Ch 4 The Tissue Level of Organization notes PDF

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Ch 4 The Tissue Level of Organization notes...

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Ch 4 : Tissues

 Histology: Histology is the study of the microscopic anatomy of cells and tissues – it is a branch of pathology. Of the 10 trillion cells in our body, no single cell type can said to be “typical”. A trained histologist can recognize over 200 distinct human cell types under the microscope and is able to distinguish a cell from pancreatic tissue as opposed to a cell from the skin. Each cell type has features particular to its function. Intracellular Junctions  Tissues are formed by grouping cells together using a variety of Intercellular Junctions .

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Intracellular Junctions connect adjacent cells mechanically at the cell membranes or through cytoskeletal elements within and between cells.

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 Tight Junctions are found where a leakproof seal is needed between cells. They keep materials from leaking out of organs like the stomach and bladder.

 Adherens Junctions make an adhesion belt (like the belt on your pants) that keeps tissues from separating as they stretch and contract.  Cadherin is a glycoprotein that forms the belt-like “plaque”.

 Desmosomes act as “spot welds”. They also use cadherin glycoprotein (plus intermediate filaments) to hook into the cytoplasm.

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 Hemidesmosomes are half-welds that join cells to the basement membrane.

 Gap Junctions are pores (connexons) that allow small substances like ions to pass between cells. If one of the cells gets sick or dies, these seal like a hatch to prevent damage to other cells.

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- tissue: a group of similar cells plus their intercellular substance (matrix) that function together to perform a specialized activity - matrix is a non-living substance produced by the cells which comes to surround the cells 1. It contains: a. protein fibers: collagen, elastic, or reticular (thin-branching collagen fibers) b. ground substance: fluid whose consistency varies from watery to gel-like - 4 basic tissues compose entire body: Epithelium, Connective Tissue, Muscle, Nervous A. EPITHELIUM - composed of tightly packed cells with little matrix creating a protective barrier - arranged in sheets of cells (single or multi-layered) - occurs in the body in two general forms: 1. covering and lining epithelium - covers organs - lines body cavities and hollow organs 2. glandular epithelium: - cells are cuboidal or columnar in shape - composes glands: a. exocrine glands (more numerous): secrete chemicals

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into ducts which typically lead onto body surfaces or into body cavities. Egs. salivary and sebaceous glands b. endocrine glands are ductless; they secrete chemicals called hormones into the blood which then travel to specific cells. Egs. pancreas, thyroid - avascular (no blood supply); this is protective - nourished by an always present underlying layer of connective tissue which IS vascular - underside anchored to c.t. by glycoproteins = basement membrane - reproduces easily - Carcinomas (a type of cancer) arises from this tissue egs. Basal cell carcinoma; Squamous cell carcinoma (cancers of epidermis which is composed of Stratified squamous epithelium) - its many specific types are classified according to: 1. cell layers a. simple: 1 layer of cells b. stratified: 2 or more layers of cells c. pseudostratified: has a false appearance of 2 layers but actually has only 1 layer 2. cell shape a. squamous: flat b. cuboidal: square c. columnar: rectangular

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Examples of specific types and their location (L) & function (F):

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gh blood vessels & heart and decreases friction of lymph flowing through lymphatic vessels - (L) top part of serous membranes (called mesothelium); (F) secretes serous fluid into pleural, pericardial, & peritoneal cavities 2. Simple cuboidal epithelium - (L) nephrons (kidney tubules); (F) absorption & secretion - (L) thyroid gland; (F) secretion of thyroid hormones into thyroid follicles 3. Simple columnar epithelium - (L) lines stomach & intestines; (F) absorption & secretion 4. Pseudostratified ciliated columnar epithelium - (L) lines airways of most of respiratory tract; (F) moves dust-laden mucus 5. Stratified squamous epithelium a. keratinized (containing water-proofing protein keratin) (L) epidermis of skin; (F) protection (body’s 1st line of defense) b. nonkeratinized (contains no keratin) (L) lines mouth, esophagus, vagina, & anal canal, and covers tongue; (F) protection 6. Transitional epithelium (L) lines urinary bladder and portions of ureter & urethra; (F) permits distention Summary:

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B. CONNECTIVE TISSUE (c.t.) - most abundant & widely distributed of the basic tissues - vascular (however, dense c.t. & cartilage have poor blood supplies) - reproduces (exception: adipose reproduces only at specific times)

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- Sarcomas (a type of cancer) arise from this tissue eg. osteosarcoma: bone cancer eg. Kaposi’s sarcoma: cancer of blood vessels of skin’s dermis - composed of widely spaced cells with a lot of matrix (exception: adipose) (cell types: fibroblasts, adipocytes, reticular cells, chondrocytes, osteocytes, erythrocytes, leukocytes, thrombocytes…) - it is the matrix which is the basis for classifying specific types - specific types: 1. Areolar (Loose) connective tissue (L) subcutaneous layer; between muscles; between organs; (F) binds structures together (“glue” of body) (L) bottom part of serous and mucous membranes; (F) structural

2. Adipose (Fat)

- during puberty is the only time adipocytes normally reproduce; otherwise, adipocytes enlarge or shrink when weight is gained or lost - during adulthood, cells only reproduce if existing cells become too large - (L) below skin; (F) insulation & cushion - (L) around eyeballs, heart, kidneys & joints; (F) cushion - (L) inside greater omentum, long bones (yellow marrow), and between muscles; (F) energy storage at 9 Calories/gram and cushion

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3. Reticular connective tissue (L) liver, spleen, lymph nodes;

(F) organ framework; filters blood flowing through liver & spleen of worn-out blood cells;

filters lymph flowing through lymph nodes of bacteria (L) binds together smooth muscle cells; (F) glue *Tissues 1, 2 & 3 above are collectively referred to as Loose connective tissue b/c the fibers are loosely intertwined and many cells are present. 4. Dense connective tissue (contains more numerous, thicker & denser fibers but considerably fewer cells than Loose connective tissue)

- 2 types: a. Dense regular connective tissue - (L) tendons; (F) cords which connect muscle to bone - (L) ligaments; (F) cords which connect bone to bone - (L) aponeuroses; (F) sheetlike tendons which connect muscle to bone or muscle or muscle b. Dense irregular connective tissue

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- (L) reticular region of skin’s dermis, periosteum, fasciae; (F) structural - (L) organ capsules (around testes, lymph nodes & kidneys); (F) protection - (L) joint capsules; (F) binds bones together at joints - heals poorly due to minimal blood supply - Systemic Lupus Erythematosus = deterioration of this tissue 5. Elastic connective tissue (L) artery walls, true vocal cords, lungs, trachea, and bronchi (F) allows stretching of various structures and organs 6. Cartilage - composed of collagen or elastic fibers embedded in a gel-like ground substance (containing in part water, glucosamine & chondroitin ). The movement of the ground substance enables cartilage to rebound after being compressed and also helps nourish the chondrocytes - intermediate between Dense connective tissue and Bone as to toughness, yet has flexibility and compression - surrounded by a membrane called the perichondrium - lacks blood vessels (except for blood vessels in the perichondrium) - receives nutrients by diffusion from blood vessels w/in the perichondrium - heals poorly - lacks nerve fibers

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- 3 types:

a. Fibrocartilage - contains large, visible collagen fibers and a small amount of ground substance. - strongest and most rigid of all the cartilage types - compressible and can withstand heavy pressure - (L) intervertebral discs; (F) shock absorber, adds height, increases spine flexibility - (L) menisci; (F) deepens socket at certain synovial joints - (L) pubic symphysis; (F) allows slight movement of hip bones b. Elastic cartilage - contains visible elastic fibers and a lot of ground substance

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- second-strongest and most flexible of all the cartilage types - (L) pinna of ear, epiglottis of larynx; auditory (Eustachian) tube; (F) flexibility c. Hyaline cartilage - contains very fine, invisible collagen fibers, a lot of ground substance, and many chondrocytes - the most abundant cartilage in the body - provides firm support with some pliability - weakest of all the cartilage types - (L) most of embryonic & fetal skeleton, costal cartilages, nose, parts of larynx, trachea, bronchi; (F) structural - (L) epiphyseal plates of growing bones; (F) allows growth of long bones - (L) articular cartilage at ends of bones (gristle); (F) at joints, reduces friction and absorbs compression 7. Bone  Bone is a connective tissue with a calcified intracellular matrix. In the right circumstances, the chondrocytes of cartilage are capable of turning into the osteocytes that make up bone tissue. - (L) skeleton; (F) support, movement (via skeletal muscles pulling bones), protection, calcium & phosphorus storage, and blood cell production (via its red bone marrow) - (L) middle ear; (F) ossicles amplify sound waves 22X

8. Blood (L) within blood vessels; (F) red blood cells (rbcs) (erythrocytes): carry O2, CO2 & H+ white blood cells (wbcs) (leukocytes): destroy germs Leukemia: cancer of the red bone marrow which produces excessive, immature wbcs platelets (thrombocytes): initiate blood clotting plasma (the matrix of blood): transportation medium

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C. MUSCLE - cells contract (shorten) when stimulated by a neuron - vascular - does not reproduce - muscle mass gets larger by increase in cell size (hypertrophy); muscle mass shrinks by decrease in cell size (atrophy) - Sarcomas arise from this tissue eg. Rhabdomyosarcoma: cancer of skeletal muscle eg. Leiomyosarcoma: cancer of smooth muscle - specific types: 1. Skeletal muscle - (L) connected to bone; (F) voluntary movement of skeleton - (L) between skull and skin; (F) facial expression - (L) between eyes & orbits; (F) eyeball movement - (L) below thoracic cavity (diaphragm); (F) respiration and divides ventral cavity into the thoracic and abdominopelvic cavities 2. Cardiac muscle (L) heart’s myocardium; (F) involuntarily pumps blood 3. Smooth muscle (L) in walls of hollow internal structures: blood vessels, airways to lungs, stomach, intestines, gallbladder, urinary bladder & uterus (F) involuntary movement which moves substance within hollow structure

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(a) Skeletal muscle cells have prominent striation and nuclei on their periphery.

(b) Smooth muscle cells have a single nucleus and no visible striations.

(c) Cardiac muscle cells appear striated and have a single nucleus.

D. NERVOUS TISSUE - vascular - composed of 2 cell types: 1. neurons - while most do not reproduce, research in 1998 on autopsied brains showed evidence of neuron reproduction in Hippocampus (memory center) of brain (L) parts are in brain, spinal cord, & nerves; (F) controls body by generating nerve impulses 2. neuroglia (glia) - reproduce; source of brain tumors called gliomas. - 5 to 50X more numerous than neurons - do not generate or conduct nerve impulses (L) surround neurons in brain, spinal cord, & nerves;

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(F) support neurons...