Digestive System (1) Flashcards
Two main groups of the digestive system
- alimentary canal (GI tract)
- accessory digestive organs
What is the alimentary canal?
- continuous muscular tube from mouth to anus
What does the alimentary canal do?
- digests food by breaking it down into smaller fragments
- absorbs digested nutrients into blood
Organs of the alimentary canal
- mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus
What are accessory digestive organs?
- teeth, tongue, salivary glands
- liver, gall bladder, pancreas
Main digestive processes in order
- ingestion
- propulsion
- mechanical breakdown
- digestion
- absorption
- defecation
What is ingestion?
- taking food into digestive tract via mouth
What is propulsion?
- moving food through alimentary canal by swallowing (voluntary) and peristalsis (involuntary)
What is peristalsis?
- alternating waves of contraction and relaxation of muscles in organ walls
- squeezes food along the tract with some mixing
What is mechanical breakdown?
- increasing surface area of ingested food, preparing it for digestion by enzymes
- include chewing, mixing food with saliva by tongue, churning in stomach, segmentation in small intestine
What is segmentation?
- rhythmic local constrictions of small intestine, moving food toward and backward
- mixes food with digestive juices and makes absorption more efficient
What is digestion generally?
- catabolic steps in which enzymes secreted into alimentary canal break down food
What is absorption?
- digested end products (vitamins, minerals, water) pass through lumen of alimentary canal into blood and lymph
- through mucosal cells by active or passive transport
What is defecation?
- elimination of ingestible substances via anus
One GI tract organ found in thorax
- esophagus
Three GT tract organs located in abdominal cavity
- stomach, small intestine, large intestine
Membranes in ventral body cavities
serous membranes
What is the peritoneum?
- serous membrane that lines abdominal cavity
- visceral peritoneum covers external surfaces of digestive organs, continuous with parietal peritoneum that lines body wall
- between 2 peritoneums is peritoneal cavity
4 basic tunics (layers) of alimentary canal: innermost to outermost
- mucosa (mucous membrane)
- submucosa
- muscularis externa
- serosa
What is mucosa of alimentary canal made up of?
- moist epithelial membrane with mucus secreting cells
- simple columnar epithelium
- mouth, esophagus and anus is stratified squamous epithelium
- lamina propria underlines the epithelium; loose areolar connective tissue; nourishes epithelium and absorbs nutrients
- muscularis mucosae is external to the lamina propria; smooth muscle cells produce local movements of mucosa
Function of the mucosa of alimentary canal
- “secrete” mucus, digestive enzymes and hormones
- “absorb” end products of digestion into blood
- “protect” against infectious disease
Submucosa of the alimentary canal
- areolar connective tissue
- rich supply of blood, lymph vessels and nerve fibres
Muscularis externa of alimentary canal
- responsible for segmentation and peristalsis
- smooth muscle cells
- inner circular layer and outer longitudinal layer
- circular layers form sphincters
Serosa of the alimentary canal
- visceral peritoneum
- areolar connective tissue covered with mesothelium
only part of alimentary canal involved in ingestion
- the mouth (oral cavity/buccal cavity)
What lines the walls of the mouth?
- thick stratified squamous epithelium
- epithelium on gums, hard palate and tongue are slightly keratinized
How does oral mucosa respond to injury?
- produces antimicrobial peptides called defensins
Function of lips and cheeks
- help keep food between teeth when we chew
- composed of skeletal muscle core covered externally by skin
Muscles in lips
orbicularis oris muscle
What is the palate?
- roof of the mouth
- anterior hard palate, posterior soft palate
The hard palate
- underlined by palatine bones and palatine processes of maxillae
- forms rigid surface against which the tongue forces food during chewing
- friction is created by corrugated mucosa on either side of its raphe (midline ridge)
Midline ridge of the hard palate
raphe
The soft palate
- formed mostly of skeletal muscle
- rises reflexively to close off nasopharynx when we swallow
What is the tongue composed of?
- interlacing bundles of skeletal muscles
What does the tongue do?
- grips food and constantly repositions it between teeth
- mixes food with saliva to form a bolus
- initiates swallowing by pushing bolus into the pharynx
- helps us form consonants when we speak
Function of the saliva
- cleanses the mouth
- dissolves food chemicals so they can be tasted
- moistens food and helps compact it into a bolus
- enzymes for breakdown
Major salivary glands
- parotid, submandibular, sublingual
- paired compound tubuloareolar glands
- develop from oral mucosa
Parotid gland
- large, triangular salivary gland
- anterior to the ear
-mostly serous cells
Submandibular gland
- size of a walnut
- lies along medial aspect of mandibular body
- mucosa that doesnt produce mucus
-mostly serous cells
Sublingual gland
- almond shaped
- anterior to the submandibular gland under tongue
- mostly mucous cells
2 types of secretory cells in salivary glands
- serous and mucus
Why is saliva hypo-osmotic?
- 97 to 99.5% water
What does saliva’s osmolarity depend on?
- active glands
- stimulus for salivation
pH of saliva
- slightly acidic (6.75 to 7)
solutes in saliva
- electrolytes
- digestive enzymes (amylase, lipase)
- proteins like lysozyme
- metabolic wastes
How does saliva protect against microorganisms?
- IgA antibodies
- lysozyme: inhibits bacterial growth in mouth, prevent tooth decay
- defensins: local antibiotics, call defensive cells into the mouth
Milk Teeth/Baby Teeth
-deciduous teeth
- first, lower central incisors at 6 months
- other teeth erupt at one to two month intervals
- 20 in total
Permanent teeth
- 32 in total
Incisors
- cutting or nipping of food
Canines
- fang-like
- tear, pierce
Premolars (bicuspids) and molars
- broad crowns with rounded cusps
- grinding and crushing
2 passageways pharynx
- oropharynx
-laryngopharynx
Mucosa of the pharynx
- stratified squamous epithelium
- mucus-producing glands
Esophagus structure and function
- muscular tube about 25 cm
- collapsed when not involved in food propulsion
- laryngopharynx -> epiglottis closes -> food routed posteriorly into larynx
Mastication (Chewing)
- cheeks and closed lips hold food between teeth
- tongue mixes food with saliva to soften
- teeth cut food
Deglutition (Swallowing)
- tongue -> bolus
What is gut brain?
- enteric nerve plexuses spread along GI tract
- “in-house” control
