Human Nutrition and Digestive System Physiology Explained

Human nutrition: digestive, respiratory, and circulatory systems play a role in their nutrition.

Digestive System

Introduces foods into the body, prepares and transforms it to enable its use by cells.

Respiratory System

Obtains the oxygen cells and eliminates CO2.

Circulatory System

Transport nutrients and oxygen to cells.

Excretory System

Release waste products outside the organism.

The Digestive System

System is form by the gastrointestinal tract and the accessory glands.

Gastrointestinal Tract

Is 8 m long and its shape varies. Starts in the mouth and ends at the anus. The parts are oral cavity pharynx, oesophagus, stomach, small, and large intestine.

The mucous membrane is an inner layer that makes up the gastrointestinal tract. It is protected by a lubricant substance called mucus and is surrounded by muscular layers: longitudinal one, second one, oblique third in this stomach.

Accessory or Ancillary Glands

Are organs that discharge their secretions in the digestive system.

• Salivary Glands: Are in the mouth and release saliva.
• The Liver: releases secretions into intestine, is in the upper right abdomen.
• The Pancreas: behind the stomach release secretions into intestine.

Digestion

Digestion is the process that transform the food into simple substances called nutrients. The process involved mechanical and chemical actions.

Mechanical Process

Is the muscular contractions that helps in crushing and mixing the food.

Chemical Process

Is performed by digestive enzymes, the enzymes with the food make chemical reactions that break the complex substances and transform into simpler components.

Digestive Process in the Mouth

The process of digestion start in the stomach, however there are three process that prepare the food: salivation, chewing, swallowing.

Salivation

Saliva is a watery liquid released by the salivary gland's, which are located under the tongue and on the sides of the mouth. The main function of saliva are:

1. Facilitates the bolus into the pharynx and oesophagus, the bolus is a rounded mass of chewed food. This is due to the fact that saliva contains MUCIN that mix with the food and lubricates the passage of it without causing damage.
2. Starts the digestion of STARCH: molecules this is made by an enzyme called AMYLASE that breaks down the most complex sugars.
3. Destroys some bacteria's using an enzyme named LYSOZYME that protects the mouth against infections.

Chewing

Is a mechanical process by which foods are ground and crushed into smaller chunks to facilitate the digestion. This process is carried out by the teeth wich are made up of calcium and fluorine. There are different types of teeth:

• Incisor: cut the food
• Canine: used to tear
• Premolar and Molar: they crush and crumble

The Digestive Process in the Stomach

Two layers of muscle allows the downward movement of the bolus creating a movement called PERISTALTIC movement. Separate the stomach and oesophagus is a valve called CARDIA that stop the reflux and between the stomach and the small intestine is another valve called PYLORUS. The bolus remains in the stomach mixed with gastric juices that are secreted by the glands that are in the inner layer of the stomach. This gastric juice contain pepsin and hydrochloric acid.

Pepsin

Is an enzyme that start protein digestion breaking proteins down into smaller fragments called peptides.

Hydrochloric Acid

Made two functions:

1. Activates pepsin enzymes and support them
2. Destroys bacteria that may be present in food

After that, the food has mixed with the gastric juices and transform into CHYME, that is a more fluid substance. Stomach is formed by 3 muscular layers, the inner layer is covered in mucus that protects from the hydrochloric acid. When the stomach reaches a high level of acidity, the pylorus opens and the chyme enters in the small intestine.

The Digestive Process in the Small Intestine

The small intestine is a tube that is around six or 7 m. It is located between the pylorus and the ILEOCECAL VALVE which separates the small intestine from the large. The small intestines have 3 sections:

• Duodenum: the initial sections (25 cm)
• Jejunum: the middle section, is the longest part
• Ilium: the final section and ends in the large intestine

Pancreas

It is a glandular organ located in the abdomen behind the stomach, it has two main functions:

1. Produce hormones — insulin and glucagon, both regulate the quantities of glucose.
2. Secretes pancreatic juice which is release into the duodenum through the AMPULLA OF VATER, in which the pancreas and the liver ducts join. Pancreatic juice contain enzymes capable of digesting different types of molecules present in food.

The Liver

It's located in the right upper part of the abdomen, the violet color is due to the amount of blood, the main function is produced bile released into the duoderm through the ampulla vater. So the bile isn't secreted continuously, it have to store in the GALLBLADDER (a bag similar like organ next to the duodenum and only release it when the food arrives to the intestine).

The bile doesn't contain digestive enzymes, it has a bile salts, it intervene in the evolution of fats which is transform fats into very small drops. The liver also captures and destroys most tonic molecules, such as the ones found in alcoholic drinks.

Digestion in the Small Intestine

Most digestive process take place in the small intestine as the chymo mixes with pancreatic juice and bile as well as intestinal juices. The intestinal juice is produced by the small intestines mucous glands, which is similar to pancreatic juice and contain enzymes that are capable of digesting all types of molecules found in foods. When the cyme mixes with the bite, pancreatic and intestinal juices it's transformed into chyle.

After digestion, foods are reduced to simpler molecules that function as nutrients for cells:

• Monosaccharides or Simple Sugars: (such as glucose) obtained from more complex carbohydrates.
• Glycerol and Fatty Acids: which are obtained from fat.
• Amino Acids: obtain from the digestion of proteins.

These nutrients must be distributed to the tissues where cells will use them to obtain energy to make new molecules.

Food Absorption

Food absorption refers to the passage of nutrients to our blood, this allows those nutrients to be distributed across the whole organism.

Villi

Are creases that covered the inner layer of the small intestine, which are full of microscopic blood capilares that collect nutrient obtain after digestion, in order to increase the surface areas as well as increasing the absorption the nutrients, the plasma membrane that forms villi has extra creases known as MICROVILLI.

The Digestive Process in the Large Intestine

The large intestine is the end part of the digestive tract, is shorter (1,5 m) and doesn't have villi or microvilli. 3 main sections:

• Cecum: the first section, it's shaped like a bag and has a narrow extension.
• The Colon: is the large part is where symbiotic bacteria of the intestinal develop.
• The Rectum: the final section that ends in the anus.

Food and Nutrients

Nutrients are biomolecules that make up our bodies and are called the proximate.

Organic Nutrients

• Carbohydrates: bread, cereals.
• Lipids: oil, butter.
• Proteins: meet, fish.

Inorganic Nutrients

Mineral salts and water.

Carbohydrates

These give us energy and there are two groups:

• Simple carbohydrates or sugars: have sweet taste. They are soluble, include monosaccharides ex. glucose and fructose (that we can find in fruits) and disaccharides -> are formed by the join of the two monosaccharides ex lactose.
• Complex carbohydrates -> aren't sweet or crystalline. They are formed by the bonding of many molecules found in simple carbohydrates. It is necessary to broke down to convert them into energy. The most important is starck and cellulose contained in vegetables fibers also belongs to this group but our body cannot use it.

Lipids

They aren't solubles and have oily apperance. 3 groups:

• Fats: these molecules are full of energy. 2 types: saturated and unsaturated.
• Membrane Lipids: these form the structures of cell membrane and cell organells.
• Lipids with Regulatory Functions: such as so me vitamins and sexual hormones.

Proteins

These nutrients are the most important structoral molecules, because about half of the weight of our cell proteins. Athough all proteins are different, they are composed of the same type of amino acids. On there are 20 different amino acids. The main function of protein is regulating the metabolism. They perform many biological functions:

• Form structures like haur, membrane, and nail.
• They transport oxygen in the blood from the lungs to the tissues.
• They work in defence against infections.
• They are responsible of muscle contraction.
• They regulate biological responses.

Mineral Salts

These are inorganic molecules. Some of their functions are structural, making up on important part of our bones and teeth and others allows organs to function correctly and help in the regulation of cellular metabolism. Different foods have different amount of minerals they abundant in fruits and vegetables and some of them are dissolved in the water, we need large amount of magnesium, potassium, calcium, and sodium and minimal amount of iron, zinc, etc.

A balance diet give us all the minerals use need, but is commonto have deficiencies of iron, calcium, and iodine.