Kulkarni 2

Structure of Tissues

WARNING! Some of the notes today consisted of labelling the figures. Ask someone who was there.
Exocrine glands secrete to the surface through a duct. Endocrine have no ducts and secrete directly into blood. Today we will learn more about glands to finish up epithelium, then we will study the rest of the tissues.
Exocrine gland classification: single duct=simple gland. Branching duct= compound gland. Secretory portion is tubular, acinar (flasklike) or alveolar. Ascinar and alveolar are not often distinguishable under the microscope.
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Simple branched tubular sometimes confuses people. The secretory portion, not the duct, is divided.
Example of coiled: in skin, the sweat gland is a simple coiled tubular gland. Section of skin does not pass through directly parallel to duct- you usually see only bits of it. Duct gets cut obliquely, secretory portion transversely.
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jejunum- can see villi and simple tubular gland.
Skin- sweat gland is simple coiled tubular gland.
Parotid gland next to ear is in bottom picture- many secretory units and few ducts. Duct is branching, so we never see it directly in the slice.
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Other way to classify glands- serous (secretions stain), mucus(secretion dissolve in water, do not stain), mixed(both together). Myoepithelial cells- muscle type with power to contract, but derived from epithelial tissue. They are known as muscle cells derived from epithelial cells, or myoepithelial cells. When they contract, they squeeze secretions (mostly mucus) out of the gland through the duct into the lumen.
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Connective tissue divides tissue into lobes and lobules. Intercalated ducts start from acina and keep joining other intercalated ducts to form larger ducts until reach striated duct until reach excretory duct. Striated duct- see striations in basal part, as in bottom right picture.
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Merocrine glands form membrane-bound secretory vacuoles, which fuse to cell membrane. Membrane is conserved. Only secretions go out. No cytoplasm or membrane lost.
Apocrine- part of cytoplasm and cell membrane goes out and is lost.
Holocrine- secretions accumulate in cell, then cell goes into lumen and disintegrates there.
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mammary gland
inactive- no glandular element, mainly connective tissue, adipose tissue, and ducts. When glands become active, secretory portion forms at end of ducts and fills connective tissue. Ducts proliferate to fill connective tissue.
Secretions- fat secreted by apocrine method in pinched-off vesicles. Proteins secreted by merocrine method.
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Endocrine glands- ducts disappear during development. Parathyroid glands are on back of thyroid(may be 2-6, not necessarily symmetrically arranged).
Adrenal glands are also known as suprarenal glands.
Pancreas is mixed; it has exocrine and endocrine components.
14 Thyroid
Follicular cells are columnar if active, cuboidal if resting. No ducts. It is an endocrine gland.
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Parafollicular cells are beside follicles. Outside follicle.
16 parathyroid
oxyphil cells not found in lower animals (rat, mouse). Are found in higher mammals (ox, human)
17 Pituitary or hypophysis cerebri- gland formed by union of 2 components, one from brain (pars nervosa) and one from oral cavity (pars distalis from pharyngeal tissue- anterior pituitary)
Adenohypophysis is composed of acidophils, basophils, and chromophobes. Neurohypophysis is reservoir for secretions of neurons. The end of axon is a bulblike structure that stores secretions. Bulblike structures are Herring bodies. Glial cells are supporting cells for neurons. Fiberlike projections are axons.
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Adrenal gland- in center- larger blood vessels in medulla. Outer part is cortex. Cortex has 3 zones. Listed outer to inner on slide.
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Connective tissue
Connects and supports epithelial tissue, muscle, nerves.
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Connective tissue is composed of cells and the extracellular matrix between cells. The matrix is secreted by the cells. ECM will disappear without viable cells. Cells include fibroblasts, mast cells, macrophages, plasma cells.
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Fibroblasts are present everywhere in connective tissues. They produce collagen, reticular, elastic fibers. Fibroblast cell itself is flat, with processes. Fibroblast gets trapped in the fibers it produces.
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Top left: In section- see fibers with cell trapped in it.
Top right: Macrophages have a kidney-shaped nucleus. They engulf everything. Put harmless substance like India ink in, macrophages will engulf it so you can see them.
Lower photo: Mast cells- lots of granules in cytoplasm.
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All 3 types fibers produced by fibroblasts. Collagen fibers form bundles (lower left). Reticular fibers are thin (seen in lymph node, upper right). They are usually stained with silver. Elastic fibers can be fibrous (as in epiglottis or blood vessel) or lamellar (sheetlike) in aorta (Bottom middle and right, respectively).

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Connective tissue
Loose allows blood vessels to pass. Few fibers and lots of space Just inside under epithelium.
Dense- mostly collagen Tightly packed.
Dense regular- tendons and ligaments. Cells in row with bundle of fibers in between.
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Adipose tissue- large cells full of fat globule. Nucleus and cytoplasm to one side. Cytoplasm at periphery.Fat dissolves in alcohol and xylene, so when we stain we see a cell with a thin rim of cytoplasm and large empty space in middle. Signet ring appearance. You can stain fat in unfixed tissues if you want to see it.
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Where more support than fibers is needed, have cartilage. Chondrocytes are cells of cartilage. Hyaline cartilage has ground glass appearance. Matrix contains ground substance and fibers. Refractive index is same, so you cannot see the fibers.
In elastic cartilage you can see the fibers clearly (lower right)
Fibro cartilage- near point of tendon insertion in bone. White fibro cartilage. Between fiber bundles, chondrocytes are present in groups.
Hyaline is present in trachea and bronchus. Elastic cartilage found in epiglottis.
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Bone tissue- Cells are osteocytes. They have processes that communicate with each other in the Haversian system. Ground substance between cells in bone does not allow diffusion. In cartilage- blood vessel are at periphery and tissue (matrix) allows for diffusion. Bone matrix does not allow diffusion. There are bony canaliculi containing cell processes which connect to the capillaries. Osteocytes form circles around capillaries so they can pass nutrition to each other. Lamellae have spaces called lacunae containing osteocytes.
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Bone cells include osteocytes, osteoblasts, osteoclasts. Mature osteocytes are trapped in matrix. Osteoblasts produce osteocytes. Osteoclasts eat unnecessary bone. Multinucleated giant cell.
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Muscle and nerve tissue
Muscle cells look like fibers. Muscle fibers are the cells themselves, unlike connective tissue fibers, in which the fibers are SECRETED by the cells.
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Actin and myosin are present in all muscle fibers. In striated muscle, they are arranged in a pattern to give striations. Non striated the actin and myosin are not regularly arranged.
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Skeletal- many nuclei at periphery
Cardiac- fibers branch and anastomize with other branches to form a network. Nucleus in center. Also have gap junction or intercalated disks. Cardiac muscle is striated muscle wih fibers branching and anastomizing, with one nucleus in center and intercalated disks or gap junction between cells.
Skeletal- long fiber with striations