The Cardiovascular System

Myocardial infarction=

heart attack

occurs when blood circulation to the muscle of the heart itself is blocked, heart cells die due to lack of oxygen, which leads to heart attack

Even if survive heart attack can still get heart failure

What are the symptoms of someone having a heart attack?

• Collapsing complaining of severe chest pain

• Like a constant heavy weight across centre of chest

• Spread into arms

• Radial artery pulse regular but weak

• Moderately obese

• Regular cigarette smoker

Draw what a ECG would look like and change during a heart attack.

DIFFUSION:

= is the newt movement of solute down a conc gradient by the innate, random movement of the solute due to its thermal energy

When is diffusion slow?

Over distance of 1mm

Diffusion is fast and effective over short distances

Important for CVS supply O2 and nutrients and remove water over a short diffusion distances

What are the functions of the Cardiovascular System?

• Delivery of O2 and nutrients to each cell

• Removal of CO2 and waste products from each cell

• Communication between organs through transport of hormones and other extracellular mediators

• Temperature regulation

• Crucial hydrodynamic device sexual reproduction

Draw overview of the lectures on cardiovascular system.

What is the key role of the cardiovascular system?

Main role is to create blood pressure since this is what drives the movement (convection) of blood

What 3 main factors determine blood pressure?

1. Cardiac output (pumping of the heart)

2. The blood vessels or Vasculature which not only carry the blood but are responsible for the resistance that creates the blood pressure

3. The various fluid compartments

What three things are need to develop a blood pressure?

1. Need pump (Heart) drives liquid around body

2. Closed system required (in blood vessels) (create pressure and resistance allows blood to flow)

3. Need liquid (need to regulate blood volume to regulate pressure)

Where is most of the blood distributed?

In the veins and venules. Acts as a reservoir

Draw a diagram for the blood distribution (at rest).

Describe the blood flow in the body at rest.

• At rest most blood is flowing through abdominal organs, kidneys and muscle

• Majority blood runs in parallel circuit which means all flow through organs is not linked (so if one organ is damaged not all will be affected as have different systems). Also means supply can be increase to a particular system.

• So exceptions including intestines which run into liver… carry food

• However if blood flow is occulted then reduction in blood to liver

Name the different parts of the blood cells.

Outline the pathway blood takes around the body.

Arteries → Arterioles → Capillaries → Venules → Vein

Describe and explain the structure of Arteries.

• Thick smooth muscle layer (tunica media) (very solid structure): Acts as pressure reservoir

• Have thick connective layer (tunica adventitia)

• Endothelial layer

• Large lumen

→ Take all pressures from systole, need to absorb pressure, need to stretch or pressure would spread to capillaries and they would burst. Expand during contraction and squeeze blood around body when heart is at rest.

Describe the structure of the Arterioles.

• Contain a thin muscular wall and small lumen

• Endothelial layer, smooth muscle

• Contraction of the smooth muscle regulates the diameter of the lumen

What are the 2 main roles of the Arterioles?

• Determine blood flow to organs (can contract or relax arterioles to control blood flow to different organs and sections of the body)

• Major determinant of mean arterial pressure (smaller lumen and artery so key to control blood pressure)

Describe and explain the structure of Capillaries.

• Single layer of endothelial cells

• Exchange of nutrients, oxygen and waste across the capillary wall but NOT proteins

• Intracellular clefts and fused vesicles channels assist the exchange

• Thin layer allows exchange of O2, CO2 and nutrients, controls fluid in different compartments

Outline how exchange occurs at the capillaries.

• Occurs mainly by diffusions down gradients

• Facilitated by the slow movement of blood and large SA within the capillaries

• On graph (Bottom (blood velocity) and top (total cross sectional area)

• Capillaries large SA so allows exchange, blood flow very slow as capillaries that allows exchange to occur (2 reasons)

Describe and explain the structure of veins and venules.

• Large diameter lumen (low resistance)

• Thin walls

• Valves: Unidirectional (no backflow , blood can only flow in one direction)

How is venous blood return to the heart through vein and venules?

• Facilitated by valves and the skeletal muscle pumps

• Veins runs close in the skeletal muscle

• Blood flow back as you move around. Muscles moving squeezes veins pushes blood up towards the heart

What is varicose veins?

• Broken valves allow the blood to flow backwards under gravity

• Blood can no longer forced back lead to accumulation of blood

Draw a diagram to summarise the structure and function of the blood vessels.

Which side of the heart is bigger and why?

LHS bigger. More muscle, provide for systemic system (RHS only pumps blood to lungs) with whole body

Draw the overall structure of the heart.

Label where the main systemic arteries are on the body.

Label where the main systemic veins are on the body.

Draw a diagram and label the internal structure of the heart.

Yellow: muscle layers

What holds values in the correct place?

Tendons

Name the valves of the heart.

• Right AV valve (tricuspid)

• Pulmonary semilunar valve

• Left AV valve (bicuspid valve)

• Aortic semilunar valve

→ All blood vessels are at the top of the heart

Draw a diagram of outer structure of the heart.

Describe the blood supply the heart.

• Heart has extensive network of blood vessels supplied with oxygenated blood via the coronary arteries (provide blood to heart)

• Coronary arteries branch off the aorta (coming from left ventricle)

• Most deoxygenated blood drains back into the right atrium via a single vein (coronary sinus) (then to vena cava)

What causes of coronary arterial disease?

• Atherosclerosis (thickening of the coronary arteries) (covered in lipids)

• Blood clots (coronary thrombosis)

• Drugs

• Surgery

What is coronary heart disease?

• Insufficient blood flow (ischemia) is associated with chest pains (angina) often radiating down left arm

• Severe blockage leads to damage (death) of the heart region and myocardial infarction or heart attack

• Ventricular fibrillation and death (heart attack)

→ Too much fatty food, build up of fat and immune cells, leads to blockage. Causes insufficient blood flow (ischemia)

How can you treat coronary arteries?

→ Can damage whole part of heart and cause heart attack (irregular beating of heart occurs)

→ Bring from arm up to heart

Leave stent to keep blood vessels open

MENINGITIS:

= Bacterial infection of the cerebral spinal fluid

* Increased pressure in brain leading to seizures and loss of consciousness

MENINGES:

Tough fibrosis membranes

Describe the blood circulation in the brain.

• Different circulation to rest of the body

• Has separate liquid layer and blood vessels

What produces Cerebral Spinal Fluid?

Produced in specialised epithelial cell called choroid

Describe what cerebral spinal fluid (CSF) is and its function.

• CSF Protects brain (cushioning effect)

• Circulation around brain and spinal cord driven by changes in circulation, respiratory and posture

• Passes into vein via valves at the top of the skull (arachnoid villus)

• Bacterial in CSF is called meningitis (increased pressure in brain leading to seizures and loss of consciousness)

Describe blood brain barrier.

• Capillaries contain tight junctions and are less permeable to many substances (blood brain barrier)

• Difficult to get drugs and proteins into brain

• Exception is lipophilic molecules such as anaesthetics, alcohol etc. (can easily cross membranes)

• Brain has no stored glycogen and requires constant supply of glucose and oxygen (damage within mins)

• Loss of blood supply and death of neurones: stroke

→ Main diffusion down a gradient

→ Facilitated by slow movement of blood and large SA

What are the two main fluid compartments of the body?

• Intracellular: 28L

• Extracellular: 14L

→ Plamsa (3L)

→ Interstitial (11L)

How are the main fluid compartments of the body maintained?

3 Forces regulate how liquid move between the compartments

1. Osmosis

2. Colloid Osmotic Pressure

3. Hydrostatic Pressure

Where do the following forces occur in the body?

a) Osmosis

b) Colloid Osmotic Pressure

c) Hydrostatic Pressure

a) Cells and Interstitium (both ways)

b) Interstitium to plasma

c) Plasma to Interstitium

HP and COP can only occur in the capillaries in peripheral parts of the body

What happens when the body fails to regulate fluid compartments?

Leads to oedema

OSMOSIS:

= Net diffusion of water across a selectively permeable membrane from a region of high water conc to one that has a lower water conc (low particle conc to high particle conc)

OSMOLES:

= a measurement of the total number of particles in a solution

One osmose (ism)= 1 mole (6.02 x 10 ‘23)

1M glucose = 1osm

1M NaCl = 2osm

Osmolarity is…

independent of molecular weight

CELLULAR MEMBRANES:

• Permeable to water

• Impermeable to solutes (ions ) eg. Na+, Cl-, K+ etc

• Osmosis determines distribution of water (eg. Size of intracellular and extracellular compartments)

OSMOTIC PRESSURE:

= pressure required to prevent osmosis

Alpha concentration of osmotically active particles in solution

Draw a diagram to show the differential levels of cation (+ve) and anoint (-ve) intracellular and extracellular compartments.

→ High volume of NaCl outside of the cell

Potassium phosphate high conc inside cell

What are the effects of changing the extracellular media upon the cell size?

The establishment of osmotic equilibrium

• Isotonic

• Hypotonic (can lead to lysis)

• Hypertonic

→ More likely extracellular has been changed rather than the cellular environment

INTERSTITIUM:

Liquid surrounds cell and tissues

PLASMA:

Liquid in blood

What is the colloid osmotic pressure?

• Capillary membrane is semi-permeable

• Permits diffusion of ions, water, O2, nutrients and waste

• NOT PROTEINS

• ONLY OCCURS IN CAPPILARIES

(absorption)

What are the concentration of solutes ad proteins in the extracellular compartments?

Very similar except from proteins

Plasma 3 times more protein

COLLOID OSMOTIC PRESSURE:

• pressure exerted by the higher levels of protein in the plasma compared with the interstitial fluid

• Draws water back into plasma by osmosis (absorption)

• 28mmHg (plasma), 3mmHg (interstitium) = 25mmHg

→ protein allows net movement of water back into the plasma

HYDROSTATIC PRESSURE:

= Is the force exerted by the blood upon the capillary walls eg. blood pressure

→ Arterial end higher pressure (larger hydrostatic pressure)

→ Venous end pressure at lot lower

Drives blood from plasma into interstitial space

Pressure drops at the blood moves through the capillaries (35mmHg) to (15mmHg)

What is overall movement across capillaries determined by?

Capillary Net Filtration Pressure (NFP)

→ Equation how much liquid is moving into and out of the blood vessel (net movement)

→ Hydrostatic pressure only in capillaries but changes down capillaries reduces as further away from capillaries

→ Varies between the arterial and venous end of the capillaries

Describe the bulk flow of fluid from the plasma.

Use lymphatic system to return liquid back into the blood system prevents swelling (oedema) in the body

LYMPH SYSTEM:

= is parallel vascular system with 2 major functions

• Is where most of the immune response occurs

• Lymph nodes, detect infection, will swell

• Cancer tend to spread to lymph nodes, huge problem when treating cancer

What are the 2 major functions of lymph systems?

1. Draining fluid from the tissues and returning to the cardiovascular system

2. Maintenance of the immune response

What happens with fat in lymphatic system?

Collects fats from the intestines/liver and deposits into veins

What is the path of fluid in the lymphatic systems?

Excess fluid passes into lymph capillaries, through lymph nodes (detection of infection) before passing back to blood stream at the neck (largest thoracic duct that drains into subclavian vein)

How is fluid moved around the lymph system?

Fluid is forced along by action of muscles and breathing (respiration)

Larger lymph vessels are surrounded by smooth muscle that contract spontaneously and driven by pacemaker cells (heart)

What is contained in lymphatic systems?

• Contain valves

• Contains white immune blood cells (lymphocytes, macrophages, dendritic cells)

• Collects antigens (proteins produced by pathogens)

• Antigens recognised by B-lymphocytes in lymph nodes leading to activation of immunity

• B-cell proliferates to produce antibodies. Lymph nodes also contain multiple other immune cells (swelling can occur)

How can oedema be caused?

• Increased capillary pressure (heart failure)

• Decrease in colloid osmotic pressure

• Blockage of lymph nodes

How does increased capillary pressure cause oedema?

• Damage heart (heart failure)

• heart doesn’t function properly lead to heart failure

• Heart will try and retain more water to increase pressure, net migration of more water outside of arterial end

How does a decrease in colloid osmotic pressure cause oedema?

→ Dop of protein in blood proteins

→ Kidney problem lose lots of proteins

→ Burns

→ Malnutrition (not enough protein consumed)

How does a blockage of lymph nodes cause oedema?

Can be caused by vasectomy, parasite infections, cancer infections, surgery damage

Give an example of intracellular oedema.

→ cells and interstitial fluid, cells can’t retain water

Summarise the regulation of fluid compartments.

CARDIAC OUTPUT (L/min):

= activity of the heart (= the pump that moves the blood (creates a pressure difference))

= Heart rate (HR) (breath/min) X Stroke Volume (SV) (L/beats)

What can cause changes in cardiac output?

• Sleep 10% decrease

• Excitement, stress 30% increase

• Pregnancy 40% increase

• Exercise 600% increase

What is heart rate driven by?

By waves of electrical activity that induce the cardiac muscle to contract

STROKE VOLUME:

= the volume of blood leaving the heart

HEART RATE:

= Number of beats per min

Healthy HR: Usually 60-70 bpm

Heart contracts from the apex upwards

What circulation is on the

a) right

b) left

side of the heart?

a) Pulmonary circulation

b) Systemic circulation

Draw a diagram to show the components of the conduction system of the heart.

What is heartbeat driven by?

By specialised myocytes composed of the Sino atrial node and the atrioventricular node.

AVN node connects atria and ventricles. Creates delay to allow atria to contract

Bundle of His= fast conducting myocytes, connect to purkinjie fibres are very wide allowing rapid conduction throughout the ventricle and simultaneously contraction

Outline the sequence of cardiac excitation.

• Delay at AV node allows atria to contract before ventricles

• Pacemaker cells spontaneously generate electrical activity… muscles spread electrical impulse across all atria (only pushes 10% of blood, vacuum draws in the rest)

• Delay AV node, spread down fibres contracts heart upwards from apex

What causes the pacemaker cells of the SA node to trigger an action potential?

• Low resting membrane potential

• Na+ leakage

  Easy for pacemaker cells to depolarise as they have leaky Na+ channels (funny channels)

  Allows sodium to enter and allow them to slowly depolarise the cell

Outline the mechanism underlying the spontaneous action potentials in the pacemaker cells (Sino-atrial node).

1. Sodium ions ‘leaking’ in through the F-type [funny] channels and calcium ions moving in through the T-type (transient) channels cause a threshold graded depolarisation

2. The rapid opening of voltage-gated calcium L-types channels is responsible for the rapid depolarisation phase

3. Reopening of potassium channels and closing of calcium channels are responsible for the repolarisation phase

→ ANS controls HR through how quickly these channels are opened or closed

→ For a cardiac nodal cell

The bigger the heart…

the slower the heart beat

What controls the overall heart rate?

Sino Atrial Node (SAN)

If heart block: heart attack can damage conductivity of heart, parts of heart could end up beating independently

Outline the mechanism of contraction of the ventricular cardiomyocytes.

1. The rapid opening of voltage-gated sodium channels is responsible for the rapid depolarisation phase

2. The prolonged ‘plateau’ of depolarisation (contraction) is due to the slow but prolonged opening of voltage-gated channels and closure of potassium channels

3. Opening of potassium channels results in the repolarisation phase

→ from ventricular muscle cell

How does calcium produce contraction of the cardiac muscles?

Calcium ions regulate the contraction of cardiac muscle:

* the entry of extracellular Ca2+ ions causes the relays of Ca from the sarcoplasmic reticulum, the source of 95% of the Ca in the systole

What is the refractory period?

Time required for the recontraction of muscle cells

* Prolonged delay allows blood to pushed all around the body: don’t want to disrupt process

Why is refractory period needed?

Allows ventricles to fill with blood prior to pumping

What is the Sino-atrial regulated by?

Autonomic nervous system

• Sympathetic system system innervates the WHOLE heart

• Parasympathetic innervates just the SA and AV heart

• Both systems are tonically active but parasympathetic dominates at rest

• Controls blood volume and HR

→ Cut vagus nerve HR will automatically increase

Outline the parasympathetic nervous system regulation of the Sino-atrial node.

1. Parasympathetic neurones release acetylcholine

2. m2 muscarinic receptors of SA node

3. Increase K+ efflux , decrease Ca2+ influx

4. Hyperpolarises cella and decrease rate of depolarisation

5. Decreases HR

6. Bradycardia

→ always activate at rest (dominates)

Outline the parasympathetic nervous system regulation of the Sino-atrial node. 

1. Sympathetic neurones release noradrenaline

2. Beta1 adrenergic receptors of SA node

3. Increase Na+ and Ca2+ influx

4. Increase rate of depolarisation

5. Increase HR

6. Tachycardia

What regulates the rate of depolarisation of the SAN?

Both the parasympathetic and sympathetic nervous system

Where is the SAN located?

At the top of the right atrium

ECG:

= is a summation of the spread of action potential through the various sections of the heart

Outline the electrical events of the cardiac cycle on a diagram.

Draw and label a diagram of ECG to summarise the meaning of the deflections of electrocardiogram.

P

Atrial depolarisation

QRS

Ventricular depolarisation