Nutrients in humans
Nutrition consists of the following processes
Nutrients
It is the process by which organisms obtain food and energy for repair, maintenance and growth of cells.
- Ingestion
1.Food enters the mouth
2.the food is then chewed and become smaller pieces to increase the surface area to volume ratio to increase the rate of digestion.
- when the food is in the mouth, the salivary glands secrete saliva which contains amylase to soften and slowly digest starch to maltose
- the tongue rolls the food into small slippery round masses which is also known as boli(singular: bolus)
- it is swallowed and enters the esophagus via pharynx
- Digestion
The esophagus has 2 layers of muscles called the longitudinal and circular muscles which is used for peristalsis. Peristalsis is the process of the food to be pushed along the gut and mixed with digestive juices. Peristalsis is a rhythmic wave like muscular contraction and relaxation in the wall of the alimentary canal.
Circular muscles and longitudinal muscles are antagonistic.
When circular muscle contracts, the longitudinal relaxes, causing the wall of the gut to constrict, making it narrower and longer, pushing the food down the esophagus
When the longitudinal muscles contract, the circular muscles will relax, the wall of the gut will dilate, becoming shorter and wider, widening the lumen to allow the food to enter.
stomach
The stomach has strong distensible muscular bag with thick and well developed muscular walls. The stomach has many gastric pits which leads to the gastric glands that secretes the gastric juices. the gastric juice is a dilute solution of Hydrochloric acid with a pH of 2. Gastric juices also contains mucus and protease called pepsin.
The dilute HCL denatures the amylase from the mouth because of its low pH. pepsinogen is activated by HCL to become pepsin. HCL provides slight acidic medium which is suitable for the activation of pepsin. HCL also kills the harmful bacteria in the food.
proteins are broken down by pepsin to form polypeptides. Food remains in the stomach for about 3 to 4 hours. The partially digested food becomes becomes liquified, forming chyme. The chyme will pass through duodenum in small amounts when the pyloric spincter relaxes and opens.
small intestine
Characteristics
Has a U-shape duodenum, jejunum and ileum
it is 6m long
the lining of the walls contains glands that secrete digestive enzymes
wall of the small intestine is also adapted to absorb digested food products and water
Chyme enters the small intestine
- stimulates the pancreas to secrete pancreatic juice
pancreatic juice contains amylase, trypsin and pancreatic lipase which pass through the pancreatic duct into duodenum
2.stimulate the gall bladder to release bile
no enzyme but increases the rate of digestion
bile pass through bile duct to duodenum
- Stimulate epithelial cells in small intestine to produce enzymes such as maltose, lipase and peptide
the food now comes into contact with
alkaline substances
pancreatic juice
bile
intestinal juice
these then neutralizes the acidic chyme
provides suitable alkaline medium for action of pancreatic and intestinal enzyme
digestions of different foods
carbohydrate digestion
lactose
sucrose
cellulose
starch
starch + pancreatic amylase = maltose
maltose + maltase = glucose
lactose + lactase = glucose + galactose
sucrose + sucrase = glucose + fructose
Therefore, carbohydrate is digested to form simple sugars which is then absorbed into blood stream
Protein digestion
protein + pepsin = polypeptides (in the stomach)
undigested protein goes to the small intestine and is further broken down
protein + trypsin = polypeptides
polypeptides + peptidase (erepsin) = amino acids
Fat digestion
bile salt emulsifies fats
lower surface tension tension of the fat reduce the attractive forces between the fat molecules
fat break into tiny fats droplets suspended in water forming emulsion
physical break up, no chemical digestion of the fat molecules has occurred yet
emulsification increases the surface area to volume ratio of the fats, speeding up their digestion of lipase
Emulsifies fat + lipase =fatty acid + glycerol
human cannot digest cellulose as there is no digestive enzyme for cellulose
- Absorption
Products of digestion such as simple sugars, amino acids, fatty acids and glycerol are absorbed throughout the small intestine
adaptations of the small intestine for absorption
Surface area of small intestine
There are membranes that separates the food substances from the blood capillaries, allowing digested food substances to pass through a thin membrane instead of a thick one
The concentration gradients of individual food substances
inner surfaces are folded
the folds have many finger like projections called villi
villi structure
have epithelial cells that have numerous microvilli which increases the surface area
have thin walls that are 1 cell thick
The small intestine is long enough to provide sufficient time for absorption
have either a lacteal or lymphatic capillary surrounded by blood capillaries
Lymphatic capillaries of the villi transports fats
Blood capillaries of the villi transport sugars and amino acids
How does absorption take place
Glucose and amino acids are absorbed by diffusion into the blood capillaries of the villi
They are also absorbed via active transport. This occurs when there is a lower concentration of these food substances in the lumen of the small intestine than in the blood capillaries
glycerol and fatty acids diffuse into the epithelium where they combine to form minute fat globules which enter the lacteals
unabsorbed and undigested food matter is stored temporarily mainly in the rectum, before it is discharged as faeces through the anus. this process is also known as egestion or defecation
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- Transport and assimilation
Assimilation is the process whereby some absorbed food substances are converted into new protoplasm or used to provide energy
Blood in the villi is now rich of nutrients
blood capillaries will unite to form larger blood vessels, which in turn will unite to form a large vein called the hepatic portal vein
transportation and usage of fats
hepatic portal vein transport nutrients to the liver
in the liver
- sugar will be converted to glycogen in the liver and stored
- some glucose is also transported by the blood leaving the liver and is distributed around the body
glucose is assimilated and then oxidized during tissue respiration to release energy for the vital activities of the cells
excess glucose is then returned to the liver and stored as glycogen. Insulin, a hormone produced by the liver, stimulates the liver cells to convert excess glucose to glycogen
when the body is in need of energy, the liver converts glycogen back to glucose which is then transported around the body by the blood to the cells
Amino acids which enter the cells are converted into new protoplasm that is used for growth and repair of worn-out parts of the body.
amino acids are also used to form enzymes and hormones
excess amino acids are deaminated into urea
Fats are absorbed into lymphatic capillaries. the lymphatic capillaries join to form larger lymphatic vessels, which discharges fats into the blood stream
fats are converted into forms that can either be broken down or stored
when there is enough glucose, fats are not broken down and are used to build protoplasm for cell membranes
when there is not enough glucose, fats are broken down to provide the energy needed for vital activities of the body.
excess fats are stored in special tissues called adipose tissues
This occurs beneath the skin and around the heart and kidneys. Adipose tissues protect these organs by acting as shock absorbers
Functions of the liver
Regulation of blood glucose concentration
production of bile
Iron storage
protein synthesis
Deamination of amino acids
Detoxification
Effects of excessive consumption of alcohol
Harmful on the digestive system
harmful on the nervous system
Depressant
alcohol stimulates acid secretion in the stomach.
Excess stomach acid increases the risk of gastric ulcers
Prolonged alcohol abuse may lead to cirrhosis, of the liver.
this causes liver cells to be destroyed and replaced with fibrous tissue, decreasing the liver's functionality
Patients with alcoholic cirrhosis may hemorrhage or have bleeding in the liver. This can lead to liver failure and subsequently, death
it slows down the brain functions (effects vary from one person to another)
Reduced self control
under the influence of alcohol, a person becomes carefree as alcohol takes away their inhibitions. decreasing self control
effect on reaction times
a person starts having slurred speech
blurred vision
poor muscular co ordination
clumsy
unable to walk steadily
social implications
neglect work and family, exhibit violent behaviour especially towards family members
They may commit crimes under the influence of alcohol
too much glucose in blood --> insulin secreted --> glucose convert to glycogen for storage --> blood glucose concentration decrease
when the red blood cells get worn out, they are destroyed in the spleen, a gland found near the liver
the liver synthesises proteins found in blood plasma from amino acids in the diet. these plasma include prothrombin and fibrinogen which are essential for clotting of blood
excess amino acids are transported to the liver .
Harmful substances may be absorbed into the blood from the gut
too little glucose in blood --> glucagon secreted --> glycogen convert to glucose and transported into the blood stream --> blood glucose concentration increases
the haemoglobin is brought to the liver
haemoglobin is broken down and the liver stores the iron that is released
Bile pigments are also formed from the breakdown of haemoglobin
their amino groups are removed and converted into urea
these substances are made harmless by the liver cells
alcohol is also broken down in the liver by enzymes called alcohol dehydrogenase which is found in liver cells.
This enzyme breaks down alcohol to a compound called acetaldehyde
Acetaldehyde is broken further to compounds that can be used in respiration to provide energy for cell activities
epiglottis refers to the flab like tissues that covers the glottis. it covers the opening to the respiratory track to prevent food from going down the trachea. Glottis is a slit like opening leading to the respiratory track.