factors affecting cardiac output (2)
- Stroke volume
2. Heart rate
Factors affecting R (peripheral resistance- 3)
- Blood viscosity
- Blood vessel length
- Blood vessel diameter
How is blood pressure regulated in the short term?
Neural controls- the cardiovascular center of the medulla oblongata.
What are the 2 subcenters of the cardiovascular center?
- Cardiac centers- cardioacceleratory center and cardioinhibitory center
- Vasomotor center- controls blood vessel diameter
Vasomotor center function
Controls blood vessel diameter (primarily that of the arterioles). Most arterioles have vasomotor tone- slightly constricted. Sympathetic activity causes vasoconstriction- increase in blood pressure.
Vasomotor tone
Slight constriction of blood vessels. Ensures that the muscle stays healthy and can easily be contracted or relaxed- degree of tone varies according to organ/part of body
The cardiovascular center is modified by which 3 factors?
- Baroreceptors
- Chemoreceptors
- Higher brain centers
Baroreceptors
Stretch receptors in walls of large arteries in neck and thorax. Best for short term changes in blood pressure- baroreceptors act quickly, like when changing head position.
What happens to the cardiovascular system when the baroreceptors are stretched?
When stretched, inhibits the cardioacceleratory system- decreases blood pressure. Vasodilation- dilating arteries reduces R (peripheral resistance). Decreased CO- parasympathetic activity increases- heart rate and contractile force drop
Chemoreceptors function
Detect changing CO2 levels, blood pH, and oxygen content in the body, which all affect blood pressure. Increase in CO2 (indicates low oxygen), pH decrease, or oxygen content drops- stimulate cardioacceleratory center. Increase in CO and vasoconstriction occur.
How do higher brain centers affect blood pressure?
Higher brain centers can affect blood pressure by relaying to the medulla. Ex- effect of fight or flight mediated by the hypothalamus
Hormones that influence blood pressure (4)
- Epinephrine/norepinephrine
- Angiotensin 2
- ANP
- Antidiuretic hormone
Epinephrine and norepinephrine
Produced by adrenal glands and used by the sympathetic nervous system. Release causes increased CO- increases blood pressure via vasoconstriction.
Angiotensin 2
A hormone produced by the kidneys. Release stimulates intense vasoconstriction- raises blood pressure quickly.
What causes angiotensin release?
Low blood pressure and low blood volume (ex- hemorrhage). Used when blood pressure gets extremely low due to these factors
Atrial natriuretic peptide (ANP)
Produced by the atria of the heart. Release acts on the kidneys to cause increase in excretion of solutes/water from body as urine- decreases blood volume and blood pressure. Causes vasodilation- decreases resistance and blood pressure
Antidiuretic hormone (ADH)
Produced by the hypothalamus. Release causes increase in water reabsorption by kidneys- increases blood volume and blood pressure. Not great for short term fixes, but severe hemorrhage is an exception.
Which mechanisms regulate blood pressure long term?
Renal (kidney) mechanisms. Kidneys consistently adjust to maintain blood volume to about 5 liters (healthy adult) and maintain BP.
When blood pressure increases, what happens in the kidneys?
When blood pressure increases, filtration by kidneys increases. Increased urine output results- decreasing blood volume and blood pressure
Renin-angiotensin-aldosterone mechanism
Increases blood pressure. Enzyme renin catalyzes reaction to create angiotensin 1. Angiotensin 1 is converted to angiotensin 2, causing a variety of effects.
During the Renin-angiotensin-aldosterone mechanism, what are the effects of angiotensin 2? (4)
- Stimulates aldosterone release from adrenal cortex- sodium absorption increases. Water follows sodium- increases blood pressure
- Stimulates pituitary to release antidiuretic hormone (ADH)
- Stimulates thirst center of the brain. Bringing in more water= higher blood volume
- Stimulates vasoconstriction
Crisis hypertension
“Crisis” hypertension reached when systolic is 180+ and/or diastolic 120+. This is extremely dangerous
Hypertension definition
Consistently high blood pressure (140/90 or higher)
Complications of chronic hypertension (4)
- Heart failure- myocardium is constantly in “overdrive”- walls weaken, heart fails
- Vascular disease- atherosclerosis (blocking and hardening of blood vessels). Affects heart, brain, kidneys, retinas.
- Stroke
- Renal failure
Atherosclerosis
Hardening of the blood pressure walls caused by poor diet. Fat sticks to blood vessels, and the walls lose the elasticity and increases resistance, increasing blood pressure
Primary hypertension
No underlying cause for hypertension. Can be caused by- heredity (some people are genetically predisposed to high blood pressure), diet, obesity, age, stress, smoking, and/or some other condition (ex- diabetes mellitus). Can’t be cured, only treated- dietary restrictions, weight loss, stop smoking, diuretics, ACE inhibitors, etc.
Secondary hypertension
Caused by another identifiable condition, like obstructed arteries, kidney disease, hyperthyroidism (fast metabolism, makes the heart work harder). Can be treated/cured by correcting the underlying condition
Hypotension
Consistently low blood pressure (90/60). Not as serious as hypertension- there is individual variation in blood pressure based on a variety of factors (heredity, physical fitness, etc.). Becomes a problem when blood flow to necessary tissues is exceptionally low
Orthostatic hypotension
Dizzy feeling resulting from fast change in head position (laying down/sitting- standing). Blood pools temporarily in feet due to gravity- not as much blood reaches the brain. Sympathetic nervous system usually quickly corrects this problem
Chronic hypotension
Low blood pressure caused by some underlying condition. Ex- hypothyroidism, severe malnutrition, inadequate adrenal cortex function
Shock definition
Inadequate circulation of blood to body tissues. Oxygen needs aren’t met, disposal needs often not met. If sustained, shock causes cell death and tissue death
Hypovolemic shock
Low blood volume, shock resulting from severe hemorrhage, severe 3rd burns, excessive vomiting/diarrhea (dysentery). If the skin is damaged through burns, there’s nothing stopping the water from leaving the body. Results in a weak pulse and intense vasoconstriction.
Vascular shock definition
Poor circulation due to extreme vasodilation. Blood volume is normal in this situation.
Types of vascular shock (3)
- Anaphylactic shock
- Neurogenic shock
- Septic shock
Anaphylactic shock
Allergic reaction occurs, massive release of histamine causes vasodilation. Epinephrine from epipen causes vasoconstriction
Neurogenic shock
Autonomic nervous system incorrectly regulated due to damage to the spinal cord, parasympathetic influence results in low blood pressure.
Septic shock
Severe systemic bacterial infection (sepsis= blood infection caused by bacteria). Chemicals released by bacteria cause severe vasodilation
Cardiogenic shock
The heart is insufficient to provide blood to tissues. Caused by myocardial damage- multiple heart attacks
Why is blood flow to tissues important?
Important for- gas exchange in lungs, filtration in kidneys, delivering oxygen and nutrients to tissue cells, absorption from digestive tract, waste removal
Intrinsic regulation of blood flow mechanisms (3)
- Autoregulation
- Metabolic control
- Myogenic control
Autoregulation of blood flow
The organ’s automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirement. It is independent of hormones or neural mechanisms
How do organs change blood flow?
By changing resistance in arterioles. Can be accomplished via metabolic (chemical) changes or myogenic (physical) changes
Metabolic control of blood flow
Autoregulation due to inadequate blood supply that leads to buildup of waste or tissue hypoxia. Causes release of nitric oxide (NO) in tissues- dilates arterioles, which increases blood supply to capillary beds of necessary tissues. This is a temporary effect
Myogenic control of blood flow
Quality of vascular smooth muscle in blood vessel wall
Increased pressure within vessels results in increased tone of smooth muscle. Blood vessels constrict- blood supply to capillary bed drops. With decreased pressure within vessels, vasodilation occurs. Blood supply to capillary bed increases.
Blood flow in skeletal muscle
Blood flow increases when skeletal muscle is used more (like during periods of exercise). Capillary density is greater in slow oxidative fibers than fast glycolytic fibers
Active hyperemia
Increase in blood flow that is proportional to increased metabolic activity. Oxygen levels low and metabolic waste production increases during activity. Norepinephrine causes vasoconstriction, but local metabolic controls override this response to cause vasodilation (blood flow increases 10x).
Blood flow in the brain
Blood flow in the brain is constantly maintained, blood will never be diverted from here during exercise. This is because the brain can’t store nutrients- constant blood supply for high metabolic rate. The brain has intense myogenic regulation. When blood pressure increases- vasoconstriction- protects smaller blood vessels from damage. When blood pressure decreases- vasodilation- ensures enough blood is supplied to the brain (oxygen, glucose, waste disposal, etc.).
Why is blood flow in the skin important?
Important for maintaining body temperature
Venous plexuses
Extensively branched network of blood vessels under the skin- blood flow ranges from 50 ml/min to 2500 ml/min. Controlled by temperature receptors, signals from higher CNS. Increase in body temp- vessels dilate, warm blood invades capillaries- heat radiates from skin to cool body. Decrease in body temp- vessels constrict, pull body away from skin surface
Where does blood flow more slowly?
Blood flows the slowest in vessels that have greatest cross-sectional area- capillaries
Why do capillaries have the largest cross sectional area when compared to other large blood vessels?
The capillaries of the body have a greater combined cross-sectional area than the aorta. Aorta is 2.5 cm squared, combined capillaries is 4500 cm squared
How do do substances pass through capillary walls?
Diffusion- movement from high concentration to low concentration
Which substances pass through capillary walls?
Gasses, most nutrients, and metabolic wastes pass from blood to tissues through thin capillary walls. Oxygen and nutrients pass from blood to tissue, while metabolic waste and CO2 moves from tissue to blood
How easily do gasses/substances pass through capillary walls?
Depends on permeability. Very permeable (ex- liver)- allows easy passage between, least permeable (ex- brain)- allows very little passage
4 routes of capillary exchange
- Diffusion through membrane (lipid-soluble substances)
- Movement through intercellular clefts (water-soluble substances)
- Movement through fenestrations (water-soluble substances)
- Transport via vesicles or caveolae (large substances)
Hydrostatic pressure
Force exerted by a fluid pressing against a wall (the push). Hydrostatic pressure pushes fluid out of the capillary through the walls
Capillary hydrostatic pressure (HPc)
Pressure that forces fluids out of capillary into interstitial space. HPc is higher at the arterial end of the capillary bed
Interstitial fluid hydrostatic pressure (HPif)
Pressure that forces fluid from interstitial space into capillary. HPif “opposes” Hc- HPif pushes fluid back into capillary. This pressure is so small that it is usually assumed to be 0 mm Hg
Colloid osmotic pressure (OPc)
Force that draws water in a certain direction (the pull), causes fluid to move back into capillary at the venous end. This pressure is created by large molecules (plasma proteins, etc) still in capillary draws fluid back in via osmosis.
What is the opposing force of colloid osmotic pressure?
Interstitial fluid colloid osmotic pressure (OPif)- force that pulls water out of capillary. Interstitial space has very few proteins, so this “force” is negligible at 1 mm Hg
Net filtration pressure
Pressure created by interactions by hydrostatic pressure and osmotic pressure. There is a net loss of fluids from circulation- more is pumped out than is returned to vessel. The “lost” fluid goes to the lymphatic system, but it is eventually returned to the vascular system.
Tissue edema definition
abnormal increase in interstitial fluid volume
Calculation of net filtration pressure
NFP= (HPc + OPif) - (HPif + OPc)
= (35 mm Hg + 1 mm Hg) - (0 mm Hg + 26 mm Hg)
= 10 mm Hg
Basic causes of tissue edema (3)
- Higher than normal outward pressure in capillaries (HPc)
- Lower than normal inward pressure in capillaries (OPc)
- Inefficient lymphatic system
What causes a higher than normal outward pressure in capillaries (causing tissue edema)?
Filtration out of capillary bed increases, fluid lost from blood at a faster rate. Causes- pregnancy, blocked/occluded vessels, congestive heart failure, unusually high blood volume
What causes a lower than normal inward pressure in capillaries (resulting in tissue edema)?
Reabsorption back into capillary bed at venous end is slowed or stops. Causes- low levels of proteins in blood
Why can an inefficient lymphatic system cause tissue edema?
Lymphatic vessels are blocked, can’t drain fluid remaining in interstitial space. Ex- infection by parasitic worm
