BackChapters 24–27: The Urinary System, Fluid/Electrolyte & Acid-Base Homeostasis, Reproductive System, and Development
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Chapter 24: The Urinary System
Functions of the Urinary System
Homeostasis: Regulates blood composition, pH, volume, and pressure.
Excretion: Removes metabolic wastes, toxins, and drugs from the body.
Hormone Production: Erythropoietin (EPO) stimulates red blood cell production; Renin regulates blood pressure.
Components of the Urinary System
Kidneys (2): Produce urine.
Ureters (2): Transport urine from kidneys to bladder.
Urinary Bladder: Temporarily stores urine.
Urethra: Conducts urine out of the body.
Kidney Position and Structure
Retroperitoneal: Located behind the parietal peritoneum, against the posterior abdominal wall.
External Anatomy
Fibrous Capsule: Deep, dense irregular connective tissue; maintains shape.
Perinephric Fat Capsule: Middle, adipose tissue; cushions and protects.
Renal Fascia: Superficial, dense irregular connective tissue; anchors kidney.
Renal Hilum: Indentation for entry/exit of renal artery, vein, nerves, and ureter.
Internal Anatomy
Renal Cortex: Outer region; contains renal columns between pyramids.
Renal Medulla: Inner region; contains renal pyramids (base faces cortex, apex/papilla faces hilum).
Renal Pelvis: Funnel-shaped; collects urine from major calyces and channels to ureter.
Urine Flow: Renal Pyramid → Minor Calyx → Major Calyx → Renal Pelvis → Ureter
Renal Blood Flow
Arterial: Renal → Segmental → Interlobar → Arcuate → Cortical Radiate (Interlobular)
Venous: Cortical Radiate → Arcuate → Interlobar → Renal (no segmental vein)
Nephron Structure and Function
Nephron: Functional unit of the kidney; ~1 million per kidney.
Parts: Renal corpuscle (glomerulus + glomerular capsule) and renal tubule (PCT, nephron loop, DCT).
Types: Cortical (short loops, dilute urine, 80–85%) and Juxtamedullary (long loops, concentrated urine, 15–20%).
Filtrate and Blood Flow Through the Nephron
Filtrate Path: Glomerulus → Glomerular capsule → PCT → Descending limb → Ascending limb → DCT → Collecting duct → Papillary duct → Minor calyx → Major calyx → Renal pelvis → Ureter → Bladder → Urethra
Nephron Processes
Process | Direction | Main Location |
|---|---|---|
Filtration | Blood → Renal tubule | Renal corpuscle |
Reabsorption | Renal tubule → Blood | Mostly PCT |
Secretion | Blood → Renal tubule | PCT & DCT |
Renal Corpuscle Structure
Glomerulus: Capillary tuft with fenestrated (leaky) endothelium for filtration.
Glomerular Capsule (Bowman’s): Double-layered; parietal (outer, simple squamous) and visceral (inner, podocytes with foot processes forming filtration slits).
Mesangial Cells: Regulate filtration surface area by contraction/relaxation.
Filtration Rate Regulation
Promote Filtration: High glomerular blood pressure, fenestrated capillaries, relaxed mesangial cells.
Oppose Filtration: Capsular hydrostatic pressure, blood colloid osmotic pressure, contracted mesangial cells.
Net Filtration Pressure (NFP):
Glomerular Filtration Rate (GFR) Regulation
GFR: Volume of filtrate formed per minute (125 mL/min in males, 105 mL/min in females).
Renal Autoregulation: Adjusts arteriole diameters to maintain GFR.
Neural Regulation: Sympathetic vasoconstriction reduces GFR.
Hormonal Regulation: ANP increases GFR; Aldosterone (RAA pathway) decreases GFR.
Transport Mechanisms
Symporter: Moves two substances in the same direction (e.g., Na+/Glucose).
Antiporter: Moves substances in opposite directions (e.g., Na+/H+).
Nephron Loop Permeability
Descending Limb: Permeable to water, not solutes.
Ascending Limb: Permeable to solutes (Na+, K+, Cl-), not water.
Hormonal Control of Urine Output
Hormone | Effect on Urine |
|---|---|
ADH | Decreases urine, increases water reabsorption |
Aldosterone | Decreases urine, increases Na+ & water reabsorption |
ANP | Increases urine, decreases Na+ reabsorption |
PTH | Increases Ca2+ reabsorption, decreases phosphate reabsorption |
RAA Pathway
Low BP → Kidney releases renin → Converts angiotensinogen to angiotensin I → ACE converts to angiotensin II → Vasoconstriction, aldosterone & ADH release, increased Na+ and water reabsorption.
Juxtaglomerular Apparatus (JGA)
Macula Densa: Chemoreceptors in nephron loop sense NaCl.
Juxtaglomerular Cells: Smooth muscle in afferent arteriole; secrete renin in response to low BP.
Urine Composition and Abnormalities
Normal: Water, urea, uric acid, creatinine, ammonia.
Abnormal: Protein (albuminuria), glucose (glucosuria), RBCs (hematuria), bilirubin, ketones.
Urinary Bladder and Micturition
Bladder: Stores up to 1 L urine; rugae allow expansion.
Micturition Reflex: Bladder stretch → Parasympathetic stimulation → Detrusor contracts, internal sphincter relaxes (involuntary), external sphincter relaxes (voluntary) → Urine exits.
Chapter 25: Fluid, Electrolyte, and Acid-Base Homeostasis
Fluid Compartments
Intracellular Fluid (ICF): 2/3 of body water; inside cells.
Extracellular Fluid (ECF): 1/3 of body water; includes interstitial fluid (80%) and plasma (20%).
Water Content and Barriers
Body Water: 55–60% of adult body mass.
Barriers: Plasma membrane (ICF/ECF), blood vessel walls (plasma/interstitial fluid).
Electrolytes
Definition: Substances that dissociate into ions in water and conduct electricity.
Functions: Osmosis, acid-base balance, electrical currents, enzyme cofactors.
Major Ions: ECF: Na+ (cation), Cl- (anion); ICF: K+ (cation), HPO42- (anion).
Major Electrolyte Functions and Regulation
Ion | Function | Regulation |
|---|---|---|
Na+ | Muscle contraction, action potentials | RAA pathway, ANP |
K+ | Muscle contraction, action potentials | Aldosterone, epinephrine, insulin |
Ca2+ | Bone, muscle contraction, blood clotting | PTH, calcitriol |
Hormonal Regulation of Water and Electrolytes
Hormone | Released When | Kidney Effect | Urine Output |
|---|---|---|---|
ADH | High osmolarity, low BP | Reabsorbs water | ↓ |
Aldosterone | Low BP, low Na+, high K+ | Reabsorbs Na+, secretes K+ | ↓ |
ANP/BNP | High blood volume/stretch | Excretes Na+ and water | ↑ |
Water Balance
Gain: GI absorption, metabolic water (cellular respiration).
Loss: Kidneys (urine), GI tract (feces), skin (perspiration), lungs (water vapor).
Dehydration vs. Overhydration
Dehydration: Loss of 2% body mass; causes include sweating, vomiting, diarrhea.
Overhydration: Excess water intake, ADH hypersecretion, renal failure.
Acid-Base Balance
Acid: Releases H+; pH < 7.
Base: Accepts H+ or releases OH-; pH > 7.
pH:
ECF pH: 7.35–7.45 (acidosis < 7.35, alkalosis > 7.45).
Buffer Systems
Protein Buffer System: Most abundant in ICF and plasma (e.g., hemoglobin).
Carbonic Acid-Bicarbonate Buffer: Key in ECF;
Phosphate Buffer System: Important in ICF and urine.
Acid-Base Disorders and Compensation
Disorder | Cause | Compensation |
|---|---|---|
Respiratory Acidosis | ↑ CO2 | Hyperventilation |
Respiratory Alkalosis | ↓ CO2 | Hypoventilation |
Metabolic Acidosis | ↓ HCO3- or ↑ acids | Hyperventilation, kidneys excrete H+ |
Metabolic Alkalosis | ↑ HCO3- or loss of H+ | Hypoventilation, kidneys excrete HCO3- |
Respiratory and Renal Compensation
Lungs: High PCO2 → ↑ respiration (blow off CO2); Low PCO2 → ↓ respiration (retain CO2).
Kidneys: Acidosis → Excrete H+, reabsorb HCO3-; Alkalosis → Retain H+, excrete HCO3-.
Chapter 26: The Reproductive System
Functions of the Reproductive System
Produce gametes (sperm, ova).
Enable fertilization and support fetal development.
Produce sex hormones (testosterone, estrogen, progesterone).
Hormonal Regulation
GnRH (hypothalamus): Stimulates FSH and LH release from anterior pituitary.
Male Reproductive Anatomy
External: Penis (copulatory organ), scrotum (houses testes).
Internal: Testes (seminiferous tubules for sperm, Leydig cells for testosterone), ducts (epididymis, ductus deferens, ejaculatory duct, urethra), accessory glands (seminal vesicles, prostate, bulbourethral glands).
Spermatogenesis
Occurs in seminiferous tubules; 60–75 days; 1 primary spermatocyte → 4 sperm.
Sperm Anatomy: Head (nucleus, acrosome), midpiece (mitochondria), tail (flagellum).
Male Hormones
Hormone | Source | Function |
|---|---|---|
GnRH | Hypothalamus | Stimulates FSH & LH |
FSH | Anterior pituitary | Stimulates Sertoli cells, spermatogenesis |
LH | Anterior pituitary | Stimulates Leydig cells (testosterone) |
Testosterone | Leydig cells | Male traits, muscle/bone growth, spermatogenesis |
DHT | Converted from testosterone | External genitalia, prostate, hair |
ABP | Sertoli cells | Concentrates testosterone in tubules |
Inhibin | Sertoli cells | Inhibits FSH, slows spermatogenesis |
Female Reproductive Anatomy
Internal: Ovaries, uterine tubes, uterus, vagina.
External: Vulva (mons pubis, labia, clitoris, vestibule), mammary glands.
Oogenesis
Begins before birth; primary oocytes arrested in prophase I until puberty.
Each primary oocyte yields 1 ovum + 3 polar bodies; meiosis II completes only if fertilization occurs.
Female Hormones
Hormone | Function |
|---|---|
GnRH | Stimulates FSH and LH release |
FSH | Follicle and oocyte maturation |
LH | Triggers ovulation, forms corpus luteum |
Estrogen | Builds endometrium, secondary sex traits |
Progesterone | Maintains uterine lining for implantation |
Relaxin | Relaxes pelvic ligaments, softens cervix |
HCG | Maintains corpus luteum in early pregnancy |
Menstrual Cycle Overview (28 Days)
Menstrual Phase (1–5): Shedding of stratum functionalis; FSH stimulates follicle growth.
Proliferative Phase (6–13): Estrogen rebuilds endometrium; dominant follicle matures.
Ovulation (14): LH surge triggers oocyte release.
Secretory Phase (15–28): Corpus luteum secretes progesterone/estrogen; maintains endometrium.
Chapter 27: Development and Heredity
Oocyte Structure
Corona Radiata: Outer follicle cells; nourish/protect oocyte.
Zona Pellucida: Glycoprotein layer; sperm binding, blocks polyspermy.
Perivitelline Space: Between zona pellucida and oocyte.
Secondary Oocyte: Cell released at ovulation.
Fertilization and Early Development
Ovulation: LH surge releases secondary oocyte into uterine tube.
Fertilization: Sperm penetrates oocyte layers; membranes fuse; meiosis II completes; zygote forms.
Cleavage: Rapid mitosis; forms blastomeres, then morula (day 3), then blastocyst (days 5–6).
Implantation: Blastocyst embeds in endometrium (day 7).
Extraembryonic Membranes
Amnion: Fluid-filled sac; cushions embryo.
Yolk Sac: Early nutrient source, blood cell formation, GI tract origin.
Allantois: Forms umbilical vessels, urinary bladder.
Chorion: Outermost; forms chorionic villi, fetal placenta.
Gastrulation and Germ Layers
Day 12: Formation of three layers:
Ectoderm: Nervous system, skin epidermis.
Mesoderm: Muscles, bones, connective tissue, etc.
Endoderm: Epithelial linings of GI, respiratory, urogenital tracts.
Placenta and Hormones
Chorionic Villi: Increase surface area for exchange; form fetal side of placenta.
Placental Hormones:
hCG: Maintains corpus luteum, detected by pregnancy tests.
Placental Lactogen: Prepares breasts, increases nutrients for fetus.
Placental Prolactin: Prepares mammary glands for milk.
Relaxin: Relaxes pelvic ligaments, softens cervix.
Progesterone/Estrogen: Maintain endometrium, prevent contractions, stimulate uterine/breast growth.
Fetal Development and Birth
Organogenesis: Most organs form in first 8 weeks (embryonic period).
Fetus: Week 9 to birth (38 weeks).
Labor Stages:
Dilation: Cervix opens to 10 cm.
Expulsion: Delivery of baby.
Placental: Delivery of placenta.
"Water breaking": Rupture of amniotic sac.
Episiotomy: Surgical incision to enlarge vaginal opening during delivery.
High-Yield Exam Facts
LH surge → Ovulation
Fertilization occurs in the ampulla of the uterine tube
Three germ layers: ectoderm, mesoderm, endoderm
Stages of labor: Dilation → Expulsion → Placental
hCG maintains corpus luteum early in pregnancy
