Human Systems

Integumentary System

An organ system consisting of the skin and its accessory structures, including the epidermis, papillary layer, reticular layer, dermis, subcutaneous layer (hypodermis), hair shaft, hair follicle, sweat pore, sweat gland duct, merocrine sweat gland, dermal papilla, arrector pili muscle, sebaceous (oil) gland, sensory nerve fiber, areolar connective tissue, adipose connective tissue, arteries, and veins.

Epidermis

The outermost layer of the skin.

Dermis

The layer of skin beneath the epidermis containing the papillary layer and reticular layer.

Papillary Layer

The superficial layer of the dermis containing dermal papillae.

Reticular Layer

The deeper, thicker layer of the dermis underlying the papillary layer.

Subcutaneous Layer (Hypodermis)

The layer of tissue directly below the dermis containing adipose connective tissue, areolar connective tissue, and blood vessels.

Sebaceous Gland

An oil-producing gland in the skin attached to a hair follicle.

Arrector Pili Muscle

A small muscle connected to a hair follicle that causes the hair to stand upright.

Merocrine Sweat Gland

A type of sweat gland that secretes fluid through a sweat gland duct directly onto the skin surface via a sweat pore.

Skeletal System

The body system composed of bones, joints, and cartilage that provides structure, support, and protection to the human body.

Muscular System

The body system composed of muscle tissue responsible for movement, posture, and heat production, categorized into skeletal muscle, cardiac muscle, and smooth muscle.

Skeletal Muscle

Voluntary muscle tissue attached to bones that facilitates body movement, including muscles like the temporalis, masseter, sternocleidomastoid, pectoralis major, biceps brachii, abdominal muscles, sartorius, quadriceps femoris, and gastrocnemius.

Cardiac Muscle

Involuntary, specialized muscle tissue found specifically in the heart.

Smooth Muscle

Involuntary muscle tissue found in the walls of intestines, internal organs, and blood vessels.

Nervous System

The body's primary control and communication network, divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Central Nervous System (CNS)

The main control center of the nervous system composed of the brain and spinal cord.

Peripheral Nervous System (PNS)

The division of the nervous system outside the CNS, consisting of nerves that connect the brain and spinal cord to the rest of the body.

Autonomic Nervous System

A functional division of the nervous system consisting of the sympathetic nerves and parasympathetic nerves.

Parasympathetic Nerves

The division of the autonomic nervous system that conserves energy and restores body resources (e.g., constricts pupils, stimulates saliva, constricts airways, slows heartbeat, stimulates activity of stomach and intestines, stimulates gallbladder, contracts bladder, and promotes erection of genitals).

Sympathetic Nerves

The division of the autonomic nervous system that prepares the body for action or "fight or flight" responses (e.g., dilates pupils, inhibits salivation, relaxes airways, increases heartbeat, inhibits stomach and intestine activity, stimulates glucose release, secretes epinephrine and norepinephrine, relaxes bladder, and promotes ejaculation/vaginal contractions).

Endocrine System

A network of glands that produce and secrete hormones into the bloodstream to regulate body processes, including the hypothalamus, pineal gland, pituitary gland, thyroid gland, parathyroid glands, thymus, adrenal glands, pancreas, ovaries, and testes.

Hypothalamus

An endocrine and nervous system structure located in the brain that controls the pituitary gland.

Pineal Gland (Epiphysis)

An endocrine gland located in the brain involved in regulating biological rhythms.

Pituitary Gland

An endocrine gland situated at the base of the brain that secretes key hormones controlling other endocrine glands.

Thyroid Gland

An endocrine gland located in the neck region responsible for regulating metabolism.

Parathyroid Glands

Small endocrine glands attached to the back of the thyroid gland involved in calcium regulation.

Thymus

An endocrine and immune organ located in the upper thoracic cavity.

Adrenal Glands (Suprarenal)

Endocrine glands located above the kidneys that secrete hormones such as epinephrine and norepinephrine.

Pancreas

An endocrine and digestive organ located in the abdomen that produces insulin and digestive enzymes.

Ovaries

Female reproductive glands that produce eggs and female sex hormones.

Testes (Testicles)

Male reproductive glands that produce sperm and male sex hormones.

Cardiovascular System

The organ system consisting of the heart, blood vessels, and blood, responsible for circulating oxygen, nutrients, and waste products throughout the body.

Heart

The central muscular organ of the cardiovascular system containing chambers such as the right auricle, right ventricle, left auricle, and left ventricle.

Pulmonary Circulation

The pathway of blood circulation between the heart and lungs via the pulmonary arteries and pulmonary veins.

Systemic Circulation

The pathway of blood circulation between the heart and the rest of the body via major vessels including the aorta, superior vena cava, inferior vena cava, hepatic portal vein, and blood vessels of organs.

Lymphatic System

An organ system and component of the immune system composed of lymphatic vessels, lymph nodes, lymph, and lymphoid organs like the tonsils, thymus, spleen, bone marrow, lacteals, and appendix.

Lymph Nodes

Small, bean-shaped structures along lymphatic vessels that filter lymph, including cervical, axillary, intestinal, iliac, and inguinal lymph nodes.

Lymphatic Vessels

Specialized vessels that transport lymph fluid throughout the body, including the thoracic duct and right lymphatic duct.

Spleen

A lymphatic organ located in the upper left abdomen that filters blood and plays a role in immunity.

Tonsils

Lymphatic tissue structures located in the pharynx/throat, such as the palatine tonsils.

Respiratory System

The organ system responsible for gas exchange between the body and environment, including the nasal structures, pharynx, larynx, trachea, bronchi, bronchial tree, and lungs.

Lungs

The primary respiratory organs located in the thoracic cavity responsible for oxygenating blood and removing carbon dioxide.

Trachea

The windpipe tube connecting the larynx to the mainstem bronchi of the lungs.

Digestive System

The organ system responsible for breaking down food, absorbing nutrients, and eliminating wastes, composed of the alimentary canal and accessory digestive organs.

Alimentary Canal Structures

The continuous pathway of the digestive tract consisting of the mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum), and anus.

Accessory Digestive Organs

Organs that assist in digestion, including the teeth, tongue, palate, uvula, salivary glands (sublingual, submandibular, parotid), liver, gallbladder, pancreatic duct, common bile duct, and pancreas.

Small Intestine

The primary site of nutrient absorption in the digestive system, composed of the duodenum, jejunum, and ileum.

Large Intestine

The portion of the digestive tract responsible for water absorption and waste formation, composed of the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum.

Urinary System

The organ system responsible for filtering waste products from the blood and producing urine, consisting of the kidneys, renal hilum, renal arteries, renal veins, ureters, urinary bladder, and urethra.

Kidneys

A pair of bean-shaped urinary organs that filter blood to produce urine.

Ureters

Muscular tubes that transport urine from the kidneys to the urinary bladder.

Urinary Bladder

A muscular sac that stores urine prior to excretion.

Urethra

The canal through which urine is discharged from the urinary bladder out of the body.

Female Reproductive System

The system of organs involved in female reproduction, including internal organs (ovaries, fallopian tubes, uterus, cervix, vagina) and external structures (labia majora, labia minora, clitoris, hymen).

Uterus

The hollow, muscular female reproductive organ where a fetus develops, consisting of the endometrium and myometrium.

Fallopian Tubes

Tubes that transport eggs from the ovaries to the uterus and serve as the typical site of fertilization.

Cervix

The lower, narrow part of the uterus that connects to the vagina, containing the internal os and external os.

Male Reproductive System

The system of organs involved in male reproduction, including the testicles (testes), scrotum, epididymis, ductus deferens (vas deferens), ejaculatory duct, seminal vesicles, prostate gland, bulbourethral gland (Cowper's gland), urethra, and penis (including corpus cavernosum, corpus spongiosum, foreskin, and glans penis).

Epididymis

A coiled structure attached to the testicle where sperm matures and is stored.

Ductus Deferens (Vas Deferens)

The tube that transports sperm from the epididymis toward the ejaculatory duct.

Prostate Gland

A male accessory gland that secretes fluid into the urethra to nourish and transport sperm.

Seminal Vesicles

Glands that secrete a significant portion of the fluid that makes up semen.

Bulbourethral Gland (Cowper's Gland)

A small male accessory gland that secretes a lubricating fluid into the urethra.