18 & 19. Urinary and Reproductive Systems

A comprehensive vocabulary review covering renal anatomy, nephron mechanics, and male and female reproductive anatomy, physiology, and estrous cycles.

Nephron

The smallest functional unit of the kidney, located across the renal cortex and renal medulla, responsible for filtration, reabsorption, and secretion.

Filtration (Renal)

The passive process occurring in the glomerulus where blood plasma is separated from blood cells and large proteins and directed into the proximal convoluted tubule.

Reabsorption (Renal)

The process where recyclable products, ions, water, and nutrients pass from the nephron tubules back into the surrounding peritubular capillaries to remain in circulation.

Secretion (Renal)

The selective movement of retained waste products from the peritubular capillaries directly into the nephron tubules for elimination from the body via urine.

Retroperitoneal Space

The anatomical region dorsal to the peritoneal cavity and adjacent to the spine where the kidneys are positioned.

Renal Capsule

The thin, outermost fibrous and adipose tissue layer that covers and protects the exterior surface of the kidney.

Renal Cortex

The superficial kidney layer situated directly beneath the renal capsule and external to the renal pyramids, containing the renal corpuscles and convoluted tubules.

Renal Medulla

The deep kidney layer located immediately beneath the renal cortex that contains the triangular renal pyramids.

Renal Pelvis

The innermost elastic, funnel-shaped cavity of the kidney that gathers newly formed urine from the collecting ducts and channels it into the ureter.

Hilum (Kidney)

The medial concave notch where renal blood vessels, nerves, and the ureter enter and leave the kidney, opening directly into the renal pelvis.

Detrusor Muscle

The smooth muscle tissue comprising the muscularis layer of the urinary bladder wall that contracts in response to parasympathetic stimulation to empty the bladder.

Micturition

The physiological act of urination, during which the detrusor muscle contracts and the internal urinary sphincter relaxes to discharge urine through the urethra.

Renal Corpuscle

The initial blood-filtering component of a nephron, consisting of the glomerulus and its surrounding Bowman's capsule.

Podocytes

Specialized simple squamous epithelial cells within the visceral layer of the glomerular membrane that wrap around capillaries and interlock to create filtration slits.

Glomerular Filtration Rate (GFR)

The total volume of fluid filtered from the glomerular capillaries into Bowman's capsule per minute, tracked clinically to gauge kidney health.

Proximal Convoluted Tubule (PCT)

The highly twisted segment of the nephron receiving filtrate from the glomerulus, lined with tall cuboidal brush-border cells containing abundant mitochondria to power active reabsorption.

Loop of Henle

The U-shaped hairpin loop of the nephron consisting of a descending limb that reabsorbs water and an ascending limb that reabsorbs sodium chloride.

Distal Convoluted Tubule (DCT)

The shorter nephron segment following the loop of Henle, lined with cuboidal cells without brush borders, which conducts fine-tuned reabsorption and forms the juxtaglomerular apparatus.

Juxtaglomerular Apparatus

A cellular complex located where the distal convoluted tubule passes between the afferent and efferent arterioles that senses blood pressure changes and secretes renin during hypotension.

Collecting Duct

The terminal tubular system that pools urine from multiple distal convoluted tubules, concentrates the filtrate by reabsorbing water, and delivers it to the renal pelvis.

Aquaporins

Transmembrane channel proteins that facilitate passive water transport across cell membranes, concentrated primarily within the collecting duct and distal convoluted tubule.

Anti-Diuretic Hormone (ADH)

A pituitary hormone that regulates water retention by mobilizing aquaporins from an inert state to an active intramembrane position on the apical surface of collecting duct cells.

Renin-Angiotensin-Aldosterone System (RAAS)

A homeostatic hormonal pathway triggered by the juxtaglomerular apparatus during hypotension that elevates blood pressure through vasoconstriction, fluid volume expansion, and sodium retention.

Blood-Urea Nitrogen (BUN)

A blood test measuring the nitrogen content of circulating urea, an amino acid breakdown byproduct excreted by functional kidneys.

Urine Specific Gravity (USG)

A diagnostic measurement of urine concentration; initial glomerular filtrate measures between $1.008$ and $1.012$, whereas normal excreted urine typically ranges from $1.001$ to $1.060$ (normally above $1.015$).

Waxy Casts

Microscopic cylindrical protein structures identified in urine sediment that develop under conditions of severely reduced tubular urine flow, pointing to chronic renal failure.

Calcium Oxalate Dihydrate Crystals

Envelope-shaped microscopic crystals in urine sediment whose formation is favored by an abnormally acidic urine pH.

Meiosis

The specialized type of cell division restricted to gamete formation that halves the chromosomal content from diploid to haploid through two successive nuclear divisions.

Diploid ($2n$)

A cell that possesses two complete sets of homologous chromosomes, replicates via mitosis, and contains the identical chromosome count as its progenitor cell.

Haploid ($n$)

A cell containing exactly one single set of chromosomes, produced through meiosis and characteristic of mature reproductive gametes.

Spermatozoa

The mature, motile male gametes that carry either an $X$ or a $Y$ chromosome, thereby determining the genetic sex of the resulting zygote upon fertilization.

Spermatogenesis

The complete developmental sequence occurring in the seminiferous tubules wherein diploid spermatogonia divide and differentiate into spermatozoa.

Spermiogenesis

The final stage of spermatogenesis in which spherical spermatids undergo metamorphosis, shed excess cytoplasm, and develop a flagellum (tail) for motility.

Scrotum

The external cutaneous sac that holds and suspends the testes outside the body cavity, lined with smooth muscle that contracts in response to cold to regulate testicular temperature.

Seminiferous Tubules

The tightly coiled tubular units within the testicular lobules where early spermatogenesis progresses from the basal lamina inward to the central lumen.

Sertoli Cells

Somatic nurse cells within the seminiferous epithelium that physically encompass, protect, and nourish germ cells throughout their development.

Leydig Cells

Interstitial endocrine cells residing in the connective tissue spaces outside the seminiferous tubules that synthesize and secrete androgens.

Epididymis

The coiled duct lining the testis, lined with stereocilia, that stores immature spermatozoa, resorbs excess fluid, and facilitates sperm maturation and mitochondrial acquisition.

Vas Deferens

The muscular conduit traveling within the spermatic cord through the inguinal ring that propels spermatozoa from the epididymis toward the ejaculatory duct.

Prostate Gland

An accessory male reproductive gland surrounding the pelvic urethra that produces alkaline secretions for seminal fluid; prone to hypertrophy and urethral obstruction in intact males.

Seminal Vesicles

Accessory reproductive glands that secrete nutritive fluids into seminal fluid; completely absent in canine and feline species.

Bulbourethral Glands

Paired accessory glands that discharge a lubricating mucous fluid into the urethra prior to ejaculation; completely absent in dogs.

Bulbus Glandis

An erectile vascular expansion located on the ventrocaudal aspect of the canine penis that engorges with blood during copulation to produce the copulatory tie.

Sigmoid Flexure

The S-shaped anatomical curve of the penis found in bulls and other ruminants, maintained by the retractor penis muscle, that straightens during erection to protrude the penis.

Penile Spines

Keratinized backwards-pointing papillae on the glans penis of tomcats that stimulate vaginal nerve endings to trigger neuroendocrine-mediated ovulation.

Oogenesis

The developmental sequence by which female germ cells differentiate within the ovary into primary oocytes, secondary oocytes, and mature ova.

Ovarian Cortex

The outer functional zone of the ovary housing developing ovarian follicles at various maturation stages embedded in cellular stroma.

Ovarian Medulla

The central vascular core of the ovary containing loose connective tissue, nerves, lymphatic vessels, and blood vessels.

Granulosa Cells

Endocrine epithelial cells lining the ovarian follicle that nourish the developing oocyte and convert androgens into estrogen under FSH influence.

Uniparous

A reproductive classification describing species (such as humans and horses) that normally produce a single offspring per gestational period from a single dominant follicle.

Multiparous

A reproductive classification describing species (such as dogs, cats, and swine) that ovulate multiple follicles simultaneously to yield litters.

Ovulation

The explosive rupture of a mature ovarian follicle triggered by an LH surge, releasing a secondary oocyte into the peritoneal space near the fallopian tube.

Corpus Luteum

A temporary endocrine structure that forms from the collapsed follicular wall post-ovulation, secreting progesterone to support pregnancy and suppress LH and FSH.

Infundibulum

The funnel-shaped cranial expansion of the oviduct edged with fringed fimbriae that sweeps over the ovary to catch the discharged oocyte.

Metritis

Severe pathological inflammation involving the muscular and endometrial layers of the uterine wall.

Estrous Cycle

The physiological reproductive cycle in domestic mammals characterized by periodic phases of sexual receptivity (estrus) and endometrial resorption in the absence of conception.

Polyestrous

An estrous pattern defined by continuous, recurring cycles throughout the calendar year, seen in cattle and swine.

Seasonally Polyestrous

An estrous cycle pattern wherein repeated cycles occur only during specific seasons of the year, characteristic of horses, sheep, and cats.

Diestrous

An estrous cycle schedule characterized by exactly two distinct cycles per calendar year, seen in dogs.

Monoestrous

An estrous pattern characterized by a single reproductive cycle occurring once per year, characteristic of foxes and minks.

Proestrus

The follicular preparatory phase of the estrous cycle during which ovarian follicles enlarge, estrogen output increases, and vaginal epithelial cells undergo cornification.

Estrus

The period of true physiological and behavioral 'heat' marked by peak estrogen levels, surges in LH and FSH, and willingness to accept mating.

Metestrus

The post-ovulatory phase of the estrous cycle during which the corpus luteum begins forming, the vaginal cornified layer sheds, and the uterine endometrium thickens.

Diestrus

The active luteal stage of the estrous cycle dominated by high progesterone secretion from the established corpus luteum; terminates via prostaglandin-induced luteolysis if pregnancy does not occur.

Anestrus

A temporary interval of complete reproductive quiescence during which the ovarian and estrous cycles are suspended.