Animal Physiology Circulation

Invertebrates often have what kind of circulatory system?

open circulatory system

• Crayfish: have a heart with tubes that go away from the heart, but once you get far enough out, the tubes just gush out hemolymph

  • hemolymph squishes around with the interstitial fluid already there

  • sinus collects this and is connected to tubes that go through the gill and back to the heart

  • has direction and control but is not closed

• Hearts are often neurogenic in these systems

Myogenic vs Neurogenic

myogenic: signal for heart beat is intrinsic to the muscle itself (don’t need the nervous system to tell it to beat)

neurogenic: nervous system has to tell the heart when to beat

Humans have what type of circulatory system?

closed circulatory system: heart with closed chambers that connects to closed tubes (blood on inside, tissue on outside)

How do amphibian hearts compare to ours?

they also have two sided hearts but unlike us, there is measurable exchange between them

• no full separation between the left and right sides of the heart

• oxygenated and deoxygenated blood is mixing in multiple different places

• mixing them is inefficient but they add efficiency since they can also exchange through their skin

What heart adaptation do crocodiles have and what does it allow them to do?

they have separation between the left and right sides of the heart but they have a shunt adaptation that allows them to shunt blood while diving

• blood goes from right into left and bypasses the lungs

• this sends blood straight back into systemic circulation to be used so they can dive for longer

When blood is pumped out to system, how many places does it go to?

One place and then it comes back to the heart

• this is more efficient because each system organ gets good oxygenated blood and not oxygen deficient blood that has already been somewhere else

What is true of the pressure of the blood returning from system?

it does not have pressure; valves are used to prevent back flow and ensure it only goes in one direction back to the heart

Compact vs. Spongy Myocardium

compact: solid tissue that does not really get fed by the blood that is in the heart chamber; instead, it is fed by coronary arteries (this is what we have)

spongy: blood inside the heart chambers can do fluid exchange with the heart muscle itself so they do not need coronary artery (found in some fish)

• some animals have combination of both of these (sharks, tuna, salmon, etc.)

Mammalian fetal circulation

fetus is floating in fluid so they don’t use lungs in the same way that adults do

• do not get oxygen from air to alveoli; they get their oxygen from the umbilical cord (from placenta)

  • mother’s capillary bed sits beside fetus’ capillary bed

• fetus has higher affinity for oxygen

Blood comes in to the fetus through the liver and there is a hole between the left and right sides of the heart to where it will mostly miss the lungs

• shunt similar to that of crocodile; closes after birth

P wave, QRS complex, and T wave

P wave: atrial depolarization; marks end of diastole

QRS complex: ventricular depolarization; systole

T wave: ventricular repolarization; marks end of systole

Cardiomyocytes

specialized heart muscle cells

• conducting system contains 1% of cardiomyocytes and they are pacemaker cells (auto rhythmic)

• contractile system contains other 99% of cardiomyocytes that squeeze and contract

Conducting system action potentials

take a couple of ms

-starts at about -60 mV

-funny sodium channels open and membrane potential depolarizes

-this opens transient calcium channels to depolarize more and reach threshold

• funny sodium channels in the early phase and transient calcium channels in the late phase bring it to threshold (this is not a graded potential → pacemaker potential)

-voltage-gated, long-lasting calcium channels open which mediates the rising phase of the action potential

-voltage-gated potassium channels open and bring potential back down to reset

Contractile system action potentials

told to contract by pacemaker cells via electrical synapses (gap junctions)

take about 250 ms

-contractile cells rest at -90 mV (like skeletal muscles)

-don’t really have graded potential because signal through gap junctions pretty much automatically brings about the action potential

-voltage-gated sodium channels open and the cell depolarizes

-long-lasting calcium channels open to keep it depolarized for a longer amount of time (plateau potential mediated by calcium long channels)

-calcium channels close and voltage-gated potassium channels open to take back down

What does the plateau potential prevent?

buildup of tension in cardiac muscle

Cardiac output

heart rate x stroke volume

-at rest, it is about 5 L/min but this is highly variable

Parasympathetic and sympathetic modulation of cardiac output are considered what type of controls and what do they each do?

extrinsic controls

• parasympathetic: increase in activity lowers heart rate to decrease cardiac output

• sympathetic: increase in activity increases heart rate and stroke volume to increase cardiac output

What are some intrinsic controls of cardiac output?

EDV and Venous return

-increasing these increase stroke volume and thus cardiac output

Frank-Starling Mechanism:

• cardiac muscle is held below optimal length

• relates EDV (X) to SV (Y)

  • like skeletal muscle graph where EDV=length and SV=tension

• as EDV increases, as does SV until it hits optimal and stops

Stroke volume (SV)

the amount of blood that comes out with one beat during ventricular ejection

End-Diastolic Volume (EDV)

the blood in the ventricle at the end of diastole after the atria contract

• when both sets of valves are shut

Ejection fraction

SV/EDV

tells us the fraction of the EDV that we eject (SV is always going to be less than EDV)

Arteries

-have lots of pressure inside them so they have very thick and muscular walls

-very compliant (ability to stretch)

-elastic (ability to return to normal shape)

-since they are muscular, they can relax/contract once you get out to the arterioles (determine where flow goes)

Veins

-no pressure in them

-thin and have very little muscle in them

Pressure during each cardiac cycle

pressure in the ventricles goes from 0 to 120 and then back to 0 with each cycle

aortic pressure starts at 120, decreases to 80 and then goes back up to 120 at the same time that the ventricles do

• prototypical 120/80 BP

Pulse pressure

how much your blood pressure is changing

• systolic pressure-diastolic pressure

Mean arterial pressure

diastolic pressure + 1/3(pulse pressure)

-normal=93 mmHg

-helps us to know how much blood is going to the tissues

The farther away you get from the heart…

the more your pressure is going to drop

What is the pressure when blood enters the capillary and why is that important?

about 30 mmHg and this is important for two reasons:

1. capillaries are thin so they cannot hold a lot of pressure

2. creates a pressure gradient across the capillary bed to keep blood flowing

Flow

change in pressure/resistance

Total peripheral resistance

all of the resistance throughout the body that the heart is pumping against

• we want this to stay relatively constant so if we decrease resistance somewhere then we have to increase resistance somewhere else

  • during exercise we decrease resistance to leg muscles to increase flow so we have to increase resistance to other places

Intrinsic controls on total peripheral resistance

changes in response to what is going on in the tissue

• shear stress

• cold/heat application

• histamine release

• local metabolic changes

Extrinsic controls on total peripheral resistance

• vasopressin

• angiotensin II

• epinephrine

• sympathetic activity

Mean arterial pressure primarily depends on what to variables

cardiac output and total peripheral resistance

Why are there fluid filled pores in the endothelium at capillaries?

the pores are leaky (everywhere except for the brain) so little things like ions, glucose, and amino acids can pass through

• allows diffusion to occur more easily

• proteins canNOT move through these pores (must have specialized transport)

Pressure differences that promote absorption and filtration

at the arteriole end, hydrostatic pressure is greater than osmotic pressure to promote ultrafiltration (11 mmHg net outward pressure)

at the venule end, hydrostatic pressure is less than osmotic pressure to promote reabsorption (9 mmHg net inward pressure)

• osmotic pressure at both ends remains constant, it is the hydrostatic pressure that decrease as you go through the capillary

Osmotic pressure comes from what?

proteins in the plasma that act as solutes that are stuck in the capillary

-albumins specifically

How much of the volume that we initially filtered is reabsorbed?

90%

• the other 10% is captured by the lymphatic system

Lymph nodes

full of immune system cells that monitor body fluids

Lacteals

where we absorb our fats