BIO 004 · Human Anatomy
The Urinary System
Block 4 · Module 4: The Urinary System
A reference for the urinary system video and lab. This page covers the gross anatomy of the kidney, the nephron, the juxtaglomerular apparatus and filtration membrane, the blood supply, and the ureters, bladder, and urethra. The focus is on the structures and the job each one does.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids respond to Study and Quiz too, with a Reveal button on each row.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level depth for this course.
- Describe the gross anatomy of the kidney and its tissue layers.
- Identify the parts of a nephron and the layers of the filtration membrane.
- Trace the blood supply of the kidney and the path of urine.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
The kidney in section
Add a labeled frontal section showing the cortex, medulla, pyramids, calyces, and pelvis.
The nephron
Add a labeled diagram of a nephron with the renal corpuscle and the tubule segments.
The urinary tract
Add a labeled view of the kidneys, ureters, bladder, and urethra.
The Urinary System, an Overview
The urinary system filters the blood and makes urine. The kidneys do the work; the rest of the system carries and stores the urine.
- Urinary systemthe kidneys, ureters, urinary bladder, and urethra
- Kidneysthe paired organs that filter the blood and form urine
- Uretersthe paired tubes that carry urine from the kidneys to the bladder
- Urinary bladderthe muscular sac that stores urine
- Urethrathe tube that carries urine from the bladder to the outside
- Roles of the kidneyfiltering wastes from the blood, balancing water, ions, and pH, and helping regulate blood pressure
The Kidneys, Gross Anatomy
The kidneys are bean-shaped organs against the back wall of the abdomen. Three tissue layers cushion and anchor each one, and the interior sorts into a cortex and a medulla.
- Locationretroperitoneal, between T12 and L3; the right kidney sits slightly lower because of the liver
- Renal hilumthe notch on the medial border where the ureter, vessels, and nerves enter and leave
- Renal capsulethe smooth, fibrous inner layer that maintains the kidney's shape
- Adipose capsulethe layer of fat around the capsule that cushions the kidney and holds it in place
- Renal fasciathe outer layer of connective tissue that anchors the kidney to the abdominal wall
- Renal cortexthe outer region of kidney tissue, just beneath the capsule
- Renal columnsextensions of the cortex that dip down between the renal pyramids
- Renal medullathe inner region of kidney tissue
- Renal pyramidsthe cone-shaped masses of the medulla, with their bases toward the cortex
- Renal papillathe tip of a renal pyramid, which drains urine into a minor calyx
- Parenchymathe functional tissue of the kidney, the cortex and pyramids together, which holds the nephrons
The Nephron
The nephron is the functional unit of the kidney, the structure that actually makes urine. It has two main parts: the renal corpuscle and the renal tubule.
- Nephronthe microscopic functional unit of the kidney; each kidney holds about one million
- Renal corpusclethe filtering head of the nephron; the glomerulus inside the glomerular capsule
- Glomerulusthe tuft of leaky, fenestrated capillaries where the blood is filtered
- Glomerular capsuleBowman's capsule; the cup that surrounds the glomerulus and collects the filtrate
- Podocytesthe cells of the inner, visceral layer of the capsule, whose foot-like processes form filtration slits
- Capsular spacethe space inside the capsule where the filtrate collects before entering the tubule
- Proximal convoluted tubulethe first, coiled segment of the renal tubule, lined with a brush border of microvilli
- Nephron loopthe loop of Henle; the U-shaped segment with a descending limb and an ascending limb
- Distal convoluted tubulethe second coiled segment of the renal tubule
- Collecting ductthe duct that gathers fluid from many nephrons and carries it toward the renal papilla
Nephrons come in two types, sorted by how deep their loop reaches. Compare them.
| Type | Features |
|---|---|
| Cortical nephrons | about 85 percent of nephrons; short loops that barely enter the medulla, wrapped by peritubular capillaries |
| Juxtamedullary nephrons | about 15 percent of nephrons; long loops that reach deep into the medulla, served by the vasa recta; they concentrate the urine |
The Juxtaglomerular Apparatus and Filtration Membrane
Where the distal tubule touches its own glomerulus, a small structure monitors and adjusts filtration. The filtration membrane itself is a three-layer sieve.
- Juxtaglomerular apparatusthe structure where the distal convoluted tubule contacts the arterioles of its own renal corpuscle
- Macula densathe cells of the distal tubule that sense the sodium and chloride concentration of the fluid
- Juxtaglomerular cellsmodified smooth muscle cells in the afferent arteriole that release renin when blood pressure is low
Blood is filtered across a three-layer membrane. Compare what each layer holds back.
| Layer | What it holds back |
|---|---|
| Fenestrated endothelium | the pored wall of the glomerular capillary; it lets plasma pass but blocks blood cells |
| Basement membrane | the layer between the capillary and the podocytes; it blocks large plasma proteins |
| Slit membranes | the filtration slits between the podocyte processes; they block medium-sized proteins |
The Blood Supply of the Kidney
Blood reaches the nephrons through a branching chain of arteries and leaves through a matching set of veins. Trace the arterial path.
- Renal arterybranches from the abdominal aorta and enters at the hilum
- Segmental and interlobar arteriescarry blood between the renal pyramids
- Arcuate arteriesarch along the bases of the pyramids, between the cortex and medulla
- Interlobular arteriesbranch up into the cortex
- Afferent arterioledelivers blood into the glomerulus
- Glomerulusthe capillary tuft where filtration occurs
- Efferent arteriolecarries blood out of the glomerulus
- Peritubular capillaries and vasa rectawrap the renal tubules, then drain into veins that lead to the renal vein
The Ureters, Bladder, and Urethra
Once urine leaves the nephrons it is collected, carried, stored, and finally released by the rest of the system.
- Minor and major calycesthe cup-shaped chambers that collect urine from the renal papillae and channel it into the renal pelvis
- Renal pelvisthe funnel-shaped cavity that collects urine and passes it into the ureter
- Uretersthe muscular tubes that carry urine from the kidneys to the bladder by peristalsis
- Trigonethe smooth triangular area at the base of the bladder, marked by the two ureter openings and the urethral opening
- Detrusor musclethe smooth muscle layer of the bladder wall that contracts to empty it
- Internal urethral sphincterthe involuntary smooth muscle ring at the bladder outlet
- External urethral sphincterthe voluntary skeletal muscle ring that gives conscious control over urination
- Male urethralonger; it passes through the prostate as the prostatic urethra, through the perineum as the membranous urethra, and through the penis as the spongy urethra
- Female urethrashorter; it opens between the clitoris and the vaginal opening
The Path of Urine
Urine leaves the nephron and flows through a fixed series of structures to the outside.
- Collecting ductgathers the fluid from many nephrons
- Minor and major calycescollect the urine draining from the renal papillae
- Renal pelvisfunnels the urine toward the ureter
- Uretercarries the urine down to the bladder
- Urinary bladderstores the urine
- Urethracarries the urine out of the body
Common Disorders of the Urinary System
Compare the common disorders of the urinary system by the structure each one affects.
| Disorder | What it is |
|---|---|
| Urinary tract infection | an infection of the urethra, bladder, or kidneys, usually by bacteria |
| Kidney stones | hardened mineral deposits that form in the kidney and can lodge in the ureter |
| Glomerulonephritis | inflammation of the glomeruli that impairs filtration |
| Renal failure | loss of the kidney's ability to filter the blood, acute or chronic |
| Nephroptosis | a floating kidney; the kidney drops from its normal position when its fat support is lost |
| Urinary incontinence | loss of voluntary control over urination, as stress, urge, overflow, or functional incontinence |
| Polycystic kidney disease | an inherited disorder in which many fluid-filled cysts enlarge the kidneys |
See also: The Accessory Digestive Organs, and The Male Reproductive System, the next page in this block.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Trace a drop of filtrate through the nephron, from the glomerulus to the collecting duct.
- Name the structures of the kidney from the cortex inward, and what each region contains.
- Trace urine from the collecting duct to outside the body, naming each structure.
- Compare the cortex and the medulla of the kidney by which parts of the nephron sit in each.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.