human biology: circulatory system
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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: - PowerPoint PPT PresentationTRANSCRIPT
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
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