Microanatomy Flashcards
What are the three layers of connective tissue that hold muscle fibres in position in skeletal muscle?
- Epimysium - outermost layer surrounding the entire muscle.
- Perimysium - surrounds bundles of muscle fibres to create a fascicle.
- Endomysium - surrounds each individual muscle fibre within the fasciculus.
What are tendons made of?
Collagen fibres.
Why are skeletal muscle fibres multinucleated?
Because lots of muscle cells fuse together during devlopment forming a myotube.
What do satellite cells become when they are stimulated to leave their normally quiescent state? When does this happen?
They become myoblasts which then proliferate and differentiate to provide new myonuclei.
This happens during:
- Growth after birth.
- Muscle hypertrophy.
- Muscle maintenance.
- Muscle repair and regeneration.
What causes skeletal muscle to have a striated appearance?
The organisation of thick and thin filaments and divisions into sarcomeres.
What are thick and thin filaments composed of?
- Thick = myosin.
- Thin = actin.
What makes the: A band, I band, H band and Z lines.
- A band = the dark stripes of the sarcomere (myosin filaments).
- I band = light region of the sarcomere (actin filaments).
- H band = the portion of the myosin filament where there is no overlap with actin.
- Z lines = the end of the sarcomere is depicted by these lines.
What are the functions of the T-tubules and sarcoplasmic reticulum?
T-tubules conduct impulses from the surface of the cell down to the sarcoplasmic reticulum which in turn provides calcium for contraction.
How are cardiac myocytes connected?
They are connected via intercalated disks (which are modified Z-lines) to form a functional syncytium.
Are the fibres straight or branching in cardiocytes?
Branching
How are smooth visceral muscles fibres often arranged?
In layers with alternating longitudinal and transversely orientated layers of cells.
Why is there a small amount of connective tissue between smooth muscle cells?
Allow for passage of nerve tracts and blood vessels.
How are smooth muscle myofilaments arranged?
The myofilaments are loosely organised and attached to focal densities in cytoplasm and focal adhesion densities (attachment plaques) at the cell membrane.
What is appositional and interstitial growth?
- Appositional = where the fibroblasts in perichondrium give rise to chondrocytes.
- Interstitial = where chondrocytes in matrix proliferate.
What are the two main components of cartilage and what do they provide?
- Collagen II (60%) - gives tensile strength.
- GAGs (chondroitin sulphate, 40%). These couple to proteins to form enormous proteoglycans. They are hydrated and give resistance to compression. Electro-osmotic.
What is the cartilage matrix made up of?
Chondrin
What are the inorganic and organic compositions of bone?
- Inorganic = mainly hydroxyapatite found in needle-like crystals or thin plates that are 8nm thick and variable in length.
- Organic = 90% type I collagen. Remaining 10% is other proteins.
What is the only way that bone can grow?
Appositional growth.
What is the outer layer of bone called?
Cortical (compact) bone.
What is the interior of bone called and what are the internal surfaces lined with?
Trabecular (cancellous, spongy) bone.
Lined with endosteum.
What are the articular and non-articular surfaces of bone lined with?
- Articular surfaces are covered with articular cartilage (hyaline).
- Non-articular surfaces are covered with periosteum.
What is the epiphyses and diaphysis and what is found inbetween them?
- Epiphyses = expanding end of bone.
- Diaphysis = shaft of bone connected to the epiphyses.
- Between is the growth plate and the transition zone called the metaphysis.
What are Haversian systems comprised of and what connects them transversely?
- 4-20 concentric lamellae surrounded by a cement line (1µm) of mineralized matrix.
- Connected by Volkmann’s canals.
What are lamellae?
Collagen laid down in sheets, 5µm thick. They alternate orientation between sheets to give greater strength.
What are the two major patterns that lamellae are arranged in?
- Circumferential = layers surrounding the bony surface.
2. Haversian systems (osteons).
What are osteoprogenitor cells and where are they found?
- Mesenchymal, fibroblast-like stem cells that generate osteoblasts.
- In cancellous (spongy) bone, found
near blood vessels. - In compact bone, found at
periosteum and endosteum.
Where are osteoblasts found and what are they responsible for?
- Found on the surface of bone.
- Responsible for deposition of osteoid (the organic component of bone matrix) and inducing mineralisation.
What are canaliculi and why are they important?
They are canals that radiate from the lacunae and contain osteocyte cell processes.
They permit diffusion of substances through the bone.
What are the possible functions of osteocytes?
- Role in Ca homeostasis.
- Responsive to mechanical forces.
- Mediate mechanically adaptive bone remodeling by acting as strain receptors.
What are bone-lining cells?
Undifferentiated, flattened cells that are found on the surface of bone that is not being remodelled. They may represent inactive osteoblasts.
What are osteoclasts and where are they found?
They are variably sized cells that are involved in the reabsorption of bone which contributes to bone remodelling and Ca homeostasis.
Found in resorption cavities (Howship’s lacunae) on the bone surface.
What are osteoclasts directly inhibited by?
Calcitonin
How are Haversian systems formed?
By osteoclasts tunneling through pre-existing bone and the tunnels being invaded by blood vessels and osteoprogenitor cells.
The osteoblasts then lay down successive bone lamellae on the walls of the tunnel.
What are the five phases of digestion?
1) Ingestion
2) Fragmentation
3) Digestion
4) Absorption
5) Elimination
What are the three layers of the gut mucosa?
1) Specialised surface epithelium are found resting on the basal lamina.
2) Lamina propria consists of loose connective tissue with blood and lymph vessels as well as nerve fibres and smooth muscle.
3) Muscularis mucosae is a thin double layer of smooth muscle.
What does the submucosa of the gut consist of?
Loose connective tissue with:
- Blood vessels
- Nerves which form plexuses
- Leukocytes
- Lipids
What is the adventitia/serosa of the gut?
A thin layer of connective tissue continuous with surrounding organs. It is bound by a simple squamous epithelium termed mesothelium.
What are the two layers of the muscularis externa?
1) Inner circular layer
2) Outer longitudinal layer
What epithelium is found in the oesophagus and what is its function?
Stratified squamous epithelium. There for physical protection as well as keeping the area moist by glandular secretions.
How can you identify the oesophagus on a histological image?
- Stratified squamous non-keratinising epithelium in the mucosa.
- Groups of mucous glands in the submucosa.
What epithelia make up the mucosa in the stomach?
Simple columnar epithelial layer of mucous secreting cells invaginating to form gastric pits that produce acid and enzymes.
What is the function of surface mucous cells in the stomach?
They secrete mucous and bicarbonate to protect cells from acidic and enzymatic properties of gastric juices and ingested food.
What is the function of mucous neck cells and where are they found?
They line the upper parts of the gastric pits and secrete mucous.
How would you recognise chief cells and parietal (oxyntic) cells on a histological slide?
- Chief cells have a condensed, basically located nucleus and a basophilic cytoplasm with granules.
- Parietal (oxyntic) cells are large, rounded cells with eosinophilic cytoplasm and a centrally located nucleus (fried egg appearance).
What is the difference in the stomach mucosa between the cardia, body and pylorus?
- Cardia has sparse glands and mainly mucous secreting cells.
- Body has densely packed glands which produce gastric juices.
- Pylorus has deep pits which are branching and coiled. Nearly all of the cells here are mucous-secreting cells.
What epithelium is found within the small intestine?
Simple columnar with a brush border of microvilli to increase the surface areas for absorption.
What are villi composed of?
Their surface layer is made up of entrocytes and goblet cells sitting on a basal lamina with a core of lamina propria consisting of loose connective tissue with blood and lymph vessels, nerve fibres and smooth muscle.
What are lacteals?
Lymphatic vessels found in villi of the small intestine that take away fats in chylomicrons.
What is the structure of a microvillus?
Its shape is maintained by actin filaments which are anchored to the cell membrane. The base of the actin filaments form part of the terminal web which is linked to the intermediate filaments of the cell.
What is the function of paneth cells and where are they found?
They release digestive enzymes, immunoglobulins and lysozymes which help destroy parasites and bacteria. They are found in the lower 3rd of the crypts in the small intestine mucosa.
What is the role of the hormones endocrine cells secrete in small intestine?
- Regulate water and electrolyte metabolism and enzyme secretion.
- Regulate gastrointestinal motility and mucosal growth.
- Stimulates the release of other hormones.
What are submucosal Brunner glands?
They are glands found in the small intestine who’s main role is to aid in neutralising the acid chyme extruded from the pylorus.
How does the jujenum differ from the duodenum?
The jujenum has the tallest villi, no Brunner’s glands and few lymphoid follicles.