Lymphatic and Immunity 1: Introduction

-

Introduction

Pathogens are microscopic organisms that cause disease, e.g. viruses, bacteria, fungi and parasites.

Antigens are targets that identify any pathogen or foreign compound.

The lymphatic system protects us against disease. Lymphocytes, the cells of the lymphatic system, respond to environmental pathogens, toxins and abnormal body cells, e.g. cancerous cells.

The immune system involves immunity, the ability to resist infection and disease. All body cells and tissues are involved in the production of immunity. The primary function of the lymphatic system is to produce immunity, and maintain and distribute lymphocytes. It is also a drainage network which maintains fluid balance between tissues, and absorbs fats from the digestive system.

Components of the lymphatic system are described below:

Lymph: fluid similar to plasma

Lymphatic vessel: carry lymph from peripheral tissues back to the venous system

Lymphoid tissues and organs: produce and store most of the lymphocytes, e.g tonsils, lymph notes, thymus and spleen

Lymphocytes: cells that participate in the immune response

Lymphatic capillaries: terminal endothelial cells loosely bound together with overlap which acts as a one-way valve to enable entrance of fluid, solutes, viruses and bacteria

Lymph node: areolar tissue with densely packed lymphocytes

NOTE: lymph from the right upper limb, right neck and right head enter the system via the right lymphatic duct which drains into the right subclavian vein. Lymph from the left upper limb, head, neck and rest of the body enters the system via the thoracic duct, which drains in to the left subclavian vein.

Lymph is pushed around the body through the contraction of smooth muscle in larger lymphatic vessels, contraction of skeletal muscles and pressure changes in the thorax due to respiration.

What are lymphocytes?

Lymphocytes are a type of leukocyte produced in lymphoid tissue, lymphoid organs and red bone marrow. There are T cells, thymus-dependent, B cells, bone marrow-derived, and natural killer cells, involved in non-specific immunity. The four types of T cells are listed below:
  1. Cytotoxic T cells attack cells infected by viruses → cell-mediated immunity
  2. Memory T cells respond to foreign substances and remain in the body to provide immunity
  3. Helper T cells stimulate T and B cell function
  4. Suppressor T cells inhibit T and B cell function
Lymphopoeisis is the production of lymphocytes. It involves bone marrow, the thymus and peripheral bone tissue. The cells produced are either Group 1 or Group 2.

Lymphoid Organs

The thymus reduces in size as well age and produces hormones important in the development and maintenance of the normal immunological defence system. Thymosin produces by the thymus promotes lymphocyte development.

The spleen removes abnormal blood cells by phagocytosis, stores iron from recycled red blood cells and initiates an immune response by B and T cells

Comments

Post a Comment

Popular posts from this blog

Growth and Development 2: Placentation and Hormones

-
How does the placenta form? The placenta forms from the embryonic trophoblastic/mesoderm tissues, as well as the maternal endometrial tissues. Vessels develop in the embryonic tissues which then supply nutrients to the foetus from the maternal blood supply. The chorion develops fingerlike villi which have become vascularised and extend to the embryo as umbilical arteries and veins. The embryo, amnion and yolk sac float in a fluid-filled chamber attached to the placenta by a body stalk. The placenta grows and begins to develop into organised regions, bulging into the uterine cavity as it grows. It becomes fully developed by the end of the third month (end of first trimester), where the foetus moves farther from the placenta connected by the umbilical cord. By 12 weeks, the placenta is providing nutrients and removing wastes, meaning it takes on the role of oestrogen and progesterone which used to be released from the corpus luteum. Decidua capsularis: endometrium surroundi...
Read more

Growth and Development 4: Labour, foetal circulation and lactation

-
What happens when we give birth? During the last week of pregnancy, oestrogen reaches a peak. This causes myometrial weakness and irritability. Then, weak 'Braxton Hicks' contractions occur, which become uterine contractions stimulated by oxytocin and prostaglandins closer to birth. Emotional and physical stress establishes a positive feedback mechanism with the hypothalamus, increasing oxytocin release. The stages of labour are summarised below:   1.   Dilation Stage (8 hours) Onset of labour Cervix dilates Foetus moves towards birth canal Contractions begin and increase in frequency Water eventually breaks   2.    Expulsion Stage (2-3 hours) Cervix pushed open by foetus Contractions increase in intensity, frequency and length Continues until foetus emerges from vagina (delivery) Surgical intervention possible: episiotomy (cutting of perineal membrane) or caesarean section Newborn health assessed immediately   3.   Plac...
Read more

Lymphatics and Immunity 3: Cell-Mediated Immunity

-
Image
What is adaptive immunity then? Adaptive or specific immunity responds to specific antigens through the coordinated action of T and B cells. It is only developed after birth. Adaptive immunity involves both cell-mediated and antibody-mediated immunity. Cytotoxic T cells provide cell-mediated immunity, providing defence against abnormal cells and pathogens inside  cells. B cells provide antibody-mediated immunity, providing defence against antigens and pathogens in body fluids. There are four properties of immunity: Specificity - response to only a specific type of antigen Versatility - production of many types of lymphocytes Memory - active lymphocytes stay in circulation and provide immunity against new exposure Tolerance - immune system ignores normal antigens What is cell-mediated immunity? T cells only recognise antigens that are bound to glycoproteins in a plasma membrane. These are termed major histocompatibility complex proteins. These proteins differ betwee...
Read more