Cardiac Physiology

Why do humans have a cardiovascular system

Evolutionary consequence of multicellular organisms - cells inside body don't have access to environment for diffusion

Hemodynamics

the study of blood moving through the circulatory system, looking at the relationship between blood flow, blood pressure, and resistance to blood flow

Formula for blood flow

F = ΔP/R

F unit

Flow (mL/min)

ΔP

Pressure difference between two fixed points (mmHg)

R

Resistance to flow (mmHg/mL/min)

Which way does blood flow

From higher pressure to lower pressure - the pressure difference is the driving force for blood flow

To have flow, the pressure difference....

Must overcome resistance to blood flow (ΔP > R)

How can our bodies change the factors effecting blood flow

By changing resistance at a constant pressure in arterioles

Hydrostatic pressure

the pressure that blood exerts on the walls of the blood vessels

What happens if there is no pressure difference between two points (ΔP = 0)

Then the flow is 0mL/min

What factors determine resistance to blood flow

blood viscosity, vessel length, vessel diameter

How does viscosity affect resistance to blood flow

Higher hematocrit = more cells in blood = more viscous blood = greater resistance to flow

How does blood vessel length effect resistance

the longer the vessel, the greater the resistance. Blood comes into contact with the vessel walls more. creating more friction

How does blood vessel diameter effect resistance

In a smaller diameter vessel, a greater proportion of blood is in contact with the wall = more friction = more resistance

- Larger diameter - blood forms concentric layers, and the inner layers do not touch the vessels

What is the use of Poiseuille's equation

Displays the relationship between viscosity, vessel radius, and vessel length for how they effect resistance

Poiseuille's equation

R = 8 L η/ π r^4
- R = resistance to blood flow
- L = vessel length
- n = blood viscsity
- r = radius

In Poiseuille's equation, resistance is proportional to:

Increased vessel length, increased viscosity

In Poiseuille's equation, resistance is indirectly proportional to:

Radius

Which factor has the greatest impact on resistance

Radius (as is it raised to the power of 4)

In which way does the human body increase resistance

Constricting and relaxing blood vessel muscle

What are the functions of the cardiovascular system

- Deliver oxygen and nutrients, and remove metabolic waste products
- Fast chemical signaling to cells by circulating hormones or neutrotransmitters
- Thermoregulation (transfer heat from muscles to the core, or lose heat through the skin)
- Mediation of inflammatory and host defense responses against invading organisms

Components of the cardiovascular system

Heart, blood vessels, blood

Types of blood vessels

arteries, arterioles, capillaries, venules, veins

Arterioles

Small branching vessels with high resistance

Capillaries

Transport of blood between small arteries and veins - exchange of materials between blood and body cells

Which way does blood flow in arteries

Away from the heart

Which does blood flow in veins

Towards the heart

Used of closed circulatory system

Greater pressures to be generated when the heart contracts

How many chambers does the heart have

4 - 2 atria, 2 ventricles

Atria

Thin walled, low pressure chambers that receive returning blood, and move blood into the ventricles

Ventricles

Thick walled, high pressure chambers that are responsible for the forward propulsion of blood when they contract

Base of the heart

Where the blood vessels attach

Septa

Divides the sides of the heart, making sure that low oxygenated and high oxygenated blood are seperate

Where does the left side of the heart pump blood to

The systemic circuit

Where does the right side of the heart pump blood to

The pulmonary circuit

Interatrial septum

Wall separating the atria

Interventricular septum

Wall separating the ventricles

Pulmonary circuit

Carries blood to and from the gas exchange surfaces of the lungs. Blood enters lungs poorly oxygenated and leaves highly oxygenated

Systemic circuit

Transports blood to and from the rest of the bodies. Oxygen leaves the left side of the heart oxygenated, and leaves tissues deoxygenated

Left side of the heart

Receives blood from the pulmonary circulation and pumps it to systemic circulation

Right side of the heart

Receives blood from the systemic circulation and pumps it to the pulmonary circulation

Order of blood flow

Moves from pulmonary circuit to the heart, and then the systemic circuit before returning to the heart

Blood flow cycle

1. Right ventricle (deoxygenated blood)
2. Pulmonary trunk/artery
3. Lungs (oxygenated here)
4. Pulmonary vein
5. Left atrium
6. Left ventricle
7. Aortic valve
8. Aorta
9. Body cells/tissues (deoxygenated)
10. Vena cava
11. Right atrium (and begin again)

Arteries

Carry blood away from the heart - mostly oxygenated blood except pulmonary trunk/artery

Veins

Carry blood to the heart - mostly deoxygenated blood except the pulmonary veins

Series flow

Blood passes through the pulmonary and systemic circuits in sequence

Parallel flow

Flow of blood to organs - each organ is supplied by a different artery, allowing for independent regulation

Which organ is an exception to parallel flow

The liver - receives blood in series

When the right ventricle contacts, where does blood flow

Blood is pumped the lungs

When the left ventricle contracts, where does blood flow

Blood pumped to the body

Distribution of blood flow during excersice

Cardiovascular system increases the rate of blood flow, and alters the distribution of blood flow to the muscles (instead of abdominal organs)

Pericardium

Fibrous sac surrounding the heart and the roots of great blood vessels leading into and out of the heart

Functions of the pericardium

- Stabilizes the heart in the thoracic cavity
- Provides protection to the heart by physically surrounding it
- Reduces friction as the heart beats by secreting the pericardial fluid
- Limits overfilling of the heart chambers, preventing sudden distention (stretching)

Structures of the pericardium

Fibrous pericardium, parietal pericardium, visceral pericardium

Fibrous pericardium

Outer layer of the pericardial sac - provides protection for the heart and stabilizes the heart in the thoracic cavity, prevents rapid overfilling of the heart

Parietal pericardium

Connected to the fibrous pericardium and attaches to it. Secretes pericardial fluid into the pericardial cavity to decrease friction during heartbeats

Pericardial cavity

Open area separating the parietal pericardium from the visceral pericardium - filled with pericardial fluid

Visceral pericardium

Innermost layer of the pericardial sac
- AKA the epicardium when it comes into contact with the heart muscle

Serous layer

Layer of cells that secrete fluid - made up by parietal + visceral pericardium

Pericarditis

inflammation of the pericardium caused by virus or bacteria - causes blood vessels to become leaky

Cardiac tamponade

acute compression of the heart caused by pericardial fluid accumulation - heart chambers cannot fill with adequate amount of blood

How to treat cardiac tamponade

Drain pericardial fluid, then treat the cause

Why is the muscle wall of the left ventricle thicker than the right ventricle

Allows the left ventricle to generate higher pressures, allowing blood to pump around the systemic circulatory system

Why is the right ventricle muscle wall not as thcik

Blood only needs to pump from the right ventricle to the lungs (pulmonary system)

Layers of the heart wall

epicardium, myocardium, endocardium

epicardium (visceral pericardium)

Layer outside heart muscle, covering the surface of the heart and connected to the myocardium.

Epicardium function

Protective layer for the heart

Myocardium

Muscular wall of the heart underneath the epicardium

Role of the myocardium

Contains myocytes (muscle cells) that contract when the heart beats

Endocardium

Innermost layer of the heart wall, lines the cavities/heart valves

Function of the endocardium

Made of endothelium - provides a smooth surface for blood to flow oveer

Which side of the heart has a thicker myocardium

Left side

Myocytes

Cardiac muscle cells (Y shaped)

Myocyte connection

Connected longitudinally - allows for greater connectivity (Y shaped cell allows for connection to 2 other myocytes)

Myocyte features

- Striated/striped with actin and myosin
- Single, centrally located nucleus
- Rich in mitochondria (ATP for muscles to contract)

How are adjacent myocytes held together

Intercalated discs

2 specialized intercellular junctions at intercalated disk

Desmosomes, gap junctions

Desmosomes

Adhering junctions that hold cells together in tissues subject to considerable mechanical stress/stretching
- Mechanically couples one heart cell to another

Proteins involved in desmosomes

Cadherins, plaques, intermediate filaments

Cadherins

Attach from one cell to cadherins of other cells

What do cadherins attach to

Dense plaques, which attach to intermediate filaments that are in the cell

Gap junctions in intercalated disks

Communicating junctions that electrically couple heart cells via ions

Use of gap junctions in heart cells

Spread action potential

Proteins in gap junctions

Connexons

Heart muscle arrangement

Spiral arrangement around heart chamber (c.f biceps - straight line)

Why is heart muscle arranged in a spiral

Helps squeeze blood into arteries when ventricles contract

How many heart valves are there

4 - 2 AV valves + 2 Semilunar valves

Bicuspid valve

valve between the left atrium and the left ventricle.

Tricuspid valve

valve between the right atrium and the right ventricle

Semilunar (arterial) valves

found between the ventricles and the arteries into which the ventricles pump their blood

Aortic valve

Semilunar valve separating the left ventricle and the aorta

Pulmonary valve

Semilunar valve separating the right ventricle and the pulmonary trunk

What are the valves made of

Collagen covered by endothelium

Valve rings

Cartilage that valves attach to

Blood flow through the valves

· Poorly oxygenated blood returns to right atrium.
· Right AV valvue - blood flows to the atrium
· Blood moved from right ventricle to pulmonary trunk via pulmonary valve
· Oxygenated blood returns to the left atrium - blood pushed through tricuspid valve to left ventricle
· Blood pushed from left ventricle to aorta via aortic valve

What is the function of the heart valves

Ensure unidirectional blood flow to the heart, preventing blood flowing backwards

How do valves open and close

Valves open/close passively due to difference in pressure

Is energy expended to open valves

No

How does a heart valve open

When the pressure is greater behind the valve, the valve opens