The Circulatory System

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The Circulatory System
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General Functions of the Circulatory System

• a. To transport inhaled oxygen from the lungs to
  the cells of the body for cellular respiration.
• b. To transport CO2 from the cells of the body
  to the lungs for exhalation.
• To distribute nutrients from the villi
  capillaries to all cells of the body.
• To transport
• a. Metabolic (nitrogenous) wastes to the
  kidneys, including urea.
• b. Toxic substances to the liver.

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• To distribute hormones to the tissues/organs on
  which they act.
• To regulate body temperature
• i. Donation/absorption of heat
• ii. Flow shunting
• To prevent blood loss through blood clotting.
• To protect the body from pathogens
  (viruses/bacteria) due to the circulation of
  antibodies and white blood cells.

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• DEFINITIONS (see fig. 13.7 p. 246)
• Systemic Circulation
• Blood pumped by the LEFT side of the heart, which
  services the entire body except the lungs.
• Pulmonary Circulation
• Blood pumped by the RIGHT side of the heart,
  which services only the lungs.
• Services provides O2 nutrients, while
  carrying away CO2 and other wastes.

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The Major Components of the Human Circulatory
System

1. Blood Vessels (5 types)
2. Blood
3. Heart

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Blood Vessels (refer to fig. 13.1 p. 240)

• Arteries
• Carry blood AWAY from the heart.
• Arteries possess the thickest walls of all
  vessel-types.
• Their walls possess three layers of tissue
• i. Inner epithelial layer (aka endothelium)-
  possesses elastic fibers and is very smooth to
  promote easy flow.
• ii. Middle smooth muscle layer (contracts or
  relaxes to regulate blood flow and pressure)
  the thickest layer
• iii. Outer fibrous epithelial tissue which
  serves a protective function. It is comprised of
  elastic fibers allowing stretching and recoiling.
• Note Veins also possess three layers of tissue,
  but their walls are not as thick as those of
  arteries.

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Vein
Artery

• The walls some major arteries (eg. Aorta) are so
  thick, they must be supplied by their own blood
  vessels.
• Arteries in the systemic circuit carry oxygenated
  blood, whereas arteries in the pulmonary circuit
  carry deoxygenated blood.
• Notice the smaller inner diameter of arteries
  compared to that of veins this, due to the
  thicker middle muscle layer in arteries.

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• ii. Arterioles
• Arterioles are vessels into which arteries have
  been divided. Arterioles have the same structure
  as arteries, but are simply smaller (they are
  barely visible to naked eye).
• It is easier for blood to enter arteries (from
  the heart or other arteries) than it is for blood
  to exit arteries and enter arterioles (due to the
  smaller diameter of arterioles) ? this creates
  noticeable/measureable blood pressure during both
  heart contraction (systole) AND relaxation
  (diastole).
• Pressure is measureable during diastole because
  arteries are never fully emptied of blood.
• This impedance by the arterioles is known as
  peripheral resistance.
• When we measure our pulse, we count the elastic
  expansion of artery walls upon systole. When we
  measure our blood pressure, devices are able to
  deduce the pressure in arteries during systole
  AND diastole (due to peripheral resistance).
• The perpetual pressure within arteries, due to
  peripheral resistance, keeps blood flowing even
  when the heart is relaxing (diastole).

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• Flow Shunting
• Blood flow into arterioles, and eventually
  capillaries, is controlled in two ways (governed
  by nerve and/or endocrine signals) (see fig. 13.2
  p. 241)
• Smooth muscles lining arterioles constrict, thus
  allowing less blood to enter however, the
  arteriole does not fully close, so some blood
  enters
• The back-up plan involves pre-capillary
  sphincter muscles contracting or relaxing in
  order to respectively close or open access into
  capillary beds if closed off, blood flows to
  venules through a thoroughfare channel so that it
  can reach more useful areas more quickly.

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Why restrict access to arterioles/capillaries
(ie. Why Flow Shunt)???

• Example scenarios
• Cold weather want blood (with heat) to flow to
  the core of the body, not peripheryblood gets
  shunted to core through the closing off of the
  peripheral arterioles/sphincter muscles.
• Exercising want blood (with O2 and nutrients) to
  flow to skeletal muscles and heart, not the
  digestive tract or other non-necessary
  placesblood gets shunted to muscles. Good or
  bad to exercise after eating and why?
• Relaxing blood shunted to digestive tract to
  pick up nutrients etc

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• iii. Capillaries
• Capillaries are tiny vessels with walls that are
  one cell thick, thus allowing for the efficient
  exchange of substances.
• They are evident in all bodily regions (very high
  cross-sectional area)almost all cuts draw blood.
• Their small diameter only allows single file
  passage of red blood cells (again, helps with
  efficient exchange of, in this case, oxygen and
  CO2).
• They surround cells/tissues like a spider web
  or basket.
• Capillaries are, at most, 0.2 µm away from any
  cell in the body (further aids the exchange of
  substances).
• Certain capillary beds may be open or closed
  depending on demands subsequent flow shunting.

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In general, only about 5-10 of the bodys blood
is in the capillaries at any one time.
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• iv. Venules
• Same structure as a vein (see below), only
  smaller.
• Collect blood from the capillaries and/or the
  thoroughfare channels and join/enlarge to form
  veins.
• v. Veins
• Thin-walled compared to arteries.
• -- this provides veins with a larger interior
  diameter than arteries.

Thinner muscle layer
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• Same three layers of tissue as arteries, but the
  middle smooth muscle layer is thinner.
• Carry blood TOWARDS the heart.
• There exists a lower blood pressure in veins
  since they are further from the heart, and
  because of the larger interior diameter.
• VALVES (one-way) assist with the upward (against
  gravity) movement of blood back to the heart
  (valves prevent the backflow of blood).
  Malfunctioning valve ? varicose vein.
• Generally, 70 of the bodys blood is in the
  veinsact as somewhat of a blood resevoir.

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ONE-WAY VALVES

• Veins are located closer to the surface of the
  body than arteries, and they are surrounded by
  skeletal muscle.
• The contraction of these skeletal muscles aid in
  blood flow through the veins (ie. The skeletal
  muscles are the hearts for the veins).
• In the systemic circuit, veins carry deoxygenated
  blood.
• In the pulmonary circuit, veins carry oxygenated
  blood

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Against Gravity
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Blood Pressure and Blood Velocity (fig. 13.9
p.248)

• Blood Pressure (BP) The hydrostatic pressure
  that blood exerts against the wall of a vessel.
• highest in arteries due to their receiving of
  blood from the heart and due to the peripheral
  resistance created by the smaller arterioles.
• that said, the BP within arteries varies with
  respect to the heart contracting (systole) and
  relaxing (diastole) ? systolic pressure is higher
  than diastolic pressure.
• BP begins to drop in arterioles as the blood
  simply gets further from the hearts push, and it
  spreads out more.
• BP in the capillaries is somewhat medium in
  that even though the blood is far from the
  hearts pump, the vessel openings are small and
  the walls are thin allowing for a greater
  hydrostatic pressure against them.

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• By the time the blood reaches the veins, its
  pressure is not affected much by the heart due to
  its travel (and coupled slow-down) through
  tiny-diameter arterioles and capillaries.
• Thus, very low BP in veins (the lowest, in fact)
• Blood is furthest from heart
• Blood experienced extreme resistance within
  arterioles/capillaries
• Veins possess a very large (relative to arteries)
  interior diameter.

BP can also increase with higher blood volume!
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• Blood Velocity the speed of blood moving through
  vessels.
• blood velocity is highest in the arteries due to
  the hearts pump
• Blood velocity is lowest in the capillaries due
  to the single-file RBC flow through them and the
  massive spreading-out of the blood to the
  millions of capillary beds in the body
• Blood velocity picks up again (but not to the
  arterial level) in veins due to their large
  interior diameter (freeway) and due to the
  action of skeletal muscles to propel the blood
  back to the heart.
• The cross-sectional area (area of vessel wall
  in contact with blood) of the vessels is greatest
  in capillaries and lowest in arteries and veins.

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Normal BP 120 mm Hg/80 mm Hg (systolic/diastolic
).
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Major Blood Vessels (fig. 13.8 p. 247)
Red vessels usually arteries except for
pulmonary circuit. Carry oxygenated blood. Blue
vessels usually veins except for pulmonary
circuit. Carry de-oxygenated blood.
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1. Aorta carries oxygenated blood out from the
   Left Ventricle of the heart and services the
   entire systemic circuit by eventually branching
   into various arteries. Houses special nerves
   cells (Aortic Bodies) that sense H, CO2, and O2
   levels in blood.
2. Coronary Arteries and Veins Arteries branch
   off of the aorta and service the actual heart
   muscle (these vessels are seen on the surface of
   the heart) (Blood in the hearts chambers does
   not actually service the heart). Coronary Veins
   carry spent blood back to the hearts
   chambers.
3. Carotid Arteries branch off of the aorta to
   service the brain/head region. Highly
   specialized ? contain special nerve cells
   (Carotid Bodies)

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• i. Chemoreceptors that detect O2, H, and CO2
  content in the blood.
• ii. Pressure Receptors that detect blood
  pressure changes.
• -- the carotid artery can be used to measure
  ones pulse.
• Jugular Veins opposite of carotid arteries.
  Carry blood from the brain/head region back to
  the heart. Possess no valves since gravity aids
  the flow.
• Subclavian Arteries/Veins service the arms.
  Within the right subclavian vein there is a union
  between the lymphatic system and the circulatory
  system.

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• Mesenteric Arteries carry blood from the aorta
  to the intestines (gut). Subdivide into villi
  capillaries.
• Hepatic Portal Vein carries blood from the
  intestines to the liver.
• Hepatic liver-related
• Hepatic Vein carries blood from the liver back
  to the heart.
• Renal Arteries/Veins service the kidneys.
• Renal kidney-related
• 10. Iliac Arteries/Veins service the legs.

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• Superior (Anterior) and Inferior (Posterior) Vena
  Cavae collect/receive all of the blood from the
  various veins of the systemic circuit and conduct
  it back into the right atrium of the heart.
• Superior Vena Cava collects blood from above
  the heart.
• Inferior Vena Cava collects blood from below
  the heart.
• 12. Pulmonary Arteries/Veins only major vessels
  of the pulmonary circuit. Pulmonary arteries
  carry deoxygenated blood from the heart to the
  lungs. Pulmonary veins carry oxygenated blood
  from the lungs back to the heart.
• Pulmonary Trunk first vessel to receive
  blood (bound for the lungs) from the heart.
  Splits into two pulmonary arteries (one for each
  lung).

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Aorta
The aorta and the coronary systemheart not shown.
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Blood

• Made up of, and will separate into, two
  components
• Plasma comprises 55 of the blood volume
• Formed Elements (Cells) comprise 45 of the
  blood volume.
• - includes Red Blood Cells (RBCs), White Blood
  Cells (WBCs), and Platelets (which are simply
  cell fragments).
• fig. 13.10 p. 249.

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• Plasma
• 90-92 water ? maintains blood volume and
  pressure transports substances due to its
  flowing and polar nature regulates temperature.
  Primarily absorbed by small and large intestines.
  
• 7-8 Plasma Proteins ? maintain blood
  O.P./volume, etc. Produced by the liver. Too
  large to leave blood through capillary exchange.
• Albumins maintain BP and blood volume transport
  bilirubin.
• Immunoglobulins antibodies that fight infection
  (pathogens) transport cholesterol.
• Fibrinogen/Prothrombin aid in blood clotting.

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• lt1 of the following combined
• Salts/Electrolytes (aka minerals) maintain OP
  and BP, pH, and aid in metabolism in many ways
  absorbed primarily in small intestine.
• Gases oxygen/carbon dioxide from lungs/tissues
  respectively
• Nutrients fats, glucose, amino acids from small
  intestine
• Nitrogenous wastes urea, uric acid, ammonia, and
  creatinine from liver
• Hormones to aid metabolism
• Vitamins from small intestine to aid in enzymatic
  reactions (vitamins act as coenzymes).

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• Formed Elements
• Red Blood Cells (RBCs) fig. 13.11 p. 250
• aka erythrocytes, RBCs are the most numerous of
  the blood cells there exist about 25 trillion in
  our (on average) 5 L of blood (in fact, RBCs
  comprise 99 of blood cells).
• Structure promotes Function
• RBC is a biconcave disk (flatter in center)
  allowing them to thread through capillaries very
  efficiently and providing them with a large SA to
  Volume ratio.
• Lack nuclei and mitochondria to help limit size
  without nuclei, RBCs live (on avg.) 120 days and
  are then destroyed (by phagocytic cells through
  phagocytosis) in the liver or spleen. Without
  mitochondria, RBCs metabolize anaerobically so
  that they do not use the very oxygen that they
  carry, in order to make their ATP energy.

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• Large SA-to-volume ratio promotes RBCs main
  function to transport O2 in the blood.
• RBCs also transport CO2 and H ions, but to a
  lesser extent than O2.
• Each RBC houses about 250 million molecules of
  hemoglobin (Hb), an iron-containing protein
  responsible for carrying O2 (primarily).
• Hb is bright red when it is carrying O2 and
  purple-red when it is not.
• Hb is made up of four tertiary proteins (two
  alpha, two beta), four heme groups, and four Fe2
  ions. It can carry up to four O2 molecules at
  any one time.
• When RBCs are destroyed/recycled, Hbs iron is
  sent to the bone marrow to be reused heme is
  converted into bilirubin in the liver (released
  as a part of bile) and the alpha and beta chains
  are hydrolyzed and the amino acids reused.

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Hb picks up O2 (and drops off CO2) in the lung
capillaries and transports it to other cells in
the body, where it then gives up the O2 (and
picks up CO2) so that it can diffuse into the
respective cells. The diagram on the left
provides information on how Hb behaves
differently in these different regions of the
body.
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• Manufacture of RBCs (fig. 13.12 p. 251)
• - RBCs are primarily formed in the marrow of
  large bones
• - bones of the chest (ribs/sternum), upper arms
  (humerus), upper legs (femur), lower arms
  (radius/ulna), lower legs (tibia/fibula), hips,
  skull.
• - multipotent stem cells in the bone marrow
  become erythroblasts (RBC precursor), which lose
  their nuclei, gain hemoglobin, and mature or
  differentiate into an erythrocyte (RBC).
• - Certain hormonal/nervous signals tell stem
  cells how to develop as they have the ability to
  form any type of blood cell.

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• Control of RBC Production
• Oxygen-sensitive chemoreceptors in various
  locations (medulla oblongata, aortic/carotid
  bodies, renal artery, hepatic vein) sense low O2
  levels in the blood.
• Stimulus sent to kidney to produce the hormone
  erythropoietin (EPO), which stimulates production
  of RBCs in bone marrow, and acts to slow the rate
  of RBC destruction this allows for more O2 to
  be carried in the blood as we exhale plenty of
  it.
• Once O2 levels are restored, chemoreceptors send
  negative feedback message to kidney to cease
  release of erythropoietin.
• Some causes of lower than average O2 levels
  exercise, loss of blood, high altitudes, poor
  hemoglobin/RBC production/formation (anemia)
• Most common cause of anemia is iron deficiency.

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Blood Typing

• A couple of definitions
• Antigen a substance that elicits a defensive
  response from the immune system. In the case of
  RBCs, an antigen (if present) is a protein that
  is displayed on the surface of the cell and
  serves as an ID tag for that cell.
• Antibody an antigen-binding protein, produced
  by certain WBCs, that bind to certain antigens,
  tagging them for destruction by phagocytic WBCs.

FYI Anti-gen Antibody generating
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• ABO System

See table 14.2 p. 278 for Popn distribution O
most common, then A, then B, then AB
Key Points If antibody B (say) comes into
contact with antigen B, it will tag each B
antigen for destruction (the blood clumps and
causes flow problems). Antibodies exist only in
the plasma. Donated blood is made up of primarily
RBCs only. Soa person with AB blood can receive
blood from anyone whereas, a person with type O
blood can donate to anyone. AB Universal
Recipient O Universal Donor.
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Another Antigen Rh protein (see fig. 14.13, p.
279 excellent figure!) An Rh antigen is present
in people with Rh blood (no antibody), and is
not present in people with Rh- blood (also, no
antibody). If a person who is Rh- is exposed to
Rh blood, antibodies will then be produced that
will tag each Rh RBC for destructionhappens
often during a pregnancy where a mother is Rh-
and her fetus is Rhthe fetus RBCs move across
the placenta (late in the pregnancy or during
delivery, when the placenta begins to break down)
and stimulate the mother to produce Rh antibodies
which can then cross the placenta (usually in a
subsequent pregnancy) to tag and destroy the
fetus RBCs. Solved by injection of anti-Rh
antibodies during, or just after, delivery of
first child, which destroy any Rh RBCs that
entered the mothers system, leading to
prevention of production of Rh antibodies in
mother and saving second fetus if he/she is Rh
as well.
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• White Blood Cells (WBCs) (fig. 13.10 p. 249)
• aka Leukocytes
• Can be granular or agranular.
• Very large in size (have a nucleus) relative to
  RBCs and platelets.
• In general, WBCs fight infection and resist
  disease by aiding in the development of immunity.
• Produced in the bone marrow from the same stem
  cells as RBCs, but follow a different
  developmental pathway.
• Two Classes and Five Types
• Class I Granular Leukocytes (filled with
  vesicles of enzymes that defend against
  invaders)
• a. Basophils release histamines that cause
  allergic reactions (clotting of area, dilation of
  vessels to allow neutrophils/monocytes to arrive).

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• b. Eosinophils attack parasites by releasing
  substances that kill them.
• c. Neutrophils attack and engulf foreign
  invaders, destroying themselves in the process
  (pus) aka phagocytes. Most numerous (60-70 of
  WBCs).
• Class II Agranular Leukocytes
• Monocytes (Macrophages) like neutrophils except
  that they possess pseudopodia (arms) that can
  extend out to capture invaders. As well, they
  may live through an encounter and even act to
  engulf dead neutrophils.
• Lymphocytes (T and B) produce antibodies that
  tag specific invaders for destruction.

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Colony-stimulating Factors (CSFs) are secreted by
living WBCs to promote the WBC developmental
pathway, leading to an increase in WBC production
(akin to EPO for RBCs).
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RBC R
Agranular WBC (Monocyte) M Granular WBC
(Eosinophil) E
M
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• Platelets (fig. 13.14 p. 254) Cell Fragments
• regulated by hormone thrombopoietin, which is
  released by the liver and/or kidneys when
  platelet counts are low.
• They lack a nucleus are fragments of
  megakaryocytes, which are derived from bone
  marrow stem cells.
• Play a major role in blood clotting when a blood
  vessel is broken, it must be repaired. In order
  for the tissue to regenerate, the blood flow
  through the cut must be stopped a clot serves
  this function.
• When a cut occurs, platelets congregate and stick
  to the irregular surface created by the cut.
• If it is a minor cut, this congregation clogs the
  hole.
• If it is a major cut, a sequence of events takes
  place

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• Platelets and damaged tissue cells release enzyme
  Prothrombin Activator, which, along with Ca2
  ions in the plasma, acts to convert the plasma
  protein prothrombin to the protein thrombin.
• The liver produces prothrombin with help from
  Vitamin K (a lack of K in diet leads to
  hemorrhagic disorders).
• Thrombin then acts as an enzyme to convert the
  plasma protein fibrinogen to fibrin, a thread
  (filament)-like protein that winds around the
  platelet congregation to stabilize it. Fibrin
  threads also capture RBCs that act to further
  plug holes in the clot.
• The fibrin web eventually contracts (like actin
  fibers) to pull the tissue back together (forms a
  scab).
• Tissue repair occurs beneath scab.
• Once repairs are complete, the clot is released
  and destroyed by the enzyme plasmin (present in
  blood).

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Ca2
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Types of Body Fluids
Name Composition
Blood Formed elements and plasma
Plasma Water, proteins, salts, etc.
Serum Plasma minus fibrinogen (after clotting)
Tissue (ECF) fluid Plasma minus proteins
Lymph Tissue Fluid in lymphatic vessels
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Capillary Exchange fig. 13.15 p. 255

• The diffusion of water, hormones, O2, nutrients,
  CO2, and other wastes occurs between the
  capillaries and the ECF (and eventually, body
  cells).
• Capillaries are very close (at most 0.2
  micrometers) to body cells, and their walls are
  one-cell thick (easy exchange).
• Water is the transfer medium for the substances
  diffusing it is the osmotic gradient that is
  followed. Thus, tonicity (Osmotic Pressure (OP))
  and Blood Pressure (BP) within capillaries are
  important to analyze.
• Ultimate goals to move O2 and nutrients from
  blood into ECF, and eventually into cells and to
  move CO2 and other wastes from ECF (originally
  from cells) into capillaries.

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• Picture two regions of the capillary the
  arterial end and the venous end.
• At the arterial end, the BP gt OP (in fact, BP
  30 mmHg and OP 21 mmHg), so there is a net
  movement (9 mm Hg) of water and its contained
  stuff (O2/nutrients) out of blood into the ECF.
  The movement of O2 and nutrients follows their
  own conc. gradients. Most water, O2, nutrients
  eventually enter cells.
• At the venous end, since the plasma proteins were
  unable to move out of the capillary, and due to
  the movement of water, OP gt BP (in fact, OP 21
  mmHg and BP 15 mm Hg). Thus, there is a net
  movement (6 mmHg) of water and its contained
  stuff (CO2/other wastes following their own
  conc. gradient) from the tissue cells/ECF into
  the capillary for eventual disposal from/by the
  body.
• The excess water (3 mmHg diff.) is taken up by
  lymph capillariesthis excess can be greater if
  the plasma proteins is lower than average.

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Nowsee the Lymphatic System
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