Integration of Body Systems Notes

C3.1 Integration of Body Systems

C3.1.1 System Integration

  • System integration is a necessary process in living systems.
  • Coordination is needed for component parts of a system to collectively perform an overall function.
  • Multiple organ systems function within each organism to sustain its life.
  • System integration is the effective collaboration, coordination, and communication of different components of the organism.
  • This depends on molecules, cells, tissues, organs, and the systems that arise from them.

C3.1.2 Cells, Tissues, Organs and Body Systems as a Hierarchy

  • Integration is responsible for emergent properties.
  • Emergent properties are "properties that are not evident in the individual components of a system, but show up when combining those components".
  • The whole is greater than the sum of its parts.
  • Example:
    • One cardiomyocyte (heart cell) cannot pump blood to the body.
    • Neither can just one chamber of the heart or the heart alone in its entirety.
    • Combining the heart with the vascular system achieves the property of pumping and carrying blood to all the body.
    • This property only emerges when different organs are integrated.

C3.1.3 Integration of Organs

  • Integration of organs in animal bodies occurs by hormonal and nervous signaling and by transport of materials and energy.
  • Two main methods of communication within the body:
    • Nervous system
    • Endocrine system
  • The bloodstream helps in the integration of organs in animal bodies.
  • The bloodstream transports materials and energy to and from organs in order to facilitate functions other than homeostasis like nutrition and excretion.
  • Nervous vs. Endocrine Systems:
    • Nervous System:
      • Organs involved: Brain, spinal cord, nerves
      • Type of communication: Electrical (action potentials)
      • Transmission method: Neurons
      • Transmission speed: Very fast
      • Target (effector): Glands or muscles
      • Duration of effect: Short-lived (until electrical impulse stops)
      • Controls: Conscious and unconscious
    • Endocrine System:
      • Organs involved: Glands
      • Type of communication: Chemical (hormones)
      • Transmission method: Blood stream
      • Transmission speed: Slower
      • Target (effector): Target cells in certain tissue
      • Duration of effect: Longer (until hormone is broken down)
      • Controls: Unconscious

C3.1.4 The Brain as a Central Information Integration Organ

  • The brain is the central information integration organ.
  • Integrates sensory inputs, contextual information, and past knowledge (memory) to generate responses and ultimately form perceptions.
  • Perception is the interpretation and organization of sensory stimuli by the brain, resulting in an internal representation of the stimuli and the conscious experience of it.
  • Memory is the mental system for receiving, encoding, and retrieving information within the brain.
  • Learning is the process of acquiring new knowledge or behavior, which leads to the strengthening of connections between neural synapses.
  • Integrating sensory inputs to form perceptions enables us to create an understanding of the world around us, which forms the basis for learning.

C3.1.5 The Spinal Cord as an Integrating Centre for Unconscious Processes

  • Conscious processes are voluntary, occur only when awake, and are carried out by the brain (specifically the cerebral hemisphere).
  • Unconscious processes are involuntary, occur both when awake and asleep, and are carried out by both the brain and the spinal cord.
  • The Central Nervous System (CNS) is composed of the brain and the spinal cord.
  • The Peripheral Nervous System (PNS) is every other nervous tissue (i.e. nerves).
  • Neurons are the functional unit of the nervous system, and are divided into three classes:
    • Sensory neurons: receive information about the internal and external environments, transmitting them to the CNS (via interneurons). They receive signals.
    • Interneurons: are the most abundant class of neurons, and work to receive information from sensory neurons or other interneurons and transmit this information to either motor neurons or other interneurons. They integrate incoming signals.
    • Motor neurons: receive signals from other neurons and convey commands to organs, glands, or muscles. They communicate signals to target cells.
  • The spinal cord is the extension of nervous tissue within the vertebral column.
  • White matter is the region with many axons (it is called ‘white’ because axons are covered with lipid-rich myelin, which appears white).
  • Grey matter is the region with many cell bodies and dendrites.
  • White matter mainly transmits information while grey matter receives and processes information.
  • Integrating their two functions within the spinal cord allows for effective response to stimuli.

C3.1.6 Input to the Spinal Cord and Cerebral Hemispheres Through Sensory Neurons

  • Sensory neurons convey messages from receptor cells to the central nervous system.
  • Sensory neurons ‘sense’ changes in the internal and external environments and transmit (input) them to the spinal cord and cerebral hemispheres within the brain (CNS).
  • The structure of sensory neurons depends on the stimulus they are sensing.

C3.1.7 Output from the Cerebral Hemispheres to Muscles Through Motor Neurons

  • Muscles are stimulated to contract.
  • The cerebrum is composed of the two cerebral hemispheres.
  • The primary motor cortex, located in the frontal lobes of the cerebrum, exhibits the highest level of voluntary control over movement (and thus over muscles).
  • It outputs a signal to motor neurons, which stimulates muscles to contract.
  • The nervous and musculoskeletal systems are integrated such that the body is able to physically respond to stimuli.

C3.1.8 Nerves as Bundles of Nerve Fibres

  • Nerves are bundles of nerve fibers (axons), containing both sensory and motor neurons (which can be myelinated or not).
  • Nerves connect/integrate the nervous system to itself and to other organs.
  • Myelinated vs. Unmyelinated Nerve Fibers:
    • Myelinated:
      • Axon diameter: Large (2−20 μm2-20 \,\mu m)
      • Myelin: Present, forming ~200-300 turns of myelin
      • Axon diameter to nerve fiber (axon + myelin) ratio: Fixed (~0.6-0.7)
    • Unmyelinated:
      • Axon diameter: Small (0.1−2 μm0.1-2 \,\mu m)
      • Myelin: Absent
      • Axon diameter to nerve fiber (axon + myelin) ratio: N/A

C3.1.9 Pain Reflex Arcs

  • Pain reflex arcs are an example of involuntary responses with skeletal muscle as the effector.
  • Pain is both a sensation and a perception.
  • Pain receptors (nociceptors) are free nerve endings that specifically respond to damaging or potentially damaging stimuli.
  • A reflex is an involuntary and instantaneous movement in response to a noxious stimulus.
  • The pain reflex arc, also known as the withdrawal response or nociceptive flexion reflex, is the neural pathway that acts on the impulse before it has reached the brain.
  • The action potential travels to the spinal cord and then to effector cells (muscle) through the following pathway:
    1. Sensation: nociceptors in upper/lower limbs sense a noxious stimulus and generate an action potential that travels through 1 afferent sensory neuron to the spinal cord.
    2. Relay: the sensory neuron transmits the action potential to a relay neuron (interneuron) in the spinal cord by means of a synapse. The interneuron then transmits the signal to an efferent motor neuron through a synapse in the spinal cord.
    3. Contraction: the motor neuron completes the reflex arc by exiting the spinal cord and entering the PNS to depolarize and cause the contraction of target muscles at the neuromuscular junction through releasing acetylcholine.
  • The reflex arc is an important evolutionary adaptation that enhances survival by quickly reacting to stimulus that damages or could damage the body.

C3.1.10 Role of the Cerebellum

  • The cerebellum is responsible for muscle coordination and balance but is unable to initiate muscle contraction.

C3.1.11 Modulation of Sleep Patterns by Melatonin

  • Melatonin secretion is part of circadian rhythms.
  • Melatonin is the only hormone produced by the pineal gland.
  • The pineal gland is located outside the blood brain barrier, losing its connection to the CNS.
    • Allows for large intake of tryptophan, the chemical the pineal gland uses to synthesize melatonin, thus allowing for high melatonin production.
    • Allows for relative protection from premature degradation by enzymes (which would otherwise lead to a 10-20-fold decrease in melatonin levels).
  • The rate of melatonin production is affected by the photoperiod (length of time during which a person is exposed to light).
  • During the day photoperiod, little melatonin is produced; however, melatonin production increases during the dark photoperiod (night).
  • In some mammals, melatonin has an inhibitory effect on reproductive functions by decreasing production and maturation of sperm, oocytes, and reproductive organs.
  • Melatonin's sleep-promoting actions are mostly caused by its feedback to the suprachiasmatic nucleus (SCN), located in the anterior part of the hypothalamus.
  • By working on the SCN, melatonin helps to synchronize the circadian rhythm by affecting both the phase (the timing of the rhythm’s trough and peak within 24 hours) and amplitude (the difference between the trough and peak) of the rhythm.

C3.1.12 Epinephrine (Adrenaline)

  • Epinephrine is secreted by the adrenal glands to prepare the body for vigorous activity.
  • Epinephrine, also known as adrenaline or the ‘fight or flight hormone/neurotransmitter’ is produced by the adrenal glands and has several functions:
    • Increasing contraction of vascular smooth muscle, pupillary dilator muscle (in the iris), and intestinal sphincter muscle
    • Increasing rate of glycogen breakdown in liver (thus increases blood sugar levels)
    • Increasing heart rate (it overrides normal homeostatic mechanisms)
    • Relaxation of bronchial smooth muscle
  • Exercise is a physiological stimulus to epinephrine secretion.

C3.1.13 Control of the Endocrine System

  • The endocrine system is responsible for internal chemical signaling within the body through the bloodstream (not to be confused with the exocrine system, which secretes into ducts).
  • It is controlled by the hypothalamus (which links the nervous and endocrine systems together) and pituitary gland.
  • The pituitary gland has an anterior lobe, which secretes Growth Hormone (GH), Prolactin, FSH, and LH (among others), and a posterior lobe, which secretes ADH and Oxytocin.

C3.1.14 Feedback Control of Heart Rate

  • Feedback control of heart rate following sensory input from baroreceptors and chemoreceptors.
  • Baroreceptors monitor blood pressure.
  • Chemoreceptors monitor blood pH and concentrations of oxygen and carbon dioxide.
  • The Medulla Oblongata is a region within the human brain that contains a cardiovascular center which regulates cardiac output and activity. It is an element of the autonomic nervous system (part of the PNS).
  • The ANS is divided into the sympathetic, parasympathetic, and enteric nervous systems.
  • Sympathetic stimulation increases heart rate and stroke volume (volume of blood ejected from ventricles per one cardiac cycle), whilst parasympathetic stimulation (via the Vagus nerve) decreases them.
  • Baroreceptors are a type of mechanoreceptors (sensory neurons that sense mechanical changes in the environment) that aid in regulating blood pressure.
  • The cardiovascular center monitors baroreceptor firing to maintain cardiac homeostasis, a mechanism called the baroreceptor reflex.
    • With increased pressure and stretch, the rate of baroreceptor firing increases, and the cardiac center decreases sympathetic stimulation and increases parasympathetic stimulation.
    • As pressure and stretch decrease, the rate of baroreceptor firing decreases, and the cardiac center increases sympathetic stimulation and decreases parasympathetic stimulation.
  • Chemoreceptors are sensory neurons that sense changes in metabolic byproducts such as carbon dioxide, pH, lactic acid, and oxygen levels.
  • These chemoreceptors provide feedback to the cardiovascular centers about the need for increased or decreased blood flow, based on the relative levels of these substances.

C3.1.15 Feedback Control of Ventilation Rate

  • Feedback control of ventilation rate following sensory input from chemoreceptors.
  • Ventilation rate is the number of breaths per unit time.
  • Chemoreceptors in the brainstem detect pH and oxygen levels, and regulate ventilation rate accordingly.
  • Since carbon dioxide dissociates into acid in blood, High CO<em>2CO<em>2 = low pH = higher ventilation rate to excrete more CO</em>2CO</em>2 and lower acidity.
  • Low CO2CO_2 = high pH = slower ventilation rate to increase blood acidity.

C3.1.16 Control of Peristalsis

  • Control of peristalsis in the digestive system by the central nervous system and enteric nervous system.
  • Peristalsis is the antagonistic contraction of longitudinal and circular smooth muscles to push food in a unidirectional manner throughout the alimentary canal.
  • Initiation of swallowing food and egestion of faeces is under the control of the (CNS); it is a voluntary and conscious process.
  • Peristalsis between these points (through the esophagus, stomach, and intestines) is under the control of the enteric nervous system (ENS); an involuntary and unconscious process.
  • The action of the ENS ensures passage of material through the gut is coordinated.

C3.1.19 Phytohormones

  • Phytohormones are signaling chemicals controlling growth, development and response to stimuli in plants.
  • Phytohormones are a large variety of signaling chemicals that control the growth, development, and stimulus response in plants.
  • Examples include indole-3-acetic acid (IAA) – the major type of auxin in plants, cytokinin, and ethene.

C3.1.20 Auxin Efflux Carriers

  • Auxin efflux carriers are an example of maintaining concentration gradients of phytohormones.
  • Auxin can diffuse freely into plant cells but not out of them.
  • If all cells coordinate to concentrate these carriers on the same side, auxin is actively transported from cell to cell through the plant tissue and becomes concentrated in part of the plant.
  • Auxin transport helps us understand how this hormone integrates different parts of the plant and allows it to react to external stimuli.
  • Two mechanisms:
    1. (directional) polar transport
      • In contrast to the other major plant hormones, auxins can be transported in a specific direction (polar transport) through parenchyma (plant tissue) cells.
      • The cytoplasm of parenchyma cells are neutral (pH = 7), but the region outside the plasma membranes of adjacent cells (the apoplast) is acidic (pH = 5).
      • When auxin is in the cytoplasm, it releases a proton and becomes an anion (IAA-).
      • It cannot pass through hydrophobic portion of the plasma membrane as an anion, but it does pass through special auxin efflux transporters called PIN proteins.
      • When IAA- enters the acidic environment of the apoplast, it is protonated, becoming IAAH.
      • This uncharged molecule can then pass through the plasma membrane of adjacent cells through diffusion or via influx transporters, but not out of the cells.
      • PIN proteins can be unevenly distributed around the cell (for example, only occurring on the bottom of the cell), which directs the flow of auxin.
    2. (non-directional) non-polar transport
      • Auxin can also pass through the sap, or phloem, of the plant as nutrients are translocated.

C3.1.18 Positive Phototropism

  • Positive phototropism is a directional growth response to lateral light in plant shoots.
  • Positive phototropism is the directional movement/growth of plant towards light (negative phototropism is movement away from light, i.e. in roots).

C3.1.21 Promotion of Cell Growth by Auxin

  • Concentration gradients of auxin cause the differences in growth rate needed for phototropism.
  • Mechanism of positive phototropism:
    1. Phototropins in one side of the plant sense more light than the other side
    2. This promotes the efflux of auxin from the lighter side to the darker, shaded side
    3. A high concentration of auxin causes the release of H+H^+ ions in the cell walls of shaded cells
    4. Lower pH disrupts bonding of cellulose molecules in cell walls, causing a loss of rigidity and elasticity
    5. Auxin also upregulates the production of expansins (proteins), which further disrupt the cell wall
    6. Auxin also increases elongation rate of darker side compared to brighter side
    7. This results in the swelling of the cell and increases the weight of the shaded side
    8. As a result, the stem begins bending towards the side exposed to more light

C3.1.22 Interactions Between Auxin and Cytokinin

  • Interactions between auxin and cytokinin as a means of regulating root and shoot growth.
  • Root tips produce cytokinin, which is transported to shoots, and shoot tips produce auxin, which is transported to roots.
  • Interactions between these phytohormones help to ensure that root and shoot growth are integrated.
  • Auxin is produced in shoot tips and transported to roots, promoting meristematic differentiation, cell elongation, leaf development, apical dominance, and tropisms whilst inhibiting lateral (horizontal) growth.
  • Cytokinin is produced in root tips and transported to shoots, promoting growth/cell division (cytokinesis) whilst inhibiting leaf and root development.
  • High levels of auxin and low levels of cytokinin induce shoot formation, whereas low levels of auxin and high levels of cytokinin induce root formation.
  • Relatively equal amounts result in callus formation, which is just filler plant tissue.
  • Thus, antagonistic and cooperative interactions can occur between the two hormones.

C3.1.23 Positive Feedback in Fruit Ripening

  • Ethene (ethylene) stimulates the changes in fruits that occur during ripening, and ripening also stimulates increased production of ethylene.
  • Once a plant reaches the seed dispersal stage during reproduction, a positive feedback mechanism is initiated between ethene and the ripening fruits.
  • The more ripening occurs, the more ethene produced, and vice versa.

C3.1.17 Observations of Tropic Responses

  • Scientists investigated the effects of auxin on phototropism; since auxin is produced in the shoot, separating the shoot from the rest of the stem by a physical barrier prevents its efflux to the shaded/darker regions, thus inhibiting phototropism.
  • You can investigate the effect of light intensity on the degree of phototropism exhibited by seedlings by measuring the angle of curvature (using a protractor), among others.
  • Qualitative vs. Quantitative Data:
    • Qualitative:
      • Non-numerical data (words)
      • Subjective
      • Used to support quantitative evidence
    • Quantitative:
      • Numerical data
      • Objective
      • Main evidence in hypothesis testing
  • Accuracy is how close an experimental result is to the true (literature) value.
  • Precision is the degree of certainty in measured data or how close trial values are to each other.
  • Reliable data = accuracy + precision
  • For example, when measuring the angle of curvature of seedlings when investigating phototropism, one can use a protractor with at least 2 decimal places for precision, and conduct at least 3-5 trials for reliability.