1.05 Circulatory System

Lecturer: Dr. Ulysses Rallon

circulatory system

• transports fluids (nutrients, electrolytes, and oxygen dissolved) throughout the body

• consists of cardiovascular system and lymphatic system

• carries away from the cells and the tissues the waste products of metabolism

ultimate waste product of metabolism

carbon dioxide and water

cardiovascular system

• the heart and blood vessels make up blood transportation network

• the heart pumps blood through the body’s vast system of blood vessels

• the blood carries nutrients, oxygen, and waste products to and from the cells

arterial system

• carries oxygenated blood except pulmonary arteries

• arterial blood = bright red in color

venous system

• carries unoxygenated blood except pulmonary veins

• venous blood = darker color

types of blood vessels

1. arteries

2. veins

3. capillaries

arteries

thick-walled system that distributes blood to the body under high pressure

arterioles

• final distributing vessels that deliver oxygenated blood to capillaries

• smallest artery

• the endothelium is supported by smooth muscles arranged in rings

anatomy of heart

blood vessel walls from inner to outer

• most vessels of the circulatory system have 3 coats or tunics:

1. tunica interna/intima

2. tunica media

3. tunica external/adventitia

tunica interna/intima

• composed of endothelium (flat squamous cells)

  • the flat cells that line the lumen of blood vessels supported by the subendothelial tissue

• internal elastic lamina

• supported by delicate connective tissue

note: capillaries consist ONLY of this tunica intima with a supporting basement membrane

tunica media

• a middle layer composed primarily of smooth muscles supposed by external elastic lamina

• most variable coat

• arteries, veins, and lymphatic ducts are distinguished by the thickness of this layer relative to the size of the lumen

  • thickness of tunica media: artery has thicker tunica media than vein

  • vein has larger lumen than artery

  • veins has valves

    • not all veins have valves

    • mostly medium-sized veins posses valves, especially those veins that are subjected to the pull of gravity

• in arteries, there are variable amounts of elastic fibers

tunica externa/adventitia

an outer layer that is made up of tough connective tissue sheath that covers the blood vessels

capillaries

made of one cell layer (endothelial cells) supported by connective tissue (basal lamina) on its external surface

types of capillaries

1. continuous capillary

2. fenestrated capillary

contiuous capillary

• no break between endothelial cells

• tighter junction

• substances crossing through would cross through phagocytosis or pinocytosis

fenestrated capillary

• breaks between intimal cells are termed “fenestrations” or “pores”

  • allow free passage of water and other substances across openings

• these “windows” or pores allow for the efficient exchange of larger molecules and fluids between the bloodstream and surrounding tissues

• the difference between the capillaries is the junction between intimal cells

  • the junction between intimal cells in continuous capillary is tighter than that of the fenestrated capillaries

• capillaries form a capillary bed

capillary bed

• interchange of oxygen, nutrients, waste products and other substances with extracellular fluid occurs

• blood from the capillary beds passes into thin-walled venules, which resembled wide capillaries

• venules drain into small veins that open into large veins

superior and inerior vena cava

• largest veins

• return poorly oxygenated blood to the heart

heart

• central part of the circulatory system that produces pressure to push blood volume towards the periphery

• muscular organ that pumps blood through the body’s vast system of blood vessels

• blood carries nutrients, oxygen, and waste products to and from the cells

cardiac muscles

involuntary, intercalated, striated muscles

four chambers of the heart

1. atrium (2)

2. ventricles (2)

atrium

• right: receives unoxygenated blood from the body through superior and inferior vena cava

• left: receives oxygenated blood from the lungs, carried by the pulmonary veins

note: thickness of muscle wall of atrium are thinner compared to ventricles because the route that they pump blood is near

ventricles

• right: thinner wall, pumps unoxygenated blood to the lungs (requires lower pressure)

• left: thicker wall, pumps oxygenated (requires higher pressure to pump blood)

valves of the heart

1. tricuspid valve

2. pulmonary valve

3. mitral valve

4. aortic valve

tricuspid valve

• guards between right atrium and right ventricle orifices

• when RA contracts, it opens allowing blood to flow from RA to RV

• when RV starts to pump, increasing pressure between lumen of RV, it will push the lips of the tricuspid valve and closes

pulmonary valve

• between RV and pulmonary artery

• when tricuspid valve closes, all pressure generated by RV are directed to pulmonic valve and opens to allow blood flow towards pulmonary artery

mitral valve

• between LA and LV

• the same principle as tricuspid valve

aortic vavle

• between LV and aorta

• same principle as pulmonary valve

circulation

1. pulmonary circulation

2. systemic circulation

pulmonary circulation

brings unoxygenated blood to the lungs

systemic circulation

distributes oxygenated blood to the rest of the body

arteries

• carry blood from the heart and distribute it to the body

• the blood passes through a series of decreasing calibers

• has a thick tunica media

• artery size and types is continuum

• there is a gradual change in morphology differentiating one type to another

the types of arteries are distinguished on the basis of:

1. overall size

2. relative amounts of elastic tissue

3. relative amount of muscle in the tunica media

4. the thickness of the wall relative to the lumen

5. function

types of arteries

1. large elastic arteries (conducting arteries)

2. medium muscular arteries (distributing arteries)

3. small arteries and arterioles

large elastic arteries

• conducting arteries

• have many elastic layers (sheets of elastic fibers) in their walls

• initially receive the cardiac output

  • cardiac output = stroke volume x heart rate

• elasticity enables them to expand when the heart contracts when they receive cardiac output

• return to normal size between cardiac contractions, pushing the blood into the medium arteries downstream

• maintains BP in the arterial system between cardiac contractions

• minimized the ebb in BP as the heart contracts and relaxed

examples: aorta, brachiocephalic artery, subclavian artery, carotid arteries, pulmonary trunk and arteries

medium muscular arteries

• distributing arteries

• walls consist chiefly of circular smooth muscle fibers

• ability to vasoconstrict, regulates the flow of blood to different parts of the body as required by circumstance (ex. activity, thermoregulation)

• pulsatile muscular wall contractions temporarily and rhythmically constrict their lumina in progressive sequence, propelling and distributing blood to various parts of the body

example: brachial artery, femoral artery

small arteries and arterioles

• relatively narrow lumina and thick muscular walls

• regulated mainly by the degree of tonus (firmness) in the smooth muscles of the arteriolar walls:

  • degree of filling of capillary beds

  • level of arterial pressure within the vascular system

• arterioles can be observed only under magnification

• the small arteries are usually not named or specifically identified during dissection

blood pressure

• mean arterial pressure is a function of cardiac output and resistance in the arterioles

  • mean arterial pressure = volume produced by the heart x vessel radius (vasodilation/vasoconstriction)

  • mean arterial pressure = cardiac output x resistance

• if arteriole has high tone (innately contracted), blood volume and pressure will encounter resistance before it reaches the tissues because of the variable resistance by arterioles

• if the tonus is above normal, hypertension (high BP) results

• for treatment of patient with hypertension, use medicati9on that has main effect on the arterioles causing relaxation of smooth muscles in the arterioles (ex. amlodipine)

note: tonicity of the arteriole is sometimes inherited

anastomoses

• communication between the multiples branches of an artery or vein

• previous numerous potential detours for blood flower in case the usual pathway is obstructed by compression, the positi9on of a joint, pathology, or surgical ligation

if main channel is occluded:

• the smaller alternated channels can increase in size in a relatively short time

• provide a collateral circulation that ensured the blood supply to structures distal to blockage

• collateral pathways require time to open adequately

  • usually insufficient to compensate for sudden occlusion or ligation

  • there are areas where collateral circulation does not exist or is inadequate to replace the main channel

anatomical/true terminal/end arteries

• arteries that do not anastomose with adjacent arteries

• occlusion of an end artery interrupts the blood supply to the structure/segment of an organ it supplies

example: arteries supplying the retina when blocked results to blindness

functional terminal arteries

• not true terminal arteries (arteries with ineffectual anastomoses)

• supply segments of the brain, liver, kidneys, spleen, and intestinals

• may also exist in the heart

caput medusae

• commonly caused by liver cirrhosis wherein tissue is scarred, hindering blood flow through the liver and causing portal hypertension

• when the portal vein is blocked, blood backs up and flows through nearby veins, causing them to enlarge and become visible

venous anatomosis

• most common

• one vein empties directly into another

• reason vein blockage is less serious than arterial blockage

arterial anatomosis

• two arteries merge

• provides collateral (alternative) routes of blood supply to a tissue

• coronary circulation and around joints

veins

• generally, return deoxygenated (venous) blood from he capillary beds to the heart

• gives veins a dark blue appearance

• veins are more abundant than arteries

• 20% of blood occupies the arteries while 80% occupies veins

• walls are thinner

  • allow large capacity for expansion, and do so when blood return to the heart is impeded by compression or internal pressure

  • example: Valsalva maneuver = taking a large breath and holding it

• their diameter is usually larger than those of the corresponding artery

• the arteries and veins can make up a circuit

• expected that half the blood volume would be in arteries and half in the veins

• veins tend to be double or multiple

  • often depicted as single vessels in illustrations for simplicity

• those that accompany deep arteries = accompanying veins

Valsalva maneuver

taking a large breath and holding it in

accompanying veins

• those that accompany deep arteries

• L. venae comitantes

• surround deep arteries in an irregular branching network

• occupy a relatively unyielding fascial vascular sheath with the artery they accompany

• the heat from arterial blood warms the cooler venous blood as it returns to the heart from a cold extremity called countercurrent heat exchanger

• stretched and flattened as the artery expands during contraction of the heart

large pulmonary veins

• atypical

• carry well-oxygenated blood (AB from lungs to heart)

• lower blood pressure in the venous system

  • the walls of veins are thinner than those of their companion arteries

  • do not pulsate or spurt blood when severed

types of veins

1. venules

2. medium veins

3. large veins

venules

• smallest veins

• drain capillary beds and join smaller vessels to form small veins

• magnification is required to observe venules

• small veins are the tributaries of larger veins that unit to form venous plexus (posterior venous arch of the foot)

• small veins are unnamed

medium veins

• drain venous plexus

• accompany medium arteries

• have valve flaps (venous valves)

  • permit unidirectional flow of venous blood towards the heart

  • segmentation of venous blood to relived distal portion of venous system from the weight of the blood subjected to pull of gravity

examples:

1. superficial vein: cephalic and basilic veins of the upper limb and great and small saphenous veins of the lower limb

2. accompanying veins: named according to the artery they accompany

large veins

• characterized by wide bundles of longitudinal smooth muscle

• a well-developed tunica adventitia

example: superior vena cava

countercurrent heat exchanger

the heat from the arterial blood warms the cooler venous blood as it returns to the heart from a cold extremity

systemic veins

• more variable than arteries

• venous anastomoses, direct or indirect, between 2 veins occur more often

• musculo-venous type of venous pump

• the outward expansion of the bellies of contracting skeletal muscles in the limb

• limited by the deep fascia

• compresses the veins

• “milking” the blood superiorly towards the heart

• the valves of the veins break up the columns of blood

• receives the more dependent parts of excessive pressure

• allow venous blood flow ONLY towards the heart

blood capillaries

• simple endothelial tubes connecting the arterial and venous sides of the circulation

• allow exchanged of materials with the interstitial or extracellular fluid (ECF)

• generally arranged in capillary beds

  • networks that connect the arterioles and venules

hydrostatic pressure

• forces blood into and through capillary bed

• forces fluid containing oxygen, nutrients, and other cellular materials out of the blood at the arterial end of the capillary bed into the extracellular spaces

• allows exchange with cells of the surrounding tissue

• capillary walls are relatively impermeable to plasma proteins

  • downstream, at the venous end of the bed, ECF now containing waste products and oxygen is reabsorbed into the blood

  • result of the osmotic pressure from the higher concentration of CHONs within the capillary

starling hypothesis

states that fluid movement across a capillary wall is determined by the balance between hydrostatic pressure (pushing fluid out) and oncotic pressure (pulling fluid in)

AV shunts

• in some regions, such as in the fingers

• direct connections between the small arterioles and venules proximal to the capillary beds they supply and drain

atrioventricular anastomoses

• permit blood to pass directly from the arterial to the venous side of the circulation without passing through capillaries

• numerous in the skin

• an important role in thermoregulation

  • in some situations, blood passes through 2 capillary beds before returning to the heart

  • a venous system linking 2 capillary beds

how to describe arteries?

example: axillary artery

1. description: location and relations (to the heart)

   • axillary fossa supplying structures around the shoulder

2. commencement: exact point where it starts

   • outer border of first rib

3. origin: the artery from which it arises from

   • subclavian artery

4. termination: landmark where it ends

   • lower border of teres major

5. branches

   • 6 branches

6. continuation

   • brachial artery

note: the anatomical landmark for dividing axillary artery is the presence of pectoralis minor muscle

lymphoid system

• provides for the drainage of surplus tissue fluid and leaked plasma proteins to the bloodstream

• removal of debris from cellular decomposition and infection

• absorption and transport dietary fat

  • lacteals = special lymphatic capillaries, receive all lipid and lipid-soluble vitamins absorbed by the intestines

• formation of a defense mechanism for the body

  • when foreign proteins drains from an infected area, antibodies specific to the protein are produced by immunologically competent cells and/or lymphocytes and dispatched to the infected area

important components of lymphatic systm

1. lymphatic plexus

2. lymphatic vessels

3. lymph

4. lymph nodes

5. lymphocytes

6. lymphoid organs

lymphatic plexus

networks of lymphatic capillaries that originate blindly in the extracellular spaces of most tissues

lymphatic vessels

body wide network of thin-walled vessels that have abundant lymphatic valves

lymph

tissue fluid that enters lymph capillaries and conveyed by lymphatic vessels

lymph nodes

small masses of lymphatic tissue locate along the course of lymphatic vessels through which lymph is filtered on its way to the venous system

lymphocytes

circulating cells of the immune system that react against foreign materials

lymphoid organs

parts of body the produce lymphocytes

superficial lymphatic vessels

• drain into deep lymphatic vessels that accompany the arteries and also receive the drainage of internal organs

• both superficial and deep lymphatic vessels traverse lymph nodes as they course proximally

• large lymphatic vessels enter large collecting vessels, called lymphatic trunk, which unite to form either right lymphatic duct or thoracic duct

lymphatic trunk

large collecting vessels

right lymphatic duct

• drains lymph from the body’s right upper quadrant

• at the root of the neck, it enters the junction of the right internal jugular and right subclavian vein, the right venous angle

thoracic duct

• drains lymph from the remainder of the body

• the lymphatic trunks draining the lower half of the body merge in the abdomen

• it ascends into and then through the thorax to enter the left venous angle

lacteals

• special lymphatic capillaries

• receive all lipid and lipid-soluble vitamins absorbed by the intestine