FAE Flashcards
(249 cards)
1
Q
What are the derivatives of ectoderm?
A
Nervous system, skin, sweat glands, hair and nails.
2
Q
What are the derivatives of the mesoderm?
A
Blood, endothelium, heart, kidney, reproductive system, bones, skeletal muscle and connective tissue.
3
Q
What are the derivatives of the endoderm?
A
Digestive tract, respiratory tract, endocrine glands and organs, auditory system and urinary system.
4
Q
What are the three parts of the primitive gut in the embryo?
A
- Foregut
- Midgut
- Hindgut
5
Q
What is the allantois?
A
A blind-ended sac that is found connected to the hindgut in the embryo. It has no function in humans.
6
Q
What is the function of the vitelline duct?
A
It connects the yolk sac to the primitive midgut through the umbilical cord.
7
Q
What will the ceolomic cavities eventually become?
A
The peritoneal cavities in the gut and the cavities surrounding the lungs in the thorax.
8
Q
What are the arteries that supply the foregut, midgut and hindgut in the embryo?
A
Foregut = coeliac trunk.
Midgut = superior mesenteric artery.
Hindgut = inferior mesenteric artery.
9
Q
What does the foregut give rise to?
A
- Pharynx
- Oesophagus
- Lower respiratory tract (trachea and lungs)
- Stomach
- Upper part of duodenum
- Bile duct
- Liver
- Pancreas
10
Q
How do the pharynx and oesophagus develop?
A
They start as a hollow tube and then get filled in with cells. These cells then die and leave the tube once more.
11
Q
What happens when development of the oesophagus and pharynx goes wrong?
A
Esophageal stenosis = where all of the cells are not removed causing a thickening of the oesophagus.
Duplication = part of the tube is blind ended - encourages bacteria to grow causing infections.
Atresia = where there is a block in the oesophagus.
12
Q
How does the respiratory tract develop?
A
The cells bud off from the pharynx and form the respiratory diverticulum which then grows downwards and becomes the lung bud.
13
Q
What is a tracheoesophageal fistula?
A
Where there is an abnormal connection between the trachea and the oesophagus that forms during development.
14
Q
How does the pancreas develop?
A
The cells bud out of the duodenum. One ventral bud and one dorsal bud (larger). The ventral is pulled around to the left and sits below the dorsal and fuses with it.
15
Q
What does the midgut give rise to?
A
- Half of the duodenum
- Jujenum
- Ilium
- Caecum and appendix
- Ascending colon
- Proximal 2/3 of the transverse colon
16
Q
How far does the midgut rotate during development?
A
270 degrees
17
Q
What is non-rotation?
A
Where the jejunoileal loops of the small bowel are not inside the large intestine, they are to the side.
18
Q
What is a volvulus?
A
A rotation of the small intestine which leads to constriction of the blood vessels. Caused by mixed rotation during development of the midgut.
19
Q
What is omphalocoele and gastroschisis?
A
Omphalocoele = where the intestinal loops end up in the umbilicus (umbilical cord).
Gastroschisis = where the intestines come out through the anterior abdominal wall just lateral to the umbilicus.
20
Q
What is Meckel’s diverticulum?
A
A small diverticulum of the small bowel that occurs in 2% of the population. It is a remnant of the umbilical cord.
21
Q
What does the hindgut give rise to?
A
- Distal 1/3 of the transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Superior part of the anal canal
- Epithelium of the urinary bladder and most of the urethra
22
Q
What is the terminal region of the hindgut called?
A
The cloaca (Latin for the sewer).
23
Q
What is the proctodeum?
A
It is a structure in the developing hindgut that will form the skin of the anal canal, the lower half of the anal canal and the most distal part of the urinary tract.
24
Q
What is the pectinate line?
A
The boundary between the hindgut and the proctodeum parts of the anus.
25
What does the rotation of the stomach mean for the vagus nerve?
The left branch of the vagus nerve is anterior after rotation and the right branch is posterior as they travel across the stomach. They become the anterior and posterior vagal trunks.
26
List the endocrine glands of the body.
- Pituitary (anterior and posterior)
- Thyroid
- Parathyroids
- Islets of Langerhans (pancreas)
- Gonads
- Pineal gland
- Hypothalamus
- Adrenal glands
27
How are protein and peptide hormones produced?
- Synthesised from DNA into preprohormones.
- Cleaved by proteolytic enzymes to form prohormones which are stored in the cell as granules in secretory vesicles.
- The active hormone is released from the vesicles by exocytosis stimulated by increase in intracellular Ca.
28
Why are steriod hormones not stored in glands?
They are fats so easily move through plasma membranes. This means they are released dependent on the rate of synthesis.
29
What causes the long half life of steroid hormones?
They are bound to albumin when they circulate through the blood.
30
What are eicosanoids?
They are local chemical messengers derived from arachidonic acid that exert a wide variety of effects in many organs and tissues. They are mainly associated with autocrine and paracrine activity.
They include prostaglandins, leukotrienes and thromboxanes.
31
What happens when steroid hormones enter the nucleus of a cell?
Steroid hormones bound to its receptor form dimers in the nucleus. These dimers then bind to the DNA and stimulate transcription of a particular gene.
32
What happens when lipid insoluble hormones bind to their receptors?
The conformation of the receptors is changed. This leads to changes in the intracellular domain and triggers a signalling cascade leading to the cell's response to the hormone.
33
What are the two main lobes of the pituitary?
- Anterior/adenohypophysis = glandular
| - Posterior/neurohypophysis
34
What are the embryological origins of the lobes of the pituitary?
- Posterior = an invagination of the forebrain (diencephalon).
- Anterior = an outgrowth of the buccal cavity (Rathke's pouch).
35
What is the infundibulum?
The stalk of the pituitary which suspends the gland from the hypothalamus. Running through it are nerve fibres from the hypothalamus.
36
What hormones does the posterior pituitary secrete?
- Antidiuretic hormone (ADH)
| - Oxytocin
37
How are hormones secreted from the anterior pituitary?
Hormones are secreted by the hypothalamus and travel down a network of capillaries called the pituitary portal blood system that run down to the anterior pituitary where the hormones are then secreted.
38
What are the five different endocrine cell types found in the anterior pituitary?
- Gonadotroph
- Corticotrophs
- Somatoroph
- Lactotroph
- Thyrotroph
39
Describe the hormone cascade from the anterior pituitary.
See diagram on slide 77 of Overview of Hormone Secretion lecture (20th FAE)
40
What is an example of negative feedback in the endocrine system?
- Hypothalamus produces TRH which triggers the anterior pituitary to release TSH.
- TSH reaches the thyroid and triggers it to release T3 and T4 which carry out the desired effects.
- T3 and T4 return to the hypothalamus and anterior pituitary and inhibit further release of TRH and TSH.
41
What are the characteristics of peptide/protein hormone secreting cells?
- Lots of RER
- Golgi
- Secretory vesicles
42
What are the characteristics of steroid-secreting cells?
- Lots of SER
- Abundant mitochondria
- Lipid droplets
43
What are the three parts of the anterior pituitary gland?
- Pars tuberalis
- Pars distalis
- Pars intermedia
44
What are the two parts of the posterior pituitary gland?
- Infundibulum (neural stalk, median eminence)
| - Pars nervosa
45
What are the glial-like cells found in the posterior pituitary?
Pituicytes
46
What are the roles of ADH/vasopressin?
- Increases water retention in the kidney.
| - Raises blood pressure by contracting vascular smooth muscle cells at high concentrations.
47
What are accumulations of hormones within the axons found in the posterior pituitary called?
Herring bodies
48
What is the pars distalis region of the anterior pituitary traditionally classified into?
- Acidophils
- Basophils
- Chromophobes
49
What cells make up acidophils?
- Somatotrophs
| - Mammotrophs
50
What cells make up basophils?
- Thyrotrophs
- Corticotrophs
- Gonadotrophs
51
What cells are chromophobes?
They are either reserve cells or resting cells that have lost their secretory granules - also the stem cell population.
52
What does the pars intermedia secrete?
Melanocyte stimulating hormone (MSH)
53
What is the isthmus of the thyroid?
It is an area of tissue that connects the left and right lobes of the thyroid gland. It lies at the level of the 2nd-4th tracheal rings.
54
What is an embryological remnant associated with the thyroid gland?
The isthmus may be joined to the hyoid bone by a fibrous cord which is a remnant of the embryological thyroglossal duct.
55
What is thyroglobulin?
It is a large glycoprotein secreted by thyroid epithelial cells which accumulate in thyroid follicles as colloids. They store the inactive hormones that the thyroid gland secretes.
56
What happens to thyroid follicular cells when they are stimulated by TSH?
- Iodinated thyroglobulin is taken up from the colloid by the follicular cells (endocytosed).
- Lysosomes then break down the iodinated tyrosine into derivatives such as T4 and T3 which are released.
57
What are parafollicular cells?
They are cells found scattered in the thyroid gland. They are larger and more rounded than the follicle cells and secrete calcitonin which inhibits Ca mobilisation.
They are also called thyroid C cells.
58
Where are parathyroid glands found?
Usually they are found embedded in the posterior border of the lateral lobes of the thyroid gland.
59
What cells make up the parathyroid gland?
- Densley-packed small chief (or principal) cells that secrete parathyroid hormone which stimulates Ca mobilisation.
- Minor population of eosinophilic oxyphil cells of an unknown function.
60
Describe the anatomy of the suprarenal/arenal glands.
- The right gland is pyramidal and the left gland is crescent-shaped.
- The glands are separated from the kidney by connective tissue but are surrounded by renal fascia.
61
Describe the two parts of the adrenal glands.
1) Cortex is derived from the coelomic epithelium lining the posterior abdominal wall.
2) Medulla is derived from an adjacent sympathetic ganglion.
62
What are the three cell zones of the adrenal gland cortex?
- Zona glomerulosa
- Zona fasciculata
- Zona reticularis
63
What does the zona glomerulosa secrete?
Mineralocorticoids (95% is aldosterone) which causes Na retention in the distal convoluted tubule of the kidney. Cells are in rounded clusters surrounded by capillaries.
64
What does the zona fasciculata secrete?
Glucocorticoids (95% cortisol) which affects glucose, lipid and protein metabolism.
65
What does the zona reticularis secrete?
Some glucocorticoids and small quantities of sex steroids (mainly weak androgens) with unknown functional significance.
66
What is the innervation to the adrenal medulla?
- Receives cholingergic preganglionic sympathetic input from the greater and lesser splanchnic nerves via the coeliac ganglion.
- On stimulation, the medulla secretes catecholamines directly into the blood (80% adrenaline and rest noradrenaline).
67
What are the Islets of Langerhans?
Rounded clusters (100-200 µm in diameter) embedded within the exocrine pancreas. The cells are arranged in irregular cords around capillaries.
68
What are the four cell types found in the Islets of Langerhans and what do they secrete?
- A or α cells (~20%) secrete glucagon
- B or β cells (~70%) secrete insulin
- D or δ cells (5-10%) secrete somatostatin
- F or PP cells (1-2%) secrete pancreatic
polypeptide
- Other, minor cell types secrete vasoactive-intestinal peptide (VIP), substance P, motilin,
serotonin, etc
69
What cells make up the suprarenal/adrenal medulla?
Chromaffin cells.
70
Why are epithelial cells dependent on diffusion for nutrients?
Because blood vessels never pass through the basement membrane, they are found in the connective tissue.
71
What is the clinical significance of the basement membrane?
In order for epithelial tumours to become metastatic, the basement membrane must be penetrated. Some cancers produce enzymes that can digest the mesh (SSC).
72
Where are squamous epithelia found?
In blood vessels and the epithelial layer of skin.
73
Where are cuboidal epithelia found?
In organs that are specialized for secretion, such as salivary glands and thyroid follicles, and those that are specialized for diffusion, such as the kidney tubules.
74
Where are columnar epithelia found?
They line most organs of the digestive tract including the stomach and small and large intestines. Simple columnar epithelia line the uterus.
75
What are psueodostratified and stratified epithelia?
Pseudostratified = all of the cells are attached to the basement membrane. A very convoluted single layer.
Stratified = not all are attached to the basement membrane. Those that are not adhere to each other.
76
What are transitional epithelia?
Where they frequently transition between contracting and stretching. These are found in the bladder and urethra. They must be waterproof and protect against toxic urine.
77
What is the difference between endocrine and exocrine?
Exocrine – secrete to free surface.
Endocrine – secrete to blood stream.
78
What is merocrine secretion?
Vesicles open onto the surface of the cell, and the secretory product is discharged from the cell - normal exocytosis.
79
What is apocrine secretion?
In sweat, mammary, prostate glands, part of the cell cytoplasm is lost into large vesicles when the product is released. This then re-grows.
80
What is the function of adherens junctions?
Joins an actin bundle in one cell to a similar bundle in a neighboring cell.
81
What are the functions of desmosomes and hemidesmosomes?
Desmosome = joins the intermediate filaments in one cell to those in a neighbouring cell.
Hemidesmosome = anchors the intermediate filaments in a cell to the basement membrane.
82
What are intermediate filaments make up of?
Keratin
83
What allows cell movement in rigid cell junctions?
The cytoskeletal and intermediate filaments.
84
What links cells to one another?
Anchor proteins (also linker proteins) are bound to cadherin dimers that link cells. Inside cells, the anchor proteins are attached to actin. Together this is an adherens junction.
85
Why are tight junctions important?
It maintains concentration/osmotic gradients as not even ions are allowed through.
86
What are two tight junction proteins?
- Claudin
| - Occludin
87
Describe the channels that make up gap junctions.
The channel consists of 6 connexin proteins that come together in a circular manner to form a connexon with a central channel. There are different forms of connexin which can form either homomeric (all the same form) or heteromeric (different forms) channels.
When the pores do not align, the channels are closed. When the connexons join, the pores open.
88
What does semi-hard cartilage mean?
They can move but will always go back to their original conformation.
89
What is the major cell component of soft connective tissue?
Fibroblasts that produce the ECM which makes up the majority of this type of connective tissue.
90
What fills the spaces in soft connective tissue?
Very hydrophilic proteoglycans and glycoproteins.
91
What are the functions of soft connective tissue?
- Space filler and mechanical support.
- Attachment and protection.
- Highway for nutrients.
- Storage for fat and Ca (contains a lot of adipose cells).
- Site of immunological defence (where white blood cells migrate into and fight pathogens.
92
What is reticular soft connective tissue?
A subset of cells within the connective tissue that looks like stars. They are found in bone marrow and lymph nodes.
93
What causes a wide variety of properties between soft connective tissues?
Variation in the types of collagen and proteoglycans as well as the presence of elastin or not.
94
What forms a large hydrated gel in soft connective tissue?
- Proteins with sugar residues = glycoproteins.
| - Glycosaminoglycans (GAGs) = long chain sugar residues.
95
What does collagen contribute in soft connective tissue?
Collagen provides the tensile strength of the matrix.
96
In what type of tissue would you find a lot of collagen in the soft connective tissue?
A tissue where you want it to be resistant to deformation or stretching e.g. the connective tissue directly under the dermis.
97
In what tissues will you find types a) I; b) II; c) III and d) IV collagen?
a) Skin, bone, tendons, dentine
b) Cartilage
c) Blood vessels, skin
d) Basement membrane (sheet collagens)
98
What fibre helps push blood through the circulation?
The energy stores in elastic fibres of the soft connective tissue when they are stretched. These are found especially in arteries close to the heart.
99
What are elastic fibres made up of?
They are made as tropoelastin which polymerises in extracellular tissue.
Microfibres of structural glycoprotein fibrillin then incorporates into a core of cross-linked elastin to form elastic fibres.
100
How many cycles of stretch-recoil can elastic fibres withstand before losing their elasticity?
2 billion
101
What is the function of adhesive proteins in soft connective tissue?
They cross-link cells of connective tissue to collagen binding them to trans-membrane receptors called integrins.
102
What are fibronectin, tenascin and laminin and where are they found?
They are all adhesive proteins.
```
Fibronectin = abundant in all connective tissue.
Tenascin = produced at wounds.
Laminin = in the basal lamina binding the epithelia to the basement membrane.
```
103
What does it mean if a cell has no integrins bound to the ECM?
They can move freely throughout the matrix.
104
What is the function of the basement membrane?
It separates the connective tissue from the epithelial layer and acts as a physical barrier to cells, maintaining the integrity of tissues. The kidney uses theirs as a filter.
105
What does the hydrated gel in soft connective tissue create?
The water in this gel creates a swelling pressure called turgor that enables the ECM to withstand compressive forces.
106
What do proteoglycans consist of?
GAGs attached to proteins. This attachment can be by linker proteins or covalent bonds. Hundreds of GAGs come off of one protein.
107
What are indigenous and immigrant cells of soft connective tissue?
Indigenous = cells that synthesise the ECM and lipid storage
Immigrant = immune system cells
108
What cells give rise to all indigenous cells of soft connective tissue?
Mesenchymal stem cells
109
What is cryptorchidism?
Undescended testes.
110
What does topographical mean?
Topographical things are things you can see with the naked eye.
111
What does somatic refer to in terms of tissue organisation?
The body as a whole and is usually used to describe the elements which make up the walls of the trunk and limbs (bone, cartilage, skeletal muscle).
112
What are the four functions of the skin?
1) Protection
2) Thermoregulation
3) Provides sensory information about the surrounding environment
4) Vitamin D synthesis
113
What are the three layers of the skin?
1) Epidermis
2) Dermis
3) Superficial fascia (hypodermis)
114
What cell types make up the epidermis?
Keratinocytes (90%), melanocytes, Langerhans cells and Merkel cells.
115
What are the functions of the deep fascia?
1) Conduction (blood vessels and nerves are found here - neurovascular bundle).
2) Movement of muscle - muscles wrapped in fascia are able to slide over each other.
3) Attachment for some muscles and bone.
4) Capsules around organs and glands.
116
What is the pathological disadvantages of deep fascia capsules in the leg?
Because the deep fascia is made of non-elastic collagen, when you get an inflammatory response in one muscle compartment (e.g. swelling) the structures within the compartment including vessels and nerves can be compressed and cut off.
117
What happens around the ankle joint to improve the efficiency of muscle action?
Condensation of deep fascia ensures that the long tendons can reach the toes and be held in position.
118
What are serous membranes?
They are thin double-layered membranes that line the internal cavities of the body and consist of mesothelium and are supported by loose connective tissue. The inner layer is intimate with the viscera and the outer is anchored to the body wall.
119
What are the three serous membranes?
1) Pleura
2) Pericardium
3) Peritoneum
120
What are the three blood vessel layers?
From inside out:
1) Tunica intima = endothelilal lining.
2) Tunica media = muscle and elastic fibres.
3) Tunica externa = connective tissue.
121
What is the role of collateral arteries?
They ensure a continuous blood flow irrespective of the position of the body. These can also be called recurrent arteries.
122
What are found in deep veins to ensure blood returns to the heart efficiently?
They have valves to stop the backflow of blood and skeletal muscles surrounding them. When the muscles contract, this helps push the blood back to the heart.
123
What does the majority of the foetal skeleton consist of?
Hyaline cartilage
124
Why is it necessary for areas of cartilage to be thin?
Because there are no neurovascular elements within cartilage, it must gain its nutrients through diffusion.
125
What are two less obvious functions of bone?
- Haemopioesis
| - Storage of Ca and phosphorus
126
What are the axial and appendicular skeletons?
- Axial = skull, ribcage, sternum, spine and coccyx.
| - Appendicular = everything else.
127
What sections are long bones divided into?
From proximal to distal:
- Proximal epiphysis (contains articular cartilage)
- Metaphysis
- Diaphysis
- Metaphysis
- Distal epiphysis (contains articular cartilage)
128
Which section of the long bone contain spongy (cancellous, trabecular) bone?
Epiphysis and metaphysis
129
What is the a) endosteum and b) periosteum?
a) Thin vascular membrane of connective tissue that lines the inner surface of the bony tissue that forms the medullary cavity.
b) Membrane that covers the outer surface of all bones except at the joints of long bones.
130
Describe the development of long bones.
- During development you start with a cartilage template. It then gets wrapped around the middle with a collar of bony material which cuts off the cartilage from its nutrients forcing it to hypertrophy and calcify. You are left with a ‘ghost’ of intracellular matrix.
- A blood vessel then enters in depositing osteoblasts which use the dead cartilage as a template.
- The bony collar continues to reach the ends during development.
- The ends of the bones form secondary ossification centres. They happen at set times (can be use for ageing).
- The epiphysial plate will continue to grow cartilage until puberty.
This is called endro
131
How are flat bones formed?
Osteoblasts lay themselves down on mesenchymal tissue and start producing matrix. The cells become embedded in the matrix and become osteocytes. More potential osteoblasts form an epithelium around it and lay down more matrix. The surface of the bone expands in all directions. This is called intramembranous ossification.
132
What are the two types of tissue found in mature bone?
- Compact
| - Spongy (helps spread the load across the entire surface of a joint)
133
What is a condyle?
A smooth rounded articular process.
134
What is a trochlea?
A smooth grooved articular process shaped like a pulley.
135
What is a ramus?
An extension of the bone at an angle to the rest of the structure.
136
What is lapsed ossification?
Where the inside of the skull joins less elaborately than the inside.
137
What are the three types of skull sutures?
From straight to elaborate:
1) Squamous
2) Serrated
3) Denticulate
138
What is the role of the peridontal ligament in a gomphosis?
It attaches the bone to the root of the tooth. It also acts as a shock absorber allowing teeth to move slightly ensuring the enamel doesn't shatter.
139
What are the five components of a synovial joint?
1) Synovial membrane
2) Synovial fluid
3) Articular cartilage
4) Joint capsule (continuous with periosteum around the bone).
5) Periosteum
Label diagram slide 33 lecture 6 FAE
140
What are thickenings of a joint capsule called?
Ligaments
141
What is the function of bursae in joints?
They act as cushions to prevent bones from hitting each other during specific movements.
142
What are tendons made of?
Dense collagenous connective tissue.
143
What are the roles of flexor and extensor muscles?
Flexor = bends the joint (decreases the joint angle).
Extensor = straightens the joint (increases the joint angle).
144
What is a synergist muscle?
A muscle that complements the action of an agonist either with the same movement or by acting as a fixator of an intervening joint.
145
What happens at the myotendinous junction?
The endo-, peri- and epimysium merge with the dense collagenous connective tissue of the tendon at the myotendinous junction.
146
What causes myoblasts to divide and fuse to form myotubes?
Growth factors.
147
What is Duchenne muscular dystrophy?
A genetic disorder characterised by the absence of dystrophin in muscle cells. This leads to progressive muscle degeneration and weakness. 30% have significant learning difficulties.
148
What is Gower's sign/manouevre?
A medical sign that indicates weakness of proximal muscles including lower limb. The patient has to use their hands and arms to 'walk' up their own body from squatting due to a lack of hip and thigh muscle strength.
149
What is the role of dystrophin in muscle cells?
It helps link the contractile apparatus to the ECM and has a structural role in stabilising the sarcolemma during contraction.
150
What happens to muscle cells when dystrophin is absent?
The muscle fibres tear themselves apart when they are being used. This causes constant damage and repair to muscle fibres leading to necrosis and fibrosis of the muscle fibres.
151
Where are all trunk and limb muscles derived from in the embryo?
Somites
152
What are the derivatives of dermomyotome?
- Skeletal muscles
- Satellite cells
- Dermis
153
What are the derivatives of sclerotome?
- Cartilage
- Vascular smooth muscle cells
- Endothelial cells
- Meninges
- Joints
- Tendons
154
What are the derivatives of myotome?
Differentiated myocytes.
155
What factors drive a precursor cell to undergo terminal differentiation to from a muscle cell?
- Myogenic precursors -> myoblasts = Myf5, Mrf4 and MyoD.
- Myoblasts -> myotubes = myogenin, Mrf4
(myogenic regulator factors - transcription factors)
156
What is muscle patterning determined by?
Extrinsic signals
157
What coordinates the formation of muscles during development? What do they go on to form?
Muscle connective tissue fibroblasts.
Forms the fascia around the muscle bundles.
158
What are the four types of glial cells found in the CNS?
1) Astrocytes
2) Oligodendrocytes
3) Microglia (macrophages of CNS)
4) Ependymal cells (line brain ventricles)
159
What are the functions of astrocytes?
- Maintenance of BBB
- Contain microfilaments which give structural strength to CNS
- Direct neural growth during development
- Stabilise structure after injury producing scar tissue
- Controls interstitial environment including neurotransmitter recycling
160
What are the neuroglia of the peripheral nervous system?
- Satellite cells (supports peripheral nerve cell bodies in ganglia)
- Schwann cells
161
What structures make up the diencephalon?
- Thalamus
- Hypothalamus
- Epithalamus
- Pineal gland
162
What are the two internal structures of the dura mater?
- Falx cerebri
| - Tentorium cerebelli
163
What absorbs excess CSF?
Arachnoid villi
164
What are the three subdivisions of the CNS?
- Somatic (supplies body wall, skeletal muscle and skin with both motor and sensory fibres)
- Nerves of special sensation (senses and balance)
- Autonomic (supplies internal organs with both motor and sensory fibres)
165
What is a unique characteristic of sensory axons in the PNS?
Their cell bodies outside the CNS are in ganglia where they do NOT synapse, in the posterior root ganglia.
166
What fibres are found in the anterior/ventral and posterior/dorsal parts of the spinal cord?
Anterior/ventral = motor fibres.
Posterior/dorsal = sensory fibres.
167
Where does the spinal cord end?
L2/3
168
What happens to spinal nerves in the cervical, lumbar and sacral areas?
The fibres undergo a redistribution into plexuses. This happens in all nerves except T2-12.
169
What is the cauda equina?
The end of the spinal cord.
170
What is a myotome?
The area that a nerve supplies in relation to skeletal muscle.
171
What is the result of nerve plexuses?
Fibres from different ventral origins crisscross each other and redistribute so that each end branch of a plexus contains fibres from several different spinal nerves and fibres from each ventral ramus travels to the periphery by different roots.
172
What advantage do nerve plexuses provide?
Because each limb muscle receives a nerve supply from more than one spinal nerve, when there is damage to a single spinal nerve muscles may weaken but they are not paralysed completely.
173
What are the roles of autonomic motor fibres?
They innervate smooth muscle and glands and in the GI tract they modulate the activity of the enteric nerve plexuses.
174
Describe the autonomic motor nerve pathway.
Consists of two neurons in series:
1) Cell body is in the CNS with the axon extending to an autonomic ganglion where it synapses.
2) The axon arising from the cell body travels to the effector organ.
175
Describe the somatic motor nerve pathway.
The cell body is found in the CNS and its axon travels all the way to the effector tissue without synapsing, there is no ganglion.
176
What are the two divisions of the motor autonomic nervous system?
1) Sympathetic
| 2) Parasympathetic
177
Where do parasympathetic and sympathetic nerves leave the spinal cord?
Parasymp = at cranial and sacral levels.
Symp = T1-L2
178
What is the sympathetic chain?
A row of ganglion lying just outside the spinal cord where sympathetic nerves synapse.
179
What is the difference between the sympathetic nerves that supply the viscera and those that supply smooth muscle and glands?
- Those that supply smooth muscle synapse in their corresponding ganglia and their post-ganglionic fibres go straight to the tissue.
- Those that supply viscera don't necessarily synapse in their corresponding ganglia and the post-ganglionic fibres tend to form plexuses.
180
What happens to sympathetic nerves in the abdomen?
The nerves do not synapse in the sympathetic chain and enter the abdomen as greater and lesser splanchnic nerves. They then reach their ganglia in front of the aorta (collateral ganglia) and synapse.
181
What is the exception to the greater splanchnic nerve?
The branch that goes straight to the adrenal medulla and does not synapse.
182
Describe pre and post ganglionic sympathetic fibres.
Pre-ganglionic are myelinated fibres that are often called white rami. These travel through posterior and anterior roots of the spinal cord.
Post-ganglionic are are grey fibres (unmyelinated).
183
Why do you feel pain down your arm when you're having a heart attack?
The sympathetic fibres that go to the heart are from T1&2. The somatic nerves that are from here supply the upper arm. The sympathetic nerves refer the pain down the arm to let the brain know there is a problem.
In order for this referral to occur, the autonomic nerves supplying the organ must be associated with the somatic nerves they are referring the pain to.
184
How do the parasympathetic cranial nerves III, VII and IX differ to the rest?
They leave the brain synapse in a ganglion and their post-sympathetic fibres go to the tissue they innervate.
The rest of the nerves leave the CNS and form plexuses on the oesophagus and in front of the aorta and then go on to supply a variety of organs and tissues. They synapse at intramural ganglia near or on the tissue/organ they are innervating.
185
What is the control centre for the autonomic nervous system?
Hypothalamus, but strong emotions from the thalamus can feed into the hypothalamus causing an effect.
186
Describe the signal cascade of the autonomic nervous system.
Hypothalamus (sometimes influenced by thalamus) -> pons (stops at pons) and medulla oblongata -> spinal cord.
187
What is PET imaging?
Positron Emission Tomography = low resolution imaging where you inject an isotope (usually Tc, technetium) into the patient and detect the presence of that isotope. Use a ring of detectors to count co-incidental gamma photons.
188
What is spacial resolution?
A measure of the smallest discernible detail in an image. This depends on the properties of the imaging device being used.
189
What is the aspect ratio of an image?
The ratio of its width to its height (typically 1).
190
What is the dynamic range of an image?
The range of intensity values used to display the image.
191
What does a low intensity resolution mean?
That you will not be able to differentiate objects that look similar.
192
What is the metadata of an image?
Information such as who the image belongs to. This is found before the image.
193
What are pixels known as in 3D images?
Voxels
194
What is the most common file type for medical imaging?
DICOM (digital imaging and communications in medicine). This is a non-compressed file format.
195
What are lossy and lossless file formats?
Lossless = you can completely recover the information.
Lossy = the information can be recovered but it uses up less space.
196
What are the three types of rendering that computers use to visualise 3D medical images on a 2D screen?
- MIP (maximum intensity projection) = can see through skin into structures.
- Surface rendering = can see a particular structure that you set in parameters.
- Volume rendering = allows you to see inside objects.
197
When were x-rays discovered?
1895
198
How are x-rays generated?
They are produced when high speed electrons strike a target material such as tungsten. The maximum energy of x-rays depends on the speed of electrons.
199
What are x-rays measured in?
keV
Typical medical energies are 30-100 keV
200
What has the least attenuation in the body?
Air followed by fat and soft tissue.
201
What does more attenuation mean for x-rays?
A whiter image.
202
What is used to detect stationary images and movies?
Stationary = digital film
Movies = flat panel detectors
203
What are you able to do with a CT that you cannot do with a X-ray?
Differentiate between different types of soft tissue.
204
How does a CT scanner work?
You have x-ray sources that generate lots of rays that are detected by multiple rows of detectors in a circle. The device spins around while the patient moves through the ring allowing lots of images to be generated very quickly.
205
Why is gamma photon emission used in medical imaging?
Because you want the particle emitted to leave the body so it can be detected. This is why you can't use alpha and beta emissions because they stay in the body.
206
What is the ideal half life of an isotope used for imaging?
Not so short that it dies before the procedure is over, but not too long because you don't want the patient to be emitting radioactive particles after the procedure.
207
What is used to detect the photons in nuclear imaging?
Gamma camera
208
How can you detect some cancers with nuclear imaging?
Cancers can develop high blood flow so can be detected if you inject a tracer.
209
What is SPECT?
Single photon emission tomography
210
What is the difference between PET and SPECT?
PET has two photons detected per annihilation event, whereas SPECT only has one photon released.
211
What is F-18 PET?
Where you put fluorine 18 on a glucose analogue which makes something that the body thinks is glucose. This allows us to measure the metabolism in the brain.
212
What is cardiac SPECT and why is it used?
Where you use technetium 99 and other gamma emitters to see blood flow in the myocardium (muscle tissue of the heart).
You can look for areas of the heart which does not show increased blood flow during stress which could indicate a coronary embolism.
213
How are PET scans turned into 3D images?
The detector collects gamma rays from different angles and uses this to form a 3D image.
214
Why is PET used for function rather than anatomy? What can be done to overcome this limitation?
Because the imaging will only detect the regions of the body where the isotope is present.
Overcome by combining PET/SPECT with CT scanners.
215
What is nuclear magnetic resonance?
Where atomic nuclei are placed in a magnetic field and are absorbing energy from a radiofrequency wave applied at a specific frequency.
When they are hit with radiowaves, the nuceli flip their orientation. When the radiowaves are stopped, the nuceli flip back and emit radiowaves which can be measured.
216
What is the resonance frequency?
The natural frequency of a system - the frequency required for the most efficient energy transfer.
217
What does MRI involve?
Localising the re-emitted radiowaves from NMR using magnetic field gradients to form an image.
218
Why is a hydrogen isotope used in MRI?
Because it has the simplest nucleus, the highest NMR sensitivity and high natural abundance in the body.
219
What is the function of gradient coils and RF coils in an MRI machine?
RF coils generate radiowaves.
Gradient coils are used to localise the signal to different parts of the body.
220
What triggered the foundations of ultrasound imaging?
The sinking of the Titanic
221
What does ultrasound imaging utilise?
Sound waves above human hearing range. They are emitted in a short pulse and what is reflected back is recorded.
222
How do ultrasounds distinguish between tissues?
By measuring the speed at which a wave returns (the position) as well as the amount of reflected energy (the density).
223
What is A-mode scanning?
Amplitude mode. Echoes are plotted on a screen as a function of depth.
224
What is M-mode imaging?
Repeated A-scans of a moving target. This is good for measuring tissue in motion.
225
What is B-mode scanning?
Brightness mode. Where you move the A-mode transducer to different positions which creates a 2D image from 1D lines.
226
What occurs between days 1 and 9 post-fertilisation in a human embryo?
The fertilised egg has travelled from the ovary, down the fallopian tube and has implanted into the uterine wall.
The embryo has gone from a collection of cells to a blastocyst.
227
What is the blastocyst?
A sphere of cells called the trophoblast with a collection of cells inside called the inner cell mass.
The trophoblast is what interacts with the uterine wall and the embryo is derived from the inner cell mass.
228
What happens to the inner cell mass after the blastocyst is formed?
It rearranges itself to form the blastodisc. This consists of two layers: epiblast and hypoblast.
229
Describe the process of gastrulation.
Primitive streak forms along the midline of the epiblast. This defines the major body axis of the embryo.
Cells move from the epiblast and go down through the primitive streak and displace the hypoblast forming the endoderm. More cells travel through the primitive streak and fill the space between the endoderm and the epiblast and these make the mesoderm. The epiblast then becomes the ectoderm.
230
Describe the process of neurulation.
The neural plate forms in the ectoderm. The edges of the plate (where it meets the epidermis) rises up and folds joining the two ends across the midline. The tube then drops down and the epidermis becomes continuous over the tube. The notochord lies below this tube.
231
What is anencephaly, craniorachischisis and spina bifida?
When the neural tube fails to close.
Anencephaly = no brain.
Craniorachischisis = the entire neural tube fails to close - entire spinal cord and brain are exposed.
Spina bifida = incomplete closure of the posterior neural tube causing the spinal cord and associated structures to lie outside the body.
232
What is the neural crest?
A population of cells at the top of the neural tube that migrate away from the tube and give rise to a number of different tissues including the neurons and glia of the peripheral nervous system.
233
What are the derivatives of the intermediate mesoderm?
Kidneys
Gonads
234
What are the derivatives of the cordamesoderm?
Notochord
235
What are the derivatives of the paraxial mesoderm?
Head
Somites
236
What do the somites go on to form?
- Sclerotome (cartilage of the verebrae)
- Syndotome (tendons)
- Myotome (skeletal muscle)
- Dermatome (dermis)
- Endothelial cells
237
What are the derivatives of the lateral plate mesoderm?
- Splanchnic
- Somatic
- Extra-embryonic
238
What is the order of mesoderm derivatives from left to right in the embryo?
Lateral plate -> Intermediate -> paraxial -> chordamesoderm -> paraxial -> intermediate -> lateral plate.
Building a human 1 slide 22.
239
In what direction do somites form in the embryo?
Posteriorly
240
What is an important role of the somites other than producing its derivatives?
It organises the peripheral nerves as well as neural crest migration and motor nerves.
241
What causes scoliosis?
Defects in somitogenesis.
242
What is the concept of epigenesis?
Where the structures of the adult form arises progressively during development.
243
What is the concept of preformation?
Where everything in the embryo is preformed and simply gets bigger during development.
244
What is a homunculus?
A tiny human that exists in the head of each sperm. This is what was believed to be the case from ancient Greece all the way to the 17th century.
245
What provides positional information in the embryo?
A gradient of different morphogens. Different cells respond to different concentrations of certain morphogens.
246
What directs the development of the ventral spinal cord and patterning of the somites?
The notochord which produces Shh.
247
What is holoprosencephaly caused by?
Mutations in Shh.
248
What is a teratogen?
An agent that can disturb the development of the embryo or fetus.
249
What causes cyclopia?
The teratogen cyclopamine which is a Shh inhibitor.
