Histo Mid Sem Flashcards
(187 cards)
1
Q
What is LUCA? What makes it common?
A
Last common universal ancestor.
Lipid bilayer, DNA, ribosomes, proteins (20AA’s)
2
Q
What is LECA?
A
Last eukaryotic common ancestor.
Bacteria, archaea, eukaryotes.
3
Q
What are multicellular metazoans?
A
Animals.
Means specialisation of cells within groups.
4
Q
What colour do eosinophilic elements stain?
A
Pink
Basic compounds attract negatively charged (acidic) dyes.
5
Q
What colour do basophilic elements stain?
A
Blue
Negatively charged groups bind positively charged (basic) dyes.
6
Q
Cell features can be divided into 3 categories, what are they?
A
Universal - derived from LUCA (bacteria, archaea, eukaryotes).
Eukaryotic - derived from LECA (protists, plants, fungi, animals).
Metazoan - derived from common ancestor of all animals (multicellular and specialised).
7
Q
What characteristics are common to every cellular organism (universal)?
A
Cell membrane Cytoplasm DNA, RNA, protein ATP as energy source NA/K pump
8
Q
What is the cell membrane?
A
Phospholipid bilayer with membrane proteins embedded within (integral), sitting on the bilayer (peripheral), or crossing the whole membrane (transmembrane).
Surface CHO chains (glycocalyx) for cell recognition, signalling and mechanical protection that attach to lipids (glycolipids) or proteins (glycoproteins).
9
Q
What can bind to intracellular receptors?
A
Steroid hormones
10
Q
What is the cytoplasm?
A
Water based gel inside the cell.
Shaped by the cell membrane and its permeability - concentrations of CO2, O2, ethanol, water and non-polar lipids.
11
Q
What is DNA transcription?
A
mRNA copy of a gene is produced by RNA polymerase.
12
Q
What is DNA translation?
A
Occurs in ribosomes in cytoplasm. Each RNA codon is translated into an AA. The AA are then polymerised into an unmodified protein.
13
Q
What are the characteristics of eukaryotes?
A
Endomembrane system
Nucleus
Mitochondria
Cytoskeleton
14
Q
What is the endomembrane system?
A
Includes nuclear envelope, ER, golgi apparatus, endosomes (lysosomes, phagosomes).
Role in compartmentalising cellular processes (eg. transcription, translation, lysis etc).
15
Q
An intensely basophilic stained cell would indicate increased….
A
Protein production.
High concentration of ribosomes and mRNA.
16
Q
What are mitochondria?
A
Present only in eukaryotes, their main function is to transform inaccessible energy bound in glucose and FA into accessible energy bound within ATP.
Has its own DNA and ribosomes as it is an enslaved endosymbiotic bacterium.
Has two membranes (inner is bacterial, outer is host - part of endomembrane system).
17
Q
Where would you expect to see a higher concentration of mitochondria within cells?
A
Cardiac and brain cells.
18
Q
What is the function of the cytoskeleton?
A
Maintain shape
Motility
Intracellular transport
19
Q
What are the 3 main components of the cytoskeleton?
A
Microfilaments - actin, movement and stability of internal structures (polarised), cell to cell adhesion.
Intermediate filaments - lie between microfilaments, myosin, vimentin, keratin, provide rigid strength within cell and anchoring to other cells.
Microtubules - large structures, made of tubular proteins, move organelles, flagella/cilia and chromosomes during mitosis, transport of vesicles within cytoplasm.
20
Q
What are some characteristics of metazoans?
A
Specialisation - all cells descended from single ovum but become specialised lineages, have diverse morphology, functions and features.
Intercellular junctions - allows communication between cells. May be chemical (tight), mechanical (adherent, desmosomes, hemidesmosomes) or communication (gap).
21
Q
Where does connective tissue originate from?
A
Mesoderm - mesenchymal cells
22
Q
What is the function of connective tissue?
A
Connect other tissues, protect and support.
23
Q
Connective tissue cells exist in a ……..
This consists of ….. and …….
A
Matrix.
Fibres and ground substance.
24
Q
Describe mesenchymal cells.
A
Large, oval or stellate. Ovoid nucleus. Loose matrix. Common in embryo, less in adult. Capable of differentiating into other connective tissue, blood vessels and haematopoietic tissue.
25
Describe fibroblasts?
Cells that make fibres - form all connective tissue.
Plump, spindle-shaped with recesses.
Basophilic cytoplasm with abundant rER and GA.
Secrete fibres and ground substance.
26
Describe fibrocytes.
Develop from fibroblasts although have smaller cytoplasm as they are less active.
Elongated spindle-shaped.
Maintain fibres and ground substance.
27
What are reticular cells? Describe them.
Specialised fibrocytes.
Stellate with spherical nucleus and basophilic cytoplasm.
In haematopoeitic and lymphatic organs and also in wound repair areas.
Secrete reticulin fibres.
Phagocytic.
28
Describe adipocytes.
Unilocular - white fat, polyhedral or spherical, contain one non-membrane bound lipid droplet, flattened and displaced nucleus and cytoplasm.
Multilocular - brown fat, many lipid droplets with central nucleus and mitochondria.
29
Describe mast cells.
Come from bone marrow but differentiate in connective tissue.
Common is skin, lung and intestine.
Spherical or ovoid shape with central nucleus.
Membrane bound cytoplasmic granules.
30
What has a similar origin, structure and function to mast cells but cannot divide and is shorter lived?
Basophils
31
Describe macrophages.
Blood monocytes that have entered tissue.
Phagocytose foreign particles.
Ovoid to spherical with kidney shaped nucleus.
Vacuoles in cytoplasm.
32
What is a fixed macrophage?
Histiocyte
33
What are macrophages?
Antigen presenting cells
34
What up regulates the production of monocytes? What are the consequences of this?
```
Inflammatory cytokines (eg. IL6).
Causes down regulation of erythrocytes as there is only so much room in the bone marrow.
```
35
Describe lymphocytes.
Spherical.
Large nucleus, small cytoplasm.
T and B cells.
36
What are plasma cells?
Effector B lymphocytes.
| Ovoid with eccentric nucleus.
37
What are the three types of fibre?
Collagen
Reticular
Elastic
38
What is collagen and what function does it have?
Protein consisting of 3 alpha pro collagen fibres.
Strength and flexibility.
Synthesised by fibroblasts mostly.
Multiple types.
39
What are the 4 basic types of collagen?
I - dermis, capsules, tendons, ligaments (fibrous connective tissue).
II - hyaline and elastic cartilage, intervetebral discs.
III - Blood vessels and nerves, stroma of organs (reticulin).
IV - Basal lamina (epithelia), muscle cells, neuroglia.
40
What are collagen fibres secreted by?
Fibroblasts.
| Secreted as glyucosylated pro collagen molecules.
41
What are reticular fibres? Describe them.
Type III collagen.
Coated in proteoglycans and glycoproteins.
Thin in flexible, branching networks.
Support cells.
42
Describe elastic fibres?
Provide elasticity.
Consist of elastin (protein) and supported by fibrillar (glycoprotein).
Synthesised as proelastin by fibroblasts.
Often in close association with collages and cartilage.
Require silver stain.
43
What are fibrous adhesive proteins?
Cohesion of fibres within the matrix and adhesion of matrix fibres to cells.
Fibronectin - binds fibres to cell membranes. Adhesion, differentiation and growth.
Laminin - large glycoprotein, basal lamina.
44
What is ground substance and what is it composed of?
Gel in which cells and fibres are suspended.
| Composed of glycosaminoglycans (GAG's), proteoglycans, plasma constituents, water and ions.
45
Discuss GAG's
Polysaccharide chains with highly polar groups (help attract water).
Hydrophilic.
Proteoglycans are GAG's bound to a protein core that bind to hyaluron.
46
Discuss loose connective tissue.
Also known as areolar connective tissue.
Very common (blood, lymph vessels, nerves, lamina of hollow organs, stroma of solid organs).
Consists of all 3 fibre types and fibrocytes.
Ground substance is plentiful.
Less than 50% fibres.
47
Discuss dense regular connective tissue.
Tendons and ligaments - one direction of tension.
More fibres (over 50%) than cells or ground substance.
Linear bundles increase tensile strength.
Mainly fibrocytes.
48
What are fibrocytes?
Inactive fibroblasts
49
What do fibroblasts make?
Procollagen, GAG's, glycoproteins.
Also make consitituents that cleave pro-collagen.
Pro-elastin.
50
Discuss dense irregular connective tissue.
Dermis of skin, aponeuroses of muscles, sclera of eyes, sheaths of nerves, capsules of organs.
Higher percentage of fibres to cells and ground substance.
Random orientation of fibre bundles for stretching and changing shape.
Fibrocytes most common cell.
51
Discuss reticular connective tissue.
Mesh of reticular cells and fibres.
Bone marrow, lymph nodes and spleen, granulation tissue.
Allows penetration by cells.
52
Discuss mucoid connective tissue.
Hypodermis, umbilical cord.
Consists of mesenchymal cells.
Extensive matrix rich in ground substance.
Basophilic.
53
Discuss adipose tissue.
Insulation and energy storage.
Consists of lobules of adipocytes and loose connective tissue.
White - unilocular.
Brown - multilocular (lots of droplets per cell), larger nucleus, lots of mitochondria and blood vessels.
54
What are the most common cells in cartilage?
Chondroblast - growing cartilage, ovoid with spherical nucleus, abundant rER, prominent GA, forms fibres and matrix for cartilage.
Chondrocyte - mature cartilage, spherical to elongate, cytoplasmic processes extend into matrix, maintains fibres and matrix.
55
What are lacunae?
Little lakes.
| Hole within matrix for osteocyte or chondrocyte.
56
Discuss the cartilage matrix.
60-80% water.
12-25% GAG's - chondroitin sulphate, keratin sulphate (important for perfusion by water and electrolytes).
8-15% fibres - type II collagen mostly, fibrous adhesive proteins.
57
What are the 3 types of cartilage?
Hyaline (collagen fibres type II)
Elastic (elastin fibres)
Fibrocartilage (collagen fibres type I)
58
Where can you find hyaline cartilage?
Foetal skeleton, growth plates of bones, articular cartilage of synovial joints, costal cartilage of ribs, airways (nasal cavity, larynx, trachea and bronchi).
59
Describe the cellular makeup and matrix of hyaline cartilage.
Chondrocytes nest in lacunae (may be multiple per lacunae).
Thin pericellular matrix that lacks collagen II, territorial matrix with fine collagen II, inter territorial matrix with coarse collagen II.
60
Describe elastic cartilage.
Elasticity and rigidity.
Larynx, epiglottis, eustachian tube, ear.
Dense network of elastic fibres.
Looks very similar to hyaline cartilage - requires silver stain (presence of elastin).
61
Discuss fibrocartilage.
Intervertebral discs, menisci of stifle joint, insertions of tendons and ligaments to bone.
Chondrocytes in rows.
Prominent bundles of collagen I fibres.
Low percentage of ground substance.
62
What are the cells of bone?
Osteoprogenitor cells
Osteoblasts - make bone matrix (collagen I, ground substance, minerals).
Osteocytes - maintain bone.
Osteoclasts - eat bone (may be multinucleate).
63
Discuss osteoprogenitor cells.
Develop from mesenchymal stem cells.
May become osteoblastic, chondroblastic, fibroblastic or adipose.
On external and internal surfaces of bone (also other tissues).
Flattened elongated cells, oval nucleus, little cytoplasm.
64
Discuss osteoblasts.
On periosteal and endosteal surfaces.
Secrete bone matrix.
Cuboidal/columnar shape, basophilic cytoplasm rich in rER.
65
Discuss osteocytes.
Inactive osteoblasts, lodge in lacunae.
Maintain bone matrix.
More lysosomes than osteoblasts.
66
Discuss osteoclasts.
From monocyte/macrophage progenitor cells.
Remove bone (fully mineralised only).
Large, multinucleate cells.
Form shallow depressions (howships lacunae) on surface of bone that is being removed.
Plasma membrane becomes folded when attached to bone - 'ruffled border'.
Secretes protons and lysosomal hydrolyses through ruffled border into howship's lacuna (acidic environment to break down bone).
67
Discuss the bone matrix.
Organic - osteoid portion produced by osteoblasts (collagen type I, GAG's, glycoproteins). Non mineralised.
Inorganic - Ca and P as micro crystals of hydroxyapatite. Other minerals deposited on collagen fibrils.
68
What does the formula Ca5(PO4)3(OH) stand for?
Hydroxyapatite
69
What are the 2 main types of bone?
Woven - newer, weaker bone, irregular cells and collagen.
| Lamellar - mature bone, lamellate cells and fine collagen.
70
Discuss Lamellar bone.
Can be cancellous - spongy/trabecular bone, epiphyses and metaphyses (ends).
Or compact - cortical bone (shaft).
Composed of cylindrical units (osteons/Haversian systems).
Haversian canal/osteonal - canal for blood vessels, nerves and endosteum.
Perforating/Volkmann's canals - link osteonal canals to peri - and endosteal surfaces.
Canaliculli - small channels allowing osteocytes to communicate and receive nutrients.
71
What is the periosteum?
Outer surface of bone.
| Outer fibrous layer (connective tissue) and inner osteogenic layer (cells).
72
What is the endosteum?
Covers inner surface of bone.
| One thin layer of osteoblasts and osteoclasts.
73
What are the 2 forms of bone formation?
Endochondral - bone develops in cartilaginous model, long bones.
Intramembranous - bone develops in connective tissue, flat bones of skull, ribs.
74
Describe the process of endochondral ossification.
1) Chondrocytes proliferate in columns.
2) Cartilage matrix mineralises.
3) Chondrocytes die by apoptosis.
4) Blood vessels invade bringing osteoprogenitor cells.
5) Osteoblasts deposit bone on cartilage matrix - forms primary trabeculae of bone.
6) Osteoclasts and osteoblasts remodel primary trabeculae to form secondary trabeculae.
Results in lengthening of long bones due to cartilage cells in physis multiplying and being replaced by bone.
75
Is bone remodelling continuous? How does it occur?
Yes, occurs throughout life.
| Osteoclasts cut through and osteoblasts follow replacing with new bone - results in osteons.
76
Where are erythrocytes produced and how long do they live for?
```
Bone marrow.
2-6months depending on species;
110d dog/cat
120d horse
125d ruminant
35d bird
```
77
Describe an erythrocyte.
Anucleate in mammals.
Eosinophilic
Disc shaped and biconcave - increases surface to volume ratio and allows efficient transport of O2 across membrane.
Few organelles - more in reticulocytes
78
What stimulates the production of new RBC's?
Low oxygen concentration.
| Fibrocytes in kidneys release erythropoietin (EPO).
79
What does the nucleus of a granulocyte look like?
Segmented.
80
What does the nucleus of monocytes and lymphocytes look like?
Non-segmented.
81
How long do neutrophils survive in circulation and tissue?
4-14hrs in circulation
| 1-4d in tissue.
82
What do neutrophils look like?
Very common.
| Segmented nucleus, pale staining cytoplasm.
83
What is the function of a neutrophil?
Phagocytose foreign matter and kill bacteria.
| Common at sites of inflammation.
84
What do eosinophils look like and what is their function?
2 main segments to nucleus.
Distinct pink granules.
1/2-8hrs in circulation
Kill metazoan parasites and modulate hypersensitivity reactions.
85
What do basophils look like? How long do they survive and what is their function?
```
Similar to mast cells, dark staining.
Very rare.
Nucleus has 2 segments, dark cytoplasm.
4-14hrs in circulation.
Anti-coagulant, vasodilatory and chemotactic effects.
```
86
What is a monocyte? How long will it survive?
Macrophage en route to tissues.
1-3d in circulation
Months-years in tissue
87
What does a monocyte look like?
Largest leukocyte.
Eccentric nucleus that is indented/slightly lobed.
Pale basophilic cytoplasm with some vacuoles.
May become multinuclear.
88
What is the function of a monocyte?
Phagocytoses foreign matter and elaborates cytokines.
89
What do lymphocytes look like?
Spherical with large nucleus, very little cytoplasm.
Strong basophilic nucleus, pale basophilic cytoplasm.
When reactive the cytoplasm becomes deeply basophilic with perinuclear clear zone.
90
What is the function of lymphocytes? How long do they survive?
Effect and regulate immune response.
| Long lived - capable of recirculating.
91
Where are lymphoctyes produced? How are they prepared for circulation.
Bone marrow.
Cloned in thymus or bursa of fabricus (birds).
Localised in lymph nodes, spleen and lymph tissue.
92
What are the 3 types of lymphocytes?
T
B
NKC
93
What are thymocytes?
Immature T cells
94
T cells effect what kind of immunity?
Cell-mediated - cytotoxic, helper, suppressor cells
95
B cells effect what kind of immunity?
Humoral - create plasma cells and produce antibodies.
96
What do NKC's do?
Destroy abnormal tissue cells.
97
How long are platelets in circulation?
17d
98
What are platelets?
Anucleate cytoplasmic fragments derived from megakaryocytes in bone marrow.
99
What inactivates platelets?
Thrombopoietin (TPO) from liver. Increased levels in bone marrow increased platelet production.
100
What are thrombocytes?
Platelets in reptiles, birds, amphibians and fish.
Derived from stem cells in bone marrow.
Have a nucleus, slightly eosinophilic cytoplasm and 'foamy' cytoplasm.
101
How do platelets and thrombocytes facilitate haemostasis?
Adhere to exposed collagen.
Aggregate as 'haemostatic plug' - get caught in mesh of fibrinogen and plug holes (decreasing blood loss).
Release clotting factors.
102
Where does haematopoiesis occur?
In liver and bone marrow of foetus.
| In red bone marrow of adults - mainly vertebrae and flat bones.
103
What comprises red bone marrow?
Haematopoietic compartment - anastomosing cords of haematopoietic cells (erythropoietic cells, megakaryocytes and granulopoietic cells).
Vascular compartment - sinusoids; adventitia of reticular cells.
104
How do new blood cells enter the sinusoids?
Perforate endothelium.
105
What are the primary lymphatic organs?
Bone marrow
Thymus
Bursa of fabricius (birds)
Gut associated lymphatic tissue of ileum (GALT)
106
What are the secondary lymphatic organs?
Lymph nodes
Spleen
Mucosa-associated lymphatic tissue (MALT) - tonsils, bronchus-associated lymphatic tissue (BALT), GALT.
Haemal nodes
107
What is the role of the thymus?
Maturation of immunologically naive lymphoid cells from bone marrow into immunologically competent T-lymphocytes.
108
What do tangible body macrophages do?
Consume malfunctioning thymocytes within thymus.
109
Where are thymocytes within the thymus?
Cortices.
110
What are thymocytes?
T-cells and their precursors.
111
What other cells are present in the thymus cortex?
Few B cells.
Epithelial reticular cells - seperate parenchyma from capsule and septa, cortex from medulla, supports thymocytes and secretes thymic hormones.
Tangible body macrophages
112
Describe the thymic medulla?
Epithelial reticular cells (collagen type 3) - supportive meshwork for thymocytes, form thymic corpuscles.
Interdigitating dendritic cells - present antigen to lymphocytes.
Small thymocytes.
113
Describe the bursa of fabricius and its function.
Site of B-lymphocyte maturation in birds.
Sac near cloaca that involutes by 6 months of age.
Has lymphatic nodules (cortex densely populated by lymphoid cells).
Nodules surrounded by bursal epithelium and septae of connective tissue.
114
What is the function of lymph nodes?
Filters antigens from lymph and produces lymphocytes.
| Arteries, veins, nerves and efferent lymphatics enter at hilus.
115
Describe the anatomy of a lymph node.
Capsule of dense irregular connective tissue.
Trabeculae from capsule penetrate cortex and medulla - structural support, carries blood vessels and nerves.
Stroma of reticular cells and fibres support parenchyma.
116
Describe the cortex and medulla of a lymph node?
Cortex - outer has primary and secondary lymphatic nodules (B cells) separated by diffuse lymphatic tissue (T cells). Deep cortex (paracortex) has diffuse lymphatic tissue (T cells).
Medulla - Branching and anastomosing cords between medullary sinuses, these contain lymphocytes, plasma cells and macrophages mixed with reticular fibres.
117
What is the difference between primary and secondary lymphatic nodules?
Primary - no germinal centre; contains naive B cells.
Secondary - germinal centre of follicular dendritic cells, lymphoblasts and tangible body macrophages. Mantle of mature B cells.
118
Describe the flow of lymph through nodes.
From afferent lymphatics (penetrate capsule) to sub capsular, trabecular, medullary sinuses and then efferent lymphatics that exit via hilus.
(Afferent and efferent have valves)
119
What cells line the sinuses of lymph nodes?
Reticular cells.
120
How are pig lymph nodes different to others?
Pigs have no single hilus, no medullary cords or sinuses.
| Opposite flow.
121
What is the function of the spleen?
Produces T and B lymphocytes.
Filters, removes and breaks down old erythrocytes.
Stores erythrocytes, platelets and iron.
Important for removal of blood parasites.
122
Describe the anatomy of the spleen.
Capsule - dense irregular connective tissue and smooth muscle, visceral peritoneum.
Trabeculae - fingers of connective tissue coming in from capsule, collagen and elastic fibres, smooth muscle, vessels and nerves.
Parenchyma of white and red pulp.
123
What is splenic white pulp?
| What colour does it stain?
Stains dark blue.
Periarteriolar lymphatic sheaths - adventitia of arteries as they leave trabeculae, sheaths of lymphocytes and central T-cell area.
Lymphatic nodules - primary or secondary
Marginal zone - between white and red pulp, many macrophages (surround capillaries - RBC forced between slits into sinuses) and B-cells.
124
What is splenic red pulp?
Surrounds white pulp.
Cords - sheathed capillaries, erythrocytes, macrophages, lymphocytes and plasma cells
Sinuses - wide vascular channels with discontinuous endothelium and basal lamina, supported by reticular fibres.
125
What is an ellipsoid?
Sheathed capillary.
Sheath is macrophages in a meshwork of reticular cells and fibres.
Blood diffuses through macrophages into splenic sinuses.
Capillary is blind ending with narrow lumen.
126
What are the differences in the spleen between species?
```
Periarteriolar lymphatic sheaths - abundant in horses dogs and pigs. Scant in ruminants and cats.
Sheathed capillaries (ellipsoids) - large in pigs, cats, smaller in horses and dogs, narrow in ruminants.
```
127
What is diffuse lymphatic tissue?
Un-encapsulated lymphocytes and lymphatic nodules.
Present in alimentary, respiratory and urogenital systems.
Superficial dermis of skin.
128
Discuss gut associated lymphatic tissue.
Aggregated lymphatic nodules - Peyer's patches.
Primary lymphatic organ in young mammals, secondary in older animals.
Primary and secondary lymphatic nodules are overlaid by modified intestinal epithelium.
129
Describe the anatomy of tonsils.
Epithelium on luminal surface.
Capsule of fibrous connective tissue at deep border.
Framework of reticular cells.
Many lymphatic nodules.
Parafollicular lymphoid tissue - mixed with plasma cells, granulocytes and macrophages.
130
What are heamal nodes?
Ruminants - adjacent to caudal vena cava.
Red to dark brown.
Perfused by muscular arteries.
Capsule of dense irregular fibrous tissue.
Blood filled sub capsular and trabecular sinuses.
Cortex of lymphoid tissue.
medulla of wide venous sinuses.
131
What are the 4 fundamental tissue types?
Epithelium
Connective tissue
Muscle
Nervous tissue
132
Is epithelium avascular?
Yes
133
What is a myofibril?
Bunch of fibres within muscle cells. Aid movement.
134
What are muscle cells called?
Myocytes.
| Myofibres or muscle fibres.
135
What are the mechanisms of muscle movement?
Sarcomere - skeletal and cardiac
| Contractile chains - smooth
136
How is movement coordinated between myocytes?
Neuromuscular junctions - skeletal
Gap junctions - cardiac, smooth
Spontaneous - cardiac, smooth
Physiochemical agents - smooth
137
What are sarcomeres?
Striations in skeletal and cardiac tissue.
One sarcomere occupies the space between the centre of one dark band and the next.
Fundamental unit of contraction.
138
How do sarcomeres contract?
Depend on presence of elevated intracellular calcium and energy (ATP) to contract.
139
What are the stages of muscle contraction in skeletal and cardiac muscle?
1) Action potential causes release of Ca from sarcoplasmic reticulum.
2) Ca binds to troponin on actin filament.
3) Moves tropomyosin away from active site, allowing myosin head to bind to actin.
4) Myosin head pulls actin and releases Pi and ADP.
5) ATP binds to myosin causing it to release actin.
6) Ca released from troponin.
7) Tropomyosin moves back over active site of actin.
140
What are the stages of contraction in smooth muscle?
1) Ca released from caveolae, binds calmodulin.
2) Activates myosin light chain kinase.
3) Phosphorylation of myosin II
4) Actin binding site exposed
5) Myosin head pulls actin.
Requires elevated concentration of intracellular Ca and ATP.
141
What is a fascicle?
Bundle of muscles that are innervated by one nerve.
142
What role does the neuromuscular junction play in Ca regulation?
Action potential reaches motor end plate, releases ACh and causes sarcolemma and T tubules to depolarise.
Causes depolarisation of sarcoplasmic reticulum and Ca channels open flooding the sarcoplasm with Ca.
143
What are gap junctions composed of?
Connexons
144
What is the sensory innervation of skeletal muscle?
Must be directly innervated to coordinate movement (neuromuscular junctions).
145
Can skeletal myocytes be multinucleate?
Yes - due to fusion of cells into fibres.
146
Describe skeletal myocytes.
```
Long cells with peripheral nuclei.
8-100um diameter, 40cm long.
Multinucleate, dark nucleus.
Eosinophilic cytoplasm
Parallel cells.
```
147
Describe myofibrils.
Fibres within muscle cells.
Full length of cells, consist of sarcomeres.
Surrounded by mitochondria, glycogen, T tubules, sarcoplasmic reticulum (Ca).
Attachment between adjacent myofibrils is via destine and vimentin at Z lines.
148
What role does the basal lamina play in muscle cells?
Surrounds them, except at intercellular junctions.
Mainly collagen, glycoproteins and proteoglycans.
Functions to adhere cells to connective tissue, filtration barrier, scaffold for regeneration, signalling for adjacent cells activity.
149
What is the endomysium?
Surrounds individual muscle cells - contains satellite cells, loose connective tissue, blood vessels and nerves.
150
What is the perimysium?
Surrounds bundle of cells.
151
What is the epimysium?
Surrounds the entire muscle and becomes tendons.
| Dense, irregular fibrous tissue.
152
How do cardiac cells coordinate movement?
Gap junctions.
153
Describe cardiac cells.
```
Involuntary - spontaneous contraction
No direct innervation
Gap junctions
Striations, branched and anastomose.
Eosinophilic cytoplasm.
Central nucleus
Rich capillary supply.
No satellite cells.
Atria myocytes are smaller.
```
154
What are purkinje fibres?
Specialised muscle cells.
| NOT NERVES
155
How do cardiac myocytes attach to each other?
Intercalated discs - no bone to anchor to.
| Complex interdigitations of adjacent cell membranes.
156
Describe smooth muscle cells.
Involuntary contraction
Spindle shaped with central nucleus.
Eosinophilic cytoplasm with no striations - no sarcomeres.
Myofilaments are orientated in different directions.
Caveolae - little holes on cell membrane that store Ca - no T tubules.
Gap junctions.
Dense bodies - cell membrane and cytoplasm to anchor actin.
157
Describe the healing and repair of cardiac muscle.
No replacement of cells.
Formation of collagen scar in place of dead myocyte.
Supports mechanical function but alters signal conduction.
158
Describe the healing and repair of skeletal muscle.
Minor regeneration done by satellite cells.
Collagen scar forms.
Decreased functionality - decreased contraction ability.
159
Describe the healing and repair of smooth muscle.
Heals really well.
Pericytes can carry out minor regeneration via division and proliferation.
Collagen scar following inflammation and invasion by fibroblasts.
160
What are the main functions of epithelium?
```
Selective barrier
Physical protection
Containment
Absorption/Excretion/Secretion
Receptors for special senses
```
161
Where can you find epithelium?
Exterior of body, lining internal cavities and tubular structures, exocrine glands and their ducts and endocrine glands and their cells.
162
How do epithelial cells maintain their internal structure?
Cytoskeleton - cytokeratin (intermediate filament).
163
What are the 3 morphological and functional domains of epithelial cells?
Apical - Apex
Lateral
Basal - attaches to basement membrane (via hemidesmosomes)
164
What kinds of apical modifications are present on epithelial cells?
```
Microvilli - brush border.
Cilia - move fluid.
Flagella
Stereocilia
Glycocalyx
```
165
What is the basement membrane?
Basal lamina and reticular lamina together.
166
Describe the basal lamina?
Synthesised by epithelial cells.
Type IV collagen, laminin and proteoglycans.
Attaches epithelial cells to connective tissues.
Semipermeable barrier and scaffold.
No blood vessels or nerves.
167
What is reticular lamina?
Part of basement membrane.
Anchors basal lamina to connective tissue fibres.
Made by epithelium and fibroblasts.
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What are the 2 forms of epithelium?
Surface - sheets of cells lining external and internal surfaces.
Glandular - secretory cells of glands.
169
What are the classes of surface epithelium?
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Simple - one layer
Stratified - >2 layers
Pseudostratified
Squamous - flat
Cuboidal
Columnar (increased absorption and secretions due to increased cytoplasm and protein production).
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170
Describe simple squamous epithelium.
Single layer, irregular flat shaped cells with serrated borders.
Spherical/oval nucleus near centre.
Weak barrier that allows exchange - vascular system, body cavities, lungs.
171
Describe simple cuboidal epithelium.
Single layer, square cells.
| Allows for some absorption and secretion in exocrine glands, ovary, kidney, thyroid.
172
Describe simple columnar epithelium.
Tall narrow cells, oval nuclei near base.
| Absorption and secretions in GIT and gall bladder.
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Describe pseudostratified columnar epithelium.
Irregular shape and size of cells.
Not all cells reach surface (basal cells) but all touch basement membrane.
Common in areas with high cell turnover - trachea and bronchi, efferent ducts, ductus deferens.
174
What is transitional epithelium?
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Pseudostratified epithelium that stretches, all cells touch basement membrane.
Flexible barrier.
Urinary tract (bladder), conjunctiva, nasopharynx, larynx.
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175
What is stratified squamous epithelium?
Several layers, surface is squamous.
| Barrier and protection for epidermis, cornea, oral cavity, oesophagus, rumen, vagina.
176
What is stratified cuboidal epithelium?
Two layers with top being cuboidal cells.
| Barrier and conduit for sweat gland ducts, ducts of exocrine glands and anorectal junction.
177
What is stratified columnar epithelium?
Several layers of cells, upper most being columnar cells.
| Barrier and conduit for ducts of exocrine glands, urethra, anorectal junction.
178
Are endothelium and mesothelium epithelium?
No - they are derived from mesoderm.
| Behave like epithelium and connective tissue.
179
How are glands classified?
Nature of secretory product
Mode of release of secretory product
Architecture of ducts and secretory cells.
180
What types of secretory products do glands have?
Serous - watery
Mucous - viscous and slimy
Seromucous - mix
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What are the modes of secretion of exocrine glands?
Merocrine - exocytosis via membrane bound vesicles.
Apocrine - exocytosis of plasmalemma-bound cytoplasm.
Holocrine - apoptosis and lysis of secretory cell.
182
Give an example of a unicellular gland?
Goblet cells
183
Describe simple exocrine glands.
Secretory cells empty into unbranched duct.
Tubular.
Acinar/alveolar.
184
Describe compound exocrine glands?
Secretory cells empty into branched duct.
Tubular.
Acinar/alveolar.
THE DUCT IS NOT SECRETORY.
185
What is acinus?
Cells around narrow lumen.
186
What is alveolus?
Cells around wide lumen.
187
What are myoepithelial cells?
Around acini/alveoli and ducts in some glands.
Within basal lamina and contain actin and myosin.
Facilitate secretion from acinus via the duct.
