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Chapter 13: Cardiovascular System

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Chapter 13: Cardiovascular System. The cardiovascular system Structure of the heart The cardiac cycle Structure and organization of blood vessels. Cardiovascular System. What is the cardiovascular system? Delivers O 2 and nutrients throughout the body and removes wastes.

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The cardiovascular system

Structure of the heart

The cardiac cycle

Structure and organization of blood vessels


Cardiovascular System

What is the cardiovascular system?

Delivers O2 and nutrients throughout the body and removes wastes.

The heart is a double pump:








Structure of the Heart - Outer

Average heart is about 14 cm by 9 cm.

The heart is enclosed by the pericardium – fibrous pericardium (outer bag) and a double-layered sack.

Fibrous pericardium

dense connective tissue

attached to the diaphragm, sternum, vertebral column and heart

Double-layered sack

visceral pericardium - innermost layer (epicardium)

pericardial cavity – between layers; serous fluid

parietal pericardium - next to fibrous pericardium


Structure of the Heart - Wall

Wall of the heart:

Epicardium (visceral pericardium)

serous membrane – connective tissue/epithelium

protects by reducing friction


thick middle layer

cardiac muscle tissue – pumps blood


inner layer

epithelium and connective tissue (elastic, collagen)

Purkinje fibers

continuous with inner linings of the blood vessels


Serous membrane

Continuous with

blood vessels


Chambers of the Heart

Four hollow chambers – left and right atrium, left and right ventricle.


Upper chambers

Thin walls

Receive blood returning to the heart.


Lower chambers

Receive blood from atria and force blood out of heart.

Septum – separates the right and left sides of the heart.


Blood into the right atrium

Blood into the right atrium



Valves control flow of blood from one chamber to another and prevents backflow (papillary muscles and chordae tendineae).

Tricuspid valve

Lies between the right atrium and right ventricle.

Allows blood to move from: right atrium  right ventricle

Pulmonary valve

At the base of the pulmonary arteries.

Allows blood to move from: right ventricle out to the lungs

Bicuspid valve

Allows blood to move from: left atrium  left ventricle



Aortic valve

Located at the base of the aorta.

Allows blood to move from: left ventricle  out to the body


Blood Supply to the Heart

Coronary artery and vein system – heart needs blood too.

Right and left coronary arteries branch off of aorta, supply blood to the tissues of the heart.

Cardiac veins deliver “used” blood to coronary sinus, and back to the right atrium.


Coronary artery disease results when coronary arteries cannot deliver blood adequately.

Usual cause: plaques in arterial walls.

Angina pectoris (pain) when body is not receiving adequate oxygen.

Myocardial infarction (heart attack) when blood supply to heart is completely blocked; muscle dies.


Cardiac Cycle

Systole (contract) and diastole (relax) = cardiac cycle

Lubb: A-V valves closed (tricuspid and bicuspid)

semilunar valves open (pulmonary and aortic)

Dupp: A-V valves open

sumilunar valves closed


Ventricles contracted

Atria relaxed

Atria contracted

Ventricles relaxed


Cardiac Conduction System

Heart contracts as a unit – functional syncytium.

Atrial and ventricular syncytia help conduct electrical signals through the heart.

Sinoatrial (S-A) node

Small elongated mass of cardiac muscle tissue located in the right atrium .

Continuous with atrial syncytium.

Can initiate impulses on their own (no outside stimulation); activity is rhythmic.


Cardiac Conduction System

Atrioventricular (A-V) node

Mass of cardiac muscle tissue located in the inferior portion of the septum, beneath the endoccardium.

Smaller fibers therefore slower impulses (delayed).

Purkinje fibers

Lead to the ventricular syncytium.


Electrocardiogram (ECG) can trace conduction of electrical signals through the heart.

P wave – depolarization of the atrial fibers

QRS complex – depolarization of ventricular fibers

T wave - repolarization


Regulation of Cardiac Cycle

The amount of blood pumped changes to accommodate the requirement of the body (ie exercise – need more blood).

Controlled by the sympathetic and parasympathetic nervous systems.

Parasympathetic: from medulla oblongata (vagus nerve).

Nerve branches to S-A and A-V nodes, and secretes acetylcholine witch decreases rate.

By increasing and decreasing signal, parasympathetic activity can increase (slow heart rate) or decrease (increase heart rate).


Sympathetic nervous system through celiac plexus to heart secretes norepinephrine increases force of contractions.

Cardiac control center in medulla oblongata maintains balance between the two.

Normally both sympathetic and parasympathetic function at a steady background level.


Baroreceptors detect changes in blood pressure

Rising pressure stretches receptors  medulla oblongata/vagus nerve  parasympathetic system  decrease pressure.

Increased temperature increases heart rate.

Ions and heart rate - excess potassium decreases it and excess calcium increases it.


Blood Vessels

Blood vessels from a closed circuit that carries blood from the heart to cells and back again.

Blood vessels = arteries, arterioles, capillaries, venules, and veins.

Arteries and arterioles - carry blood away from heart

Capillaries - site of exchange

Venules and veins - return blood to heart



Strong, elastic vessels that carry blood away from the heart.

Arteries subdivide into thinner tubes until the give rise to arterioles.


Endothelium (tunica interna) - prevents platelet aggregation secretes substances that control diameter of blood vessel.

Tunica media - smooth muscle and connective tissue. Innervated by sympathetic nerves (vasoconstriction).

Missing in smallest arteries

Tunica externa - connective tissue; is vascularized.



Smallest-diameter blood vessels which connect the smallest arterioles and the smallest venules.

Capillaries most permeable - substance are exchanged between the blood and tissue fluid through slits separating endothelial cells.


Especially so in liver, spleen and red marrow (so cells can enter and leave circulation).

Blood flow can vary to different parts of the body, too.


Blood is forced through arteries and arterioles vessel walls are too thick for blood components to pass through.

In capillaries, oxygen and nutrients move out by diffusion; CO2 in (via lipid membrane, channels, etc.).

Blood pressure moves molecules out by filtration.

Plasma proteins maintain osmotic pressure of blood.



Returning blood to the heart.

Venules are continuous with capillaries; take in some returned fluid (rest is retained by tissues or returned to blood via lymphatic system).

Veins have thinner walls; less muscle; but can hold much more blood.

Many veins in limbs have valves to prevent backflow.

Varicose veins arise when pressure on valves is prolonged.


Blood Pressure

Blood flow is generally equal to cardiac output.

Blood flow affected by pressure and resistance.

Blood pressure = the force that is exerted by blood against blood vessel walls.

Resistance depends on size of blood vessel and thickness (viscosity) of blood.


Blood pressure is highest in large arteries will rise and fall as heart pumps.

highest with ventricular systole

lowest with ventricular diastole

pulse pressure is the difference between the two

Resistance is highest in capillaries.


Control of Blood Pressure

Regulation of cardiac output:

contraction strength

heart rate

venous return - skeletal muscles and breathing rate


Regulation of Blood Flow

Long term regulation of blood flow (hormones)

If blood pressure is too low:

ADH (antidiuretic hormone) promotes water retention.

Angiotensin II - in response to renin

signal (renin) produced by kidney

drop in blood pressure

stimulation by sympathetic nervous system

sodium levels too low


What happens?

vasoconstriction (by angiotensin II)

what will that do to blood pressure?

ADH is secreted

aldosterone is secreted

EPO (erythropoietin) secreted by kidneys if blood volume is too low.

ANP secreted if blood pressure is too HIGH



Hypertension = arterial pressure is too high

Sometimes cause is unknown, or is secondary to disease.

Variety of causes/ risk factors are known:

sedentary lifestyle



diet (excess sodium; cholesterol; calories in general)



genetic factors



Heart has to work harder; left ventricle enlarges.

Atherosclerosis may affect coronary.

Arteries as well (which have to work harder anyway)  heart disease.

Deficient blood supply to other parts of body.

Damage to blood vessels accumulates.

Heart failure


Treatment of high blood pressure

Quit smoking; adjust diet; exercise

Drug therapies - strategies differ

Reduce heart rate

calcium channel blockers

reduce calcium flow into heart

muscle and therefore heart rate

relax smooth muscle lining

coronary arteries

beta blockers (reduce stimulation by sympathetic nervous system).


Diuretics reduce blood volume.

ACE inhibitors interfere with renin-angiotensin pathway.

Vasodilators (such as nitroglycerin) open up blood vessels (reduce resistance).

If heart is actually failing, digitalis increases efficiency of heat muscle.

Anti-hypertensive drugs may be taken in combination.


Exercise is Good

Why is exercise good for the heart?

A trained heart is bigger

pumps blood more efficiently (at a lower rate)

stroke volume increases (due to stronger

contractions, allowing for lower rate)

other benefits: higher aerobic capacity

(contributing to efficiency)

Note that this takes training!


See pg. 351-

359 for all




The heart is a double pump, delivering blood to the lungs for oxygenation, and then to the body.

Blood leaves the heart through arteries, and returns to the heart through veins.

The heart rate is regulated by a conducting system (the heart beats about 100,000 times per day)!

The cardiac cycle is regulated by the cardiac center in the medulla oblongata which regulates sympathetic and parasympathetic input.


Exercise (i.e., needs), temperature and ion balance also affect heart rate.

Cardiac rate is also controlled by long-term responders such as ADH, angiotensin, EPO and ANP.

Blood (arterial) pressure is affected by heart action, blood volume, peripheral resistance, and blood viscosity.

Inability to regulate blood pressure can contribute to disease.


Arteries and veins have structural characteristics appropriate to bringing blood to the cells and then back to the heart.

Circulatory system allows for adjustments to exercise, digestion and other necessary functions.