A&P Exam 2

What makes up 99% of the heart?

cardiomyocytes

What are the characteristics of cardiomyocytes?

• striated

• one nucleus

• stimulation from pacemaker cells is needed for contraction

• Always aerobic (lot of mitochondria, lots of capillaries, lots of myoglobin)

• intercalated disks

• gap junctions—> functional syncytium

• desmosomes stitch cells together

What does the connective tissue do in the heart?

• acts as a fibrous skeleton—> supports chambers and blood vessels

• prevents overstretching

• electrical insulator

Conducting System Cells

• do n ot contract

• spontaneously depolarize

• no resting membrane potential

How do nodal cells activate?

cell repolarizes, funny channels open once the membrane hits -60 mV (lot of Na+ in, little K+ out), transient Ca 2+ channels open (lets Ca 2+ in), L-type Ca 2+ channels open (lets Ca 2+ in) allowing rapid depolarization, cell repolarizes and K+ channels open and K+ leaves the cell

Why are funny channels called funny channels?

they open when the membrane is negative (hyperpolarized) instead of when its positive

What is a funny channel considered? What does that mean for the channel?

• An HCN—> hyperpolarization activated cyclic nucleotide gated channel

  • Means that the channel is controlled by cAMP and opens with voltage

what does affecting the rate of repol and depol

impacts heart rate

how does cardiomyocyte activation work?

cardio myocytes have a resting membrane potential of -90 mV, electrotonic current from adjacent cell (Na+ or Ca 2+), cell depolarizes to about 30 mV and opens voltage gated Na+ channels open, L-type Ca 2+ channels and slow outward rectifying K+ channels open and then plateau, fast outward rectifying K+ channels and repolarization

When does the absolute refractory period occur?

During the plateu

Can any new action potentials form during ABS?

absolutely not

The plateau

• allows for tension development

• no tetanus

• prevents re-entry arrhythmia

K-ATP channels

• open in response to low blood flow in the heart (myocardial ischemia) or as a response to being hit in the chest at a specific point in the AP

• Heart rate increases but there is no filling of ventricles so no blood is pumped

What can a short plateau lead to?

Re-entry arrythmia

systole

contraction; emptying

Diastole

relaxation; filling

EDV

End diastolic volume, about 130 mL

ESV

End systolic volume, around 60 mL

SV

Stroke; the amount of blood ejected in one cycle, around 70 mL

Does electrical or mechanical come first?

Electrical always precedes mechanical

CO

Cardiac Output

amount of blood pumped in a minute

L/min

CO= SV x heartrate

Heart Rate (HR)

changed by a chronotrope

ACh

Norepinephrine/epinephrine

What system is ACh associated with?

parasympathetic

What system are NE/Epi associated with?

sympathetic

What senses chronotropes?

Chemoreceptors, baroreceptors, and proprioceptor

Where does a change in HR occur?

The SA node

An HCN channel..

is a hyperpolarization activated cyclic nucleotide gated channel

• uses cAMP

Sympathetic changes

• increase cAMP

• more funny channels

• steeper faster depol

  • higher HR

Parasympathetic changes

• lower cAMP

• fewer channels open

• longer/slower depol

  • lower HR

What would a ca channel blocker do to heartrate? Why?

Would slow HR bc it would block the transient and long type Ca channels

What is the formula for SV

EDV-ESV= SV

What changes SV?

Inotropes

What is one example of an inotrope?

The sympathetic nervous

• Epi/ NE

• increases cAMP

• activation of kinases, phosphorylates Ca channels on SR

• release Ca, bind to troponin

  • more crossbridges= stronger contractions

A second way to change stroke volume is…

Preload- how much is in the ventricle prior to contraction

• increases EDV

  • exercising/activity mobilizes venous return to R atrium

• Increases stretch

• stimulates stronger R ventricle contraction

Frank Starling Law

more in = more out

length tension relationship

Other ways to increase EDV are:

• hydration

• longer ventricle filling time

  • a fast HR means less fill time

Whats a third inotrope?

Afterload—> resistance of blood in the arterial system

• increased ESV

• Altering contraction makes the heart work harder to pump less blood

  • more blood left over

Hemodynamics

the study of blood flow and the factors that affect it

Continuous capillaries

no gaps

Fenestrated capillaries

like a castle wall, some holes

Sinusoid capilaries

look like swiss cheese

Elastic arteries

• 3 thick layers

• High pressure

• stretch and recoil w/ ventricular ejection

  • pulsatile flow

Muscular arteries

• smooth muscle layer

• lower pressure, weaker pulsatile flow

• vasoconstrict and vasodilate to control flow

arterioles

• vasoconstrict and vasodilate to control flow

• low pressure, smooth flow

• primary resistance vessel

capillaries

• gas exchange

• filtration and reabsorbtion

Poiseuille’s Law

Flow of fluid through a tube

• laminar flow

• Q= deltaP/R

what has the biggest impact on resistance?

vasoconstriction and vasodilation

serial resistance

resistances of continuous capillaries added together

Parallel resistances

resistance of each divided by the number of those vessels

What is blood pressure?

• hydrostatic pressure

• linked to volume

• drives blood flow and tissue profusion

BP=

systolic/diastolic

systolic

ventricles contract, sv is ejected into the arterial system

diastolic

ventricles relax, blood moves further into arterial siystem, volume down

Dicrotic notch

closing of aortic valve

pulse pressure

systolic-diastolic

Mean Arteriole Pressure

Diastolic + PP/3

What does high blood pressure mean?

heart is working too hard

Blood flow

L/min, same as cardiac output

TPR

total peripheral resistance, R of all blood vessels in the circuit

Qflow

delta P/ R

CO

BP/TPR

What does Qflow(pulmonary) equal

Qflow sys

If CO > runoff

increased blood volume, increased blood pressure

Vasoconstriction of the arterioles

increases R and decreases runoff

Vasodilation of the arterioles

decreases resistance and increases runoff

Why do we have lungs?

• to get O2 for aerobic respiration

• dispose of CO2

• for gas exchange

What does CO2 do in the body?

CO2 + H2O = H2CO3= H+ + HCO3-

What does an abundance of free H+ ions do in the body?

decreases pH of the body when in excess and can impact the marginal stability of proteins

What are the two regions of the respiratory system

The conducting system and the respiratory membrane

What does the conducting system do/ contain?

• tubes that carry air, filter, humidify

• Includes:

  • pharynx

  • trachea

  • mucus glands

  • primary bronchi

  • lungs

  • hyaline cartilage rings

What do mucus glands do?

• called goblet cells

• capture particles (dust, pollen, etc)

• pseudostratified ciliated columnar

• mucociliary defense

What do the hyaline cartilage rings do?

keep tubes open, laminar air flow

How many levels of branching are in the conducting portion?

there are 16 levels of branching

What does the respiratory membrane do/consist of

• The only place in the body where gas exchange can occur

• consists of

  • roughly 300m alveoli

  • smooth muscles on bronchioles

What do the sooth muscles do?

Control air flow through bronchodilation and bronchoconstriction

What are the parts of an alveoli?

• smooth muscle cells

• simple squamous epithelium

• water

• Surfactant

• Type 2 alveolar cell

• macrophages

What is a type 1 alveolar cell and what does it do?

A simple squamous epithelium—> forms respiratory membrane, ideal for gas exchange

What does surfactant do?

Breaks up the bonds between water to prevent surface tension, prevents the alveolus from collapsing, a detergent

What produces surfactant?

Type 2 alveolar cells

What does the respiratory membrane consist of?

Type 1 alveolar cells, a shared basement membrane, and the capillary endothelium

What are the ideal conditions for diffusion?

minimum x- small distance for diffusion

Maximize surface area

What lifts the ribcage during breathing?

The external intercostals

What houses and surrounds the lungs? (in order)

• pleural cavity

• parietal pleura

• plural space w/ fluid

• visceral pleura

Ventilation

movement in and out of the lung

What pulls air in?

Diaphragm contracting (Volume increasing, pressure decreasing), alveolar pressure is less than atmospheric pressure

What causes an exhale?

Diaphragm relaxing (volume decreasing, pressure increasing), alveolar pressure exceeds alveolar pressure

What is Boyle’s law?

P= 1/V

• inverse relationship between pressure and volume

Dalton’s Law

Air is a mixture of gases and the total pressure is the sum of the partial pressure of these gases

• largely made of N2 and O2

Why is the pressure of O2 in the lungs stable at 100 mmHg?

constant ventilation bringing in fresh air and removing stale air

Henry’s law

the movement of gas across an air water interface

What is PO2 in the right ventricle?

20-40 mmHg

What is PO2 in the left atrium?

100 mmHg

What is PCO2 in the right vent?

45 mmHg

What is PCO2 in the lung?

40 mmHg

What is the concentration of a gas equal to?

solubility x partial pressure

Is PCO2 soluble in water? What does this mean for it’s gradiant?

Pretty soluble in H2O, can have a smaller gradient and still diffuse

Is O2 soluble in H2O? What does this mean for it’s gradient?

Not very soluble in O2, has to have a bigger gradient

How long does it take for blood to pass the lung (transit time)?

0.75 seconds

How long does it take for blood in the capillaries to equilibrate and for gas exchange to occur?

0.25 seconds

Does alveolar PO2 fluctuate?

No it remains fairly stable