Human Biology: Circulatory System

Lesson 3: Structure and Function of the Heart (Inquiry into Life pg. 220-226)

Today’s Objectives Describe the inter-relationships of the structures of the

heart, including: Identify and give functions (including direction of blood flow) for the

major structures of the heart Recognize heart structures using both internal and extrenal diagram

views Analyse the relationship between heart rate and blood

pressure, including: Describe the location and functions of the sinoatrial (SA) node,

atrioventricular (AV) node, and Purkinje fibres Describe how the autonomic nervous system increases and

decreases heart rate and blood pressure Differentiate between systolic and diastolic pressures Describe hypertension and hypotension and their causes Demonstrate the measurement of blood pressure

Heart Quiz

Parts of the Heart (video) Left and Right Atria –

Collecting Chambers Right: collects blood from

Venae Cavae Left: Collects blood from

Pulmonary Veins Left and Right

Ventricles – Pumps Right: Sends blood to the

lungs via the Pulmonary Trunk

Left: Sends blood to the body via the Aorta

Parts of the Heart Atrioventricular Valves

Valves between the atria and ventricles Prevent backflow of blood Right side valve called “Tricuspid Valve”

Has three cusps, or flaps Also called right atrioventricular valve

Left side valve called “Bicuspid Valve” Has two cusps, or flaps Also know as the mitral valve or left atrioventricular

valve Chordae Tendonae

Strong, fibrous strings that support the A.V. valves

Keep the flaps from inverting with the force of blood flow

Heart Valves

Parts of the Heart Semi-lunar Valves (no chordae tendonae)

Between ventricles and the Aorta (Aortic Valve) Between the ventricles and the Pulmonary Trunk

(Pulmonary Valve) Pulmonary Trunk

Branches off to form the Pulmonary Artery Receives blood from the right ventricle

Septum (Ventricular Septum) The wall of the Heart Separates the left and right sides of the Heart

Diagram (quiz…)

Cardiac Cycle and Intrinsic Beat Contraction of the Heart is a two step process:

Systole – Contraction of the Heart Diastole – Relaxation of the Heart

Each heart beat (Cardiac Cycle) consists of: TIME ATRIA VENTRICLES0.15 Sec Systole Diastole0.30 Sec Diastole Systole0.40 Sec Diastole Diastole0.85 Sec Average time of 70 beats per minute

Cardiac Cycle The ventricles have a stronger and longer contraction

because blood must be pumped throughout the body

The “lub-dup” sound of the heart is due to the closing of the valves: first the atrioventricular, then the semi-lunar

The beat of the heart is said to be intrinsic, meaning it will beat without any nervous system stimulation It can be removed from the body and still continue

beating!) The beat is controlled by a special type of tissue

called Nodal Tissue, which has both muscular and nervous tissue characteristics

Nodal Tissue There are two locations of Nodal Tissue in the Heart: 1) SA Node (Sinoatrial Node)

Found in the upper wall of the right atrium 2) AV Node (Atrioventricular Node)

Found at the bottom of the right atrium near the Septum The SA Node (also called the pacemaker) initiates the

heartbeat and sends out an excitation impulses every 0.85 seconds.

The impulse causes both Atria to contract. The impulses are sent to the AV Node Via the bundle of His.

When the impulse reaches the AV Node, an impulse is sent from the AV Node, down the Purkinje Fibers causing both ventricles to contract.

Electrocardiograms (EKG) An electrocardiogram registers the voltage

change across the surface of the heart as it beats. The letters PQRST are the standard labels used to

identify the parts of the EKG The P curve records the simultaneous contraction

of the atria as they drive the blood out into their ventricles

The QRS is the contraction of the ventricles as they drive the blood out into their respective arteries

The T marks the recovery of the Ventricles (restoration of the normal electrical condition, preparing them for the next contraction)

Autonomic Control of the Heart The rate of the heart can also be controlled by the

nervous system The heart rate center is located in the Medulla

Oblongata of the brain. The SA Node is connected to the brain by the vagus

nerve (cranial nerve #10) This nerve pathway is called the Autonomic

Nervous System (not under conscious control) Has two systems that affect the Heart Rate:

Parasympathetic System – causes the heart beat to slow down

Sympathetic System – causes the heart beat to increase during times of stress

 Autonomic Nervous System Factors such as a need for oxygen or the

blood pressure level determine which of those systems become active

When the brain perceives that the blood is getting delivered to the tissues too slowly, or if blood

pressure is low, the brain will signal the SA Node to speed up its contraction.

Blood Pressure Ventricles pump a volume of blood (approx 70

ml) each time they contract Must have elastic, expandable walls The force of blood against the blood vessel

walls is known as Blood Pressure Blood Pressure is not constant The term Systolic pressure (or Systole)

refers to the blood pressure when the ventricles contract

The term Diastolic pressure (Diastole) refers to the blood pressure when the heart is at rest

Pulse As blood is pumped through the arteries, the

arterial walls swell, then relax This swelling can be felt in any artery that

runs close to the surface Blood pressure is normally measured along

the brachial artery of the arm A reading of 120/80 is quite normal

120 - Systolic reading as ventricles contract 80 – Diastolic reading as the heart relaxes

Blood Pressure Changes A number of things can affect the blood pressure: Hypertension: High Blood Pressure

Example: 140/90 or 125/90 Diet and Lifestyle are often to blame for elevated

blood pressure Reasons for Hypertension:

Stress Plaques – formed by fatty acid deposits from digested

foods; line the walls of the arteries, making the radius smaller, thereby raising blood pressure, (Arteriosclerosis, Stroke, Heart Attack)

High Salt Intake – retains water – greater fluid volume leads to greater volume of blood

Blood Pressure Changes Hypertension continued..

Smoking Stimulants Lack of Exercise Diet – amount of food and type Working too hard Age, Sex, Race

Hypotension Low Blood Pressure

Blood does not reach all organs Example: 110/70

Reasons for Hypotension: Cuts or amputated limbs Drugs Hormones

Effects of Blood Pressure Change Proper Kidney function can only be

maintained if there is a sufficient pressure for filtration

Luckily, the body can adjust blood pressure Monitored by the Hypothalmus (part of the

brain), the body can dilate (widen) arterioles thus lower blood pressure in them, or constrict (narrow) them to raise the blood pressure