Control of heart rate

What hormones increase heart rate?

• Adrenaline

• Noradrenaline

• Thyroxin

What controls the heart rate?

Cardiovascular control centre in the medulla oblongata

What does the acceleratory centre do?

Speed up heart rate

What does the inhibitory centre do?

Slows it down

What nervous system and nerve is used to speed up the heart rate?

• Sympathetic nervous system

• Accelerator nerve

What nervous system and nerve is used to slow down heart rate?

• Parasympathetic nervous system

• Vagus nerve

What receptors are located in the blood vessels?

1. Baroreceptors

2. Chemoreceptors

What do baroreceptors detect?

Changes in blood pressure

In which blood vessels will barorecepters be found?

• aorta

• vena cava

• carotid arteries

What do chemoreceptors detect?

Changes in pH of the blood

Why would the pH of the blood change?

During exercise more carbon dioxide is released into the blood - makes pH decrease due to carbonic acid

Which blood vessels would chemoreceptors be found in?

• aorta

• carotid artery

• medulla

How are impulses from the cardiovascular control centre transmitted?

Motor neurones in the autonomic nervous system (ANS)

What are the two parts of the ANS?

1. Sympathetic

2. Parasympathetic

What are some physiological mechanisms triggered by the parasympathetic nervous system?

• Pupils constrict

• Stimulates salivation

• Inhibits heart

• Constricts bronchi

• Stimulates digestive activity

• Stimulates gall bladder

• Contracts bladder

• Relaxes rectum

What are some physiological mechanisms triggered by the sympathetic nervous system?

• Pupils dilate

• Inhibits salivation

• Relaxes bronchi

• Accelerates heart

• Inhibits digestive activity

• Stimulates glucose to be released by liver

• Secretion of adrenaline and noradrenaline

• Relaxes bladder

• Contracts rectum

When are adrenaline and noradrenaline released?

Times of stress / physical activity

What is the physiological effect of adrenaline on liver cells?

1. Adrenaline is secreted by the adrenal medulla

2. Binds to adrenergic receptors on cell membrane of hepatocytes

3. Activates an enzyme in cell membrane called adenylyl cyclase

4. Enzyme catalyses production of secondary messenger cAMP from ATP

5. cAMP activates a cascade of enzyme-controlled reactions which result in glycogenolysis

6. Glucose is released by liver cells into the blood

7. Use increased glucose conc. and rate of respiration increases

What organ does adrenaline have an inhibitory effect on?

Pancreas - insulin

Why do the pupils dilate when stressed?

Allows more light in - gives better image of threatening situation

Why may defecation and urination occur when stressed?

May deter predators and decreased body weight allows faster movement

Why do arterioles to digestive system constrict when stressed?

Less blood travels to the gut, where it’s not needed as much

Why does heart rate increase when stressed?

Allows for more aerobic respiration for increased ATP production

Why does sweat production increase when stressed?

Prevents body overheating when exercise level increases

Why are endorphins released when stressed?

Natural painkillers allow the body to push beyond normal limits

Why does ventilation rate and depth increase when stressed?

More oxygen is taken in to be used in aerobic respiration

Why do blood glucose levels rise when stressed?

Glycogen is broken down and released from the liver

Why does metabolic rate increase when stressed?

Increased respiration releases ATP, more glycogenolysis occurs

Why do the erector pili muscles contract when stressed?

Hairs are raised on end; evolutionary adaptation to frighten an enemy

Why do arterioles to liver and muscles dilate when stressed?

More blood travels to these areas to collect and supply glucose