22. Mechanical and Chemical Digestion Flashcards
what are the four steps for food processing?
ingestion - the act pf eatomg
digestion - process of breaking down food into molecules small enouigh to absorb
absorbtion - uptake of nutrients by body cells
elimination - occurs as undigested material passes out of the digestinve compartment
what is intracelluar digestioin?
food particles that are englufed via endocytosis and digested within food vacuoles
what is extracelluar digestion?
breakdown of food particles outside of cells. requires a complex body plan (mammals)
what are the four segments of the GI and what are two parts of each one
headgut - mouth and pharynx
foregut - oesogphagus and stomach
midgut - intestine
hindgut - colon, caecum and rectum
what is the general structure of the GI tract? three points
mucousa
submucousa
muscularis layer
study image
what is the structure and function of the mucousa in the GI tract? three points
stucture - single layer of epithelial cells lining the gut
functions - they are mostly secretory and abobitve
have underlying connective tissue which has immune cells
what is the stucuture and name two thing that submucousa can be?
submucouasa is the connective tissue lying underneath a mucous membrane.
can be blood and lymph vessels or nerves
what is the stucture and function of the muscularis layer?
structure - a thin muscle layer in the GI
propells nutrients unidirectionally from the lumen to the submucousa
what is peristalis movement in the GI tract?
the wave-like movement including the contraction and relaxation within the GI tract to push the contents forward
what are the two types of movement in the GI tract and what do they do?
peristalis - moving contents forward
segmentation - responsible for mixing
what does digestion depend on?
hydrolytic enymes to break down large molecules
what are the three types of digestive enymes?
intraluminal
membrane - associated
intracelluar
describe the digestion of the headgut
chew into smaller pieces to increase durface area of food
saliva acts as chemical digetion and a buffer
salivary amylase - intiates breakfdown of glucose
tounge tastes food
oesophgus takes food from the pharyx and down to the stomcah via peristalis
what is the structure and funciton of the stomach? Foregut.
name the four gastric juices secreted as well
its elastic - to store and mix food
secretes gastic juice including hydrochloric acid, pepsinogen, mucus and intrinsic factor (absorbtion of vitamin B12)
what causes pepsinogen to go from an inactive zymogen to the active enyme?
it has a masking sequence on the pepsinogen molecule but the low pH of the stomach activated the pepsinogen
how does the stomach protect itself from autodigestion of the HCL? two points
keeps pepsinogen seperatley from HCL (HCL stimulates pepsinogen to be in the active form, pepsin breaks down proteins and the stomach is protein)
stomach is lined with a layer of mucous from the mucous neck cells
what is the function of the small intestine?
its the major site of digestion and absorbtion (note - the stomach does not absorb nutrients)
how does the stomach pass on its conents to the small intestine?
small amounts of chyme is released into the small intestine mixed with gastic juices. the pancrease escretes bicarbonate to neutralise the chyme from the stomach
what is the order of pancreatic proteases?
trypsin –> trypsinogen
procarboxypeptidase –> carboxypeptidase
chymotrypisnogen –> chymostrypisin
trypsin also stimulates carboxypeptidase and chymotrypsin
results in the hydrolysis of peptides
what is the function of bile located in the gall bladder?
helps with the digestion of fats into fatty acids
what is the process of fat digestion? 5 steps
fat is consumed in a meal
bile is released from the ggall bladder
bile + fat create milecelles
pancreatic lipase produce fatty acids and monoglycerides
absorbtion of fatty acids and monoglyrides to form triglycerides
what is the function of the large intestine (colon)
to reabsorb water to be secreted back into the GI organs becasue lots of water is used in them.
fibre is broken down in the colon
