Anatomy and Physiology Study Guide for the HESI Exam

Cardiovascular System

The cardiovascular system, also known as the circulatory system, is responsible for transporting oxygen, nutrients, hormones, and waste throughout the body. It consists of three main components:

the heart—a muscular organ that pumps blood through the body
blood vessels—a network of arteries, veins, and capillaries that transport blood
blood—a specialized fluid that delivers oxygen and nutrients while removing waste

The Heart

The heart is a muscular organ with four chambers:

atria (right & left) —receive blood from the body and lungs
ventricles (right & left)—pump blood to the lungs and the rest of the body

Blood flow through the heart follows this pathway:

Deoxygenated blood enters the right atrium via the superior and inferior venae cavae.
It passes through the tricuspid valve into the right ventricle. The tricuspid valve prevents backflow from the right ventricle to the right atrium during contraction.
The right ventricle pumps blood through the pulmonary valve into the pulmonary arteries, which send it to the lungs for oxygenation.
Oxygenated blood returns to the left atrium via the pulmonary veins.
It moves through the mitral (bicuspid) valve into the left ventricle.
The left ventricle pumps blood through the aortic valve into the aorta, which distributes it to the rest of the body.

Electrical Conduction of the Heart

The electrical conduction system of the heart controls the heartbeat. The primary pacemaker of the heart is the sinoatrial (SA) node, which generates electrical impulses that regulate heart contractions.

The conduction pathway follows this sequence:

sinoatrial (SA) node—located in the right atrium; it initiates the heartbeat
atrioventricular (AV) node—delays the impulse slightly to allow the atria to contract before the ventricles
bundle of His—conducts the impulse toward the ventricles
purkinje fibers—distribute the impulse throughout the ventricles, causing them to contract

The chordae tendineae are not part of the electrical conduction system; instead, they are fibrous cords that help prevent valve prolapse by anchoring the heart valves to the ventricles.

Blood

Blood is a connective tissue composed of plasma, red blood cells, white blood cells, and platelets:

plasma—the liquid portion of blood, which carries hormones, carbon dioxide, nutrients, and waste
red blood cells (erythrocytes)—transport oxygen via hemoglobin and help remove carbon dioxide
white blood cells (leukocytes)—play a vital role in the immune system, producing antibodies to fight infections
platelets (thrombocytes)—assist in blood clotting to prevent excessive bleeding

The process of blood cell formation, known as hematopoiesis, occurs primarily in the bone marrow, where red blood cells, white blood cells, and platelets are produced.

The normal pH of blood ranges between 7.35 and 7.45, making it slightly alkaline. The average adult body contains approximately five to six quarts (4.7 to 5.5 liters) of blood.

Blood Types and Compatibility

Blood type is determined by the presence or absence of A and B antigens on red blood cells. The four major blood types are:

type A—has A antigens and anti-B antibodies
type B—has B antigens and anti-A antibodies
type AB—has both A and B antigens, but no antibodies, making it the universal recipient. This means a person with type AB blood can receive blood from any blood type (A, B, AB, or O) without experiencing an immune reaction.
type O—has no antigens, but both anti-A and anti-B antibodies, making it the universal donor because it can be transfused into any blood type

The Rh factor (positive or negative) further classifies blood. A person who is Rh-positive has the Rh antigen, while an Rh-negative person does not. This is crucial in blood transfusions and pregnancy compatibility.

Blood Flow and Circulation

The cardiovascular system circulates blood through two main pathways:

pulmonary circulation—carries deoxygenated blood from the heart to the lungs, where carbon dioxide is exchanged for oxygen
systemic circulation—delivers oxygen-rich blood from the heart to the rest of the body, supplying tissues with nutrients and oxygen while removing waste

Blood vessels enter and exit bones through foramina, small openings that allow arteries, veins, and nerves to pass through.

Blood Vessels

Blood vessels form a vast network that enables circulation:

arteries—Arteries carry oxygenated blood away from the heart under high pressure and have thick, muscular walls to withstand this pressure.
veins—Veins carry deoxygenated blood back to the heart under low pressure and have thinner walls. They also contain valves to prevent backflow.
capillaries—Capillaries are the smallest blood vessels. They are where gas exchange occurs and from which oxygen diffuses from the blood into tissues, while carbon dioxide moves into the bloodstream to be exhaled.

Blood Pressure

Blood pressure is the force exerted by circulating blood on vessel walls. It is measured in millimeters of mercury (mm Hg) and consists of:

systolic pressure—the pressure in arteries when the heart contracts (should be less than 120 mm Hg)
diastolic pressure—the pressure in arteries when the heart relaxes (should be under 80 mm Hg)

Pulse

The pulse rate is the number of heartbeats per minute (bpm). A normal resting pulse for a healthy adult is between 60 and 100 bpm.

Respiratory System

The respiratory system facilitates the exchange of gases—oxygen and carbon dioxide—between the body and the environment. It consists of the lungs, trachea, bronchi, diaphragm, and associated muscles. The primary functions of the respiratory system include:

delivering oxygen to the bloodstream for cellular respiration
removing carbon dioxide, a metabolic waste product
regulating blood pH through gas exchange

The diaphragm is a dome-shaped sheet of muscle located at the base of the lungs. It facilitates breathing by expanding and contracting the chest cavity.

The Lungs and Airway Structures

The lungs are the primary organs of respiration and contain millions of tiny air sacs called alveoli, where gas exchange occurs. Air enters the respiratory system through the following structures:

nasal cavity—filters, warms, and humidifies incoming air
pharynx (throat)—a passageway that connects the nasal cavity to the larynx
larynx (voice box)—houses the vocal cords and prevents food from entering the airway
trachea (windpipe)—a tube reinforced with cartilage rings that directs air into the lungs
bronchi—formed where the trachea splits into two bronchi, one of which enters each lung
bronchioles—smaller branches of the bronchi that distribute air throughout the lungs
alveoli—tiny air sacs where oxygen and carbon dioxide are exchanged with the bloodstream

The Breathing Process

Breathing is a mechanical process driven by the contraction and relaxation of the diaphragm and intercostal muscles (muscles between the ribs).

Inhalation (Inspiration)

The diaphragm contracts, moving downward, and the intercostal muscles expand the ribcage.
Lung volume increases, lowering pressure inside the lungs.
Air is drawn into the lungs through the trachea and bronchi.
Oxygen diffuses into the alveoli and enters the bloodstream.

Exhalation (Expiration)

The diaphragm relaxes, returning to its dome shape.
Lung volume decreases, increasing pressure inside the lungs.
Carbon dioxide-rich air is forced out through the respiratory tract.

Note: The volume of air moved in and out of the lungs during a normal breath is called tidal volume.

Respiratory Control and Regulation

The primary stimulus for breathing is the level of carbon dioxide (CO\(\bf_2\)) in the blood, rather than oxygen. When CO\(_2\) levels rise, receptors in the aorta, carotid artery, and medulla oblongata detect the change. The medulla oblongata and pons, located in the brainstem, then send signals to increase breathing rate and depth to expel excess CO\(_2\) and restore balance.

Types of Respiration

Respiration occurs at two levels:

external respiration—the exchange of oxygen and carbon dioxide between the lungs and the blood via the alveoli
internal respiration—the exchange of gases between the blood and body tissues at the cellular level

Digestive System

The digestive system processes food, extracts nutrients, and eliminates waste. It consists of the gastrointestinal (GI) tract, also known as the alimentary canal, and accessory organs such as the liver, pancreas, and gallbladder. The GI tract includes the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus.

The Digestive Process

Digestion begins in the mouth, where food is chewed into smaller pieces and mixed with saliva, which contains enzymes that initiate chemical breakdown. The salivary glands produce different types of secretions:

parotid glands—produce serous (watery) secretions rich in enzymes
submandibular glands—produce a mix of serous fluid and mucus
sublingual glands—produce mostly mucin, a thick secretion that lubricates food for swallowing

Once food is formed into a bolus, it is swallowed and moves into the esophagus, which connects the pharynx (throat) to the stomach. The lower esophageal sphincter (also called the cardiac sphincter) prevents stomach acid from refluxing into the esophagus.

The Stomach

In the stomach, food is mixed with gastric secretions, which contain hydrochloric acid (HCl) and enzymes such as pepsin, which break down proteins. The stomach also churns food, mechanically breaking it down into a semi-liquid mixture called chyme.

Chyme exits the stomach through the pyloric sphincter, which regulates the flow of partially digested food into the duodenum, the first section of the small intestine.

The Small Intestine: Digestion and Nutrient Absorption

The small intestine is the primary site for digestion and nutrient absorption. It is divided into three sections:

duodenum—receives chyme from the stomach and mixes it with bile (from the liver) and pancreatic enzymes for further breakdown
jejunum—the primary site for nutrient absorption into the bloodstream
Ileum—absorbs vitamin B12, bile salts, and remaining nutrients before passing undigested material to the large intestine

The pancreas plays a crucial role in this process by producing digestive enzymes such as:

amylase—breaks down carbohydrates
lipase—breaks down fats
proteases—break down proteins

Additionally, the pancreas produces insulin, which regulates blood sugar levels.

The liver supports digestion by producing bile, which aids in fat digestion. It also stores glycogen, vitamins, and minerals and detoxifies blood. Bile is stored in the gallbladder and released into the small intestine when needed.

The Large Intestine: Water Absorption and Waste Formation

After nutrients have been absorbed in the small intestine, undigested food and waste enter the large intestine, where water and electrolytes are reabsorbed. The large intestine consists of five sections. The undigested food and waste travel through them in this order:

cecum—a pouch that connects the small and large intestines. The appendix, a narrow, finger-shaped tube, is attached to the cecum in the lower right quadrant of the abdomen. While it was once thought to be unnecessary, research now suggests the appendix may play a minor role in immune function by housing beneficial gut bacteria.

ascending colon—travels upward along the right side of the abdomen

transverse colon—extends across the abdomen

descending colon—travels downward on the left side

sigmoid colon—leads to the rectum, which stores feces until elimination

Once the rectum fills, waste is expelled through the anus during defecation.

Sphincters of the Digestive System

Sphincters are muscular valves that control the passage of food and waste:

lower esophageal sphincter (cardiac sphincter)—prevents acid reflux from the stomach into the esophagus
pyloric sphincter—controls the release of chyme from the stomach into the small intestine
anal sphincter—regulates defecation