5. Human Digestive System Flashcards
Digestion
Definition
Digestion is the process that breaks down complex food substances into simple, soluble molecules that are small enough to be absorbed into body cells.
Physical Digestion
Definition + Examples
Physical digestion is the mechanical breakdown of food into smaller particles to increase the surface area to volume ratio, for a faster rate of chemical digestion by digestive enzymes.
Examples: Chewing in mouth, churning action in stomach, emulsification of fats in duodenum
Chemical Digestion
Definition
Chemical digestion is the breakdown of large food molecules into small soluble molecules, catalysed by digestive enzymes through hydrolytic reactions.
Ingestion
Definition
Ingestion is the act of taking food into the mouth.
Digestion in the mouth
Types of digestion that take place + What happens after
Physical digestion: Chewing
Chemical digestion: Salivary amylase
Afterwards, the thoroughly chewed food is rolled into a bolus by the tongue. The bolus is then swallowed and enters the oesophagus.
Saliva
Where it is produced + What it contains + Function
- Produced by salivary glands in the mouth
- Contains salivary amylase which digests starch into maltose
- Help to soften and moisten food
Saliva has a pH of 6.5 - 7.5
Salivary Amylase
What it is + Where it is found + Function + Optimum pH
- Salivary amylase is an enzyme found in saliva
- Digests starch into maltose
- Optimum pH of 6.5 to 7.5
Peristalsis
Definition + Function + State of muscles
Peristalsis is the rhythmic, wave-like, muscular contractions of the wall of the alimentary canal.
It functions to mix and propel food down the alimentary canel.
Behind the food:
- Longitudinal muscles are relaxed
- Circular muscles are contracted
The alimentary canel is the digestive tract from the mouth to the anus
Stomach
What it is
An elastic, muscular bag with thick muscular walls.
Stomach has pH 2
Gastric Juice
Where it is produced + What it contains
- Secreted by gastric glands in the stomach when the bolus enters the stomach
- Contains mainly hydrochloric acid, pepsin & rennin
Hydrochloric acid in the stomach
Function
- Provides an acidic medium suitable for the action of enzymes in the stomach
- Kills bacteria
- Changes inactive forms of enzymes to active forms: converts pepsinogen to pepsin
Pepsin
What it is + Where it is found + Function + Optimum pH
- Pepsin is an enzyme found in gastric juice
- Digests proteins into polypeptides
- Optimum pH of 2
Polypeptides are long chains of amino acids
Rennin
What it is + Where it is found + Function
- Rennin is an enzyme found in gastric juice
- Converts soluble milk protein caseinogen into insoluble caesin, causing coagulation of milk
Coagulation: process of a liquid changing to a solid/semi-solid state
Digestion in the stomach
Types of digestion that take place + What happens after
Physical digestion: Churning
Chemical digestion: Pepsin
After a few hours, the partly digeted food will become liquified, forming chyme, which passes into the duodenum in small amounts.
Churning
What it is + Function
Churning is a form of physical digestion in the stomach.
Function is to:
- Mix food with gastric juice
- Break down food into smaller particles to increase the surface area to volume ratio, for a faster rate of chemical digestion by digestive enzymes
What are the 3 sections of the small intestine?
Duodenum, jejunum & ileum (highly coiled)
Digestion in the small intestine
Types of digestion that take place
Physical digestion: Emulsification of fats by bile
Chemical digestion: 8 types of digestive enzymes
Bile
What it is + Where it is produced + Function
What it is:
- Bile is a thick, yellowish-green fluid
- Contains bile salts and bile pigments
- Alkaline - neutralises chyme from the stomach
Where it is produced:
- Produced by liver, stored in gall bladder temporarily, secreted into the duodenum via the bile duct
Function:
- Functions to emulsify fats, to physically break down large fat droplets into tiny fat droplets to increase surface area to volume ratio for a higher rate of chemical digestion by lipases
- Creates an alkaline environment suitable for the action of enzymes by reducing the acidity of chyme
Enzymes secreted by the pancreas via the pancreatic duct
Names + Functions
- Pancreatic amylase - digests starch into maltose
- Trypsin - digests proteins into polypeptides
- Pancreatic lipase - digests fats into fatty acids + glycerol
Enzymes secreted by intestinal glands
Names + Functions
- Maltase - digests maltose into glucose
- Sucrase - digests sucrose into glucose + fructose
- Lactase - digests lactose into glucose + galactose
- Peptidase - digests polypeptides into amino acids
- Intestinal lipase - digests fats into fatty acids + glycerol
Gall bladder
Function
- Stores bile produced by the liver temporarily
- Secretes bile into the duodenum via the bile duct
Components of Undigested and Unabsorbed Matter in the Large Intestine
- Mainly cellulose
- Water
- Bile pigments
- Dead cells from intestinal lining
- Dead & live bacteria
Large Intestine
Function
Large intestine functions to absorb water (by osmosis) and mineral salts (by facilitated diffusion or active transport) from undigested matter into the blood stream.
Egestion / Defecation
Definition
Egestion/defacation is the elimination of undigested material from the alimentary canal.
4 adaptations of the small intestine
- Small intestine is long: To provide sufficient time for absorption of nutrients to take place
- Inner walls of the small intestine have many transverse folds bearing many finger-like projections called villi. Each villus possesses numerous microvilli: To increase the surface area to volume ratio for faster absorption of digested food substances by diffusion
- The epithelium of the villus is 1 cell thick: To reduce the distance for digested products to diffuse into the cappilaries and lacteal, for faster absorption of digested food substances by diffusion
- The small intestine consists of a dense network of blood capillaries and lacteal within the villi: The continuous transport of digested food substances away from the small intestine maintains a steep concentration gratident, for faster absorption of digested food substances by diffusion
Products of Digestion
- Monosaccharides (glucose, fructose, galactose)
- Amino acids
- Fatty acids
- Glycerol
- Water
The products of digestion are absorbed throughout the small intestine, especialy in the highly coiled ileum.
Glucose and amino acids in the small intestine
How they are absorbed + How they are transported away
Glucose and amino acids are absorbed by facilitated diffusion or active transport (depending on the concentration gradient between the intestinal lumen and blood capillaries) into the blood capillaries of the villi.
Blood capillaries join to form venules which then join to form the hepatic portal vein. The hepatic portal vein carries blood rich in glucose and amino acids to the liver to be processed.
Fatty acids and glycerol in the small intestine
How they are absorbed + How they are transported away
Fatty acids and glycerol are absorbed by simple diffusion into the epithelial cells of the villi, where they recombine to form minute fat globules, which then diffuse into the lacteal.
Fat globules are transported away from the small intestine by the lacteal.
Assimilation
Definition
Assimilation is the utilisation of absorbed nutrients and how the body deals with excess nutrients.
Assimilation of Glucose
Utilisation + How the body deals with excess
Utilisation:
- Glucose is a substrate for respiration to release energy for cellular activities.
How the body deals with excess (high blood glucose concentration):
- Excess glucose is converted into glycogen by the liver cells and stored.
- This is stimulated by insulin, a hormone produced by islets of Langerhans in the pancreas.
When there is low blood glucose concentration:
- When blood glucose is low, glycogen is converted into glucose by the liver cells.
- This is stimulated by glucagon, a hormone produced by islets of Langerhans in the pancreas.
Assimilation of Amino Acids
Utilisation + How the body deals with excess
Utilisation:
- Used in the synthesis of new cells, for growth and repair of worn out cells.
- To synthesise important proteins: enzymes, hormones, antibodies, transport & structural proteins.
How the body deals with excess:
- Excess amino acids are deaminated in the liver.
- Their amino group is removed and converted into urea.
- The remaining carbon residue is converted into glucose.
Assimilation of Lipids
Utilisation + How the body deals with excess
Utilisation:
- Required to maintain cell membranes (phospholipid bilayer).
- Required to produce steroid hormones.
- Required to protect vital organs.
- When there is inadequate supply of glucose and glycogen, fats will be broken down in the liver to provide energy.
How the body deals with excess:
- Excess lipids are stored in adipose tissues under the skin.
- In adipose cells, fat droplets can collect in the cytoplasm and increase in size and number to form one large globule of fat in the middle of the cell, pushing the cytoplasm into a thin layer and nucleus to one side.
- Groups of adipose cells form adipose tissue.
Liver
6 main functions
- Bile production (plays a role in digestion of fats)
- Regulation of blood glucose (homeostasis)
- Protein synthesis of proteins in blood (e.g. fibrinogen)
- Deamination of excess amino acids
- Breakdown of red blood cells
- Detoxification
Breakdown of red blood cells by the liver
The liver breaks down haemoglobin in red blood cells and stores the released iron.
Detoxification of blood by liver
The liver converts harmful substances into harmless ones.
Enzymes (alcohol dehydrogenase) break down alcohol into acetaldehyde, which can be futher broken down into glucose.
Catalase breaks down hydrogen peroxide (toxic by-product of celluar activities) into water and oxygen.
Effects of excessive alcohol consumption
Alcohol is a depressant (slows down brain and nervous system) that when consumed in excess, results in:
- reduced self-control
- longer reaction times / slower reflex action
- cirrhosis of the liver
