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The basic components of the human digestive system begins at the mouth. Food is swallowed through the esophagus and into the kidney-shaped stomach. The liver is located on top of the stomach, and the pancreas is underneath. Food passes from the stomach to the long, winding small intestine. From there it enters the wide large intestine before passing out the anus. At the junction of the small and large intestine is a pouch called the cecum.
The components of the human digestive system are shown. The GI tract is the tube that includes the oral cavity, esophagus, stomach, small intestine, large intestine, and rectum. The accessory organs are those that indirectly join to this tube via ducts and include the salivary glands, liver, gall bladder, and pancreas.

Oral cavity

Both physical and chemical digestion begin in the mouth or oral cavity    , which is the point of entry of food into the digestive system. The food is broken into smaller particles by mastication, the chewing action of the teeth. All mammals have teeth and can chew their food to begin the process of physically breaking it down into smaller particles.

The chemical process of digestion begins during chewing as food mixes with saliva, produced by the salivary glands ( [link] ). Saliva contains mucus that moistens food and buffers the pH of the food. Saliva also contains lysozyme, which has antibacterial action. It also contains an enzyme called salivary amylase    that begins the process of converting starches in the food into a disaccharide called maltose. Another enzyme called lipase is produced by cells in the tongue to break down fats. The chewing and wetting action provided by the teeth and saliva prepare the food into a mass called the bolus    for swallowing. The tongue helps in swallowing—moving the bolus from the mouth into the pharynx. The pharynx opens to two passageways: the esophagus and the trachea. The esophagus leads to the stomach and the trachea leads to the lungs. The epiglottis is a flap of tissue that covers the tracheal opening during swallowing to prevent food from entering the lungs.

Illustration A shows the parts of the human oral cavity. The tongue rests in the lower part of the mouth. The flap that hangs from the back of the mouth is the uvula. The airway behind the uvula, called the pharynx, extends up to the back of the nasal cavity and down to the esophagus, which begins in the neck. Illustration B shows the two salivary glands, which are located beneath the tongue, the sublingual and the submandibular. A third salivary gland, the parotid, is located just in front of the ear.
(a) Digestion of food begins in the mouth. (b) Food is masticated by teeth and moistened by saliva secreted from the salivary glands. Enzymes in the saliva begin to digest starches and fats. With the help of the tongue, the resulting bolus is moved into the esophagus by swallowing. (credit: modification of work by Mariana Ruiz Villareal)

Esophagus

The esophagus is a tubular organ that connects the mouth to the stomach. The chewed and softened food (i.e. the bolus) passes through the esophagus after being swallowed. The smooth muscles of the esophagus undergo peristalsis (contractions) that pushes the food toward the stomach. The peristaltic wave is unidirectional—it moves food from the mouth the stomach, and reverse movement is not possible, except in the case of the vomit reflex. The peristaltic movement of the esophagus is an involuntary reflex; it takes place in response to the act of swallowing and you don't exert conscious control over it.

Ring-like muscles called sphincters form valves in the digestive system. The gastro-esophageal sphincter (a.k.a. lower esophageal or cardiac sphincter) is located at the stomach end of the esophagus. In response to swallowing and the pressure exerted by the bolus of food, this sphincter opens, and the bolus enters the stomach. When there is no swallowing action, this sphincter is shut and prevents the contents of the stomach from traveling up the esophagus. Acid reflux or “heartburn” occurs when the acidic digestive juices escape back into the esophagus and the low pH irritates the unprotected surface. Prolonged and repeated exposure of the esophagus to this acidity can cause physical damage.

Questions & Answers

How many bones of 1 year childrean
R.k Reply
208
Rani
A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults
Manali
Somebudy seys me 300
R.k
A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults h
Manali
I ask you about beby bones
R.k
i cann't say about 1 year baby's bones bt on birth baby has 300 bones
Manali
Ok thank you goodnight
R.k
good night
Manali
have a sweat dream
Rani
it's 300 bones because it a baby
Jasper
figure of male reproduction
Rani Reply
front view of male reproductive system
Rani
front view of male reproductive system
Rani
what is Actin? I don't understand this definition
Rhonda Reply
Actin is a family of globular multi-functional proteins that form microfilaments. 
Lauren
what is the difference between a vaccine and a antiserum
Silver Reply
An antiserum contains antibodies already produced and is used to pass on immune responses. A vaccine contains a substance that stimulates the production of antibodies to create an immune response.
Nana
A vaccine a preparation of antigens for one (or more) diseases that is given to stimulate active immunity and protect against the disease (s). while an antiserum either neutralizes the "infection " or stimulates your immune system to attack an infection.
Oliver
what is deoxyribonucleic acid
Carlene Reply
A negatively charged molecule; polymer of nucleotides found in the nucleus of a cell ... DNA.
Abayomi
guys u needs your help i am in this conversation but i don't understand what you guys were talking about please i need your help.
Asali
Hi
Janelle
hi
Oliver
hello
Rani
how are you doing?
Jasper
DNA is genetic material which is present in cell DNA is made up of nitrogen base,phosphate group and pentose sugar.
Manali
hi
Jasper
give a front view of male reproductive system
Rani
to maintain certain biological activities of cell
jeeni Reply
what are difference between maleriya and dengue
Shaili Reply
caused by two different agents.. malaria is caused by Culex mosquito in birds and Anopheles in humans.. while dengue fever is caused by Aedes mosquito
Rayyan
what is oral pill
Rani
what is oral pilli
Rani
pili is hair like appendages found on cell surface and play important role in cause disease
Manali
correct
Jasper
what is immune system
Shaili Reply
system that defends the body against invading microbes n pathogens... (white blood cells makes immune system)
Rayyan
what is interferon's ?
maya Reply
interferon is any group of glycoproteins, produce by the immune system.
Henry
what is immune system
Shaili
immune system is the defence mechanism that protect our body to unwanted particles
Manali
the difference between human biology and principles of biology
Henry Reply
human biology is the studying of stucture and of function of the body and the principles of how humans interacts with men, animal and plants around them and the social activities that take place.
Kay-Anna
human biology is the studying of human body structures function in the way of interacting physical and internal. while biology is the study of living and non living things.
shanta
what is Mitosis/Meiosis? What are the similarities and differences?
Abayomi Reply
differences: occurence... one in somatic n other in germ cells no of daughter cells.. 2 and in meisis 4. genetic recombination... only occurs in meiosis during crossing over no. of chromosomes.. remains same in mitosis n reduced to half in meiosis major phases... similar karyokinesis n cytokinesis
Rayyan
karyokinesis... divided into prophase.. meta.. ana.. and telophase... in meiosis.. further division into meiosis 1 and meiosis11 so phases are named as pro1..meta1..ana1..and telo1
Rayyan
differences among phases.. prophase.. other changes similar.. but diff occur in meiosis where synapsis, crossing over,chiasmata formation and tetrad form metaphase... in mitosis chromosomes align at equatorial plate.. in meiosis homologouy chromosomes align at equatorial plate.
Rayyan
anaphase.. in mitosis chromatids gets separated in meiosis chromosomes gets separated.. meiosis 11 is similar to mitosis except that during interkinesis.. duplication in S phase doesnt occur
Rayyan
What is the difference between prokaryotic and eukaryotic organisms
AAlfred Reply
Prokaryotic cell are unicellular, lacks a membrane bound organelles ... e.g bacteria and archea. Eukaryotic cells are multicellular, membrane bound organelles ... e.g Animals, Plants, Fungi, Algae.
Abayomi
in one line prokaryotic cell's nucleus is under develop and eukaryotic cell's nucleus is well develop
Manali
what are organelles
Lorella Reply
Organelles are specialized structures in the that perform a specific function. Examples: mitochondrial , Golgi apparatus, etc.
Francis
Organelles are specialized structures in the cell that perform a specific function. Examples: mitochondrial, ribosomes, etc.
Francis
what connect bone to bone
Rebecca Reply
ligaments
Abayomi
what is the function of appendix?
Isaya Reply
it don't have any function
Rebecca

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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