Digestive system - Part 1 Flashcards
The organs of the digestive system are divided into two groups. These are?
Alimentary canal (GI tract/digestive tract)
Accessory digestive organs
What are the accessory digestive organs?
Teeth and tongue.
Salivary glands, gallbladder, liver, pancreas
What are the different digestive processes?
Ingestion Propulsion Mechanical digestion Chemical digestion Absorption Defecation
What is ingestion?
Taking of food into the mouth
What is propulsion?
Movement of food
Voluntary - swallowing
Involuntary - peristalsis - move food down the esophagus and SI
What is mechanical digestion?
Mechanical breakdown of food, preparation for chemical digestion.
Chewing, churning of stomach, segmentation
What is chemical digestion?
Where does it occur?
Chemical breakdown of complex molecules to simple components via enzymes secreted by digestive glands.
Mouth, stomach, pancreas, SI
What is absorption?
Transport of digested nutrients from GI tract into the blood/lymph
What is defecation?
Elimination of indigestible substances as feces
Describe peristalsis.
Major means of propulsion
Adjacent segments of the alimentary canal relax and contract
Involuntary
Controlled by smooth muscle
Describe segmentation.
Rhythmic local contractions of the intestine.
Mechanically breaks down food and mixes it with digestive juices.
(only in SI)
Gives maximum contact with digestive juices (chemical breakdown)
What are the four layers of the alimentary canal?
Mucosa
Submucosa
Muscularis externa
Serosa
What is the innermost layer of the alimentary canal wall?
What are the rest, in order?
Mucosa
Submucosa
Muscularis externa
Serosa
What does the mucosa consist of?
Epithelium - non-keratinized stratified squamous epithelium
- simple columnar epithelium
Lamina Propia - areolar CT
Muscularis mucosae
What does the submucosa contain?
What tissue type does it have?
Contains blood and lymphatic vessels, and nerve fibres
Moderately dense areolar CT containing elastic fibres
The GI tract is a ______ membrane. Why?
Mucous
Open to the outside
Why can the mucosal layer be two different tissue types?
In the mouth, esophagus, anus and rectum - will have non-keratinized stratified squamous epithelium - protect against abrasion
Simple columnar epithelium for the rest - more absorptive role and secretion of mucus
What is the CT tissue layer under the mucous membrane?
Lamina propria - areolar CT
What does the muscularis mucosa do?
Small layer of muscle.
If tiny fluid particles get lodged, can twitch to dislodge food lodged in the epithelium.
Which parts of the alimentary canal have skeletal muscle? Which have smooth?
Mouth, pharynx, majority of esophagys, external anal sphincter
The rest is smooth muscle in one of two layers.
What are the two layers of smooth muscle in the muscularis externa?
Circular muscularis
- inner layer - squeezes gut tube
Longitudinal muscularis
- outer layer, shortens gut tube
Describe the serosa.
Outermost layer
Visceral peritoneum
Mesothelium and areolar CT.
What is malt?
Immune cells - part of areolar CT
Smooth muscle:
Primarily found in walls of _______.
Fibres ________.
Have ___ ______-located nucleus.
Grouped into sheets:
- Longitudinal layer - ________ to long axis of organ
- circular layer - deeper layer, fibres run around the ________ of organ
Viscera elongated one centrally-located Parallel circumference
Describe contractions in smooth muscle.
Delayed contractions, takes a while to contract.
Prolonged contraction, can hold contractions for a while - doesn’t fatigue as quickly
What is the peritoneum?
What is the visceral peritoneum?
What is the parietal peritoneum?
What is the peritoneal cavity?
Serous membranes of the abdominal cavity.
Visceral peritoneum - surrounds digestive organs
Parietal peritoneum - likes the abdominal body wall
Peritoneal cavity - a slit-like potential space
What is a mesentery?
Double layer of peritoneum.
Holds organs in place
Sites of fat storage.
Provides a route for circulatory vessels and nerves.
What is the falciform ligament?
Attach liver and diaphragm to anterior abdominal wall.
What are retroperitoneal organs?
Behind the peritoneum
Major organ is the kidneys
Kidney
- affixed to _____ abdominal wall
- ____ and ____ for protection
posterior
CT, fat
Describe the mouth/oral cavity mucosal layer.
- Non-keratinized stratififed squamous epithelium
- Lamina propria
- Heals very quickly due to multiple layers and capacity to regenerate
Tongue:
- Interlacing ______ of _____ muscle covered with _______ membrane
- ______ food and _______ it
- Tongue bounces food off the ______
- Helps form some _______
fascicles, skeletal, mucous
grips, repositions
palate
consonants
What is the labial frenulum?
Connects lips to gums
What is the palate?
Forms the roof of the mouth
What is the lingual frenulum?
Secures tongue to floor of mouth
What is done for tongue tied babies?
Lingual frenulum too far forward, sometimes clip it back a bit
What are the pharynx cavities pertinent to digestion?
Oropharynx and laryngopharynx.
What are the oropharynx and lanryngopharynx layers?
Lined with stratified squamous epithelium, non-keratinized
How is the bolus propeled to the esophagus from the pharynx?
Muscular contractions help propel the bolus into the esophagus
Epithelium:
- Tissue here is what?
- When empty, the mucosa and submucosa are in what arrangement?
- What lubricates the bolus?
- What are the changes in the muscularis externa?
- Does the esophagus have a serosa layer?
Non-keratinized stratified squamous epithelium
When empty, mucosa and submucosa are in longitudinal folds
Mucous glands secrete lubricating mucous
Skeletal muscle for first third, transitions to smooth muscle for last third
Not called serosa because the esophagus is not suspended within the peritoneal cavity, called the adventitia
The esophagus is a _________ muscular tube.
What does the esophagus expand against?
How does the bolus get lubricated?
collapsible
trachealis muscle
Bolus pushes against glands to secrete and coat it, ease passage in esophagus
What is the cardiac sphincter?
Closes lumen to prevent stomach acid from entering the esophagus
Also called the lower esophageal sphincter.
Acid reflux is an issue with what?
Cardiac sphincter, lets acid splash up into the esophagus.
What are the two phases of swallowing?
Voluntary phase
Involuntary phase
Describe the voluntary phase of swallowing.
Tongue pushes food to back of oral cavity
Describe the involuntary phase of swallowing.
Pharyngeal stage
Breathing stops and airways are closed.
Soft palate and uvula are lifted to close off nasopharynx,
Epiglottis bent to cover larynx
Stomach: - Site where food is churned into \_\_\_\_\_\_ Secretion of \_\_\_\_\_\_ begins digestion. - functions under \_\_\_\_\_\_ conditions Some substances are absorbed directly through the stomach. These are?
chyme
pepsin
acidic
water, electrolytes, aspirin, alcohol
What are the folds in the stomach called? What do they do?
Rugae
Increase surface area and allow the stomach to accomodate more food
What is one difference between the stomach and other parts of the GI tract?
Stomach has three muscular layers - also have oblique layer, innermost
– takes stomach and jacknifes it to force food through pyloric sphincter into duodenum
What is the epithelium of the stomach?
What does this epithelium secrete?
What is the mucosa dotted with?
Simple columnar epithelium
- secretes bicarbonate-buffered mucus
Mucosa dotted with gastric pits with deeper gastric glands
Gastric pits contain what?
What do each do?
Mucous neck cells - secrete a special mucus
Parietal cells - secrete HCL and gastric intrinsic factor
Chief cells - secretes pepsinogen
Why buffered mucus?
Neutralizes acid. Protects stomach lining.
What causes stomach growling?
Gas and air bubbles get produced by the stomach during digestion.
When chyme is in the system don’t hear the bubbles, when there is no chyme, hear them.
What is the longest portion of the alimentary canal?
What is the site of the most enzymatic digestion?
SI
What are the three subdivisions of the SI?
Duodenum, jejunum, ileum
Duodenum:
- Receives digestive enzymes from the ______ and bile from the ______ and ________.
pancreas
liver, gallbladder
Within the duodenum, the _____ is attached.
Gallbladder stores _______, liver produces it.
pancreas
bile
What are the modifications for absorption?
Circular folds
Villi
Microvilli
Length
What are circular folds?
Transverse ridges of mucosa and submucosa
What are villi?
Finger-like extension of the mucosa
Covered with simple columnar epithelium made up of absorptive cells
What are microvilli?
Further increases SA for absorption
How does length increase absorption?
maximize time for chyme to spiral through
maximizes contact with digestive enzymes
