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IB Biology Option D: Human Physiology > D.4: Function of The Heart > Flashcards

D.4: Function of The Heart Flashcards

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1
Q

Cardiac muscle

8 points

A
  • unique to the heart
  • striated appearance similar to skeletal muscle
  • shorter and wider than skeletal muscles, only one nucleus per cell
  • have more mitochondria, as they are more reliant on aerobic respiration than skeletal muscle
  • not under voluntary control (myogenic)
  • y shaped and being electrically connected allows cardiac muscle to move as if it was one cell
  • cells are not fused together, but are connected by gap junctions at intercalated discs
  • Also means that while electrical signals can pass between cells, each cell is capable of independent contraction
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2
Q

What are intercalated disks?

A
  • Intercalated disks join the ends of the cardiac muscle cells
  • have a double membrane which contains gap junctions providing channels of connected cytoplasm between the cells, allowing for movement of ions and low electrical resistance (faster signal propagation and contraction in three dimensions)
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3
Q

Systole

A

Contraction of the heart

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4
Q

Diastole

A

Relaxation of the heart

After every contraction of the heart, there is a period of insensitivity to stimulation (i.e. a refractory period)
This recovery period (diastole) is relatively long, and allows the heart to passively refill with blood between beats, also helps prevent heart tissue becoming fatigued, allowing contractions to continue for life

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5
Q

Contraction and relaxation of heart steps

A
  • SA (sinoatrial) node is sent by cardiac muscles and travels through the heart muscles, causing the atria to contract/undergo systole
  • SA node reaches AV (atrioventricular) node
  • AV node sends signal down the septum
  • Bundle of his receives impulse from the AV node, conducts signal to send to left and right bundle branches
  • bundle branches send signal through the wall between ventricles
  • bundle branches are connected to purkinje fibres near the base of the heart, signal sent throughout the heart via purkinje fibres
  • signal results in ventricle undergoing systole
  • atrioventricular valves snap shut
  • ventricles empty and semilunar valves close
  • ventricles begin diastole
  • atrioventricular valves open and ventricles fill with blood
  • all four chambers full with blood
  • once atria fully filled and ventricles 70% filled, one cycle is complete
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6
Q

AV node delay

A
  • The AV node propagates electrical signals more slowly than the SA node, creating a (0.12 s) delay in the passing on of the signal
  • The delay in time following atrial systole allows for blood to fill the ventricles before the atrioventricular valves close
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7
Q

What features result in the delay in contraction of ventricles by the AV node?

A
  • The AV node cells have a smaller diameter and do not conduct as quickly.
  • There is a relatively reduced number of Na+ channels in the membranes of AV node cells
  • a more negative resting potential
  • a prolonged refractory period within the cells of the AV node.
  • There are fewer gap junctions between the cells of the AV node.
  • There is relatively more non-conductive connective tissue in the node
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8
Q

What helps purkinje fibres conduct signals rapidly?

A
  • have relatively fewer myofibrils
  • have a bigger diameter
  • have higher densities of voltage-gated sodium channels
  • have high numbers of mitochondria
  • have high glycogen stores
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9
Q

What causes the sound of the heartbeat?

A
  • first heart sound is caused by the closure of the atrioventricular valves at the start of ventricular systole “lubb”
  • second heart sound is caused by the closure of the semilunar valves at the start of ventricular diastole “dupp”
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10
Q

electrocardiograph

A

A machine used to measure electrical activity of the heart to generate data called an electrocardiogram

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11
Q

sequence of electrical events in a normal heartbeat:

A
  • P wave: represents depolarisation of the atria in response to signalling from the sinoatrial node (i.e. atrial contraction)
  • QRS complex: represents depolarisation of the ventricles (i.e. ventricular contraction), triggered by signals from the AV node
  • T wave: represents repolarisation of the ventricles (i.e. ventricular relaxation) and the completion of a standard heart beat
  • Between these periods of electrical activity are intervals allowing for blood flow (PR interval: (btwn P wave and QRS complex) and ST segment: (btwn QRS complex and T wave))
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12
Q

Examples of Heart Conditions

can be identified using an electrocardiograph

A
  • Tachycardia (elevated resting heart rate = >120 bpm) and bradycardia (depressed resting heart rate = < 40 bpm)
  • Arrhythmias (irregular heart beats that are so common in young people that it is not technically considered a disease)
  • Fibrillations (unsynchronised contractions of either atria or ventricles leading to dangerously spasmodic heart activity)
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13
Q

Cardiac output

A

the amount of blood the heart pumps through the circulatory system in one minute

it can be a medical indicator of how efficiently the heart can meet the demands of the body

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14
Q

The two key factors which contribute to cardiac output:

A

heart rate and stroke volume

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15
Q

Equation of cardiac output:

A

Cardiac Output (CO) = Heart Rate (HR) (Beats/min) × Stroke Volume (SV) (mL/beat)

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16
Q

What is heart rate affected by?
(Nervous system, hormones)

A

exercise, age, disease, temperature and emotional state
An individual’s heart rate is controlled by both nervous and hormonal signals:
- Heart rate is increased by the sympathetic nervous system and decreased by parasympathetic stimulation (vagus nerve)
- Heart rate can also be increased hormonally via the action of adrenaline / epinephrine

17
Q

Heart rate definition
(typical pulse)

A
  • Heart rate describes the speed at which the heart beats, measured by the number of contractions per minute (or bpm)
  • Each ventricular contraction forces a wave of blood through the arteries which can be detected as a pulse
  • The typical pulse rate for a healthy adult is between 60 – 100 beats per minute
18
Q

Stroke volume definition

A
  • Stroke volume is the amount of blood pumped to the body (from the left ventricle) with each beat of the heart
  • It is affected by the volume of blood in the body, the contractility of the heart and the level of resistance from blood vessels
19
Q

What is blood pressure affected by?

+ how stroke volume afects BP

A
  • Site of measurement (e.g. arteries have much higher pressure than veins)
  • Posture
  • Diameter of blood vessel (e.g. vasodilation: the widening of blood vessels as a result of the relaxation of the blood vessel’s muscular walls)
  • Changes in stroke volume will affect the blood pressure – more blood or more resistance will increase the overall pressure
  • Fluid retention or loss
20
Q

Hypertension definition

A
  • an abnormally high blood pressure – either systolic, diastolic or both (systolic: 140 mm Hg or higher diastolic: 90 mm Hg or higher)
  • Hypertension itself does not cause symptoms but in the long-term leads to consequences caused by narrowing blood vessels
  • constant high blood pressure can weaken
    an artery causing a section of the wall to enlarge and form a bulge called an aneurysm. An aneurysm can burst and cause internal bleeding. They can form in any artery in the body but are most common in the aorta.
21
Q

Common causes of hypertension

A
  • Tobacco use
  • Other Conditions: High blood pressure can also be secondary to other conditions (e.g. kidney disease) or caused by some medications
  • Exercise: a sedentary lifestyle
  • Diet: salt or fat-rich diets and excessive alcohol
22
Q

Thrombosis definition
(+ loc. and how this affects body)

A
  • The formation of a clot within a blood vessel that forms part of the circulatory system
  • Thrombosis in the coronary arteries leads to heart attacks, while thrombosis in the brain causes strokes
23
Q

How does thrombosis occur?

cause??

A
  • caused by cholesterol: occurs in arteries when the vessels are damaged as a result of the deposition of cholesterol (atherosclerosis)
  • Atheromas (fat deposits) develop in the arteries and significantly reduce the diameter of the vessel (leading to hypertension)
  • The high blood pressure damages the arterial wall, forming lesions known as atherosclerotic plaques
  • If a plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow
  • If the thrombus becomes dislodged it becomes an embolus and can cause blockage at another site
24
Q

Coronary heart disease definition

A
  • build-up of plague in the coronary arteries
  • the consequence of atherosclerosis (thickening or hardening of the arteries caused by a buildup of plaque in the inner lining of an artery) in the blood vessels that supply and sustain heart tissue
25
Q

risk factors for CHD: A GODDESS

CHD = coronary heart disease

A
  • Age – Blood vessels become less flexible with advancing age
  • Genetics – Having hypertension predispose individuals to developing CHD
  • Obesity – Being overweight places an additional strain on the heart
  • Diseases – Certain diseases increase the risk of CHD (e.g. diabetes)
  • Diet – Diets rich in saturated fats, salts and alcohol increases the risk
  • Exercise – Sedentary lifestyles increase the risk of developing CHD
  • Sex – Males are at a greater risk due to lower oestrogen levels
  • Smoking – Nicotine causes vasoconstriction, raising blood pressure
26
Q

Artificial pacemakers are typically used to treat one of two conditions:

A
  • Abnormally slow heart rates (bradycardia)
  • Arrhythmias arising from blockages within the heart’s electrical conduction system
27
Q

What is blood pressure

how is it measured and what is typical?

A
  • Definition: The force of circulating blood on the walls of the arteries
  • Blood pressure measurements typically include two readings – representing systolic and diastolic blood pressures
  • Systolic blood pressure is higher, as it represents the pressure of the blood following the contraction of the heart (ventricular systole)
  • Diastolic blood pressure is lower, as it represents the pressure of the blood while the heart is relaxing between beats (ventricular diastole)
  • A typical adult is expected to have an approximate blood pressure in their brachial artery of 120/80 mmHg to 140/90 mmHg

IB Biology Option D: Human Physiology (4 decks)

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