digestive system Flashcards
define Peristalsis
a wave of muscular contractions that moves behind the bolus - pushing it downwards
stronger than gravity
it is aided by mucus secreted from the walls (lubrication)
define Gastroesophageal sphincter
boundary between the stomach and oesophagus
supposed to stop food from rising out of the stomach
heart means that the sphincter is leaking gastric juices into your oesophagus
stomach - mechanical digestion
mechanical digestion occurs in the stomach by waves of muscular contractions that move along the stomach wall.
the stomach has three muscle layers- circular, longitudinal and an extra oblique layer, this enables lots of ways to churn the food and mix it with the gastric juices
the food is converted into a liquid called chyme
stomach - chemical digestion
chemical digestion in the stomach uses an enzyme from the gastric juices known as pepsin.
this enzyme breaks bonds between amino acids in proteins.
the stomach is an acidic environment and contains hydrochloric acid- which enables pepsin to function correctly (makes the ph optimal)
this acid can also kill bacteria that enters the stomach
mucus is also produces and lines the stomach -protects cells lining the stomach
stomach structure
- two sphincters:
Oesophageal-prevents juices entering the oesophagus
pyloric-controls delivery of chyme into the small intestine - 3 layers of muscle: churning (mechanical digestion)
mucosa- lining of the stomach
rugae- folding of mucosa that increases SA
gastric glands in rugae that produces gastric juice:
pepsin, mucus,HCL
state the functions of the Liver
-largest gland in the body
-main function is to produce bile
the liver also plays other role:
-regulating blood sugar levels
-creates blood proteins - clotting factors like fibrin
-detoxification of alcohol and drugs
state the primary function of the gall bladder
stores bile and release it into the duodenum (small intestine)
define bile and bile salts
does not contain any digestive enzymes
contains bile salts
bile salts:
do mechanical digestion of fats
they increase the SA of fats- emulsifies them by breaking them into smaller droplets
this makes it easier for other enzymes (lipases) to digest
function of pancreas and what it produces
both an exocrine (produces digestive enzymes) and endocrine glad (produces hormone’s )
its products have an alkaline Ph (pH over 7)
-helps to neutralise the acid from the stomach when it reaches the small intestine.
produces many digestive enzymes:
Pancreatic amylase (breaks down starch)
pancreatic lipase (breaks down fats)
trypsin (breaks down proteins into smaller chains of amino acids)
deoxyribonucleases and ribonucleases (breaks down RNA and DNA)
Duodenum
-first and shortest section of the small intestine
-connected to the pyloric sphincter of the stomach
- chyme is mixed with intestinal juices, bile and pancreatic juice unitl its digestion is complete.
jejunum
the middle section of the small intestine
-primary site of nutrient absorption
ileum
final and longest section of the small intestine.
empties into the large intestine via the Ileocecal sphincter
absorbs any nutreients that were missed in the jejunum
how does the small intestine achieve a large surface area?
by folds upon folds upon folds.
the mucosa is folded
along the mucosa are small finger like projections called villi.
these calls along the villi have microvilli on the surface
define villi and microvilli
finger like projections = increase the SA of the small intestine to aid with nutrient absorption
how does absorption occur in the small intestine
villi and micro villi
diffusion- nutrients go from HC to LC from small intestine to the cells on the villi
active transport- energy is used to move nutrients against the conc. gradient into the cell
