13: Genitourinary (a.k.a. Urogenital ) System
- Page ID
- 100215
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 13.1: Overview of the Renal (Urinary) System
- The renal (urinary) system consists of the kidneys, ureters, urinary bladder, and urethra, working together to filter blood and eliminate waste as urine. Beyond waste removal, the kidneys regulate blood volume, blood pressure, electrolytes, and acid–base balance, while also producing hormones such as erythropoietin and activating vitamin D.
- 13.2: The Kidneys — Exterior and Interior Structures
- The kidneys are retroperitoneal, bean-shaped organs protected by a fibrous capsule, a cushion of fat, and the renal fascia. They receive a large portion of cardiac output to support continuous blood filtration. Internally, they are organized into an outer cortex and inner medulla with renal pyramids, where nephrons filter blood and begin urine formation. Filtered fluid drains into the renal pelvis at the hilum and then into the ureter on the way to the bladder.
- 13.3: Nephron — The Functional Unit of the Kidneys
- The nephron is the kidney’s microscopic functional unit, composed of a renal corpuscle for filtration and a tubular system for reabsorption and secretion. The filtrate's composition is precisely adjusted as it moves from the glomerulus through the proximal tubule, loop of Henle, distal tubule, and collecting duct. The hormone ADH regulates water reabsorption in the distal nephron, helping control urine concentration, blood volume, and osmolarity.
- 13.4: Formation and Analysis of Urine
- Urine forms through filtration, reabsorption, and secretion, allowing the kidneys to regulate fluid, electrolytes, and pH while eliminating wastes. Although large volumes of filtrate are produced daily, nearly all is reabsorbed, leaving only 1–2 liters of urine. Urinalysis assesses physical, chemical, and microscopic features to detect disorders such as diabetes, kidney damage, or urinary tract infections.
- 13.5: Urine Transport and Elimination
- Urine flows from the renal pelvis through the ureters to the bladder for storage, then exits via the urethra. Peristalsis, one-way valves, and the detrusor muscle enable transport and storage, while the micturition reflex coordinates sphincter relaxation for controlled release. Structural differences in the male and female urethra explain common clinical patterns such as higher UTI risk in females and obstruction from prostate enlargement in males.
- 13.6: Kidney Stones
- Kidney stones (nephrolithiasis) are solid crystals — most commonly calcium-based — that form in the kidneys when urine becomes concentrated. They often remain silent in the kidney but cause severe, colicky flank pain and possible hematuria when they obstruct a ureter. Diagnosis is best made with CT imaging, and treatment ranges from spontaneous passage to shock wave lithotripsy or surgical removal, depending on size and location.
- 13.7: Water Balance
- Water balance depends on coordinated regulation by the kidneys, thirst mechanism, and ADH to match intake with loss and maintain stable blood volume and osmolarity. Dehydration reduces blood volume, impairs temperature regulation, and can lead to heat exhaustion or heat stroke, while overhydration dilutes plasma sodium and may cause brain swelling. Factors such as age, exercise, heat, altitude, and alcohol consumption can disrupt this balance by altering thirst signals, fluid loss, or ADH releas
- 13.8: Overview of the Human Reproductive System
- The reproductive system produces haploid gametes, supports fertilization, and enables pregnancy and birth through male and female structures regulated by hormones. Testes produce sperm and testosterone, while ovaries produce ova, estrogen, and progesterone; fertilization restores the diploid chromosome number. Mitosis maintains body cells, whereas meiosis generates genetically unique haploid gametes essential for inheritance across generations.
- 13.9: Testes and Male Gamete Production
- The testes, housed in the scrotum, produce sperm and secrete testosterone. Within the seminiferous tubules, spermatogonia undergo mitosis and meiosis to form haploid spermatids, which mature through spermiogenesis into spermatozoa; Sertoli cells support developing germ cells, and Leydig cells produce testosterone. Mature sperm gain motility in the epididymis and are structurally specialized with a head (acrosome and nucleus), mitochondria-rich midpiece, and flagellum for movement.
- 13.10: Duct System and Accessory Glands
- Sperm leave the seminiferous tubules, mature and are stored in the epididymis, then travel through the ductus deferens, ejaculatory duct, and urethra during ejaculation. Along the way, accessory glands add seminal fluid: seminal vesicles provide fructose-rich, alkaline fluid; the prostate adds enzymes and protective secretions; and the bulbourethral glands supply lubricating mucus. Together these secretions form semen, which nourishes, protects, and transports sperm for successful delivery.
- 13.11: Hormonal Regulation of the Male Reproductive System
- Male reproductive function is regulated by the hypothalamic–pituitary–gonadal axis: GnRH from the hypothalamus stimulates the anterior pituitary to release LH and FSH. LH acts on Leydig cells to produce testosterone, while FSH supports Sertoli cells and spermatogenesis. Testosterone drives sperm production, male secondary sex characteristics, and reproductive development from fetal life through adulthood.
- 13.12: Ovaries and Female Gamete Production
- The ovaries, located on either side of the uterus, produce oocytes and the hormones estrogen, progesterone, and small amounts of testosterone. Oogenesis begins before birth with primary oocytes arrested in meiosis I. After puberty, one oocyte resumes meiosis each cycle, and a secondary oocyte is ovulated, completing meiosis II only if fertilized. Folliculogenesis is the process by which ovarian follicles grow and mature to support and prepare an oocyte for ovulation.
- 13.13: Uterus and Uterine Tubes — Structures That Support Fertilization and Pregnancy
- The uterine tubes capture and move the oocyte toward the uterus. Fertilization usually occurs in the ampulla. The uterus — made of perimetrium, myometrium, and hormonally responsive endometrium — supports implantation, pregnancy, and menstruation, while cervical mucus regulates sperm entry. Tubal scarring can impair fertility, and follicle depletion ultimately leads to menopause.
- 13.14: Hormonal Regulation of the Female Reproductive Cycles
- The menstrual cycle synchronizes ovarian events (follicular phase, ovulation, luteal phase) with uterine changes (proliferative and secretory phases) through FSH, LH, estrogen, and progesterone. Estrogen rebuilds the endometrium and triggers ovulation, while progesterone stabilizes it. Without pregnancy, hormone levels fall and menstruation begins.