Abdominal regions
Ab regions
- Most digestive organs are in the abdominopelvic cavity
9 regions
- 3 superior: right and left hypochondriac, central epigastric
- 3 middle- right and left lumbar regions, central umbilical region
- 3 inferior- right and left iliac regions, central hypogastric
Peristalsis and segmentation
Peristalsis
- Wave of muscular contraction occurs throughout the GI tract
- Adjacent segments alternatively contract and relax
Segmentation
- Back and forth churning that occurs mainly in the small intestine
- Non- adjacent segments alternatively contract and relax
Digestive system processes/ functions
Ingestion: acquisition of nutrients
Propulsion: Movement of food through the GI tract (peristalsis)
Mechanical breakdown: Chewing, churning and segmentation
Digestion: Food molecules are broken down
Absorption: Transport of nutrients from the digestive system to the circulatory system
Defacation: Elimination of feces
The peritoneal cavity and peritoneum
Visceral peritoneum: covers the external surfaces of most digestive organs
The parietal peritoneum: lines the body wall and is continuous with the visceral peritoneum
Peritoneal cavity: between the visceral and parietal peritoneum, contains fluid to reduce friction
Mesenteries
A double layer of peritoneum that extends from the body wall to the digestive organs.
Functions= Hold organs in place, store fat, route for vessels
Ventral mesenteries
- Falciform ligament: liver to anterior abdomen wall and diaphragm
- Lesser omentum: liver to the lesser curvature of the stomach
- Greater omentum: greater curvature of stomach to posterior abdominal wall
Dorsal mesenteries
Greater momentum: Greater curvature of stomach to posterior abdominal wall
Mesentary= supports coils of jejunum and ilium
Transverse mesocolon:
- Transverse colon to posterior abdominal wall
Sigmoid mesocolon= sigmoid colon to posterior pelvis wall
Intraperitoneal vs Retroperitoneal
- Organs that are suspended into the peritoneal cavity contain mesenteries, are referred to as intraperitoneal organs, and are moveable
- Organs that are not suspended into the peritoneal cavity lack mesenteries, are retroperitoneal and are immobile. e.g. pancreas, kidneys, duodenum, ascending and descending colon
Anatomy of the alimentary canal wall
Same 4 layers from the oesophagus to the 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
- The muscularis externa- external to the submucosa
2 layers: Circular muscularis- inner layer and longitudinal muscularis- outer layer
- The serosa: the outermost layer
Oral cavity
- Entranceway for food
- Oral vestibule- space between teeth and lips
- oral cavity proper
- Hard and soft palate- form roof of mouth
- Palatoglossal arch- anchors tongue to soft palate
- Palatopharyngeal arch- anchors tongue to oropharynx
- Lined with thick stratified epithelium
Oropharyngeal isthmus is the entranceway from the oral cavity to the pharynx
The tongue
Functions
- Assistance in chewing
- Sensory fxn: touch, temperature and taste
- Secretion of mucins and the enzyme lingual lipase that aids in breaking down triglycerides
3 types of projections of mucosa:
- Filiform- roughen
- Fungiform and vallate
- Papillae- tastebuds
Tonsils
Patches of lymphatic tissue are found at the entrance of the pharynx. Projection against ingested and inhaled pathogens
- Pharyngeal tonsils are in the posterior wall of the nasopharynx
- Palatine tonsils are in the posterolateral region of the oral cavity
- Lingual tonsils are along the posterior 1/3 of the tongue
Salivary glands
Functions= lubricate the oral cavity and moisten food. Dissolve chemicals that stimulate the taste buds. Anti-microbial substances. Parasympathetic innervation stimulates salivary gland secretion
Parotid
- Anterior to the ear
- 25-30% of saliva passes to oral
- Cavity via the parotid duct
- Glossopharyngeal nerve
Sublingual
- Inferiorly to the tongue
- 3-5% of saliva passes to oral cavity via sublingual ducts
- Facial nerve
Submandibular
- Inferior to the mandible
- 60-70% of saliva passes to mouth floor via submandibular duct
- Facial nerve
Mastication
Jaw opening muscles:
- Digastric: TMJ depression and larynx elevation
- Mylohyoid: TMJ depression, floor of mouth elevation and hyoid elevation
- Geniohyoid: TMJ depression, larynx elevation and hyoid retraction
Jaw closing muscles:
- Masseter: TMJ elevation, retraction and protraction of the mandible, side-to-side movements
- Medial pterygoid =: TMJ elevation, side-to-side movements
Esophagus
From the mouth, food passes into the oropharynx and laryngopharynx before entering the oesophagus
- Hollow muscular tube connecting the pharynx to the stomach- begins at the cricoid cartilage
- Located within the mediastinum, posterior to the trachea and medial to the aorta
- Through esophageal hiatus
- Skeletal muscle or first one-third of length
- Mixture of skeletal and smooth muscle for middle 1/3 of length
- Smooth muscle from inferior one-third of length
- Wall secretes a lubricant
The stomach
- Storage of digested food
- Mechanical breakdown of ingested food
- Chemical digestion via acids and enzymes (primarily protein digestion)
- Ingested food now called chyme
4 important regions - Fundus
- cardia
- body
- pyloric region
Small intestine
- The longest part of the alimentary canal
- Site of most enzymatic digestion and absorption
- Receives secretion provided by pancreas and gall bladder (liver)
- Begins at pyloric sphincter and ends at ileocecal value
- 3 sub-divisions (duodenum 5% + jejunum 40% + ileum 60%)
- Innervation: Parasympathetic fibres from vagus nerve; Sympathetic from thoracic splanchnic nerve
Duodenum (C- shaped tube)
- Mixing bowl- chyme with bile and pancreatic secretions
- Originates from pyloric sphincter
- Retroperitoneal apart from the most proximal part, which is intraperitoneal
- Connects to the liver by the lesser omentum
- Covered by a lining of mucous membrane- protects epithelium from acid chyme
- Receives digestive enzymes
Secretions - Bile and pancreatic enzymes travel to the duodenum via the main pancreatic and bile duct
- Sphincters control entry of bile and pancreatic juices
- Enter the wall of the duodenum at the hepatopancreatic ampulla which opens into the major duodenal papilla
Jejunum and Ileum
Jejunum
- Important digestive and absorptive functions
- Begins at the duodenal: jejunal junction
- Intraperitoneal suspended by the mesentery proper
Ileum
- Absorption of vitamin B12; salts and all products of digestion that were not absorbed by the jejunum
- Intraperitoneal suspended by the mesentery proper
The ileum ends at a sphincter, the ileocecal value, which controls the flow of material from the ileum into the cecum of the large intestine
Circular folds (plicae circulares)
- Transverse ridges of mucosa and submucosa
- Increase surface for absorption and to slow the passage of food, all parts of the small intestine contain plicae: circular folds of the intestinal lining
- They appear in duodenum and jejunum prominently and become less common in the ileum
Intestinal villi and microvilli
- Intestinal villi are finger-like projections which are located on the mucosal surface of all parts of the intestine and increase the surface area of the intestinal wall
- Covered by simple columnar epithelium of enterocytes, which absorb digested nutrients
Microvilli - Finger-like projections of plasma membrane on apical surface of columnar epithelial cells
Increase surface area for absorption and chemical digestion
