Key Takeaways
- The GI tract path: mouth → pharynx → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine → rectum → anus
- Chemical digestion uses enzymes: amylase (carbs), pepsin (protein in stomach), lipase (fats), trypsin (protein in SI)
- Most nutrient absorption occurs in the small intestine, especially the jejunum; the large intestine absorbs water and electrolytes
- The liver produces bile, detoxifies blood, and stores glycogen; the gallbladder stores and concentrates bile
- The kidneys filter blood, regulate fluid/electrolyte balance, and produce urine; the functional unit is the nephron
- Urine formation involves three processes: glomerular filtration, tubular reabsorption, and tubular secretion
- The male reproductive system produces sperm (testes) and delivers them via the vas deferens and urethra
- The female reproductive system produces eggs (ovaries), with the uterus supporting pregnancy; the menstrual cycle averages 28 days
Digestive, Urinary & Reproductive Systems
These three systems handle nutrient processing, waste elimination, and reproduction — all essential topics for nursing care.
Digestive System
The digestive system breaks food into absorbable nutrients through mechanical digestion (physical breakdown) and chemical digestion (enzymatic breakdown).
GI Tract Pathway
| Organ | Function | Key Process |
|---|---|---|
| Mouth | Mechanical: chewing; Chemical: salivary amylase | Starch digestion begins |
| Pharynx | Swallowing (deglutition) | Epiglottis prevents aspiration |
| Esophagus | Peristalsis moves food to stomach | No digestion or absorption |
| Stomach | Mechanical: churning; Chemical: HCl + pepsin | Protein digestion begins; chyme produced |
| Small intestine | Major site of digestion and absorption | Nutrients absorbed into blood |
| Large intestine | Water and electrolyte absorption | Feces formed |
| Rectum/Anus | Storage and elimination | Defecation |
Small Intestine Regions
| Region | Function |
|---|---|
| Duodenum | Receives bile (from liver/gallbladder) and pancreatic enzymes; chemical digestion |
| Jejunum | Primary site of nutrient absorption |
| Ileum | Absorbs vitamin B12 and bile salts |
Digestive Enzymes
| Enzyme | Source | Substrate | Product |
|---|---|---|---|
| Salivary amylase | Salivary glands | Starch | Maltose |
| Pepsin | Stomach (chief cells) | Protein | Peptides |
| Pancreatic lipase | Pancreas | Fats | Fatty acids + glycerol |
| Trypsin | Pancreas | Protein | Amino acids |
| Lactase | Small intestine (brush border) | Lactose | Glucose + galactose |
| Sucrase | Small intestine (brush border) | Sucrose | Glucose + fructose |
| Bile | Liver (stored in gallbladder) | Fat globules | Emulsified fat (not an enzyme) |
Stomach Cell Types and Their Secretions
| Cell Type | Secretion | Function |
|---|---|---|
| Parietal cells | Hydrochloric acid (HCl) | Kills bacteria; activates pepsinogen; denatures proteins |
| Chief cells | Pepsinogen | Converted to pepsin by HCl; begins protein digestion |
| Mucous cells | Mucus | Protects stomach lining from acid and enzyme damage |
| G cells | Gastrin (hormone) | Stimulates parietal cells to produce more HCl |
| D cells | Somatostatin | Inhibits gastrin release (negative feedback) |
Clinical connection: Peptic ulcers often result from Helicobacter pylori infection, which damages the mucous layer and exposes the stomach wall to acid. NSAIDs (aspirin, ibuprofen) can also weaken the mucous barrier.
Accessory Organs
| Organ | Function |
|---|---|
| Liver | Produces bile, detoxifies blood, stores glycogen, produces plasma proteins |
| Gallbladder | Stores and concentrates bile |
| Pancreas | Produces digestive enzymes + bicarbonate (exocrine); insulin and glucagon (endocrine) |
Urinary System
The urinary system filters blood, maintains fluid and electrolyte balance, and eliminates waste as urine.
Components
| Structure | Function |
|---|---|
| Kidneys (2) | Filter blood; produce urine |
| Ureters (2) | Transport urine from kidneys to bladder |
| Urinary bladder | Stores urine (capacity ~500 mL) |
| Urethra | Expels urine from the body |
The Nephron — Functional Unit of the Kidney
Each kidney contains approximately 1 million nephrons. Urine formation involves three processes:
| Process | Location | Function |
|---|---|---|
| Glomerular filtration | Glomerulus → Bowman's capsule | Blood pressure forces water and small solutes out of blood |
| Tubular reabsorption | Proximal tubule, loop of Henle, distal tubule | Useful substances (glucose, amino acids, water, ions) returned to blood |
| Tubular secretion | Proximal and distal tubules | Additional waste (H+, K+, drugs) added to urine |
Normal urine output: 0.5-1 mL/kg/hour (approximately 1,500 mL/day for adults)
Reproductive Systems
Male Reproductive System
| Structure | Function |
|---|---|
| Testes | Produce sperm (spermatogenesis) and testosterone |
| Epididymis | Sperm maturation and storage |
| Vas deferens | Transports sperm from epididymis |
| Seminal vesicles | Produce fructose-rich fluid for sperm nutrition |
| Prostate gland | Produces alkaline fluid to neutralize vaginal acidity |
| Urethra | Shared pathway for urine and semen |
Female Reproductive System
| Structure | Function |
|---|---|
| Ovaries | Produce eggs (oogenesis) and hormones (estrogen, progesterone) |
| Fallopian tubes (oviducts) | Site of fertilization; transport egg to uterus |
| Uterus | Supports fetal development during pregnancy |
| Cervix | Lower portion of uterus; opening to vagina |
| Vagina | Birth canal; receives sperm |
The Menstrual Cycle (~28 days)
| Phase | Days | Events |
|---|---|---|
| Menstrual | 1-5 | Uterine lining sheds (menstruation) |
| Follicular | 1-13 | FSH stimulates follicle development; estrogen rises |
| Ovulation | Day 14 | LH surge triggers egg release from ovary |
| Luteal | 15-28 | Corpus luteum produces progesterone; uterine lining thickens |
If fertilization does not occur, progesterone drops → menstruation begins (new cycle).
Fertilization and Early Development
| Event | Timing | Details |
|---|---|---|
| Fertilization | Within 24 hours of ovulation | Sperm meets egg in the fallopian tube; forms a zygote |
| Implantation | Days 6-10 after fertilization | Blastocyst embeds in the uterine wall (endometrium) |
| Embryonic period | Weeks 3-8 | Major organ systems develop; most vulnerable to teratogens |
| Fetal period | Week 9 to birth | Growth, maturation, and refinement of organs |
Pregnancy hormones:
- hCG (human chorionic gonadotropin): Produced by the placenta; maintains the corpus luteum; detected by pregnancy tests
- Estrogen: Stimulates uterine growth and breast development
- Progesterone: Maintains the endometrium; prevents uterine contractions
- Relaxin: Softens the cervix and relaxes pelvic ligaments before birth
Structural Organization of the GI Tract Wall
The GI tract wall has four layers from innermost to outermost:
| Layer | Description |
|---|---|
| Mucosa | Innermost; secretes enzymes and mucus; absorbs nutrients |
| Submucosa | Contains blood vessels, nerves, and lymphatic tissue |
| Muscularis | Smooth muscle layers responsible for peristalsis |
| Serosa | Outermost protective layer (connective tissue) |
Peristalsis is the wave-like muscular contraction that moves food through the GI tract. It is an involuntary process controlled by the smooth muscle in the muscularis layer.
Where does most nutrient absorption occur in the digestive system?
The functional unit of the kidney is the:
Which organ produces bile?
Arrange the digestive tract organs in the correct order that food passes through them.
Arrange the items in the correct order
On approximately what day of the menstrual cycle does ovulation typically occur?
The three processes of urine formation are glomerular filtration, tubular reabsorption, and tubular _____.
Type your answer below