C3 Notes

Body Systems Integration

Cell, Tissue, Organ, Organ System, Organism

• Cell: Basic structural & functional unit in a living organism.
• Tissue: Group of cells of similar structure working together to perform a similar function.
• Organ: Made from different tissues working together to perform specific functions.
• Organ System: Groups of organs with related functions, working together to perform body functions.
• Organism: Living being made up of these four levels of organization.

System Integration

• Definition: System integration in biology refers to the process by which different parts of an organism (cells, tissues, organs, organ systems) work together to maintain overall functioning, stability, and health.

Why System Integration is Needed

• Life requires an organism to survive, reproduce, and adapt.
• Multicellular organisms achieve this through the interaction of various body systems.
• Body systems are interdependent; a change in one system can affect others.
• Example: Respiratory efficiency impacts cardiovascular health, influencing nervous system function.
• Reproduction requires the interaction of hormonal, nervous, and reproductive systems for processes like gametogenesis, fertilization, and pregnancy.

Emergent Property

• Definition: An attribute, quality, or characteristic that arises from the interactions of smaller/simpler parts; the smaller parts do not have this complexity on their own.
• "Greater than the sum of its parts."

Reductionist Approach vs. Systems Approach

• Reductionist Approach:
  • Involves breaking down complex biological systems into their simplest components to understand individual part functions (e.g., a cell).
• Systems Approach:
  • Studies the function of greater systems, not just individual parts.
  • Needed to understand emergent properties.

Benefits and Limitations of Approaches

• Systems Approach:
  • Gives an understanding of how the body works together.
  • Lacks understanding of how and why the parts work.
• Reductionist Approach:
  • Understands how individual cells function (e.g., molecular interactions).
  • May overlook interactions and complexities of systems as a whole.

Hierarchy of Subsystems

• Cells, tissues, organs, and body systems as a hierarchy integrated in a multicellular living organism.

Tissue Types

• Four basic tissue types in the human body:
  • Epithelial
  • Connective
  • Muscle
  • Nervous

Organs

• Structures composed of at least two different types of tissues working together to perform specific, complex functions.
  • Examples: Heart, skin.
  • In plants: roots, stems, leaves.

Organ Systems

• Groups of organs that collaborate to perform major functions necessary for the survival of the organism.

Emergent Properties at Each Level of Organization

• Cellular Level: The characteristics of "life" emerge.
• Tissue Level (Heart): Synchronized contractions due to interactions among cardiac cells.
• Organ Level (Heart): Tissues work together to pump blood.
• Organ System Level (Cardiovascular): Components transport blood throughout the body.
• Organism Level: Able to use blood to perform interconnected functions needed to survive and reproduce.

Integration of Organs in Animal Bodies

• Hormonal and nervous signaling.
• Transport of materials and energy.

Mechanisms for Organ System Integration

• Two primary mechanisms:
  • Nervous system
  • Endocrine system

Nervous System

• Coordinates actions via transmission of electrochemical signals.
• Signals transmitted by neurons.

Neuron Function

• Basic function: to send and/or receive electrical signals.
  • Dendrites: receive signals.
  • Axons: propagate signals to the axon terminal and synapse.
  • Cell body: contains the nucleus and organelles.

Endocrine System

• Comprised of ductless glands that release chemicals (hormones) into the blood to regulate body functions.

Hormones

• Chemical messengers transported via the bloodstream to act on distant target cells.

Comparison of Nervous and Endocrine Systems

Blood

• Primary transport medium of the body.
• Facilitates the exchange of gases, nutrients, waste products, hormones, and immune factors between organs and tissues.

Brain as Central Information Integration Organ

• Acts as an integration and coordination system for the control of body systems.
• Processes sensory information and relays responses to effector organs (or other parts of the brain).
• Input sources: sensory neurons (touch, smell, sight) and hormones.

Processes of Learning and Memory

• Learning and memory involves three main stages:
  • Encoding
  • Storage
  • Retrieval

Stages of Memory

• Sensory inputs: Vast majority are forgotten within milliseconds.
• Short term memory: can store information for up to about 1 minute (e.g., a phone number).
• Encoding: converting short-term memories into long-term memories.
• Retrieval: accessing stored information to be actively used in cognitive processes (e.g., speaking, cooking).

Spinal Cord as Integrating Center

• For unconscious processes.

Central Nervous System (CNS)

• Brain and spinal cord.

Peripheral Nervous System (PNS)

• All the “peripheral nerves” that link the CNS to the body’s receptors and effectors.

CNS Tissues

• Two distinct regions:
  • White matter
    • Composed of bundles of myelinated axons that connect grey matter regions together.
    • Myelin acts as an insulator; nerve signals are transmitted at greater speed.
  • Grey matter
    • Composed of neuronal cell bodies, dendrites, and unmyelinated nerve fibers.
    • Functions as the region where information is processed.

Conscious vs. Unconscious Processing

Spinal Cord and Conscious Thoughts

• All conscious thoughts and decisions are made in the brain.
• The spinal cord relays conscious information from the brain and coordinates unconscious processes.

Neuron Types

• Three main types:
  • Sensory (i.e., pain, temperature sensing)
  • Relay (to interpret input from sensory neurons)
  • Effector/motor (to stimulate muscles to move)

Sensory Receptors

• Specialized cells that detect various stimuli and convert them into electrical signals.
  • Rods and cones (vision)
  • Mechanoreceptors (touch, pressure, vibration, stretch)
  • Chemoreceptors (smell, taste)
  • Thermoreceptors (cold and warm)
  • Nociceptors (pain)

Skin

• Equipped with various specialized sensory receptors for mechanical, thermal, and nociceptive (pain) stimuli.

Motor Neurons

• Transmit signals from the CNS to muscles and glands, resulting in motor responses.
• Stimulate muscle cells to contract.

Nerve

• A bundle of nerve fibers (axons) held together by connective tissue, along with blood vessels and supporting structures.
• A nerve is NOT the same thing as a neuron.

Nerve Structure

• Nerves are sorted into bundles called fascicles.
• Axons of individual neurons can be myelinated or unmyelinated.
• Blood vessels are present to transport nutrients and waste.
• Nerves can contain sensory neurons, motor neurons, or both.
• Structures visible in a nerve transverse cross section:
  • Epineurium
  • Blood vessels
  • Endoneurium
  • Perineurium
  • Axon
  • Myelin sheath
  • Schwann cell
  • Fibroblast
  • Macrophages

Reflex and Reflex Arc

• Reflex: A rapid, involuntary response to a stimulus that occurs without conscious thought.
• Reflex arc: The neural pathway that mediates a reflex.
  • Components:
    • Receptor + sensory neuron
    • Integration center (CNS)
    • Motor neuron
    • Effector

Reflex Arc Components

• Receptors: Respond to specific stimuli (touch, pressure, pain, temperature).
• Sensory neuron: Transmits sensory information from the receptor to the CNS.
• Integration center: Consists of synapses within the CNS where sensory input is processed.
• Motor neuron: Carries the motor output from the integration center to the effector organ.
• Effector: Muscle or gland that carries out the response to the stimulus.

Cerebellum

• Located at the base of the brain; separate structure.
• Responsible for coordinating unconscious motor functions, such as balance and movement coordination.

Circadian Rhythms and Melatonin

• Circadian rhythms: The body’s physiological responses to the 24-hour day-night cycle.
• Melatonin: Hormone that plays a role in the control of circadian rhythms.

Melatonin Secretion

• Light-sensitive tissue lining the back of the retina sends signals to the suprachiasmatic nucleus (SCN).
• The SCN acts as a “central pacemaker” that synchronizes the body with the external light-dark cycle, and signals the pineal gland to produce melatonin.
• Melatonin is secreted in response to periods of darkness (daylight inhibits production), resulting in higher concentrations at night.

Melatonin Regulation

• Melatonin secretion is suppressed by bright light (primarily blue wavelengths).
• Over a prolonged period, melatonin secretion becomes entrained to anticipate the onset of darkness and the approach of day.
• Melatonin promotes activity in nocturnal animals and promotes sleep in diurnal animals (e.g., humans).
• Melatonin levels naturally decrease with age, leading to changes in sleeping patterns.

Epinephrine (Adrenaline)

• Both as a neurotransmitter and a hormone.
• Plays a key role in the body’s “fight-or-flight” response.

Epinephrine Function

• Made and released by the adrenal glands.
• Released by nerve endings to stimulate other nerve cells, muscle cells, or gland cells.
• Effects are rapid but short-lived, preparing the body for immediate physical exertion.

Epinephrine Mechanism of Action

• A potential threat is registered in the brain (amygdala).
• Signals are sent from the hypothalamus to stimulate the adrenal glands to release epinephrine and cortisol.
• Adrenaline is released into the bloodstream, resulting in:
  • Breakdown of glycogen into glucose.
  • Increase in blood pressure.
  • Heart rate increase.
  • Dilated pupils.
  • Slow in digestion.
  • Increased breathing rate.

Hypothalamus and Pituitary Gland

• Hypothalamus:
  • Section of the brain that links the nervous and endocrine systems to maintain homeostasis.
  • Receives information from nerves and initiates endocrine responses.
• Pituitary gland:
  • Lies just below the hypothalamus; receives instructions from it.
  • Produces and releases hormones that carry out bodily functions, including growth, metabolism, and reproduction.

Body Processes Monitored by Hypothalamus

• Sleep/wake
• Pain
• Vision
• Thirst, water balance, blood volume, blood pressure

Heart Rate Feedback Control

• Base heart rate is determined within the heart by specialized cells.
• The brain does NOT control base heart rate.
• However, the medulla oblongata monitors blood pressure and the presence/absence of chemicals in the blood.

Medulla Oblongata Nerves

• Based on these, the medulla oblongata can increase / decrease heart rate as needed by sending signals via two specific nerves that connect the medulla to the SA and AV nodes:
  • Accelerator nerve: increases heart rate, primarily in response to adrenaline (epinephrine).
  • Vagus nerve: decreases heart rate in response to hormones (e.g., insulin).

Receptors Regulating Heart Rate

• Two main types of receptors that contribute to this regulatory process:
  • Baroreceptors: Respond to blood pressure changes (“baro” = relating to pressure)
  • Chemoreceptors: Respond to changes in chemical composition of blood (e.g. pH, $O<em>2$/$CO</em>2$ levels)

Receptor Location

• Baroreceptors are stretch-sensitive sensory receptors located in the carotid sinuses (in the neck) and the aortic arch (of the heart).
  • When blood pressure rises, the arterial walls stretch more, stimulating the baroreceptors to increase their firing rate
• Chemoreceptors are in carotid sinuses and the aortic arch which monitor the chemical composition of the blood, especially levels of $O<em>2$, $CO</em>2$, and pH.

Ventilation Rate Feedback Control

• During exercise, the body's metabolism increases, leading to an increase in $CO_2$ production.

CO2 Production and Blood pH

• The relationship between $CO_2$ production and blood pH is an inverse one.
• When the body produces more $CO_2$, the concentration of hydrogen ions ($H^+$) increases, leading to a decrease in blood pH.
• Constant feedback control of ventilation rate is necessary to ensure that blood composition is within an acceptable homeostatic range
• When blood $CO<em>2$ levels are high, the medulla stimulates increased rate and depth of breathing, which leads to a normal $CO</em>2$ blood level.

Peristalsis

• Wave-like motion of smooth muscles contacting to move food through the alimentary canal.

Peristalsis Process

• When you swallow, muscles from the esophagus onward contract in a wave-like motion, pushing the bolus (chewed food) through the alimentary canal.
• Behind the bolus, smooth muscles lining the esophagus contract, forcing it forward.
• The smooth muscles just in front of the bolus relax, making a wave of contracting motion that moves the bolus smoothly.

Nervous Systems and Digestion

• The process of digestion involves both voluntary and involuntary mechanisms:
  • You voluntarily control when/how you chew and swallow, and when you egest feces (via the CNS).
  • Everything between the mouth and anus is under involuntary control by the enteric nervous system (ENS).
  • The ENS controls the movement of food via peristalsis.
• The CNS (brain and spinal cord) have various points of contact with the digestive tract to ensure this is carried out precisely.