Transcript Ch49_Lecture

49
Circulatory Systems
49 Circulatory Systems
• 49.1 Why Do Animals Need a Circulatory
System?
• 49.2 How Have Vertebrate Circulatory
Systems Evolved?
• 49.3 How Does the Mammalian Heart
Function?
• 49.4 What Are the Properties of Blood and
Blood Vessels?
• 49.5 How Is the Circulatory System
Controlled and Regulated?
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.
49.1 Why Do Animals Need a Circulatory System?
Some animals do not need circulatory
systems:
• Single-celled organisms exchange
directly with the environment.
• Structures and body shapes allow
exchange between cells and the
environment.
Example: gastrovascular cavities
49.1 Why Do Animals Need a Circulatory System?
Larger animals must use circulatory
systems to deliver nutrients and remove
wastes.
Extracellular fluid consists of:
• Fluid in the circulatory system (blood
plasma).
• Fluid around the cells (interstitial fluid).
49.1 Why Do Animals Need a Circulatory System?
In an open circulatory system
extracellular fluid:
• Combines with the fluid of the
circulatory system
• Squeezes through intercellular
spaces when the animal moves
Fluid returns to the heart through ostia
or open vessels.
Figure 49.1 Circulatory Systems (Part 1)
49.1 Why Do Animals Need a Circulatory System?
In a closed circulatory system blood
is kept separate from the interstitial
fluid.
Blood is pumped through the vascular
system by one or more hearts.
Figure 49.1 Circulatory Systems (Part 2)
Videos:
• Hemolymph circulation (fruit fly)
• Circulation in a tadpole
Advantages of closed circulatory systems:
• Faster transport through vessels.
• Blood can be directed to specific
tissues.
• Specialized carriers can travel in the
vessels and transport hormones or
nutrients to specific sites.
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.
The closed vascular system contains:
• Arteries: carry blood away from the
heart and branch into arterioles that
feed the capillary beds.
• Capillaries: the site of exchange
between blood and tissue fluid.
• Venules: drain the capillary beds and
form veins, which deliver blood back
to the heart.
49.2 How Have Vertebrate Circulatory Systems Evolved?
Fish hearts have two chambers:
• Atrium: receives blood from the
body.
• Ventricle: receives pumped blood
from the atrium and sends it to the
gills.
Blood from the gills collects in the
aorta and is distributed throughout
the body.
Fish Heart
49.2 How Have Vertebrate Circulatory Systems Evolved?
Lungfish have adapted to
breathe in air as well as
water.
A lung formed from the gut
functions in air.
A divided atrium separates
blood into pulmonary and
systemic circuits—it can
receive blood from either
the lung or other tissues.
Lungfish Heart
49.2 How Have Vertebrate Circulatory Systems Evolved?
Amphibians have three-chambered
hearts.
A ventricle pumps blood to the lungs
and body.
One atrium receives oxygenated blood
from the lungs, a second atrium
receives blood from the body.
The ventricle directs the flow to the
pulmonary or systemic circuit.
Amphibian Heart
49.2 How Have Vertebrate Circulatory Systems Evolved?
Reptiles have three- or fourchambered hearts and two aortas:
• The left aorta receives oxygenated
blood from the left side of the
ventricle and delivers it to the body.
• The right aorta can receive blood
from either side of the ventricle.
Reptilian Heart
49.2 How Have Vertebrate Circulatory Systems Evolved?
The reptilian ventricle is partly divided
by a septum.
When the animal is breathing, blood
flows to the pulmonary circuit.
When the animal is not breathing,
blood flows to the systemic circuit.
49.2 How Have Vertebrate Circulatory Systems Evolved?
Crocodilians have two ventricles, each
with an aorta.
The aortas are connected to each
other and the amount of blood going
to either circuit can be altered.
Blood is directed to a circuit by
changes in resistance.
Crocodilian Heart
Birds and mammals:
4-chambered hearts and separate
pulmonary and systemic circuits with
the following advantages:
• Systemic circuit always receives blood
with higher O2 content.
• Gas exchange is maximized.
• Circuits can operate at different
pressures.
Bird and Mammalian Heart
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.
Valves prevent backflow of blood:
• Atrioventricular valves lie 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.
Figure 49.2 The Human Heart and Circulation
Anatomy PPT: Blood Flow, circulation
Figure 49.2 The Human Heart and Circulation
The Vena Cavae:
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
Rt atrium...then what?
Blood passes from the right atrium
through an AV valve into the right
ventricle.
The atrium contracts, then the
ventricle—the 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 an AV valve.
The left atrium contracts, then the
ventricle—the aortic valve opens and
blood circulates through the aorta.
Systole & Diastole
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
Figure 49.3 The Cardiac Cycle
Video:
• Human heart BEATING!!!!
Practice Drawing it!!
Figure 49.3 The Cardiac Cycle (Part 2)
Brain Break!
49.3 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.
Figure 49.4 Measuring Blood Pressure
Photo 49.6 Blood pressure being measured with a sphygmomanometer and stethoscope.
PACEMAKER CELLS
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.
49.3 How Does the Mammalian Heart Function?
The primary pacemaker cells are in the
sinoatrial node.
The resting membrane potential of
these cells is less negative and not
stable so that cells gradually reach
threshold.
Action potentials are broader and
slower to return to resting potential.
49.3 How Does the Mammalian Heart Function?
Ion channels in pacemaker cells are
different from other cardiac cells:
• Na+ channels are more open, so
membrane potential is less negative.
• The action potential of pacemaker
cells is due to voltage-gated Ca2+
channels, which open more slowly
than Na+ channels—changes shape
of action potential.
49.3 How Does the Mammalian Heart Function?
The unstable resting potential of
pacemaker cells is due to activity of
cation channels.
Pacemaker cells have channels that
are more permeable to Na+ than to
K+.
Na+ enters cells more easily than K+
leaves, so resting membrane
potential becomes less negative.
Figure 49.5 The Autonomic Nervous System Controls Heart Rate
49.3 How Does the Mammalian Heart Function?
The nervous system controls heart
rate by influencing resting potential:
• Norepinephrine from sympathetic
nerves increases permeability of
Na+/K+ and Ca2+ channels.
• The resting potential rises more
quickly and action potentials are
closer together.
49.3 How Does the Mammalian Heart Function?
• Acetylcholine from parasympathetic
nerves increases permeability of K+
and decreases that of Ca2+ channels.
• The resting potential rises more
slowly and action potentials are
farther apart.
49.3 How Does the Mammalian Heart Function?
Heart muscle contraction is
coordinated:
• An action potential is generated in
the sinoatrial node.
• The action potential spreads through
gap junctions in the atria and they
contract together, but it does not
spread to the ventricles.
49.3 How Does the Mammalian Heart Function?
The action potential in the atria
stimulates the atrioventricular node.
The node consists of non-contracting
cells that send action potentials to the
ventricles via the bundle of His.
The bundle divides into right and left
bundle branches that run to the tips
of the ventricles.
49.3 How Does the Mammalian Heart Function?
From the tip, fibers spread throughout
the ventricles and are called Purkinje
fibers.
A contraction spreads rapidly and
evenly throughout the ventricles.
The delay between the contraction of
atria and ventricles ensures proper
blood flow.
Figure 49.6 The Heartbeat (Part 1)
Figure 49.6 The Heartbeat (Part 2)
49.3 How Does the Mammalian Heart Function?
Ventricular muscle fibers contract for
much longer than skeletal muscle
fibers.
Their extended action potential is due
to a longer opening of voltage-gated
Ca2+ channels, and increased
availability of Ca2+ to stimulate
contraction.
Figure 49.7 The Action Potential of Ventricular Muscle Fibers
49.3 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.
49.3 How Does the Mammalian Heart Function?
Wave patterns of an electrocardiogram
are labeled: letters correspond to an
event:
• P: Depolarization of the atria
• Q,R, and S: Depolarization of the
ventricles
• T: Relaxation and repolarization of
the ventricles
Figure 49.8 The Electrocardiogram
49.4 What Are the Properties of Blood and Blood Vessels?
Blood is a connective tissue made of
cells in a liquid extracellular matrix,
called plasma.
The packed-cell volume or hematocrit
is the part of the blood made up of
cells.
Most of the cells are erythrocytes, or
red blood cells, that transport gases.
49.4 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.
Hypoxia-inducible factor 1 (HIF-1) is a
transcription factor‘—in the kidney it
activates the gene for erythropoietin.
49.4 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.
49.4 What Are the Properties of Blood and Blood Vessels?
Bone marrow also 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.
Photo 49.16 Human red bone marrow. LM, silver stain.
Photo 49.17 Human red blood cells magnified 400×.
Photo 49.18 Red blood cells in glomerular capillary; erythroblast with cytoplasmic organelles. TEM.
Figure 49.10 Blood Clotting (Part 1)
49.4 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.
Figure 49.10 Blood Clotting (Part 2)
Photo 49.19 Blood clot containing red blood cells, platelets, and fibrin. SEM.
Plasma contains:
• Gases
• Ions
• Nutrients
• Proteins
• Other molecules: hormones and
vitamins
Photo 49.15 Human blood; right, whole blood; left, centrifuged into serum and red blood cells.
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.
Photo 49.1 Human artery. LM, H&E stain, 26×.
Photo 49.2 Human arteriole. LM, 160×. H&E stain.
Arrrrrrrrrtery diameter
When the diameter of an artery
changes so does its resistance—
blood flow changes as a result.
Neuronal and hormonal mechanisms
control the resistance by influencing
the smooth muscle cells.
Figure 49.11 Anatomy of Blood Vessels (Part 1)
Figure 49.11 Anatomy of Blood Vessels (Part 2)
Videos:
• Blood vessel formation
• Blood flow in humans
49.4 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.
49.4 What Are the Properties of Blood and Blood Vessels?
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.
Figure 49.12 A Narrow Lane
49.4 What Are the Properties of Blood and Blood Vessels?
Starling’s forces are two opposing
forces that maintain water balance in
the capillaries:
• Blood pressure: forces water and
small solutes out.
• Osmotic pressure: created by the
large molecules that cannot leave
(also called colloidal osmotic
pressure).
49.4 What Are the Properties of Blood and Blood Vessels?
Blood pressure is higher at the arterial
end of the capillary bed and drops at
the venous end.
Osmotic pressure is constant along the
capillary.
If blood pressure is higher than the
osmotic pressure, fluid leaves the
capillary—if blood pressure is lower,
fluid returns to the capillary.
Figure 49.13 Starling’s Forces (Part 1)
Figure 49.13 Starling’s Forces (Part 2)
49.4 What Are the Properties of Blood and Blood Vessels?
Edema is an accumulation of fluid in
the extracellular space and can be
caused by:
A fall in blood protein levels are due to
disease.
Histamine release: increases capillary
permeability, relaxes smooth muscle
in arterioles and raises blood
pressure in the capillaries.
49.4 What Are the Properties of Blood and Blood Vessels?
Bicarbonate ions (HCO3–) converted
from CO2 contribute to the osmotic
force that draws water into the
capillary.
The increased concentration of HCO3–
ions at the venous end raises the
osmotic pressure.
Capillaries
Capillaries in different tissues are
highly selective for the sizes of
molecules that can pass.
The blood–brain barrier refers to the
high selectivity of brain capillaries,
which do not have fenestrations.
Photo 49.7 Blood vessels and mast cells in vascular bed just below skin surface of rat. LM.
Photo 49.8 Human red blood cells, in capillary lined with simple squamous epithelium. LM, 160×.
Veins
Veins are called capacitance vessels
because they are very expandable
and blood will accumulate in them.
Blood returning from below the heart is
assisted by skeletal muscle
contractions that squeeze the veins.
One-way valves in the veins prevent
backflow.
Figure 49.14 One-Way Flow
Pump U
Up!
Photo 49.3 Frog vein filled with red blood cells. LM, Giemsa stain, 100×.
Photo 49.4 Human vein, LM, trichrome stain, 64×.
Photo 49.5 Normal red blood cells in a human venule. SEM, 3500×.
49.4 What Are the Properties of Blood and Blood Vessels?
The Frank–Starling law: a property of
cardiac muscle cells that increases
cardiac output.
These cells contract more forcefully if
stretched by an increase in the
volume of returning blood.
Both leg muscle contractions and
breathing actions help return venous
blood to the heart.
49.4 What Are the Properties of Blood and Blood Vessels?
The lymphatic system returns
interstitial fluid to the blood.
When the fluid enters the vessels it is
called lymph.
Lymphatic capillaries ultimately merge
into two thoracic ducts; they empty
into veins in the neck.
49.4 What Are the Properties of Blood and Blood Vessels?
Lymph nodes along the vessels are
the site of lymphocyte production.
Lymph nodes remove microorganisms
and foreign materials by
phagocytosis, and act as filters.
Photo 49.9 Diffuse lymph tissue from the esophagus of a frog. LM, H&E stain.
Photo 49.10 Diffuse lymph nodule in rat trachea. LM, H&E stain.
Photo 49.11 Human lymph node: pale follicular (germinal) centers around periphery in cortex. LM.
Photo 49.12 Human tonsil with underlying lymphoid tissue; two prominent lymphoid follicles. LM.
Photo 49.13 Human spleen with lymphoid nodule surrounded by red pulp. LM, H&E stain.
Photo 49.14 Plasma cells and lymphoblasts in medulla of rat lymph node. TEM.
49.4 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.
49.4 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.
49.4 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.
49.4 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.
49.4 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
Figure 49.15 Atherosclerotic Plaque
49.5 How Is the Circulatory System Controlled and Regulated?
Autoregulatory mechanisms are
local actions in the capillary bed that
cause the arterioles to constrict or
dilate.
The nervous and endocrine systems
respond to changes in the capillary
beds by changes in:
• Breathing rate, heart rate, and blood
distribution
49.5 How Is the Circulatory System Controlled and Regulated?
Blood flow from an arteriole to a
capillary bed can be shut off by
smooth muscle precapillary
sphincters.
Autoregulation depends on smooth
muscle being sensitive to its
chemical environment.
49.5 How Is the Circulatory System Controlled and Regulated?
Autoregulation matches local flow to
local need.
Hyperemia: Low O2 and high CO2
levels cause smooth muscle to relax,
increasing blood supply and bringing
in O2 and decreasing CO2.
Figure 49.16 Local Control of Blood Flow
49.5 How Is the Circulatory System Controlled and Regulated?
Local changes contribute to changes
in central blood pressure and
composition.
Endocrine and nervous systems
respond to the changes to return
blood pressure and composition to
normal.
49.5 How Is the Circulatory System Controlled and Regulated?
Arteries and arterioles are innervated
by the sympathetic division of the
autonomic nervous system.
The neurotransmitter norepinephrine
causes arterioles to contract.
In skeletal muscle, acetylcholine
causes arterioles to relax and
increases blood flow to the muscle.
49.5 How Is the Circulatory System Controlled and Regulated?
Hormones regulate arterial pressure:
• Epinephrine: released from adrenal
medulla in response to a fall in
arterial pressure or the fight-or-flight
response: arterioles contract.
• Angiotensin: produced when blood supply to the
kidneys fails: reduces flow to peripheral tissues
and directs it to essential organs.
49.5 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.
Figure 49.17 Control of Blood Pressure through Vascular Resistance
49.5 How Is the Circulatory System Controlled and Regulated?
Increased activity of the stretch
receptors signals rising blood
pressure:
• Response: Inhibition of sympathetic
nervous system and increased
parasympathetic input.
• Result: Heart slows and arterioles
dilate, blood pressure falls.
49.5 How Is the Circulatory System Controlled and Regulated?
Chemoreceptors send feedback to the
cardiovascular control center:
• In the medulla, chemoreceptors are
activated by rising arterial CO2 levels.
• In the aorta and carotid arteries
chemoreceptors respond to falling
arterial CO2 levels.
Figure 49.18 Regulating Blood Pressure
49.5 How Is the Circulatory System Controlled and Regulated?
Adaptations such as greater blood
volume and higher concentrations of
hemoglobin and myoglobin allow
marine mammals to stay underwater.
The diving reflex slows the heart and
constricts major blood vessels going
to all but critical tissues.
Hypometabolic: having a metabolic
rate lower than a basal rate.
Figure 49.19 Elephant Seal Diving Ability (Part 1)
Figure 49.19 Elephant Seal Diving Ability (Part 2)
Figure 49.19 Elephant Seal Diving Ability (Part 3)