digestive system Flashcards
what is heterotrophy?
that all animals obtain energy and nourishment from molecules made by other organisms
what is digestion?
the hydrolysis of macromolecules into their subunits catalysed by enzymes
what are the 4 macromolecules and their monomers
-carbohydrates go to monosaccharides
-proteins go to amino acids
-nucleic acids go to nucleotides
-triglycerides go to monoglycerides and fatty acids
what are the 5 main processes that take place in the digestive system
1.ingestion
2.digestion
3.absorption
4.motility
5.excretion
what is the order of structures in the GI tract?
1.mouth
2.pharynx
3.oesophagus
4.stomach
5.small intestine
6.large intestine
7.rectum
8.anus
what does the mouth do in digestion and what salivary glands does the mouth contain?
mechanical and chemical digestion:
-parotid
-submandibular
-sublingual
-minor glands in inner cheeks
what does saliva do and name the three types of salivary enzymes and their examples
it lubricates food and forms a bolus for swallowing:
-amylase
-proteolytic enzymes, lipases, phosphates
-lysozyme and IgA antibodies
what is the pharynx
a tube composed of skeletal muscle lined with mucous membrane and muscular contractions propel food into oesophagus
what is the oesophagus
muscular tube that secretes mucus, it’s peristaltic movements moves food into the stomach
How does the stomach do chemical digestion
by secreting gastric juice:
-parietal cells in gastric glands secrete HCL which lowers the pH to 1.5-2 and so kills many bacteria
-chief cells secrete pepsinogen to form pepsin that hydrolyses protein
how are proteins broken down in the stomach?
pepsinogen gets hydrolysed via HCL into pepsin and the proteins get hydrolysed via pepsin into peptides
how does pepsin digest proteins?
pepsin digests proteins and peptides by cleaving preferentially after the N terminal of aromatic amino acids such as phenylalanine
give three things gastrin does
-simulates secretion of gastric juice
-increases motility of the GI tract
-relaxes the pyloric sphincter
what does pancreatic juice contain?
-water, salts, sodium bicarbonate
-digestive enzymes
what digestive enzymes are in pancreatic juice?
-pancreatic amylase
-trypsin
-chymotrypsin
-elastase
-carboxypeptidase
-pancreatic lipase
-ribonuclease
-deoxyribonuclease
what does the liver do?
-solubilises fat for attack by lipases via release of bile from the gall bladder
-removes toxins
-phagocytoses worn out blood cells and bacteria
-stores and metabolises nutrients and vitamins
what enzymes does the small intestine release?
-maltase, sucrase and lactase
-peptidases
-ribonuclease
-deoxyribonuclease
what are the three secretions of the small intestine and what do they do?
-secretin: regulates the secretions of the stomach, pancreas and osmoregulation throughout the body
-cholecystokinin: simulates release of digestive enzymes from pancreases and bile from gall bladder acting as a hunger suppressant
-gastric inhibitory polypeptide (GIP) simulates insulin secretion
What are the parts of the small intestine?
jejunum, ileum, villi
what are the secretory organs in the digestive system?
-salivary glands
-stomach
-liver
-pancreas
-small intestine
how are monosaccharides absorbed into the epithelial cells of the villus?
-glucose and galactose diffuse by active transport
-fructose by facilitated diffusion
how are amino acids, dipeptides and tripeptides absorbed into the eputhelial cells of the villus?
active transport
how are short chain fatty acids absorbed into the epithelial cells of the villus?
via diffusion
How are lipids absorbed into the epithelial cells of the villus?
the micelles simply diffuse
how is vitamin A and carotenoids absorbed through the villus and into the blood?
- receptor mediated passive diffusion
- either incorporated into HDLs and secreted into blood plasma or into chylomicrons and secreted into the lymph
what vitamins does the liver store?
lipophilic vitamins such as A, D, E and K
what sections does the large intestine consist of?
-caecum (appendix)
-colon
-rectum
-anal canal
-anus
what does the large intestine epithelium contain?
-no villi
-numerous microvilli in absorptive cells
-many goblet cells secreting lubricative mucus
Give an example of symbiotic bacteria in the GI tract
lactobacillus acidophilus and this produces vitamin B
what is helicobacter pylori?
bacteria in the GI tract that causes gastritis and gastric and duodenal ulcers
what proteins does pepsin not digest?
proteins that have bonds containing valine, alanine or glycine
which layer of the GI tract is closest to ingested food?
serosa
what kind of epithelium is that of the stomach?
simple columnar epithelium
