Organization of the Human Body

Organization of the Human Body

• The human body is composed of several levels of organization:
  • Chemical level: atoms, molecules, and compounds
  • Cellular level: cells, the basic structural and functional units of life
  • Tissue level: groups of similar cells that perform specific functions
  • Organ level: structures composed of two or more types of tissues that perform specific functions
  • Organ system level: groups of organs that work together to perform specific functions
  • Organismal level: the entire human body

Body Regions

• The human body can be divided into several regions:
  • Axial region: includes the skull, vertebral column, ribs, and sternum
  • Appendicular region: includes the upper and lower limbs
  • Head and neck region: includes the face, skull, and neck
  • Thoracic region: includes the chest cavity and organs
  • Abdominal region: includes the abdominal cavity and organs
  • Pelvic region: includes the pelvis and organs

Body Cavities

• The human body contains several cavities:
  • Cranial cavity: contains the brain
  • Vertebral cavity: contains the spinal cord
  • Thoracic cavity: contains the heart, lungs, and major blood vessels
  • Abdominal cavity: contains the digestive organs and kidneys
  • Pelvic cavity: contains the reproductive organs and bladder

Directional Terms

• Directional terms are used to describe the location of structures in the body:
  • Anterior: front
  • Posterior: back
  • Superior: above
  • Inferior: below
  • Medial: toward the midline
  • Lateral: away from the midline
  • Proximal: toward the point of attachment
  • Distal: away from the point of attachment

Anatomical Position

• The anatomical position is a standard reference point used to describe the body:
  • Standing upright
  • Feet shoulder-width apart
  • Arms at the sides
  • Palms facing forward
  • Toes pointing forward

Organization of the Human Body

• The human body is composed of six levels of organization, in order: chemical, cellular, tissue, organ, organ system, and organismal.
• The cellular level is the basic structural and functional unit of life.
• Organs are composed of two or more types of tissues that perform specific functions.
• Organ systems are groups of organs that work together to perform specific functions.

Body Regions

• The human body can be divided into six regions: axial, appendicular, head and neck, thoracic, abdominal, and pelvic.
• The axial region includes the skull, vertebral column, ribs, and sternum.
• The appendicular region includes the upper and lower limbs.

Body Cavities

• The human body contains five cavities: cranial, vertebral, thoracic, abdominal, and pelvic.
• The cranial cavity contains the brain.
• The thoracic cavity contains the heart, lungs, and major blood vessels.
• The abdominal cavity contains the digestive organs and kidneys.

Directional Terms

• There are 8 directional terms used to describe the location of structures in the body: anterior, posterior, superior, inferior, medial, lateral, proximal, and distal.
• Anterior refers to the front of the body.
• Posterior refers to the back of the body.
• Superior refers to above or higher than.
• Inferior refers to below or lower than.

Anatomical Position

• The anatomical position is a standard reference point used to describe the body.
• In the anatomical position, the body is standing upright, with feet shoulder-width apart, arms at the sides, palms facing forward, and toes pointing forward.

Muscular System

Overview

• Muscular system enables movement, maintains posture, and regulates body temperature
• Composed of three types of muscles: skeletal, smooth, and cardiac

Skeletal Muscles

• Also known as striated muscles
• Voluntary muscles that can be controlled consciously
• Attached to bones, help move the body's skeleton
• Multi-nucleated, striated appearance, and have fast-twitch and slow-twitch fibers
• Functions: movement of the body, maintenance of posture, and regulation of body temperature

Smooth Muscles

• Also known as non-striated muscles
• Involuntary muscles that cannot be controlled consciously
• Found in walls of hollow organs and blood vessels
• Single nucleus, non-striated appearance, and spontaneous contraction and relaxation
• Functions: movement of substances through organs (e.g. digestion, peristalsis), and regulation of blood pressure

Cardiac Muscles

• Found only in the heart
• Involuntary muscles that cannot be controlled consciously
• Characteristics: branching fibers, striated appearance, and self-excitable
• Functions: pumping of blood throughout the body, and regulation of heart rate

Muscle Tissue Functions

• Provide movement, support, protection, and stabilization for the body
• Functions include maintaining posture, regulating body temperature, and protecting internal organs

Muscle Fiber Types

• Slow-twitch (Type I) fibers: low force generation, high endurance, and used for low-intensity, long-duration activities
• Fast-twitch (Type II) fibers: high force generation, low endurance, and used for high-intensity, short-duration activities

Nervous System

Organization

• The nervous system consists of the Central Nervous System (CNS) and Peripheral Nervous System (PNS)
• The CNS includes the brain and spinal cord, while the PNS comprises nerves that connect the CNS to the rest of the body

Central Nervous System (CNS)

Brain

• The cerebrum is the largest part of the brain, divided into left and right hemispheres
• The cerebellum coordinates movement and balance
• The brainstem connects the cerebrum and cerebellum to the spinal cord
• The meninges are protective membranes surrounding the brain and spinal cord

Spinal Cord

• The spinal cord extends from the base of the brain to the lower back
• Its functions include transmitting messages, regulating reflexes, and controlling autonomic functions

Peripheral Nervous System (PNS)

Somatic Nervous System

• The somatic nervous system controls voluntary motor functions, including skeletal muscles
• It also transmits sensory information to the CNS

Autonomic Nervous System

• The autonomic nervous system regulates involuntary functions, such as heart rate, blood pressure, digestion, and respiration
• It is divided into the sympathetic (fight or flight) and parasympathetic (rest and digest) systems

Neurons

• Neurons are the basic functional units of the nervous system
• A neuron consists of dendrites that receive signals, a cell body containing the nucleus and organelles, an axon that transmits signals, and terminal buttons that release neurotransmitters

Neurotransmission

• A synapse is the gap between the terminal button of one neuron and the dendrite of an adjacent neuron
• Neurotransmitters are chemical messengers released by terminal buttons
• Receptors bind to neurotransmitters, generating a response in the receiving neuron

Circulatory System

Overview

• The circulatory system is also known as the cardiovascular system
• It is responsible for transporting oxygen and nutrients to cells and removing waste products
• The system consists of three main components: the heart, blood vessels, and blood

Heart

• The heart is a muscular organ that pumps blood throughout the body
• It is located in the thoracic cavity, between the lungs
• The heart has four chambers: right atrium, right ventricle, left atrium, and left ventricle
• Right atrium receives oxygen-depleted blood from the body
• Right ventricle pumps blood from the right atrium to the lungs
• Left atrium receives oxygen-rich blood from the lungs
• Left ventricle pumps blood from the left atrium to the rest of the body

Blood Vessels

• Arteries carry oxygen-rich blood away from the heart to the rest of the body
• Veins carry oxygen-depleted blood back to the heart
• Capillaries are tiny vessels where oxygen and nutrients are exchanged with cells

Blood

• Blood is a liquid tissue that transports oxygen, nutrients, and waste products
• It is composed of plasma and formed elements
• Plasma is the liquid portion of blood that carries proteins, nutrients, and waste products
• Formed elements include red blood cells, white blood cells, and platelets
• Blood functions include oxygen transport, nutrient transport, waste removal, regulation of body temperature, and maintenance of pH balance

Blood Circulation

• Pulmonary circulation is the circulation of blood between the heart and lungs
• Systemic circulation is the circulation of blood between the heart and the rest of the body
• Coronary circulation is the circulation of blood within the heart itself

Blood Pressure

• Blood pressure is the force exerted by blood on the walls of blood vessels
• It is measured in mmHg (millimeters of mercury)
• Normal blood pressure range is 90-120 mmHg (systolic) and 60-80 mmHg (diastolic)

Organ Systems

Overview

• There are 11 major organ systems in the human body, which work together to maintain overall health and homeostasis.

1. Nervous System

• The nervous system controls and coordinates body functions, interprets and responds to sensory information.
• It consists of the Central Nervous System (CNS: brain and spinal cord) and the Peripheral Nervous System (PNS: nerves that connect CNS to the rest of the body).

2. Circulatory System

• The circulatory system transports oxygen and nutrients to cells, and removes waste products.
• It consists of the heart, blood vessels (arteries, veins, and capillaries), and blood that carries oxygen, nutrients, and waste products.

3. Respiratory System

• The respiratory system brings oxygen into the body and removes carbon dioxide.
• It consists of the lungs, trachea, and bronchi.

4. Digestive System

• The digestive system breaks down food into nutrients that can be absorbed and utilized by the body.
• It consists of the mouth, esophagus, stomach, small intestine, and large intestine.

5. Endocrine System

• The endocrine system produces and regulates hormones that control various bodily functions.
• It consists of glands (pancreas, thyroid, adrenal, pituitary, and others) that produce hormones.

6. Integumentary System

• The integumentary system protects the body from external damage, regulates body temperature, and aids in sensation.
• It consists of the skin, hair, nails, and exocrine glands that produce sweat, oil, and wax.

7. Immune System

• The immune system defends the body against pathogens and diseases.
• It consists of white blood cells, the lymphatic system, and other organs and tissues that aid in immune function.

8. Muscular System

• The muscular system allows for movement, maintains posture, and regulates body temperature.
• It consists of skeletal muscles, smooth muscles, and cardiac muscles.

9. Skeletal System

• The skeletal system provides support, protection, and movement for the body.
• It consists of bones, joints, ligaments, and tendons.

10. Urinary System

• The urinary system removes waste and excess fluids from the body.
• It consists of the kidneys, ureters, bladder, and urethra.

11. Reproductive System

• The reproductive system produces sex cells and supports the development of a fetus during pregnancy.
• It consists of male (testes, epididymis, vas deferens, prostate gland, urethra) and female (ovaries, fallopian tubes, uterus, cervix, vagina) reproductive organs.