4.6 The Urinary and Reproductive Systems
Key Takeaways
- The nephron is the kidney's functional unit; about 1 million per kidney form urine through filtration, reabsorption, and secretion
- Filtration happens at the glomerulus; the proximal tubule reabsorbs 100% of glucose and amino acids; ADH and aldosterone fine-tune water and sodium recovery
- Kidneys regulate blood pressure (renin), make erythropoietin, activate vitamin D, and maintain acid-base balance near blood pH 7.4
- Sperm form in the seminiferous tubules of the testes (spermatogenesis); eggs mature in ovaries (oogenesis); fertilization occurs in the fallopian tube
- An LH surge triggers ovulation around day 14; the menstrual cycle has menstrual, follicular, ovulation, and luteal phases
Why These Systems Matter on the TEAS
The urinary system filters blood, removes nitrogenous waste, and keeps the body's internal fluid chemistry within a narrow survivable range. The reproductive system produces gametes (sex cells) and the hormones that drive sexual development and pregnancy. Both appear frequently on the ATI TEAS 7 Science section because nurses constantly monitor urine output, electrolytes, and fluid balance, and because reproductive physiology underlies obstetric and gynecologic care.
Expect questions that ask you to name the functional unit of the kidney, place a step of urine formation in the right tubule segment, match a hormone to its effect, or identify where fertilization occurs. The system is easier to remember when you trace one drop of fluid from blood to bladder.
Urinary System Organs
| Organ | Function |
|---|---|
| Kidneys | Filter blood, produce urine, regulate fluid, electrolytes, and pH |
| Ureters | Transport urine from kidneys to bladder by peristalsis |
| Urinary bladder | Stores urine until elimination |
| Urethra | Carries urine out of the body |
The kidneys sit retroperitoneally on either side of the spine. Each is organized into an outer renal cortex, an inner renal medulla (containing the loops of Henle and collecting ducts), and a funnel-shaped renal pelvis that collects finished urine and channels it into the ureter.
The Nephron: The Functional Unit
The nephron is the microscopic functional unit of the kidney, and each kidney holds roughly 1 million of them. Memorize the parts in the order fluid flows through them, because the TEAS often asks what happens "next."
| Part | Role in Urine Formation |
|---|---|
| Glomerulus | Capillary tuft where blood is filtered |
| Bowman's capsule | Cup that surrounds the glomerulus and catches filtrate |
| Proximal convoluted tubule (PCT) | Reabsorbs most nutrients, water, and ions |
| Loop of Henle | Concentrates urine; reabsorbs water and salt |
| Distal convoluted tubule (DCT) | Fine-tunes ion and water reabsorption and secretion |
| Collecting duct | Final water reabsorption under ADH control |
The Three Steps of Urine Formation
- Filtration — At the glomerulus, blood pressure forces water, glucose, ions, and wastes out of the blood and into Bowman's capsule. Large items (blood cells, proteins) stay in the blood. The kidneys filter an enormous volume each day, so most of that fluid must be recovered.
- Reabsorption — In the tubules, useful substances move back into the blood. The PCT reabsorbs essentially 100% of glucose and amino acids plus most sodium and water.
- Secretion — The tubules actively add extra wastes (such as hydrogen ions, potassium, and some drugs) from blood into the forming urine, which is how the kidney fine-tunes blood pH and ion levels.
Fluid, Electrolyte, and pH Balance
The kidney is the body's master regulator of internal chemistry, and two hormones do most of the fine-tuning:
- Antidiuretic hormone (ADH), released by the posterior pituitary, makes the collecting duct more permeable to water. More ADH means more water reabsorbed and small, concentrated urine; less ADH means dilute urine. ADH rises during dehydration.
- Aldosterone, from the adrenal cortex, tells the DCT and collecting duct to reabsorb sodium (water follows the sodium) and to secrete potassium. It raises blood volume and blood pressure.
The kidney also defends acid-base balance: it excretes hydrogen ions and reclaims bicarbonate to keep blood pH near 7.4. When blood is too acidic, the tubules secrete more H+.
Kidney Functions Beyond Making Urine
- Regulate blood pressure by releasing the enzyme renin
- Produce erythropoietin (EPO), which signals bone marrow to make red blood cells
- Activate vitamin D, supporting calcium absorption
- Maintain acid-base (pH) balance
- Balance electrolytes such as sodium, potassium, and calcium
Male Reproductive System
| Structure | Function |
|---|---|
| Testes | Produce sperm and the hormone testosterone |
| Seminiferous tubules | Site of sperm production inside the testes |
| Epididymis | Stores and matures sperm |
| Vas deferens | Carries sperm toward the urethra |
| Seminal vesicles | Add fructose-rich fluid for sperm energy |
| Prostate gland | Adds alkaline fluid that protects sperm |
| Urethra | Shared pathway for urine and semen |
Spermatogenesis occurs continuously after puberty in the seminiferous tubules, driven by testosterone, following the path: spermatogonia to primary spermatocyte to secondary spermatocyte to spermatid to mature sperm.
Female Reproductive System and the Menstrual Cycle
| Structure | Function |
|---|---|
| Ovaries | Produce eggs (ova) and the hormones estrogen and progesterone |
| Fallopian tubes | Carry the egg toward the uterus; usual site of fertilization |
| Uterus | Houses and nourishes a developing fetus |
| Endometrium | Uterine lining that thickens then sheds each cycle |
| Cervix | Lower neck of the uterus opening into the vagina |
The roughly 28-day menstrual cycle has four phases, controlled by four hormones:
- Menstrual phase — the endometrium sheds (days 1–5)
- Follicular phase — FSH matures a follicle and estrogen rebuilds the endometrium
- Ovulation — a surge of LH (luteinizing hormone) releases the egg, about day 14
- Luteal phase — the corpus luteum releases progesterone to maintain the lining
Example: A patient charts a 28-day cycle with no period this month. Working backward: ovulation (the LH surge) happens about day 14, fertilization occurs in the fallopian tube, and high progesterone from the corpus luteum keeps the endometrium intact instead of shedding — a logical sequence the TEAS expects you to reconstruct from the hormones involved.
Which structure is the functional unit of the kidney?
In which step of urine formation are glucose and amino acids returned to the blood?
Antidiuretic hormone (ADH) increases water reabsorption primarily in which part of the nephron?
Match each reproductive or kidney hormone to its main effect.
Match each item on the left with the correct item on the right
Place the parts of the nephron in the order that filtrate flows through them.
Arrange the items in the correct order