Essential Functions of Human Body Systems and Coordination

Skeletal System: Functions and Joints

Skeletal System Functions

• Support the body structure.
• Protect vital organs.
• Provide points of attachment for muscles.
• Manufacture blood cells (hematopoiesis).
• Store calcium and phosphorus.

Joints: Connections Between Bones

Joints are places where bones connect. They are classified by the degree of movement they permit:

• Fixed Joints (Synarthroses): Do not permit movement (e.g., skull sutures).
• Slightly Movable Joints (Amphiarthroses): Allow limited movement (e.g., vertebrae).
• Freely Movable Joints (Diarthroses): Allow bone movement in all directions (e.g., knee).

Sensory Receptors and Stimuli Perception

Types of Receptors

• Internal Receptors (Interoceptors): Perceive changes occurring inside the body (e.g., blood pressure, pH).
• External/Sensory Receptors (Exteroceptors): Perceive stimuli from the external environment.

Classification of External Receptors

• Mechanoreceptors: Detect mechanical stimuli (pressure, touch, vibration).
• Thermoreceptors: Detect temperature variations (heat and cold).
• Chemoreceptors: Detect chemical substances (taste, smell, blood chemistry).
• Photoreceptors: Light-sensitive receptors (vision).
• Nociceptors: Sensitive to pain.

Endocrine Coordination and Hormonal Regulation

Hormones are chemical messengers produced by glands when required. Their secretion is primarily managed by a feedback mechanism controlled by the hypothalamus in the brain.

Hormonal Feedback Loop

1. The hypothalamus stimulates the pituitary gland.
2. The pituitary gland stimulates other endocrine glands.
3. Hormones regulate specific target organs or cells.

The system maintains homeostasis: an increase in the amount of hormones above a certain level typically halts their further secretion (negative feedback).

Muscular System: Functions and Muscle Types

Muscular System Functions

• Enable movement by contracting and pulling on the bones.
• Maintain the body's posture through muscle tone.
• Generate heat (thermogenesis).

Classification of Muscle Shapes

• Fusiform: Long muscles that are narrower at the ends (e.g., biceps).
• Flat: Muscles with equal length and width (e.g., pectoral muscles).
• Circular (Sphincter): Muscles that surround an opening, opening and closing it (e.g., the orbicularis oris muscle, which opens and closes the lips).

Coordination of Movement: Voluntary and Reflex Actions

Voluntary Actions (Conscious Control)

Voluntary actions are conscious and coordinated by the encephalon (brain).

1. A receptor perceives the stimulus.
2. A sensory nerve transmits the impulse to the central nervous system.
3. The cerebral cortex converts the information into a conscious sensation and generates a response command.
4. A motor nerve transmits the command to the effector organ.
5. An effector organ (muscle or gland) carries out the response.

Reflex Actions (Involuntary Control)

Reflex actions are involuntary, automatic responses coordinated by the spinal cord.

The pathway is similar to voluntary actions, except for the processing step (Step 3):

1. A receptor perceives the stimulus.
2. A sensory nerve transmits the impulse.
3. An interneuron in the spinal cord generates an immediate response command, bypassing the cerebral cortex.
4. A motor nerve transmits the command to the effector organ.
5. An effector organ carries out the response.

Major Endocrine Glands and Hormones