( 7f ) Chemoreceptors Continued

There are 2 Types of Chemoreceptors that respond to something different

1. Peripheral Chemoreceptors

what’s the other type?

Central Chemoreceptors

“Central”

because they’re located in the

Central Nervous System

specifically in the

Medulla Oblongata _(BRAIN)

_{( NOT IN SPINAL CORD )}

remember

Medulla Oblongata is where basic vital signs are controlled

★ Central Chemoreceptors in the Medulla Oblongata monitors a chemical and sends a signal to the DRG to adjust our breathing

Do Central Chemoreceptors respond to

a DROP in P_O2 ( ⭣P_O2 )

NO

Again, that would ONLY happen in a

life threatening emergency

what DO Central Chemoreceptors respond to?

CO₂ in the BLOOD

what’s the DOMINATE CONTROL over ventilation?

( movement of air in/out lungs )?

CO₂ levels

what’s the DOMINATE CONTROL over breathing?

CO₂ levels

sidenote

former students said

TEAS exam asks question of “which of these is most important for controlling breathing?”

• oxygen?

• CO₂?

the answer is

CO₂

example

Competitive Swimmers before they dive in will

hyperventilate ( breathing out as much CO₂ as they can )

why?

So they can hold their breath for LONGER underwater!!

how?

if CO₂ accumulates that FORCES us to

BREATHE

→ causing us to not hold our breath anymore

what receptor tracks the CO₂ accumulation to trigger breathing?

Central Chemoreceptors

Blood Brain Barrier Capillary next to Medulla Oblongata

( where central chemoreceptors are! )

Scenario Shown

Increased P_CO2 in the blood

can CO₂ cross the blood brain barrier?

YES

why

CO₂ is

• Lipid Soluble

• Small

CO₂ CAN go into the

BRAIN

so far CO₂ crosses out of blood into brain

what happens to CO₂ in the brain?

the chemical reaction!!

_{→ cerebral spinal fluid has water ( H2O ) that CO2 can react with!}

what do the Central Chemoreceptors ACTUALLY respond to?

Hydrogen Ions ( H⁺ )

BUT WHERE did the Hydrogen Ions ( H⁺ ) COME FROM?

the REACTION represented by CO₂ that entered the brain!

notice in chart

underneath

(⭡P_CO2 )

it says

( ⭡H⁺ ) Increase of Hydrogen in the BRAIN

which is from this reaction!

when we have HIGH CO₂ in the BLOOD

that leads to

Hydrogen ( H⁺ ) in the BRAIN

_{→ from CO2 crossing into brain and causing reaction}

Hydrogen ( H⁺ ) in the BRAIN

Central Chemoreceptors respond to

Do Central Chemoreceptors respond to Hydrogen ( H⁺ )

IN BLOOD THAT’S NOT IN THE BRAIN?

( from lactic acid, fatty acids, etc )

NO

_{that’s what peripheral chemoreceptors do!}

it can’t because of the

Blood Brain Barrier

reminder

Capillary Cells in the brain are FUSED together by TIGHT JUNCTIONS

= no pores!

the ONLY way something can go in/out is

ACROSS the CELL MEMBRANE

Can Hydrogen ( H⁺ ) cross the cell membrane?

NO

why?

it’s a CHARGED PARTICLE ( + POLAR )
which can’t go through phospholipid bilayer ( + NON-POLAR )

meaning

Hydrogen ( H⁺ ) CANNOT cross the

Blood Brain Barrier

Meaning

Hydrogen ( H⁺ ) coming DIRECTLY FROM THE BLOODSTREAM

( ex. lactic acid )

CANNOT

Stimulate the Central Chemoreceptors in the BRAIN !!

H⁺ can ONLY REACH Central Chemoreceptors through CO₂ reaction !!

why in chart it says

⭡H⁺ in blood does not effect central chemoreceptors

“cannot penetrate the blood brain barrier”

Summary Chart of Chemoreceptors

Peripheral Chemoreceptors

Located : Carotid Bodies + Aortic Bodies

Do NOT respond to: P_O2 ( unless its super dramatic )

DOES responds to: Increased Hydrogen ( H⁺ ) in BLOOD

→ from metabolic acidosis mostly

→ also responds a LITTLE BIT to increased P_CO2

Central Chemoreceptors

Located : Medulla Oblongata

Responds to: Changes to Extracellular Fluid ( ECF ) in Brain

Stimulated by: P_CO2 via ( through the means of ) Hydrogen ( H⁺ ) in BRAIN

→ because of the chemical reaction!

figure that puts it all together

Aortic Bodies + Carotid Bodies

brings information where?

UP to the DRG

DRG will send it’s adjusting signals out to the

• Diaphragm

• External Intercostal Muscles

which will adjust breathing accordingly

So we’ve covered:

1. How we get air in and out

2. How we exchange the gases

there’s one more piece to talk about!

Transportation of Gases