Digestive System Flashcards
Mechanical Digestion
Physical breakdown of food into smaller particles
Teeth and churning action of stomach and intestines
Chemical Digestion
Series of hydrolysis reactions that break macromolecules into their monomers
Enzymes from saliva, stomach, pancreas, and intestines
Results of Chemical Digestion
Polysaccharides into monosaccharides
Proteins into amino acids
Fats into glycerol and fatty acids
Which buffer system uses HPO4 to buffer secreted acid in the kidney?
The Phosphate Buffer System
What is responsible for the detection of blood osmolarity?
Osmoreceptors located in the hypothalamus
What does not elicit the release of aldosterone?
ADH
Does not have anything to do with sodium
Subdivisions of the Digestive System
Digestive tract and accessory organs
Digestive Tract
16 foot long tube extending from the mouth to anus
Accessory Organs
Aid in digestion but are not part of the alimentary canal
Teeth, tongue, liver, gallbladder, pancreas, salivary glands
Layers of the GI Tract
- Mucosal layer
- Submucosal layer
- Muscularis layer
- Serosa layer
Mucosa
Inner lining
Stratified squamous epithelium, simple columnar epithelium, lamina propria, muscularis mucosae
Stratified Squamous Epithelium
In mouth, esophagus, and anus
Tough
Simple Columnar Epithelium
Secretes enzymes and absorbs nutrients Specialized cells (goblet cells) secrete mucous onto cell surface Enteroendocrine cells secrete hormones controlling organ function
Lamina Propria
Thin layer of loose connective tissue
Contains blood vessels and lymphatic tissue
Muscularis Mucosae
Thin layer of smooth muscle
Causes folds to form in mucosal layer
Increases local movements increasing absorption with exposure to “new” nutrients
Submucosa
Loose connective tissue containing blood vessels, glands, and lymphatic tissue
Meissner’s Plexus: parasympathetic, causes vasoconstriction
Muscularis
Skeletal muscle for voluntary control in mouth, pharynx, upper esophagus, and anus
Smooth muscle for mixing, crushing, and propelling food by peristalsis
Auerbach’s Plexus for sympathetic and parasympathetic innervation of smooth muscle layers
Serosa
Serous membrane
Covers all organs and walls of cavities not open to the outside of the body
Secretes slippery fluid
Consists of connective tissue covered with simple squamous epithelium
Peritoneum
Visceral layer covers organs
Parietal layer lines the walls of the body cavity
Greater Omentum
Prevents organs from moving around
Hangs down from the stomach
Contains blood and lymphatic vessels
Mesocolon
Connects intestines together
Lesser Omentum
Connects stomach to liver
“Beer belly”
Lips and Cheeks
Contain buccinator muscle that keeps food between upper and lower teeth
Oral Cavity Proper
Hard palate, soft palate, and uvula
Tongue
Responsible for moving food
Attached to hyoid, mandible, hard palate, and styloid process
Tooth Structure
- Crown
- Neck
- Roots
- Pulp cavity
Composition of Teeth
Enamel
Dentin
Cementum
Enamel
Hardest substance in the body
Calcium phosphate or carbonate
Dentin
Calcified connective tissue
Cementum
Bone-like
Periodontal ligament penetrates it
Saliva
Moistens, dissolves food for taste, begins starch and fat digestion, cleanses teeth, inhibits bacteria, and binds food together into bolus
Amylase
Begins starch digestion
Lingual Lipase
Digests fat after it reaches the stomach
Lysozyme
Enzyme that kills bacteria
Immunoglobin A
Inhibits bacterial growth
Electrolytes
Na+, K+, Cl-, phosphate, and bicarbonate
Salivation
Salivary nuclei in the medulla oblongata and pons
Parasympathetic function
Mumps
Myxovirus that attacks the parotid gland
Pharynx
Funnel-shaped tube extending from internal nares to the esophagus (posteriorly) and the larynx (anteriorly)
Esophagus
Collapsed muscular tube
Histology of the Esophagus
Mucosa: stratified squamous
Submucosa: large mucous glands
Muscularis: upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth
Adventitia: connective tissue blending with surrounding connective tissue (no peritoneum)
Swallowing
Upper sphincter relaxes when larynx is lifted
Peristalsis pushes food down
Lower sphincter relaxes as food approaches
Swallowing: Oral Phase
Voluntary
Bolus formed in the mouth
Oropharynx–>Laryngopharynx
Pharyngeal Phase
Involuntary
Tongue and soft palate block food and drink
Esophagus widens
Esophageal Phase
Peristalsis
Brain swallowing center + myenteric plexus in esophageal wall
Muscle above bolus constricts
Anatomy of Stomach
Left side of stomach
Cardia, Fundus, Body, Pylorus
Pylorospasm
Muscle fibers of sphincter fail to relax, trapping food in the stomach
Vomiting occurs to relieve pressure
Pyloric Stenosis
Narrowing of sphincter indicated by projectile vomiting
Must be corrected surgically
Stomach Mucous Cell
Secretes mucous
Cardiac, pyloric glands
Stomach Regenerative Cells
Base of gastric pits
Divide rapidly
New cells migrate upward
Stomach Parietal Cells
Secrete HCl, intrinsic factor, ghrelin
Found mostly in gastric glands
Stomach Chief Cells
Most numerous
Secrete gastric lipase, pepsinogen
Lower 1/2 of gastric glands
Stomach Enteroendocrine Cells
Found in the lower end of the gland
Secrete hormones and paracrine messengers
At least 8 different kinds
Stomach Muscularis
Longitudinal, Circular, and Inner Oblique
Stomach Mechanical Digestion
Gentle mixing waves
More vigorous waves from body to pyloric region
Intense waves near the pylorus
Stomach Chemical Digestion
Protein digestion begins as HCl denatures protein, transforms pepsinogen into pepsin
Fat digestion continues as gastric lipase splits triglycerides in milk fat
Regulation of Gastric Secretion and Motility
- Cephalic phase
- Gastric phase
- Intestinal phase
Cephalic Phase
Gets the stomach ready
Cerebral cortex stimulates parasympathetic nervous system
Vagus nerve increases stomach muscle and glandular activity
Gastric Phase
“Stomach Working”
Nervous control keeps stomach active
Endocrine system influences stomach activity
GI Reflexes
Short Reflex: reflex arc where stimulus, integration, and effector are all located in the GI system
Long Reflex: reflex arc where integration occurs in the brain or spinal cord; vasovagal reflex
Functions of Hydrochloric Acid
- Activates enzymes pepsin and lingual lipase
- Breaks up connective tissues and plant cell walls
- Converts ingested ferric ions to ferrous ions that can be used for hemoglobin
- Destroys ingested bacteria and pathogens
Intrinsic Factor (Parietal Cells)
Essential for absorption of B12 by small intestine
Necessary for RBC production (pernicious anemia)
Pepsin (Chief Cell)
Secreted as pepsinogen
HCl converts it to pepsin, which activates more pepsinogen
Gastric Lipase (Chief Cell)
Gastric lipase + lingual lipase digests 10-15% of dietary fat
Remainder in the small intestine
Intestinal Phase
Gastric activity INCREASES
Enterogastric reflex=duodenum INHIBITING stomach
Chyme stimulates duodenal cells to release SECRETIN, CCK, and GASTRIC INHIBITORY PEPTIDE to SUPPRESS gastric secretion and motility
