MBBS NOTES

  Special types of Active Transport (Macro- Molecules)  This includes vesicular transport...which includes Endocytosis and Exocytosis ENDOCYTOSIS  Endocytosis includes.. 1. Pinocytosis (cell drinking)  2. Phagocytosis (cell eating)  3. Receptor mediated endocytosis  Vesicular exocytosis includes basically release of neuro transmitter e.g. ACh Pinocytosis (Cell drinking) It is the process of engulfing liquid substances by enfolding of cell membrane e.g. Reabsorption by renal tubular epithelial cells  Phagocytosis (cell eating)  Engulfing the solid particles e.g. bacteria, dead cells and foreign particles by the cells. This process involves three steps i) Attachment stage i) Engulfment stage iii) Degradation stage   Receptor mediated endocytosis In this process substance binds with special receptor protein on the cell membrane. Then protein-substance complex is engulfed by the cell membrane by the process of endocytosis e.g. Transport of iron, cholesterol into the cell, LDL and Vita B12

  Definition of Apoptosis Apoptosis word comes from Greek word Apo means- away and ptosis means fall. Apoptosis is defined as programmed cell death. For example - RBC's life span is 120 days while WBC's life span is only few days. Majority of the cells show apoptosis. But rate of apoptosis varies from cell to cell, Some cells have very high rate of apoptosis, for example cells in intestine & and in bone marrow.   Physiological significance & mechanism i)During embryogenesis & developmental stage , there is high rate of apoptosis. During embryogenesis, degeneration of Mullerian duct in male foetus occur due to apoptosis Webs between fingers and toes are removed due to apoptosis  Developmental brain remodelling and immune system development require apoptosis ii)During adult life too, apoptosis plays an important role by removing old and less functioning cells. These cells are replaced by to better functioning young cells   Mechanism- Procaspases activated to Caspase

Myaesthenia Gravis Is a serious and sometimes fatal, autoimmune disease in which skeletal muscles are weak and tire easily. The myoneural junction is unable to transmit signals from the nerve fibers to muscle fibers, thereby causing paralysis of the involved muscles. Women are affected more than men in 3:2 ratio,.   Etiology- It is caused by the formation of circulating antibodies to the nicotinic acetylcholine receptors. The anti-AchR antibodies have following three major functions: they compete with Ach to bind to AchR, producing receptor blockade; they induce endocytosis of AchR; and they damage the postsynaptic membrane. Thus, the Ach released at the nerve terminal is not able to produce adequate EPP (end plate potential) to excite the muscle fiber. The reason for the development of autoimmunity to Ach receptors in this disease is still unknown,   Clinical Features- The weakness increases during prolonged use of the muscle and improves after rest or sleep. Thus, the patient feels

  Membrane Transport Proteins 1) Pores: rare, eg. Aquaporins (Water Channels) by ADH at DCT & CT (osmosis),  2) Channels: eg. Ion Channels (Ligand gated, Voltage gated, Mechanically gated) simple diffusion   3) Carriers:   a. Uniporters (facilitated diffusion), b. Pumps (primary active transport),  c. Symporters (secondary co-active transport),  d. Antiporters (secondary counter-active transport)   Classification of Transport across cell membrane   1) Passive transport- Passive transport is the transport of a substance along electrochemical gradient. It does not require energy. Its types are-  1.1 Osmosis 1.2 Simple Diffusion 1.3 Facilitated Diffusion 2) Active transport- Active transport is the transport of a substance against electrochemical gradient (uphill). It requires energy  2.1) primary active transport 2.2) secondary- coactive transport & secondary- counter active transport  3) Special types of Active Transport (Macro- Molecules)-  3.1) Endocytosis  3.2) Exocytosis

The pineal gland is a small, pea-shaped gland in the brain. It produces and regulates hormone melatnoni.  It is known from comparative anatomy that the pineal gland is a vestigial remnant of what was a third eye located high in the back of the head in some lower animals Functions of Pineal gland  Pineal gland is believed to have role in the following functions.  (1) enhancing sex,  (2) staving off (preventing) infection,  (3) promoting sleep,  (4) enhancing mood, and  (5) increasing longevity (as much as 10 to 25 percent) MELATONIN & CIRCADIAN RHYTHMS Pineal pinealocytes contain melatonin and the enzymes responsible for its synthesis from serotonin, and they secrete the hormone into the blood and the cerebrospinal fluid Secretion of melatonin The cyclic activity of the suprachiasmatic nucleus (SCN) sets up a circadian rhythm for melatonin release. This rhythm is entrained to light/dark cycles by neurons in the retina. Light signals are relayed via the retinohypothalamic (RHT) fiber

Thymus is a specialized primary lymphoid organ of the immune system. It is situated behind the sternum in upper and anterior part of chest. It consists of a capsule, outer cortex and inner medulla. T cell maturation Functions of Thymus The thymus facilitates the maturation of T cells which are responsible for cell mediated immunity. T cells begin as hematopoietic precursors from the bone-marrow, and then migrate to the thymus for maturation, where they are referred to as thymocytes.  In the thymus they undergo a process of maturation, which involves ensuring the cells react against antigens (positive selection), but that they do not react against antigens found on body tissue (negative selection). Once mature, T cells emigrate from the thymus to lymphnodes to provide vital functions in the immune system  Positive selection This process occurs in the cortex of Thymus. The survival and nature of the T cell in thymus depends on its interaction with surrounding thymic epithelial cells. Her