Download Unit K * Heart Structure and Function

Heart Structure and Function
pp. 242-245
Heart Anatomy
The Heart:
• Function: circulates the blood
throughout the body
• very muscular organ about the size of a
fist.
• Surrounded by fluid & a pericardial sac
• 2 pumps (right side pumps blood to
lungs & left side pumps blood to the rest
of the body)
• Left & right sides divided by SEPTUM
• 4 chambers
• 2 smaller ATRIA (singular: ATRIUM) located on top
• 2 larger VENTRICLES located on bottom
- Left side is thicker/larger b/c it pumps to the
body
- Right side is thinner b/c it just pumps to nearby
lungs
• AV (artioventricular) VALVES
are located between atria &
ventricles
- Prevent backflow
- Right AV valve also called
TRICUSPID valve
- Left AV valve also called
BICUSPID or MITRAL valve
- CHORDAE TENDINAE are
strong fibrous strings that
support the AV valves &
keep them from inverting
• SEMILUNAR VALVES are
located between the heart &
artery
- NO chordae tendinae
Coronary arteries and veins
1. Vitally important blood vessels that
supply blood to the heart muscle
itself
2. Heart does not use the blood in its
inner chambers.
3. Arteries branch off the aorta just
above the aortic semilunar valve, and
lie on the outside of the heart.
4. Coronary veins empty into the right
atrium.
Path of Blood Through the Heart:
A. DEOXYGENATED blood enters the right atrium through the
SUPERIOR & INFERIOR VENA CAVA
B. RIGHT ATRIUM contracts, pushing blood through the TRICUSPID
VALVE & into the RIGHT VENTRICLE.
B. Right ventricle contracts, pushing blood through the PULMONARY
SEMILUNAR VALVE & into the PULMONARY TRUNK.
C. The pulmonary trunk divides into PULMONARY ARTERIES, which
take the deoxygenated blood to the capillaries of the LUNGS.
E. At the lungs, carbon dioxide diffuses out of the blood &
oxygen diffuses into it.
F. OXYGENATED blood moves into the PULMONARY
VEINS, which take to the LEFT ATRIUM
G. Left atrium CONTRACTS, pushing blood through the
BICUSPID VALVE into the LEFT VENTRICLE.
H. Left ventricle CONTRACTS, pushing blood through
the AORTIC SEMILUNAR VALVE into the AORTA
I.
Aorta divides into smaller arteries, which carry
oxygenated blood to all body tissues.
NOTE:
• Deoxygenated blood NEVER MIXES with
oxygenated blood.
• Two atria contract simultaneously, and the two
ventricles also contract simultaneously.
Heartbeat
Two phases:
1. "Lub" = closing of AV
valves.
a. atria contracting
b. ventricles relaxing
2. “Dub” = closing of the
semi-lunar valves.
a. atria relaxing
b. ventricles contracting
3. All chambers relax
Note: Valve problems – heart murmur
Control of Heart
• Heart muscle tissue can
contract on its own =
intrinsic
• Cardiac cells will
coordinate their
contractions if cells touch
Coordination of Heartbeat
• Heart has NODAL TISSUE which has characteristics
of nerve & muscle tissue
• 2 nodes:
1) SA node – sinoatrial node
- upper back wall of rt. Atrium
- Initiates heartbeat by sending out a signal
every 0.85 seconds making atria contract
- both atria contract almost simultaneously
- Called “pacemaker” because it keeps beat
regular
2) AV node – atrioventricular node
- base of right atrium
- receives signal from SA node
- sends out signals along “Bundle of His” down
septum to Purkinje fibres
- Purkinje fibres spread through ventricles
- Purkenje fibres stimulate cardiac muscles at
base of ventricles
- ventricles contract
Control by the Brain:
• MEDULLA OBLANGATA controls heart rate
• brain signals SA node through VAGUS nerve & sets
heart rate
• Regulation is autonomic (not under conscious control)
• Nervous impulses are sent via autonomic nervous
system
• Sympathetic branches tell heart to “SPEED UP!”
• Parasympathetic branches tell heart to “SLOW
DOWN!”
• Various factors (stress, oxygen levels, blood pressure)
determine how the autonomic system will affect heart
rate.