Human Organ Systems

Organ Systems Overview

• The human body contains several organ systems that work in a coordinated manner.
• Major systems include the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems.
• The integumentary system (skin, hair, nails) provides protection, regulates temperature, and detects sensations.
• The skeletal system (bones, joints) supports the body, protects organs, and facilitates movement.
• The muscular system (skeletal muscles) enables movement, maintains posture, and generates heat.
• The nervous system (brain, spinal cord, nerves) controls and coordinates bodily functions and responses.
• The endocrine system (glands) secretes hormones that regulate various bodily functions.
• The cardiovascular system (heart, blood vessels) transports oxygen, nutrients, and wastes.
• The lymphatic system (lymph vessels, lymph nodes) defends against disease and maintains fluid balance.
• The respiratory system (lungs, airways) enables gas exchange (oxygen and carbon dioxide).
• The digestive system (gastrointestinal tract, accessory organs) processes food and absorbs nutrients.
• The urinary system (kidneys, bladder) eliminates waste and regulates fluid and electrolyte balance.
• The reproductive systems (male and female) enable procreation.

Nervous System Anatomy

• The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS consists of the brain and spinal cord, while the PNS includes all nervous tissue outside the CNS.
• The nervous system consists of neurons and glial cells.
• Neurons transmit electrical signals.
• Glial cells support and protect neurons.
• Neurons have a cell body (soma), dendrites, and an axon.
• Dendrites receive signals, and the axon transmits signals.
• Axons can be myelinated or unmyelinated.
• Myelin is a fatty substance that insulates axons and increases the speed of signal transmission.
• The PNS is further divided into the somatic nervous system and the autonomic nervous system (ANS).
• The somatic nervous system controls voluntary movements of skeletal muscles.
• The autonomic nervous system regulates involuntary functions of smooth muscle, cardiac muscle, and glands.
• The ANS has two divisions: the sympathetic and parasympathetic nervous systems.
• The sympathetic nervous system prepares the body for "fight or flight" responses.
• The parasympathetic nervous system promotes "rest and digest" functions.

Brain

• The brain is the control center of the nervous system.
• Major regions include the cerebrum, cerebellum, diencephalon, and brainstem.
• The cerebrum is the largest part of the brain and is responsible for higher-level functions.
• The cerebrum is divided into two hemispheres, each with four lobes: frontal, parietal, temporal, and occipital.
• The frontal lobe is involved in motor control, planning, and higher-level cognitive functions.
• The parietal lobe processes sensory information such as touch, temperature, and pain.
• The temporal lobe is involved in auditory processing, memory, and language.
• The occipital lobe processes visual information.
• The cerebellum coordinates movement and maintains balance.
• The diencephalon includes the thalamus and hypothalamus.
• The thalamus relays sensory information to the cerebrum.
• The hypothalamus regulates body temperature, hunger, thirst, and the endocrine system.
• The brainstem connects the brain to the spinal cord.
• The brainstem includes the midbrain, pons, and medulla oblongata.
• The brainstem controls vital functions such as breathing, heart rate, and blood pressure.

Spinal Cord

• The spinal cord is a long, cylindrical structure that extends from the brainstem.
• The spinal cord transmits signals between the brain and the rest of the body.
• The spinal cord is protected by the vertebral column.
• The spinal cord has a central gray matter region surrounded by white matter.
• Gray matter contains neuron cell bodies and synapses.
• White matter contains myelinated axons.
• Spinal nerves emerge from the spinal cord and innervate the body.

Peripheral Nervous System

• The peripheral nervous system (PNS) consists of all nervous tissue outside the CNS.
• The PNS includes cranial nerves and spinal nerves.
• Cranial nerves emerge from the brain and innervate the head and neck.
• There are 12 pairs of cranial nerves, each with specific sensory or motor functions.
• Spinal nerves emerge from the spinal cord and innervate the rest of the body.
• There are 31 pairs of spinal nerves, each with sensory and motor fibers.
• The PNS transmits sensory information to the CNS and carries motor commands from the CNS to the body.

Human Body Systems

• The human body is organized into several interacting systems.
• The organ systems include the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems.
• The integumentary system protects the body from the external environment.
• The skeletal system provides support and facilitates movement.
• The muscular system enables movement and generates heat.
• The nervous system controls and coordinates bodily functions.
• The endocrine system regulates bodily functions through hormones.
• The cardiovascular system transports oxygen, nutrients, and wastes.
• The lymphatic system defends against disease and maintains fluid balance.
• The respiratory system enables gas exchange.
• The digestive system processes food and absorbs nutrients.
• The urinary system eliminates waste and regulates fluid balance.
• The reproductive system enables procreation.
• Maintaining homeostasis, a stable internal environment, requires the coordinated action of all organ systems.
• Disease occurs when one or more organ systems fail to function properly, disrupting homeostasis.