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The Circulatory System
The function of the circulatory system is to transport nutrients, oxygen, CO2, wastes and
heat. 70 kg person has 96000 km of vessels and 60 trillion cells
Blood vessels
Forms a continuous, closed system. Blood always flows in the same direction. There are
three types of vessels; veins, arteries and capillaries.
*be able to compare – use a table
1. Arteries – takes blood away from the heart, are wide, made up of elastic layer with
circular muscles, and is smooth on the inside. Arteries expand and contract with the flow
of blood – elastic. Have the greatest pressure on them – highest blood pressure. Have
narrow lumen to maintain pressure. Arteries branch off into smaller vessels called
arterioles which eventually lead to (artery cut pulses out – can travel 30 cm/sec)
2. Capillaries –made up of flat cells called squamous cells gaps between the walls. Walls
are only one cell thick. Only vessels that are permeable, so dense that no cell is more
than one cell away from a cap. (every cell in the liver is in direct contact, why?) Have a
narrow lumen to fit into small places. So narrow that RBC are squashed as they pass
through. Pressure greatly reduced. Caps eventually branch into venules and then into
(have about 96000 km of them, are easily damaged – bruising, red eyes, travel 0.026
cm/sec)
3. Veins – return blood to the heart. Have thinner walls than arteries, less elastic. Wide
lumen to decrease resistance to flow. Don’t have internal muscles but uses skeletal
muscles. Many have valves which prevent backflow. Vein cuts ooze, varicose veins,
stretching in the morning, soldiers fainting standing too long
Not enough blood to fill all vessels all the time. The body is constantly redirecting blood
to where it is needed. No area is completely without blood but some have reduced flow.
Caps have sphincter muscles to allow this redirecting. At any one time, only 5-10% of
caps have blood flowing through them but all cells are being feed.
Three circulatory systems though all connected; pulmonary system, systemic system and
coronary system – arteries supply heart muscle with oxygen and nutrients.
Lab on strength of arteries vs veins page 214 and precision of manual vs electronic
pulse meters p213 of tiger book.
The Heart Weighs about 300 g, weight of an apple, located just left of center,
surrounded by pericardium membrane and fluid. ** be able to draw and show the
relative thicknesses of the walls
Addition to heart dissection – page 212 tiger text
Deoxygenated blood from the body enters through the superior and inferior vena cava
into right atrium. (atria→plural). When full, A.V. valve opens, atrium contracts and
blood forced into right ventricle. When ventricle full, A.V. closes and S.L valve opens
→ ventricle contracts and forces blood out of heart in the pulmonary artery into the
pulmonary system. Artery divided into two, left and right and goes to lungs. They
rebranch into arterioles and capillaries. It’s in the caps that oxygen and CO2 are
exchanged. Oxygenated blood returns to heart via the pulmonary vein on left side to left
atrium. The pressure it exerts causes the AV valve to open, left ventricle, SL valve and
out via the aorta. The aorta arches and branches up to the heart and the coronary system,
and to the rest of the body through the systemic system. Aorta the thickest artery with the
greatest pressure.
35-40 seconds for one trip while watching TV, 10 seconds when exercising, heart
uses 80% of oxygen it gets while the body uses only 25% (efficiency and/or
need?)hole in the septum.
Heartbeat – ventricles contract together, atria contract together, systole – period when
ventricles contract, SL valves open and AV valves closed, Diastole – period when
ventricles relaxing and filling up and atrium contracting, SL closed, AV open. Together,
the whole process is called the cardiac cycle.
inverse relationship between size and heart rate – elephant is 25/min while shrew is
600/min, lub-dub is sound of valves closing. Rheumatic fever valves damaged,
blood leaks back – ph-t-t-t sound. Body compensates by beating faster.
Control of heart’s tempo
Heart muscle is myogenic – can contract on its own, independent or nervous or hormonal
stimulation. But nerves and hormones do affect the heart beat. Beats about 70/min
pumping about 5-6 liters of blood. The stimulus for pumping is embedded in the wall of
the right atrium. It is a specialized tissue called the pacemaker (or sino-atrial node) It
establishes the rhythm of the heart by sending impulses to make the atria contract. (also a
set of tissue, called Purkinje fibers, in the ventricles that pick up the stimulus and
get the ventricles to contrite – need to be that split second behind the atria) If
impulses become disordered, random → ventricular fibrillation or V-fib. A
temperature increase of 1 C raises the heart rate 10 beats/min, which is why fever
gives a high heart rate.
The heart speeds up or slows down through involuntary control. The two main ways are
through nerves or hormones. The sympathetic nervous system causes the heart to speed
up. The parasympathetic system will show the heart back down. One of many examples
of antagonistic pairs in the body. The hormone adrenalin or epinephrine will speed up the
heart and can work with the sympathetic system.
Both systems are controlled by the brain – the medulla oblongata. The medulla will
monitor the blood and respond to changes in pH and CO2 levels. As exercise increases,
there will be a buildup of CO2 and lactic acid from cellular respiration, which will signal
the medulla to speed up the heart.
Blood pressure
The surge of blood through the arteries can be felt at certain pressure points – called the
pulse. Arteries should expand and contract with eh surge of the blood and is expressed as
a fraction 120/80. The top number is systole and the bottom is diastolic pressure.
Nerves and hormones can also cause the vessels to vasodilate and vasoconstriction.
Thrombosis – clot in blood vessels Embolus – moving clot Myocardial infarction –
heart attack Blushing is vasodilatation of the caps in face Hypertension –Shock or
severe bleeding can cause low blood pressure . Pressure receptors in the walls of the
aorta and carotid arteries inform the brain. Ca2+ ions needed for heart muscle to
contract and vessels constrict. During heart attack, it is necessary to keep vessels
open so give calcium blockers
Human body DVD program 7 #3 heart disease
The Blood
The blood is composed of four main substances; plasma (about 55%), erythrocytes,
leukocytes and platelets
a) Plasma – about 90% water, good solvent. Contains different types of plasma proteins
like fibrinogen and immunoglobin proteins (makes antibodies) and LDL and HDL.
Carries nutrients, wastes (urea) gases such as oxygen and CO2, enzymes, hormones and
heat.
b) Erythrocytes – (RBC) most numerous cells in blood (about 90%). 4.5 million in
women, 5 million in men, will increase at higher altitudes, disk shaped, life span of
about 120 days, biconcave and flexible – form = function. No nucleus, red due to
haemoglobin –Hb – a protein pigment that has iron as one of its components. Produced
by stem cells in red bone marrow (ribs, vertebrae, breastbone). Controlled by negative
feedback. Stem cells are pluripotent – not completely differentiated, can only become
any other blood cells.
Hb has an affinity to oxygen to form oxyhemoglobin – lacks of oxygen for 3-5
minutes leads to cell death. Hb has a greater affinity to CO – about 230 times
greater. RBC are broken down by spleen and liver. Iron stored in liver to make
new RBC. Anemia – hemorrhagic, pernicious (lack of vitamin B), iron-deficiency,
septicemia (infection)
Sickle-cell anemia – improper formation of RBC – a genetic defect, cells are fragile can
lead to jaundice. Jaundice – old RBC not cleared away due to malformation of liver.
c) Leukocytes – (WBC) fewer in number than RBC. Have a nucleus, can leave the
capillaries, produced in bone marrow but modified in lymph nodes, spleen and thymus
gland. (can live from 24 hours to 10 years)
Two main types – phagocytes and lymphocytes. Phagocytes or macrophages, can leave
the blood to do their job, using phagocytosis. Are non-specific to diseases – attack any
foreign antigen. Some produce histamines, which increase inflammation and heparin
to balance clotting aspect. Many replaced at a rate of 100,000,000,000/day.
Lymphocytes are made in bone marrow but migrate to nodes etc to be modified as they
are* specific to foreign antigens.*
d) Platelets – responsible for blood clotting.
Pluripotent – ability to develop into any type of cell. Stem cells are pluripotent to some
degree (I think that is the difference) Stem cells found in bone marrow are semi –
pluripotent in that they can made any blood cells when stimulated. As few as 30 bone
marrow stem cells can repopulate bone marrow – leukemia. Embryonic stems cells
should be completely pluripotent.
Serum – blood plasma without clotting factor; interstitial fluid similar to blood
plasma except it has fewer proteins – cap walls are not very permeable to proteins.
HL
A wound causes platelets and cells to be damaged which release chemicals called clotting
factors. This causes Ca2+ and prothrombin (inactive form found in blood) to join to form
thrombin, an enzyme. Thrombin catalyses the conversion of soluble fibrinogen into
fibrous protein fibrin. This will form a net to capture RBC. Vitamin K is coenzyme
needed for thrombin. Haemophilia – missing one or more of the clotting factors – is
genetic meaning..