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Questions and Answers
What was the primary source of confusion regarding the circulatory system for many centuries?
What was the primary source of confusion regarding the circulatory system for many centuries?
Which ancient figure is credited with understanding the basic principle of blood circulation?
Which ancient figure is credited with understanding the basic principle of blood circulation?
According to the information, what specific idea did Huang Ti propose regarding blood circulation?
According to the information, what specific idea did Huang Ti propose regarding blood circulation?
In which time period did Huang Ti reportedly believe that blood flowed around the body and back to the heart?
In which time period did Huang Ti reportedly believe that blood flowed around the body and back to the heart?
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Which aspect of the circulatory system caused confusion for a long time?
Which aspect of the circulatory system caused confusion for a long time?
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Which layer of a blood vessel contains smooth muscle, collagen, and elastic tissue, contributing to its strength?
Which layer of a blood vessel contains smooth muscle, collagen, and elastic tissue, contributing to its strength?
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What is the function of the vasa vasorum found in the tunica externa of larger blood vessels?
What is the function of the vasa vasorum found in the tunica externa of larger blood vessels?
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Which type of artery is best suited to withstand the pressure surges resulting from systole due to its elastic properties?
Which type of artery is best suited to withstand the pressure surges resulting from systole due to its elastic properties?
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What is a key characteristic of arterioles that enables them to regulate blood flow to specific organs?
What is a key characteristic of arterioles that enables them to regulate blood flow to specific organs?
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Which condition involves blood accumulating between the tunics of an artery, often due to degeneration of the tunica media?
Which condition involves blood accumulating between the tunics of an artery, often due to degeneration of the tunica media?
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Where are the carotid sinuses, which monitor blood pressure, located?
Where are the carotid sinuses, which monitor blood pressure, located?
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What is the primary function of the aortic bodies?
What is the primary function of the aortic bodies?
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Which type of capillary has endothelial cells with tight junctions and intercellular clefts, allowing for the passage of small solutes?
Which type of capillary has endothelial cells with tight junctions and intercellular clefts, allowing for the passage of small solutes?
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What is the role of precapillary sphincters in capillary beds?
What is the role of precapillary sphincters in capillary beds?
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Why are veins considered capacitance vessels?
Why are veins considered capacitance vessels?
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What structural feature do medium veins possess that is responsible for preventing the backflow of blood?
What structural feature do medium veins possess that is responsible for preventing the backflow of blood?
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What is a portal system in the circulatory system?
What is a portal system in the circulatory system?
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Using the formula 𝐹 α ∆𝑃/𝑅, if the pressure difference (∆P) between two points doubles and the resistance (R) remains constant, what happens to the flow (F)?
Using the formula 𝐹 α ∆𝑃/𝑅, if the pressure difference (∆P) between two points doubles and the resistance (R) remains constant, what happens to the flow (F)?
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What is the mean arterial pressure (MAP) if a patient has a blood pressure reading of 130/80 mm Hg?
What is the mean arterial pressure (MAP) if a patient has a blood pressure reading of 130/80 mm Hg?
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Which of the following has the most powerful influence on blood flow?
Which of the following has the most powerful influence on blood flow?
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Flashcards
Circulatory System
Circulatory System
The system that circulates blood throughout the body.
Blood Flow
Blood Flow
The movement of blood through the circulatory system.
Huang Ti
Huang Ti
Ancient Chinese emperor who understood blood circulation.
Heart
Heart
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Ancient Beliefs
Ancient Beliefs
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Types of blood vessels
Types of blood vessels
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Arteries
Arteries
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Veins
Veins
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Capillaries
Capillaries
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Tunica media
Tunica media
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Aneurysm
Aneurysm
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Baroreceptors
Baroreceptors
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Chemoreceptors
Chemoreceptors
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Varicose veins
Varicose veins
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Blood pressure (BP)
Blood pressure (BP)
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Pulse pressure
Pulse pressure
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Vasomotion
Vasomotion
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Peripheral resistance
Peripheral resistance
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Autoregulation
Autoregulation
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Hormonal control of BP
Hormonal control of BP
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Study Notes
Introduction
- Blood flow's path confused scientists for centuries
- Chinese Emperor Huang Ti (2697-2597 BC) correctly theorized blood circulates around the body and back to the heart
- Roman physician Galen (129-c.199) believed blood flowed back and forth, with the liver creating blood and organs consuming it
- English physician William Harvey (1578-1657) conducted experiments demonstrating a continuous blood circuit pumped by the heart
- Improvements in microscopes led to the discovery of capillaries by van Leeuwenhoek and Malpighi
- Harvey's work marked a shift towards experimental physiology, capable of overturning established dogma
General Anatomy of the Blood Vessels
- Blood vessels are categorized into three types:
- Arteries: carry blood away from the heart
- Veins: carry blood back to the heart
- Capillaries: connect the smallest arteries to smallest veins, forming a closed circuit
Micrographs of Blood Vessels
- Illustrative images show the structure of arteries and veins under a microscope
- Arteries have three layers (tunica interna, tunica media, and tunica externa)
- Veins also have three layers, with distinctions including valves
The Vessel Wall
- Walls of arteries and veins are composed of three tunics (layers): tunica interna, tunica media, and tunica externa
- Arteries: endothelium, smooth muscle, and connective tissue
- Veins: endothelium, smooth muscle, connective tissue, and valves
Tunica Interna (Tunica Intima)
- The innermost layer of blood vessels
- Structure: simple squamous epithelium (endothelium)
- Function: selectively permeable barrier; secretes chemicals to regulate dilation/constriction; repels blood cells to prevent clotting; produces adhesion molecules to attract immune cells when needed.
Tunica Media
- The middle layer of arteries
- Structure: smooth muscle layered with connective tissue, and elastic fibers
- Function: strengthens blood vessels, resisting rupture; contraction of smooth muscle controls blood vessel diameter
Tunica Externa (Tunica Adventitia)
- The outermost layer
- Structure: loose connective tissue, often merging with neighboring structures (e.g., nerves, other vessels)
- Function: anchors the vessel, provides pathways for nerves and lymphatic vessels; contains small blood vessels (vasa vasorum) to supply the outer portion of the vessel walls
Histology of Blood Vessels
- Detailed microscopic structure of various blood vessels (arteries, veins, capillaries) across the different sizes and types
- Illustrative diagrams depicting the layers (tunics) and lumen of each type of blood vessel (venules, arterioles, medium and large veins and arteries)
Arteries Classified by Size
- Conducting arteries (elastic or large):
- Largest arteries
- Examples: aorta, common carotid, subclavian, pulmonary trunk, common iliac arteries
- Contain a well-developed elastic lamina to withstand pressure
- Distributing arteries (muscular or medium):
- Distribute blood to specific organs
- Examples: brachial, femoral, renal, splenic arteries
- Predominantly smooth muscle and less elastic tissue
- Resistance arteries (small):
- Thicker tunica media than large arteries
- Examples: arterioles
- Regulate blood flow to specific areas.
- Metarterioles (thoroughfare channels):
- Short vessels that connect arterioles directly to venules
- Allow blood to bypass capillary beds
Aneurysms
- A weak point in an artery or heart wall forms a bulging sac
- Blood accumulates between layers, often due to tunica media degeneration
- Common locations include abdominal aorta, renal arteries, and arterial circle at the base of the brain
- Often caused by atherosclerosis or hypertension.
Arterial Sense Organs
- Sensory structures monitoring blood pressure and chemistry, transmitting information to regulate heart rate, blood vessel diameter, and respiration
- Carotid sinuses:
- Baroreceptors in the walls of the internal carotid artery
- Monitor blood pressure
- Transmit signals via the glossopharyngeal nerve
- Allow for baroreflex
- Carotid bodies:
- Chemoreceptors near the carotid arteries
- Monitor blood chemistry (pH, O2, and CO2)
- Transmit signals via the glossopharyngeal nerve to control respirations
- Aortic bodies:
- Chemoreceptors in the walls of the aortic arch
- Structure and function similar to carotid bodies
- Use the vagus nerve to communicate with the brainstem
- Carotid sinuses:
Capillaries
- Exchange vessels where gasses, nutrients, wastes, and hormones are exchanged between blood and tissues
- Structure: thin walls composed of endothelium and basal lamina
- Types of capillaries differ in permeability:
- Continuous capillaries: occur in most tissues, with tight junctions and intercellular clefts
- Fenestrated capillaries: occur in sites of rapid absorption or filtration (e.g., kidneys, small intestine), with pores
- Sinusoids: irregular, leaky capillaries found in specialized tissues (e.g., liver, bone marrow) and can allow larger molecules to pass through
Capillary Beds
- Networks of capillaries, usually supplied by a single arteriole or metarteriole
- Regulation of blood flow in the capillary beds involves precapillary sphincters
- At any given time, about 75% of the body's capillaries are closed to conserve blood flow.
Veins
- Capacitance vessels where blood returns to the heart
- Structure: thin walls, flaccid (easily collapsible), and have valves
- Function: hold large amounts of blood
- Pressure: low blood pressure (average 10 mm Hg)
Types of Veins
- Postcapillary venules: smallest veins, more porous than capillaries; leukocytes leave bloodstream through venule walls
- Muscular venules: one or two layers of smooth muscle in the tunica media
- Medium veins: have a thin tunica media, a thick tunica externa, and venous valves, and control blood flow back to the heart
- Venous sinuses: especially thin walls; no smooth muscle
- Large veins: diameter greater than 10 mm; have a tunica media with smooth muscle; thick tunica externa.
Varicose Veins
- Blood pools in veins, often in the lower legs, causing dilated and visible veins
- Result from weakened valves, hereditary factors, obesity, and pregnancy.
Circulatory Routes
- There are different types of circulatory routes that blood flow can take
- Simple route: Heart → Arteries → Arterioles → Capillaries → Venules → Veins
- Portal system: blood flows through two consecutive capillary networks before returning to the heart. Examples include the hypothalamus-anterior pituitary, kidneys, and intestines-liver
- Anastomosis: convergence of two blood vessels other than capillaries
- Arteriovenous anastomosis: artery directly flows into vein
- Venous anastomosis: one vein empties into another
- Arterial anastomosis: two arteries merge, thus providing alternate routes for blood supply
Variations in Circulatory Pathways
- Different anatomical configurations of blood vessels
Blood Pressure, Resistance, and Flow
- Blood pressure: force exerted by blood against vessel walls (recorded as systolic and diastolic pressures)
- Resistance: opposition to blood flow (influenced by blood viscosity, vessel length, and vessel radius)
- Flow: rate of blood movement through a vessel (affected by pressure and resistance) -Important to deliver nutrients and oxygen, and remove metabolic wastes.
Hypertension and Hypotension
- Hypertension: chronic elevated blood pressure (>140/90). Consequences: weakened arteries, aneurysms, atherosclerosis
- Hypotension: chronic blood pressure below normal range. Associated with blood loss, dehydration, or anemia
BP Determined by 3 Variables
- Cardiac output
- Blood volume
- Resistance to flow
Peripheral Resistance
- Resistance to blood flow from the heart
- Three main factors influencing resistance:
- Blood viscosity
- Vessel length
- Vessel radius -Peripheral resistance is influenced by vasoreflexes
Hormonal Control
- Hormones regulating blood pressure:
- Angiotensin II: potent vasoconstrictor, increases blood pressure; its synthesis involves the renin-angiotensin system
- Aldosterone: promotes Na+ retention in the kidneys, increasing blood volume and pressure
- Natriuretic peptides: lowers blood pressure by increasing Na+ excretion by the kidneys
Neural Control
- Neural control over blood vessels:
- Vasomotor center in the medulla oblongata regulates the activity of sympathetic and parasympathetic neurons influencing blood vessel diameter
- Baroreflexes: measure blood pressure; activate negative feedback loop to adjust blood pressure
- Chemoreflexes: measure blood chemistry and regulate respirations
- Medullary ischemic reflex: brain's self-protective mechanism to increase blood pressure if perfusion drops.
Local Control
- Autoregulation: ability of tissues to maintain their own blood supply, regulated locally by metabolic factors and vasoactive molecules
- Reactive hyperemia: increase in blood flow after a period of decreased perfusion
- Angiogenesis: growth of new blood vessels, essential for wound healing and in response to tissue damage
Two Purposes of Vasomotion
- General control of blood pressure
- Routing blood flow between different body regions
Differences in Systemic Blood Flow (at rest vs. exercise)
- Different regions receive varying blood flow depending on physiological requirements
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