Histology and Functions of Digestive and Urinary Systems

Parotid Gland

Composed mainly of serous acini (dark-staining, enzyme-rich), with ducts (intercalated and striated). Surrounded by connective tissue septa.

Parotid Gland Function

Produces serous saliva rich in amylase to begin starch digestion.

Parotid Gland Interaction

Saliva enters the oral cavity via Stensen's duct, mixing with food during mastication.

Esophagus

Mucosa: Stratified squamous non-keratinized epithelium (protective). Submucosa: Contains esophageal glands (mucous). Muscularis externa: Skeletal (upper third), mixed (middle third), smooth muscle (lower third). Adventitia: Fibrous connective tissue.

Esophagus Function

Transports food from mouth to stomach via peristalsis.

Esophagus Interaction

Receives bolus from pharynx; enters stomach at cardiac sphincter.

Liver

Made of lobules: central vein, radiating hepatic plates of hepatocytes. Portal triads: bile duct, hepatic artery, portal vein. Sinusoids: lined with Kupffer cells (macrophages).

Liver Function

Metabolism, detoxification, bile production.

Liver Interaction

Sends bile to gallbladder via hepatic ducts; processes nutrients via hepatic portal vein from intestines.

Gallbladder

Mucosa: Simple columnar epithelium with microvilli (absorption). No submucosa; folded mucosa (appears glandular). Muscularis: Smooth muscle layer.

Gallbladder Function

Stores and concentrates bile.

Gallbladder Interaction

Releases bile into cystic duct → common bile duct → duodenum during digestion.

Stomach

Mucosa: Simple columnar epithelium with gastric pits and glands. Cells: parietal (HCl), chief (pepsinogen), mucous neck, G cells (gastrin). Muscularis externa: 3 layers (oblique, circular, longitudinal).

Stomach Function

Mechanical digestion and protein breakdown.

Stomach Interaction

Receives bolus from esophagus; turns it into chyme; passes it to duodenum.

Greater Omentum

Loose connective tissue, adipose, blood vessels, immune cells.

Greater Omentum Function

Fat storage, immune defense (milky spots), limits spread of infection.

Greater Omentum Interaction

Drapes over intestines; attaches from greater curvature of stomach to transverse colon.

Lesser Omentum

Thin double layer of peritoneum with vessels (e.g., hepatic portal vein).

Lesser Omentum Function

Stabilizes position of stomach and liver.

Lesser Omentum Interaction

Connects lesser curvature of stomach and proximal duodenum to liver.

Pancreas

Exocrine acini: Dark-staining cells with zymogen granules (enzymes). Ducts: Intercalated → intralobular → main pancreatic. Endocrine islets of Langerhans: Lighter-staining (insulin, glucagon).

Pancreas Function

Secretes digestive enzymes and bicarbonate (exocrine); hormones (endocrine).

Pancreas Interaction

Delivers enzymes to duodenum via pancreatic duct.

Duodenum

Mucosa: Villi with simple columnar epithelium + goblet cells. Submucosa: Contains Brunner's glands (alkaline mucus).

Duodenum Function

Receives chyme; neutralizes acid; begins enzymatic digestion.

Duodenum Interaction

Connects to stomach (pyloric sphincter); receives bile/pancreatic enzymes via ampulla of Vater.

Ileum

Mucosa: Shorter villi than duodenum; more goblet cells. Submucosa: Contains Peyer's patches (lymphoid nodules).

Ileum Function

Final absorption of nutrients, B12, bile salts.

Ileum Interaction

Connects to cecum at ileocecal valve.

Cecum

Histology: Similar to colon: simple columnar epithelium with goblet cells; no villi.

Cecum Function

Absorbs fluid and salts; mixes with mucus.

Cecum Interaction

Receives chyme from ileum; connects to ascending colon.

Colon

Histology: Mucosa: Smooth with crypts of Lieberkühn; abundant goblet cells.

Colon Function

Absorption of water, electrolytes; forms feces.

Colon Interaction

Fecal material moves segmentally from cecum → ascending → transverse → descending → sigmoid colon.

Rectum

Histology: Similar to colon but with more goblet cells; transitions to stratified squamous epithelium near anal canal.

Rectum Function

Stores feces until defecation.

Rectum Interaction

Connects sigmoid colon to anal canal; works with sphincters for elimination.

Parotid Gland

Histology: Serous acini only (dark staining); ducts (intercalated and striated).

Parotid Gland Function

Produces enzyme-rich saliva (amylase).

Parotid Gland Connection

Drains via Stensen's duct into oral cavity near upper second molar.

Sublingual Gland

Histology: Mostly mucous acini (light staining) with some serous demilunes.

Sublingual Gland Function

Secretes mucous-rich saliva.

Sublingual Gland Connection

Multiple small ducts open into floor of mouth near Wharton's duct.

Hard Palate

Histology: Stratified squamous keratinized epithelium, with underlying bone.

Hard Palate Function

Forms anterior roof of mouth; separates oral and nasal cavities.

Hard Palate Connection

Continuation of oral cavity; aids in mastication and speech.

Oral Pharynx

Histology: Stratified squamous non-keratinized epithelium.

Oral Pharynx Function

Passageway for food and air.

Laryngopharynx

Histology: Stratified squamous epithelium.

Laryngopharynx Function

Guides food to esophagus; behind larynx.

Laryngopharynx Connection

Connects oral cavity → esophagus (posteriorly) and larynx (anteriorly).

Esophagus

Histology: Mucosa: Stratified squamous epithelium; Submucosa: Esophageal glands (mucus); Muscularis externa: Skeletal (top), mixed (middle), smooth (bottom); Adventitia.

Esophagus Function

Peristaltic transport of bolus.

Esophagus Connection

Pharynx → stomach via lower esophageal (cardiac) sphincter.

Liver

Histology: Lobules with central vein, plates of hepatocytes, sinusoids, Kupffer cells; Portal triads: bile duct, portal vein, hepatic artery.

Liver Function

Produces bile, metabolizes nutrients, detoxifies blood.

Liver Connections

Bile flows from hepatocytes → bile canaliculi → bile ductules → left/right hepatic ducts → common hepatic duct; Joins with cystic duct → common bile duct → duodenum.

Gallbladder

Histology: Simple columnar epithelium, no submucosa, folded mucosa; Smooth muscle wall.

Gallbladder Connection

Releases bile via cystic duct into common bile duct → duodenum.

Stomach

Histology: Simple columnar epithelium, gastric pits and glands (parietal, chief, G cells). Regions: Cardia, Fundus, Body, Pylorus. Curvatures: Lesser (medial), Greater (lateral). Valves: Cardiac sphincter (entry), Pyloric sphincter (exit). Function: Mechanical digestion, chemical breakdown (mainly proteins). Connection: Esophagus → stomach → duodenum.

Greater Omentum

Histology: Fatty peritoneal fold with vessels and immune cells. Function: Cushions, immune surveillance, infection isolation. Connection: Hangs from greater curvature of stomach to transverse colon.

Pancreas

Histology: Exocrine acini (enzymes, bicarbonate), Islets of Langerhans (hormones). Function: Digestive enzymes (exocrine); hormones (endocrine). Connection: Enzymes flow via main pancreatic duct to join common bile duct → duodenum (via ampulla of Vater).

Duodenum

Histology: Villi, Brunner's glands (submucosa), few goblet cells. Function: Neutralizes chyme, begins enzymatic digestion.

Jejunum

Histology: Long villi, many plicae circulares, fewer goblet cells. Function: Major site of nutrient absorption.

Ileum

Histology: Shorter villi, Peyer's patches (lymphoid nodules). Function: Absorbs B12, bile salts. Connection: Ends at ileocecal valve to cecum.

Large Intestine

Histology: Simple columnar epithelium with crypts and abundant goblet cells, Teniae coli (longitudinal muscle bands). Function: Absorbs water, forms feces. Connection: Ileocecal valve → cecum → ascending → transverse → descending → sigmoid.

Ileocecal Valve

Histology: Thickened smooth muscle. Function: Prevents backflow of colonic contents. Connection: Junction between ileum and cecum.

Appendix

Histology: Similar to colon, but with abundant lymphoid tissue. Function: Possible immune role (gut flora reserve). Connection: Projects from posterior cecum near ileocecal junction.

Rectum

Histology: Columnar epithelium, transitions to stratified squamous at anal canal, many goblet cells; longitudinal muscle continuous (no teniae coli). Function: Fecal storage and controlled elimination. Connection: Leads to anal canal; works with internal/external sphincters.

Kidney

Histology: Covered by a fibrous renal capsule, internally divided into cortex and medulla. Function: Filters blood, forms urine, regulates electrolytes and blood pressure. Connection: Connected to ureter → bladder → urethra.

Ureter

Histology: Mucosa: Transitional epithelium (urothelium), Muscularis: Inner longitudinal, outer circular smooth muscle, Adventitia. Function: Propels urine from kidney to bladder via peristalsis.

Urethra

Histology: Transitional epithelium → pseudostratified/stratified columnar → stratified squamous (near orifice). Function: Conducts urine (and semen in males) to the outside. Connection: Bladder → external urethral orifice.

Cortex (Kidney)

Histology: Contains renal corpuscles, PCT, DCT, and peritubular capillaries. Function: Filtration and reabsorption. Appearance: Outer, granular region.

Medulla

Composed of renal pyramids containing loops of Henle and collecting ducts

Function of Medulla

Concentration of urine

Appearance of Medulla

Inner striated region

Renal Pyramids

Mostly collecting ducts and loops of Henle

Function of Renal Pyramids

Urine concentration and transport

Connection of Renal Pyramids

Drain into minor calyces at renal papillae

Major and Minor Calyx

Transitional epithelium

Function of Major and Minor Calyx

Collect urine from pyramids

Connection of Major and Minor Calyx

Minor calyces drain from papillae; Major calyces form from merging minors → join into renal pelvis

Renal Columns

Cortical tissue between pyramids

Function of Renal Columns

Provide structural support and contain interlobar arteries/veins

Pelvis

Funnel-shaped reservoir for urine before ureter

Histology of Pelvis

Transitional epithelium

Sinus

Cavity housing pelvis, calyces, vessels, fat

Renal Artery

Brings oxygenated, unfiltered blood into kidney

Renal Vein

Returns filtered, deoxygenated blood

Pathway of Renal Blood Flow

Renal artery → segmental → interlobar → arcuate → interlobular → afferent arteriole

Renal Corpuscle

Components: Glomerulus + Bowman's capsule

Function of Renal Corpuscle

Site of filtration

Histology of Renal Corpuscle

Simple squamous lining in capsule; fenestrated capillaries in glomerulus

Renal Capsule

Dense irregular connective tissue

Function of Renal Capsule

Protective outer covering

Glomerulus

Fenestrated capillary tuft

Function of Glomerulus

Filters plasma into Bowman's space

Connection of Glomerulus

Fed by afferent arteriole, drained by efferent arteriole