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Orbicularis oris


Orbicularis oris muscle is located in area of mouth that surrounds the lips. It originates from maxilla(upper jaw) and mandible(lower jaw) and inserts into the skin that surrounds the lips.

Contraction of the muscle narrows orifice of mouth puckering the lip. It also helps in playing flute.


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Following are the salient adaptations of villi that make them good absorbers:

  • Villi are single cell thick. Thus nutrients don't have to travel longer distance in order to diffuse into bloodstream. This increase the rate of diffusion. Hence absorption rate is also increased.

  • Villi have rich network of blood capillaries . Thus a steep concentration gradient is maintained between inside of small intestine and blood.

  • Most important is: Apical membranes of Villi further form many finger-like projections called microvilli or brush borders. Villi together with it's microvilli tremendously increase surface area of absorption. And hence supports effective absorption of nutrients into blood.

  • Villi have permeable membranes . Thus, nutrients can easily get their way through them.


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After hearing the word 'absorption' the first organ which hop into mind is small intestine. But wait! Because there are two other also:

Small Intestine #to# #90%#absorption.
Large intestine #to# about #5%# absorption.
Stomach #to# about #5%# absorption.


Absorption in Stomach
The role of stomach in absorption is not that salient. Mostly water #(H_2O)# and alcohol#(C_2H_5OH)#, salt, and simple sugars can be absorbed directly through the stomach wall.

Stomach mainly facilitates absorption of vitamin #B_12#. However, most substances in our food need a little more digestion and must travel into the intestines before they can be absorbed.


Absorption in Small intestine
Small intestine is called as small because of its shorter diameter. But if we consider length, it's not at all small. It's about #"6-7 meters"# long tube which is coiled in order to fit in smaller portion of abdomen. Maximum absorption of nutrients takes place in small intestine.

The paramount features of small intestine which make it spectacular absorbing agent of several nutrients are: #color(orange)"The internal wall (mucosa) is made "# #color(orange)" up of folds, each of which has many tiny finger-like"# #color(orange)" projections known as villi, on its surface."# #color(green)"Apical membranes of villi further form many hair"# #color(green)"like outgrowths called microvilli and it appear as brush border under microscope."# Total area of absorption in small intestine becomes incredible large due to infoldings, villi and microvilli*.


Villi are structurally adapted to absorb maximum nutrients at faster rate. For example: villi are single cell thick, thus nutrients can easily cross their permeable membranes to get into bloodstream & villi are also supplied with rich network of capillaries and also contain vessels known as lacteal of lymphatic system.

Small intestine absorbs almost all the nutrients i.e. amino acids, glucose, bile salts, fatty acids and glycerols and is also crucial in the absorption of fat-soluble vitamins (Vitamin A, D, E and K) & vitamin #B_12#. Absorbed fat and fat soluble vitamins enter lacteal.


Absorption in Large intestine or Colon
There are trillions of bacteria, yeasts, and parasites living in our intestines, mostly in the colon. Over 400 species of organisms live in the colon.

Large intestine is primarily involved in absorption of water. However, it also absorbs some ions and nutrients released by gut bacteria, specially several vitamins e.g vitamin K. It also absorbs water which remains in the undigested food.
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Arteries, veins, capillaries.




  • Carry blood away from the heart and deliver oxygen-rich blood to the tissues of the body (except for the pulmonary artery which carries deoxygenated blood to lungs)
  • Have very elastic wall which help to withstand the pressure created as the heart pumps the blood
  • Each artery is lined by smooth tissue and has three layers:

outer tunica externa, comparatively thicker middle layer tunica media and inner tunica interna/endothelium.



  • Carries deoxygenated blood towards the heart (except pulmonary veins which carries oxygenated blood from lungs)
  • Have thinner nonelastic wall
  • Unlike to arteries they are under low pressure and rely on muscle contractions to return blood to the heart
  • Have valves which prevent the blood from flowing in the opposite direction
  • Also have three layers:


  • Smallest of the body's blood vessels
  • Have very thin wall made of only endothelium
  • Perform oxygen, carbondioxide, nutrients and waste exchange between blood and tissues easily
  • They are connection between veins and arteries



The nerves cells are rather long which enables communication with distant body parts. The dendrites allow for communication with other neurons. Myelin surrounding the axon of a neuron acts as an insulator.



The above example is a very general description. In fact, neurons can be categorized into three groups based on their function:

Sensory neurons:

  • Carry impulses from the receptors (cells that detect the stimuli i.e. heat or pressure) to the central nervous system (CSN).

  • They have longer dendrites and shorter axons due to carrying of impulses from sensory organs to the spinal cord or brain.

  • In general, sensory neurons are very long cells as they have to carry the impulses from the body to the place where the response occurs.

Motor Neurons

  • Carry impulses from the CSN to the effector (cells responding to the stimuli i.e organs, muscles)

  • They have long axons and shorter dendrites due to the passage of impulses from spinal cord or brain to the effector organs/cells.

Relay neurons

  • Co-ordinate responses

  • They are known as link neurons in the CNS due to their function which is to link sensory neurons with the motor neurons





These are the main diaphragms present in our body,which acts as partitioning agent as well as weight bearer.

1 .THE DIAPHRAGM : Present at the junction of thoracic and abdominal cavity.

2 .PELVIC DIAPHRAGM : Present at the junction of abdomen proper above and pelvic cavity below.

3 .UROGENITAL DIAPHRAGM : Present at the junction of greater pelvis above and perineum below.

4. DIAPHRAGMA ORIS : This is a muscle bulk formed by the myelohyoid muscle which bears the weight of the tongue.

5. DIAPHRAGMA SELLA : It covers the pituitary gland,present inside the middle cranial fossa.

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