David Sadava H. Craig Heller Gordon H. Orians William K. Purves David M. Hillis Biologia.blu C

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David Sadava H. Craig Heller Gordon H. Orians
William K. Purves David M. Hillis
Biologia.bluC Il corpo umanoCirculatory
System and Blood
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Circulatory System and Blood

• Why do humans need a circulatory system?
• How have vertebrate circulatory systems evolved?
• How does the mammalian heart function?
• What are the properties of blood and blood
  vessels?
• How is the circulatory system controlled and
  regulated?

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Circulatory System and Blood - Why do humans need
a circulatory system?

• A circulatory system consists of
• a muscular pump - the heart
• a fluid - blood
• a series of conduits - blood vessels.
• Together these are called the cardiovascular
  system.

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Circulatory System and Blood - How have
vertebrate circulatory systems evolved?

• Two circulatory circuits have evolved
• pulmonary circuit - blood is pumped from the
  heart to the lungs and back again
• systemic circuit - blood travels from the heart
  to the rest of the body and back to the heart.

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Circulatory System and Blood - How have
vertebrate circulatory systems evolved?

• The closed vascular system contains
• arteries carry blood away from the heart and
  branch into arterioles that feed the capillary
  beds
• capillaries are the site of exchange between
  blood and tissue fluid
• venules drain the capillary beds and form veins,
  which deliver blood back to the heart.

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Circulatory System and Blood - How does the
mammalian heart function?

• The human heart has four chambers two atria and
  two ventricles.
• The right heart pumps blood through the pulmonary
  circuit.
• The left heart pumps blood through the systemic
  circuit.

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Circulatory System and Blood - How does the
mammalian heart function?

• Valves prevent backflow of blood
• atrioventricular valves between the atria and
  ventricles and prevent backflow when ventricles
  contract
• the pulmonary valve and aortic valve lie between
  the ventricles and the major arteries and prevent
  backflow when ventricles relax.

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Circulatory System and Blood - How does the
mammalian heart function?
The human heart and circulation (part 1)
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Circulatory System and Blood - How does the
mammalian heart function?
The human heart and circulation (part 2)
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Circulatory System and Blood - How does the
mammalian heart function?

• The right atrium receives deoxygenated blood from
  the body through large veins
• superior vena cava - blood from upper body
• inferior vena cava - blood from lower body.

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Circulatory System and Blood - How does the
mammalian heart function?

• Blood passes from the right atrium through an AV
  valve into the right ventricle.
• The atrium contracts, then the ventriclethe AV
  valve closes and blood is pumped through the
  pulmonary artery to the lungs.
• Oxygenated blood returns to the left atrium of
  the heart through the pulmonary veins.
• The ventricle fills as blood enters through AV
  valve.
• The left atrium contracts, then the ventriclethe
  aortic valve opens and blood circulates through
  the aorta.

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Circulatory System and Blood - How does the
mammalian heart function?

• In the cardiac cycle both sides of the heart
  contract at the same time first the two atria
  contract, then the two ventricles.
• Two phases
• systole - when ventricles contract
• diastole - when ventricles relax.

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Circulatory System and Blood - How does the
mammalian heart function?
The cardiac cycle
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Circulatory System and Blood - How does the
mammalian heart function?

• Blood pressure changes are measured with a
  sphygmomanometer and a stethoscope.
• Systolic value pressure needed to compress an
  artery so blood does not flow.
• Diastolic value pressure needed to allow
  intermittent flow though the artery.

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Circulatory System and Blood - How does the
mammalian heart function?
Measuring blood pressure
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Circulatory System and Blood - How does the
mammalian heart function?

• Cardiac muscle functions as a pump
• cells are in electrical contact with each other
  through gap junctions, spread of action
  potentials stimulates contraction in unison
• some cells are pacemaker cells and can initiate
  action potentials without input from the nervous
  system.

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Circulatory System and Blood - How does the
mammalian heart function?
The heart beat (part 1)
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Circulatory System and Blood - How does the
mammalian heart function?
The heart beat (part 2)
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Circulatory System and Blood - How does the
mammalian heart function?

• An electrocardiogram (ECG) uses electrodes to
  record events in the cardiac cycle.
• Large action potentials in the heart cause
  electrical current to flow outward to all parts
  of the body.
• Electrodes register the voltage difference at
  different times.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Arteries and arterioles are called resistance
  vessels because their resistance can vary
• walls have elastin and collagen that allow them
  to stretch and recoil
• smooth muscle cells in the walls allow them to
  dilate or constrict.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• When the diameter of an artery changes so does
  its resistanceblood flow changes as a result.
• Neuronal and hormonal mechanisms control the
  resistance by influencing the smooth muscle cells.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?
Anatomy of blood vessels
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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Blood pressure and flow through large arteries
  are high, and are lower through the capillaries.
• Pressure is reduced in smaller vessels because
• arterioles are highly branched
• capillaries contribute an enormous surface area.
• Capillary walls are a single layer of endothelial
  cells and have tiny holes called fenestrations.
• Capillary beds are permeable to water, ions, and
  small molecules, but not to large proteins.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?
One-way flow
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Circulatory System and Blood How is the
circulatory system controlled and regulated?

• The cardiovascular control center in the medulla
  controls heart rate and vessel constriction.
• In the carotid arteries and the aorta
• baroreceptors (stretch receptors) monitor blood
  pressure changes
• chemoreceptors send information about blood
  composition.

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Circulatory System and Blood How is the
circulatory system controlled and regulated?
Regulating blood pressure
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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Red blood cells are generated in the bone marrow.
  
• Erythropoietin, a hormone released in the kidney
  in response to hypoxia, controls red blood cell
  production.
• Red and white blood cells originate from
  pluripotent stem cells in the bone marrow.
• These cells constantly divide and can
  differentiate into a variety of blood cells.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?
Blood cells (part 1)
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Circulatory System and Blood - What are the
properties of blood and blood vessels?
Blood cells (part 2)
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Circulatory System and Blood - What are the
properties of blood and blood vessels?
Blood cells (part 3)
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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Immature red blood cells divide and produce
  hemoglobin while in the bone marrow.
• When cells are 30 percent hemoglobin the
  organelles break down and the cells enter the
  circulation.
• Cells circulate about 120 days before rupturing
  as they pass through narrow capillaries, as in
  the spleen.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Bone marrow produces megakaryocytes that break
  off cell fragments called platelets.
• Platelets initiate blood clotting when activated
  by collagen exposed in damaged blood vessels.
• They release chemical clotting factors which
  activate other platelets.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Steps in blood clotting
• cell damage and platelet activation
• inactive enzyme prothrombin converts to active
  form, thrombin
• thrombin cleaves fibrinogen and forms fibrin
• fibrin threads form mesh that clots blood and
  seals vessel.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?
Blood clotting
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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Plasma contains
• Gases
• Ions
• Nutrients
• Proteins
• Other molecules, hormones and vitamins

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Atherosclerosis hardening of the arteries.
• The endothelial lining of arteries is damaged by
  high blood pressure, smoking, diet, or
  microorganisms.
• Plaque forms at sites of damage.
• Damaged cells attract migration of smooth muscle
  cells.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Smooth muscle cells have cholesterol deposits
  that make the plaque fatty.
• Connective tissue and calcium deposits make the
  artery wall less elastic, or hardened.
• A thrombus, or blood clot, may form if platelets
  stick to the plaque.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• The coronary arteries supply blood to the heart
  muscle.
• Atherosclerosis in these arteries reduces blood
  flow marked by chest pain and shortness of
  breath.
• Coronary thrombosis if a thrombus forms in a
  coronary artery it can lead to a heart attack, or
  myocardial infarction.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• An embolus is a piece of a thrombus
• it may cause an embolism if it lodges in a blood
  vessel.
• if the embolism is in the brain the cells fed by
  that artery will die - a stroke.

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Circulatory System and Blood - What are the
properties of blood and blood vessels?

• Causes of atherosclerosis
• genetic predisposition
• age
• environmental risk factors (high-fat diet,
  smoking, sedentary lifestyle)
• medical conditions (hypertension, obesity,
  diabetes).

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Circulatory System and Blood - What are the
properties of blood and blood vessels?
Atherosclerotic plaque