TEAS Science: The Digestive and Urinary Systems — Complete Review

The digestive and urinary systems show up on the TEAS Science section every single time. ATI loves these topics because they test whether you truly understand how the body processes nutrients and eliminates waste, two functions that every nurse must know cold. This guide walks you through every organ, every process, and every high-yield detail so nothing on test day catches you off guard.

Why These Two Systems Are Tested Together

Digestion and urinary function are linked by one big idea: the body takes in what it needs and removes what it does not. The digestive system breaks food into absorbable nutrients and sends waste to the large intestine. The urinary system filters the blood, recovers useful molecules, and excretes dissolved waste as urine. Understanding both systems together helps you see the full picture of how the body maintains homeostasis.

The Digestive System: Organs and Their Functions

The digestive tract is one long tube from mouth to anus, called the alimentary canal or GI tract. Each section has a specific job. Memorize these and you will answer most TEAS digestive questions correctly.

• Mouth: Mechanical digestion through chewing (mastication) and chemical digestion of starches by salivary amylase.
• Pharynx and Esophagus: Transport food to the stomach via peristalsis, the wave-like muscle contractions that push food along the entire GI tract.
• Stomach: Churns food with hydrochloric acid (HCl) and pepsin to break down proteins. Produces a semi-liquid mixture called chyme.
• Small Intestine: The primary site of nutrient absorption. Divided into three segments — duodenum, jejunum, and ileum.
• Large Intestine (Colon): Absorbs water and electrolytes from remaining material. Houses beneficial bacteria that produce vitamin K and some B vitamins.
• Rectum and Anus: Store and eliminate solid waste (feces).

Accessory Organs You Must Know

Several organs assist digestion without food passing directly through them. The TEAS frequently tests these because students often overlook them.

• Liver: Produces bile, which emulsifies (breaks apart) fats so enzymes can digest them. Also detoxifies blood and stores glycogen.
• Gallbladder: Stores and concentrates bile produced by the liver, releasing it into the duodenum when fats are present.
• Pancreas: Secretes pancreatic juice containing lipase (digests fats), pancreatic amylase (digests starches), and trypsin (digests proteins). Also releases bicarbonate to neutralize stomach acid in the duodenum.

Chemical Digestion: Enzymes and Where They Work

The TEAS tests enzyme specificity, meaning which enzyme breaks down which nutrient and where. This table-style breakdown is the fastest way to lock it in.

• Salivary amylase → starches → mouth
• Pepsin → proteins → stomach (activated by HCl)
• Pancreatic amylase → starches → small intestine (duodenum)
• Trypsin → proteins → small intestine (duodenum)
• Lipase → fats → small intestine (duodenum)
• Lactase, maltase, sucrase → specific sugars → small intestine (brush border)

Notice the pattern: carbohydrate digestion starts in the mouth, protein digestion starts in the stomach, and fat digestion happens almost entirely in the small intestine with help from bile.

Nutrient Absorption in the Small Intestine

The small intestine is lined with tiny finger-like projections called villi, and each villus is covered with even smaller microvilli. Together they create an enormous surface area for absorption. This is one of the most commonly tested concepts on the TEAS.

• Duodenum: Receives chyme from the stomach, bile from the gallbladder, and pancreatic juice. Most chemical digestion is completed here.
• Jejunum: The primary absorption site for amino acids, sugars, and fatty acids.
• Ileum: Absorbs vitamin B12, bile salts, and any remaining nutrients. Bile salts are recycled back to the liver.

The Large Intestine and Elimination

By the time material reaches the large intestine, most nutrients have been absorbed. The colon's primary job is to reclaim water and compact waste. Sections of the large intestine to know include the cecum (where the appendix attaches), ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal. Bacteria in the colon ferment remaining fiber and produce gases and vitamins.

The Urinary System: Structure and Function

The urinary system has four main organs. Know each one and its role.

• Kidneys (2): Filter blood, remove metabolic waste (urea, creatinine), regulate fluid and electrolyte balance, and help control blood pressure.
• Ureters (2): Muscular tubes that transport urine from each kidney to the bladder via peristalsis.
• Urinary Bladder: A muscular sac that stores urine until it is voluntarily released.
• Urethra: The tube through which urine exits the body during urination (micturition).

Inside the Kidney: The Nephron

The nephron is the functional unit of the kidney, and it is one of the highest-yield topics on the TEAS. Each kidney contains about one million nephrons. Understanding the nephron means understanding how urine is formed.

Urine formation happens in three steps:

• Glomerular Filtration: Blood enters the glomerulus (a knot of capillaries) under high pressure. Water, salts, glucose, amino acids, and waste are pushed into Bowman's capsule. Blood cells and large proteins stay in the blood.
• Tubular Reabsorption: As filtrate moves through the proximal convoluted tubule, loop of Henle, and distal convoluted tubule, useful substances (glucose, amino acids, most water, sodium) are reabsorbed back into the blood.
• Tubular Secretion: Additional waste products and excess ions (hydrogen, potassium) are actively moved from the blood into the tubule to be excreted in urine.

Hormones That Regulate the Urinary System

The TEAS tests your understanding of how hormones control kidney function. Two hormones come up most often.

• ADH (Antidiuretic Hormone): Released by the posterior pituitary gland when the body is dehydrated. ADH makes the collecting ducts more permeable to water, so more water is reabsorbed and urine becomes concentrated.
• Aldosterone: Released by the adrenal cortex. Aldosterone increases sodium reabsorption in the distal tubule, which pulls water back into the blood by osmosis, raising blood volume and blood pressure.
• Renin-Angiotensin-Aldosterone System (RAAS): When blood pressure drops, the kidneys release renin, which triggers a chain reaction leading to angiotensin II (a vasoconstrictor) and aldosterone release. The result is increased blood pressure.

How the Digestive and Urinary Systems Work Together

These two systems cooperate to maintain the body's internal environment. The digestive system absorbs nutrients and water from food. The liver processes absorbed nutrients and produces urea (a nitrogen waste product from protein metabolism). The kidneys then filter urea out of the blood and excrete it in urine. Meanwhile, both systems help regulate water balance: the large intestine reabsorbs water from digested material, and the kidneys fine-tune total body water by adjusting urine concentration.

When the TEAS asks a question connecting two body systems, look for these kinds of functional links. Understanding the connections, not just memorizing individual organs, is what earns you the hardest points.

Common TEAS Questions and How to Answer Them

Here are the question patterns you are most likely to see on the TEAS for these two systems.

• Where does most chemical digestion occur? → Small intestine (duodenum).
• Where does most nutrient absorption occur? → Small intestine (jejunum).
• What is the role of bile? → Emulsifies fats (does NOT digest them — lipase does).
• What is the functional unit of the kidney? → The nephron.
• What does ADH do? → Increases water reabsorption, producing concentrated urine.
• What structure increases the surface area of the small intestine? → Villi and microvilli.
• What waste product do the kidneys primarily filter? → Urea (from protein metabolism).
• Which organ produces bile? → The liver (the gallbladder stores it, not produces it).

Study Strategy for These Systems

Start by tracing the path of food from mouth to anus, naming each organ and its function. Then trace the path of blood through the kidney nephron, from glomerulus to collecting duct. Drawing simple diagrams of both pathways is one of the most effective study techniques for visual learners.

• Use flashcards for enzyme-substrate pairs (salivary amylase → starch, pepsin → protein, lipase → fat).
• Practice labeling a blank nephron diagram from memory.
• Quiz yourself on the three steps of urine formation: filter, reabsorb, secrete.
• Review the hormones ADH and aldosterone until you can explain their effects without notes.

The Bottom Line

The digestive and urinary systems are guaranteed points on the TEAS if you study them the right way. Know the path food takes, know which enzymes act where, understand how the nephron filters blood, and learn how ADH and aldosterone regulate water balance. These are not abstract concepts — they are the foundation of nursing care, and ATI tests them because nurses use this knowledge every day.