Endocrine System & Hormonal Regulation

• Endocrine System


  • Sends chemical signals (hormones)
  • Slower transmission (seconds to hours)
  • Can affect multiple target cells
  • Long-term effects
• Transport of Materials and Energy

  The circulatory system plays a crucial role in organ integration by transporting:

  • Oxygen and nutrients
  • Hormones
  • Waste products
  • Heat
• Glucose regulation:

  1. Pancreas releases insulin into the bloodstream
  2. Blood carries insulin to various organs
  3. Liver and muscle cells respond by taking up glucose from the blood
• Diurnal Pattern of Melatonin Secretion

  1. Melatonin levels are low during the day
  2. As darkness falls, melatonin secretion increases
  3. Melatonin levels peak in the middle of the night
  4. Levels decrease as morning approaches

  This pattern helps establish a regular cycle of sleeping and waking.
• Melatonin and Circadian Rhythms

  Melatonin is a hormone secreted by the pineal gland that plays a crucial role in regulating our sleep-wake cycle, also known as the circadian rhythm.
• Epinephrine (Adrenaline) and Body Preparation

  Epinephrine, also known as adrenaline, is secreted by the adrenal glands in response to stress or excitement. It prepares the body for vigorous activity through widespread effects.
• Effects of Epinephrine on Cardiovascular System:

  • Increases heart rate and force of contraction
  • Dilates blood vessels in skeletal muscles
  • Constricts blood vessels in non-essential organs
  • Dilates bronchioles, increasing airflow to lungs
• Effects of Epinephrine on Respiratory System:

  • Dilates bronchioles, increasing airflow to lungs
• Effects of Epinephrine on Metabolic Effects:

  • Stimulates breakdown of glycogen to glucose (glycogenolysis)
  • Increases blood glucose levels
• Effects of Epinephrine on Muscular System:

  • Increases blood flow to skeletal muscles
  • Enhances muscle contractility
• How Epinephrine Facilitates Intense Muscle Contraction

  1. Increased blood flow to muscles provides more oxygen and nutrients
  2. Elevated blood glucose provides readily available energy
  3. Enhanced cardiac output ensures efficient delivery of oxygen and removal of waste products
  4. Improved respiratory function increases oxygen uptake
• Both melatonin and epinephrine demonstrate how hormones can have widespread effects on the body, integrating various systems to produce complex physiological responses. Melatonin coordinates our daily rhythms, while epinephrine prepares us for sudden, intense activity.
• Control of the Endocrine System


  The hypothalamus and pituitary gland form the master control center of the endocrine system.
• Pituitary Gland:

  • Often called the "master gland"
  • Anterior pituitary produces tropic hormones
  • Posterior pituitary stores and releases hormones produced by the hypothalamus
• Hypothalamus:

  • Produces releasing and inhibiting hormones
  • Controls the pituitary gland
• General Mechanism

  1. Hypothalamus detects changes in the body
  2. It releases hormones that act on the pituitary
  3. Pituitary releases hormones that act on target glands
  4. Target glands produce and release their specific hormones
  5. These hormones affect various body functions
• Feedback Control of Heart Rat

  Heart rate is regulated through negative feedback mechanisms involving baroreceptors and chemoreceptors.
• Baroreceptors

  • Location: Carotid sinus and aortic arch
  • Function: Monitor blood pressure
• Chemoreceptors

  • Location: Carotid bodies and aortic bodies
  • Function: Monitor blood pH, O₂, and CO₂ levels
• Feedback Mechanism

  1. Receptors detect changes in blood pressure or blood chemistry
  2. Sensory neurons transmit this information to the medulla oblongata
  3. Medulla processes the information and coordinates a response
  4. Motor neurons carry signals from the medulla to the heart
  5. Heart adjusts its rate and stroke volume accordingly
• If blood pressure increases:

  1. Baroreceptors detect the change
  2. They send signals to the medulla
  3. Medulla increases parasympathetic stimulation and decreases sympathetic stimulation
  4. This causes the heart rate to decrease
  5. Blood pressure returns to normal
• Role of the Medulla

  The medulla oblongata plays a crucial role in this feedback system:

  1. Integrates inputs from baroreceptors and chemoreceptors
  2. Coordinates responses through autonomic nervous system
  3. Controls heart rate through:

  • Sympathetic stimulation (increases heart rate)
  • Parasympathetic stimulation (decreases heart rate)
• Chemoreceptor Influence

  Chemoreceptors respond to:

  • Decreased O₂ levels
  • Increased CO₂ levels
  • Decreased pH (increased acidity)

  When these changes are detected, the medulla typically increases heart rate and respiratory rate to restore normal blood chemistry.
• Both the endocrine control system and the heart rate feedback mechanism demonstrate the intricate ways in which the body maintains homeostasis. The hypothalamus-pituitary axis provides broad, often long-term control over various body functions, while the baroreceptor and chemoreceptor reflexes allow for rapid, moment-to-moment adjustments in cardiovascular function.
• Feedback Control of Ventilation Rate

  Ventilation rate is primarily controlled by chemoreceptors responding to changes in blood pH, CO₂, and O₂ levels.
• Causes of pH Changes in Blood

  1. Increased CO₂: Forms carbonic acid, lowering pH
  2. Decreased O₂: Can lead to lactic acid production, lowering pH
  3. Metabolic processes: Can produce acids or bases
• Chemoreceptor Locations

  1. Central chemoreceptors: In the medulla oblongata of the brainstem
  2. Peripheral chemoreceptors: In carotid and aortic bodies
• Feedback Mechanism

  1. Chemoreceptors detect changes in blood pH, CO₂, or O₂
  2. Signals are sent to the respiratory center in the medulla
  3. Medulla adjusts breathing rate and depth
  4. Signals are sent to the diaphragm and intercostal muscles
  5. Ventilation rate changes to restore normal blood chemistry
• If CO₂ levels increase:

  1. Central chemoreceptors detect the resulting pH decrease
  2. They signal the respiratory center in the medulla
  3. The medulla increases nerve impulses to breathing muscles
  4. Breathing rate and depth increase
  5. More CO₂ is exhaled, restoring normal pH
• Control of Peristalsis in the Digestive System

  Peristalsis, the wave-like muscle contractions that move food through the digestive tract, is controlled by both the central nervous system (CNS) and the enteric nervous system (ENS).
• Central Nervous System Control

  1. Voluntary control of:

  • Initiation of swallowing
  • Egestion of feces

  1. Involves conscious decision-making and motor control from the brain
• Enteric Nervous System Control

  1. Involuntary control of peristalsis between swallowing and egestion
  2. Often called the "second brain" of the gut
  3. Can function independently of the CNS
  4. Coordinates the passage of material through the gut
• Peristalsis Process


  1. Stretch receptors in gut wall detect presence of food
  2. ENS neurons are activated
  3. Circular muscles contract above the food bolus
  4. Longitudinal muscles contract below the food bolus
  5. This coordinated action propels food along the digestive tract
• Both ventilation control and digestive peristalsis demonstrate the body's ability to maintain homeostasis through complex feedback mechanisms and coordinated nervous system control. These systems allow for both rapid responses to immediate needs and long-term regulation of vital physiological processes.
• Example of Positive Feedback Mechanisms


  During childbirth:

  1. Contractions begin
  2. Oxytocin is released
  3. Oxytocin stimulates stronger contractions
  4. More oxytocin is released
  5. Process continues until birth occurs