Biology and Biotechnology

How many Phases of Digestion? Cephalic Phase During the cephalic phase of digestion, the smell, sight, thought,or initial taste of food activates neural centers in the cerebral cortex, hypothalamus, and brain stem. The brain stem then activates The facial (VII),glossopharyngeal (IX), and vagus (X) nerves.The facial and glossopharyngeal nerves stimulate the salivary glands to secrete saliva, while the vagus nerves stimulate the gastric glands to secrete gastric juice. The purpose of the cephalic phase of digestion is to prepare the mouth and stomach for food that is about to be eaten. Gastric Phase : Once food reaches the stomach, the gastric phase of digestion begins. Neural and hormonal mechanisms regulate the gastric phase of digestion to promote gastric secretion and gastric motility. • Neural regulation. Food of any kind distends the stomach and stimulates stretch receptors in its walls.Chemoreceptors in the stomach monitor the pH of the stomach chyme. When the stomach walls are di...

What is Negative Feedback Mechanisms ? In human body systems controlled by negative feedback, the effector response decreases or negates the effect of the original stimulus, maintaining or restoring homeostasis (thus the term negative feedback).  1) Control of body temperature is similar to the non-physiological example of a domestic central heating system. 2)  The thermostat (temperature detector) is sensitive to changes in room temperature (variable factor). 3)  The thermostat is connected to the boiler control unit (control centre), which controls the boiler (effector).  4)  The thermostat constantly compares the information from the detector with the preset temperature and, when necessary, adjustments are made to alter the room temperature.  5)  When the thermostat detects the room temperature is low, it switches the boiler on. The result is output of heat by the boiler, warming the room.  6)  When the preset temperature is reached, the ...

  Respiratory System Anatomy • Describe the anatomy and histology of the nose, pharynx, larynx, trachea, bronchi, and lungs. • Identify the functions of each respiratory system structure. The respiratory system (RES-pi-ra-toˉr-e¯) consists of the nose, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs . Its parts can be classified according to either structure or function. Structurally, the respiratory system consists of two parts:  (1) The upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures;  (2) the lower respiratory system includes the larynx, trachea, bronchi, and lungs. Functionally, the respiratory system also consists of two parts.  (1) The conducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs. These include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles; their function is to filter...

  Introduction : The body contains not only millions of different T cells but also millions of different B cells, each capable of responding to a specific antigen. Cytotoxic T cells leave lymphatic tissues to seek out and destroy a foreign antigen, but B cells stay put. In the presence of a foreign antigen, a specific B cell in a lymph node, the spleen, or mucosa-associated lymphatic tissue becomes activated. Then it undergoes clonal selection, forming a clone of plasma cells and memory cells. Plasma cells are the effector cells of a B cell clone; they secrete specific antibodies, which in turn circulate in the lymph and blood to reach the site of invasion. What does activate clonal Selection? Activation and Clonal Selection of B Cells During activation of a B cell, an antigen binds to B-cell receptors(BCRs). These integral transmembrane proteins are chemically similar to the antibodies that eventually are secreted by plasma cells. Although B cells can respond to an unproce...

What is antigen and antiggen receptor and how its work? Antigens and Antigen Receptors Antigens have two important characteristics: immunogenicity and reactivity. Immunogenicity is the ability to provoke an immune response by stimulating the production of specific antibodies, the proliferation of specific T cells, or both. The term antigen derives from its func- tion as an antibody generator. Reactivity is the ability of the antigen to react specifically with the antibodies or cells it provoked. Strictly speaking, immunologists define antigens as substances that have reactivity; substances with both immunogenicity and reactivity are considered complete antigens. Commonly, however, the term antigen implies both immunogenicity and reactivity, and we use the word in this way.  Entire microbes or parts of microbes may act as antigens. Chemical components of bacterial structures such as flagella, capsules, and cell walls are antigenic, as are bacterial toxins. Nonmicrobial examples ...

  What is spleen and what is importance of Spleen? Spleen The oval spleen is the largest single mass of lymphatic tissue in the body, measuring about 12 cm (5 in.) in length .It is located in the left hypochondriac region between the stomach and diaphragm. The superior surface of the spleen is smooth and convex and conforms to the concave surface of the diaphragm. Neighboring organs make indentations in the visceral surface of the spleen—the gastric impression (stomach), the renal impres- sion (left kidney), and the colic impression (left colic flexure of large intestine). Like lymph nodes, the spleen has a hilum. Through it pass the splenic artery, splenic vein, and efferent lymphatic vessels.  A capsule of dense connective tissue surrounds the spleen and is covered in turn by a serous membrane, the visceral peritoneum. Trabeculae extend inward from the capsule. The capsule plus tra- beculae, reticular fibers, and fibroblasts constitute the stroma of the spleen; the p...

What is Lymphatic system? Lymphatic system Structure and Function The lymphatic system (lim-FAT-ik) consists of a fluid called lymph, vessels called lymphatic vessels that transport the lymph,a number of structures and organs containing lymphatic tissue (lymphocytes within a filtering tissue), and red bone marrow. The lymphatic system assists in circulating body fluids and helps defend the body against disease-causing agents. As you will see shortly, most components of blood plasma filter through blood capillary walls to form interstitial fluid. After interstitial fluid passes into lymphatic vessels, it is called lymph (LIMF - clear fluid). The major difference between interstitial fluid and lymph is location: Interstitial fluid is found between cells, and lymph is located within lymphatic vessels and lymphatic tissue. Lymphatic tissue is a specialized form of reticular connective tissue  that contains large numbers of lymphocytes. Recall from Chapter 19 that lymphocytes are agran...

Castration (kas-TRA¯-shun -  to prune) Removal, inactivation, or de- struction of the gonads; commonly used in reference to removal of the testes only. Colposcopy (kol-POS-ko¯-pe¯; colpo- -  vagina; -scopy -  to view) Visual inspection of the vagina and cervix of the uterus using a culpo- scope, an instrument that has a magnifying lens (between 5 and 50) and a light. The procedure generally takes place after an unusual Pap smear. Culdoscopy (kul-DOS-ko¯-pe¯; -cul- -  cul-de-sac; -scopy -  to examine) A procedure in which a culdoscope (endoscope) is inserted through the posterior wall of the vagina to view the rectouterine pouch in the pelvic cavity. Dysmenorrhea (dis-men-o¯r-E¯-a; dys- -  difficult or painful) Pain associ- ated with menstruation; the term is usually reserved to describe menstrual symptoms that are severe enough to prevent a woman from functioning normally for one or more days each month. Some cases are caused by uterine tumo...

 [• How do oral contraceptives reduce the likelihood of pregnancy? • How do some methods of birth control protect against sexually transmitted diseases? • What is the problem with developing an oral contraceptive pill for males? ] Surgical Sterilization Sterilization is a procedure that renders an individual incapable of further reproduction. The principal method for sterilization of males is a vasectomy (va-SEK-toˉ-me¯; -ectomy -  cut out), in tubes, the tubes can be tied and/or cut, and sometimes they are cauterized. In any case, the result is that the secondary oocyte cannot pass through the uterine tubes, and sperm cannot reach the oocyte. Non-incisional Sterilization Essure® is one means of non-incisional sterilization that is an alternative to tubal ligation. In the Essure procedure, a soft micro-insertcoil made of polyester fibers and metals (nickel–titanium and stainless steel) is inserted with a catheter into the vagina through the uterus, and into each uterine tube...

  Glomerular Diseases A variety of conditions may damage the kidney glomeruli, either directly or indirectly because of disease elsewhere in the body. Typically, the filtration membrane sustains damage, and its permeability increases. Glomerulonephritis (gloˉ-mer-uˉ-loˉ-ne-FRIˉ-tis) is an inflammation of the kidney that involves the glomeruli. One of the most common causes is an allergic reaction to the toxins produced by streptococcal bacteria that have recently infected another part of the body, especially the throat.  The glomeruli become so inflamed, swollen, and engorged with blood that the filtration membranes allow blood cells and plasma proteins to enter the filtrate. As a result, the urine contains many erythrocytes (hematuria) and a lot of protein. The glomeruli may be permanently damaged, leading to chronic renal failure. Nephrotic syndrome  (nef-ROT-ik) is a condition characterized by proteinuria (proˉ-teˉn-OO-reˉ-a), protein in the urine, and hyperlipidemia...