Human Body Systems

Posted on Sep 19, 2024 in Biology

Nervous System

1. Duties

  • Sensory: Receptors detect stimuli and send them to the CNS.
  • Integration: CNS processes information and makes decisions.
  • Motor: Decisions from the CNS are sent as a response.

2. Nerve Impulse

A signal is transmitted from one neuron to another. It enters through the dendrites, travels along the axon, and ends at the axon terminal. Neurotransmitters (e.g., acetylcholine) are released to communicate with the subsequent neuron.

Neuromuscular Junction: Connection between a neuron and a muscle fiber.

Motor End Plate: The axon terminal of the neuron in contact with the muscle fiber.

3. CNS (Central Nervous System)

Composed of the brain and spinal cord.

  • Brain: Responsible for voluntary thinking and actions. It has 4 regions:
    • Cerebrum: Controls voluntary actions and thinking.
    • Diencephalon: Contains the thalamus (processes sensory input) and hypothalamus (maintains homeostasis).
    • Cerebellum: Coordinates and modifies movements.
    • Brain Stem: Maintains muscle tone.
  • Spinal Cord: Two-directional channels (afferent and efferent) for information flow. Integrates spinal reflexes.

4. PNS (Peripheral Nervous System)

  • Autonomic Nervous System: Controls involuntary functions. Composed of the sympathetic (activates during stress) and parasympathetic (promotes relaxation) systems.
  • Somatic Nervous System: Composed of sensory neurons (carry information from the body to the CNS – afferent) and motor neurons (carry responses from the CNS to the body – efferent).

5. Sensorimotor Integration

  • Sensory Input: Sensory information enters the CNS through receptors and is processed in integration centers (brain and spinal cord) to generate motor responses.
  • Motor Control: Can produce reflex responses. Two types of reflexes:
    • Myotatic Reflex: Defense mechanism involving muscle contraction, dependent on muscle spindles.
    • Tendon Reflex: Involves muscle relaxation, dependent on Golgi tendon organs.

Muscle Fibers

Two types:

  1. Slow-twitch (ST): More resistant to fatigue, more mitochondria, more myoglobin, more sarcoplasm. Suitable for aerobic efforts.
  2. Fast-twitch (FT): More myofibrils, larger diameter, higher ATPase activity, more sarcoplasmic reticulum. Suitable for anaerobic efforts.

Hypertrophy

Thickening of muscle fibers. Two types:

  1. Sarcoplasmic: Increase in sarcoplasm (fluid). Contributes to muscle size.
  2. Sarcomeric: Increase in actin and myosin filaments. Contributes to muscle strength.

Muscle Contraction

Muscle is composed of tendons, muscle belly, fasciae, capillaries, nerves, etc. Each fiber is composed of smaller units.

  • Sarcolemma: Cell membrane.
  • Myofibrils: Filaments that extend along the fiber.
  • Sarcoplasm: Cytoplasm of the muscle cell.
  • T-tubules: Extensions of the sarcolemma. Transmit impulses from the sarcolemma to the myofibrils.
  • Sarcoplasmic Reticulum: Network of tubules that store calcium.

Each fiber is composed of myofibrils -> sarcomeres -> myofilaments (actin and myosin).

Muscle -> Muscle fascicles -> Muscle fibers -> Myofibrils -> Sarcomeres -> Actin and Myosin.

Skeletal System

Bone is formed by the epiphysis (ends) and diaphysis (middle). Bone cells are generated in the diaphysis.

Types of Joints

  • Fibrous (Synarthrosis): Immovable joints.
  • Cartilaginous (Amphiarthrosis): Slightly movable joints.
  • Synovial (Diarthrosis): Freely movable joints.

Metabolism

Sum of all chemical reactions in cells.

ATP: Molecule needed for muscle movement. Stored in small quantities and lasts for 1-2 seconds.

ATP is consumed and recovered through:

  • Phosphocreatine: Molecule that quickly creates energy. Used in anaerobic, alactic efforts (2-7 seconds).
  • Anaerobic Glycolysis: ATP production without oxygen. Short anaerobic efforts. Lactic acid is produced.
  • Aerobic Oxidation of Glucose: ATP production with oxygen. Long aerobic efforts. Glucose and fatty acids are oxidized with oxygen to produce energy.

Respiratory System

1. Functions

  • Uptake and transport of air to the lungs.
  • Gas exchange (oxygen uptake and carbon dioxide removal).
  • Filtering, heating, and humidifying air.

2. Structure and Components

  • Upper Respiratory Tract: Nostrils, mouth, pharynx, larynx.
  • Lower Respiratory Tract: Trachea, bronchi, bronchioles (air distribution), alveoli (gas exchange).
  • Lungs: Air distribution through the bronchi, gas exchange in the alveoli.

3. Respiratory Function

Respiration: The process of gas exchange.

Phases:

  1. Pulmonary Ventilation: Inspiration and expiration (driven by pressure gradients).
  2. Pulmonary Diffusion: Gas exchange between alveolar air and capillary blood across the respiratory membrane.
  3. Gas Transport: Oxygen transport to tissues and carbon dioxide elimination. Oxygen is transported bound to hemoglobin and dissolved in plasma.
  4. Tissue Gas Exchange: Oxygen delivery to tissues and carbon dioxide removal from tissues.

4. Regulation of Respiration

  • Voluntary control (motor cortex).
  • Involuntary control (brainstem).

5. Lung Volumes and Capacities

  • Tidal Volume: Volume of air inhaled and exhaled during a normal breath.
  • Respiratory Frequency: Number of breaths per minute.
  • Residual Volume: Volume of air remaining in the lungs after a forced exhalation.
  • Vital Capacity: Maximum volume of air that can be exhaled after a maximum inhalation.
  • Minute Ventilation: Volume of air inhaled and exhaled per minute.
  • Inspiratory Reserve Volume: Volume of air that can be inhaled after a normal inhalation.
  • Expiratory Reserve Volume: Volume of air that can be exhaled after a normal exhalation.

Circulatory System

Systole: Heart contraction.

Diastole: Heart relaxation.

Cardiac Cycle: One complete sequence of systole and diastole.

1. Functions of the Heart

  • Distribution of oxygen and nutrients.
  • Elimination of waste products.
  • Maintenance of body temperature.
  • Protection against disease.
  • Transportation of hormones.

Functional Parameters of the Circulatory System:

  • Heart Rate (HR): Number of heartbeats per minute.
  • Cardiac Output (Q): Volume of blood ejected by the heart per minute.
  • Blood Pressure (BP): Pressure exerted by blood on artery walls.
  • Blood Flow: Distribution of blood to different parts of the body.

2. Components of the Circulatory System

  • Heart: Pumps blood.
  • Blood Vessels: Arteries, veins, capillaries.
  • Blood: Composed of plasma, red blood cells, white blood cells, and platelets.
  • Erythropoietin (EPO): Hormone that stimulates red blood cell production.
  • Capillaries: Microscopic vessels that connect arteries and veins. Function in nutrient and waste exchange.