The Mammalian Circulatory System

1
The Mammalian Circulatory System

• A Closer Look

2
Cardiac Cycle

• Cardiac Cycle Defined
• One complete sequence of pumping and filling of
  the heart
• Systole Contraction phase of the cycle
• Diastole Relaxation phase of the cycle
• Duration of Cycle
• About .8 seconds
• This results in an average heart rate of 70
  beats/min
• Think about this. . .
• An average heart beats for 75 years without
  stopping. Can you think of a human made machine
  that could do something like this with no
  maintenance? The heart is an amazing organ!

3
Cardiac Output

• Cardiac Output depends on two factors
• Heart Rate
• Stroke Volume
• Average Stroke Volume is 75 ml (1/3 cup)
• Amount of blood the heart pumps each cycle (every
  .8 of a second)
• Total Cardiac Output 70 beats/min x 75 ml
  5,250 ml/min 5.25 liters/min
• Think of a 1 liter drink. The average heart pumps
  the equivalent of five 1 liter drinks each
  minute. It turns out that the average amount of
  blood in a person is also 5 liters. So, every
  minute, all the blood has circulated through the
  body.
• During heavy exercise this can increase five fold

4
What Causes the Heart to Beat?

• Sinoatrial Node (SA Node or Pacemaker)
• Sinus cavity or depression
• Atrial in the atrium
• Node A collection of tissue
• The SA Node is a collection of nervous tissue
  located in the wall of the right atrium that
  spontaneously creates a periodic electrical
  signal. This signal propagates through both the
  right and left atria causing the atria to
  contract.
• Atrioventricular Node (AV Node)
• A collection of nervous tissue in the wall
  between the atria and ventricles. It delays the
  signal so the atria can fully contract before
  propagating the electrical signal into the
  ventricles through the Bundle branches and
  Purkinje fibers causing the ventricles to
  contract.

5
Things to Remember About the Pacemaker

• No signal from the brain is necessary to tell
  the pacemaker to produce its regular signal. It
  will continue to send out its regular rhythmic
  signal 70 times every minute for 75 years or
  more- all on its own!
• The brain and various chemicals in the body can
  influence the pace of the pacemaker.
• Much of this is autonomic (not under conscious
  control)
• A stressful situation can cause the pace to
  increase
• Use of Heart Rate in Polygraph Tests (Lie
  Detectors)
• A dangerous situation can cause the pace to
  increase
• Fight or Flight Response
• An attractive member of the opposite sex can
  cause the pace to increase

6
Blood Vessels Circulation

• Five different kinds of vessels exist in the
  circulatory system
• Arteries Carry blood away from heart
• Arterioles Arteries divide into these smaller
  vessels that take blood to the capillaries
• Capillaries Smallest vessels in the circulatory
  system. They touch every cell in the body.
  Oxygen, carbon dioxide, nutrients, and wastes
  diffuse through the capillary walls.
• Venules Capillaries merge into these larger
  vessels
• Veins Venules merge into these even larger
  vessels. Veins return blood to the heart.

7
Blood Vessels

• Arteries
• Thickest walled vessels since they experience the
  greatest pressure in the system
• Generally not found near the skin surface
• Capillaries
• Thinnest walled vessels since molecules must
  diffuse across it.
• Only have an endothelial cell layer and a
  basement membrane.
• Veins
• Thicker walls than capillaries but thinner than
  arteries since this is a low pressure system
• Have valves to prevent backflow of blood because
  of the low pressure
• Can be found near skin surface because of their
  low pressure

8
Blood Pressure The Basics

• Blood Pressure Pressure the blood exerts against
  the vessel walls
• Due to
• Force of heart contraction
• Size of the arterioles which provide peripheral
  resistance
• Smooth muscles in the wall of the arterioles can
  relax or tighten and in turn alter blood
  pressure.
• Arteries are surrounded by walls that are very
  elastic. These elastic walls help maintain
  pressure in the system during the phase of the
  cardiac cycle in which the heart is not
  contracting (diastole).
• As the cross-sectional area of the system
  increases due to the increasing number of
  vessels- arterioles and capillaries- the pressure
  drops.

9
Measuring Blood Pressure

• Pulse
• Bulging of arteries with each heart beat. Way to
  measure heart rate. Can be detected fairly
  easily at several places
• Radial Artery On forearm, next to the wrist
• Carotid Artery In neck
• Sphygmomanometer
• Instrument for measuring blood pressure in the
  artery in the arm.
• Measures the systolic pressure (highest pressure)
  and diastolic pressure (lowest pressure) in the
  artery during a complete cardiac cycle.

10
Blood Flow in Capillaries

• At any one time only 5-10 of capillaries have
  blood flowing through them
• This way blood is used where it is needed
• Control of blood flow through capillary beds
• Smooth muscle surrounding arterioles
• Pre-capillary sphincters

11
Movement of Material In and Out of the
Circulatory System

• Occurs in the capillary
• Blood Pressure causes material to leave the
  capillary
• 85 leaves!
• By diffusion across the membrane oxygen
• By bulk flow through clefts between cells water,
  sugar, salts
• Some material doesnt leave the capillary
• Red Blood Cells
• Large proteins (plasma proteins)
• Osmotic Pressure cause material to return to
  capillary
• 85 returns this way

12
Blood

• Considered a connective tissue
• Made of two kinds of materials
• Plasma (55)
• 90 water
• Many ions
• Proteins
• Cells (45)
• Red Blood Cells (Erythrocytes)
• No nuclei nor mitochondria
• Packed with hemoglobin to transport oxygen
• White Blood Cells (Leucocytes)
• Five types
• Fight infection
• Platlets
• Pieces of cell used in clotting

13
Differentiation of Blood Cells

• Blood Cells are produced in the bone marrow
• All blood cells originate from what is known as a
  pluripotent stem cell
• Pluripotent Can become any blood cell
• The buzz in the media about stem cells is
  referring to embryonic stem cells- the original
  cells from which any cell can be derived. They
  are totipotent.
• Totipotent Can become any cell!!
• Since any cell can be derived from them the
  implications are enormous. We will talk about
  these stem cells and the issues surrounding them
  later in the course.

14
Totipotent versus Pluripotent

• Totipotency is the ability of a single cell,
  usually a stem cell, to divide and produce all
  the differentiated cells in an organism, or even
  extraembryonic tissues. For example, a plant
  cutting can be used to grow an entire plant.
  Human development begins when a sperm fertilizes
  an egg and creates a single totipotent cell. In
  the first hours after fertilization, this cell
  divides into identical totipotent cells.
  Approximately four days after fertilization and
  after several cycles of cell division, these
  totipotent cells begin to specialize.
• Totipotent is as opposed to pluripotent and
  multipotent. Totipotent cells have total
  potential. They specialize into pluripotent cells
  that can give rise to most, but not all, of the
  tissues necessary for fetal development.
  Pluripotent cells undergo further specialization
  into multipotent cells that are committed to give
  rise to cells that have a particular function.
  For example, multipotent blood stem cells give
  rise to the red cells, white cells and platelets
  in the blood.

15
Blood Clotting

• The blood is an amazing substance that carries
  with it the ability to automatically fix holes in
  the pipes that are carrying it- the blood
  vessels
• Do not learn the details- just admire the process

16
Cardiovascular Deaths

• The Cardiovascular System is a mission critical
  system. If it fails the organism dies.
• Aside from cancer the leading causes of death in
  the US are. . .
• Heart Attacks
• Strokes
• Due to Atherosclerosis
• The artery walls becomes infiltrated with
  connective tissue and lipids forming what is
  called plaque. Sometimes the artery walls even
  becomes hardened with calcium.
• Prevents blood flow which causes
• Heart attacks if it happens to arteries that
  feed the heart
• Strokes if it happens to arteries in the brain