ectotherm
an organism that relies primarily on environmental heat sources to maintain its body temperature
Ectotherms and endotherms use their circulatory systems to help maintain body temperature.
endotherm
an organism that relies primarily on internal heat sources to maintain its body temperature
An animal that maintains a constant body temperature in the face of environmental changes is called an endotherm.
interstitial fluid
the fluid found between cells in the body, similar in constitution to the fluid component of blood, but without the high concentrations of proteins
The body’s fluids include blood plasma, fluid that exists within cells, and the interstitial fluid that exists in the spaces between cells and tissues of the body.
kidney
the organ that performs excretory and osmoregulatory functions
Excess water, electrolytes, and wastes are transported to the kidneys and excreted, helping to maintain osmotic balance.
nephron
the functional unit of the kidney
Each of the kidneys contains more than a million tiny units called nephrons that filter blood containing the metabolic wastes from cells.
osmoregulation
the mechanism by which water and solute concentrations are maintained at desired levels
The processes that maintain homeostasis of these two factors are called thermoregulation and osmoregulation.
osmotic balance
the appropriate values of water and solute concentrations for a healthy organism
Osmoregulation is the process of maintaining salt and water balance (osmotic balance) across membranes within the body.
renal artery
the artery that delivers blood to the kidney
Blood enters each kidney from the aorta, the main artery supplying the body below the heart, through a renal artery.
renal vein
the vein that drains blood from the kidney
The blood then collects in larger and larger vessels and leaves the kidney in the renal vein.
set point
the target value of a physiological state in homeostasis
The goal of homeostasis is the maintenance of equilibrium around a specific value of some aspect of the body or its cells called a set point.
ureter
the urine-bearing tubes coming out of the kidney
Here we focus on the urinary system, which is comprised of the paired kidneys, the ureter, urinary bladder and urethra (Figure 11.3).
urethra
the tube that conducts urine from the urinary bladder to the external environment
Here we focus on the urinary system, which is comprised of the paired kidneys, the ureter, urinary bladder and urethra (Figure 11.3).
urinary bladder
the structure that the ureters empty the urine into the appropriate values of water and solute concentrations for a healthy organism
Here we focus on the urinary system, which is comprised of the paired kidneys, the ureter, urinary bladder and urethra (Figure 11.3).
amylase
an enzyme found in saliva and secreted by the pancreas that converts carbohydrates to maltose
It also contains an enzyme called salivary amylase that begins the process of converting starches in the food into a disaccharide called maltose.
anus
the exit point of the digestive system for waste material
The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until it is excreted through the anus.
bile
a digestive juice produced by the liver; important for digestion of lipids
Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion.
bolus
a mass of food resulting from chewing action and wetting by saliva
The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus for swallowing.
colon
the largest portion of the large intestine consisting of the ascending colon, transverse colon, and descending colon
The undigested food is sent to the colon from the ileum via peristaltic movements.
chyme
a mixture of partially digested food and stomach juices
The partially digested food and gastric juice mixture is called chyme.
esophagus
a tubular organ that connects the mouth to the stomach
The food is then swallowed and enters the esophagus—a long tube that connects the mouth to the stomach.
essential nutrient
a nutrient that cannot be synthesized by the body; it must be obtained from food
These nutrients are termed essential nutrients, meaning they must be eaten, because the body cannot produce them.
gallbladder
the organ that stores and concentrates bile
Bile is produced in the liver and stored and concentrated in the gallbladder; it enters the duodenum through the bile duct.
large intestine
a digestive system organ that reabsorbs water from undigested material and processes waste matter
The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until it is excreted through the anus.
liver
an organ that produces bile for digestion and processes vitamins and lipids
The kidneys are a pair of bean-shaped structures that are located just below the liver in the body cavity.
mineral
an inorganic, elemental molecule that carries out important roles in the body
The main functions of the colon are to extract the water and mineral salts from undigested food, and to store waste material.
oral cavity
the point of entry of food into the digestive system
Both physical and chemical digestion begin in the mouth or oral cavity, which is the point of entry of food into the digestive system.
pancreas
a gland that secretes digestive juices
Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion.
pepsin
an enzyme found in the stomach whose main role is protein digestion
Protein digestion is carried out by an enzyme called pepsin in the stomach chamber.
peristalsis
wave-like movements of muscle tissue
Using peristalsis, or wave-like smooth-muscle contractions, the muscles of the esophagus push the food toward the stomach.
rectum
the area of the body where feces is stored until elimination
It has three parts: the cecum, the colon, and the rectum.
salivary gland
one of three pairs of exocrine glands in the mammalian mouth that secretes saliva, a mix of watery mucus and enzymes
The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands (Figure 11.5).
small intestine
the organ where digestion of protein, fats, and carbohydrates is completed
Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion.
stomach
a saclike organ containing acidic digestive juices
The food is then swallowed and enters the esophagus—a long tube that connects the mouth to the stomach.
vitamin
an organic substance necessary in small amounts to sustain life
The monosaccharides, amino acids, bile salts, vitamins, and other nutrients are absorbed by the cells of the intestinal lining.
alveolus
(plural: alveoli) (also, air sacs) the terminal structure of the lung passage where gas exchange occurs
Gas exchange between the lung and blood takes place in the alveolus.
aorta
the major artery that takes blood away from the heart to the systemic circulatory system
Blood enters each kidney from the aorta, the main artery supplying the body below the heart, through a renal artery.
artery
a blood vessel that takes blood away from the heart
Blood enters each kidney from the aorta, the main artery supplying the body below the heart, through a renal artery.
atrium
(plural: atria) a chamber of the heart that receives blood from the veins
There is one atrium and one ventricle on the right side and one atrium and one ventricle on the left side.
bicuspid valve
a one-way opening between the atrium and the ventricle in the left side of the heart
This blood passes through the bicuspid valve to the left ventricle where the blood is pumped into the aorta.
bronchi
(singular: bronchus) smaller branches of cartilaginous tissue that stem off of the trachea; air is funneled through the bronchi to the region where gas exchange occurs in the alveoli
The end of the trachea divides into two bronchi that enter the right and left lung.
bronchiole
an airway that extends from the main bronchus to the alveolar sac
Like the trachea, the bronchus and bronchioles are made of cartilage and smooth muscle.
capillary
the smallest blood vessel that allows the passage of individual blood cells and the site of diffusion of oxygen and nutrient exchange
Capillary beds contain a large number, 10’s to 100’s of capillaries that branch among the cells of the body.
cardiac cycle
the filling and emptying the heart of blood caused by electrical signals that cause the heart muscles to contract and relax
The main purpose of the heart is to pump blood through the body; it does so in a repeating sequence called the cardiac cycle.
closed circulatory system
a system that has the blood separated from the bodily interstitial fluid and contained in blood vessels
Blood circulates inside blood vessels and circulates unidirectionally from the heart around one of two circulatory routes, then returns to the heart again; this is a closed circulatory system.
diaphragm
a skeletal muscle located under lungs that encloses the lungs in the thorax
During inhalation the diaphragm descends creating a negative pressure around the lungs and they begin to inflate, drawing in air from outside the body.
diastole
the relaxation phase of the cardiac cycle when the heart is relaxed and the ventricles are filling with blood
These two phases are called the systole (contraction) and diastole (relaxation), respectively (Figure 11.21).
electrocardiogram (ECG)
a recording of the electrical impulses of the cardiac muscle
This information can be observed as an electrocardiogram (ECG) a recording of the electrical impulses of the cardiac muscle.
inferior vena cava
the major vein of the body returning blood from the lower parts of the body to the right atrium
The renal vein joins the inferior vena cava, the main vein that returns blood to the heart from the lower body.
larynx
the voice box, located within the throat
From the nasal cavity, air passes through the pharynx (throat) and the larynx (voice box) as it makes its way to the trachea (Figure 11.9).
nasal cavity
an opening of the respiratory system to the outside environment
The air enters the body through the nasal cavity located just inside the nose (Figure 11.9).
open circulatory system
a circulatory system that has the blood mixed with interstitial fluid in the body cavity and directly bathes the organs
Open circulatory systems are found in invertebrate animals in which the circulatory fluid bathes the internal organs directly even though it may be moved about with a pumping heart.
pharynx
the throat
The tongue helps in swallowing—moving the bolus from the mouth into the pharynx.
primary bronchus
(also, main bronchus) a region of the airway within the lung that attaches to the trachea and bifurcates to form the bronchioles
The primary bronchus divides, creating smaller and smaller diameter bronchi.
pulmonary circulation
the flow of blood away from the heart through the lungs where oxygenation occurs and then back to the heart
One that pumps blood through pulmonary circulation to the lungs, and the other that pumps blood through systemic circulation to the rest of the body’s tissues (and the heart itself).
superior vena cava
the major vein of the body returning blood from the upper part of the body to the right atrium
The superior vena cava drains blood from the head and from the veins that come from the arms.
systemic circulation
the flow of blood away from the heart to the brain, liver, kidneys, stomach, and other organs, the limbs, and the muscles of the body, and then back to the heart
The main artery of the systemic circulation is the aorta; it branches into major arteries that take blood to different limbs and organs.
systole
the contraction phase of cardiac cycle when the ventricles are pumping blood into the arteries
These two phases are called the systole (contraction) and diastole (relaxation), respectively (Figure 11.21).
trachea
the cartilaginous tube that transports air from the throat to the lungs
The pharynx opens to two passageways: the esophagus and the trachea.
tricuspid valve
a one-way opening between the atrium and the ventricle in the right side of the heart
This deoxygenated blood then passes to the right ventricle through the tricuspid valve, which prevents the backflow of blood.
vein
a blood vessel that brings blood back to the heart
Some animals have adaptions to their circulatory system that enable them to transfer heat from arteries to veins that are flowing next to each other, warming blood returning to the heart.
ventricle
(of the heart) a large chamber of the heart that pumps blood into arteries
In humans, the heart is about the size of a clenched fist; it is divided into four chambers: two atria and two ventricles.
adrenal gland
the endocrine gland associated with the kidneys
The endocrine glands include the pituitary, thyroid, parathyroid, adrenal glands, gonads, pineal, and pancreas.
down-regulation
a decrease in the number of hormone receptors in response to increased hormone levels
When the number of receptors decreases in response to rising hormone levels, called down-regulation, cellular activity is reduced.
endocrine gland
the gland that secretes hormones into the surrounding interstitial fluid, which then diffuse into blood and are carried to various organs and tissues within the body
These cells may compose endocrine glands, may be tissues or may be located in organs or tissues that have functions in addition to hormone production.
exocrine gland
the gland that secretes chemicals through ducts that lead to skin surfaces, body cavities, and organ cavities.
The endocrine glands differ from the exocrine glands.
hormone
a chemical released by cells in one area of the body that affects cells in other parts of the body
The movement of chyme from the stomach into the small intestine is regulated by hormones, stomach distension and muscular reflexes that influence the pyloric sphincter.
intracellular hormone receptor
a hormone receptor in the cytoplasm or nucleus of a cell
Hormones cause changes in target cells by binding to specific cell-surface or intracellular hormone receptors, molecules embedded in the cell membrane or floating in the cytoplasm with a binding site that matches a binding site on the hormone molecule.
parathyroid gland
the gland located on the surface of the thyroid that produces parathyroid hormone
Most people have four parathyroid glands; however, the number can vary from two to six.
pituitary gland
the endocrine gland located at the base of the brain composed of an anterior and posterior region; also called hypophysis
The pituitary gland, sometimes called the hypophysis, is located at the base of the brain (Figure 11.23a).
thymus
the gland located behind the sternum that produces thymosin hormones that contribute to the development of the immune system
These include the heart, kidneys, intestines, thymus, and adipose tissue.
thyroid gland
an endocrine gland located in the neck that produces thyroid hormones thyroxine and triiodothyronine
The thyroid gland is located in the neck, just below the larynx and in front of the trachea (Figure 11.23 b).
up-regulation
an increase in the number of hormone receptors in response to increased hormone levels
In up-regulation, the number of receptors increases in response to rising hormone levels, making the cell more sensitive to the hormone and allowing for more cellular activity.
appendicular skeleton
the skeleton composed of the bones of the upper limbs, which function to grasp and manipulate objects, and the lower limbs, which permit locomotion
The appendicular skeleton is composed of the bones of the upper and lower limbs.
auditory ossicles
(also, middle ear bones) the bones that transduce sounds from the air into vibrations in the fluid-filled cochlea
The auditory ossicles of the middle ear transmit sounds from the air as vibrations to the fluid-filled cochlea.
axial skeleton
skeleton that forms the central axis of the body and includes the bones of the skull, the ossicles of the middle ear, the hyoid bone of the throat, the vertebral column, and the thoracic cage (ribcage)
The pelvic girdle attaches to the lower limbs of the axial skeleton.
cardiac muscle tissue
the muscle tissue found only in the heart; cardiac contractions pump blood throughout the body and maintain blood pressure
The contractions of cardiac muscle tissue pump blood throughout the body and maintain blood pressure.
cartilaginous joint
a joint in which the bones are connected by cartilage
Cartilaginous joints are joints in which the bones are connected by cartilage (Figure 11.26 b).
fibrous joint
a joint held together by fibrous connective tissue
The bones of fibrous joints are held together by fibrous connective tissue.
hyoid bone
the bone that lies below the mandible in the front of the neck
The hyoid bone lies below the mandible in the front of the neck.
joint
the point at which two or more bones meet
Other diseases affect the joints, such as arthritis, which can make movement difficult and, in advanced cases, completely impair mobility.
myofibril
the long cylindrical structures that lie parallel to the muscle fiber
Within each muscle fiber are myofibrils, long cylindrical structures that lie parallel to the muscle fiber.
myofilament
the small structures that make up myofibrils
Myofibrils are composed of smaller structures called myofilaments.
pectoral girdle
the bones that transmit the force generated by the upper limbs to the axial skeleton
The pectoral girdle bones transfer force generated by muscles acting on the upper limb to the thorax.
pelvic girdle
the bones that transmit the force generated by the lower limbs to the axial skeleton
It also includes the pectoral, or shoulder girdle, which attaches the upper limbs to the body, and the pelvic girdle, which attaches the lower limbs to the body (Figure 11.25).
sarcolemma
the plasma membrane of a skeletal muscle fiber
They attach to the plasma membrane, called the sarcolemma, at their ends, so that as myofibrils shorten, the entire muscle cell contracts (Figure 11.28).
sarcomere
the functional unit of skeletal muscle
The thick and thin filaments alternate with each other in a structure called a sarcomere.
skeletal muscle tissue
forms skeletal muscles, which attach to bones and control locomotion and any movement that can be consciously controlled
Skeletal muscle tissue forms skeletal muscles, which attach to bones and sometimes the skin and control locomotion and any other movement that can be consciously controlled.
skull
the bone that supports the structures of the face and protects the brain
The bones of the skull support the structures of the face and protect the brain.
smooth muscle tissue
the muscle that occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as the respiratory tract and blood vessels
Smooth muscle tissue occurs in the walls of hollow organs such as the intestines, stomach, and urinary bladder, and around passages such as in the respiratory tract and blood vessels.
synovial joints
the only joints that have a space between the adjoining bones
Synovial joints are the only joints that have a space between the adjoining bones (Figure 11.26 c).
thoracic cage
(also, ribcage) the skeleton of the chest, which consists of the ribs, thoracic vertebrae, sternum, and costal cartilages
The thoracic cage, also known as the rib cage consists of the ribs, sternum, thoracic vertebrae, and costal cartilages.
vertebral column
(also, spine) the column that surrounds and protects the spinal cord, supports the head, and acts as an attachment point for ribs and muscles of the back and neck
The vertebral column, or spinal column, surrounds and protects the spinal cord, supports the head, and acts as an attachment point for ribs and muscles of the back and neck.
action potential
a momentary change in the electrical potential of a neuron (or muscle) membrane
In the axon, this “signal” will become a self-propagating brief reversal of the resting membrane potential called an action potential.
amygdala
a structure within the limbic system that processes fear
One important structure within the limbic system is a temporal lobe structure called the amygdala.
autonomic nervous system
the part of the peripheral nervous system that controls bodily functions
The autonomic nervous system serves as the relay between the CNS and the internal organs.
axon
a tube-like structure that propagates a signal from a neuron’s cell body to axon terminals
Transmission of a signal between neurons is generally carried by a chemical, called a neurotransmitter, which diffuses from the axon of one neuron to the dendrite of a second neuron.
basal ganglia
an interconnected collections of cells in the brain that are involved in movement and motivation
It includes the cerebral cortex, limbic system, basal ganglia, thalamus, hypothalamus, cerebellum, brainstem, and retinas.
brainstem
a portion of brain that connects with the spinal cord; controls basic nervous system functions like breathing and swallowing
It includes the cerebral cortex, limbic system, basal ganglia, thalamus, hypothalamus, cerebellum, brainstem, and retinas.
central nervous system (CNS)
the nervous system made up of the brain and spinal cord; covered with three layers of protective meninges
The brain is the part of the central nervous system that is contained in the cranial cavity of the skull.
cerebellum
the brain structure involved in posture, motor coordination, and learning new motor actions
For example, dendrites from a Purkinje cell in the cerebellum are thought to receive contact from as many as 200,000 other neurons.
cerebral cortex
the outermost sheet of brain tissue; involved in many higher-order functions
It includes the cerebral cortex, limbic system, basal ganglia, thalamus, hypothalamus, cerebellum, brainstem, and retinas.
cerebrospinal fluid (CSF)
a clear liquid that surrounds the brain and fills its ventricles and acts as a shock absorber
The space between the arachnoid and pia maters is filled with cerebrospinal fluid (CSF).
corpus callosum
a thick nerve bundle that connects the cerebral hemispheres
A thick fiber bundle called the corpus callosum (corpus = “body”; callosum = “tough”) connects the two hemispheres.
dendrite
a structure that extends away from the cell body to receive messages from other neurons
Dendrites are tree-like structures that extend away from the cell body to receive messages from other neurons at specialized junctions called synapses.
depolarization
a change in the membrane potential to a less negative value
This opening allows sodium ions to enter the neuron and results in depolarization of the membrane—a decrease in the voltage across the neuron membrane.
frontal lobe
the part of the cerebral cortex that contains the motor cortex and areas involved in planning, attention, and language
The frontal lobe is located at the front of the brain, over the eyes.
glia
(also, glial cells) the cells that provide support functions for neurons
The nervous system is made up of neurons, specialized cells that can receive and transmit chemical or electrical signals, and glia, cells that provide support functions for the neurons.
hippocampus
the brain structure in the temporal lobe involved in processing memories
For mammals, new neurons also play an important role in learning: about 1,000 new neurons develop in the hippocampus (a brain structure involved in learning and memory) each day.
hypothalamus
the brain structure that controls hormone release and body homeostasis
The processes of temperature control are centered in the hypothalamus of the advanced animal brain.
limbic system
a connected brain area that processes emotion and motivation
It includes the cerebral cortex, limbic system, basal ganglia, thalamus, hypothalamus, cerebellum, brainstem, and retinas.
membrane potential
a difference in electrical potential between the inside and outside of a cell
The difference in total charge between the inside and outside of the cell is called the membrane potential.
meninges
(singular: meninx) the membranes that cover and protect the central nervous system
The vertebrate central nervous system contains the brain and the spinal cord, which are covered and protected by three meninges.
myelin sheath
a cellular extension containing a fatty substance produced by glia that surrounds and insulates axons
Some axons are covered with a special structure called a myelin sheath, which acts as an insulator to keep the electrical signal from dissipating as it travels down the axon.
neuron
a specialized cell that can receive and transmit electrical and chemical signals
Others, like jellyfish, lack a true brain and instead have a system of separate but connected nerve cells (neurons) called a “nerve net.”
occipital lobe
the part of the cerebral cortex that contains visual cortex and processes visual stimuli
The occipital lobe is located at the back of the brain.
parasympathetic nervous system
the division of autonomic nervous system that regulates visceral functions during relaxation
There are two divisions of the autonomic nervous system that often have opposing effects: the sympathetic nervous system and the parasympathetic nervous system.
parietal lobe
the part of the cerebral cortex involved in processing touch and the sense of the body in space
The parietal lobe is located at the top of the brain.
peripheral nervous system (PNS)
the nervous system that serves as the connection between the central nervous system and the rest of the body; consists of the autonomic nervous system and the sensory-somatic nervous system
The peripheral nervous system (PNS) is the connection between the central nervous system and the rest of the body.
sensory-somatic nervous system
the system of sensory and motor nerves
The sensory-somatic nervous system is made up of cranial and spinal nerves and contains both sensory and motor neurons.
spinal cord
a thick fiber bundle that connects the brain with peripheral nerves; transmits sensory and motor information; contains neurons that control motor reflexes
The vertebral column, or spinal column, surrounds and protects the spinal cord, supports the head, and acts as an attachment point for ribs and muscles of the back and neck.
sympathetic nervous system
the division of autonomic nervous system activated during stressful “fight-or-flight” situations
The sympathetic nervous system under control of the hypothalamus directs the responses that effect the changes in temperature loss or gain that return the body to the set point.
synapse
a junction between two neurons where neuronal signals are communicated
Dendrites are tree-like structures that extend away from the cell body to receive messages from other neurons at specialized junctions called synapses.
synaptic cleft
a space between the presynaptic and postsynaptic membranes
Neurons communicate between the axon of one neuron and the dendrites, and sometimes the cell body, of another neuron across the gap between them, known as the synaptic cleft.
temporal lobe
the part of the cerebral cortex that processes auditory input; parts of the temporal lobe are involved in speech, memory, and emotion processing
The temporal lobe is located at the base of the brain and is primarily involved in processing and interpreting sounds.
thalamus
the brain area that relays sensory information to the cortex
It includes the cerebral cortex, limbic system, basal ganglia, thalamus, hypothalamus, cerebellum, brainstem, and retinas.
threshold of excitation
the level of depolarization needed for an action potential to fire
The threshold of excitation must be reached for the neuron to “fire” an action potential.
These terms were extracted from Concepts of Biology – 1st Canadian Edition by Charles Molnar and Jane Gair, eCampusOntario (originally published by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License. Chapter content adapted from Concepts of Biology by OpenStax (© Rice University), licensed under CC BY 4.0.