Year 11 Human Biology - Digestive Sytsem

what is the role of this system

to ingest food and mechanically and chemically break it down into simple molecules so it can be accessible to cells

what is digestion

the process of breaking down food into smaller molecules so that cells can absorb/use them for metabolism

what is mechanical digestion

physical break up of food into smaller pieces, increasing the surface area of the food particles for efficient enzyme activity

what does mechanical digestion involve

mastication, peristalsis, churning and emulsification

what is chemical digestion

breaking down of complex carbs into smaller molecules by enzyme action so they can be absorbed into blood or lymph

what are the roles of the digestive system

• ingestion

• mechanical digestion

• chemical digestion

• peristalsis

• absoprtion of nutrients into blood

• elimination of undigested food

• excretion of bile pigments

what are the main components of this system

alimentary canal → tube from mouth to anus

accessory organs → e.g. teeth, liver etc

describe the strucutre and fucntion of the mouth

the mouth takes in food and begins chemical and mechanical digestion

it contains the accessory organs of the teeth and the tongue and salivary glands

describe the teeth

incisors → pointy spades, bitng and cutting of food

canines → concial points for tearing food

pre molars → broader crown

molars → very broad crown for grinding food

what is the teeth formula

2 1 2 3 (upper)

------- half of jaw x 2 + 32 teeth

2 1 2 3 (lower)

describe the tongue

mixes food with saliva to form bolus (soft round mass of food to be swallowed)

describe salivary glands

secrete saliva (liquid rich in salivary amylase and mucus)

mucus lubricates mouth

salivary amylase breaks down 50% of starch into shorter chains

describe the strucutre and function of the pharynx

common passage of food and air

stratified epithelium lining coated in mucosa

describe the structure and the function of the oesophagus

muscular tube (circular and longitudinal smooth muscle) which takes food to the stomach

stratified epithelium lining with mucosa

what is peristalsis, in reference to digestive system

wave of involuntary muscular contractions of the walls of tubular organs

in the digestive system it moves food along the alimentary canal

how does peristalsis work in oesophagus

the circular msucles contract behind bolus

long muscles contract, shortneing path

muscles in front of bolus remain relaxed

describe the structure and the function of the stomach

a muscular organ which acts as a widening in the alimentary canal

brings about mechanical digestion by churing

has 3 muscle layers and is lined with mucosa

contains gastric pits, into glands which release mucus, inactive enzyme pepsinogen and HCl

what do mucus, pepsinogen and HCl do

the mucus protects the stomach lining, muscles etc

the pepsinogen is activated into pepsin which starts digestion of proteins

HCl activates pepsin by supplying H+ ions and kills bacteria

what produces mucus in the stomach

goblet cells

what is the pyloric sphincter

a circular muscle at the end of the stomach which regulates the passage of chyme

describe the structure and function of the small intestine

6\.5m long narrow tube

3 sections → duodenum, jejunum, ileum

site of majority of digestion

digests all food groups

site of majority of absoprtion

what adaptive features does the small intestine have

mucosa is long and permanently folded

2 layers of smooth muscles for peristalsis and segmentation

glands which secrete digestive enzymes

villi and microvilli increase surface area

rich blood supply

lacteal

carrier proteins

many mitochondria for energy for transport

what are the pancreatic juice enzymes and their role

pancreatic amylase → break starch into shorter polysaccharide chains

pancreatic protease (trypsin) → breaks polypeptides into dipeptides

pancreatic lipase → breaks lipids into fatty acids and glycerol

ribonuclease and deoxxyribonuclease → break DNA and RNA into nucletodies

where are pancreatic juices secreted into

duodenum

why are pancreatic juices basic

because presence of HCO3- ions provides optimum pH

what are the intestinal juice enzymes and their roles

intestinal protease → break dipeptides into amino acids

intestinal amylases: a) sucrase → break sucrose into fructose + glucose

b) maltase → break maltose into 2 glucose

c) lactase → break lactose into galacatose and glucose

intestinal lipase → break lipids into fatty acids and glycerol

how does mechanical digestion occur in the small intestine

segmentation (forward and backward motion of food)

peristalsis

emulsification of lipids and fat by bile

how does bile emulsify fats and lipids

it breaks large fat globules into smaller fat droplets with larger surface area

what is bile

a green brown secretion of the liver which contaisn bile pigments ( like bilirubin) and bile salts

it is concentrated and stored in gallbladder

how is bile pigments formed

the breaking down of red blood cells in the liver

describe absoprtion in the small intestine

water and water soluble vitmans diffuse simply and by osmosis

glucose and amino acids are carried by active transport

minerals diffuse

describe absoprtion of fatty acids and glycerol

they diffuse into villi epithelial cells where they are reassembled into lipids and covered in proteins, forming a chylomicron

chylomicrons are actively transported into lacteal in the villus

what is the lacteal

lymph vessel inside villus

describe the large intestine

large diameter

1\.5m length

no digestive enzymes secreted

contains good bacteria and minerals and some vitamins (k)

what do the good bacteria do in the large intestine

finish digestion of organic molecules

produce vitamin K

what occurs in the large intestine

formation of faeces by removal of water

storage of faeces

elimination

defacation

describe elimination and defacation

elimination is the removal of undigested or indigestable matter

defacation is the passing of faeces via the anus into an external environment

name the parts of the large intestine in order of which matter moves through it

cecum, ascedning colon, transverse colon, descending colon, sigmoid colon