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Animal Body Organization and Systems


adrenal gland

one of two endocrine glands located on the top of each kidney consisting of the cortex and the medulla that release hormones that help regulate critical functions in the body, such as blood pressure, the immune system, and the metabolism

alveolus (plural, alveoli)

small air sac in the lungs where gas exchange occurs in mammals


vessel that transports blood away from the heart to the lungs or to the body tissues

atrium (plural, atria)

in the vertebrate heart, a chamber that receives blood from the veins


tiny, thin-walled blood vessel that is the site of nutrient and gas exchange

cardiovascular system

a body system in which blood flows through the body, with the help of the heart, to transport nutrients, waste, and gases

cilium (plural, cilia)

a small, hair-like projection from cells that functions to filter air in the respiratory system

digestive system

a body system that aids in the metabolic processing of food for nutrients and energy

endocrine system

a body system that consists of different glands used to produce hormones that regulate body functions

excretory system

a body system whose function is to dispose of metabolic wastes and control body fluid composition in response to external or internal stimuli


the body's processes to physiologically regulate its internal environment with response to fluctuations that occur in the internal or external environment


chemical compound that signals growth and development which is secreted from endocrine glands


a structure in the brain that links the nervous and endocrine systems, responding to signals from other parts of the brain and hormone feedback mechanisms

immune system

a body system consisting of a complex network of organs that contain cells used to recognize pathogens in the body

musculoskeletal system

a body system that aids in movement and posture and provides support to the body

myelin sheath

an insulating membrane wrapped around the axons of most nerve cells of vertebrates

nervous system

a body system that consists of a neural network that includes the brain, spinal cord, and nerves that connects all the organs in the body and regulates body functions


a structure, formed from more than one tissue, with a specific function

organ system

a group of organs with a common function


an endocrine gland located near the stomach and small intestine that secretes digestive enzymes that help with digestion and releases hormones to help maintain healthy glucose levels in the body

parathyroid gland

one of four small endocrine glands located near or within the thyroid gland that release hormones that help maintain calcium and phosphorus levels in the body


a form of asexual reproduction in which an unfertilized egg cell becomes a new organism


disease-causing organism or virus that causes harm to a host organism

pineal gland

a small endocrine gland located in the brain that plays a role in the production of melatonin, a hormone that aids in the regulation of sleep patterns

pituitary gland

an endocrine gland located near the bottom of the brain, often called the master gland because its hormones control several other endocrine glands

thyroid gland

an endocrine gland located in the front of the neck that produces thyroid hormones that help regulate metabolic processes, heat production, and the development and function of other organ systems


specialized cells that are grouped together to perform a common function

trachea (plural, tracheae)

respiratory structure found in both invertebrates and vertebrates that connects the mouth to the lungs.


blood vessel that returns blood to the heart


in the vertebrate heart, a chamber that pumps blood away from the heart