The digestive system Flashcards
What are the 6 basic processes included in digestion?
- ingestion
- secretion
- mixing and propulsion
- digestion
- absorption
- defecation
What are the 4 layers of the GI tract?
-mucosa
-submucosa
-muscularis
-serosa
What is the mucosa layer made up from?
-epithelium
-aerolar connective tissue
-muscle layers
What is the submucosa layer made up from and what is its function?
-has areolar tissue that binds the mucosa to the muscularis
-contains many blood and lymphatic vessels that receive absorbed food molecules
What is the muscularis layer made up from and what is its function?
-contains skeletal muscle to produce voluntary swallowing
-and smooth muscle which has involuntary contractions to help break down food, mix it with digestive secretions and propel it along the tract
What is the serosa layer made up from?
-a serous membrane composed of areolar connective tissue and simple squamous epithelium
What are the 4 types of tooth found in the mouth and what are there functions?
- incisors= cut food
- canines= tear food
- premolars= crush and grind food
- molars= grind food
What is the function of the uvula in the mouth?
Prevents swallowed food from entering the nasal cavity
What is mechanical digestion in the mouth?
when food is chewed (masticated) and manipulated by the tongue, ground by the teeth and mixed with saliva
What are the 2 main muscles in the mouth used for mechanical digestion?
-Masseter
-Buccinator
What are the 3 main muscles in the mouth used for chemical digestion?
-sub-lingual
-sub-mandibular
-parotid
What is the pharynx and what is it composed of?
-the throat
-a funnel shaped tube composed of skeletal muscle and lined by mucous membrane
What is the oesophagus?
-a muscular tube that connects the pharynx to the stomach
What is found at each end of the oesophagus formed by the muscularis?
-the upper oesophageal sphincter (UES) which consists of skeletal muscle
-the lower oesophageal sphincter (LES) which consists of smooth muscle
What is peristalsis and what does it consist of?
-a series of wave like muscle contractions that move food from the mouth to the stomach
-theres a voluntary stage from the mouth to the oropharynx (middle part of the throat behind the mouth)
-involuntary stage/ pharyngeal stage from the upper oesophageal sphincter to the oesophagus
What 2 body organs does the stomach connect?
the oesophagus to the duodenum (first part of the small intestine)
What are the 4 main regions of the stomach?
- the cardia
- fundus
- body
- pylorus
What 4 basic layers also compose the stomach wall?
- mucosa
- submucosa
- muscularis
- serosa
What is the term rugae?
when the stomach is empty the mucosa lies in large folds (called rugae)
What do the glands on the surface of the stomach produce?
-mucus
-hydrochloric acid
-pepsin
-intrinsic factor
-gastrin
What is chyme and how is it produced?
-pulpy acidic fluid which passes from the stomach to the small intestine
-made by mechanical digestion mixing waves that macerate food and mix it with gastric juice
How is the enzyme pepsin involved in chemical digestion?
it breaks the peptide bonds between the amino acids of proteins
What does the mucus produced do in the stomach?
-it is secreted by mucous cells coats the mucosa forming a thick barrier between the cells of the stomach lining and the gastric juice
What does the lingual lipase produced by the tongue do?
-digests triglycerides into fatty acids and diglycerides in the acid environment in the stomach
What does the mucous cells of the stomach absorb?
-some water
-ions
-short chain fatty acids
-certain drugs (e.g aspirin)
-alcohol
After how many hours from eating has the stomach emptied its contents into the small intestine?
Within 2 to 4
What are the 3 main structures that the small intestine is divided into?
-duodenum
-jejunum
-ileum
How is the small intestine highly adapted for digestion and absorption?
-its glands produce enzymes and mucus
-the microvilli, villi and circular folds of its walls provide a large surface area
What does mechanical digestion in the small intestine involve?
-segmentations (divides and mixes chyme)
-migrating waves of peristalsis
What do the enzymes found in pancreatic juice, bile and microvilli do to aid absorption?
break down disaccharides to monosaccharides
What is protein digestion completed by?
Peptidases
What does pancreatic lipase do to aid absorption?
breaks down triglycerides into fatty acids and monoglycerides
What does nucleases do to aid absorption?
break down nucleic acids to pentoses and nitrogenous bases
What percentage of absorption takes place in the small intestine?
90% (10% occurs in stomach and large intestine)
Define absorption and the processes which occur within it
-the passage of nutrients from digested food in the gastrointestinal tract into the blood or lymph
-occurs mostly in the small intestine
-simple diffusion, faciliitated diffusion, osmosis and active transport occur
What 3 things does the small intestine also absorb?
-water
-electrolytes (ions)
-vitamins
Where is the pancreas located in the body and what organ part does it connect to?
-found behind the stomach
-passes secretions to the duodenum
What is the pancreas made up of?
-small clusters of glandular epithelial cells called acini
What makes up the exocrine part of the pancreas and what do these cells do?
The acini make up the exocrine part and the cells within acini secrete a mixture of fluid and digestive enzymes called pancreatic juice
What makes up the endocrine part of the pancreas and what do these do?
-the islets of Langerhans
-secrete hormones
What types of cells are found within the islets of langerhans and what do these cells do?
-alpha cells= secrete glucagon
-beta cells= secrete insulin
What enzymes are contained in the pancreatic juices?
-pancreatic amylase= to digest starch
-carboxypeptidase trypsin + chymotrypsin= to digest proteins
-pancreatic lipase= to digest triglycerides
-RNA/DNA= to digest nucleic acids
Why is it good that the pancreas is highly vascular?
-having a rich blood supply allows enzymes to be passed on to other structures
What are the units for blood sugar?
mmol/L or mg/dl
What are the 4 main lobes in the liver?
- right lobe
- left lobe
- quadrate lobe
- caudate lobe
What is the gallbladder?
-the sac located in a depression under the liver that stores and stores the bile produced by the liver
What are the several components that make up the liver microscopically?
-hepatocytes (liver cells)
-bile canaliculi
-hepatic sinusoids
-reticuloendothelial (kupffer) cells
-central veins
-hepatic veins
What part of the liver produces bile?
the hepatocytes
What is the function of bile?
To emulsify lipids
What enzyme is produced that causes the gallbladder to contract?
cholecystokinin = cck(pz)
What are the 2 main components of bile?
-sodiumglycochozate
-taurocholate
What functions does the liver perform?
-secretion of bile
-phagocytosis of bacteria and dead or foreign material by the stellate reticuloendothelial cells
-carbohydrate, lipid and protein metabolism
-processing of drugs and hormones
-excretion of bilirubin
-storage of vitamins and minerals
Where does the large intestine extend from and to in the body?
from the ileocecal sphincter to the anus
What 4 regions does the large intestine consist of?
- cecum
- colon
- rectum
- anal canal
What 4 portions is the colon of the large intestine divided into?
Ascending
Transverse
Descending
Sigmoid portions
What 2 types of cells does the mucosa contain?
-numerous absorptive cells that absorbs water
-goblet cells that secrete mucus
What is mass peristalsis?
a strong peristaltic wave that drives the contents of the colon into the rectum
What is the large intestines main functions?
to absorb water, ions (e.g sodium and chloride) and some dietary vitamins
What do faeces consist of chemically?
-water
-inorganic salts
-sloughed-off epithelial cells from the mucosa of the gastrointestinal tract
-bacteria
-products of bacteria decomposition
-unabsorbed digested materials
-indigestible parts of food
What is defecation?
-The elimination of feaces from the rectum
-its a reflex action aided by voluntary contractions of the diaphragm and abdominal muscles and relaxation of the external anal sphincter
What is micturition?
The technical term for wee
