Module 2: topic 2 the heart and the lungs

Heart: function + structure(basic)

The organ responsible for pumping blood through the body and to the lungs

• made up of cardiac muscle and CT

• Fist-sized ( generally)

• 250-300g in females and 300 to 350 in males

Heart: location in relation to other structures

• sits within the thoracic cavity ( alongside the lungs)

• behind the sternum and to the left

• base of the heart starts at the 3rd rib

• bottom of the heart at the 5th rib

anatomical features of the heart

The superior portion of the heart (base) contains the arteries, veins and atria

The inferior position of the heart, which is pointy is the apex and contains the ventricles

Right atrium + ventricle

Right atrium

• receives deoxygenated blood from the inferior and superior vena cava from the body

• Pumps the blood through the valves via constriction into the right ventricle through the tricuspid valve

Right ventricle

• receives deoxygenated blood from the right ventricle via the tricuspid valve

• Constricts and pumps blood through the pulmonary valve and into the pulmonary artery to deliver blood to lungs for reoxygenation

Left atrium + ventricle

Left atrium

• receives oxygenated blood from the lungs via the pulmonary vein

• Pumps blood by constriction and moves the blood through the bicuspid valve into the Left ventricle

Left ventricle

• receives oxygenated blood from the left atrium via the bicuspid valve

• constructs and pumps blood through the aortic or mitral valve and to the body through the Aorta

coronary arteries

The vessels that supply oxygenated blood to the heart tissue (myocardium)

• has a right and left artery

• positioned in the epicardium and extends into myocardium

• done because blood moves through the heart too quickly to be absorbed into heart wall

1st layer of the heart wall

Endocardium

• Structure: comprised of endothelium and loose CT and contains blood vessels

• Location: lines the chambers and the valves

• Function: allows for quick, smooth movement of blood

2nd layer of heart wall

Myocardium

• Location: forms the middle bulk of the wall

• Structure: comprised of the heart muscle

• Function: Constricts and relaxes to move blood through the heart

• is limited in self-repair as it has no stem cells

3rd layer of heat wall

Epicardium

• Location: outermost layer of the heart that forms part of the visceral pericardium

• structure: contains protcetive mesothelium(lubricating) + CT

• contains blood vessels and nerves for the heart muscle

pericardium definitaion + strcture

a double membrane sav surrounding the heart that is comprised of 2 layers

• Fibrous pericardium: stronger outlayer

• serous pericardium: inner layer attached to the epicardium of the heart

Pericardium functions

• fixes and stabilises the heart in the mediastinum

• Physically limits the filling of the heart to prevent the overfilling

• lubricate the heart to reduce friction from the heartbeat

• protects the heart from infection

Fibrous pericardium - outer layer

Tissue: dense, irregular CT

Function: protects and anchors to the ribcage

structure: rigid to prevent over stretching

serous pericardium inner layer

tissue: mesothelium (secretes fluid for the pleural cavity) + CT

Structure: consists of two layers

• Perietal Pericardium ( mesothelium)

• Visceral pericardium ( epicardium)

pericardial cavity

the space between the layer of the pericardium that is filled with 15-50ml of fluid to reduce friction

Heart valves + types

flaps of endocardium that control the passage of blood through the heart and connected vessels, and prevent back flow

• Atrioventricular valves(AV) - found between the atrium and the ventricle

• Semilunar valves - found between the ventricle and the vessels

heart valves general structure

consists of a layer of collagen, elastin and proteoglycan and is lined with endocardium

• thin but resistant to pressure

• made of 2-3 flaps or cusps

AV types

Bicuspid: 2-cusp valve that is found between the left atrium and ventricle

Tricuspid: a 3-cusp valve between the right atrium and right ventricle

What structures allows AV values to close

• chordinae tendinae: cord-like tendons made of collagen and elastin

• Papillary muscle: attached to the heart wall and tendinae

How does blood move through valves when chambers constrict

Blood moves through the valves due to changes in blood pressure during contraction

When atria constrict, pressure in the atrium increases, AV opens through forces, and blood flows into the ventricles, which are at a lower pressure

When the ventricle constricts, pressure in the ventricle increases, papillary muscles contract, pulling on chordinea tendinea, valve is pulled closed

Semilunar valves

Pulmonary valves: a three-cusped valve that forms moon-like shapes that are found between the right ventricle and the pulmonary trunk/vein

Aortic valves(mitral): a three cuspid valves that forms a moon like structure found between the left ventricle and the aorta

process at which blood moves through Semilunar valves

The opening and closing of the valves depend on the difference in pressure between the chamber and the vessel

When the ventricle contracts, the ventricular pressure increases above the vessel, and blood is pushed through the valve

When the atrium contracts, the pressure in the ventricle falls, blood in the vessels falls back towards the ventricle and fills the divots in the cusps, and blood pushes the cusps closed.

How does blood flow through the body (circuit based)

1. deoxygenated blood returns to the heart from the systemic circuit through the vena cava and into right artium

2. blood is pumped out of the heart and through the arteries to the lungs for reoxygenation

3. oxygenated blood goes back to the heart

4. Blood is pumped out of the heart and through the systemic system to the body

Cardiac conduction system

The stimulation of the muscle using electrical signals allows the muscle in the atrium and ventricle to contract in sequence

• is generated by the heart, allowing it to set its own rhythm

• atrium contracts, ventricle relaxes and vise versa

pacemaker cells

Cells in the heart that generate the electrical signals to ensure proper coordination

• make up 1% of the muscle in the heart

• forms part of a conductive network in the heart

• sets heart beat at 80 - 100 bpm

step 1 of the conduction pathway

The SA (sino atrial) nodes on the outside of the right atrial wall, below the vena cava, are stimulated by the pacemaker cells (referred to as the depolarisation of the atrium)

• stimulation causes the contraction of the left and right atrium, which at the same time causes them to push blood into their respective ventricle

• signal recahes the left atria via the interatrial bundle or Bachmann’s bundle

Step 2 of the conduction pathway

the electrical signal makes ite way via the Intermodel branches to the AV nodes found at the junction between the right atria and ventricle

• slows and delays the spped of the signal by 0.1 seconds to allow for atrium to finish contracting before the ventricle can contrcat

step 3 of conduction pathway

signal travels along an AV bundle that separates into a left and right bundle branch

• found on the wall between the ventricles

• supplies electrical signals to each side of the heart

Step 4 of conduction pathway

Branches from the tip of the AV bundle branches called Purkinje fibres, begin at the apex and extend upwards to the cardiac muscle in the ventricle wall

• signals the ventricle to contract

what is the cardiac cycle + features

The conduction system that initiates and coordinates the electrical signals for contraction and relaxation

• creates pressure differnces for blood flow

Basic principles of the cardiac cycle

• diastole: the relaxation of the chambers that causes the chamber pressure to lower and fill with blood as the volume of the chamber increases ( diastolic pressure = the minimum amount of blood in the heart during relaxation)

• systole: contraction of the chambers in the heart that pushes the blood out of the chamber/ heart and increases pressure while decreasing volume ( systolic pressure = maximum amount of blood pushing against the heart walls in contraction

what occurs before the cardiac cycle

all of the chambers are relaxed and begin to fill passively as there is more pressure in the vessels compared to the chamber

Cardiac cycle: phase 1 (atrial systole)

The atrium contrcats causing a decrease in the volume of the chamber and an increase in the pressure

• AV valves open, forcing the blood in the atrium to fill the remaining space in the ventricle

Cardiac cycle: phase 2 (early ventricular systole)

The beginning of ventricular contraction (isovolumetric contraction) at which the pressure in the ventricle exceeds the now relaxed atrium casing the AV valve to close

• pressure in the ventricle is not great enough to open the semilunar valves

• Contraction only occurs at the apex of the heart as the action potential reaches the AV nodes

Cardiac cycle: phase 3 (Late ventricular systole)

The end of ventricular contraction at which the pressure is high enough to open the semilunar valves causing the blood in the chambers to be released into the lower-pressure vessels

• signal in the conduction system reaches the prukinje fibres

Cardiac cycle: phase 4 (early ventricular diastole)

beginning of ventricular relaxation (isovolumetric relaxation) that leads to a decrease in ventricular pressure that is less than the arteries causing blood in vessels to push back, fill the pouches in the semilunar valves, holding them closed

• ventricle pressure is still greater than atrial pressure

• AV valves are closed

Cardiac cycle: phase 5 Late ventricular diastole)

end of ventricular relaxation where both the atrium and ventricles are relaxed, causing blood from the high-pressure veins to fill the atrium

• ventricular pressure is lower than atrium pressure causing the AV valves to open allow the ventricle to fill passively until at 70% capacity

Cardiac output + influcnces

the amount of blood leaving the herat per minutes (L/min)

• influenced by heart rate and stroke volume ( Q = SV x HR)

• can also depend on vessel competency and the oxygen composition of the blood

Heart rate

Number of heartbeats per minute (bpm) that can change due to O2 and CO2 levels, physical activity and excitement/stress

• regulated by the nervous or endocrine system

• resting HR = 60 -100bpm depending on age, health and conditioning

Stroke volume

The amount of blood pumped out of the heart with each contraction

• can be affected by age, gender, fitness level or duration of the contraction

• average = 70ml/beat

Stroke volume - influences

• The size of the heart may mean it can hold more or less blood, at which to expel

• Heart contractability, or the force behind the pumping of the blood

• preload - how much the heart stretches open and fills before ventricle contraction

• Afterload - pressure generated by the heart to be used for contraction

How does cardiac output and distribution differ when exercising

cardiac output increases when exercising with more blood being pumped to the muscle and skin (heat release) and less blood being pumped to the organs

Cardiovascular regulation strategies

There is not enough blood to go to every tissue at once, so blood distribution needs to be regulated via

• auto-regulation at the local tissue level

• Nervous system

• endocrine system

Auto regulation

causes the increase or decrease in blood flow to tissues via capillaries depending on activity

• protects capillaries from burst with too much blood

• can have a myogenic or metabolic stimulus

Autoregulation: Metabolic stimulus

stimulus: change in chem composition due to an increase in metabolic activity ( decrease in O2 and increase in CO2 and pH)

receptor/effector: changes are detected by endothelial cells in the vessel that release NO to dilate vessels and increase blood flow

• more efficiently clear out waste products from metabolic activity in tissue

Autoregulation: myogenic stimulus

Stimulus: an increase in pressure/blood flow pushing against the artery walls, causing overstretching in smooth muscle

Receptor: Mechanoreceptors in the smooth muscle that are sensitive to the stretch

Effector: smooth muscle contracts to lower the pressure/ flow and protect the capillaries

Neural regulation

The short-term regulation of the cardiovascular system by the cardiovascular centre in the medulla oblongata in the brain stem

• responds to changes in blood pressure (wall stretch) or changes in blood chemistry

What areas of the brain regulate the cardiovascular center

• Cardioaccelerator centre (stimulates HR and SV via the sympathetic NS ( cardiovascular nerve)

• Cardioinhibitory centre ( slows HR and SV via the vagus nerve in the parasympathetic NS

• Vasomotor ( controls the smooth muscle in blood vessels through changes in diameter via the release of a neurotransmitter like norepinephrine from the sympathetic NS)

types of neural receptors

Chemoreceptors: detect changes in chemical composition (gases, pH and ion concentration) in the aortic body, carotid body or the medulla

Bioreceptors: ( detect vessel streching in the aortic arch or the carotid artery sinus)

Communication process of the brain

1. Changes in detected by the given receptors

2. Info travels back to the specific centre in the brain stem

3. the brain tells the effector organs to elicit a certain response

Bioreceptor example: Increased BP

Stimulus: an increase in the stretch of the aortic or carotid sinus

Response: cardioinhibitory centre is stimulated, activating the parasympathetic NS and the Vasomotor centre is inhibited which decreases sympathetic NS stimulation

Restoration: Vasodilation to increase the expulsion of CO2 and decreases resistance of the vessel. lower heart rate and pumping force leading to lower BP

Bireceptor example: decreased BP

stimulus: decrease in stretch of aortic and carotid body sinus

Response: Cardioacceltory centre and Vasomotor are stimulated

Restoration: Vasoconstriction causes a decrease in CO2 level, and blood moves more slowly through the heart, increasing resistance with decreased surface area, leading to an increase in heart rate and force that casing the BP to rise.

Chemoreceptor example: increased CO2 and decreased O2 + pH

Stimulus: change in blood chemistry ( increase in CO2, decrease in O2, and pH)

Response: cardioacceleratory centre and Vasomotor are stimulated

Restored: increase in Heart rate and force that increases blood flow to tissue, increased vasoconstriction that increases resistance and enhances the delivery of O2 and the removal of waste

Endocrine regulation

the release of hormone/ chemical messengers from glands or cells through the cardiovascular system in order to enact a response

• long-term response: hormone from the kidneys, brain or adrenal glands

• short-termL adrenaline and noradrenaline

What is the reain- Angiotensin system

a long-term fix to a change in BP or fluid volume

• receptor: kidney

What does the Effector do to decrease BP and blood volume

1. Kidney releases Renin into the bloodstream which turns angiotensinogen from the liver into angiotensin I

2. Angiotensin converting enzyme (ACE) is released from the lungs and converts angiotensin I into II

3. Angiotensin II stimulates aldosterone release from the adrenal gland, which causes the kidney to reabsorb salt and water from the blood

4. blood volume and pressure increase

5. OR angiotensin II stimulates vasocontriction, which increases BP

What is erythropoietin

a hormone secreted by the kidney that can promote RBC production and increase blood volume and pressure

Respiratory system functions

• moves air in and out of the lungs (pulmonary ventilation)

• exchanges O2 and CO2 between the air and blood

• Protects the body from airborne threats using mucous and cilia

• produces sound for communication ( vocal cords)

• enables our sense of smell ( activates olfactory receptors and nerves)

upper and lower respiratory system organs

Upper respiratory system: nose, nasal cavity, sinuses and the pharynx

Lower Respiratory system: Larynx, trachea, bronchi, bronchioles and alveoli

Conduction zone of system

structures in the respiratory system that bring in air but are not responsible for gas exchange

• everything but the alveoli and bronchioles

Respiratory zone of system

Sites of gas exchange between air in lungs and blood in vessels

• alveoli and bronchioles

Nose

air enters via the nostrils, goes into the nasal cavity and sinuses

• Hair: filters incoming dust and debris (prevents it from entering lungs)

• Mucous traps pathogens by trapping them

• warms and humidifies incoming air and cool and absorbs water from outgoing air

Pharynx

a muscular tube that allows for the passage of air and food

• initiates swallowing

• assists in speech

Larynx

The vocal cords that produce sound as air passes through them (glottis)

• prevents food from entering the trachea (epiglottis)

Lungs: location + structure

found in the thoracic cavity, enclosed by two layers of serous membrane called the pleura

• made up of a spongy air-filled flesh and contains bronchi, bronchioles and alveoli

what is the Pleura

The fluid-filled sack surrounding each of the lungs is made up of two layers

• Parietal pleura: the outer layer that attaches to the chest wall

• Visceral pleura: inner layer covering the surface of the lungs

• Pleural cavity: the space between the membranes that is filled with fluid secreted from the membranes that is used for lubrication

anatomical organisation of lungs

The top of the lungs is called the apex and the bottom is the base

front view

• right lung has a Superior, inferior and middle lobe ( is smaller than the left to make room for the heart)

• The left lung is larger and only has a superior and inferior lobe

Back view

• The right lung contains a groove in which the heart can sit and a hilum where the primary bronchi and vessels enter the lungs

• The left lung contains a groove for the aorta along with a very similar hilum

what are the components in the bronchiol tree

• trachea

• Bronchi

• bronchioles

• alveoli

Trachea

a tube that brings air from the outside of the body that is found anterior to the oesophagus ( extends into the mediastinum)

• composed of a tube supported by C-shaped rings of cartilage that are connected by dense CT

• C’ are connected by an elastic fibre and their ends allow the structure to expand

what to the trachea branch into

1 branch of tubes is called a generation

1 trachea branches into 2 primary bronchi - secondary bronchi (lobar) - tertiary (segmental) bronchi - bronchioles - terminal bronchioles - respiratory bronchioles - alveoli sacs

What happens to the cartilage rings and they get further down the tree

As you flow down the progression of the tree, the cartilage ring becomes more and more fragmented until it no longer exists

• still provides support

• cartilage is no longer present in bronchioles and below

bronchioles

branch off of the tertiary bronchi and are made of walls of smooth muscle that are flexible to allow for diameter changes

• intertwined with nerves from the auto NS hat regulate air flow into alveoli

Nerve examples

parasympathetic NS activates causing the release of acetylcholine that cause the constriction of bronchi to reduce air flow

sympathetic NS activates causing bronchidilation to increase diameter of bronchi and increase air flow

What is found in a bronchiole tubule

• terminal bronchi

• Respiratory bronchi

• alveolar ducts

• alveolar ducs

• alveolar

has its own blood and lymph supply

alveolar

Sacs are comprised of tiny cup-shaped sacs that increase the surface area for diffusion

• multiple alveoli make an alveolar sac

• Each alveolar sac has its own capillaries and venules for exchange

Alveoli Type 1

structure: cup-shaped sacs made of simple squamous tissue comprised of alveolar type 1 cells aka type 1 Pneumocytes

function: the site of gas exchange in the pulmonary circuit

appearance of cells: has long cytoplasmic extensions

alveoli type 2

Structure: comprised of cuboidal epithelial cells with microvilli, comprised of less abundant alveoli type 2 cells aka pneumocytes type 2

function: produces pulmonary surfactant to reduce the surface tension of water in the blood at the site of exchange

Pumonary surfactant + function

a viscous mixture of fat and proteins that lines the outside of the alveoli at the air-blood interface

• reduces the surface area of the aqueous fluid secreted by the lung by breaking the attractive bonds between water molecules

• this lowers the force required to keep alveoli open and prevent fluid from entering lungs causing collapse

alveolar macrophages

Macrophages that move through the interstitial spaces and onto the alveolar fluid surface

• removes any dust and debris so it does enter the blood

Respiratory mucosa: location

Lines the area of the respiratory system that is directly in contact with the atmosphere

• surfaces such as the nasal cavity, parts of the pharynx, larynx, trachea, bronchi and bronchioles

respiratory Mucosa: structure

comprised of respiratory epithelium + underlining alveolar CT (lamina propria)

• ciliated columnar epithelium

• goblet cells are used to secrete mucous to trap particles

• cilia move in a sweeping motion to remove mucous

• psuedostratified

Respiratory mucosa: pharynx structure

made up of stratified squamous for protection against food particles

alveolar tissue

contains layers of simple squamous for gas exchange, contains only type 1 cells

Respiartory membrane function + structure

the air blood barrier with a thickness of half a micron at which O2 and CO2 are exchanged through diffusion

contains

• alveolar type 1

• fused basement membrane between alveolar and capillary

• endothelial cells lining the capillaries

Fick’s law of diffusion

The rate of diffusion across a membrane is

• proportional to the area of a membrane (A)

• inversely proportional to membrane thickness(d)

• proportional to the difference in pressure (delta p)

what does fick’s law tell us about gas exchange

• An increase in the surface area of the membrane leads to an increase in the rate of diffusion

• the higher the pressure difference between the capillary lumen and the alveolar air space, the faster the rate of diffusion

• an increase in the distance (width of membrane) leads to a decrease in the rate of diffusion