Torso

The torso, also known as the trunk, is the central part of the human body that lies between the neck and the pelvis. It serves as the primary axis of the body and houses major organs within the thoracic and abdominal cavities, including the heart, lungs, digestive organs, and reproductive structures. The torso includes the chest, back, abdomen, and pelvis, providing structural support and attachment points for the limbs.

Location

The torso is located between the neck (superiorly) and the pelvis (inferiorly). It extends from the base of the neck to the inguinal region and is bordered posteriorly by the vertebral column (spine) and anteriorly by the rib cage and abdominal wall.

Anatomy

The torso, also known as the trunk, is the central part of the human body that connects the neck to the pelvis. It is a complex structure that contains vital organs and systems, provides structural support, and serves as the attachment site for the upper limbs and lower limbs. The torso is divided into the thoracic cavity (chest), abdominal cavity, and pelvic cavity.

Divisions of the Torso

The torso is anatomically divided into three main regions:

Thorax (Chest)

• Located in the upper portion of the torso.
• Enclosed by the rib cage and bounded by the diaphragm inferiorly.
• Contains vital organs, including the heart and lungs.

Abdomen

• Located between the thorax and pelvis.
• Contains digestive organs, such as the stomach, liver, intestines, pancreas, and kidneys.

Pelvis

• The lower portion of the torso, bounded by the pelvic bones.
• Contains organs of the urinary system (e.g., bladder) and reproductive systems, as well as portions of the digestive system.

Skeletal Framework

The skeletal structure of the torso provides support, protection, and attachment for muscles and organs.

Thoracic Cage (Rib Cage)

• Composed of 12 pairs of ribs, the sternum (breastbone), and the thoracic vertebrae (T1–T12).
• Protects the heart, lungs, and major blood vessels.

Vertebral Column (Spine)

The spinal column runs along the posterior aspect of the torso and provides structural support.

Composed of:

• Cervical Vertebrae (C1–C7): In the neck region.
• Thoracic Vertebrae (T1–T12): Form the upper back and attach to the ribs.
• Lumbar Vertebrae (L1–L5): Form the lower back and support the abdominal region.
• Sacrum and Coccyx: The fused vertebrae in the pelvic region.

Pelvic Bones

• Include the ilium, ischium, and pubis, which fuse to form the pelvis.
• The pelvis supports the weight of the upper body and forms the boundary of the pelvic cavity.

Muscles of the Torso

The torso is surrounded and supported by multiple layers of muscles that enable movement, posture, and protection.

Muscles of the Thorax

Intercostal Muscles:

• Located between the ribs.
• Include the external intercostals, internal intercostals, and innermost intercostals, which assist with breathing.

Diaphragm:

• A dome-shaped muscle that separates the thorax and abdomen.
• Plays a major role in respiration.^[6]

Pectoral Muscles:

Pectoralis Major and Pectoralis Minor cover the anterior chest wall and assist with movements of the arms and shoulders.

Serratus Anterior:

A fan-shaped muscle along the lateral thoracic wall, stabilizing the scapula.

Abdominal Muscles

The abdominal wall contains layers of muscles that provide support and flexibility:

Rectus Abdominis:

A vertical muscle running along the anterior abdomen, forming the “six-pack” appearance.

External Oblique:

The outermost muscle layer running diagonally.

Internal Oblique:

Lies beneath the external oblique, running in the opposite diagonal direction.

Transversus Abdominis:

• The deepest muscle layer running horizontally.
• These muscles provide support to the abdominal organs and assist with movements like bending, twisting, and respiration.

Back Muscles

The muscles of the back support the spine and torso:

• Trapezius: A large triangular muscle in the upper back.^[3]
• Latissimus Dorsi: Covers the mid-to-lower back and assists with shoulder movement.
• Erector Spinae: A group of deep muscles running parallel to the spine, providing postural support.

Cavities of the Torso

The torso contains three major body cavities that house vital organs:

Thoracic Cavity

Bounded by the rib cage and diaphragm.

Contains:

• Lungs: Located within the pleural cavities.
• Heart: Enclosed within the pericardial cavity.
• Major blood vessels, such as the aorta and vena cava.
• Esophagus: Passes through the thorax en route to the stomach.

Abdominal Cavity

Located below the diaphragm and above the pelvic cavity.

Contains digestive and urinary organs, including:

• Stomach
• Liver
• Gallbladder
• Pancreas
• Kidneys
• Small Intestine and Large Intestine

Pelvic Cavity

Bounded by the pelvic bones.

Contains organs of the urinary system, reproductive system, and distal digestive tract, including:

• Bladder
• Rectum
• Uterus and Ovaries (in females)
• Prostate (in males)

Blood Supply and Lymphatics

The torso has an extensive blood supply and lymphatic network:

Major Arteries:

• Aorta: The main artery that runs through the thoracic and abdominal cavities.
• Subclavian Arteries: Supply blood to the upper limbs and thorax.
• Renal Arteries: Supply the kidneys in the abdominal cavity.

Major Veins:

• Superior Vena Cava: Returns blood from the head and upper limbs to the heart.
• Inferior Vena Cava: Returns blood from the lower limbs and abdomen to the heart.

Lymphatics:

The torso contains lymph nodes that filter lymph and play a role in immunity. Major groups include:

• Axillary Nodes (in the armpits).^[1]
• Mediastinal Nodes (in the thoracic cavity).
• Inguinal Nodes (in the pelvis).

Nerves of the Torso

The torso is innervated by nerves that originate from the spinal cord and autonomic nervous system:

• Spinal Nerves: Arise from the thoracic and lumbar spinal cord, innervating muscles and skin.
• Intercostal Nerves: Run between the ribs, controlling the intercostal muscles and sensation in the thorax.
• Lumbar Plexus: Provides nerve supply to the lower abdomen and pelvis.
• Sympathetic Trunk: Part of the autonomic nervous system, running alongside the spine, regulating visceral functions like respiration and digestion.

Surface Landmarks of the Torso

Key surface landmarks include:

• Clavicles: Define the superior border of the thorax.
• Sternal Angle: A ridge at the junction of the manubrium and body of the sternum.
• Costal Margin: The lower edge of the rib cage.
• Umbilicus (Navel): Located at the center of the abdomen.
• Linea Alba: A fibrous line running vertically down the center of the abdomen.

Function

The torso, or trunk, serves as the central region of the human body, connecting the neck, upper limbs, and lower limbs while housing and protecting vital organs. It plays a critical role in supporting posture, enabling movement, respiration, digestion, and circulation. The skeletal framework, muscles, cavities, and nervous systems within the torso work together to maintain essential bodily functions. Below is a detailed breakdown of its functions:

Structural Support

The torso provides the primary structural support for the human body:

• The vertebral column (spine) forms the central axis, supporting the head, neck, and torso weight while transmitting it to the pelvis and lower limbs.
• The rib cage supports and protects the thoracic organs (heart, lungs) while providing a stable structure for breathing movements.
• The pelvis at the lower part of the torso supports the abdominal contents and connects the spine to the lower limbs.

This strong structural framework maintains the body’s upright posture and balance.

Protection of Vital Organs

The torso encloses and protects critical organs within its cavities:

Thoracic Cavity

• The rib cage shields the heart, lungs, and major blood vessels (e.g., aorta, vena cava) from external trauma.
• The sternum and ribs form a protective bony cage.

Abdominal Cavity

The abdominal wall muscles and lumbar vertebrae protect the digestive organs, including the stomach, intestines, liver, pancreas, and kidneys.

Pelvic Cavity

• The pelvic bones and associated ligaments protect the bladder, reproductive organs, and distal parts of the intestines (e.g., rectum).
• The torso’s skeletal and muscular structures act as shields, reducing the risk of injury to the vital organs.

Respiration (Breathing)

The torso plays a vital role in respiration by housing the lungs and supporting the mechanics of breathing:

Diaphragm

The diaphragm, a dome-shaped muscle at the base of the thoracic cavity, contracts and relaxes to change thoracic volume, driving inhalation and exhalation.^[8]

Intercostal Muscles

These muscles between the ribs expand and contract the rib cage during breathing, allowing the lungs to inflate and deflate.

Thoracic Cavity

• The thoracic cavity maintains space for the lungs to expand and contract with each breath.
• The torso ensures a continuous supply of oxygen to the body and facilitates the removal of carbon dioxide.

Movement and Locomotion

The torso is essential for body movements, balance, and locomotion:

Spinal Flexibility:

The vertebral column allows movements such as:

• Flexion: Bending forward.
• Extension: Straightening or leaning backward.
• Lateral Flexion: Bending sideways.
• Rotation: Twisting of the torso.

Muscular Support:

• The abdominal muscles (e.g., rectus abdominis, obliques) and erector spinae muscles enable bending, twisting, and stabilizing movements.^[7]
• Back muscles like the trapezius and latissimus dorsi assist in arm and shoulder movement.

Pelvic Support:

• The pelvis connects the torso to the lower limbs, transferring body weight for activities like walking, running, and climbing.
• The torso’s muscles and vertebrae work in unison to maintain posture, allow complex movements, and support overall mobility.

Housing the Digestive System

The torso contains the abdominal cavity, which houses the majority of the digestive organs:

• The esophagus passes through the thorax into the abdomen to deliver food to the stomach.
• The stomach processes food, while the small intestine and large intestine absorb nutrients and water.
• The liver and pancreas produce digestive enzymes and bile essential for digestion.
• The abdominal wall muscles assist in defecation by increasing intra-abdominal pressure.

The torso facilitates digestion, absorption, and elimination of waste.

Circulation of Blood

The torso supports blood circulation by housing major blood vessels and the heart:

• The heart, located in the thoracic cavity, pumps oxygenated blood to the body and receives deoxygenated blood for reoxygenation.
• Major arteries and veins pass through the torso:
  • Aorta: The main artery carrying blood from the heart to the body.
  • Vena Cava: Large veins returning blood to the heart.

The torso ensures continuous oxygen delivery and nutrient transport to organs and tissues.

Lymphatic and Immune Functions

The torso contains major lymphatic structures that support immunity and fluid balance:

• Lymph nodes, located in the thorax, abdomen, and pelvis, filter lymphatic fluid to trap pathogens.^[5]
• The spleen, located in the upper abdomen, acts as a blood filter and produces immune cells.

The torso’s lymphatic system plays a key role in maintaining immune defense and fluid homeostasis.

Reproductive System

The pelvic cavity, located in the lower part of the torso, houses the reproductive organs:

• In males: Includes the prostate gland, seminal vesicles, and parts of the reproductive ducts.
• In females: Contains the uterus, ovaries, fallopian tubes, and vagina.

The torso supports reproduction, pregnancy, and childbirth by providing space and protection for these organs.

Balance and Posture

The torso plays a critical role in maintaining balance and posture:

• The spine and its surrounding muscles provide stability, supporting the body against gravity.
• Core muscles (abdominal muscles, obliques, and erector spinae) stabilize the trunk during movements, preventing injuries.^[3]

Postural stability ensures proper alignment of the body for daily activities.

Thermoregulation

The torso helps regulate body temperature:

• The skin on the torso contains sweat glands that release sweat to cool the body.
• Muscular activity within the torso (e.g., shivering) generates heat in cold conditions.

The torso’s central role in metabolism and circulation supports thermoregulation.

Clinical Significance

The torso houses vital organs and systems, making it a focal point for various clinical conditions that can impact overall health and survival.

Thoracic Conditions

• Respiratory Disorders: Diseases like pneumonia, pleuritis, and lung cancer affect the lungs housed in the thoracic cavity.
• Cardiac Conditions: The heart, located within the thorax, is prone to disorders such as coronary artery disease, arrhythmias, and heart failure.
• Rib Fractures: Trauma to the thorax can damage the rib cage, leading to pain and compromised breathing.

Abdominal Disorders

• Conditions such as appendicitis, gastric ulcers, liver cirrhosis, kidney stones, and hernia involve abdominal organs like the stomach, intestines, liver, and kidneys.^[2]
• Peritonitis: Inflammation of the abdominal lining can occur due to infections or organ rupture.

Spinal Conditions

Disorders like scoliosis, herniated discs, and spinal fractures affect the vertebral column, leading to pain, nerve compression, and reduced mobility.

Pelvic Disorders

The pelvic cavity houses reproductive organs, making it prone to conditions like uterine fibroids, ovarian cysts, and prostate enlargement.

Trauma and Injuries

Penetrating or blunt trauma to the torso can cause life-threatening injuries to the heart, lungs, major vessels, or abdominal organs.

Musculoskeletal Issues

Weakness or injury to the core muscles can result in poor posture, lower back pain, or instability.