Homestatsis and Feedback loops

Resting Heart Rate (Negative Feedback)

1. Stimulus: decreased Heart rate or decreased blood pressure (like during rest, blood loss, or low O₂)

2. Receptors: Baroreceptors in aortic and carotid sinus detect decreased pressure

3. Afferent Pathway: Signals travel via glossopharyngeal (IX) and vagus (X) nerves to medulla oblongata

4. Control Center: Medulla oblongata (cardioacceleratory center)

5. Efferent Pathway: Sympathetic nerves send impulses to the heart

6. Effectors: SA node and cardiac muscle cells

7. Response: increased Heart rate and increased cardiac output

Homeostasis Restored: Normal heart rate and blood flow are restored

paragraph form when heart rate drops

When heart rate or blood pressure drops, baroreceptors detect reduced stretch in arteries and alert the medulla. The medulla’s cardioacceleratory center activates the sympathetic nervous system, sending signals that increase heart rate and contractile force. As cardiac output rises, blood pressure and oxygen delivery stabilize, restoring homeostasis.

DECREASING HEART RATE (Negative Feedback)

1. Stimulus: increased Heart rate or increased blood pressure (during exercise or stress)

2. Receptors: Baroreceptors in aortic arch and carotid sinus detect increased pressure

3. Afferent Pathway: Signals sent via glossopharyngeal and vagus nerves to medulla oblongata

4. Control Center: Medulla oblongata (cardioinhibitory center)

5. Efferent Pathway: Parasympathetic fibers of the vagus nerve

6. Effectors: SA node and cardiac muscle

7. Response: decreased Heart rate and decreased cardiac output

Homeostasis Restored: Heart rate returns to normal range (60–100 bpm)

Paragraph from when HR + BP rises:

When heart rate and blood pressure rise, baroreceptors sense arterial stretch and signal the medulla. The medulla activates the parasympathetic system, slowing the heart rate through the vagus nerve. As heart rate and cardiac output decrease, blood pressure returns to normal, maintaining internal stability.

INCREASING BLOOD PRESSURE (Negative Feedback)

1. Stimulus: decreased Blood pressure (from dehydration, blood loss, or rest)

2. Receptors: Baroreceptors in aortic arch and carotid sinus detect decreased stretch

3. Afferent Pathway: Signals sent to medulla oblongata

4. Control Center: Medulla oblongata

5. Efferent Pathway: Sympathetic nerves stimulate vasoconstriction and increase heart rate

6. Effectors: Heart and blood vessels

7. Response: increased Heart rate, increased contractility, and vasoconstriction → increased blood pressure

Homeostasis Restored: Blood pressure returns to normal (~120/80 mmHg)

Paragraph when BP drops:

When blood pressure drops, baroreceptors signal the medulla to activate sympathetic pathways. This increases heart rate and constricts blood vessels, which raises blood pressure and ensures proper blood flow to tissues. Once levels normalize, the baroreceptors reduce signaling, ending the response.

DECREASING BLOOD PRESSURE (Negative Feedback)

1.Stimulus: increased Blood pressure (after exercise or stress)

2. Receptors: Baroreceptors in aortic arch and carotid sinus detect increased stretch

3. Afferent Pathway: Signals travel to medulla oblongata

4. Control Center: Medulla oblongata

5. Efferent Pathway: Parasympathetic signals reduce cardiac activity; sympathetic tone decreases

6. Effectors: Heart and blood vessels

7. Response: decreased Heart rate, vasodilation → decreased blood pressure

Homeostasis Restored: Blood pressure returns to normal (~120/80 mmHg)

Paragraph when BP rises:

When blood pressure increases, baroreceptors detect greater arterial stretch and inform the medulla. The medulla reduces sympathetic activity and increases parasympathetic output, slowing the heart and dilating vessels. These changes lower blood pressure back to a normal, balanced range.

INCREASING RESPIRATION RATE (Negative Feedback)

1. Stimulus: increased CO₂ or decreased pH in blood

2. Receptors: Chemoreceptors in carotid and aortic bodies detect changes

3. Afferent Pathway: Signals sent to medulla oblongata and pons

4. Control Center: Medulla oblongata (respiratory center)

5. Efferent Pathway: Phrenic and intercostal nerves

6. Effectors: Diaphragm and intercostal muscles

7. Response: increased Rate and depth of breathing → CO₂ expelled → pH restored

Homeostasis Restored: Normal CO₂ and pH (≈7.4)

Paragraph when CO2 rises:

When CO₂ levels rise and blood becomes acidic, chemoreceptors alert the medulla. The respiratory center increases breathing rate and depth, allowing more CO₂ to be exhaled. As CO₂ decreases and pH normalizes, the system returns to homeostasis.

DECREASING RESPIRATION RATE (Negative Feedback)

1. Stimulus: decreased CO₂ or increased pH in blood

2. Receptors: Chemoreceptors in carotid and aortic bodies

3. Afferent Pathway: Signals sent to medulla oblongata

4. Control Center: Medulla oblongata (respiratory center)

5. Efferent Pathway: Phrenic and intercostal nerves

6. Effectors: Diaphragm and intercostal muscles

7. Response: decreased Breathing rate/depth → Retain CO₂ → pH decreases to normal

Homeostasis Restored: CO₂ and pH balanced

Paragraph when CO2 drops:

When CO₂ drops too low, chemoreceptors send fewer signals to the medulla, which slows breathing. This causes CO₂ to accumulate, slightly lowering pH back to normal, keeping internal gas levels stable.

DECREASING BLOOD GLUCOSE (AFTER EATING – Negative Feedback)

1. Stimulus:  Blood glucose increases (after eating)

2. Receptors/Control Center: Pancreas detects high glucose

3. Hormone: Insulin released by β-cells

4. Efferent Pathway: Insulin travels through bloodstream

5. Effectors: Body cells absorb glucose; liver stores glycogen

6. Response:  Blood glucose goes down to normal (≈70–100 mg/dL)

Homeostasis Restored: Blood glucose balanced

Paragraph when glucose rises:

When blood glucose rises after a meal, the pancreas releases insulin. Insulin signals cells to absorb glucose and the liver to store excess as glycogen. As glucose decreases, insulin secretion slows, maintaining balance.

INCREASING BLOOD GLUCOSE (FASTING – Negative Feedback)

1. Stimulus: decreased Blood glucose (between meals)

2. Receptors/Control Center: Pancreas detects low glucose

3. Hormone: Glucagon released by α-cells

4. Efferent Pathway: Glucagon travels through bloodstream

5. Effectors: Liver breaks down glycogen into glucose

6. Response: increased Blood glucose to normal

Homeostasis Restored: Blood glucose stabilized

Paragraph when glucose drops:

When blood sugar drops, the pancreas releases glucagon, prompting the liver to convert glycogen back into glucose and release it into the bloodstream. Once levels normalize, glucagon secretion stops, maintaining energy balance.

BODY TEMPERATURE FEEDBACK LOOPS

1. Stimulus:  Body temperature above 37°C

2. Receptors: Thermoreceptors in skin and hypothalamus

3. Control Center: Hypothalamus

4. Effectors: Sweat glands, skin blood vessels

5. Response: Sweating and vasodilation → body cools down

Homeostasis Restored: Normal body temperature

Paragraph when temp rises:

When body temperature rises, the hypothalamus activates sweat glands and dilates skin vessels to release heat. As the body cools, these responses reduce, keeping core temperature stable.

INCREASING TEMPERATURE (When Too Cold – Negative Feedback)

1. Stimulus: Body temperature below 37°C

2. Receptors: Thermoreceptors in skin and hypothalamus

3. Control Center: Hypothalamus

4. Effectors: Skeletal muscles, blood vessels

5. Response: Shivering and vasoconstriction → body warms up

Homeostasis Restored: Normal temperature

Paragraph when temp increases :

When the body gets too cold, the hypothalamus triggers shivering and narrows skin blood vessels to conserve heat. These actions raise internal temperature until balance is restored.

Homeostasis:

Body’s ability to maintain stable internal conditions

( Controlled by nervous and endocrine systems through feedback loops)

Negative vs. Postive loop

Negative Feedback: Response reverses the original change (stabilizes).

Positive Feedback: Response amplifies the change (until event finishes).