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Lecture 12

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Biological Sciences
Connie Potroff

1 Lecture 12 The Lymphoid System (chapter 23) **Assigned Readings: p.612-613 “lymphoctyes” (includes the type of lymphocytes and lymphocytes in the immune response – FIG 23.6) Introduction The lymphoid system consists of: Lymph Lymphatic vessels Lymphoid organs An Overview of the Lymphoid System Lymph consists of: Interstitial fluid Lymphocytes *Macrophages Functions of the Lymphoid System Primary lymphoid structure (thymus gland) causes differentiation of lymphocytes resulting in: T cells, B cells, and NK cells **Secondary lymphoid structures (lymph nodes and tonsils) consist of lymphocytes and more B cells to battle infectious agents Maintains normal blood volume Maintains chemical composition of the interstitial fluid Provides an alternative route for the transport of: Hormones Nutrients Waste products The blood pressure in capillaries is about 35 mm Hg This pressure forces solutes and waste out of the plasma into the interstitial fluid area Some interstitial fluid enters the lymphoid system The lymphoid system eventually connects with the venous system Structure of Lymphatic Vessels Small lymphatic vessels are called - Lymphatic capillaries Large-diameter lymphatic vessels are called - Lymphatic ducts Lymphatic capillaries have greater permeability *Lymphatic capillaries have anchoring filaments that connect to the surrounding connective tissue to keep the capillaries open Larger lymphatic vessels have valves just like most veins, unidirectional flow Valves of Lymphatic Vessels Pressure in the lymphatic vessels is lower than the pressure in the veins Valves prevent the backflow of lymph *Skeletal muscles contract to help propel lymph *Inhalation decreases thoracic pressure, which helps to move lymph toward the venous system (subclavians) Lymphocytes Lymphocytes are the primary cells of the lymphoid system They respond to: © 2012 Pearson Education, Inc. 2 Invading bacteria and viruses Abnormal body cells such as cancer cells (NK cells) Foreign proteins such as toxins released by some bacteria Types of Lymphocytes T cells (Thymus-dependent cells) B cells (bone marrow–derived cells) NK cells (natural killer cells) Lymphoid organs include: Lymph nodes Thymus gland Spleen Lymph Nodes Scattered throughout the body Lymphoid tissue and lymph nodes are in high concentrations where the body is more susceptible to injury or invasion High concentrations can be found in the following areas: cervical region, axillary region, breasts, abdominal region, inguinal region **Structure of a Lymph Node Lymph nodes consist of: Capsule with afferent vessels Subcapsular space Outer cortex Germinal center Medulla Medullary cords Hilum with efferent vessels The Spleen Largest lymphoid organ (12 cm in length) Located on the left edge of the stomach Not a vital organ, but in infant spleen is important for the production of RBCs Capsule *Red pulp (contains large quantities of blood) destroys old RBCs *White pulp (forms lymphoid nodules) contains germinal centres for lymphocyte production, removal of blood borne antigens Trauma to ribs may lead to damage to spleen, if you rupture your spleen, must have a spleenectomy immediately – 90% mortality rate if not removed because of blood loss (spleen is redundant organ because lymph nodes and liver also clean blood) The Senses Introduction Sensory information arrives at the CNS Information is “picked up” by sensory receptors Sensory receptors are the interface between the nervous system and the internal and external environment General senses Refers to temperature, pain, touch, pressure, vibration, and proprioception (position of the body) TTPPPV Special senses © 2012 Pearson Education, Inc. 3 Refers to smell, taste, balance, hearing, and vision Receptors and Receptive Fields Free nerve endings are the simplest receptors These respond to a variety of stimuli Receptors of the retina (for example) are very specific and only respond to light information that is relayed from the receptor to a specific neuron in the CNS The General Senses Mechanoreceptors Tactile receptors (table 18.1- p.473) Provide sensations of touch, pressure, and vibrations o 2 types of tactile receptors: Unencapsulated tactile receptors Free nerve endings are common in the dermis Tactile discs are in the stratum basale layer Root hair plexus monitors distortions and movements of the body surface Encapsulated tactile receptors Tactile corpuscle: common on eyelids, lips, fingertips, nipples, and genitalia Ruffini corpuscle: in the dermis, sensitive to pressure and distortion Lamellated corpuscle: consists of concentric cellular layers / sensitive to vibrations The Special Senses Include: Olfaction (smell), Gustation (taste), Equilibrium & Hearing, Vision Olfaction (Smell) The olfactory epithelium consists of: Olfactory receptors Supporting cells Basal cells Olfactory Discrimination The epithelial receptors have different sensitivities and we therefore “detect” different smells Olfactory receptors can be replaced The replacement activity decli
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