Science Study Guide for the NLN NEX

Human Anatomy and Physiology

Anatomy is the study of the structures of the human body, and physiology is the study of the functions that those structures perform. This section will provide an overview of the various systems of the human body and how they operate.

The Cardiovascular System

Image source: https://openstax.org/books/anatomy-and-physiology-2e/pages/20-5-circulatory-pathways

The right side of the heart receives deoxygenated blood from the body and sends it through the tricuspid valve into the right ventricle and from there into the lungs via the pulmonary arteries (one left and one right artery), where it is oxygenated. The pulmonary valve controls the flow of blood from the heart to the lungs. The oxygenated blood returns to the heart through the pulmonary veins and enters the left atrium. From the left atrium, the oxygenated blood travels to the left ventricle, where it is pumped out through the aorta to circulate blood throughout the body. The mitral valve keeps blood from back flowing from the left ventricle into the left atrium. The aortic valve keeps blood from back flowing from the aorta into the left ventricle. The circulation of blood through the lungs is called pulmonary circulation, and the circulation of blood through the body is called systemic circulation.

When the heart is relaxed and filling with blood, it is in diastole. When it is contracting and pushing blood through the arteries, it is in systole. The arteries are vessels that move away from the heart. They branch out and narrow into smaller and smaller vessels. The smallest vessels are capillaries, and they represent the end of the outgoing circuit of blood. Blood then returns to the heart through veins, which converge into larger and larger vessels until they return to the heart to begin circulation anew.

Blood

Blood is composed of various substances. The liquid portion is the plasma, which contains dissolved nutrients and minerals. Red blood cells contain hemoglobin, a protein that binds with oxygen to transport it throughout the body. White blood cells are part of the immune system, which finds and destroys pathogens. Platelets are small fragments that aid in clotting the blood.

The Endocrine System

The endocrine system is a series of glands throughout the body that produce chemicals that serve various functions. This system relies on other systems, such as the cardiovascular, digestive, or lymphatic systems, to transport its chemicals through the body.

Homeostasis

Homeostasis is a condition of internal balance. The body relies on the coordination of all of its systems and spends most of its energy in maintaining this steady state. The endocrine system aids in keeping the conditions of the body in balance. When the body senses that some condition is out of balance, it creates a negative feedback mechanism that responds to correct the imbalance.

Hormones

Hormones are proteins that trigger responses in target organs of the body. One example is the human growth hormone, which sends signals to cells to grow and divide and increases the nutrients supplied to cells.

Glands

Glands are organs that secrete hormones. Some major glands in the endocrine system are:

• pituitary—Found in the brain, it oversees the functions of other glands.

• hypothalamus—Also in the brain, it helps control appetite, temperature, and blood pressure.

• thyroid—Located in the throat, it aids in the body’s metabolic rate.

• adrenal gland—Located above the kidneys, it aids in metabolism and blood pressure.

• pancreas—Located near the stomach, it releases insulin and glucagon, which regulate blood sugar levels.

The Digestive System

The purpose of the digestive system is to extract nutrients from food. These nutrients are then used by the body for energy and provide the building blocks for the body’s cells and tissues. Digestion has two components: mechanical and chemical.

Mechanical Digestion

Mechanical digestion involves the physical breakdown of food through actions such as chewing and the churning of the stomach. Breaking the food into smaller pieces increases the surface area upon which the chemicals of the digestive system can act to digest food more quickly.

Chemical Digestion

In chemical digestion, the body excretes enzymes and other chemicals that break down the molecules that food particles are made of. Enzymes are proteins that speed up chemical reactions. The salivary glands in the mouth excrete amylase, an enzyme that begins breaking down complex carbohydrates. Water aids in breaking down certain molecules in a process called hydrolysis. In the stomach, the gastric juice is a mixture of enzymes that break down specific food molecules. Protease is an enzyme that specializes in breaking down proteins, and bile from the liver helps break down lipids, or fats. The mass of partially digested food in the stomach at the end of mechanical and chemical digestion is called chyme.

Digestive Organs

The alimentary canal is the system through which food passes from ingestion (eating) to egestion (expelling waste). Organs that are involved in digestion but are not part of the alimentary canal (such as the liver or pancreas) are called accessory organs. Food begins in the mouth, then continues to the pharynx, the passageway that connects the mouth to the esophagus. Food is prevented from entering the windpipe by a flap called the epiglottis. The esophagus is the tube that connects the pharynx to the stomach. The liver is a large organ that creates bile, among other functions. The bile is held in the gallbladder, a small sac next to the liver, until it passes into the stomach. The pancreas is near the stomach and secretes hormones that sense and regulate blood sugar levels.

The pyloric sphincter is a band of muscle that allows the passage of chyme from the stomach to the small intestine, where most of the absorption of nutrients will take place. The inner surface of the small intestine is lined with villi, small finger-like projections that increase the surface area of the small intestine and help with the absorption of nutrients. Food is moved through the small intestine by peristalsis, the wave-like movement of smooth muscle. After food has traveled through the small intestine, it reaches the large intestine, or colon, where stools are formed and water is absorbed. Waste passes through the rectum and is excreted out of the anus at the end of the alimentary canal.

Image source: https://openstax.org/books/anatomy-and-physiology-2e/pages/23-1-overview-of-the-digestive-system

The Integumentary System

The integumentary system is a vital part of the human body, responsible for protecting the internal organs and maintaining homeostasis. It is composed primarily of the skin, which is the largest organ of the body, and its associated structures. As future healthcare professionals, nursing students must understand the anatomy, functions, and significance of the integumentary system, as it plays a crucial role in patient care, wound healing, and defense against pathogens.

Organs in the System

The integumentary system is made up of several key components, including the skin, hair, nails, glands, and sensory receptors.

• The skin itself consists of three primary layers: the epidermis (outer layer), dermis (middle layer), and hypodermis (subcutaneous layer). Each of these layers has specific functions, such as protecting against external damage, regulating temperature, and storing fat.

• Hair and nails serve as protective barriers and are made of keratin, while glands like sweat and sebaceous glands help regulate body temperature and keep the skin hydrated.

• Sensory receptors in the skin allow the body to respond to changes in the environment, such as touch, pressure, and temperature.

Function of the System

The integumentary system has several vital functions, the most important of which is protection. The skin acts as the first line of defense against harmful microorganisms, physical injury, and ultraviolet radiation.

Additionally, the system helps in thermoregulation, as sweat glands release sweat to cool the body, and blood vessels constrict or dilate to regulate heat retention or loss.

Another critical function is sensation, with specialized receptors that detect pain, temperature, and touch.

The skin also plays a role in excretion by eliminating waste through sweat and vitamin D synthesis, essential for calcium absorption and bone health.

This multifunctional system is essential for maintaining overall body homeostasis and health.

The Lymphatic/Immune System

Another system that works in conjunction with the circulatory system is the lymphatic system. Some of the fluid that is delivered to cells by the circulatory system is retained as interstitial fluid in the space between cells. The lymphatic system contains lymph capillaries that return this fluid to the circulatory system. Lymph nodes are enlarged lymphatic vessels that contain cells that fight infection, making the lymphatic system part of the immune system as well.

The Musculoskeletal System

The skeletal system (bones) and the muscular system (muscles) are often combined as the musculoskeletal system because they serve the same purpose: the support, protection, and movement of the body.

Bones

Bones are made of mature cells called osteocytes. The inner section of a bone contains a jelly-like substance called red marrow that is responsible for creating the many types of blood cells. Individual bones connect to comprise the skeleton. The skeleton can be divided into two sections: the axial, which is the main trunk of the body, including the skull, vertebrae, and rib cage, and the appendicular, which is made up of the hips, arms, and legs. One disorder associated with bones is osteoporosis, which is when bones become more brittle and weak, making them more likely to break.

Connective Tissue

The place where bones are joined together are called joints. Bones are attached to other bones by connective tissues called ligaments. Many joints have strong, flexible connective tissues called cartilage between them to cushion the joint. When this cartilage breaks down over time, the bones can rub together and cause pain in a condition known as osteoarthritis. Another type of arthritis is rheumatoid arthritis in which joints swell and cause pain.

Muscles

Muscles are made of flexible fibers that cause motion in the body. There are three types of muscles:

• smooth muscles—These are long muscles found in the intestines, esophagus, and other organs that coordinate the involuntary movement of substances through the body.

• cardiac muscles—Found only in the heart, these muscles are constantly contracting and expanding to pump blood through the body.

• skeletal muscles—These are attached to bones by connective tissue called tendons and help coordinate movement. Flexor muscles help bend joints, and extensor muscles help to straighten them.

The Nervous System

The nervous system is responsible for gathering information from both outside and inside the body, interpreting the information, and directing the body to respond to stimuli.

The Two Nervous Systems

The nervous system can be divided into two sections with separate sets of organs and tissues.

Central Nervous System (CNS)

The CNS includes the brain and spinal cord. These are the main processing centers that interpret incoming information and send responses.

Peripheral Nervous System (PNS)

The PNS consists of spinal nerves that branch off from the spinal cord and cranial nerves that branch off from the brain and brain stem. Nerves are bundles of neurons, the individual cells that make up the nervous system. The peripheral nervous system can be further divided into the somatic nervous system, which controls voluntary, conscious activity, and the autonomic nervous system, which controls involuntary, subconscious activity.

One example of the PNS and CNS working together is during a reflex arc, which is the neural pathway responsible for reflexes such as pulling your hand back from a hot stove before you even feel the pain. During the reflex arc, an impulse travels from the sensory organ through the PNS to the CNS, which sends a signal back through the PNS to muscles that will carry out the reflex.

Neurons

Neurons are the individual cells that make up the nervous system. They are composed of three main parts. The cell body is the large part of a neuron that contains organelles such as the nucleus and mitochondria. The dendrites branch out from the cell body and receive impulses from other neurons. The axon is a long tube that is responsible for sending impulses to neighboring cells. The axon ends in an axon terminal.

There are three types of neurons in the body: sensory neurons send impulses from the PNS to the CNS, interneurons send message through the brain and spinal cord, and motor neurons send impulses from the CNS to the PNS.

Between the axon terminal of one neuron and the dendrite of another, there is a gap known as the synaptic cleft, or synapse. Neurons communicate with each other by sending chemicals called neurotransmitters across the synapse.

Electrical signals travel through neurons due to a difference in electrical charge between the inside and outside of the membrane. Sodium and potassium are two ions that are pumped into or out of the cell in response to neurotransmitters, changing the electrical charge and causing an impulse to be sent through the neuron.

The Brain

The brain is the main neural center that processes perceptions and sensations, and it contains different tissues and structures that have various responsibilities. The largest part of the brain is the cerebrum, which has two halves, or hemispheres. Below that is the cerebellum, which controls balance and movement, among other things. The brain stem connects the brain to the spinal cord. The medulla oblongata is the portion of the brain stem that connects directly with the spinal cord before it exits the skull.

The Reproductive System

Reproduction is the creation of a new organism. In humans, reproduction is sexual, which means it requires cells from two separate individuals to create a new human. The two cells provided by each individual are called gametes, and they each contain half of the parental DNA. Normal body cells are diploid, meaning they have two copies of each chromosome, but gametes are haploid, having only one copy of each chromosome.

Male Sexual Organs

The gametes formed by males are sperm. They are created in the testes, which are held in a pouch of skin called the scrotum. Sperm travel through the ductus deferens (or vas deferens) and out of the penis during ejaculation. The hormone testosterone, produced in the testes, helps regulate the production of sperm.

Female Sexual Organs

The gametes formed by females are ova, or eggs. They are created in the ovaries. Ova begin as oocytes (immature egg cells). During ovulation, oocytes mature into ova, then travel through the fallopian tubes to the uterus, the organ that holds a developing baby. Ovulation occurs roughly every 28 days, with the release of one or more ova at a time. The endometrium, the lining of the uterus, thickens during this time to prepare for fertilization. If the egg is not fertilized, the lining sheds during menstruation.

Fertilization

Fertilization occurs when an ovum is joined with a sperm cell. The new cell created by their union is a zygote. The cell begins to divide rapidly to produce more cells, which will continue to divide, organize, and specialize to form the tissues and organs of the new baby. About eight weeks after fertilization, the developing baby has recognizably human body structures and systems. At this point until birth, it is called a fetus. To provide nourishment and oxygen for the fetus as it develops, an organ called the placenta forms in the lining of the uterus. The fetus is attached to the placenta through the umbilical cord, which contains blood vessels that deliver nutrients and remove waste products.

The Respiratory System

The purpose of the respiratory system is to take in oxygen and to expel carbon dioxide, a waste product. It works in conjunction with the cardiovascular system, which delivers oxygen from the lungs to the cells of the body and picks up oxygen from cells to be released in the lungs.

Organs

The path of airflow into the lungs begins in the mouth and nose. It then travels to the pharynx (the passageway that both food and air travel through), the larynx (an enlarged part of the airway that contains the vocal cords), and the trachea (a flexible tube that leads down into the chest). The trachea branches into two passageways called bronchi that lead to the right and left lungs. The bronchi further branch into smaller passageways called bronchioles, finally ending in alveoli, small air pouches that are surrounded by capillaries.

Function

The diaphragm is a muscle below the lungs that controls airflow. When it contracts, the lungs fill with air, and when it relaxes, air is expelled. When air moves from outside the body to inside it, that is external respiration, whereas when oxygen is transported to cells by the circulatory system, that is internal respiration.

The Excretory System

The excretory system includes several organs that work in conjunction to rid the body of waste products by way of the urinary and digestive systems.

The Kidneys

The kidneys are the main excretory organs of the body. Their function is to filter toxins from the blood. The kidneys contain nephrons, which are the active structures that filter the blood. Each nephron contains a glomerulus (a capillary that delivers blood to the nephron to be filtered), which is surrounded by Bowman’s capsule (the kidney tissue that filters the blood). The filtered fluid then enters the proximal convoluted tubule, goes down and back up a looping tube called the loop of Henle, and then out through the distal convoluted tubule into a collecting duct.

The filtered fluid created by the kidneys is called urine. The ureter is a tube leading out of the kidney that transfers urine to the urinary bladder, where it is held until ready to be released. It travels out of the body through the urethra.

Other Excretory Organs

Aside from the kidneys, other organs of the body have excretory functions. The skin’s sweat glands secrete excess water, salt, and waste. The liver secretes bile, which carries away waste that has been processed by the liver (this is in addition to its digestive function of breaking down fats). The lungs collect carbon dioxide from the blood and expel it. The large intestine forms feces at the final stage of digestion.

The Senses

The senses are described as sight, touch, taste, smell, and hearing. All of these senses require sensory organs that activate nerve receptors, sending signals to the brain to be interpreted. Some of our most intricate sensory organs are the eyes and ears, the anatomy of which are detailed here.

Sight

Image source: https://openstax.org/books/anatomy-and-physiology-2e/pages/14-1-sensory-perception

The first structure responsible for sensing images is the cornea, a clear outer covering that allows light into the eye. Light travels through a hole called the pupil, which can expand or contract depending on the intensity of light. The iris is the colored part of the eye responsible for opening and closing the pupil. Light travels through an oval structure called the lens, which can bend in order to focus the image on a receptor at the back of the eye called the retina.

The retina contains two types of specialized receptors: rod cells, which are more sensitive to dim light, and cone cells, which can sense a variety of colors. The messages they interpret are sent to the brain through the optic nerve.

Hearing

Image source: https://openstax.org/books/anatomy-and-physiology-2e/pages/14-1-sensory-perception

The external ear includes the auricle (a fleshy outer structure that directs sound waves into the ear canal), the ear canal, and the tympanic membrane (flexible tissue that vibrates in response to sound waves). The middle ear is made up of three small bones: the malleus, incus, and stapes. These bones transfer vibrations to the inner ear, which contains the cochlea (a fluid-filled bony spiral responsible for relaying sound information to the brain via the cochlear nerve) and the vestibule (a set of arching bones responsible for maintaining balance).