BLOOD PLASMA

 

INTRODUCTION: Plasma is the liquid part of blood and is approximately 91% water. The solvent ability of water enables the plasma to transport many types of substances. Nutrients absorbed in the digestive tract, such as glucose, amino acids, and minerals, are circulated to all body tissues. Waste products of the tissues, such as urea and creatinine, circulate through the kidneys and are excreted in urine.

Hormones produced by endocrine glands are carried in the plasma to their target organs, and antibodies are also transported in plasma. Most of the carbon dioxide produced by cells is carried in the plasma in the form of bicarbonate ions (HCO3^–). When the blood reaches the lungs, the CO2 is re-formed, diffuses into the alveoli, and is exhaled. Also in the plasma are the plasma proteins. Proteins

COMMON CONSTITUENTS OF PLASMA: The clotting factors prothrombin, fibrinogen, and others are synthesized by the liver and circulate until activated to form a clot in a ruptured or damaged blood vessel. Albumin is the most abundant plasma protein. It too is synthesized by the liver. Albumin contributes to the colloid osmotic pressure of blood, which pulls tissue fluid into capillaries. This is important to maintain normal blood volume and blood pressure. Other plasma proteins are called globulins. Alpha and beta globulins are synthesized by the liver and act as carriers for molecules such as fats. The gamma globulins are antibodies produced by lymphocytes. Immunoglobulins

Antibodies initiate the destruction of pathogens and provide us with immunity. Plasma also carries body heat. Heat is one of the by-products of cell respiration (the production of ATP in cells). Blood is warmed by flowing through active organs such as the liver and muscles. This heat is distributed to cooler parts of the body as blood continues to circulate.

RELATED;

1.  RED BLOOD CELLS  

2.  COMPONENTS OF BLOOD  

3.  THE ABO BLOOD GROUPING

4.  WATER

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THE PLASMA MEMBRANE

 

INTRODUCTION:  The plasma membrane separates the cell from the external environment and encapsules the microcellular organelles.  It has highly selective permeability properties so that the entry and exit of compounds are regulated via specific protein-like channels also known as pores.  

The cellular metabolism is in turn influenced and probably regulated by the membrane which is metabolically very active.  The enzyme, nucleotide phosphatase or 5' nucleotidase and alkaline phosphatase are seen on the outer part of cell membrane; they are therefore called ecto-enzymes.

COMPONENTS OF THE MEMBRANE:  Membranes are mainly made up of lipids, proteins and small amount of carbohydrates.  The contents of these compounds vary according to the nature of the membrane.  The carbohydrates are present as glycoproteins and glycolipids.  Phospholipids are the most common lipids present and they are amphipathic in nature.  Cell membranes also contain cholesterol.

FLUID MOSAIC MODEL:  The lipid bilayer was originally proposed by Davson and Danielle in 1935.  Later, the structure of the biomembranes was described as a fluid mosaic model.  The phospholipids are arranged in bilayers with the polar head groups oriented towards the extracellular side and the cytoplasmic side with a hydrophobic core.  The distribution of the phospholipids is such that choline containing phospholipids are mainly in the external layer and ethanolamine and serine containing phospholipids in the inner layer.  The lipid bilayer shows free lateral movement of its components, hence the membrane is said to be fluid in nature. Fluidity enables the membrane to perform endocytosis and exocytosis.  However, the components do not freely move from inner to outer layer, or outer to inner layer (flip-flop movement is restricted).  During apoptosis (programmed cell death), flip-flop movement occurs.  This Flip-flop movement is catalyzed by enzymes.  Flippases catalyse the transfer of amino phospholipids across the membrane.  Floppases catalyse the outward directed movement which is ATP dependent.  This is mainly seen in the role of ABC proteins mediating the efflux of cholesterol and the extrusion of drugs from cells.  The MDR (multi drug resistance) associated p-glycoprotein is a floppase.

The cholesterol content of the membrane alters the fluidity of the membrane.  When cholesterol concentration increases, the membrane becomes less fluid on the outer surface, but more fluid in the hydrophobic core.

RELATED;

1.  LIPIDS

2.  CHEMICALS OF LIFE

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SECRETS OF THE HUMAN BODY

SECRETS OF THE HUMAN BODY:  Our body is large compared to microbes and plants, multicellular and have totally different genetic makeup from all kinds of life.  The human body is seen as a rounded mass of some staggering 75 kg for a average adult but it has some features that anyone who never go through comprehensive anatomy can not analyze.  When we talk about anatomy, we mean the organ and system components and the way they are organised in the body.  It takes even longer for one to appreciate that the body is prone to more than 500 medical conditions that can cause ill-health.  And when it comes to use of drugs and substances, less is known about their interaction with the various body systems.  I already talked about dynamics of drugs and the human body in some of my previous discussions.  In this article, we are going to look at some of the most important need to know hidden secrets of the human body.

RELATED:

1.  BODY ORGANS

2.  HUMAN ANATOMY

3.  DYNAMICS OF DRUGS AND THE HUMAN BODY

STRUCTURE OF THE GASTROINTESTINAL TRACT

INTRODUCTION: The GI tract is one of the most complex and important organ systems. It comprises the alimentary canal, a hollow structure extending from the mouth to the anus, and associated glandular organs that empty their contents into the canal.

LENGTH OF THE SYSTEM: The alimentary canal is 7–9 m in the adult and includes the mouth, esophagus (23–25 cm), stomach, small intestine (duodenum, jejunum, ileum; 6–7 m), large intestine (cecum and colon; 1.0–1.5 m), rectum, and anus.

CONNECTIONS AND ACCESSORY ORGANS: The canal is connected to the salivary glands, the pancreas, and the gallbladder, the sources of exocrine secretions that play an essential role in digestion.

ANATOMICAL MAKEUP OF GIT: The wall of the GI tract is composed of four main layers. From the lumen outward, these include the mucosa, submucosa, muscularis externa, and serosa. The precise structure of some of these layers, most notably the mucosa, varies from one region of the GI tract to the next. The mucosa has three components: specialized epithelial cells that line the lumen; the underlying lamina propria, a layer of connective tissue that contains small blood and lymphatic vessels, immune cells, and nerve fibers; and the muscularis mucosa, a thin layer of muscle cells. The muscularis mucosa is an important boundary in determining whether cancer of the GI tract is still localized to its site of origin or is likely to have metastasized (ie, spread to distant regions of the body). The submucosa is a layer of loose connective tissue directly beneath the mucosa containing larger blood and lymphatic vessels and a nerve plexus of the intrinsic or enteric nervous system, termed the submucosal nerve (Meissner) plexus. This nerve plexus is particularly important for secretion control in the GI tract. 

In some areas, the submucosa also contains glands and lymphoid tissue. The muscularis externa is composed of an inner circular and an outer longitudinal layer of smooth muscle and is responsible for the motility of the GI tract. Between these muscle layers lies the myenteric nerve (Auerbach) plexus, a division of the enteric nervous system that regulates motility. The serosa is an outer sheath of squamous mesothelial cells and connective tissues, where larger nerves and blood vessels travel in a bed of connective and adipose tissue.

RELATED;

1. ENTERIC NERVOUS SYSTEM  

2. DISEASES THAT AFFECT THE GIT

3.  PEPTIC ULCER DISEASE

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