Organ Systems, Body Cavities, and Body Membranes

Organ Systems Overview

  • An organ is defined as a group of tissues performing a common function.

  • Organ systems are formed by organs with similar functions working together.

  • Some organ systems, like the respiratory system, occupy specific body cavities.

  • Others, such as the muscular and circulatory systems, are distributed throughout the body.

  • Organs and body cavities are lined with membranes, many of which secrete fluid for lubrication.

Standard Anatomical Terminology

  • From a psychological perspective, standard terms are crucial for referring to human anatomical parts, and many apply to other organisms.

  • Human anatomical terms always relate to a body in the upright standing position.

  • Ventral or anterior: Refers to the front of the body.

  • Dorsal or posterior: Refers to the back of the body.

  • Superior: Means toward the head.

  • Inferior: Means toward the feet.

  • Medial: Closer to the midline of the body.

  • Lateral: Away from the midline of the body.

  • Proximal: (When referring to an appendage like an arm or leg) Closer to the trunk of the body.

  • Distal: (When referring to an appendage) Away from the trunk of the body.

Interaction of Organ Systems

  • Just as organs cooperate within an organ system, organ systems also collaborate within the body.

  • Some organs, like the pancreas, can be involved in the function of more than one organ system (e.g., both endocrine and digestive systems).

  • Beyond major organs, other structures and glands often contribute to the overall operation of an organ system.

Body Cavities

  • The human body is divided into two primary cavities:

    1. The Ventral Cavity

    2. The Dorsal Cavity

Ventral Cavity

  • In early development, the ventral cavity is referred to as the coleolum.

  • It later subdivides into three main cavities:

    • Thoracic Cavity:

      • Contains the lungs and the heart.

      • Separated from the abdominal cavity by the diaphragm, a horizontal muscle.

    • Abdominal Cavity:

      • Located below the diaphragm.

      • Contains the stomach, liver, spleen, pancreas, gallbladder, and most of the small and large intestines.

    • Pelvic Cavity:

      • Contains the rectum, urinary bladder, internal reproductive organs, and the remaining parts of the small and large intestines.

  • Males have an external extension of the abdominal wall called the scrotum, which encloses the testes.

Dorsal Cavity

  • The dorsal cavity consists of two parts:

    1. Cranial Cavity:

      • Located within the skull.

      • Contains the brain.

    2. Vertebral Canal:

      • Formed by the vertebrae.

      • Contains the spinal cord.

Body Membranes

  • Body membranes line cavities and the internal spaces of organs and tubes that open to the outside.

  • There are four main types of body membranes:

    1. Mucous membranes

    2. Serous membranes

    3. Synovial membranes

    4. Meninges

Mucous Membranes

  • Location: Line the tubes of the digestive, respiratory, urinary, and reproductive systems.

  • Composition: Consist of an epithelium overlying loose, fibrous connective tissue. The epithelium includes specialized cells that secrete mucus.

  • Function: Secreted mucus protects the body from invasion by bacteria and viruses. It also protects the walls of the stomach and small intestine from digestive juices.

    • Example: More mucus is secreted and expelled during a cold to help remove pathogens.

    • Example: Protection against digestive juices breaks down when a person develops an ulcer.

Serous Membranes

  • Location: Line the closed cavities of the body (e.g., surrounding the lungs, heart, and within the abdominal cavity).

  • Secretion: Secrete a watery fluid that keeps the membranes lubricated.

  • Function: Support internal organs and compartmentalize the large thoracic and abdominal cavities.

  • Specific Names based on Location:

    • Pleurae: Line the thoracic cavity and cover the lungs.

    • Pericardium: Covers the heart.

    • Peritoneum: Lines the abdominal cavity and covers its organs.

  • Mesentery: A double layer of peritoneum that supports abdominal organs and attaches them to the abdominal wall.

Synovial Membranes

  • Composition: Composed only of loose connective tissue.

  • Location: Line the cavities of freely movable joints.

  • Secretion: Secrete synovial fluid into the joint cavity.

  • Function: This fluid lubricates the ends of bones, allowing them to move freely.

    • Example: In rheumatoid arthritis, the synovial membrane becomes inflamed and thickens, restricting joint movement.

Meninges

  • Location: Found within the dorsal cavity.

  • Composition: Composed only of connective tissue.

  • Function: Serve as a protective covering for the brain and spinal cord.

    • Example: Meningitis is a life-threatening infection of the meninges.