1. Definition
Cardiovascular reflexes are neural mechanisms that help maintain blood
pressure (BP), heart rate (HR), and blood flow in response to various
internal or external changes.
2. Types of
Cardiovascular Reflexes
|
Type of Reflex |
Sensor Location |
Function |
|
1. Baroreceptor Reflex |
Carotid sinus, Aortic arch |
BP regulation (↓ HR if ↑ BP) |
|
2. Chemoreceptor Reflex |
Carotid and aortic bodies |
Response to ↓ O₂, ↑ CO₂, ↑ H⁺ (↑ HR) |
|
3. Bezold-Jarisch Reflex |
Ventricular walls |
↓ HR and BP (in response to stretch) |
|
4. Bainbridge Reflex |
Right atrium |
↑ HR due to ↑ venous return |
|
5. Cushing's Reflex |
Brain (medulla) |
↑ BP + ↓ HR (response to ↑ ICP) |
3. Detailed Explanation
of Major Reflexes
A. Baroreceptor Reflex
(Important!)
Receptors:
- Carotid
sinus (CN IX – glossopharyngeal nerve)
- Aortic
arch (CN X – vagus nerve)
Function:
- Maintains short-term
BP regulation
- If BP ↑ →
Baroreceptors stimulated → ↓ HR & vasodilation → BP ↓
- If BP ↓ →
↓ Baroreceptor firing → ↑ HR & vasoconstriction → BP ↑
B. Chemoreceptor Reflex
Location:
- Carotid
bodies and aortic bodies
Stimuli:
- ↓ O₂, ↑
CO₂, ↑ H⁺
Action:
- Stimulates
vasoconstriction
- ↑ BP and ↑
respiratory rate
C. Bezold–Jarisch Reflex
Location:
- Receptors
in the ventricular walls (especially left ventricle)
Action:
- Causes bradycardia,
hypotension, and apnea
- Activated
by chemical irritants or overdistention
D. Bainbridge Reflex
Location:
- Stretch
receptors in the right atrium
Stimulus:
- ↑ Venous
return (↑ atrial pressure)
Action:
- ↑ Heart
rate to prevent overfilling of heart
E. Cushing’s Reflex
Stimulus:
- ↑
Intracranial Pressure (ICP)
Classic Triad:
- ↑ BP
(hypertension)
- ↓ HR
(bradycardia)
- Irregular
respiration
Purpose:
- Protect
brain perfusion during increased ICP
4. Summary Table
|
Reflex Name |
Stimulus |
Response |
|
Baroreceptor |
↑ or ↓ BP |
↓ or ↑ HR & BP |
|
Chemoreceptor |
↓ O₂, ↑ CO₂, ↑ H⁺ |
↑ BP & respiratory rate |
|
Bainbridge |
↑ Venous return |
↑ HR |
|
Bezold–Jarisch |
Stretch/irritation |
↓ HR & BP |
|
Cushing’s Reflex |
↑ ICP |
↑ BP, ↓ HR |
5. Clinical Importance
- Baroreceptor
failure → labile BP
- Cushing’s
triad → sign of brain herniation
- Reflexes
help guide fluid therapy, drug use, and anesthesia
Mnemonic to Remember
Reflexes: "BB-CBC"
- Baroreceptor
- Bainbridge
- Chemoreceptor
- Bezold–Jarisch
- Cushing's
