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BSC NURSING SEM1 APPLIED ANATOMY UNIT 3 The Digestive system

  • Structure of alimentary canal and accessory organs of digestion

Structure of Alimentary Canal and Accessory Organs of Digestion

Alimentary Canal

The alimentary canal is a continuous tube that begins at the mouth and ends at the anus, responsible for digestion and absorption of food. It consists of the following structures:

  • Mouth

Mouth: Detailed Anatomy and Functions

The mouth, also called the oral cavity, is the starting point of the digestive system. It plays a crucial role in mechanical digestion, chemical digestion, and the initial processing of food. Below are its key components and their details:

Anatomy of the Mouth

1. External Structures

  • Lips (Labia)
    • Form the entrance of the mouth and help in articulation and food intake.
    • Covered externally by skin and internally by mucous membrane.
    • Contains muscles like the orbicularis oris for movement.

2. Oral Cavity

  • Vestibule: The space between the lips/cheeks and teeth.
  • Oral Cavity Proper: The main space, enclosed by the palate, tongue, and teeth.

3. Teeth

  • Function: Mechanical digestion by chewing (mastication), breaking food into smaller pieces.
  • Types:
    • Incisors: Cutting food (8 total).
    • Canines: Tearing food (4 total).
    • Premolars: Grinding food (8 total).
    • Molars: Crushing food (12 total, including wisdom teeth).
  • Composition: Enamel, dentin, pulp cavity, cementum, and periodontal ligament.

4. Tongue

  • A muscular organ covered with mucosa and taste buds.
  • Functions:
    • Mechanical digestion: Moves food during chewing and assists in swallowing.
    • Taste perception: Taste buds detect sweet, sour, salty, bitter, and umami tastes.
    • Speech: Helps in articulation of sounds.
  • Regions: Tip, body, and root.

5. Palate

  • Forms the roof of the mouth and separates the oral and nasal cavities.
  • Parts:
    • Hard Palate: Bony front part.
    • Soft Palate: Muscular back part, ending in the uvula, which prevents food from entering the nasal cavity during swallowing.

6. Salivary Glands

  • Major Salivary Glands:
    • Parotid glands (largest): Near the ears, secrete serous saliva rich in amylase.
    • Submandibular glands: Below the jaw, secrete mixed saliva (serous and mucous).
    • Sublingual glands: Under the tongue, secrete primarily mucous saliva.
  • Minor Salivary Glands: Scattered throughout the mucosa of the lips, cheeks, and palate.
  • Saliva Functions:
    • Moistens and lubricates food for easier swallowing.
    • Begins chemical digestion of carbohydrates (salivary amylase).
    • Contains lysozyme and antibodies for antimicrobial protection.

7. Cheeks (Buccal Walls)

  • Lateral walls of the oral cavity.
  • Assist in holding food in place during chewing.

8. Uvula

  • A conical structure hanging from the soft palate.
  • Helps prevent food from entering the nasal passages during swallowing.

9. Frenulum

  • Lingual Frenulum: Connects the tongue to the floor of the mouth.
  • Labial Frenulum: Attaches the lips to the gums.

Functions of the Mouth

  1. Ingestion
    • Entry point for food and liquids.
  2. Mechanical Digestion
    • Chewing by teeth breaks food into smaller pieces.
    • Tongue and cheeks manipulate food into a bolus.
  3. Chemical Digestion
    • Salivary amylase begins breaking down carbohydrates.
  4. Taste Sensation
    • Taste buds on the tongue detect flavors, enhancing the sensory experience of eating.
  5. Speech
    • Lips, tongue, and teeth help articulate sounds.
  6. Defense Mechanism
    • Saliva contains enzymes and antibodies to fight off pathogens.
  7. Swallowing (Deglutition)
    • The tongue and soft palate assist in pushing the food bolus into the pharynx.
  • Pharynx

Pharynx: Detailed Anatomy and Functions

The pharynx is a muscular, funnel-shaped structure that serves as a common pathway for both food and air. It connects the nasal and oral cavities to the larynx (voice box) and esophagus (food pipe). The pharynx is divided into three regions: the nasopharynx, oropharynx, and laryngopharynx.

Anatomy of the Pharynx

1. Location and Structure

  • Location: Extends from the base of the skull to the level of the sixth cervical vertebra (C6).
  • Structure:
    • Composed of skeletal muscles covered by a mucous membrane.
    • Divided into three regions:
      1. Nasopharynx (upper part)
      2. Oropharynx (middle part)
      3. Laryngopharynx (lower part)

2. Regions of the Pharynx

a. Nasopharynx
  • Location: Behind the nasal cavity, above the soft palate.
  • Function: Serves as a passageway for air.
  • Structures within the Nasopharynx:
    • Pharyngeal Tonsils (Adenoids): Lymphatic tissue that helps in immune defense.
    • Eustachian Tube Openings: Connects the nasopharynx to the middle ear, equalizing pressure between the ear and the atmosphere.
b. Oropharynx
  • Location: Behind the oral cavity, extending from the soft palate to the hyoid bone.
  • Function: Serves as a pathway for both air and food.
  • Structures within the Oropharynx:
    • Palatine Tonsils: Located on either side of the oropharynx; part of the lymphatic system.
    • Lingual Tonsils: Found at the base of the tongue.
    • Faucial Arches: Separate the oral cavity from the oropharynx.
c. Laryngopharynx (Hypopharynx)
  • Location: Below the oropharynx, extending from the hyoid bone to the esophagus and larynx.
  • Function: Guides food and air to their respective pathways—esophagus (food) and larynx (air).
  • Structures within the Laryngopharynx:
    • Epiglottis: A flap of cartilage that prevents food from entering the trachea during swallowing.

3. Muscles of the Pharynx

The pharynx has two types of muscles:

a. Circular Muscles (Constrictor Muscles)
  • Help in pushing food down the esophagus during swallowing.
  • Includes:
    • Superior constrictor
    • Middle constrictor
    • Inferior constrictor
b. Longitudinal Muscles
  • Shorten and widen the pharynx during swallowing and speech.
  • Includes:
    • Stylopharyngeus
    • Palatopharyngeus
    • Salpingopharyngeus

4. Nerve Supply

  • Motor Nerves: Mostly supplied by the vagus nerve (cranial nerve X).
    • Stylopharyngeus muscle is supplied by the glossopharyngeal nerve (cranial nerve IX).
  • Sensory Nerves:
    • Nasopharynx: Maxillary nerve (branch of trigeminal nerve, cranial nerve V).
    • Oropharynx: Glossopharyngeal nerve (cranial nerve IX).
    • Laryngopharynx: Vagus nerve (cranial nerve X).

5. Blood Supply

  • Arterial Supply:
    • Branches from the external carotid artery, including the ascending pharyngeal, facial, maxillary, and lingual arteries.
  • Venous Drainage:
    • Drains into the internal jugular vein.

Functions of the Pharynx

  1. Passageway for Air and Food
    • Directs air to the larynx and trachea.
    • Guides food to the esophagus.
  2. Swallowing (Deglutition)
    • Facilitates the movement of food from the mouth to the esophagus.
    • The constrictor muscles push the bolus down, while the epiglottis prevents food from entering the trachea.
  3. Speech Production
    • Acts as a resonating chamber, contributing to voice quality.
  4. Immune Defense
    • Lymphatic tissue in the tonsils traps and destroys pathogens entering through the nasal or oral cavities.
  • Esophagus

Esophagus: Detailed Anatomy and Functions

The esophagus is a muscular tube that connects the pharynx to the stomach, allowing the transport of food and liquids. It is a crucial component of the digestive system, facilitating the passage of ingested material through coordinated muscular contractions.

Anatomy of the Esophagus

1. Location and Structure

  • Length: Approximately 25–30 cm (10–12 inches) in adults.
  • Location: Extends from the lower end of the pharynx (at the level of the cricoid cartilage, C6 vertebra) to the stomach (at the level of T10–T11 vertebrae).
  • Path:
    • Passes through the neck, thorax, and diaphragm before entering the abdominal cavity.
    • Pierces the diaphragm at the esophageal hiatus (T10 vertebra level).

2. Layers of the Esophagus

The esophageal wall has four layers, similar to other parts of the gastrointestinal tract:

  1. Mucosa:
    • Innermost layer lined with stratified squamous epithelium for protection against mechanical damage.
    • Contains mucus-secreting glands to lubricate the passage of food.
  2. Submucosa:
    • Composed of connective tissue with blood vessels, lymphatics, and nerves.
    • Contains esophageal glands for additional mucus secretion.
  3. Muscularis Externa:
    • Responsible for peristalsis (wave-like muscular contractions).
    • Upper one-third: Composed of skeletal muscle (voluntary control).
    • Middle one-third: Mixed skeletal and smooth muscle.
    • Lower one-third: Composed of smooth muscle (involuntary control).
  4. Adventitia/Serosa:
    • Outermost layer composed of connective tissue.
    • Provides structural support and anchors the esophagus to surrounding tissues.

3. Regions of the Esophagus

  1. Cervical Esophagus:
    • Upper portion located in the neck.
    • Begins at the lower end of the pharynx and extends to the thoracic inlet.
  2. Thoracic Esophagus:
    • Middle portion located in the chest.
    • Lies posterior to the trachea and anterior to the vertebral column.
  3. Abdominal Esophagus:
    • Short segment located in the abdominal cavity.
    • Connects to the stomach at the gastroesophageal junction.

4. Sphincters of the Esophagus

  1. Upper Esophageal Sphincter (UES):
    • Located at the junction of the pharynx and esophagus.
    • Composed of skeletal muscle and prevents the entry of air into the esophagus during respiration.
    • Relaxes during swallowing.
  2. Lower Esophageal Sphincter (LES):
    • Located at the gastroesophageal junction.
    • Composed of smooth muscle and prevents reflux of gastric contents into the esophagus.
    • Incompetence of this sphincter leads to gastroesophageal reflux disease (GERD).

5. Blood Supply

  • Arterial Supply:
    • Cervical esophagus: Inferior thyroid artery.
    • Thoracic esophagus: Esophageal branches of the thoracic aorta.
    • Abdominal esophagus: Left gastric artery and inferior phrenic arteries.
  • Venous Drainage:
    • Cervical esophagus: Drains into the inferior thyroid vein.
    • Thoracic esophagus: Drains into the azygos and hemiazygos veins.
    • Abdominal esophagus: Drains into the portal vein via the left gastric vein.

6. Lymphatic Drainage

  • Upper Esophagus: Drains into deep cervical lymph nodes.
  • Middle Esophagus: Drains into posterior mediastinal lymph nodes.
  • Lower Esophagus: Drains into left gastric and celiac lymph nodes.

7. Nerve Supply

  • Motor Nerves:
    • Skeletal muscle in the upper esophagus is innervated by the recurrent laryngeal nerve (branch of the vagus nerve).
    • Smooth muscle in the lower esophagus is innervated by the vagus nerve (parasympathetic) and the esophageal plexus.
  • Sensory Nerves:
    • Carry sensations such as pain and stretch, mainly through the vagus nerve and sympathetic fibers.

Functions of the Esophagus

  1. Transport of Food and Liquids
    • Moves food from the pharynx to the stomach via peristalsis (coordinated wave-like muscle contractions).
  2. Protection
    • The stratified squamous epithelium protects the esophageal wall from abrasion by food particles.
  3. Prevention of Reflux
    • The LES acts as a barrier to prevent stomach acid from entering the esophagus.

Mechanism of Swallowing (Deglutition)

  1. Oral Phase:
    • Voluntary phase where the tongue pushes the bolus into the pharynx.
  2. Pharyngeal Phase:
    • Involuntary phase where the UES relaxes to allow food into the esophagus.
  3. Esophageal Phase:
    • Involuntary phase where peristalsis propels the bolus downward.
    • The LES relaxes to allow food into the stomach.
  • Stomach

Stomach: Detailed Anatomy, Functions, and Clinical Aspects

The stomach is a muscular, J-shaped organ in the upper abdominal cavity, primarily responsible for storing food, mechanical and chemical digestion, and controlling the release of food into the small intestine.

Anatomy of the Stomach

1. Location

  • Situated in the epigastric, umbilical, and left hypochondriac regions of the abdomen.
  • Lies between the esophagus (above) and duodenum (below).

2. Shape and Parts of the Stomach

The stomach is divided into five regions:

  1. Cardia:
    • The area surrounding the opening of the esophagus into the stomach.
    • Contains the cardiac sphincter, which prevents the backflow of gastric contents into the esophagus.
  2. Fundus:
    • The dome-shaped portion superior to the cardia.
    • Usually filled with gas in radiological images.
  3. Body (Corpus):
    • The largest central portion of the stomach.
    • Primarily involved in mechanical digestion and mixing of food with gastric juices.
  4. Pylorus:
    • The funnel-shaped distal region of the stomach.
    • Divided into two parts:
      • Pyloric Antrum: Wider portion.
      • Pyloric Canal: Narrow portion that leads to the duodenum.
    • Ends with the pyloric sphincter, regulating the passage of chyme into the small intestine.
  5. Greater and Lesser Curvatures:
    • Greater Curvature: Outer convex border where the greater omentum attaches.
    • Lesser Curvature: Inner concave border where the lesser omentum attaches.

3. Layers of the Stomach Wall

The stomach wall is composed of four layers:

  1. Mucosa:
    • Innermost layer lined with simple columnar epithelium.
    • Contains gastric pits leading to gastric glands that secrete gastric juices.
      • Parietal cells: Secrete hydrochloric acid (HCl) and intrinsic factor.
      • Chief cells: Secrete pepsinogen and gastric lipase.
      • Mucous cells: Produce mucus to protect the stomach lining.
      • G cells: Secrete gastrin (a hormone that stimulates gastric secretion).
  2. Submucosa:
    • Connective tissue containing blood vessels, lymphatics, and nerves.
  3. Muscularis Externa:
    • Composed of three layers of smooth muscle:
      • Outer longitudinal layer.
      • Middle circular layer.
      • Inner oblique layer (unique to the stomach).
    • Responsible for churning food and mixing it with gastric juices.
  4. Serosa (Visceral Peritoneum):
    • Outermost protective layer that reduces friction with surrounding organs.

4. Blood Supply

  • Arterial Supply:
    • From branches of the celiac trunk:
      • Left gastric artery (lesser curvature).
      • Right gastric artery (lesser curvature).
      • Left gastroepiploic artery (greater curvature).
      • Right gastroepiploic artery (greater curvature).
      • Short gastric arteries (fundus).
  • Venous Drainage:
    • Corresponding veins drain into the portal vein via the splenic and superior mesenteric veins.

5. Nerve Supply

  • Parasympathetic Innervation:
    • By the vagus nerve (increases gastric secretion and motility).
  • Sympathetic Innervation:
    • By the celiac plexus (decreases gastric secretion and motility).

Functions of the Stomach

  1. Storage of Food:
    • Temporarily stores ingested food and releases it gradually into the duodenum.
  2. Mechanical Digestion:
    • Churning and mixing of food with gastric secretions to form chyme.
  3. Chemical Digestion:
    • Hydrochloric acid denatures proteins and kills microorganisms.
    • Pepsin (activated from pepsinogen) begins the digestion of proteins.
  4. Absorption:
    • Limited absorption occurs in the stomach (e.g., alcohol, certain drugs, and small amounts of water).
  5. Intrinsic Factor Secretion:
    • Essential for vitamin B12 absorption in the ileum.
  6. Hormone Secretion:
    • Gastrin regulates gastric secretions and motility.

Gastric Secretions

The stomach produces approximately 2–3 liters of gastric juice per day, composed of:

  1. Hydrochloric Acid (HCl):
    • Lowers stomach pH to 1.5–3.5, aiding in digestion and antimicrobial activity.
  2. Pepsinogen:
    • Converted to pepsin, which digests proteins.
  3. Mucus:
    • Protects the stomach lining from acidic and enzymatic damage.
  4. Intrinsic Factor:
    • Binds with vitamin B12, facilitating its absorption.
  5. Gastrin:
    • Stimulates the secretion of HCl and pepsinogen.
  • Small Intestine
  • Small Intestine

Small Intestine: Detailed Anatomy, Functions, and Clinical Aspects

The small intestine is a long, coiled tube responsible for the majority of digestion and nutrient absorption. It extends from the stomach’s pylorus to the large intestine and is divided into three parts: the duodenum, jejunum, and ileum.

Anatomy of the Small Intestine

1. Location and Structure

  • Length: Approximately 6–7 meters (20–23 feet) in adults.
  • Location: Occupies the central and lower abdominal cavity.
  • Divisions:
    1. Duodenum (25–30 cm, shortest segment).
    2. Jejunum (about 2.5 meters).
    3. Ileum (about 3.5 meters, longest segment).

2. Layers of the Small Intestine Wall

Similar to the rest of the gastrointestinal tract, the small intestine has four layers:

  1. Mucosa:
    • Epithelium: Simple columnar cells with goblet cells that secrete mucus.
    • Villi: Finger-like projections that increase surface area for absorption.
    • Crypts of Lieberkühn: Contain cells that secrete intestinal juices and enzymes.
    • Peyer’s Patches: Lymphoid tissue in the ileum that helps in immune defense.
  2. Submucosa:
    • Contains connective tissue, blood vessels, lymphatics, and nerves.
    • Brunner’s Glands: Found in the duodenum; secrete alkaline mucus to neutralize stomach acid.
  3. Muscularis Externa:
    • Inner circular and outer longitudinal smooth muscle layers responsible for peristalsis and segmentation.
  4. Serosa:
    • Outermost layer composed of connective tissue covered by the visceral peritoneum.

3. Parts of the Small Intestine

a. Duodenum
  • Location: First part, shaped like a “C,” surrounding the head of the pancreas.
  • Function:
    • Receives chyme from the stomach and secretions from the liver (bile) and pancreas.
    • Major Duodenal Papilla: Opening where bile and pancreatic juices enter via the common bile duct and pancreatic duct.
    • Neutralizes acidic chyme using bicarbonate.
b. Jejunum
  • Location: Middle section, mostly in the upper left quadrant of the abdomen.
  • Function:
    • Major site of nutrient absorption, including carbohydrates, proteins, and lipids.
    • Highly vascularized, with long villi and folds called plicae circulares.
c. Ileum
  • Location: Final section, mostly in the lower right quadrant of the abdomen.
  • Function:
    • Absorbs vitamin B12, bile salts, and any remaining nutrients.
    • Contains abundant Peyer’s patches for immune protection.
    • Ends at the ileocecal valve, which regulates the flow of material into the large intestine and prevents backflow.

4. Blood Supply

  • Arterial Supply:
    • Branches of the superior mesenteric artery supply the jejunum and ileum.
  • Venous Drainage:
    • Blood drains into the superior mesenteric vein, which joins the portal vein.

5. Lymphatic Drainage

  • Lacteals: Specialized lymphatic vessels in the villi absorb dietary fats.
  • Lymph nodes include mesenteric lymph nodes, which filter lymph.

6. Nerve Supply

  • Parasympathetic Innervation: By the vagus nerve (increases motility and secretions).
  • Sympathetic Innervation: By the superior mesenteric plexus (reduces motility and secretions).

Functions of the Small Intestine

  1. Digestion:
    • Enzymes from the pancreas and bile from the liver aid in chemical digestion.
    • Intestinal juices contain enzymes like maltase, sucrase, lactase, and peptidase.
  2. Absorption:
    • Over 90% of nutrient absorption occurs here.
    • Carbohydrates: Absorbed as monosaccharides.
    • Proteins: Absorbed as amino acids.
    • Fats: Absorbed as fatty acids and glycerol via lacteals.
    • Vitamins and Minerals: Water-soluble vitamins (e.g., B and C) and fat-soluble vitamins (A, D, E, K) are absorbed.
  3. Immune Function:
    • Peyer’s patches protect against pathogens.
  4. Motility:
    • Segmentation: Mixes chyme with digestive juices.
    • Peristalsis: Moves chyme toward the large intestine.
  • Large Intestine

Large Intestine: Detailed Anatomy, Functions, and Clinical Aspects

The large intestine, also known as the colon, is the final part of the gastrointestinal tract. Its primary functions are the absorption of water and electrolytes, the formation of feces, and the storage of waste before elimination.

Anatomy of the Large Intestine

1. Location and Structure

  • Length: Approximately 1.5 meters (5 feet).
  • Diameter: Larger than the small intestine, hence the name.
  • Location: Extends from the ileocecal junction to the anus.

2. Divisions of the Large Intestine

  1. Cecum:
    • A pouch-like structure at the beginning of the large intestine.
    • Located in the lower right abdominal quadrant.
    • Connected to the ileum via the ileocecal valve, which prevents backflow of fecal matter.
    • Attached to the cecum is the appendix, a narrow, worm-like structure containing lymphoid tissue.
  2. Colon:
    • The main part of the large intestine, divided into four regions:
      1. Ascending Colon:
        • Extends upward from the cecum along the right side of the abdomen.
        • Ends at the hepatic flexure (right colic flexure) near the liver.
      2. Transverse Colon:
        • Runs horizontally across the abdomen from the hepatic flexure to the splenic flexure (left colic flexure).
      3. Descending Colon:
        • Extends downward along the left side of the abdomen from the splenic flexure.
      4. Sigmoid Colon:
        • S-shaped segment that connects the descending colon to the rectum.
  3. Rectum:
    • A straight segment located in the pelvic cavity.
    • Stores feces before elimination.
  4. Anal Canal:
    • The terminal part of the large intestine.
    • Surrounded by the internal anal sphincter (involuntary control) and the external anal sphincter (voluntary control).

3. Layers of the Large Intestine Wall

Similar to the small intestine, the large intestine has four layers:

  1. Mucosa:
    • Lined with simple columnar epithelium and goblet cells for mucus secretion.
    • Lacks villi but contains crypts for lubrication and absorption.
  2. Submucosa:
    • Contains connective tissue, blood vessels, lymphatics, and nerves.
  3. Muscularis Externa:
    • Inner circular layer and outer longitudinal layer.
    • The outer longitudinal layer is organized into three bands called taeniae coli, creating sac-like pouches called haustra.
  4. Serosa/Adventitia:
    • Outermost layer; serosa is present in areas covered by peritoneum.

4. Blood Supply

  • Arterial Supply:
    • From branches of the superior mesenteric artery (cecum, ascending colon, and transverse colon) and inferior mesenteric artery (descending colon, sigmoid colon, and rectum).
  • Venous Drainage:
    • Via the superior mesenteric vein and inferior mesenteric vein, which drain into the portal vein.

5. Lymphatic Drainage

  • Lymph drains into regional lymph nodes and ultimately into the thoracic duct.

6. Nerve Supply

  • Parasympathetic Innervation:
    • Vagus nerve supplies the cecum, ascending colon, and transverse colon.
    • Pelvic splanchnic nerves supply the descending colon, sigmoid colon, and rectum.
  • Sympathetic Innervation:
    • From the superior and inferior mesenteric plexuses.

Functions of the Large Intestine

  1. Absorption:
    • Absorbs water, electrolytes (e.g., sodium, chloride), and vitamins (e.g., vitamin K produced by gut bacteria).
  2. Formation and Storage of Feces:
    • Undigested material and waste products are compacted into feces.
  3. Microbial Activity:
    • Hosts gut microbiota, which ferment undigested carbohydrates and produce short-chain fatty acids and gases.
  4. Defecation:
    • Expels feces through the anal canal.
  5. Immune Function:
    • Contains lymphoid tissue to protect against pathogens.

Accessory Organs of Digestion

These organs assist in digestion but are not part of the alimentary canal.

  1. Salivary Glands
    • Parotid, submandibular, and sublingual glands produce saliva, which contains enzymes like amylase.
  2. Liver

Liver: Detailed Anatomy, Functions, and Clinical Aspects

The liver is the largest internal organ and gland in the human body. It plays a central role in metabolism, detoxification, bile production, and other vital processes. Located in the upper right quadrant of the abdomen, it is protected by the rib cage.

Anatomy of the Liver

1. Location

  • Found in the right hypochondriac and epigastric regions, extending slightly into the left hypochondriac region.
  • Positioned inferior to the diaphragm and superior to the stomach, duodenum, and right kidney.

2. Size and Shape

  • Weight: Approximately 1.4–1.6 kg (3–4 lbs) in adults.
  • Shape: Wedge-shaped, with a smooth, convex surface on top (diaphragmatic surface) and a concave underside (visceral surface).

3. Lobes of the Liver

The liver is divided into anatomical and functional lobes:

  1. Anatomical Lobes:
    • Right Lobe: Larger and contains the gallbladder fossa.
    • Left Lobe: Smaller and extends towards the left.
    • Caudate Lobe: Located near the inferior vena cava.
    • Quadrate Lobe: Located near the gallbladder.
  2. Functional Lobes:
    • Based on blood supply and bile drainage, divided into right and left functional lobes.

4. Surface Anatomy

  • Diaphragmatic Surface:
    • Smooth and convex, facing the diaphragm.
  • Visceral Surface:
    • Contains depressions for adjacent organs (stomach, duodenum, kidney).
    • Includes key structures in the porta hepatis:
      • Portal vein
      • Hepatic artery
      • Common bile duct

5. Blood Supply

  • Dual Blood Supply:
    • Hepatic Artery: Supplies oxygenated blood (~25% of blood flow).
    • Portal Vein: Supplies nutrient-rich blood from the gastrointestinal tract (~75% of blood flow).
  • Venous Drainage:
    • Blood from the liver drains into the hepatic veins, which empty into the inferior vena cava.

6. Microscopic Structure

  • Lobules: Functional units of the liver, hexagonal in shape.
  • Components:
    • Hepatocytes: Liver cells responsible for most liver functions.
    • Sinusoids: Blood-filled spaces where oxygenated and nutrient-rich blood mix.
    • Kupffer Cells: Specialized macrophages that remove debris and pathogens.
    • Bile Canaliculi: Small ducts that collect bile produced by hepatocytes.

Functions of the Liver

  1. Metabolism:
    • Carbohydrate Metabolism: Regulates blood glucose levels (glycogenesis, glycogenolysis, gluconeogenesis).
    • Protein Metabolism: Synthesizes plasma proteins (e.g., albumin, clotting factors) and deaminates amino acids.
    • Lipid Metabolism: Produces cholesterol, lipoproteins, and triglycerides; converts excess carbohydrates into fat.
  2. Detoxification:
    • Detoxifies harmful substances (e.g., alcohol, drugs, toxins).
    • Converts ammonia (toxic) into urea for excretion.
  3. Bile Production:
    • Produces bile, which emulsifies fats for digestion and absorption in the small intestine.
  4. Storage:
    • Stores glycogen, vitamins (A, D, E, K, B12), and minerals (iron, copper).
  5. Immune Function:
    • Kupffer cells destroy old red blood cells, bacteria, and foreign particles.
  6. Hormone Regulation:
    • Metabolizes hormones like insulin, glucagon, and steroid hormones.
  7. Synthesis:
    • Produces clotting factors (e.g., fibrinogen, prothrombin).
    • Synthesizes angiotensinogen, a precursor involved in blood pressure regulation.
  8. Excretion:
    • Excretes bilirubin (a breakdown product of hemoglobin) and cholesterol in bile.

Bile and Biliary System

1. Bile Composition

  • Water, bile salts, bilirubin, cholesterol, and electrolytes.

2. Biliary Tree

  • Intrahepatic Bile Ducts: Begin in the liver.
  • Common Hepatic Duct: Formed by the union of right and left hepatic ducts.
  • Cystic Duct: Connects the gallbladder to the common bile duct.
  • Common Bile Duct: Carries bile to the duodenum.
  • Gallbladder

Gallbladder: Detailed Anatomy, Functions, and Clinical Aspects

The gallbladder is a small, pear-shaped organ located beneath the liver. It plays a key role in the storage and concentration of bile, which is essential for the digestion and absorption of fats.

Anatomy of the Gallbladder

1. Location

  • Situated on the visceral (underside) surface of the right lobe of the liver.
  • Lies within the gallbladder fossa of the liver.

2. Size and Shape

  • Length: Approximately 7–10 cm.
  • Capacity: About 30–50 mL of bile.
  • Shape: Pear-shaped with a wide base and a narrow neck.

3. Parts of the Gallbladder

  1. Fundus:
    • The rounded distal portion that projects below the inferior margin of the liver.
    • Palpable when enlarged.
  2. Body:
    • The main part of the gallbladder that lies in contact with the liver, stomach, and transverse colon.
  3. Neck:
    • The narrow portion leading to the cystic duct.
    • Contains the spiral valve (valve of Heister), which regulates bile flow and prevents collapse of the duct.

4. Biliary System

The gallbladder is part of the biliary tree, which carries bile from the liver to the small intestine:

  • Cystic Duct: Connects the gallbladder to the common bile duct.
  • Common Hepatic Duct: Formed by the right and left hepatic ducts from the liver.
  • Common Bile Duct: Formed by the union of the cystic duct and common hepatic duct. It carries bile to the duodenum.
  • Sphincter of Oddi: Regulates bile flow into the duodenum and prevents reflux.

5. Blood Supply

  • Arterial Supply:
    • Cystic artery, typically a branch of the right hepatic artery.
  • Venous Drainage:
    • Cystic veins drain into the portal vein or liver sinusoids.

6. Lymphatic Drainage

  • Lymph flows into the cystic lymph nodes and then into the hepatic lymph nodes.

7. Nerve Supply

  • Parasympathetic Innervation: Vagus nerve stimulates gallbladder contraction.
  • Sympathetic Innervation: Celiac plexus.
  • Sensory Innervation: Right phrenic nerve (pain referred to the right shoulder).

Functions of the Gallbladder

  1. Storage of Bile:
    • Stores bile produced by the liver (500–1000 mL daily) and releases it as needed.
  2. Concentration of Bile:
    • Absorbs water and electrolytes, increasing bile concentration by 5–10 times.
  3. Release of Bile:
    • Responds to the hormone cholecystokinin (CCK), released by the small intestine in response to fatty foods.
    • Contracts to release bile into the duodenum through the common bile duct.

Bile: Composition and Function

Composition:

  • Water, bile salts, bile pigments (bilirubin), cholesterol, and electrolytes.

Functions:

  • Emulsification of Fats: Bile salts break down fat into smaller droplets for easier digestion by lipase.
  • Absorption of Fat-Soluble Vitamins: Aids in the absorption of vitamins A, D, E, and K.

Clinical Significance

Common Gallbladder Disorders

  1. Cholelithiasis (Gallstones):
    • Hardened deposits of bile components (cholesterol, bilirubin, or calcium salts).
    • Can cause pain (biliary colic) and block bile flow.
  2. Cholecystitis:
    • Inflammation of the gallbladder, often due to gallstones.
    • Symptoms include severe right upper abdominal pain, fever, and nausea.
  3. Choledocholithiasis:
    • Presence of gallstones in the common bile duct.
    • Can lead to jaundice, dark urine, pale stools, and severe pain.
  4. Gallbladder Polyps:
    • Small growths in the gallbladder; usually benign but may require monitoring.
  5. Gallbladder Cancer:
    • Rare but aggressive cancer often discovered late due to vague symptoms.
  6. Biliary Dyskinesia:
    • Functional disorder with abnormal gallbladder contraction.

Symptoms of Gallbladder Disorders

  • Pain in the right upper abdomen or back (often after fatty meals).
  • Nausea and vomiting.
  • Jaundice (yellowing of skin and eyes, if bile flow is obstructed).
  • Fever and chills (in cases of infection).

Diagnostic Tests

  1. Ultrasound:
    • First-line imaging to detect gallstones, inflammation, or other abnormalities.
  2. HIDA Scan (Hepatobiliary Iminodiacetic Acid Scan):
    • Assesses gallbladder function and bile flow.
  3. Endoscopic Retrograde Cholangiopancreatography (ERCP):
    • Combines endoscopy and X-rays to visualize bile ducts and treat blockages.
  4. Magnetic Resonance Cholangiopancreatography (MRCP):
    • Non-invasive imaging of bile ducts and gallbladder.
  5. Blood Tests:
    • Check liver function (e.g., bilirubin, alkaline phosphatase) and inflammatory markers.

Treatment Options

  1. Medications:
    • Ursodeoxycholic acid to dissolve small cholesterol stones (in selected cases).
  2. Cholecystectomy (Gallbladder Removal):
    • Laparoscopic Cholecystectomy: Minimally invasive surgery.
    • Open Cholecystectomy: Required for complicated cases.
  3. ERCP:
    • Used to remove stones from the bile ducts or place stents.
  4. Dietary Modifications:
    • Avoid fatty and fried foods to reduce symptoms.
  • Pancreas

Pancreas: Detailed Anatomy, Functions, and Clinical Aspects

The pancreas is a glandular organ located in the abdomen. It serves both endocrine and exocrine functions, playing a vital role in digestion and blood glucose regulation.

Anatomy of the Pancreas

1. Location

  • Lies retroperitoneally in the upper abdomen.
  • Situated behind the stomach and in front of the first and second lumbar vertebrae.
  • Extends transversely across the posterior abdominal wall.

2. Size and Shape

  • Length: Approximately 12–15 cm.
  • Weight: About 80–120 grams.
  • Shape: Elongated, tapering from the head to the tail.

3. Parts of the Pancreas

  1. Head:
    • The broadest part, nestled in the curve of the duodenum.
    • Contains the uncinate process, which extends posteriorly to the superior mesenteric vessels.
  2. Neck:
    • Narrow part connecting the head to the body.
    • Lies anterior to the superior mesenteric vessels.
  3. Body:
    • The elongated central portion.
    • Lies anterior to the abdominal aorta and the left renal vein.
  4. Tail:
    • The tapered end of the pancreas.
    • Lies in close proximity to the spleen.

4. Pancreatic Duct System

  • Main Pancreatic Duct (Duct of Wirsung):
    • Runs the length of the pancreas.
    • Joins the common bile duct and opens into the duodenum at the ampulla of Vater (major duodenal papilla).
    • Regulated by the sphincter of Oddi.
  • Accessory Pancreatic Duct (Duct of Santorini):
    • Opens into the duodenum at the minor duodenal papilla (if present).

5. Blood Supply

  • Arterial Supply:
    • Head: Supplied by the superior pancreaticoduodenal artery (branch of the gastroduodenal artery) and inferior pancreaticoduodenal artery (branch of the superior mesenteric artery).
    • Body and Tail: Supplied by branches of the splenic artery.
  • Venous Drainage:
    • Drains into the portal vein via the superior mesenteric vein and splenic vein.

6. Nerve Supply

  • Parasympathetic Innervation: Vagus nerve stimulates pancreatic secretion.
  • Sympathetic Innervation: Celiac and superior mesenteric plexuses.

Functions of the Pancreas

The pancreas has dual roles: exocrine and endocrine.

1. Exocrine Function

  • Pancreatic Acini:
    • Exocrine cells produce digestive enzymes.
  • Enzymes:
    • Amylase: Digests carbohydrates.
    • Lipase: Digests fats.
    • Proteases (e.g., trypsin, chymotrypsin): Digest proteins.
  • Bicarbonate:
    • Neutralizes acidic chyme entering the duodenum from the stomach.

2. Endocrine Function

  • Islets of Langerhans:
    • Clusters of endocrine cells scattered throughout the pancreas.
    • Types of Cells:
      • Alpha Cells: Produce glucagon, which raises blood glucose.
      • Beta Cells: Produce insulin, which lowers blood glucose.
      • Delta Cells: Produce somatostatin, which inhibits insulin and glucagon secretion.
      • PP Cells: Produce pancreatic polypeptide, which regulates exocrine function.
  • Hormones:
    • Maintain glucose homeostasis and regulate metabolism.

Clinical Significance

Common Disorders

  1. Pancreatitis:
    • Inflammation of the pancreas.
    • Acute Pancreatitis: Sudden onset, often caused by gallstones or alcohol.
    • Chronic Pancreatitis: Long-term inflammation, often due to alcohol abuse or genetic factors.
  2. Diabetes Mellitus:
    • Type 1: Autoimmune destruction of beta cells, leading to insulin deficiency.
    • Type 2: Insulin resistance and impaired insulin secretion.
  3. Pancreatic Cancer:
    • Most commonly adenocarcinoma originating from exocrine cells.
    • Symptoms: Jaundice, weight loss, abdominal pain, and back pain.
  4. Cystic Fibrosis:
    • Genetic disorder affecting exocrine glands, leading to thickened pancreatic secretions and digestive issues.
  5. Pancreatic Insufficiency:
    • Insufficient production of digestive enzymes, leading to malabsorption and nutrient deficiencies.

Symptoms of Pancreatic Disorders

  • Abdominal pain (epigastric, radiating to the back).
  • Nausea and vomiting.
  • Weight loss.
  • Jaundice (if bile ducts are obstructed).
  • Fatty stools (steatorrhea) in cases of exocrine insufficiency.

Diagnostic Tests

  1. Blood Tests:
    • Elevated levels of amylase and lipase indicate pancreatitis.
    • Glucose tests for diabetes.
  2. Imaging:
    • Ultrasound: To detect gallstones or structural abnormalities.
    • CT Scan: To assess pancreatic inflammation or tumors.
    • MRI/MRCP: For detailed imaging of the pancreas and biliary tree.
  3. Endoscopic Ultrasound (EUS):
    • To detect small tumors or cysts.
  4. Biopsy:
    • For diagnosing pancreatic cancer.

Treatment Options

  1. For Pancreatitis:
    • Supportive care: Fasting, IV fluids, pain management.
    • Address underlying causes (e.g., gallstone removal, alcohol cessation).
  2. For Pancreatic Cancer:
    • Surgery (e.g., Whipple procedure).
    • Chemotherapy and radiation.
  3. For Diabetes:
    • Insulin therapy or oral hypoglycemic agents.
    • Lifestyle modifications.
  4. For Exocrine Insufficiency:
    • Pancreatic enzyme replacement therapy (PERT).
  • Teeth and Tongue

Teeth and Tongue: Detailed Anatomy, Functions, and Clinical Aspects

Teeth

Teeth are hard, calcified structures embedded in the gums, playing a crucial role in mechanical digestion and speech.

1. Structure of a Tooth

Each tooth has three main parts:

  1. Crown:
    • The visible part of the tooth above the gumline.
    • Covered with enamel, the hardest substance in the body.
  2. Neck:
    • The region where the crown and root meet, at the gumline.
  3. Root:
    • The part embedded in the jawbone.
    • Anchored by the periodontal ligament.

4 Layers of a Tooth

  1. Enamel:
    • Outer covering of the crown.
    • Protects the tooth from wear and decay.
  2. Dentin:
    • Beneath the enamel, forms the bulk of the tooth.
    • Transmits sensations to the pulp.
  3. Pulp:
    • Inner soft tissue containing blood vessels, nerves, and connective tissue.
    • Provides nourishment and sensation to the tooth.
  4. Cementum:
    • Covers the root and attaches it to the periodontal ligament.

2. Types of Teeth

Humans have two sets of teeth during their lifetime:

  1. Primary Teeth (Deciduous/Milk Teeth):
    • Total: 20 teeth (10 in each jaw).
    • Appear between 6 months and 2 years of age.
  2. Permanent Teeth:
    • Total: 32 teeth (16 in each jaw).
    • Erupt between 6 and 12 years of age (except wisdom teeth, which may appear later).

Classification of Teeth

  1. Incisors (8):
    • Function: Cutting food.
    • Location: Front of the mouth.
  2. Canines (4):
    • Function: Tearing food.
    • Location: Next to incisors.
  3. Premolars (8):
    • Function: Crushing and grinding food.
    • Location: Between canines and molars.
  4. Molars (12):
    • Function: Grinding food.
    • Location: Back of the mouth.

3. Functions of Teeth

  1. Mechanical Digestion:
    • Chewing (mastication) breaks food into smaller pieces.
  2. Speech:
    • Helps in articulation of sounds.
  3. Aesthetic Appearance:
    • Contributes to facial structure and smile.

4. Common Disorders

  1. Dental Caries (Cavities):
    • Decay caused by bacteria breaking down sugar into acid.
  2. Gingivitis:
    • Inflammation of the gums.
  3. Periodontitis:
    • Advanced gum disease affecting periodontal tissues.
  4. Malocclusion:
    • Misalignment of teeth.
  5. Tooth Sensitivity:
    • Pain due to exposed dentin.

Tongue

The tongue is a muscular organ located in the oral cavity, essential for taste, speech, and digestion.

1. Structure

  1. Parts:
    • Tip (Apex): Most anterior, mobile part.
    • Body: Central part.
    • Root: Posterior part attached to the floor of the mouth.
  2. Surfaces:
    • Dorsal Surface: Upper surface, covered with papillae.
    • Ventral Surface: Underside, smooth and contains veins.
  3. Muscles:
    • Intrinsic Muscles: Change the shape of the tongue.
    • Extrinsic Muscles: Move the tongue in various directions (e.g., genioglossus, styloglossus).

2. Papillae of the Tongue

  1. Filiform Papillae:
    • Small, conical projections, provide friction.
    • No taste buds.
  2. Fungiform Papillae:
    • Mushroom-shaped, scattered over the tongue.
    • Contain taste buds.
  3. Circumvallate Papillae:
    • Large, dome-shaped, located at the back of the tongue in a V-shape.
    • Contain numerous taste buds.
  4. Foliate Papillae:
    • Leaf-shaped, located on the sides of the tongue.
    • Contain taste buds.

3. Functions of the Tongue

  1. Taste Sensation:
    • Taste buds detect sweet, sour, salty, bitter, and umami (savory).
  2. Mechanical Digestion:
    • Moves food during chewing and shapes it into a bolus for swallowing.
  3. Speech:
    • Helps articulate sounds and words.
  4. Cleaning:
    • Cleans the oral cavity by sweeping food particles.

4. Nerve Supply

  1. Motor Nerves:
    • Hypoglossal nerve (cranial nerve XII).
  2. Sensory Nerves:
    • Anterior Two-Thirds:
      • General sensation: Lingual nerve (branch of mandibular nerve).
      • Taste sensation: Chorda tympani (branch of facial nerve).
    • Posterior One-Third:
      • General and taste sensation: Glossopharyngeal nerve (cranial nerve IX).
  3. Root of Tongue:
    • Supplied by the vagus nerve (cranial nerve X).

5. Blood Supply

  • Arterial Supply: Lingual artery (branch of the external carotid artery).
  • Venous Drainage: Lingual vein drains into the internal jugular vein.
  • Peritoneum
  • A membranous layer that supports and protects the organs of the digestive system.
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Categorized as BS NURSING SEM 1 ANATOMY, Uncategorised