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Human Body Systems: Blood, Excretion, and Sensory Functions

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Human Blood Components

Blood Plasma

  • Composed of: Water, mineral salts, glucose, proteins, vitamins, hormones.

Red Blood Cells (Erythrocytes)

  • Lack a nucleus.
  • Biconcave shape.
  • Contain hemoglobin.
  • Density: Approximately 4.5 to 5 million per mm³ (varies by sex).
  • Function: Transport of substances (e.g., oxygen).

White Blood Cells (Leukocytes)

  • Much larger than red blood cells.
  • Less numerous.
  • Involved in the body's defense mechanisms.
  • An increase often indicates an infection or immune response.

Platelets (Thrombocytes)

  • Cell fragments.
  • Approximately 300,000 per mm³.
  • Crucial for the process of blood coagulation (clotting).

The Excretory System

Components of the Urinary Tract

  • Inferior Vena Cava
  • Adrenal Glands (though not directly part of excretion, they are anatomically associated)
  • Kidneys
  • Ureters
  • Urethra
  • Aorta
  • Renal Artery
  • Renal Vein
  • Bladder

Kidney Structure and Function

  • Shape: Bean-shaped organs.
  • Function: Filters blood plasma to produce urine.
  • Internal Structures:
    • Renal Cortex
    • Renal Medulla
    • Renal Pyramids
    • Renal Papillae
    • Renal Pelvis
    • Renal Capsule (outer covering)
    • Ureter (tube exiting the kidney)

The Sensory System

Understanding Stimuli

A stimulus is a change in our environment or within us that we perceive and that provokes a response from our body.

Receptors: Definition and Types

Receptors are specialized structures designed to receive information and transform it into nerve impulses.

  • Internal Receptors (Interoceptors): Capture changes within the internal environment of the body (e.g., blood pressure, body temperature).
  • External Receptors (Exteroceptors): Capture changes from the external environment.

Types of Senses

These are groupings of external receptors, allowing us to perceive the world around us:

  • Touch (Skin)
  • Smell (Nose)
  • Taste (Tongue)
  • Hearing (Ears)
  • Balance (Ears)
  • Vision (Eyes)

The Sense of Touch (Tactile Sense)

The sense of touch is primarily located in the skin, utilizing various types of receptors:

  • Thermoreceptors: Capture differences in temperature between the external and internal environment, creating sensations of cold and heat.
  • Nociceptors: Respond to harmful stimuli or aggression against the skin, resulting in the sensation of pain.
  • Mechanoreceptors: Detect changes in pressure and touch, allowing us to perceive contact with objects.

The Sense of Taste (Gustation)

The sense of taste allows us to perceive flavors through specialized taste buds located primarily on the tongue.

The Ear: Hearing and Balance

Audition (Hearing Process)

  1. Sound waves enter the pinna (outer ear) and travel through the ear canal.
  2. The sound waves cause the tympanum (eardrum) to vibrate.
  3. Vibrations are transmitted through the chain of ossicles (malleus, incus, stapes).
  4. The stapes transmits vibrations to the oval window of the cochlea (a snail-shaped structure).
  5. Fluid within the cochlea moves, stimulating specialized hair cells (cells of hearing).
  6. These cells generate nerve impulses, which are sent via the cochlear nerve to the brain for interpretation.

Equilibrium (Balance)

Balance is maintained by structures within the inner ear:

  • Semicircular Canals: Detect rotational movements of the head.
  • Vestibule (Utricle and Saccule): Detect linear acceleration and head position relative to gravity.

These structures contain fluid and receptor cells that send signals via the vestibular nerve to the brain, allowing us to maintain our sense of balance.

The Sense of Vision

Process of Vision

  1. Light enters the eye, passing through the cornea and pupil.
  2. The lens focuses the light, creating an image on the retina.
  3. The retina contains specialized photoreceptor cells (rods and cones).
  4. These photoreceptors convert light into nerve impulses.
  5. The nerve impulses are transmitted via the optic nerve to the brain for visual processing.

Common Visual Conditions

  • Myopia (Nearsightedness): Difficulty seeing distant objects clearly.
  • Hyperopia (Farsightedness): Difficulty seeing near objects clearly.

Eye Anatomy and Protection

The eye is a spherical, bulging organ. Eyelids provide protection from external elements. The lacrimal glands produce tears that clean and lubricate the eye, which is filled with a viscous fluid.

Key Eye Structures

  • Iris
  • Cornea
  • Pupil
  • Lens (Crystalline Lens)
  • Sclera
  • Blind Spot
  • Optic Nerve
  • Fovea
  • Retina
  • Choroid

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