Cells Of The Nervous System I Neurones

Cells Of The Nervous System I Neurones

pediagenosis    March 23, 2023   

Cells Of The Nervous System I: Neurones

There are two major classes of cells in the nervous system: the neuroglial cells and neurones, with the latter making up only 10– 20% of the whole population. The neurones are specialized for excitation and nerve impulse conduction (see Chapters 14, 15 and 17), and communicate with each other by means of the synapse (see Chapter 16) and so act as the structural and functional unit of the nervous system.

Membrane Potentials

Membrane Potentials

pediagenosis    March 23, 2023   

Membrane Potentials

Electrochemical potentials are present across the membranes of virtually all cells in the body. Some cells, such as nerve and muscle cells, are capable of generating rapidly changing electrical impulses, and these impulses are used to transmit signals along their membranes. In other cells, such as glandular cells, membrane potentials are used to signal the release of hormones or activate other functions of the cell. Generation of membrane potentials relies on (1) diffusion of current-carrying ions, (2) development of an electrochemical equilibrium, (3) establishment of a RMP, and (4) triggering of action potentials.

Movement of Substances across the Cell Membrane

Movement of Substances across the Cell Membrane

pediagenosis    March 23, 2023    Comment   

Movement of Substances across the Cell Membrane

Movement through the cell membrane occurs in essentially two ways: passively, without an expenditure of energy, or actively, using energy-consuming processes. The cell membrane can also engulf a particle, forming a membrane-coated vesicle; this membrane-coated vesicle is moved into the cell by endocytosis or out of the cell by exocytosis.

Initiation Of The Heart Beat And Excitation Contraction Coupling

Initiation Of The Heart Beat And Excitation Contraction Coupling

pediagenosis    March 23, 2023   

Initiation Of The Heart Beat And Excitation – Contraction  Coupling

The process linking depolarization to contraction is called excitation - contraction coupling. The basics of action potentials (APs) are described in Chapter 5.

Lactation

Lactation

pediagenosis    March 21, 2023   

Lactation

Milk, which sustains mammalian infants through the first few months of life, is produced by the mammary glands (Fig. 53) under the influence of the pituitary protein hormone prolactin (Chapter 44). The glands comprise several lobules that are composed of acini (also called alveoli), similar in structure to the salivary glands and the exocrine pancreas (Chapters 37 and 40). The lobules empty into lactiferous ducts. As the ducts approach the areola (nipple), they open out to form lactiferous sinuses before narrowing again to emerge at the ampulla on the nipple. The ducts and sinuses are organized so that milk collects within them rather than flowing freely to the ampulla. They are lined by myoepithelial cells that contract to expel milk from the breast. Progesterone, oestrogen, prolactin, cortisol and growth hormone are all required to complete development of the mammary glands, which occurs during the late stages of pregnancy; for the rest of adult life the glandular tissue is rather small. Milk is formed by intense activity of the epithelial cells lining the acinus. The acinar secrete fats (triglycerides), proteins (principally casein, α-lactalbumin and lactoglobulin B) and sugars (mostly lactose) to produce an isotonic liquid that is roughly 4% fat, 1% protein and 7% sugar, with almost 100 additional trace nutrients, including many ions (including Ca²⁺), some immunoglobulins (antibodies) in the form of IgA (Chapter 10) and growth factors, such as insulin-like growth factor-1 (IGF-1) and epidermal growth factor (EGF) (Chapter 46). Colostrum, the first secretion of the mammary glands after birth, is particularly rich in protein, but has a lower sugar concentration than mature milk. It also contains high levels of antibodies (Chapter 10) that provide the infant with basic immunological protection in the first days of life. At least four secretory processes are synchronized in the epithelial cells, exocytosis, lipid synthesis and secretion, transmembrane secretion of ions and water, and transcytosis of extra-alveolar proteins such as hormones, albumin and immunoglobulins from the interstitial spaces.

Control Of Metabolic Fuels

Control Of Metabolic Fuels

pediagenosis    March 21, 2023   

Control Of Metabolic Fuels

Animal cells utilize glucose and fatty acids as fuels to generate the energy-rich molecule adenosine triphosphate (ATP) (Chapter 3). The blood levels of these molecules must be carefully controlled to ensure a steady supply of fuel to active tissues, a task that is complicated by the tendency of many animals (not ruminants) to eat discrete meals rather than continuously. Immediately after a meal, circulating levels of fuel molecules rise and any excess to immediate requirements is stored. This requires the transport of the molecules into cells (primarily liver, skeletal muscle and the fat-storing cells of adipose tissues) and the synthesis of storage molecules, such as glycogen, a polymer of glucose, triglycerides (fats) and, to a lesser extent, proteins. As time after a meal increases, the consumption of blood glucose and fatty acids necessitates the activation of tissue energy stores. Glycogen is broken down into glucose, triglycerides are converted into free fatty acids and ketone bodies and, if the fast is prolonged, proteins are catabolized to provide a supply of amino acids that can be converted to glucose (gluconeogenesis). The body thus alternates between two states, which can be described as anabolic, in which storage molecules are manufactured, and catabolic in which the same molecules are broken down (Fig. 43a). Switching between these states is controlled mainly by hormones, with the pancreatic proteins insulin and glucagon being the prime movers of the anabolic and catabolic processes, respectively. In addition, growth hormone (Chapter 47), cortisol, adrenaline (epinephrine) and noradrenaline (norepinephrine) (Chapter 49) can stimulate catabolic processes (Fig. 43a). There is growing evidence that hormones produced from fat (e.g. leptin) and the gut (e.g. ghrelin from the stomach) are involved in energy homeostasis, including controlling food intake, energy expenditure and adiposity.

From Genes to Proteins

From Genes to Proteins

pediagenosis    March 21, 2023    Comment   

From Genes to Proteins

Although DNA determines the type of biochemical product needed by the cell and directs its synthesis, it is RNA through the process of translation, which is responsible for the actual assembly of the products.

Prenatal Screening and Diagnosis

Prenatal Screening and Diagnosis

pediagenosis    March 20, 2023   

Prenatal Screening and Diagnosis.

The purpose of prenatal screening and diagnosis is not just to detect fetal abnormalities but also to allay anxiety and provide assistance to prepare for a child with a specific disability. Prenatal screening cannot be used to rule out all possible fetal abnormalities. It is limited to determining whether the fetus has (or probably has) designated conditions indicated by late maternal age, family history, or well-defined risk factors.

DnA structure and Function

DnA structure and Function

pediagenosis    March 20, 2023    Comment   

DnA structure and Function.

The DNA molecule that stores the genetic information in the nucleus is a long, double-stranded, helical structure. DNA is composed of nucleotides, which consist of phosphoric acid, a five-carbon sugar called deoxyribose, and one of four nitrogenous bases (Fig. 6.1). These nitrogenous bases carry the genetic information and are divided into two groups: the pyrimidine bases, thymine (T) and cytosine (C), which have one nitrogen ring, and the purine bases, adenine (A) and guanine (G), which have two. The backbone of DNA consists of alternating groups of sugar and phosphoric acid, with the paired bases projecting inward from the sides of the sugar molecule.

Mechanisms of Cell Injury

Mechanisms of Cell Injury

pediagenosis    March 20, 2023    Comment   

Mechanisms of Cell Injury.

The mechanisms by which injurious agents cause cell injury and death are complex. Some agents, such as heat, produce direct cell injury. Other factors, such as genetic derangements, produce their effects indirectly through metabolic disturbances and altered immune responses. There seem to be at least three major mechanisms whereby most injurious agents exert their effects: