Cardiovascular SystemUnit 10

Structure and Function

Three parts: Heart Blood vessels Blood

Function = transports oxygen, nutrients, cell wastes, hormones, etc., distributes body heat

Anatomy of the Heart

Approximately the size of a fist, hollow, cone-shaped

Inside the bony thorax between the lungs

Pointed apex is angled toward left hip, rests on the diaphragm at the same level as the fifth intercostal space

Broader base points towards right shoulder blade, beneath second rib

Anatomy of the Heart

Anatomy of the Heart

Enclosed by a double sac of serous membrane = pericardium

The thin epicardium hugs the external surface of the heart and is part of the heart wall

Myocardium = thick middle layer made of thick bundles of cardiac muscles twisted into ring-like arrangements, this is the layer that actually contracts

Endocardium = thin inner layer, lubricated sheet of endothelium, continuous with the linings of the blood vessels leaving and entering the heart, allows blood to flow more smoothly

Pericarditis = inflammation of the pericardium, causes pericardial layers to stick to each other, forming painful adhesions that interfere with heart movements

Anatomy of the Heart

Anatomy of the Heart

Four chambers Atria = top chambers, receive blood

Right atrium = receives from body, deoxygenated blood

Left atrium = receives from lungs, oxygenated blood Ventricles = bottom chambers, pump blood out

of heart Left ventricle = pumps to body, oxygenated blood Right ventricle = pumps to lungs, deoxygenated

blood Interventricular and interatrial septum =

divides heart longitudinally

Anatomy of the Heart

Major Heart Vessels

Vena cava = brings blood from body to right atrium Superior vena cava = blood from above the

heart Inferior vena cava = blood from below the heart

Pulmonary veins = bring blood from lungs to left atrium

Aorta = large artery that carries blood from left ventricle to rest of body

Pulmonary arteries = carry blood from right ventricle to lungs

Major Heart Vessels

Heart Valves

Allow blood to flow in only one direction: atria ventricles arteries

Atrioventricular valves (AV) = between atrial and ventricular chambers Bicuspid valve= two cusps (flaps of endocardium),

between left atrium and ventricle, also known as mitral valve

Tricuspid valve = three cusps, between right atrium and ventricle

Chordae tendineae – “heart strings,” anchor cusps to ventricles, help keep them closed

Semilunar valves = base of the two large arteries Pulmonary semilunar valve = base of pulmonary artery Aortic semilunar valve = base of aorta

Heart Valves

How does the heart beat?

Double pump – right side = pulmonary (lungs), left side = systemic (rest of body)

Both atria contract together and both ventricles contract together

How does the heart beat? Cardiac cycle = start of one heart beat

to the initiation of the next Heart usually beats ~75 times per minute Cardiac cycle usually lasts ~0.8 seconds

Systole = heart contraction Diastole = heart relaxation Three main phases of cardiac cycle:

1. Mid-to-late diastole 2. Ventricular systole 3. Early diastole

How does the heart beat?

1. Mid-to-late diastole: Heart in complete relaxation pressure in heart is low, blood is

flowing passively into the atria Semilunar valves are closed AV valves are open The atria contract and force the blood into the ventricles

2. Ventricular systole: The pressure building in the ventricles closes the AV valves, then

opens the semilunar valves Blood rushes out of ventricles into arteries Atria are relaxed during this phase and starting to fill up with

blood again 3. Early diastole:

Ventricles relax and semilunar valves close to prevent backflow ventricles are completely closed chambers, pressure drops

When the pressure drops low enough, the AV valves open

How does the heart beat? Cardiac muscles can contract spontaneously,

even if all nervous connections are severed. Different rhythms in different areas of the

heart atria = 60 beats/minute, ventricles = 20-40 beats/minute needs unifying control

Two main systems: intrinsic conduction system (nodal system) and autonomic nervous system

Autonomic nervous system acts like “brakes” or “gas pedal” decrease or increase heart rate

How does the heart beat? Intrinsic conduction system is built into the heart

tissue – found nowhere else in the body Causes heart depolarization from atria to ventricles Enforces rate of ~75 beats per minute Path of signal:

Sinoatrial (SA) node – right atrium “pacemaker” Atrioventricular (AV) node – junction of atria and

ventricles Atrioventricular (AV) bundle (bundle of His) – junction of

atria and ventricles Right and left bundle branches – to right and left of

bundle of His Purkinje fibers – spread throughout ventricle muscle walls

Warm up video questions – Copy on your own paper

1. What is the new craze sweeping the nation? 2. “Out through your ______, in through your

________.” 3. What are two signs that you’re “not

circulating right?” (These are mentioned at different times in the video).

4. What are the four parts of the heart mentioned in the song?

5. What does circulation take to your cells? 6. What does circulation get rid of for your cells? 7. What jobs do red and white blood cells have? http://www.youtube.com/watch?v=5tTkxYeNF9Q

Electrocardiogram (ECG)

Traces the flow of electric current through the heart

3 waves: P wave – small, signals depolarization of

atria before they contract QRS complex – the “peak,” symbolizes

depolarization of ventricles before they contract, repolarization of atria is generally hidden by this complex

T wave – repolarization of ventricles

Electrocardiogram (ECG)

Blood Vessels

Blood circulates through the body in a closed transport system “vascular system”

Leaves the heart in large arteries Moves to smaller arteries arterioles

capillary beds Capillary beds drain into venules small

veins veins leading to heart Arteries, arterioles, veins, and venules =

transporting blood Capillaries = where the exchange between

tissue cells and blood occur

Blood Vessels

Blood Vessels

Blood vessels (except for capillaries) have three coats, or tunics

Tunica interna – Lines the interior of the vessels, thin layer of endothelium resting on loose layer of connective tissue, cells fit close together to make slippery surface that decreases friction as blood flows through

Tunica media – bulky middle coat, smooth muscle and elastic tissue, controlled by sympathetic nervous system, changes diameter of blood vessels and therefore, blood pressure

Tunica externa – outermost layer, fibrous connective tissue, supports and protects vessels

Blood Vessels

Blood Vessels

Arteries tend to have thicker walls than veins Some larger arteries even have elastic laminae,

complete sheets of elastic tissue within their tunica media

Arteries must be able to expand as blood is forced into them and relax when it leaves during diastole walls must be strong and stretchy to handle continuous changes in pressure

Veins have thinner walls and have much lower pressure Sometimes have to work against gravity Lumens are larger than those in arteries Valves to prevent backflow of blood Skeletal muscles help “milk” blood back to heart Inhaling also causes a drop in pressure that causes the

big veins near the heart to expand and fill

Blood Vessels

Capillary walls are just one cell layer thick easier to make exchanges between blood and tissue cells

Capillary beds = interweaving networks of tiny capillary vessels

Microcirculation – flow of blood from arteriole capillary bed venule

Two parts to capillary bed: Vascular shunt – vessel that connects to

arteriole and venule at opposite ends of bed True capillaries – actual exchange vessels,

10-100 per bed

Blood Vessels

Capillaries form such an intricate network so that no substance has to diffuse very far to enter or leave a cell

Space between tissue cells and capillaries is filled with interstitial fluid

Substances move according to their concentration gradients high to low

Can take one of four “routes:” 1. Diffuse directly across plasma membrane if they are lipid

soluble (ex. Respiratory gases) 2. Endocytosis or exocytosis – moving within vesicles 3. Fluid can flow through intercellular clefts (gaps between

cells) 4. Small solutes and fluids can move through fenestrated

capillaries, which are usually found where absorption or filtration is a priority (ex. Intestine, kidneys)

Only substances that cannot pass through these “routes” will remain in capillaries (ex. Proteins, blood cells)

Important arteries

Ascending aorta Aortic arch Thoracic aorta Abdominal aorta Right and left

common iliac arteries Brachiocephalic artery Right and left

subclavian arteries Right and left

common carotid arteries

Important Veins

Superior and inferior vena cava Brachiocephalic vein Internal and exterior jugular veins Vertebral vein Subclavian vein Basilic vein Cepalic vein Hepatic portal vein Hepatic veins Renal veins Internal, external, and common

iliac veins Great saphenous vein (longest in

body) Femoral vein Fibular vein Anterior and posterior tibial veins

Special Circulations – Brain

Need continuous blood supply to the brain Two pairs of arteries: internal carotid arteries and vertebral

arteries Internal carotid arteries go through neck and temporal

bone, then divides into anterior and middle cerebral arteries Vertebral arteries go through base of neck then join inside

the skull to form basilar artery, which serves the brain stem and cerebellum. It then divides again to form the posterior cerebral arteries.

Anterior and posterior blood supplies are connected by small communicating arterial branches a complete circle of connecting blood vessels called the circle of Willis

Circle of Willis protects brain by providing more than one route for blood to reach the brain in case of clots or impaired blood flow

Special Circulations - Brain

Special Circulations – Hepatic Portal

Drains blood from digestive organs, spleen, and pancreas and delivers it to the liver through the hepatic portal vein

Liver processes the nutrients from food to help maintain the balance of glucose, fat, and protein concentrations in the blood some get removed for storage

Liver is drained by hepatic veins inferior vena cava

Unique because normally arteries capillaries veins, but in this case, veins feed the liver circulation

Special Circulations – Hepatic Portal

Special Circulations - Fetal Nutrient, excretory, and gas exchanges all happen

through placenta because lungs and digestive system are not yet functioning.

Nutrients and oxygen move from mother to baby while wastes move in the other direction.

Umbilical cord has three blood vessels: one umbilical vein and two umbilical arteries

Vein carries blood with nutrients and oxygen to baby while the arteries carry CO2 and other waste to the placenta

Blood flows mainly to the heart of the fetus, bypassing the immature liver through the ductus venosus which enters the inferior vena cava

Special Circulations - Fetal Since lungs aren’t being used, two shunts help

bypass them Blood entering right atrium goes straight to left

atrium through foramen ovale Blood that makes it to the right ventricle is

pumped out pulmonary trunk to ductus arteriosus, where it is pumped back to the aorta.

At birth, the foramen ovale closes and the ductus arteriosus collapses and is converted to fibrous ligamentum arteriosum (connects aorta to pulmonary artery)

Special Circulations - Fetal

Physiology of Circulation

Pulse – rhythmic expansion and recoil of arteries resulting from heart beating can be felt outside of body when an artery is close to the body surface

Pulse can be influenced by activity, postural changes, and emotions

Pressure points – points where pulse can be most easily felt; they are compressed to stop blood flow during hemorrhaging

Physiology of Circulation

Blood pressure = pressure blood exerts against inner walls of blood vessels

The force that keeps blood circulating continuously, even between heartbeats blood moves from high to low pressure

Systolic pressure – pressure in the arteries at the peak of ventricle contraction

Diastolic pressure – pressure when ventricles are relaxing

Blood pressure is measured in millimeters of mercury (mm Hg) and with the systolic pressure over the diastolic pressure (ex. 120/80)

Hypertension = chronic high blood pressure (140/90 or higher)

Physiology of Circulation

Blood pressure is usually measured through the auscultatory method:

Blood flow is stopped through an inflated blood pressure cuff.

As the pressure in the cuff is slowly released, the examiner listens carefully for two signals.

The first signal is a soft tapping sound as blood starts to spurt through the artery this is recorded as systolic pressure.

The second signal is when the tapping sound can no longer be heard this point is recorded as diastolic pressure

Physiology of Circulation

Blood pressure is directly related to cardiac output and peripheral resistance (the amount of friction encountered by the blood as it flows through the vessels)

Factors that can affect blood pressure: Age Weight Time of day Exercise Body position Emotional state Drugs Kidneys Temperature Diet