Transcript L4 Capillaries and Tissue Fluid

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Essentially …..
But longitudinal section not a cross section
Learning Outcomes
• Identify the structure of the capillary (extra material for
arteries and veins)
• Compare and contrast vasodilation and constriction
• Identify what the tissue fluid is made up of
• Explain how it is made and the return to the bloodstream
Four parts in arteries and veins:
central lumen
• blood flows through here
• much smaller in arteries
tunica intema (inner layer)
• made of endothelium cells, lines the lumen and reduces
friction as the blood flows through the vessel
tunica media (middle layer)
• middle layer of smooth muscle cells, collagen and elastic
fibres
• much more strong and thick in arteries, allowing them to
stretch and recoil to accommodate the surge of blood
after each contraction of the heart (creates the pulse)
Four parts in arteries and veins:
tunica media (middle layer)
• middle layer of smooth muscle cells, collagen and elastic
fibres
• much more strong and thick in arteries, allowing them to
stretch and recoil to accommodate the surge of blood
after each contraction of the heart (creates the pulse)
• smooth muscle can contract or relax, causing
vasoconstriction or vasodilation to control blood flow.
tunica externa (outer layer)
• outer layer consisting of collagen fibres and some elastin
fibres.
Vasoconstriction and vasodilation
• Change due to demands on the body
• Smooth muscle in artery can contract or relax, causing
vasoconstriction or vasodilation to control blood flow.
• For example if you are doing exercise your muscles will
be using up more oxygen – a greater blood supply will be
able to meet this demand by ARTERIOLES becoming
DILATED.
• But same volume of blood – so they need to become
constricted somewhere else ..... The intestines
• Hence the rule “don’t go swimming straight after eating a
meal – wait 2 hours!”
Capillaries
• Steady flow of blood by time reaches
small arteries/arterioles and capillaries
• Substances exchanged in capillaries
between cells and blood
Capillary Beds
• Networks of capillaries very
dense, so close that every
living cell is located close to a
capillary
• This closeness and numerous
capillaries are also important
in terms of the exchange of
materials between blood and
cells.
• So what is exactly in the
blood? What is it made up of?
Blood .....
• 3 main parts ; red blood cells
(carry O2 and some CO2),
white blood cells (next unit we
will study unit 4, fights foreign
bodies) and plasma including
platelets (needed for clotting).
• Plasma is a yellow watery
substance that is mainly made
up of water and contains
many dissolved substances
such as glucose, amino acids,
respiratory gases (mainly
CO2) plasma proteins and
useful ions (electrolytes).
Under Pressure ....
• Blood is at high pressure arriving from the arterioles to
the capillaries.
• This pressure difference causes much of the plasma in
the blood to be forced through thin walls – and is called
tissue fluid – process called PRESSURE FILTRATION
• What do you think will be in the tissue fluid?
Pressure
Filtration
Blood Plasma
Tissue Fluid (interstitial)
• Dissolved gases
• Dissolved gases
• Glucose
• Glucose
• Amino acids
• Amino acids
• Useful Ions
• Useful Ions
• Hormones
• Hormones
• Plasma proteins
• Plasma proteins
Same except very exception
(fibrinogen / albumin etc.) (fibrinogen
/ albumin etc.)
of plasma proteins
Diffusion
• High concentration to a low concentration
• Soluble food molecules (glucose/amino acids), dissolved
oxygen and useful ions diffuse down a concentration
gradient into nearby cells.
• The cells diffuse out carbon dioxide, metabolic waste
substances (such as urea) into the tissue fluid ready for
excretion (MRS GREN)
Osmosis .....
• Tissue fluid has a high water concentration (no proteins)
• Blood plasma has a low water concentration (mainly
proteins)
• Thus by osmosis;
much of the tissue
fluid returns.
• Some of the tissue
fluid does not ....
Tissue Fluid Excess
• Excess tissue fluid is absorbed by thin walled lymphatic
vessels which are found in connective tissue.
• When the tissue fluid enters the lymphatic vessel it is
termed “lymph”
Lymphatic System
• No pump like the heart –
so movement in vessels
by surrounding muscles
contracting in
breathing/moving causing
compression in these
vessels.
• Vessels join into 2
lymphatic ducts which
enter vein in arm.
Lymphatic System
• Blind ended tubes (closed at one end)
• Valves prevent backflow of lymph in larger vessels
• Specialised part of the cardiovascular system mainly as
made from blood fluid and returns to the bloodstream.
Demonstrate – when things go wrong!
• Odema – tissue fluid accumulates in in the space
between cells and blood vessels. Causes swelling
• 3 main causes ; malnutrition, blood pressure and
parasites
High blood pressure
Think about
how this will
system will be
affected ....
More arrows into tissue fluid, so more being made
than drained away by lymphatic system so
acculumates
Malnutrition
• Dietary deficiency can cause insufficient protein being
taken in by the body
• Think about pressure filtration and what a lack of plasma
proteins could cause .....
Pressure
Pressure
from
from heart
heart
Little/ no fluid returned, lymph
due
not copeOsmosis
with extra,
so gathers
to proteins
in abdomen,
kwashiorkor
Parasites - Elephantiasis
• Parasitic worm enters lymph system – when
they mature they block lymph vessels,
especially the leg lymph vessels.
• So what does that mean for excess fluid?
Build up in neighbouring tissue
Excessive growth of infected
area
Loop Da Loop
Review – Test Your Knowledge
1. Give two structural difference between an artery and a
vein
2. Give one functional difference between an artery and a
vein
3. What is tissue fluid?
4. Name a substance that passes from body cells into
tissue fluid
5. Briefly describe two methods by which tissue fluid
returns to the bloodstream
6. Briefly describe the means by which lymph in a lymph
vessel is forced along the lymphatic system
7. What structures prevent backflow of lymph?
8. Which structures enable lymph to return to the blood
circulatory system?
Review – Test Your Knowledge ANSWERS
1. Thin muscular walls in vein, thick muscular walls in artery,
valves in veins, not arteries.
2. Veins towards heart, arteries away from heart (not
deoxygenated due to pulmonary)
3. Liquid from pressure filtration in capillary, mainly made of
plasma dissolved molecules/gases – NOT proteins
4. Carbon dioxide, urea
5. Back to blood capillary via osmosis (protein causes
concentration difference) or absorbed into thin walled
lymphatic vessels, into lymph, which joins at ducts to
bloodstream
6. Periodic pressure when surrounding muscles are
contracting causes lymph to be pushed along vessel
7. Valves
8. Two lymphatic ducts
Tissue Fluid
Tissue Fluid
• What is the role of tissue fluid?
It is the fluid which allows the exchange of substances
between the blood and cells
• What substances are found in tissue fluid?
glucose, amino acids, fatty acids, salts and oxygen = all
delivered to the cells.
carbon dioxide and other waste substances = removed
from the cells.
Hydrostatic pressure
Hydrostatic Pressure
• As the capillaries are narrower than the
arterioles, a pressure builds up which forces
tissue fluid out of the blood plasma = hydrostatic
pressure.
• This pressure is resisted by:
• Pressure of the tissue fluid on the capillaries (from the
outside)
• The lower water potential of the blood (caused by
plasma proteins – too large to leave the blood)
• Overall, pressure pushes tissue fluid and small
molecules out of the capillary, leaving cells and
large proteins behind = ultrafiltration.