3 tissues assignment

• Epithelia:

  • Epithelia is plural for epithelium
  • Covers cells
  • Two types:
  • Covering epithelia: cover external body surfaces and line internal body cavities and tubes
  • Glandular epithelia: secretory, found in aggregates called glands beneath body surfaces
  • Characteristics of epithelia:
  • Continuous sheets of cells covering exterior surfaces of the body
  • Line internal closed cavities and body tubes
  • Communicate with the outside environment (e.g., alimentary, respiratory, and genitourinary tracts)
  • Make up secretory portions of glands and their ducts
• • Found in sensory receptive regions of certain sensory organs (e.g., ear and nose)
  • Functions of epithelia:
  • Cover and lining surfaces (e.g., skin)
  • Involved in absorption (e.g., intestine), secretion (e.g., glands), and can be sensory
  • Provide physical protection (e.g., skin)
  • Act as a barrier between the inside and outside of the gut
• Epithelia characteristics:

  • Continuous sheets of cells covering the body surface
  • Stand on a basement membrane providing attachment and selective filtration barrier
  • Avascular, rely on diffusion for exchange of oxygen and metabolites
  • Cell-cell junctions to bind adjacent cells
  • Communication junctions (gap junctions) for communication between adjacent cells
• Importance of covering tissue:

  • Selective diffusion for transfer of gases, nutrients, and waste products
  • Absorption/secretion functions (e.g., absorption of nutrients from the gut, secretion of enzymes for digestion)
  • Physical protection (e.g., skin)
  • Containment as a barrier between the inside and outside of the gut
• Glandular Epithelia:

  • Glands are an organised collection of secretory epithelial cells
  • Exocrine glands retain continuity with the surface via a duct, secretions delivered into ducts
  • Endocrine glands lose direct continuity with the surface, secretions released directly into the bloodstream
• Blood:

  • Consists of blood plasma and cells
  • Functions include transportation of gases, nutrients, waste, cells, and hormones throughout the body
  • Blood constituents: cells and plasma
  • Blood cells: erythrocytes (red blood cells), leucocytes (white blood cells), platelets (thrombocytes)
  • Plasma accounts for 55% of blood volume, consists of water, proteins, lipids, inorganic ions, and glucose
• Red Blood Cells (Erythrocytes):

  • Most numerous type of cells in blood
  • Essential for transport of carbon dioxide and oxygen
  • Lifecycle involves maturation in bone marrow, production of haemoglobin, and eventual breakdown after about 120 days
  • Iron in haemoglobin extracted by the liver and spleen, remaining heme excreted as bile pigments
• White Blood Cells:

  • Less common than red blood cells
  • Divided into granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes)
  • Functions include immune responses, phagocytosis, and inflammatory reactions
• Haemopoiesis:

  • Process by which mature blood cells develop from precursor cells
  • Continues throughout embryonic and adult life, new cells constantly replace mature cells in circulation
• Haemopoisis:

  In the embryo, haemopoiesis occurs at different stages in the yolk sac, the liver, the spleen, lymph nodes and the bone marrow
• Haemopoisis:

  In the adult, erythrocytes, granulocytes, monocytes and platelets are formed in the bone marrow
• Haemopoisis:

  In the adult, lymphocytes are formed mainly in the lymph nodes, spleen, thymus and lymphatic nodules of the gastrointestinal tract
• Haemopoisis:

  Lymphocytes present in lymph nodes, spleen, thymus and lymphatic nodules of the gastrointestinal tract originate directly or indirectly from the bone marrow
• All precursor cells have common features:

  • Larger in diameter than mature red and white blood cells
  • Nuclei have non-condensed chromatin
  • Cytoplasm is rich in free ribosomes
• Contractility is a fundamental property of cells and the majority of them contain essentially the same contractile machinery as that found in muscle cells
• Skeletal Muscle:

  • Contractions move part of the skeleton
  • Also called 'voluntary' because usually its contractions are under your control
  • Has a stripy appearance due to the repeating structure of the muscle with many myofibrils (fibers) made up of repeating units called muscle sarcomeres
  • Each sarcomere is 2.5 mm long
• Cardiac Muscle:

  • Makes up the muscular walls of the heart (myocardium)
  • 'Involuntary' because its contractions are not under your control
  • Has a similar ultrastructural organisation to skeletal muscle
  • Has a stripy appearance due to repeating units called muscle sarcomeres
• Smooth Muscle:

  • Found in the walls of most blood vessels and tubular organs such as the intestine
  • 'Involuntary'
  • Does NOT have a stripy appearance
  • Contractile proteins myosin and actin are much more randomly arranged than in skeletal or cardiac muscle
• In all types of muscle, contraction is caused by the sliding interaction of thick myosin filaments along thin actin filaments
• The cytoplasm of muscle cells is often called sarcoplasm, the smooth ER is the sarcoplasmic reticulum, and the muscle cell membrane and its external lamina are the sarcolemma
• Exercise enlarges the skeletal musculature by stimulating formation of new myofibrils and growth in the diameter of individual muscle fibers
• Tissue growth by an increase in the number of cells is termed hyperplasia, which takes place readily in smooth muscle