Chapter 16 Glossary, Summary, and Practice Questions

KEY TERMS

action potential a momentary change in the electrical potential of a neuron (or muscle) membrane

adrenal gland the endocrine gland associated with the kidneys

alveolus (plural: alveoli) (also, air sacs) the terminal structure of the lung passage where gas exchange occurs

amygdala a structure within the limbic system that processes fear

amylase an enzyme found in saliva and secreted by the pancreas that converts carbohydrates to maltose

anus the exit point of the digestive system for waste material

aorta the major artery that takes blood away from the heart to the systemic circulatory system

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

artery a blood vessel that takes blood away from the heart

atrium (plural: atria) a chamber of the heart that receives blood from the veins

auditory ossicles (also, middle ear bones) the bones that transduce sounds from the air into vibrations in the fluid-filled cochlea

autonomic nervous system the part of the peripheral nervous system that controls bodily functions

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)

axon a tube-like structure that propagates a signal from a neuron’s cell body to axon terminals

basal ganglia an interconnected collections of cells in the brain that are involved in movement and motivation

bicuspid valve a one-way opening between the atrium and the ventricle in the left side of the heart

bile a digestive juice produced by the liver; important for digestion of lipids

bolus a mass of food resulting from chewing action and wetting by saliva

brainstem a portion of brain that connects with the spinal cord; controls basic nervous system functions like breathing and swallowing

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

bronchiole an airway that extends from the main bronchus to the alveolar sac

capillary the smallest blood vessel that allows the passage of individual blood cells and the site of diffusion of oxygen and nutrient exchange

cardiac cycle the filling and emptying the heart of blood caused by electrical signals that cause the heart muscles to contract and relax

cardiac muscle tissue the muscle tissue found only in the heart; cardiac contractions pump blood throughout the body and maintain blood pressure

cartilaginous joint a joint in which the bones are connected by cartilage

central nervous system (CNS) the nervous system made up of the brain and spinal cord; covered with three layers of protective meninges

cerebellum the brain structure involved in posture, motor coordination, and learning new motor actions

cerebral cortex the outermost sheet of brain tissue; involved in many higher-order functions

cerebrospinal fluid (CSF) a clear liquid that surrounds the brain and fills its ventricles and acts as a shock absorber

chyme a mixture of partially digested food and stomach juices

closed circulatory system a system that has the blood separated from the bodily interstitial fluid and contained in blood vessels

colon the largest portion of the large intestine consisting of the ascending colon, transverse colon, and descending colon

corpus callosum a thick nerve bundle that connects the cerebral hemispheres

dendrite a structure that extends away from the cell body to receive messages from other neurons

depolarization a change in the membrane potential to a less negative value

diaphragm a skeletal muscle located under lungs that encloses the lungs in the thorax

diastole the relaxation phase of the cardiac cycle when the heart is relaxed and the ventricles are filling with blood down-regulation a decrease in the number of hormone receptors in response to increased hormone levels ectotherm an organism that relies primarily on environmental heat sources to maintain its body temperature electrocardiogram (ECG) a recording of the electrical impulses of the cardiac muscle

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

endotherm an organism that relies primarily on internal heat sources to maintain its body temperature

esophagus a tubular organ that connects the mouth to the stomach

essential nutrient a nutrient that cannot be synthesized by the body; it must be obtained from food

exocrine gland the gland that secretes chemicals through ducts that lead to skin surfaces, body cavities, and organ cavities.

fibrous joint a joint held together by fibrous connective tissue

frontal lobe the part of the cerebral cortex that contains the motor cortex and areas involved in planning, attention, and language

gallbladder the organ that stores and concentrates bile

glia (also, glial cells) the cells that provide support functions for neurons

hippocampus the brain structure in the temporal lobe involved in processing memories

hormone a chemical released by cells in one area of the body that affects cells in other parts of the body

hyoid bone the bone that lies below the mandible in the front of the neck

hypothalamus the brain structure that controls hormone release and body homeostasis

inferior vena cava the major vein of the body returning blood from the lower parts of the body to the right atrium

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

intracellular hormone receptor a hormone receptor in the cytoplasm or nucleus of a cell

joint the point at which two or more bones meet

kidney the organ that performs excretory and osmoregulatory functions

large intestine a digestive system organ that reabsorbs water from undigested material and processes waste matter

larynx the voice box, located within the throat

limbic system a connected brain area that processes emotion and motivation

liver an organ that produces bile for digestion and processes vitamins and lipids

membrane potential a difference in electrical potential between the inside and outside of a cell meninges (singular: meninx) the membranes that cover and protect the central nervous system mineral an inorganic, elemental molecule that carries out important roles in the body

myelin sheath a cellular extension containing a fatty substance produced by glia that surrounds and insulates axons

myofibril the long cylindrical structures that lie parallel to the muscle fiber

myofilament the small structures that make up myofibrils

nasal cavity an opening of the respiratory system to the outside environment

nephron the functional unit of the kidney

neuron a specialized cell that can receive and transmit electrical and chemical signals

occipital lobe the part of the cerebral cortex that contains visual cortex and processes visual stimuli

open circulatory system a circulatory system that has the blood mixed with interstitial fluid in the body cavity and directly bathes the organs

oral cavity the point of entry of food into the digestive system

osmoregulation the mechanism by which water and solute concentrations are maintained at desired levels osmotic balance the appropriate values of water and solute concentrations for a healthy organism pancreas a gland that secretes digestive juices

pancreas the organ located between the stomach and the small intestine that contains exocrine and endocrine cells

parasympathetic nervous system

relaxation

the division of autonomic nervous system that regulates visceral functions during

parathyroid gland the gland located on the surface of the thyroid that produces parathyroid hormone parietal lobe the part of the cerebral cortex involved in processing touch and the sense of the body in space pectoral girdle the bones that transmit the force generated by the upper limbs to the axial skeleton

pelvic girdle the bones that transmit the force generated by the lower limbs to the axial skeleton

pepsin an enzyme found in the stomach whose main role is protein digestion

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

peristalsis wave-like movements of muscle tissue

pharynx the throat

pituitary gland the endocrine gland located at the base of the brain composed of an anterior and posterior region; also called hypophysis

primary bronchus (also, main bronchus) a region of the airway within the lung that attaches to the trachea and bifurcates to form the bronchioles

pulmonary circulation the flow of blood away from the heart through the lungs where oxygenation occurs and then back to the heart

rectum the area of the body where feces is stored until elimination

renal artery the artery that delivers blood to the kidney

renal vein the vein that drains blood from the kidney

salivary gland one of three pairs of exocrine glands in the mammalian mouth that secretes saliva, a mix of watery mucus and enzymes

sarcolemma the plasma membrane of a skeletal muscle fiber

sarcomere the functional unit of skeletal muscle

sensory-somatic nervous system the system of sensory and motor nerves

set point the target value of a physiological state in homeostasis

skeletal muscle tissue forms skeletal muscles, which attach to bones and control locomotion and any movement that can be consciously controlled

skull the bone that supports the structures of the face and protects the brain

small intestine the organ where digestion of protein, fats, and carbohydrates is completed

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

spinal cord a thick fiber bundle that connects the brain with peripheral nerves; transmits sensory and motor information; contains neurons that control motor reflexes

stomach a saclike organ containing acidic digestive juices

superior vena cava the major vein of the body returning blood from the upper part of the body to the right atrium

sympathetic nervous system the division of autonomic nervous system activated during stressful “fight-or-flight” situations

synapse a junction between two neurons where neuronal signals are communicated synaptic cleft a space between the presynaptic and postsynaptic membranes synovial joints the only joints that have a space between the adjoining bones

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

systole the contraction phase of cardiac cycle when the ventricles are pumping blood into the arteries

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

thalamus the brain area that relays sensory information to the cortex

thoracic cage (also, ribcage) the skeleton of the chest, which consists of the ribs, thoracic vertebrae, sternum, and costal cartilages

threshold of excitation the level of depolarization needed for an action potential to fire

thymus the gland located behind the sternum that produces thymosin hormones that contribute to the development of the immune system

thyroid gland an endocrine gland located in the neck that produces thyroid hormones thyroxine and triiodothyronine

trachea the cartilaginous tube that transports air from the throat to the lungs

tricuspid valve a one-way opening between the atrium and the ventricle in the right side of the heart up-regulation an increase in the number of hormone receptors in response to increased hormone levels ureter the urine-bearing tubes coming out of the kidney

urethra the tube that conducts urine from the urinary bladder to the external environment

urinary bladder the structure that the ureters empty the urine into

vein a blood vessel that brings blood back to the heart

ventricle (of the heart) a large chamber of the heart that pumps blood into arteries

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

vitamin an organic substance necessary in small amounts to sustain life

CHAPTER SUMMARY

Homeostasis and Osmoregulation

Homeostasis is a dynamic equilibrium that is maintained in body tissues and organs. It is dynamic because it is constantly adjusting to the changes that the systems encounter. It is an equilibrium because body functions are kept within a normal range, with some fluctuations around a set point. The kidneys are the main osmoregulatory organs in mammalian systems; they function to filter blood and maintain the dissolved ion concentrations of body fluids. They are made up internally of three distinct regions—the cortex, medulla, and pelvis. The blood vessels that transport blood into and out of the kidneys arise from and merge with the aorta and inferior vena cava, respectively. The nephron is the functional unit of the kidney, which actively filters blood and generates urine. The urine leaves the kidney through the ureter and is stored in the urinary bladder. Urine is voided from the body through the urethra.

Digestive System

There are many organs that work together to digest food and absorb nutrients. The mouth is the point of ingestion and the location where both mechanical and chemical breakdown of food begins. Saliva contains an enzyme called amylase that breaks down carbohydrates. The food bolus travels through the esophagus by peristaltic movements to the stomach. The stomach has an extremely acidic environment. The enzyme pepsin digests protein in the stomach. Further digestion and absorption take place in the small intestine. The large intestine reabsorbs water from the undigested food and stores waste until elimination.

Carbohydrates, proteins, and fats are the primary components of food. Some essential nutrients are required for cellular function but cannot be produced by the animal body. These include vitamins, minerals, some fatty acids, and some amino acids. Food intake in more than necessary amounts is stored as glycogen in the liver and muscle cells, and in adipose tissue. Excess adipose storage can lead to obesity and serious health problems.

Circulatory and Respiratory Systems

Animal respiratory systems are designed to facilitate gas exchange. In mammals, air is warmed and humidified in the nasal cavity. Air then travels down the pharynx and larynx, through the trachea, and into the lungs. In the lungs, air passes

through the branching bronchi, reaching the respiratory bronchioles. The respiratory bronchioles open up into the alveolar ducts, alveolar sacs, and alveoli. Because there are so many alveoli and alveolar sacs in the lung, the surface area for gas exchange is very large.

The mammalian circulatory system is a closed system with double circulation passing through the lungs and the body. It consists of a network of vessels containing blood that circulates because of pressure differences generated by the heart.

The heart contains two pumps that move blood through the pulmonary and systemic circulations. There is one atrium and one ventricle on the right side and one atrium and one ventricle on the left side. The pumping of the heart is a function of cardiomyocytes, distinctive muscle cells that are striated like skeletal muscle but pump rhythmically and involuntarily like smooth muscle. The signal for contraction begins in the wall of the right atrium. The electrochemical signal causes the two atria to contract in unison; then the signal causes the ventricles to contract. The blood from the heart is carried through the body by a complex network of blood vessels; arteries take blood away from the heart, and veins bring blood back to the heart.

Endocrine System

Hormones cause cellular changes by binding to receptors on or in target cells. The number of receptors on a target cell can increase or decrease in response to hormone activity.

Hormone levels are primarily controlled through negative feedback, in which rising levels of a hormone inhibit its further release.

The pituitary gland is located at the base of the brain. The anterior pituitary receives signals from the hypothalamus and produces six hormones. The posterior pituitary is an extension of the brain and releases hormones (antidiuretic hormone and oxytocin) produced by the hypothalamus. The thyroid gland is located in the neck and is composed of two lobes. The thyroid produces the hormones thyroxine and triiodothyronine. The thyroid also produces calcitonin. The parathyroid glands lie on the posterior surface of the thyroid gland and produce parathyroid hormone.

The adrenal glands are located on top of the kidneys and consist of the adrenal cortex and adrenal medulla. The adrenal cortex produces the corticosteroids, glucocorticoids and mineralocorticoids. The adrenal medulla is the inner part of the adrenal gland and produces epinephrine and norepinephrine.

The pancreas lies in the abdomen between the stomach and the small intestine. Clusters of endocrine cells in the pancreas form the islets of Langerhans, which contain alpha cells that release glucagon and beta cells that release insulin. Some organs possess endocrine activity as a secondary function but have another primary function. The heart produces the hormone atrial natriuretic peptide, which functions to reduce blood volume, pressure, and Na+ concentration. The gastrointestinal tract produces various hormones that aid in digestion. The kidneys produce erythropoietin. The thymus produces hormones that aid in the development of the immune system. The gonads produce steroid hormones, including testosterone in males and estrogen and progesterone in females. Adipose tissue produces leptin, which promotes satiety signals in the brain.

Musculoskeletal System

The human skeleton is an endoskeleton that is composed of the axial and appendicular skeleton. The axial skeleton is composed of the bones of the skull, ossicles of the ear, hyoid bone, vertebral column, and ribcage. The skull consists of eight cranial bones and 14 facial bones. Six bones make up the ossicles of the middle ear, while the hyoid bone is located in the neck under the mandible. The vertebral column contains 26 bones and surrounds and protects the spinal cord. The thoracic cage consists of the sternum, ribs, thoracic vertebrae, and costal cartilages. The appendicular skeleton is made up of the upper and lower limbs. The pectoral girdle is composed of the clavicles and the scapulae. The upper limb contains 30 bones in the arm, the forearm, and the hand. The pelvic girdle attaches the lower limbs to the axial skeleton. The lower limb includes the bones of the thigh, the leg, and the foot.

The structural classification of joints divides them into fibrous, cartilaginous, and synovial joints. The bones of fibrous joints are held together by fibrous connective tissue. Cartilaginous joints are joints in which the bones are connected by cartilage. Synovial joints are joints that have a space between the adjoining bones. The movement of synovial joints includes angular and rotational. Angular movements are produced when the angle between the bones of a joint changes. Rotational movement is the movement of a bone as it rotates around its own longitudinal axis.

The body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Muscles are composed of individual cells called muscle fibers. Muscle fibers consist of myofilaments composed of the proteins actin and myosin arranged in units called sarcomeres. Contraction of the muscle occurs by the combined action of myosin and actin fibers sliding past each other when the myosin heads bind to the actin fiber, bend, disengage, and then repeat the process.

Nervous System

The nervous system is made up of neurons and glia. Neurons are specialized cells that are capable of sending electrical as well as chemical signals. Most neurons contain dendrites, which receive these signals, and axons that send signals to other neurons or tissues. Glia are non-neuronal cells in the nervous system that support neuronal development and signaling.

There are several types of glia that serve different functions.

Neurons have a resting potential across their membranes and when they are stimulated by a strong enough signal from another neuron an action potential may carry an electrochemical signal along the neuron to a synapse with another neuron. Neurotransmitters carry signals across synapses to initiate a response in another neuron.

The vertebrate central nervous system contains the brain and the spinal cord, which are covered and protected by three meninges. The brain contains structurally and functionally defined regions. In mammals, these include the cortex (which can be broken down into four primary functional lobes: frontal, temporal, occipital, and parietal), basal ganglia, thalamus, hypothalamus, limbic system, cerebellum, and brainstem—although structures in some of these designations overlap.

While functions may be primarily localized to one structure in the brain, most complex functions, like language and sleep, involve neurons in multiple brain regions. The spinal cord is the information superhighway that connects the brain with the rest of the body through its connections with peripheral nerves. It transmits sensory and motor input and also controls motor reflexes.

The peripheral nervous system contains both the autonomic and sensory-somatic nervous systems. The autonomic nervous system provides unconscious control over visceral functions and has two divisions: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is activated in stressful situations to prepare the animal for a “fight-or- flight” response. The parasympathetic nervous system is active during restful periods. The sensory-somatic nervous system is made of cranial and spinal nerves that transmit sensory information from skin and muscle to the CNS and motor commands from the CNS to the muscles.

ART CONNECTION QUESTIONS

• Figure 16.2 When bacteria are destroyed by leukocytes, pyrogens are released into the blood. Pyrogens reset the body’s thermostat to a higher temperature, resulting in fever. How might pyrogens cause the body temperature to rise?
• Figure 16.7 Which of the following statements about the digestive system is false?
• Chyme is a mixture of food and digestive juices that is produced in the stomach.
• Food enters the large intestine before the small intestine.
• In the small intestine, chyme mixes with bile, which emulsifies fats.
• The stomach is separated from the small intestine by the pyloric sphincter.
• Figure 16.9 Which of the following statements about the human respiratory system is false?
• When we breathe in, air travels from the pharynx to the trachea.
• The bronchioles branch into bronchi.
• Alveolar ducts connect to alveolar sacs.

REVIEW QUESTIONS

• When faced with a sudden drop in environmental temperature, an endothermic animal will .

• experience a drop in its body temperature
• wait to see if it goes lower

d. Gas exchange between the lungs and blood takes place in the alveolus.

• Figure 16.10 Which of the following statements about the circulatory system is false?
• Blood in the pulmonary vein is deoxygenated.
• Blood in the inferior vena cava is deoxygenated.
• Blood in the pulmonary artery is deoxygenated.
• Blood in the aorta is oxygenated.
• Figure 16.14 Goiter, a disease caused by iodine deficiency, results in the inability of the thyroid gland to form T3 and T4. The body typically attempts to compensate by producing greater amounts of TSH. Which of the following symptoms would you expect goiter to cause?
• Hypothyroidism, resulting in weight gain, cold sensitivity, and reduced mental activity.
• Hyperthyroidism, resulting in weight loss, profuse sweating and increased heart rate.
• Hyperthyroidism, resulting in weight gain, cold sensitivity, and reduced mental activity.
• Hypothyroidism, resulting in weight loss, profuse sweating and increased heart rate.

• increase muscle activity to generate heat
• add fur or fat to increase insulation
• How are wastes carried to the kidney for removal?

• in cells

• in the urine
• in blood
• in interstitial fluid
• What is the cause of a fever of 38.3 °C (101 °F)?

• too much heat produced by the body
• upward adjustment of the body temperature set point
• inadequate cooling mechanisms in the body
• the heat caused by a viral or bacterial infection
• Where does the majority of fat digestion take place?

• mouth
• stomach
• small intestine
• large intestine
• The bile from the liver is delivered to the .

• stomach
• liver
• small intestine
• colon
• Which of the following statements is not true?

• Essential nutrients can be synthesized by the body.
• Vitamins are required in small quantities for bodily function.
• Some amino acids can be synthesized by the body, while others need to be obtained from diet.
• Vitamins come in two categories: fat-soluble and water-soluble.
• The respiratory system .
• provides body tissues with oxygen
• provides body tissues with oxygen and carbon dioxide
• establishes how many breaths are taken per minute
• provides the body with carbon dioxide
• Which is the order of airflow during inhalation?

• nasal cavity, trachea, larynx, bronchi, bronchioles, alveoli
• nasal cavity, larynx, trachea, bronchi, bronchioles, alveoli
• nasal cavity, larynx, trachea, bronchioles, bronchi, alveoli
• nasal cavity, trachea, larynx, bronchi, bronchioles, alveoli
• Where does the right ventricle send blood?
• the head
• the upper body
• the lungs
• the lower body
• 
  During the systolic phase of the cardiac cycle, the heart is .
• contracting
• relaxing
• contracting and relaxing
• filling with blood
• How do arteries differ from veins?
• Arteries have thicker wall layers to accommodate the changes in pressure from the heart.
• Arteries carry blood.
• Arteries have thinner wall layers and valves and move blood by the action of skeletal muscle.
• Arteries are thin walled and are used for gas exchange.
• Most of the hormones produced by the anterior pituitary perform what function?
• regulate growth
• regulate the sleep cycle
• regulate production of other hormones
• regulate blood volume and blood pressure
• What is the function of the hormone erythropoietin?

• stimulates production of red blood cells
• stimulates muscle growth
• causes the fight-or-flight response
• causes testosterone production
• Which endocrine glands are associated with the kidneys?
• thyroid glands
• pituitary glands
• adrenal glands
• gonads
• Among other bones, the axial skeleton includes the

.

• thoracic cage and vertebral column
• thoracic cage and pectoral girdle
• skull and pelvic girdle
• pectoral and pelvic girdles
• The pectoral girdle supports the .
• arms
• legs
• skull
• thoracic cage
• Which component is responsible for initially stimulating a muscle contraction?
• proteins
• electrochemical signals
• plasma membranes
• striations
• What kind of muscle tissue is found surrounding the urinary bladder?
• cardiac
• skeletal
• striated

• smooth
• Neurons contain , which can receive signals from other neurons.
• axons
• mitochondria
• dendrites
• Golgi bodies
• The part of the brain that is responsible for coordination during movement is the .
• limbic system

CRITICAL THINKING QUESTIONS

• Describe how the body’s mechanisms maintain homeostasis?
• Why is excretion important in order to achieve osmotic balance?
• What is the role of the accessory organs in digestion?
• What is the role of minerals in maintaining good health?
• Discuss why obesity is a growing epidemic.
• Describe the function of these terms and describe where they are located: main bronchus, trachea, alveoli.
• How does the structure of alveoli maximize gas exchange?
• Describe the cardiac cycle.
• What is a similarity and a difference between an exocrine gland and an endocrine gland?
• 
  thalamus
• cerebellum
• parietal lobe
• Which part of the nervous system directly controls the digestive system?
• parasympathetic nervous system
• central nervous system
• spinal cord
• sensory-somatic nervous system

• Describe how hormone receptors can play a role in affecting the size of the responses of tissues to hormones.
• Many hormone systems regulate body functions through opposing hormone actions. Describe how opposing hormone actions regulate blood-glucose levels?
• What movements occur at the hip joint and knees as you bend down to pick something up?
• How are neurons similar to other cells? How are they unique?
• What are the main functions of the spinal cord?
• What are the main differences between the sympathetic and parasympathetic branches of the autonomic nervous system?
• What are the main functions of the sensory-somatic nervous system?