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WINDSOR UNIVERSITY SCHOOL OF MEDICINE . Cardio Vascular Physiology Dr.Vishal Surender.MD. objectives. Overview of the cardiovascular system Cardiac muscle and the heart The heart as a pump Excitation-contraction coupling and relaxation in cardiac muscle. FUNCTIONS OF THE CVS.

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windsor university school of medicine
WINDSOR UNIVERSITYSCHOOL OF MEDICINE

Cardio Vascular Physiology

Dr.Vishal Surender.MD.

objectives
objectives
  • Overview of the cardiovascular system
  • Cardiac muscle and the heart
  • The heart as a pump
  • Excitation-contraction coupling and relaxation in cardiac muscle
slide3

FUNCTIONS OF THE CVS

  • Rapid transport of O2 and nutrients, and removal of CO2 (H+) and waste products.
  • • Control system: distributes hormones to tissues
  • • Regulates body temperature
structure of the heart
Structure of the Heart

The heart is composed mostly of myocardium

Figure 14-7e–f

structure of the heart1
Structure of the Heart

The heart valves ensure one-way flow

slide8

The 2 pumps pump at the same time

The LV and the RV contract ~ simultaneously

The LV and the RV eject the ~ same volume of blood.

Contraction of the Heart = SYSTOLE

Relaxation of the Heart = DIASTOLE

cardiac muscle versus skeletal muscle
Cardiac Muscle versus Skeletal Muscle
  • Smaller and have single nucleus per fiber
  • Have intercalated disks
    • Desmosomes allow force to be transferred
    • Gap Junctions provide electrical connection
  • T-tubules are larger and located at Z-lines.
  • Sarcoplasmic reticulum is smaller
  • Mitochondria occupy one-third of cell volume
cardiac muscle

9

10

1

Action potential enters

from adjacent cell.

Ca2+

Ca2+

3 Na+

2 K+

ECF

1

ATP

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

3 Na+

Ryanodine

receptor-channel

Ca2+

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

Ca2+

stores

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

ATP

Ca2+

spark

Ca2+

8

Ca2+ ions bind to troponin

to initiate contraction.

6

5

7

Relaxation occurs when

Ca2+ unbinds from troponin.

Ca2+ signal

Ca2+

8

Ca2+ is pumped back

into the sarcoplasmic

reticulum for storage.

7

6

Actin

9

Ca2+ is exchanged

with Na+.

10

Na+ gradient is maintained

by the Na+-K+-ATPase.

Myosin

Relaxation

Contraction

Cardiac Muscle

Excitation-contraction coupling and relaxation in cardiac muscle

cardiac muscle1

1

Action potential enters

from adjacent cell.

ECF

1

ICF

Ryanodine

receptor-channel

SR

Sarcoplasmic

reticulum

(SR)

T-tubule

Cardiac Muscle
cardiac muscle2

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

2

SR

Sarcoplasmic

reticulum

(SR)

T-tubule

Cardiac Muscle
cardiac muscle3

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

Ca2+

T-tubule

Cardiac Muscle
cardiac muscle4

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

4

Ca2+

spark

Cardiac Muscle
cardiac muscle5

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

Ca2+

spark

5

Ca2+ signal

Cardiac Muscle
cardiac muscle6

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

Ca2+

spark

Ca2+ ions bind to troponin

to initiate contraction.

6

5

Ca2+ signal

6

Contraction

Cardiac Muscle
cardiac muscle7

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

Ca2+

spark

Ca2+ ions bind to troponin

to initiate contraction.

6

5

7

Relaxation occurs when

Ca2+ unbinds from troponin.

Ca2+ signal

Ca2+

7

6

Actin

Myosin

Relaxation

Contraction

Cardiac Muscle
cardiac muscle8

1

Action potential enters

from adjacent cell.

Ca2+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

Ca2+

stores

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

ATP

Ca2+

spark

Ca2+

8

Ca2+ ions bind to troponin

to initiate contraction.

6

5

7

Relaxation occurs when

Ca2+ unbinds from troponin.

Ca2+ signal

Ca2+

8

Ca2+ is pumped back

into the sarcoplasmic

reticulum for storage.

7

6

Actin

Myosin

Relaxation

Contraction

Cardiac Muscle
cardiac muscle9

9

1

Action potential enters

from adjacent cell.

Ca2+

Ca2+

3 Na+

ECF

1

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

Ryanodine

receptor-channel

Ca2+

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

Ca2+

stores

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

ATP

Ca2+

spark

Ca2+

8

Ca2+ ions bind to troponin

to initiate contraction.

6

5

7

Relaxation occurs when

Ca2+ unbinds from troponin.

Ca2+ signal

Ca2+

8

Ca2+ is pumped back

into the sarcoplasmic

reticulum for storage.

7

6

Actin

9

Ca2+ is exchanged

with Na+.

Myosin

Relaxation

Contraction

Cardiac Muscle
cardiac muscle10

9

10

1

Action potential enters

from adjacent cell.

Ca2+

Ca2+

3 Na+

2 K+

ECF

1

ATP

2

Voltage-gated Ca2+

channels open. Ca2+

enters cell.

ICF

3 Na+

Ryanodine

receptor-channel

Ca2+

3

Ca2+ induces Ca2+ release

through ryanodine

receptor-channels (RyR).

2

3

SR

Sarcoplasmic

reticulum

(SR)

Ca2+

stores

4

Local release causes

Ca2+ spark.

Ca2+

T-tubule

5

Summed Ca2+ Sparks

create a Ca2+ signal.

4

ATP

Ca2+

spark

Ca2+

8

Ca2+ ions bind to troponin

to initiate contraction.

6

5

7

Relaxation occurs when

Ca2+ unbinds from troponin.

Ca2+ signal

Ca2+

8

Ca2+ is pumped back

into the sarcoplasmic

reticulum for storage.

7

6

Actin

9

Ca2+ is exchanged

with Na+.

10

Na+ gradient is maintained

by the Na+-K+-ATPase.

Myosin

Relaxation

Contraction

Cardiac Muscle
cardiac muscle contraction
Cardiac Muscle Contraction
  • Can be graded
  • Sarcomere length affects force of contraction
  • Action potentials vary according to cell type.
  • Digoxin, a drug used in heart failure improves the contractility of the heart by indirectly
  • increasing intracellular Ca ++. It works by blocking the Na pump such that the Na gradient is reduced, resulting in less Ca being expelled from the myocyte and consequently intracellular Ca ++ levels increase and the contractile force is enhanced
myocardial contractile cells

PX = Permeability to ion X

PNa

1

+20

2

PK and PCa

0

-20

PK and PCa

3

0

-40

Membrane potential (mV)

PNa

-60

-80

4

4

-100

0

100

200

300

Time (msec)

Phase

Membrane channels

0

Na+ channels open

1

Na+ channels close

2

Ca2+ channels open; fast K+ channels close

3

Ca2+ channels close; slow K+ channels open

4

Resting potential

Myocardial Contractile Cells

-The cardiac action potential has 5 distinct phases (0, 1, 2, 3 and 4).

Action potential of a cardiac contractile cell

myocardial contractile cells1

PX = Permeability to ion X

+20

0

-20

0

-40

Membrane potential (mV)

PNa

-60

-80

-100

0

100

200

300

Time (msec)

Phase

Membrane channels

0

Na+ channels open

Myocardial Contractile Cells
myocardial contractile cells2

PX = Permeability to ion X

PNa

1

+20

0

-20

0

-40

Membrane potential (mV)

PNa

-60

-80

-100

0

100

200

300

Time (msec)

Phase

Membrane channels

0

Na+ channels open

1

Na+ channels close

Myocardial Contractile Cells
myocardial contractile cells3

PX = Permeability to ion X

PNa

1

+20

2

PK and PCa

0

-20

0

-40

Membrane potential (mV)

PNa

-60

-80

-100

0

100

200

300

Time (msec)

Phase

Membrane channels

0

Na+ channels open

1

Na+ channels close

2

Ca2+ channels open; fast K+ channels close

Myocardial Contractile Cells
myocardial contractile cells4

PX = Permeability to ion X

PNa

1

+20

2

PK and PCa

0

-20

PK and PCa

3

0

-40

Membrane potential (mV)

PNa

-60

-80

-100

0

100

200

300

Time (msec)

Phase

Membrane channels

0

Na+ channels open

1

Na+ channels close

2

Ca2+ channels open; fast K+ channels close

3

Ca2+ channels close; slow K+ channels open

Myocardial Contractile Cells
myocardial contractile cells5

PX = Permeability to ion X

PNa

1

+20

2

PK and PCa

0

-20

PK and PCa

3

0

-40

Membrane potential (mV)

PNa

-60

-80

4

4

-100

0

100

200

300

Time (msec)

Phase

Membrane channels

0

Na+ channels open

1

Na+ channels close

2

Ca2+ channels open; fast K+ channels close

3

Ca2+ channels close; slow K+ channels open

4

Resting potential

Myocardial Contractile Cells
myocardial contractile cells6
Myocardial Contractile Cells

Refractory periods and summation in skeletal and cardiac muscle