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22 The Respiratory System The Respiratory System • Basic functions of the respiratory system • Supplies body with oxygen • Disposes of carbon dioxide • Four processes involved in respiration • Pulmonary ventilation • External respiration • Transport of respiratory gases • Internal respiration Functional Anatomy of the Respiratory System • Respiratory organs • Nose, nasal cavity, and paranasal sinuses • Pharynx, larynx, and trachea • Bronchi and smaller branches • Lungs and alveoli Organs of the Respiratory System • Divided into • Conducting zone • Respiratory zone The Nose • Provides an airway for respiration • Moistens and warms air • Filters inhaled air • Resonating chamber for speech • Houses olfactory receptors The Nose • Size variation due to differences in nasal cartilages • Skin is thin—contains many sebaceous glands The Nasal Cavity • External nares—nostrils • Divided by nasal septum • Continuous with nasopharynx • Posterior nasal apertures—choanae Nasal Cavity • Two types of mucous membrane • Olfactory mucosa • Near roof of nasal cavity • Houses olfactory (smell) receptors • Respiratory mucosa • Lines nasal cavity • Epithelium is pseudostratified ciliated columnar The Upper Respiratory Tract Respiratory Mucosa • Consists of • Pseudostratified ciliated columnar epithelium • Goblet cells within epithelium • Underlying layer of lamina propria • Cilia move contaminated mucus posteriorly Nasal Conchae • Superior and middle nasal conchae • Part of the ethmoid bone • Inferior nasal conchae • Separate bone • Project medially from the lateral wall of the nasal cavity • Particulate matter • Deflected to mucus-coated surfaces The Pharynx • Funnel-shaped passageway • Connects nasal cavity and mouth • Divided into three sections by location • Nasopharynx • Oropharynx • Laryngopharynx • Type of mucosal lining changes along its length The Nasopharynx • Superior to the point where food enters • Only an air passageway • Closed off during swallowing • Pharyngeal tonsil (adenoids) • Located on posterior wall • Destroys entering pathogens • Contains the opening to the pharyngotympanic tube (auditory tube) • Tubal tonsil • Provides some protection from infection The Oropharynx • Arch-like entranceway—fauces • Extends from soft palate to the epiglottis • Epithelium • Stratified squamous epithelium • Two types of tonsils in the oropharynx • Palatine tonsils—in the lateral walls of the fauces • Lingual tonsils—covers the posterior surface of the tongue The Laryngopharynx • Passageway for both food and air • Epithelium • Stratified squamous epithelium • Continuous with the esophagus and larynx 22 The Respiratory System The Larynx • Three functions • Voice production • Provides an open airway • Routes air and food into the proper channels • Superior opening is • Closed during swallowing • Open during breathing Nine Cartilages of the Larynx • Thyroid cartilage • Shield-shaped, forms laryngeal prominence (Adam’s apple) • Three pairs of small cartilages • Arytenoid cartilages • Corniculate cartilages • Cuneiform cartilages • Epiglottis • Tips inferiorly during swallowing The Larynx • Vocal ligaments of the larynx • Vocal folds (true vocal cords) • Act in sound production • Vestibular folds (false vocal cords) • No role in sound production • Epithelium of the larynx • Stratified squamous—superior portion • Pseudostratified ciliated columnar—inferior portion The Larynx • Voice production • Length of the vocal folds changes with pitch • Loudness depends on the force of air across the vocal folds • Sphincter function of the larynx • Valsalva’s maneuver—straining • Innervation of the larynx • Recurrent laryngeal nerves (branch of vagus) The Trachea • Descends into the mediastinum • C-shaped cartilage rings keep airway open • Carina • Marks where trachea divides into two primary bronchi • Epithelium • Pseudostratified ciliated columnar The Trachea Bronchi in the Conducting Zone • Bronchial tree • Extensively branching respiratory passageways • Primary bronchi (main bronchi) • Largest bronchi • Right main bronchi • Wider and shorter than the left Bronchi in the Conducting Zone • Secondary (lobar) bronchi • Three on the right • Two on the left • • • Tertiary (segmental) bronchi • Branch into each lung segment Bronchioles • Little bronchi, less than 1 mm in diameter Terminal bronchioles • Less than 0.5 mm in diameter Changes in Tissue Composition along Conducting Pathways • Supportive connective tissues change • C-shaped rings replaced by cartilage plates • Epithelium changes • First, pseudostratified ciliated columnar • Replaced by simple columnar, then simple cuboidal epithelium • Smooth muscle becomes important • Airways widen with sympathetic stimulation • Airways constrict under parasympathetic direction Structures of the Respiratory Zone • Consists of air-exchanging structures • Respiratory bronchioles—branch from terminal bronchioles • Lead to alveolar ducts • Lead to alveolar sacs Structures of the Respiratory Zone • Alveoli • ~300 million alveoli account for tremendous surface area of the lungs • Surface area of alveoli is ˜140 square meters Structures of the Respiratory Zone • Structure of alveoli • Type I cells—single layer of simple squamous epithelial cells • Surrounded by basal lamina • Alveolar and capillary walls plus their basal lamina form • Respiratory membrane Structures of the Respiratory Zone • Structures of alveoli (continued) • Type II cells—scattered among type I cells • Are cuboidal epithelial cells • Secrete surfactant • Reduces surface tension within alveoli • Alveolar macrophages 22 The Respiratory System Anatomy of Alveoli and the Respiratory Membrane Anatomy of Alveoli and the Respiratory Membrane The Respiratory Zone • Features of alveoli • Surrounded by elastic fibers • Interconnect by way of alveolar pores • Internal surfaces • A site for free movement of alveolar macrophages Gross Anatomy of the Lungs • Major landmarks of the lungs • Apex, base, hilum, and root • Left lung • Superior and inferior lobes • Fissure—oblique • Right lung • Superior, middle, and inferior lobes • Fissures—oblique and horizontal Gross Anatomy of the Lungs Anterior View of Thoracic Structures Bronchopulmonary Segments Blood Supply and Innervation of the Lungs • Pulmonary arteries • Deliver oxygen-poor blood to the lungs • Pulmonary veins • Carry oxygenated blood to the heart • Innervation • Sympathetic, parasympathetic, and visceral sensory fibers • Parasympathetic—constrict airways • Sympathetic—dilate airways 22 The Respiratory System Transverse Cut through the Superior Thorax The Pleurae • A double-layered sac surrounding each lung • Parietal pleura • Visceral pleura • Pleural cavity • Potential space between the visceral and parietal pleurae • Pleurae help divide the thoracic cavity • Central mediastinum • Two lateral pleural compartments Diagram of the Pleurae and Pleural Cavities Location of Lungs in Thoracic Cavity The Mechanisms of Ventilation • Two phases of pulmonary ventilation • Inspiration—inhalation • Expiration—exhalation Inspiration • Volume of thoracic cavity increases • Decreases internal gas pressure • Action of the diaphragm • Diaphragm flattens • Action of intercostal muscles • Contraction raises the ribs Inspiration • Deep inspiration requires • • • • Scalenes Sternocleidomastoid Pectoralis minor Erector spinae—extends the back Expiration • Quiet expiration—chiefly a passive process • Inspiratory muscles relax • Diaphragm moves superiorly • Volume of thoracic cavity decreases • Forced expiration—an active process • Produced by contraction of • Internal and external oblique muscles • Transverse abdominis muscles Changes in Thoracic Volume 22 The Respiratory System Neural Control of Ventilation • Most important respiratory center • VRG—ventral respiratory group • Located in reticular formation in the medulla oblongata • Neurons generate respiratory rhythm Respiratory Centers in the Brain Stem Neural Control of Ventilation • Respiratory center • Generates baseline respiration rate • In the reticular formation of the medulla oblongata • Chemoreceptors • Sensitive to rising and falling oxygen levels • Central chemoreceptors—located in medulla • Peripheral chemoreceptors • Aortic bodies • Carotid bodies Location of Peripheral Chemoreceptors Disorders of Lower Respiratory Structures • Bronchial asthma • A type of allergic inflammation • Hypersensitivity to irritants in the air or to stress • Asthma attacks characterized by • Contraction of bronchiole smooth muscle • Secretion of mucus in airways Disorders of Lower Respiratory Structures • Cystic fibrosis (CF)—inherited disease • Exocrine gland function is disrupted • Respiratory system affected by • Oversecretion of viscous mucus 23 The Digestive System Overview of the Digestive System • Organs are divided into two groups • Alimentary canal • Mouth, pharynx, and esophagus • Stomach, small intestine, and large intestine • Accessory digestive organs • Teeth and tongue • Gallbladder, salivary glands, liver, and pancreas • Accessory organs are connected to the alimentary canal by ducts • Secretions contribute to breakdown of foodstuffs The Alimentary Canal and Accessory Digestive Organs Digestive Processes • Ingestion—occurs in the mouth • Propulsion—movement of food • Peristalsis—major means of propulsion • Mechanical digestion—prepares food for chemical digestion • Chewing, churning food in stomach, segmentation • Segmentation is rhythmic local constrictions of intestine Digestive Processes • Chemical digestion—complex molecules broken down to chemical components • Mouth • Stomach • Small intestine • Absorption—transport of digested nutrients • Defecation—elimination of indigestible substances as feces Digestive Processes Peristalsis • Major means of propulsion • Adjacent segments of the alimentary canal relax and contract Segmentation • Rhythmic local contractions of the intestine • Mixes food with digestive juices Abdominal Regions • Four lines divide abdominal wall into nine regions • Midclavicular lines—vertical lines of grid • Subcostal plane—superior horizontal line • Connects inferior points of costal margin • Transtubercular plane—inferior horizontal line • Connects tubercles of iliac crests Nine Regions of Anterior Abdominal Surface • How regions relate to abdominal viscera Abdominal Quadrants • A simpler method of sectioning the anterior abdominal wall • Right upper quadrant • Left upper quadrant • Right lower quadrant • Left lower quadrant The Peritoneal Cavity and Peritoneum • Peritoneum—a serous membrane • Visceral peritoneum—surrounds digestive organs • Parietal peritoneum—lines the body wall • Peritoneal cavity—a slit-like potential space The Peritoneal Cavity and Peritoneum • Mesentery—a double layer of peritoneum • Holds organs in place • Sites of fat storage • Provides a route for circulatory vessels and nerves The Peritoneal Cavity and Peritoneum • Retroperitoneal organs • Behind the peritoneum • Peritoneal organs • Digestive organs that keep their mesentery Mesenteries • Superficial view of abdominal organs Mesenteries • Lesser omentum attaches to lesser curvature of stomach Mesenteries • • Greater omentum—a “fatty apron” of peritoneum Greater omentum and transverse colon reflected Mesenteries • Sagittal section through the abdominopelvic cavity • Mesenteries attach to posterior abdominal wall Secondarily Retroperitoneal Organs • Initially formed within peritoneum • Become retroperitoneal • Fuse to posterior abdominal wall Summary of Intraperitoneal and Secondarily Retroperitoneal Organs Histology of the Alimentary Canal Wall • Same four layers from esophagus to anus • The mucosa—innermost layer • Consists of • Epithelium • Lamina propria • Muscularis mucosae • The submucosa—external to the mucosa • Contains blood and lymphatic vessels, nerve fibers Histology of the Alimentary Canal Wall • The muscularis externa—external to the submucosa • Two layers • Circular muscularis—inner layer • Longitudinal muscularis—outer layer • The serosa—the outermost layer • Is the visceral peritoneum Smooth Muscle • Primarily found in walls of viscera • Fibers elongated • Have one centrally located nucleus • Grouped into sheets • Longitudinal layer—parallel to long axis of organ • Circular layer—deeper layer, fibers run around circumference of organ Smooth Muscle Contraction • Myofilaments operate by interaction with cytoskeleton • Dense bodies—correspond to Z-discs of skeletal muscle Innervation of Smooth Muscle • Innervated by ANS • Few fibers per sheet innervated • Sheet of smooth muscle contracts as a unit • Exceptions • Iris of eye • Arrector pili muscles in skin Nerve Plexuses • Myenteric nerve plexus • Lies between circular and longitudinal muscularis • Controls peristalsis and segmentation • Submucosal nerve plexus • Lies in submucosa • Signals glands to secrete • Innervation • Sympathetic and parasympathetic motor fibers • Visceral sensory fibers 23 The Digestive System The Mouth and Associated Organs • The mouth—oral cavity • Mucosal layer • Stratified squamous epithelium • Lamina propria • The lips and cheeks • Formed from orbicularis oris and buccinator muscles, respectively Anatomy of the Mouth • The labial frenulum • Connects lips to gum • The palate • Forms the roof of the mouth The Tongue • Interlacing fascicles of skeletal muscle • Grips food and repositions it • Helps form some consonants • • • Intrinsic muscles—within the tongue Extrinsic muscles—external to the tongue Lingual frenulum • Secures tongue to floor of mouth The Superior Surface of the Tongue • Tongue papillae • Filiform papillae—no taste buds • Fungiform papillae • Circumvallate papillae • Sulcus terminalis • Marks border between mouth and pharynx • Posterior one-third of tongue lies in oropharynx • Lined with lingual tonsil The Teeth • Deciduous teeth—20 teeth • First appear at 6 months of age • Permanent teeth—32 teeth • Most erupt by the end of adolescence • Dental formula—shorthand • Way to indicate number and position of teeth • 2I, 1C, 2P, 3M Tooth Structure • Longitudinal section of tooth in alveolus The Salivary Glands • Produce saliva • Compound tubuloalveolar glands • Parotid glands • Parotid duct—parallel to zygomatic arch • Contains only serous cells • Submandibular glands • Lies along medial surface of mandible • Sublingual glands • Lies in floor of oral cavity • Contains primarily mucous cells The Salivary Glands The Pharynx • Oropharynx and laryngopharynx • Passages for air and food • Lined with stratified squamous epithelium • External muscle layer • Consists of superior, middle, and inferior pharyngeal constrictors The Esophagus • Gross anatomy—muscular tube • Begins as a continuation of the pharynx • Joins the stomach inferior to the diaphragm • Cardiac sphincter—closes lumen to prevent stomach acid from entering esophagus The Esophagus • Microscopic anatomy • Epithelium is stratified squamous epithelium • When empty, mucosa and submucosa in longitudinal folds • Mucous glands—primarily compound tubuloalveolar glands • Muscularis externa • Skeletal muscle first third of length • Adventitia—most external layer The Stomach • Site where food is churned into chyme • Secretion of pepsin begins protein digestion • Functions under acidic conditions • Food remains in stomach approximately 4 hours • Regions of the stomach • Cardiac region • Fundus • Body • Pyloric region Microscopic Anatomy of the Stomach • Muscularis has three layers • Circular and longitudinal layers and oblique layer • Epithelium is simple columnar epithelium • Mucosa dotted with gastric pits • Gastric glands—deep to gastric pits Microscopic Anatomy of the Stomach • Gastric glands of fundus and body • Mucous neck cells • Secrete a special mucus • Parietal (oxyntic) cells • Secrete hydrochloric acid and gastric intrinsic factor • Chief (zymogenic) cells • Secrete pepsinogen • Pepsinogen is activated to pepsin when it encounters acid in the gastric glands The Small Intestine—Gross Anatomy • Longest portion of the alimentary canal • Site of most enzymatic digestion and absorption • Three subdivisions • Duodenum • Jejunum • Ileum • Innervation • Parasympathetic fibers from vagus nerve • Sympathetic from thoracic splanchnic nerves The Duodenum • Receives digestive enzymes and bile • Main pancreatic duct and common bile duct enter duodenum • Sphincters control entry of bile and pancreatic juices The Small Intestine—Microscopic Anatomy • Modifications for absorption • Circular folds (plicae circulares) • Transverse ridges of mucosa and submucosa • Villi • Finger-like projections of the mucosa • Covered with simple columnar epithelium • Microvilli • Further increase surface area for absorption Histology of the Intestinal Wall • Absorptive cells • Uptake digested nutrients • Goblet cells • Secrete mucus that lubricates chyme • Enteroendocrine cells • Secrete hormones • Intestinal crypts • Epithelial cells secrete intestinal juice 23 The Digestive System The Large Intestine • Digested residue contains few nutrients • Small amount of digestion by bacteria • Main functions • Absorb water and electrolytes • Mass peristaltic movements force feces toward the rectum Gross Anatomy of Large Intestine • Subdivided into • Cecum, vermiform appendix, colon, rectum, anal canal • Special features of large intestine • Teniae coli • Thickening of longitudinal muscularis • Haustra • Puckering created by teniae coli • Epiploic appendages • Fat-filled pouches of visceral peritoneum Gross Anatomy of Large Intestine • Cecum • Blind pouch • Beginning of large intestine • Vermiform appendix • Contains lymphoid tissue • Neutralizes pathogens • Colon • Divided into distinct segments • Ascending, transverse, descending, and sigmoid colon Gross Anatomy of Large Intestine • Rectum • Descends along the inferior half of the sacrum • Anal canal • The last subdivision of the large intestine • Lined with stratified squamous epithelium Vessels and Nerves of the Large Intestine • First half of large intestine • Arterial supply—superior mesenteric artery • Innervation • Sympathetic innervation—superior mesenteric and celiac ganglia • Parasympathetic innervation—vagus nerve Vessels and Nerves of the Large Intestine • Distal half of large intestine • Arterial supply—inferior mesenteric artery • Innervation • Sympathetic innervation—inferior mesenteric and hypogastric plexuses • Parasympathetic innervation—pelvic splanchnic nerves Microscopic Anatomy of Large Intestine • Villi are absent • Contains numerous goblet cells • Intestinal crypts—simple tubular glands • Lined with simple columnar epithelial tissue • Epithelium changes at anal canal • Becomes stratified squamous epithelium The Liver • Largest gland in the body • Performs over 500 functions • Digestive function • Bile production • Performs many metabolic functions The Liver Microscopic Anatomy of the Liver • Hepatocyte—functional cells of the liver • Portal triad composed of • Bile duct tributary • Branch of hepatic portal vein • Branch of hepatic artery • Kupffer cells—destroy bacteria Microscopic Anatomy of the Liver • Some functions of hepatocytes • Rough ER manufactures blood proteins • Smooth ER produces bile salts, detoxifies poisons • • • • • Peroxisomes detoxify poisons (alcohol) Golgi apparatus packages secretory products Mitochondria provide energy for liver processes Glycosomes store sugar Great capacity for regeneration The Gallbladder • Stores and concentrates bile • Expels bile into duodenum • Bile emulsifies fats • Cholecystokinin—released from enteroendocrine cells in response to fatty chyme The Gallbladder 23 The Digestive System The Pancreas • Exocrine function • Acinar cells make, store, and secrete pancreatic enzymes • Enzymes are activated in the duodenum • Endocrine function • Produces insulin and glucagon • Regulates blood sugar The Exocrine Pancreas: Histology Peptic Ulcers • Are erosions of the mucosa of a region of the alimentary canal • Gastric ulcers • Occur in pyloric region of the stomach • Duodenal ulcers • Occur in duodenum of the small intestine Peptic Ulcers • Caused by Helicobacter pylori • H. pylori • Acid-resistant • Binds to gastric epithelium • Induces oversecretion of acid and inflammation Peptic Ulcers Disorders of the Digestive System • Intestinal obstruction • Mechanical obstructions • Adhesions, tumors, or foreign objects • Nonmechanical obstruction • Halt in peristalsis • Trauma • Intestines touched during surgery Disorders of the Digestive System • Inflammatory bowel disease • Inflammation of intestinal wall • Crohn’s disease • Ulcerative colitis • Viral hepatitis • Jaundice and flu-like symptoms • Major types—A, B, C, and G Disorders of the Digestive System • Cystic fibrosis and the pancreas • Pancreatic ducts become blocked with mucus • Clogged ducts prevent pancreatic juices from entering small intestine • Leads to malabsorption of fats and other nutrients Embryonic Development of the Digestive System • Alimentary canal formed in week 3 • Encloses tubular portion of yolk sac • Vitelline duct • Landmark dividing into three regions • Forgut • Midgut • Hindgut Embryonic Development of the Digestive System The Digestive System in Later Life • Middle age—gallstones and ulcers • Old age—activity of digestive organs decline • Fewer digestive juices and enzymes produced • Absorption is less efficient • Dehydration of fecal mass leads to constipation • Diverticulosis and cancer of digestive organs 24 The Urinary System The Urinary System • Important functions of the kidneys • Maintain the chemical consistency of blood • Filter many liters of fluid from blood • Send toxins, metabolic wastes, and excess water out of the body • Main waste products • Urea • Uric acid • Creatinine Organs of the Urinary System • Kidneys • Ureters • Urinary bladder • Urethra Organs of the Urinary System Location and External Anatomy of Kidneys • Located retroperitoneally • Lateral to T12–L3 vertebrae • Average kidney is 12 cm tall, 6 cm wide, 3 cm thick • Hilum • On concave surface • Vessels and nerves enter and exit • Fibrous capsule surrounds the kidney • Perirenal fat—external to renal capsule • Renal fascia—external to perirenal fat Internal Gross Anatomy of the Kidneys • Frontal section through the kidney • Renal cortex • Renal pyramids • Renal pelvis • Major calicies • Minor calicies • Gross vasculature • Renal arteries branch into segmental arteries • Segmental arteries branch into interlobar arteries • Arcuate arteries branch from interlobar arteries Internal Gross Anatomy of the Kidneys • Nerve supply—renal plexus • A network of autonomic fibers • An offshoot of the celiac plexus • Supplied by sympathetic fibers from • Lowest thoracic splanchnic nerve • First lumbar splanchnis nerve Mechanisms of Urine Production • Filtration • Filtrate of blood leaves kidney capillaries • Reabsorption • Most nutrients, water, and essential ions reclaimed • Secretion • Active process of removing undesirable molecules Nephron Structure • Nephron is composed of • Renal corpuscle • Renal tubule 24 The Urinary System The Nephron • Renal corpuscle—first part of nephron • Glomerulus and glomerular capsule • Glomerulus—tuft of capillaries • Capillaries of glomerulus are fenestrated • Glomerular (Bowman’s) capsule • Parietal layer—simple squamous epithelium • Visceral layer—consists of podocytes Filtration Membrane • The filtration membrane • Filter that lies between blood in the glomerulus and capsular space • Consists of three layers 1.Endothelium of the capillary 2.Slits between foot processes of podocytes 3.Basement membrane Filtration Membrane • Basement membrane and slit diaphragm • Hold back most proteins • Allow through • Water • Ions • Glucose • Amino acids • Urea Renal Corpuscle and the Filtration Membrane Renal Corpuscle and the Filtration Membrane Renal Tubule • Filtrate proceeds to renal tubules from glomerulus • Proximal convoluted tubule • Nephron loop • Descending limb • Thin segment • Thick segment • Distal convoluted tubule • Collecting ducts • Receive urine from several nephrons • Play an important role in conserving body fluids Classes of Nephron • Cortical nephrons • 85% of nephrons • Juxtamedullary nephrons • 15% of nephrons • Contribute to kidney’s ability to concentrate urine Blood Vessels Associated with Nephrons • Nephrons associate closely with two capillary beds • Glomeruli • Peritubular capillaries in cortical nephrons or vasa recta in juxtamedullary nephrons Blood Vessels Associated with Nephrons • Glomeruli • Produce filtrate that becomes urine • Fed and drained by arterioles • Afferent and efferent arteriole • Efferent arteriole has a smaller diameter than afferent arteriole • Generate 1 liter of fluid every 8 minutes • 99% of filtrate is resorbed by tubules Blood Vessels Associated with Nephrons • Peritubular capillaries • Arise from the efferent arterioles • Are adapted for absorption • Low-pressure, porous capillaries • All molecules secreted by nephrons into urine are from peritubular capillaries Blood Vessels Associated with Nephrons • Vasa recta • Continue from efferent arterioles of juxtamedullary nephrons • Are thin-walled looping vessels • Descend into the medulla • Are part of the kidney’s urine concentrating mechanism 24 The Urinary System Juxtaglomerular Apparatus • Juxtaglomerular apparatus • Functions in regulating blood pressure • An area of specialized contact between terminal end of the ascending limb and afferent arteriole • Granular cells—modified smooth muscle cells with secretory granules • Contain the hormone renin • Renin—secreted in response to falling BP in afferent arteriole Juxtaglomerular Apparatus • Macula densa—end of nephron loop • Adjacent to granular cells • Tall, closely packed epithelial cells • Monitor solute concentration in the filtrate • Signal granular cells to secrete renin • Initiates renin-angiotensin mechanism Juxtaglomerular Apparatus • • Mesangial cells • Located around base of the glomerulus • Regulated blood flow within the glomerulus Extraglomerular mesangial cells • Interact with macula densa and granular cells • Help regulate blood pressure Ureters • Carry urine from the kidneys to the urinary bladder • Oblique entry into bladder prevents backflow of urine • Histology of ureter • Mucosa—transitional epithelium • Muscularis—two layers • Inner longitudinal layer • Outer circular layer • Adventitia—typical connective tissue Ureters Urinary Bladder • A collapsible muscular sac • Stores and expels urine • Full bladder—spherical • Expands into the abdominal cavity • Empty bladder—lies entirely within the pelvis Urinary Bladder • Urachus—closed remnant of the allantois • Prostate gland • In males • Lies directly inferior to the bladder • Surrounds the urethra Urinary Bladder • Urinary bladder is composed of three layers 1. Mucosa—transitional epithelium 2. Thick muscular layer—detrusor muscle 3. Fibrous adventitia Urethra • Epithelium of urethra • Transitional epithelium • At the proximal end (near the bladder) • Stratified and pseudostratified columnar—mid urethra (in males) • Stratified squamous epithelium • At the distal end (near the urethral opening) Urethra • Internal urethral sphincter • Involuntary smooth muscle • External urethral sphincter • Voluntarily inhibits urination • Relaxes when one urinates Urethra • In females • Length of 3–4 cm • In males—20 cm in length; three named regions • Prostatic urethra • Passes through the prostate gland • Membranous urethra • Through the urogenital diaphragm • Spongy (penile) urethra • Passes through the length of the penis Micturition Disorders of the Urinary System • Urinary tract infections • More common in females • Burning sensation during micturition • Renal calculi • Kidney stones • Bladder cancer • 3% of cancers—more common in men • Kidney cancer • Arises from epithelial cells of uriniferous tubules The Urinary System Throughout Life • Embryo develops three pairs of kidneys • Pronephros • Mesonephros • Metanephros • Only metanephros persists to become the adult kidneys • Metanephric kidney produces urine by fetal month 3 • Contributes to the volume of amniotic fluid The Urinary System Throughout Life • Kidney and bladder function declines with advancing age • Nephrons decrease in size and number • Tubules less efficient at secretion and reabsorption • Filtration declines • Recognition of desire to urinate is delayed • Loss of muscle tone in the bladder 17 The Endocrine System The Endocrine System: An Overview • A system of ductless glands • Secrete messenger molecules called hormones • Interacts closely with the nervous system • Endocrinology • Study of hormones and endocrine glands Endocrine Organs • Scattered throughout the body • Pure endocrine organs • Pituitary, pineal, thyroid, parathyroid, and adrenal glands • Organs containing endocrine cells • Pancreas, thymus, gonads, and the hypothalamus • Hypothalamus is a neuroendocrine organ • Produces hormones and has nervous functions • Endocrine cells are of epithelial origin Location of the Major Endocrine Glands Hormones • Classes of hormones • Amino acid–based hormones • Steroids—derived from cholesterol • Basic hormone action • Circulate throughout the body in blood vessels • Influences only specific tissues—target cells • A hormone can have different effects on different target cells Control of Hormones Secretion • Secretion triggered by three major types of stimuli • Humoral—simplest of endocrine control mechanisms • Secretion in direct response to changing ion or nutrient levels in the blood • Parathyroid monitors calcium • Responds to decline by secreting hormone to reverse decline Control of Hormones Secretion • Secretion triggered by three major types of stimuli (continued) • Neural • Sympathetic nerve fibers stimulate cells in the adrenal medulla • Induces release of epinephrine and norepinephrine • Hormonal • Stimuli received from other glands • Certain hormones signal secretion of other hormones • Hypothalamus secretes hormones stimulates pituitary stimulates other glands Types of Endocrine Gland Stimuli Control of Hormones Secretion • Always controlled by feedback loops • Blood concentration declines below a minimum • More hormone is secreted • Blood concentration exceeds maximum • Hormone production is halted The Pituitary Gland • Secretes nine major hormones • Attached to the hypothalamus by the infundibulum • Two basic divisions of the pituitary gland • Adenohypophysis (anterior lobe) • Has three major divisions • Pars distalis, pars intermedia, and pars tuberalis • Nuerohypophysis—has two major divisions • Pars nervosa and infundibular The Pituitary Gland The Anterior Lobe • The pars distalis—largest division of the anterior lobe • Contains five different endocrine cells • Makes and secretes seven different hormones • Tropic hormones regulate hormone secretion by other glands • Include: TSH, ACTH, FSH, LH The Anterior Lobe • GH, PRL, and MSH • Act directly on non-endocrine target tissues The Anterior Lobe • Growth hormone (somatotropic hormone) • Produced by somatotropic cells • Stimulates body growth by stimulating increased protein production and growth of epiphyseal plates • Stimulates growth directly and indirectly by the liver’s secretion of insulinlike growth factor-1. The Anterior Lobe • Thyroid-stimulating hormone • Produced by thyrotropic cells • Signals thyroid gland to secrete thyroid hormone • Adrenocorticotropic hormone • Stimulates the adrenal cortex to secrete hormones that help cope with stress The Anterior Lobe • Melanocyte-stimulating hormone • In humans, MSH functions in appetite supression • Gonadotropins—are produced by gonadotropic cells • FSH and LH The Anterior Lobe • Prolactin—produced by prolactin cells • Targets milk-producing glands in the breast—stimulates milk production • Endocrine cells of the pars distalis • Clustered in spheres and branching cords Hypothalamic Control of Hormone Secretion from the Anterior Lobe • The hypothalamus • Controls secretion of anterior lobe hormones • Exerts control by secreting • Releasing hormones—prompt anterior lobe to release hormones • Inhibiting hormones—turn off secretion of anterior lobe hormones • Releasing hormones • Are secreted like neurotransmitters • Enter a primary capillary plexus • Travel in hypophyseal portal veins to a secondary capillary plexus • From the secondary capillary plexus, hormones secreted by the anterior lobe enter general circulation and travel to target organs The Posterior Lobe • Is structurally part of the brain • Its axons make up the hypothalamic– hypophyseal tract • Arises from neuronal cell bodies in the hypothalamus • Supraoptic nucleus • Paraventricular nucleus The Posterior Lobe • Does not make hormones • Stores and releases hormones made in the hypothalamus • Releases two peptide hormones • Antidiuretic hormone (ADH) • Oxytocin The Posterior Lobe • ADH (vacopressin) • Made in supraoptic nucleus • Targets kidneys to resorb water • Oxytocin • Produced in the paraventricular nucleus • Induces smooth muscle contraction of reproductive organs, ejects milk during breast feeding, and signals contraction of the uterus during childbirth The Thyroid Gland • Located in the anterior neck • Largest pure endocrine gland • Composed of follicles and areolar connective tissue • Produces two hormones • Thyroid hormone (TH) • Calcitonin 17 The Endocrine System The Parathyroid Glands • Lie on the posterior surface of the thyroid gland • Contain two types of endocrine cells • Chief cells • Produce parathyroid hormone (PTH) • Increases blood concentration of Ca2+ • Oxyphil cells • Function unknown The Adrenal (Suprarenal) Glands • Pyramid-shaped glands located on the superior surface of each kidney • Supplied by about 60 suprarenal arteries • Nerve supply is almost exclusively sympathetic fibers The Adrenal (Suprarenal) Glands • Two endocrine glands in one • Adrenal medulla—a cluster of neurons • Derived from neural crest • Part of the sympathetic nervous system • Adrenal cortex—forms the bulk of the gland • Derived from somatic mesoderm • All adrenal hormones help one cope with danger, terror, or stress The Adrenal Medulla • Chromaffin cells • Are modified ganglionic sympathetic neurons • Secrete amine hormones epinephrine and norepinephrine • Enhance “fight-or-flight” response • Hormones are stored in secretory vesicles • Are arranged in spherical clusters and some branching cords The Adrenal Cortex • Secretes lipid-based steroid hormones • Cortex is composed of three layers (zones) • Zona glomerulosa—cells arranged in spherical clusters • Zona fasciculata—cells arranged in parallel cords; contains lipid droplets • Zona reticularis—cells arranged in a branching network The Adrenal Cortex • Hormones are corticosteroids • Adrenal corticosteroids are of two main classes • Mineralocorticoids • Glucocorticoids Mineralocorticoids • Aldosterone—secreted by the zona glomerulosa • Secreted in response to decline in blood volume or blood pressure • Is the terminal hormone of the renin-angiotensin mechanism Glucocorticoids • Cortisol is the main type • Secreted by zona fasciculata and zona reticularis • Helps the body deal with stressful situations The Adrenal Gland–Gross and Microscopic Stress and the Adrenal Gland The Pineal Gland • Located on the roof of the diencephalon • Shaped like a pine cone • “Pineal sand” is radiopaque • Used as a landmark to identify other brain structures in X rays • Pinealocytes secrete melatonin • A hormone that regulates circadian rhythms The Pancreas • Located in the posterior abdominal wall • Contains endocrine and exocrine cells • Exocrine cells • Acinar cells—secrete digestive enzymes • Endocrine cells • Pancreatic islets—islets of Langerhans • About one million islets—scattered throughout the pancreas The Pancreas • Main endocrine cell types • Alpha cells ( cells)—secrete glucagon • Signals liver to release glucose from glycogen • Raises blood sugar • Beta cells ( cells)—secrete insulin • Signals most body cells to take up glucose from the blood • Promotes storage of glucose as glycogen in liver • Lowers blood sugar The Pancreas • Pancreatic islets contain two rare cell types • Delta (∂) cells • Secrete somatostatin • Inhibits secretion of insulin and glucagon • F (PP) cells • Secrete pancreatic polypeptide • May inhibit exocrine activity of the pancreas The Thymus • Located in the lower neck and anterior thorax • Important immune organ • Site at which T-lymphocytes arise from precursor cells The Gonads • Main sources of sex hormones • Testes and ovaries • Male • Interstitial cells secrete androgens • Primarily testosterone • Promotes the formation of sperm • Maintains secondary sex characteristics The Gonads • Female • Ovaries • Androgens secreted by the theca folliculi • Converted to estrogen by follicular granulosa cells • Estrogen • Maintains secondary sex characteristics • Progesterone • Prepares the uterus for pregnancy Other Endocrine Structures • Endocrine cells occur within • The heart • Atria contain atrial natriuretic peptide (ANP) • The GI tract • Enteroendocrine cells • The placenta • Sustains the fetus and secretes several steroid protein hormones Other Endocrine Structures • The kidneys • Cells of the juxtaglomerular apparatus (JGA) secrete renin • Endothelial cells and interstitial connective tissue—secrete erythropoietin • The skin • Modified cholesterol molecules convert to a precursor of vitamin D Pituitary Disorders • Gigantism • Hypersecretion of GH in children • Pituitary dwarfism • Hyposecretion of GH • Diabetes insipidus • Pars nervosa does not make enough ADH Disorders of the Pancreas: Diabetes Mellitus • Caused by • Insufficient secretion of insulin • Resistance of body cells to the effects of insulin • Type 1 diabetes • Develops suddenly, usually before age 15 • T cell–mediated autoimmune response destroys beta cells Diabetes Mellitus • Type 2 diabetes • Adult onset • Usually occurs after age 40 • Cells have lowered sensitivity to insulin • Controlled by dietary changes and regular exercise Disorders of the Thyroid Gland • Grave’s disease • Most common type of hyperthyroidism • Immune system makes abnormal antibodies • Stimulates the oversecretion of TH by follicle cells • Leads to nervousness, weight loss, sweating, and rapid heart rate Disorders of the Thyroid Gland • Myxedema • Adult hypothyroidism • Antibodies attack and destroy thyroid tissue • Low metabolic rate and weight gain are common symptoms Disorders of the Thyroid Gland • Endemic goiter • Due to lack of iodine in the diet • Cretinism • Hypothyroidism in children • Short, disproportionate body, thick tongue, and mental retardation Disorders of the Adrenal Cortex • Cushing’s syndrome • Caused by hypersecretion of glucocorticoid hormones—usually a pituitary tumor • Addison’s disease • Hyposecretory disorder of the adrenal cortex • Deficiencies of both mineralocorticoids and glucocorticoids Thyroid Disorders The Endocrine System Throughout Life • Thyroid gland • Forms from a thickening of endoderm on the floor of the pharynx • Parathyroids and the thymus gland • From endoderm lining the pharyngeal pouches Embryological Origin of Selected Endocrine Organs • Pineal gland • Originates from ependymal cells • Pituitary gland—dual origin • Adenohypophysis originates from the roof of the mouth • Neurohypophysis grows inferiorly from the floor of the brain Embryological Origin of Selected Endocrine Organs • Adrenal gland—dual origin gland • Adrenal medulla—from neural crest cells of nearby sympathetic trunk ganglia • Adrenal cortex—from mesoderm lining the coelom The Endocrine System Throughout Life • Endocrine organs operate effectively until old age • Anterior pituitary • Increase in connective tissue and lipofuscin • Decrease in vascularization and number of hormone-secreting cells • Adrenal cortex • Normal rates of glucocorticoid secretion continue • Adrenal medulla • No age-related changes in catecholamines The Endocrine System Throughout Life • Thyroid hormones • Decrease slightly with age • Parathyroid glands • Little change with aging • GH, DHEA, and the sex hormones • Marked drops in secretion with age 25 The Reproductive System The Reproductive System • Primary sex organs • Testes • Ovaries • Accessory sex organs • Glands • External genitalia The Male Reproductive System • Testes are located within the scrotum • The scrotum—Skin and superficial fascia surrounding the testes • Positioning provides an environment 3˚ cooler than body temperature • Dartos muscle—layer of smooth muscle • Cremaster muscle—bands of skeletal muscle surrounding the testes • Elevates the testes Relationship of the Testes to the Scrotum The Testes • Are enclosed in a serous sac—the tunica vaginalis • Tunica albuginea—fibrous capsule of the testes • Divides each testis into 250–300 lobules • Lobules contain 1–4 coiled seminiferous tubules • Epididymis • Comma-shaped structure on posterior testis Nerves and Vessels • Arterial supply of the testes • Testicular arteries • • Testicular veins arise from the pampiniform plexus • Pampiniform plexus helps keep testes cool Testes innervated by parasympathetic and sympathetic divisions of ANS Microscopic Anatomy • Seminiferous tubules • Separated by areolar connective tissue • Epithelium consists of • Spermatogenic cells—sperm-forming cells • Columnar sustentacular cells—support cells Microscopic Anatomy • Spermatogenic cells produce sperm • Sperm formation • 400 million sperm formed per day • Begins at puberty • Process takes 75 days • Cells differentiate and move toward the lumen • Spermatogonia—stem cells • Primary spermatocytes • Secondary spermatocytes • Spermatids • Sperm Microscopic Anatomy • Sustenocytes • Surround spermatogenic cells • Extend from basal lamina to the lumen • Tight junctions between cells • Blood-testis barrier • Assist sperm production • Secrete testicular fluid and androgen-binding protein Microscopic Anatomy • Myoid cells—surround seminiferous tubules • Contract rhythmically • Interstitial cells (Leydig cells) • Secrete testosterone • Secretion regulated by LH The Epididymis • Duct of the epididymis is 6m long (when uncoiled) • Dominated by pseudostratified columnar epithelium • Bears tufts of stereocilia—immotile, long microvilli • 20-day journey for sperm to move through • Gain the ability to swim and to fertilize an egg through the acrosomal reaction The Ductus Deferens • Stores and transports sperm • Hisotology of the ductus deferens • Epithelium—pseudostratified columnar • Thick muscularis • Adventitia The Ductus Deferens • Trace the course of the ductus deferens The Spermatic Cord • Contains • Ductus deferens • Testicular blood vessels • Nerves • Superior portion of ductus deferens • Runs through inguinal canal The Urethra • Carries sperm from ejaculatory ducts to “outside” • Three parts of male urethra • Prostatic • Membranous • Spongy 25 The Reproductive System Accessory Glands • The seminal vesicles • Lie on the posterior surface of the urinary bladder • Secretes about 60% of the volume of semen • Fluid contains • Fructose to nourish sperm • Substances to enhance sperm motility • Prostaglandins • Substances that suppress immune response against semen • Enzymes that clot and then liquefy semen Accessory Glands • The prostate gland • Encircles the prostatic urethra • Consists of 20—30 compound tubuloalveolar glands • Secretes about 25—30% of seminal fluid • Contains substances that • Enhance sperm motility • Enzymes that clot and then liquefy semen Accessory Glands • The bulbourethral glands • Pea-sized glands inferior to the prostate gland • Produce a mucus • Mucus enters spongy urethra prior to ejaculation • Neutralizes traces of acidic urine • Lubricates urethra The Penis • External anatomy • Shaft—body • Glans penis—distal expanded end • Prepuce—foreskin • Removed during circumcision The Penis • Internal anatomy • Three erectile bodies • One corpus spongiosum • Surrounds spongy urethra • Two coropora cavernosa • Contain sinuses, make up most of the penis • Male sexual response • Erection—parasympathetic control • Ejaculation—sympathetic control The Male Perineum • Contains—scrotum, root of penis, anus • Diamond-shaped area between • Pubic symphysis anteriorly • Coccyx posteriorly • Ischial tuberosities laterally Spermatogenesis • Divided into three stages • Stage 1—spermatogonia divide by mitosis • Type A—maintain the germ cells • Type B—differentiate into primary spermatocytes • Stage 2—meiosis I and meiosis II • Meiosis I—forms two secondary spermatocytes • Meiosis II—each spermatocyte forms two spermatids Spermatogenesis • Stage 3—spermiogenesis • The four spermatids differentiate into spermatozoa • Spermatozoa shed superfluous cytoplasm • Composed of • Head, midpiece, and tail Spermatogenesis • Sustenocytes surround spermatogenic cells • Bound together by tight junctions • Divides seminiferoustubules into • Basal compartment • Adluminal compartment Spermatogenesis • Tight junctions between sustenocytes • Blood-testis barrier • Protects developing sperm from the immune system Spermatogenesis • Spermatogenesis—controlled by • Follicle stimulating hormone • Testosterone • Secretions from sustenocytes also influence spermatogenesis • Androgen-binding protein concentrates testosterone near spermatogeneic cells • Inhibin—inhibits FSH The Female Reproductive System • Produces gametes (ova) • Prepares to support a developing embryo • Undergoes changes according to the menstrual cycle • Menstrual cycle is the monthly cycle as it affects all female reproductive organs • Includes • Ovaries • Uterine tubes, uterus, and vagina The Ovaries • Small, almond-shaped organs • Produce ova • Held in place by ligaments and mesenteries • Broad ligament • Suspensory ligament • Ovarian ligament • Ovarian arteries—arterial supply • Innervated by both divisions of the ANS Internal Structure of the Ovaries • Tunica albuginea • Fibrous capsule of the ovary • Covered in simple columnar epithelium • Ovarian cortex—houses developing oocytes • Follicles—multicellular sacs housing oocytes • Ovarian medulla—loose connective tissue • Contains blood vessels, lymphvessels, and nerves Structure of the Ovary 25 The Reproductive System The Uterine Tubes • Receive ovulated oocyte • Parts of the uterine tube • Infundibulum—distal end of uterine tube • Surrounded by fimbriae • Ampulla—middle third of uterine tube • Usual site of fertilization • Isthmus—medial third of uterine tube The Uterus • Lies anterior to rectum—posterior to bladder • Anteverted (anteflexed) usual position of uterus • Parts of the uterus • Fundus—rounded superior portion • Cervix—“neck” of uterus • Cervical canal—communicates with vagina inferiorly • Internal os—opening connecting with uterine cavity • External os—inferior opening of cervix Supports of the Uterus • Uterus is supported by • Mesometrium—anchors uterus to lateral pelvic walls • Lateral ligaments—horizontal from cervix and vagina • Round ligaments—bind uterus to the anterior pelvic wall Uterine Wall • Wall of the uterus composed of • Perimetrium, myometrium, and endometrium • Embryo burrows into endometrium • Endometrium has two layers • Functional layer • Basal layer Uterine Wall • Uterine arteries—send branches to the uterine wall and divide into arcuate arteries • Radial arteries reach the endometrium and branch into • Straight arteries—to basal layer • Spiral arteries—to functional layer • Undergo degeneration and regeneration with menstrual cycle The Female Menstrual Cycle and Oogenesis • Monthly menstrual cycle • Due to hormonal fluctuations in ovaries and uterus • Ovarian cycle—stimulates production of ovarian follicles and oocytes • Uterine cycle—prepares uterine wall for implantation The Ovarian Cycle • Has three successive phases • Follicular phase • Ovulation • Luteal phase The Ovarian Cycle • Follicular phase • First half of the ovarian cycle • 6–12 primordial follicles stimulated to develop • Growth stimulated by FSH from anterior pituitary • Primordial follicle becomes a primary follicle • Zona pellucida—glycoprotein coat surrounding oocyte • Theca folliculi—internal layer secretes hormones The Ovarian Cycle • Follicular phase (continued) • Antrum forms • A fluid filled cavity between granulose cells • Primary follicles become a secondary follicle • Corona radiata—coat of granulosa cells surrounding oocyte • Secondary follicle enlarges and becomes • Vesicular (Graafian) follicle—ready to be ovulated The Ovarian Cycle • Ovulation • Occurs about halfway through each ovarian cycle (Day 14) • One mature oocyte exits from one ovary • Enters peritoneal cavity • Swept into uterine tube • Sudden increase in LH is signal for ovulation The Ovarian Cycle • Luteal phase • Occurs after ovulation in last half of the ovarian cycle • Remaining follicle becomes a corpus luteum • Secretes progesterone • Acts to prepare for implantation of an embryo • If no implantation • Corupus luteum dies and becomes a corpus albicans Oogenesis • Takes many years to complete • Primordial follicles are arrested (stalled) in meiosis I • Surge of LH also causes primary oocyte to compete meiosis I Oogenesis • Oogenesis produces only one ovum and three polar bodies • Polar bodies do not contribute to developing embryo • Meiosis II is completed only if sperm penetration occurs The Uterine Cycle • Series of cyclic phases of the endometrium • • • Phases coordinate with the ovarian cycle Endometrial phases directed by FSH and LH Phases of uterine cycle • Menstrual phase—days 1–5 • Stratum functionalis is shed • Proliferative phase—days 6–14 • Secretory phase—days 15–28 The Menstrual Cycle Structural and hormonal changes The Vagina • Consists of three coats • Adventitia—fibrous connective tissue • Muscularis—smooth muscle • Mucosa—marked by transverse folds • Consists of lamina propria and stratified squamous epithelium • Hymen—an incomplete diaphragm • Fornix—recess formed at the superior part of the vagina 25 The Reproductive System The External Genitalia and Female Perineum Deep Structures of the External Genitalia and Female Perineum The Mammary Glands • Breasts—modified sweat glands • Glandular structure—undeveloped in nonpregnant women • Milk production—starts at or after childbirth Pregnancy • Events leading to fertilization • Sperm binds to the zona pellucida • Undergoes the acrosomal reaction • Release of enzymes to form a slit in the zona pellucida • Fusion of oocyte and sperm plasma membranes • Cortical reaction • Enzymes prevent any other sperm from binding to the egg • Fertilization—chromosomes of male and female gametes join Events Leading to Fertilization 25 The Reproductive System Implantation • Blastocyst begins implantation • About 6 days after conception • Blastocyst consists of • An inner cell mass and outer trophoblast • Trophoblast forms two layers • Cytotrophoblast—inner layer • Syncytiotrophoblast—outer layer Formation of the Placenta • Embryonic and maternal tissues contribute to the placenta Anatomy of the Placenta • Exchanges across the chorionic villi between maternal and fetal blood • Provide fetus with nutrients and oxygen • Dispose of its wastes • Allow hormonal signals to be sent to the mother • By Week 13 the placenta is fully formed Anatomy of the Placenta • Placental barrier consists of • All three layers of the chorionic villi • Sugars, fats, and oxygen diffuse from mother to fetus • Urea and carbon dioxide diffuse from fetus to mother • Syncytiotrophoblast—secretes substances that regulate events of pregnancy • Maternal antibodies transported across placenta • Viruses, alcohol, and heroin cross the placental barrier 25 The Reproductive System Childbirth • Parturition—266 days after fertilization • Labor—events that expel the infant from the uterus Reproductive System Cancers in Males • Testicular cancer • Affects 1 of 50,000 males • Commonly from early-stage spermatogenic cells • Increase of 50% from 1974 to 1990 • Cured in 95% of cases Reproductive System Cancers in Males • Prostate cancer • Slow-growing—arises from peripheral glands • Risk factors • Fatty diet • Genetic predisposition Reproductive System Cancers in Females • Ovarian cancer—arises from cells in the germinal epithelium • Endometrial cancer—arises from the endometrium of the uterus • Cervical cancer—slow-growing, arises from epithelium at the tip of the cervix Reproductive System Cancers in Females • Breast cancer—second most common cause of cancer deaths in women • 97% occurs in women over 50 • Treatment • Surgical removal of the mass (lumpectomy) • Radiation therapy • Administration of selected hormones • Chemotherapy Embryonic Development of the Sex Organs • Embryo at 5–6 weeks is sexually indifferent • Mesonephric ducts—future male ducts • Paramesonephric ducts—future female ducts Embryonic Development of the Sex Organs Embryonic Development of the Sex Organs • Male embryos—sexual differentiation begins in Week 7 • Mesonephric duct becomes • Epididymis • Ductus deferens • Ejaculatory duct • Paramesonephric ducts degenerate Embryonic Development of the Sex Organs • Female embryos—sexual differentiation begins in Week 8 • Cortical portion of immature ovaries form ovarian follicles • Paramesonephric duct becomes • Uterus • Uterine tubes • Superior part of vagina • Mesonephric ducts degenerate Embryonic Development of the Sex Organs • Development of the external genitalia Embryonic Development of the Sex Organs Decent of the Gonads Puberty • Period of life between ages 10–15 • Reproductive organs grow to their adult size • Events of puberty occur in the same sequence in all individuals • Age at which events of puberty occur varies widely Puberty • Male secondary sex characteristics • Enlargement of the scrotum and testes (about age 13) • Appearance of pubic, axillary, and facial hair • Lengthening of vocal folds—deepening voice • Musculoskeletal system increases in mass • Sexual maturation—mature sperm in semen • Female secondary sex characteristics • Budding breasts (around age 11) • Menarche—the first menstruation • Other estrogen-induced secondary sex characteristics • Increase in subcutaneous fat • Widening and lightening of the bones of the pelvic girdle • Appearance of axillary and pubic hair • Estrogen-induced growth spurt from age 12-17 Menopause • Female reproductive peak—late 20s • Around age 35—rate of follicle degeneration increases • Ovulation and menstruation cease—age 46–54 • Ovaries stop secreting estrogen • Reproductive organs and breasts begin to atrophy
