digestive system Flashcards
define nutrition?
the process by which an organism obtains and uses it’s food
define digestion?
the physical and chemical breakdown of food into small soluble particles that can be absorbed and transported
explain physical vs chemical digestion?
physical= the mechanical breakdown of food. It involves the teeth
chemical= involves enzymes breaking down the food. mouth, stomach, intestines
what does each digest:
amylase
protease
lipase
starch
protein
lipids or fats
explain the stages in human nutrition?
ingestion= food is taken into the alimentary canal
digestion= food is broken down into smaller soluble pieces
absorption= the movement of digested from the alimentary canal into the blood system
assimilation= absorbed food is converted to new cell substances or used to provide energy
egestion= removal of unabsorbed material from digestive system as faeces
explain 3 ways food can be mechanically broken down?
1) teeth
2) contractions in stomach wall
3) peristalsis
define peristalsis?
Involuntary muscular contraction in the wall of the alimentary canal, that causes food to move along the canal
name and explain the four types of teeth?
incisors= chisel shaped with sharp edges- cut, slice and bite
canines= long, pointed teeth. grip, stab and tear
premolars= contain cusps. crush and chew
molars= large teeth located in the back of the mouth. crush and chew
name the dental formula
2 (I 2/2 C 1/1 PM 2/2 M 3/3)
what does saliva consist of?
water, salt , amylase, lysozyme
PH of 7, it is destroyed when it reaches the stomach as the PH here is lower
what is the function of lysozyme?
helps kill micro-organisms
function of oesophagus?
muscular tube, 25 cm long
connects the pharynx to the stomach
moves down by peristalsis
function of stomach?
J shaped muscular bag
stores and digests food
churns and mixes food with gastric juice forming chyme
what are the roles of the cardiac sphincter muscle and the pyloric sphincter muscle?
cardiac sphincter= circular muscle which contracts to close entry from oesophagus to the stomach
pyloric sphincter muscle= circular muscle which contracts to close the entry to duodenum from the stomach
what is the stomach lining called?
mucosa
mucosa has many folds in it forming millions of gastric glands which secrete gastric juice
what does gastric juice consist of?
mucous
pepsinogen
hydrochloric acid
explain what mucous is?
produced by goblet cells
they are alkaline to prevent the stomach from digesting itself
explain what pepsinogen is?
produced by chief cells
inactive enzyme made active when converted into pepsin by acid in the stomach.
pepsin digests protein to peptides
explain what hydrochloric acid is?
PH of 1/2
kills many bacteria, loosens food, converts pepsinogen to pepsin
what is the function of the small intestine?
muscular tube 5-6m long
function: digestion and absorption
has 3 main parts: duodenum, jejunum, ileum
explain the duodenum?
most digestion takes place here as the chyme from the stomach is mixed with enzymes from the duodenum and the pancreas and bile from the liver
function of ileum and jejunum?
to absorb the end products of digestion: amino acids, simple sugars and fats.
these end products pass into blood capillaries and then the hepatic portal vein brings these nutrients directly to the liver
adaptions of small intestine?
1) long: provides sufficient time for digestion and absorption
2) presence of microvilli: increases surface area for absorption
3) villi walls are 1 cell thick: allows for food nutrients to diffuse quickly
describe the function of a single villus?
fatty acids and glycerol are absorbed into the lacteal, all others are absorbed into blood vessels
