DIGESTION AND METABOLISM OF FATand

ABSORPTION OF FATTY SUBSTANCES THROUGH SKIN

PRESENTED BY Dr. LALRAVI SAHU

2ND YEAR PG SCHOLAR DEPARTMENT OF PANCHKARMA ,SDMCAH

HASSSAN

CONTENTS

• INTRODUCTION

• FAT-SOURCES, CLASSIFICATION

• DIGESTION

• METABOLISM

• SKIN

• ABSORPTION THROUGH SKIN

• CONCLUSION

INTRODUCTION

• Fat….A natural oily substance occurring in animal bodies, especially when deposited as a layer under the skin or around certain organs.

• Fats are the water insoluble substances and are not absorbed by body directly. Besides that Lipids store large amounts of energy

9 kcal/gram due to energy rich fatty acid chain

• The terms "oil", "fat", and "lipid" are often confused.

• "Oil" normally refers to a fat with short or unsaturated fatty acid chains that is liquid at room temperature.

• "fat" may specifically refer to fats that are solids at room temperature.

• "Lipid" is the general term, as a lipid is not necessarily a triglyceride. Fats, like other lipids, generally hydrophobic, and are soluble in organic solvents and insoluble in water.

IMPORTANCE OF FATS IN HUMAN PHYSIOLOGY

• Fats are the sources of essential fatty acids, an important dietary requirement. They provide energy, Vitamins A, D, E, and K are fat-soluble, meaning they can only be digested, absorbed and transported in conjunction with fats.

• Fats play a vital role in maintaining healthy skin and hair, insulating body organs against shock, maintaining body temperature, and promoting healthy cell function.

DIGESTION AND ABSORPTION OF FATS

• Most of the fat in the human diet is in the form of triacylglycerol (TAG), which consists of three fatty acids linked to glycerol. In the digestive tract, TAG is hydrolyzed by the enzyme lipase, to release free fatty acids and monoglycerides.

triacylglycerol (TAG) Emulsification and digestionTAG is hydrolyzed by the enzyme lipase, to release free fatty acids and

monoglycerides

• Micellesmonoglycerides and fatty acids associate with bile salts and

phopholipids to form micelles

• Chylomicrons• Chylomicrons are lipoproteins, special particles that are designed for

the transport of lipids in the circulation

• Cholesterol absorption

Emulsification and digestion• Lipids are hydrophobic, and thus they are poorly soluble in

the aqueous environment of the digestive tract.

• The digestive enzyme, lipase, is water soluble and can only work at the surface of fat globules.

• Digestion is greatly aided by emulsification, the breaking up of fat globules into much smaller emulsion droplets. 

• Bile salts and phospholipids are amphipathic molecules that are present in the bile.

• Emulsification greatly increases the surface area where water-soluble lipase can work to digest TAG.

Micelle

Micelles• After digestion, monoglycerides and fatty acids associate

with bile salts and phopholipids to form micelles. Micelles are about 200 times smaller than emulsion droplets

• Micelles are necessary because they transport the poorly soluble monoglycerides and fatty acids to the surface of the enterocyte where they can be absorbed. As well, micelles contain fat soluble vitamins and cholesterol.

• Only freely dissolved monoglycerides and fatty acids can be absorbed, NOT the micelles. Because of their nonpolar nature diffuse across the plasma membrane of the enterocyte. 

Chylomicrons

lacteals

Chylomicrons• Once inside the enterocyte, monoglycerides and fatty acids

are re-synthesized into TAG. The TAG is packaged, along with cholesterol and fat soluble vitamins, into chylomicrons. Chylomicrons are lipoproteins, special particles that are designed for the transport of lipids in the circulation.

• they are too large to enter typical capillaries. Instead they enter lacteals, lymphatic capillaries that poke up into the center of each villus. Chylomicrons then flow into the circulation via lymphatic vessels, which drain into the general circulation at the large veins in the chest.

Cholesterol absorption

• Some of the cholesterol in the small intestine is dietary cholesterol, and some is put there by the liver, arriving via the bile. Of the total cholesterol that passes through the small intestine

• Only half is typically absorbed, and the rest is eliminated in the feces. Thus, cholesterol in the bile is an example of a substance that is targeted for excretion via the digestive tract.

ABSORPTION OF FATTY SUBSTANCES THROUGH SKIN

ABSORPTION OF FATTY SUBSTANCES THROUGH SKIN

• Absorption of substances through the skin depends on a number of factors, the most important of which are concentration, duration of contact, solubility of medication, and physical condition of the skin and part of the body exposed.

• Skin (percutaneous, dermal) absorption is a term that describes the transport of chemicals from the outer surface of the skin both into the skin and into circulation.

Factors influencing absorption• Concentration

• Temperature

• Duration of contact

• Solubility of medication

• Physical condition of the skin

• Part of the body exposed including the amount of hair on the skin.

fastest to slowest: Scrotal > Forehead > Armpit≥ Scalp > Back = Abdomen > Palm = under surface of the foot

Structures influencing absorption

• To be absorbed through the skin, a chemical or any fat must pass through the epidermis, glands, or hair follicles.

• Chemicals must pass through the seven cell layers of epidermis before entering the dermis where they can enter the blood stream or lymph and circulate to other areas of the body. 

• Toxins and toxicants can move through the layers by passive diffusion.

Absorption of fat

• The stratum corneum is the outermost layer of the epidermis and the rate-limiting barrier in absorption of an agent.

•  Thus, how quickly something passes through this thicker outer layer determines the overall absorption.

• The stratum corneum is primarily composed of lipophilic cholesterol, cholesterol esters and ceramides. Thus lipid-soluble chemicals or fat make it through the layer and into the circulation faster, however nearly all molecules penetrate it to some minimal degree.

• Cross and Roberts, 2004;Down and Harvey, 2003; Schuetz et al., 2005

The skin’s barrier properties come from the highly impermeable outer layer called stratum corneum, which is just 10 – 20 μm thick. Drugs that cross the stratum corneum barrier can generally diffuse to deeper capillaries for systemic distribution.• Mitragotri, 2006

Approach to increasing skin permeability involves heating the skin , either long exposures at moderate temperatures or very short exposures at high temperatures.

Conclusion• Digestion of fat mostly occurs in the small intestine with help

of bile under the action of lipase enzyme by converting TAG into micelles, micelles into chylomicrons and again chylomicrons to TAG.

• TAG is absorbed by lymph circulation through villis, and then poured into the circulation.

• Fat gets absorbed through skin easily because skin is lypophilic in nature under the influence of temperature and condition of skin.

I’m not fat, I’ve just got a lot of potential energy!

•THANK YOU