anatomy and physiology of rectum and vagina

Views:
 
Category: Education
     
 

Presentation Description

aim to suppositories

Comments

Presentation Transcript

ANATOMY AND PHYSIOLOGY OF RECTUM AND VAGINAL CAVITY :

ANATOMY AND PHYSIOLOGY OF RECTUM AND VAGINAL CAVITY BY Dr. Ramanjireddy Tatiparthi JIMMA UNIVERSITY Class 1 _II Year_ Ramanji SECTION 6

Anatomy and Physiology of the rectum:

The rectum is the last part of the colon, forming the last 15 – 20 cms of the GI (gastro intestinal ) tract. Organ with a relatively flat wall surface, without villi. It contains only 2 – 3 ml of inert mucous fluid with pH of 7.5 . Mild environment / drug can change pH Large intestine function absorb H 2 O and electrolytes Low surface area  poor absorption, when compare small intestine Rectum usually empty of feces Anatomy and Physiology of the rectum

Rectal Blood Circulation:

Rectal Blood Circulation

PowerPoint Presentation:

Middle & inferior hemorrhoidal veins – Iliac vein -> inferior vena cava Superior hemorrhoidal vein – Inferior mesenteric -> Hepatic portal -> Liver Middle and inferior – Drug goes directly into systemic circulation – No first pass metabolism by liver – Drug avoids stomach and digestive enzymes ABSORPTION OF DRUGS FROM THE RECTUM

Anatomy and Physiology of the Vagina:

Anatomy and Physiology of the Vagina The vagina is a fibro-muscular tube lined with stratified epithelium, connecting the external and internal organs of reproduction. The vagina has an outer covering of areolar tissue a middle layer of smooth muscle and an inner lining of stratified squamous epithelium that forms the ridges . It has no secretory glands, but the surface is kept moist by cervical secretions. Between puberty and the menopause Lactobacillus acidophilus microbes are normally present and they secrete lactic acid , maintained the pH between 4.9 and 3.5 . The acidity inhibits the growth of most microbes that may enter the vagina from the perineum.

Anatomy and Physiology of the Vagina:

Anatomy and Physiology of the Vagina

Absorption of drugs from the vagina :

Absorption of drugs from the vagina Absorption takes place by passive diffusion of unionized molecules following apparent first-order kinetics The outermost layer of cells in the vagina is protected by a complex mixture of proteins and polysaccharides called mucus. Most of this fluid comes from the cervix and is usually thick and glutinous. The viscosity of this cervical fluid is controlled by hormone levels. The vaginal epithelium is very sensitive to estrogen and progesterone. Estrogen decreases the fluid viscosity and progesterone increases the viscosity of cervical fluid. The pH of the adult vagina is acidic because of the conversion of glycogen to lactic acid

Challenges of DD through vagina and rectum :

Challenges of DD through vagina and rectum Physiological factors affecting rectal absorption 1- Quantity of fluid available: The quantity of fluid available for drug dissolution is very small (approximately 3 ml). Thus the dissolution of slightly soluble substances is the slowest step in the absorptive process. 2- The properties of rectal fluid: The rectal fluid is neutral in pH (7 – 8) and has no buffer capacity. 3- Contents of the rectum: When systemic effects are desired, greater absorption may be expected from an empty rectum as the drug will be in good contact with the absorbing surface of the rectum. 4- Circulation route: The lower hemorrhoidal veins surrounding the colon receive the absorbed drug and initiate its circulation throughout the body, bypassing the liver. Lymphatic circulation also assists in the absorption

PowerPoint Presentation:

Physicochemical factors affecting rectal absorption 1- Drug solubility in vehicle: - The rate at which a drug is released from a suppository and absorbed by the rectal mucous membrane is directly related to its solubility in the vehicle or, in other words, to the partition coefficient of the drug between the vehicle and the rectal liquids. - When drugs are highly soluble in the vehicle the tendency to leave the vehicle will be small and so the release rate into the rectal fluid will be low. 2- Particle Size: - For drugs present in a suppository in the undissolved state, the size of the drug particle will influence its rate of dissolution and its availability for absorption. - The smaller the particle size the more readily the dissolution of the particle the greater chance for rapid absorption.

PowerPoint Presentation:

3- Nature of the base: The base must be capable of melting, softening, or dissolving to release its drug components for absorption. If the base interacts with the drug inhibiting its release drug absorption will be impaired or even prevented. Also, if the base is irritating to the mucous membranes of the rectum it may initiate a colonic response and a bowel movement incomplete drug release and absorption. 4- Spreading Capacity: - The rapidity and intensity of the therapeutic effects of suppositories are related to the surface area of the rectal mucous membrane covered by the melted base : drug mixture (the spreading capacity of the suppositories). This spreading capacity may be related to the presence of surfactants in the base.

Physiological factors affecting vaginal absorption:

Physiological factors affecting vaginal absorption

Physicochemical factors affecting vaginal absorption:

Physicochemical factors affecting vaginal absorption Molecular weight Lipophilicity Ionization Surface charge Chemical nature

Mechanisms of drugs absorption from vagina :

Mechanisms of drugs absorption from vagina Diffusion through the cell due to a concentration gradient ( transcellular route ), Vesicular or receptor-mediated transport mechanism Diffusion between cells through the tight junctions ( intercellular route ).

Methods of enhancing drug Absorption:

Methods of enhancing drug Absorption The low absorption can be the result of poor membrane permeability due to molecular size, lack of lipophilicity (e.g. steroidal drugs) fluid volume, estrus cycle and pH of local area. This problem can overcome by penetration enhancers to facilitate the transport of these molecules and improve the bioavailability. In general, enhancers improve the absorption of these molecules by one or several combined mechanisms: 1) By increasing intracellular transport or use of penetrating agents e.g. PEG. 2) By increasing the contact time between the dosage form and the membrane by using muco-adhesive polymers e.g. Carbopol 934, 940, etc and formulation of gel and by increasing viscosity of formulation. 3) By increasing local area blood flow , thereby raising the concentration gradient across the mucosa.

PowerPoint Presentation:

4) By the use of bio-adhesive preparations have been developed as a new type of controlled release form for the treatment of both topical and systemic diseases. 5) By the use of chelating agents as a penetration enhancers in vaginal formulations. Eg ., leuprolide , carboxylic acids with chelating ability are co-administered. 6) By the use of pro-drugs enhances drug permeability through modification of the hydrophilicity or lipophilicity of the drug. 7) Modification of chemical structure of the drug molecule , thus making it selective, site specific and a safe drug delivery system. 8) By the use of gel formulation is an extreme case of viscosity enhancement through the use of viscosity enhancers. So the dosing frequency can be decreased to once or twice a day. Example of vaginal gel is metronidazole gel. It is most popular vaginal gel. Mostly hydrogels are used for the intravaginal gel drug delivery system.

authorStream Live Help