Cellular Organisation of Tissues Flashcards
1
Q
What occurs in the nucleolus?
A
The production of the subunits of the ribosomes. It contains ∼300 clusters of rRNA gene on the tips of 5 pairs of chromosomes
2
Q
What is the size of a eukaryotic ribosome?
A
80S (60S + 40S)
3
Q
What is the relationship between the nuclear envelope and the endoplasmic reticulum?
A
The nuclear envelope is continuous with the endoplasmic reticulum
4
Q
What ER is associated with protein synthesis?
A
Rough endoplasmic reticulum
5
Q
What ER is associated with lipid metabolism?
A
Smooth endoplasmic reticulum
6
Q
Where are the cis and trans-Golgi located in relation to the ER and the periphery of the cell
A
Cis-phase Golgi- towards the endoplasmic reticulum
Trans-phase Golgi- towards the periphery of the cell
7
Q
What are peroxisomes? Give one example.
A
A membrane-bound organelle containing enzymes involved in lipid and oxygen metabolism
eg catalases, peroxidases
8
Q
What are microtubules, what is their function?
A
Polymers of α and β-tubulin, ∼20nm in diameter. Involved in cell shape and act as tracks for movement of other organelles and cytoplasmic components within the cell.
9
Q
What protein monomer is the major component of cilia and flagella?
A
Microtubules
10
Q
What protein monomer forms the mitotic spindle?
A
Microtubules
11
Q
What are intermediate filaments and what is their function?
A
A group of polymers of filamentous proteins which form rope-like filaments. 10-15nm in diameter
12
Q
What protein monomer gives mechanical strength to a cell?
A
Intermediate filaments
13
Q
What type of intermediate filament do epithelial have, which also connects desmosomes?
A
Cytokeratins
14
Q
What type of intermediate filament do mesenchymal cells have?
A
Vimentin
15
Q
What are mesenchymal cells? (4)
A
Cells of the connective tissue Fibroblasts (many tissues) Chondrocytes (cartilage) Osteocytes (bone) Muscle cells (skeletal, cardiac, smooth)
16
Q
What kind of intermediate filament do neurones have?
A
Neurofilament protein
17
Q
Where are nuclear laminins found? What is their function?
A
They form a network on the internal surface of the nuclear envelope and are involved in stabilising the envelope
18
Q
What are actin microfilaments? Where are they found?
A
Polymers of the filamentous actin (f-actin). Associated with adhesion belts in epithelia and endothelia, and with other plasma membrane proteins. Involved in cell shape and cell movement (crawling of cells; cell contractility especially in muscle). Has accessory proteins (e.g. myosin- acts with actin to control actin organisation and cell movement)
19
Q
What are haematopoietic cells?
A
Cells of the blood and of the bone marrow from which they are derived
20
Q
What are neural cells? (2)
A
Cells of the nervous system having two main types Neurones (carry electrical signals) Glial cells (support cells)
21
Q
What cell type do carcinomas originate?
A
Epithelial cells
22
Q
What cell type do sarcomas originate?
A
Mesenchymal cells
23
Q
What cell type do leukaemias originate?
A
Haematopoietic cancer from bone marrow cells
24
Q
What cell type do lymphomas originate?
A
Haematopoietic cancer from lymphocytes
25
What cell type do neuroblastomas originate?
Neural cell cancer from neurones
26
What cell type do gliomas originate?
Neural cell cancer from glial cells
27
What is the apical surface of a cell?
Faces in towards the lumen
28
What is a cell junction?
A multiprotein complex that provides contact between neighbouring cells
29
What is the extracellular matrix?
Material deposited by cells which form the "insoluble" part of the external environment. It is a complex network of proteins and carbohydrates filling the space between cells. It comprises of both fibrillar and non-fibrillar components
It may be poorly organised (e.g. loose connective tissue) or highly organised (e.g. tendon, bone, basal lamina)
30
Generally in what two forms to you find cell-cell junctions?
Zonulae (belts) and maculae (spots)
31
What is an apical junctional complex found in epithelia?
Cell-cell junctions
| Tight junctions nearest the apex, then an adhesion belt , then desmosomes scattered throughout the lateral membrane
32
What is a zonular occludens?
Belt/occluding junctions- points on adjacent membranes that form close contacts at apical lateral membranes
33
What is a zonula adherens?
Adhesion belt- Usually formed just basal to the apical tight junction. The transmembrane adhesion molecule is cadherin. Cadherin is associated with the actin cytoskeleton
34
What is a Macula adherens?
A desmosome. Found at multiple spots between adjacent cell membranes, provides good mechanical continuity between cells.
35
What is a macula communicans?
A gap junction. Made up of clusters of pores formed from 6 identical subunits in the membrane. These pores are continuous with pores in adjacent membranes. They allow passage of ions and small molecules between cells.
36
What can effect the opening and closing of a gap junction? (4)
pH, Ca2+ concentration, voltage and some signalling molecules
37
What is a chemical synapse, where are they found?
Mainly in neural tissue. They are button-like junctions formed between neurones or between neurones and target cells (e.g. muscle). Information is passed one-way via a chemical signalling system.
38
What are the different types of epithelial cell classification? (5)
```
Simple squamous
Simple cuboidal
Simple columnar
Stratified squamous
Pseudostratified
```
39
Why is cell polarity important in epithelial cells?
For secretion, transport and absorption it must be unidirectional. Cell polarity gives directionality to epithelial function. Membrane polarity is key to epithelial polarity
40
Give an example of a cell feature that would organise it for absorption, secretion, protection or transport?
Absorption- Microvilli brush border or enterocytes
Secretion- goblet cells
Protection- thick skin, made up of the epidermis, dermis and hypodermis
Transport- mitochondria (for active transport)
41
What is an exocrine secretory function?
Secretes into a duct or lumen
42
What is an endocrine secretory function?
Secretes into the bloodstream
43
What are the different types of exocrine gland epithelium organisation? (6)
```
Simple tubular
Simple branched tubular
Simple coiled tubular
Simple branched alveolar
Compound tubular
Compound alveolar
```
44
What is constitutive secretion?
Secretory vesicles, as they are formed, move directly into the plasma membrane and release their contents
45
What is stimulated secretion?
Secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents when stimulated
46
What cell type is the epidermis?
Keratinized stratified squamous epithelium
47
What is the function of ECM?
It provides physical support, it determines the mechanical and physicochemical properties of the tissue. It influences growth, adhesion and differentiation status of the cells and tissues with which it interacts and it is essential for development, tissue function and organogenesis
48
What is connective tissue?
Tissue that is rich in ECM. They contain a spectrum of collagens, multi-adhesive glycoproteins and proteoglycans (ECM) together with component cells
ECM+cells
49
What is the structure of collagen, what amino acids?
Three α-chains forming a triple helix
| Characteristically it is [gly-x-y]repeat: x is often proline and y is often hydroproline
50
What is the process of fibrillar collagen biosynthesis?
1) Synthesis of pro-α chain
2) Hydroxylation of selected prolines and lysines
3) Glycosylation of selected hydroxylysines
4) Self-assembly of three pro-α chains
5) Procollagen triple helix formation
6) Secretion
7) Cleavage of propeptides
8) Self-assembly into fibril
9) Aggregation of collagen fibrils to form a collagen fibre
51
What effect does vitamin C have on collagen?
Vitamin C deficiency results in under hydroxylated collagens with dramatic consequences for tissue stability
52
What residues are responsible for covalent cross-link formation in collagen?
Lysine and hydroxylysine
53
What are elastic fibres made up of?
Elastin core, and microfibrils which are rich in the protein fibrillin
54
What causes Marfan's syndrome?
Mutation in fibrillin 1
55
What is the structure of elastin?
Consists of two types of segments that alternate along the polypeptide chain: hydrophobic regions and α-helical regions rich in alanine and lysine. Many lysine chains are covalently cross-linked
56
What is the structure of laminins?
It consists of three chains, one of each α, β, and γ forming a cross-shaped molecule. It is a very large multi-adhesive molecule that interacts with cell surface receptors (integrins and dystroglycan)
57
What are fibronectins?
A major connective tissue glycoprotein. They can exist as insoluble fibrillar matrix or soluble plasma protein (both derived from one gene- alternate splicing at mRNA level). They are multi adhesive and have no known mutations in humans- they are essential for life
58
What connective tissue is important in migration in embryogenesis, regulating cell adhesion, tissue repair, and wound healing?
Fibronectins
59
What proteins are responsible for connecting the ECM to the actin cytoskeleton of cells?
Integrins
60
What is the structure of proteoglycans?
A core protein to which one or more glycosaminoglycan (GAG) chains are covalently attached. Some have one single GAG chain attached, whereas some large proteoglycans carry ∼100 GAG chains
61
What is the structure of glycosaminoglycans (GAGs)
They are long unbranched sugars consisting of repeating disaccharides. One of the two sugars in repeating disaccharides is always amino sugar. Many GAGS are sulfated or carboxylated and highly negatively charged.
They occupy a huge volume compared to their mass and they can be very resistant to compression.
62
What are the 4 types of GAG chains that attach to a proteoglycan?
Hyaluronan
Chondroitin sulphate or dermatan sulphate
Heparan sulphate
Keratan sulphate
63
What are the distinct features of hyaluronan (hyauronic acid)?
Unique- simply a carbohydrate chain, no core protein. It is synthesised at the cell surface, not in the ER/Golgi. It is unsulphated and is a single long chain, up to 25,000 repeated disaccharides. It has a huge size- save volume as a bacterium
64
What is decorin, what is it's function?
It is a small proteoglycan. It binds to collagen fibres and is essential for fibre formation.
65
What is the most abundant type of cartilage?
Hyaline Cartilage
66
What is hyaline cartilage, where is it found, what is it's function?
Most abundant type of cartilage found in the nose, larynx, trachea, bronchi, the ventral ends of ribs and the articular ends of bones. It is rich in aggrecan (core protein) and functions to cushion the ends of long bones
67
Why is aggrecan suited to a role in cartilage?
```
It is perfectly suited to resist compressive forces
The GAGs (e.g. chondroitin sulfate) of aggrecan are highly sulfated, and there are also a large number of carboxyl groups. These multiple negative charges attract cations such as Na+ that are osmotically active. Large quantities of water are therefore retained by this highly negatively charged environment. Under compressive load, water is given up but regained once the load if reduced.
```
68
What causes congenital muscular dystrophy?
Absence of α2 in laminin 2
69
What symptoms are characteristic of congenital muscular dystrophy?
Hypotonia (abnormally decreased muscle tension), generalised weakness and deformities in the joint
70
What causes osteoarthritis? What is it?
Excessive loss of extracellular matrix (ECM degradation). Characteristic thinning and destruction of cartilage.
With age: cleavage of aggrecan by aggrecanase and metalloproteinase. Loss of aggrecan fragments to synovial fluid
71
What are the main fluid compartments of the body and roughly what size are each?
```
Intracellular=55% of body water
Extracellular= 45% of body water made up of:
Interstitial fluid= 36% of body water
Blood plasma= 7% of body water
Transcellular fluid= 2% of body water
```
72
What percentage fluid are men and women?
Women 55%
| Men 60%
73
What is the main extracellular and intracellular cation?
Extracellular: Na+
Intracellular: K+
74
What is the main extracellular and intracellular anion?
Extracellular: Cl-
Intracellular: Organic phosphates
75
Is pH higher intracellularly or extracellularly?
Intracellularly
76
Is osmolarity higher intracellularly or extracellularly?
Osmolarity is equal
77
What is diffusion?
The spontaneous movement of solutes
78
What is osmosis?
The diffusion of water down its own concentration gradient
79
What is osmolarity?
A measure of the concentration of all solute particles in a solution
80
What is tonicity?
The measure of the effective osmotic pressure gradient of two solutions separated by a semi-permeable membrane. It is only influenced by cells which cannot cross the membrane (e.g. is a solution is hypertonic it has a greater concentration than the other side of the membrane)
81
Is transport of ions or urea across a membrane through a ligand or voltage-gated channel active or passive?
Passive
82
What are three types of passive transport across a membrane?
Diffusion
Through channels (ligand or voltage-gated)
On carriers
83
What are two examples of transport against the concentration gradient?
```
Active transport
On carriers (uses down-hill movement of one solute coupled to another)
```
84
What is the colloid osmotic pressure?
The osmotic pressure due to plasma proteins
85
What substances are exchanged through capillary endothelial cells?
Plasma
Exchangeable proteins are moved across by vesicular transport
Lipid-soluble substances pass through endothelial cells
Small water-soluble substances pass through the pores between cells
86
In oedema what happens to the relationship between hydrostatic pressure and colloid osmotic pressure?
Hydrostatic pressure > Colloid osmotic pressure
87
What is oedema?
The swelling of a tissue because of excess interstitial fluid
88
How does the lymphatic fluid return to the circulation?
In nodes: 50%
| Lymphatic ducts in the subclavian region: 50%
89
Oedema is one of the cardinal signs of what?
Inflammation
90
What stimuli usually result in oedema? (2)
Infectious and inflammatory
91
What can cause oedema? (4)
Insect bite
Obesity
Breast cancer survivor
Elephantiasis
92
What is haemolysis?
The rupture or destruction of red blood cells
93
What kind of solution would cause the rupture of red blood cells?
A hypotonic salt solution
94
What three structures make up the brainstem?
Midbrain
Pons
Medulla
95
What part of the brain is the source or target of all cranial nerves?
Brainstem
96
What part of the brain has an important role in motor coordination, balance and posture?
Cerebellum
97
What three structures make up a neurone?
Soma (contains nucleus and ribosome)
Axon (originates at axon hillock, usually covered in myelin)
Dendrites (highly branched cell body not covered in myelin)
98
What is the most abundant cell type within the CNS?
Astrocytes
99
What are astrocytes? What is their function?
Astrocytes are able to proliferate. They are structural cells that hold neurones in place, the perform cell repair, they release and reuptake neurotransmitters and they are immune cells- considered "facultative macrophages"
100
What are the two types of myelin producing cells?
Oligodendrocytes
| Schwann cells
101
What are the features of oligodendrocytes?
Variable morphology and function
Numerous projections that form internodes of myelin
One oligodendrocyte- myelinates many axons
102
What are the features of Schwann cells?
Produce myelin for peripheral nerves
| One Schwann cell- myelinates one axon segment
103
What cell produces myelin for the CNS?
Oligodendrocytes
104
What is the composition of myelin which allows it to provide electrical insulation?
Rich in lipids, low water content
105
What is the molar ratio or cholesterol:phospholipids:glycolipids in myelin?
4:3:2 to 4:4:2
106
What is the name for the process in which the impulse in an axon jumps along from node to node?
Saltatory conduction
107
What are microglial cells?
Specialised cells of the CNS- similar to macrophages
108
What are ependymal cells?
Epithelial cells lining fluid-filled ventricles that regulate the production and movement of cerebrospinal fluid
109
Is extracellular Na+, Cl-, Ca2+ and K+ higher or lower than intracellular?
Na+: high
Cl-: high
Ca2+: high
K+: low
110
In neuronal cells is the negative charge on the inside or outsode of the cell?
Inside
111
What is the resting membrane potential?
-70mV
| between -40 to -90mV
112
At resting membrane potential are voltage-gated sodium and potassium channels open or closed?
Closed
113
At what voltage do the voltage-gated sodium channels open and cause membrane depolarisation?
-55mV
114
How is an action potential generated?
1) Resting membrane potential at -70mV (voltage-gated sodium and potassium channels are closed)
2) Stimulus causes a small amount of sodium ion influx into the neurone until it reaches -55mV
3) At -55mV voltage-gated sodium channels open causing depolarisation of the membrane to +40mV
4) At +40mV voltage-gated potassium channels open cause K+ efflux from the cell
5) Hyperpolarisation then occurs to around -75mV
6) Voltage-gated channels then close and Na+K+ pumps return the membrane to resting potential
115
What is a graded potential?
Membrane depolarisation which is not sufficient to create an action potential
116
What are the small gaps in the myelin sheath along an axon called?
Nodes of Ranvier
117
How does an axon synapse function?
1) Once the action potential has travelled along the presynaptic neurone it reaches the presynaptic terminal and causes voltage-gated calcium channels to open
2) There is an influx of calcium which allows synaptic vesicles containing neurotransmitter to fuse with the plasma membrane of the presynaptic neurone and release the neurotransmitter into the synpatic cleft.
3) The neurotransmitter binds to receptors on the post-synaptic neurone membrane. These receptors modulate postsynaptic activity
4) The neurotransmitter then dissociated from the receptor and is recycled by transporter proteins or metabolised by enzymes in the synaptic cleft
118
What are the names of the two types of muscles that form a pair to produce movement?
Flexor
| Extensor
119
What is a concentric isotonic contraction?
Muscle tension rises to meet the resistance, then remains the same as the muscle shortens (think bicep curl bending arm up)
120
What is an eccentric isotonic contraction?
The muscle lengthens due to the resistance being greater than the force the muscle is producing (think releasing a bicep curl)
121
What is an isometric contraction?
Tension develops in the muscle but the muscle does not change length (think holding a weight in bent arm but not moving it)
122
What cells are skeletal muscles made up of?
Myofibres
123
Describe myofibres
Large and cylindrical
Multinucleate
Packed with myofibrils
124
Describe myofibrils and the bands that make them up
Light and dark bands giving them a 'striated' appearance
A-band: dark bands, intersected by darker H-zone
I-band: light bands intersected by dark Z-line
Sarcomere: Functional unit of muscle- lies between two Z-lines
125
What is a sarcomere?
The functional unit of muscle that lies between two Z-lines
126
What makes up the Z-line?
α-actinin
| CapZ
127
What initiates muscle contraction?
Increased cytosolic calcium concentration
128
Is cytosolic calcium in skeletal muscle cells low or high?
Low
129
How to skeletal muscle cells maintain low cytosolic calcium?
The Ca2+ATPase pump
130
What happens in excitation-contraction coupling in skeletal muscle?
Excitation
1) Action potential propagates along myofibre membrane (sarcolemma) and through the T-tubule system
2)The action potential activates the dihydropyridine receptors located on the T-tubule membrane and causes a conformational change which causes ryanodine receptors (RyRs) to open
3) RyRs are located on the membrane of the sarcoplasmic reticulum (SR) and when they open a Ca2+ efflux occurs from SR to myofibre from intracellular stores
Contraction
4) The rise in Ca2+ within the myofibre initiates contraction
5) Ca2+ binds to trophonin on actin fibres
6) This causes movement of tropomyosin allowing myosin heads to bind to actin
7) ADP phosphorylation causes myosin head pivots ('power stroke') which pulls the actin filaments towards the centre of the sarcomere
8) ATP hydrolysis then 'recharges' the myosin head
131
What proteins make up the sarcomere? (7)
```
Actin
Myosin
Titin
Nebulin
Tropomysin
CapZ
Tropomodulin
```
132
What is the structure of actin?
Two twisted α-helices
133
What is the role of titin in the sarcomere?
Very large 'spring-like' filaments anchoring myosin to the Z-line
134
What protein holds myosin in place in the sarcomere?
Titin
135
What proteins are associated with actin in the sarcomere?
```
Tropomyosin
Troponin
Nebulin
CapZ
Tropomodulin
```
136
What is the sliding filament theory?
1) After Ca2+ has been released into the myofibre it binds with troponin which causes tropomyosin to move, exposing the myosin binding site on actin.
2) Myosin binds to ATP and breaks it down to ADP + Pi (but this remains attached). Myosin then uses the energy from this to bind to actin and perform a 'power stroke', pulling the actin filament towards the centre of the sarcomere
3) Myosin then releases the ADP + Pi and is then able to bind a new ATP molecule
4) Once it has bound to a new ATP molecule myosin releases actin and is 'recharged'
137
What is the function of intercalated disks in cardiac muscle?
Specialised regions connecting individual cardiomyocytes so all cells can work at the same time.
Contain numerous gap junctions which allow action potentials to spread rapidly from cell to cell
138
How does the mechanism of contraction differ in skeletal and cardiac muscle?
It is the same
139
What receptor is initially activated by the action potential in skeletal muscle?
Dihydropyridine receptors
140
What receptor is initially activated by the action potential in cardiac muscle?
Voltage-gated calcium channels
141
What is the name for cardiac muscle cells?
Cardiomyocytes
142
What type of muscle is cardiac muscle?
Striated muscle
143
What three effects does calcium have in cardiomyocytes?
1) Causes further depolarisation
2) Binds to troponin (initiates contraction)
Causes Ca2+ induced Ca2+ release (CICR) by binding to ryanodine receptors on the sarcoplasmic reticulum
144
Where do you find smooth muscle in the body?
Present in the walls of all hollow organs (e.g. blood vessels, GI tract)
145
Explain the process of excitation-contraction coupling in smooth muscle
1) Depolarisation activates voltage-gated calcium channels
2) Ca2+-CaM complex forms which activates myosin light-chain kinase (MLCK)
3) MLCK phosphorylates myosin light chains (MLC20)
4) This forms cross-bridges with actin filaments which causes a contraction
146
What is toxic epidermonecrolysis?
A drug reaction which causes the epidermis to apoptose
147
What are the functions of the skin? (8)
1) Protect against injury
2) Protect against pathogenic organisms
3) Waterproofing and fluid conservation
4) Thermoregulation
5) Protection against radiation (absorption of UV and vit D production)
6) Surface for grip
7) Sensory organ
8) Cosmetic
148
What are the layers of the skin? (3/4)
Epidermis, dermis, subcutis (fat and fascia)
149
What are the apendigeal structures of the skin?
```
Pilosebaceous unit (follicle, hair shaft, sebaceous gland and pilo erecti muscle)
Sweat glands (apocrine and eccrine)
```
150
What cells does the epidermis consist of?
Keratinocytes
151
What are the four layers of the epidermis?
Stratum corneum (top)
Stratum granulosum
Stratum spinosum
Stratum basale (nearest dermis)
152
What cells, other than keratinocytes, are found in the epidermis, and what are their functions?
Melanocyte: involved in production of melanin
Langerhans cell: antigen presenting cell
Merkel cell: involved in sensation
153
What are the four stages of development of a keratinocyte?
Basal cell
Prickle cell
Granular cell
Keratin
154
What mutation is common in eczema patients? What sign is common with this mutation?
Filagrin gene mutation
| Palmar hyperlinearity is a common sign
155
Defects in what layer of the skin lead to eczema?
Stratum corneum
156
Where does the epidermis attach to the dermis?
In the dermo-epidermal junction (basement membrane zone)
157
What attaches the epidermis to the dermis?
Hemi-desmosomes, anchoring plaques and proteins
158
What constitutes the dermis?
Supportive connective tissue consisting of collage, elastin and glycosaminoglycans
159
What is the thickness of the dermis?
0.1mm to 3mm
160
What cells synthesise collagen, elastin and glycosaminoglycans in the dermis?
Fibroblasts
161
What immune cells are found in the dermis?
Dermal dendritic cells and other immune competant cells
162
What is the subcutaneous layer made up of?
Connective tissue and fat
163
What are melanocytes? Where are they found?
Melanocytes are dendritic cells located in the basal layer of the epidermis
164
In melanocytes, what organelles are melanin produced in?
Melanosomes
165
How is melanin transferred to keratinocytes and how does it protect cells?
Melanin is packaged into granules which move down the dendritic processes in melanocytes and are transferred to adjacent keratinocytes by phagocytosis.
The melanin granules form a protective cap around the keratinocyte nuclei- protects DNA from UV damage
166
What frequency of UV radiation stimulates melanocytes to product more melanin?
1) 230-260nm
2) 260-290nm
3) 290-320nm
4) 320-350nm
3) 290-320nm
167
Is variation in racial skin pigmentation caused by differences in melanocyte number or from a differing number and size of melanosomes produced?
A differing number and size of melanosomes produced
168
Where is hair follicle density greatest of the body?
Face
169
What are the functions of the hair? (4)
1) Protection (UV, injury, eyelashes)
2) Sensation (hairs have sensory innovation)
3) Thermoregulation (minimal in humans)
4) Communication/ sexual attraction
170
What are the three types of hair?
1) Lanugo
2) Vellus
3) Terminal
171
What is the structure of lanugo hair, where is it found?
Fine and long
Seen in foetus at 20 weeks- shed before birth
Occurs in anorexia
172
What is the structure and location of vellus hair?
Short, fine and light coloured
| Covers most of the body
173
What is the structure of terminal hair, where is it found, how does it originate?
Long, thicker and darker
Scalp, eyebrows, eyelashes, pubic, axillary, beard
Originates as vellus hair, differentiation is stimulated at puberty by androgens
174
What muscle in the skin contracts with cold, fear or emotion to erect the hair and produce 'goose pimples'?
Arrector pili muscles
175
What do seaceous glands produce?
Sebum
176
What is the portion of hair above the sebaceous duct called?
Infundibulum
177
What is the structure of a termial hair?
Inner medulla
Cortex- packed keratinocytes
Outer cuticle
178
What is the growing phase of hair called?
Anagen
179
What are the phases of hair growth?
Anagen
Catagen
Telogen
180
How long is anagen and what percentage of hair is in this phase at one time?
3-7 years for scalp
4 months for eyebrows
80-90% of scalp hair are in anagen
181
How long is catagen and what percentage of hair is in this phase at one time?
3-4 weeks
| 10-20% of scalp hair are in catagen
182
What percentage of hair is in telogen at one time?
50-100 hairs shed per day
183
What occurs in catagen?
The resting phase of hair growth
Hair protein synthesis stops
Follicle retreats towards the surface
184
What occurs in telogen?
The shedding phase of hair growth
| Presence of hairs with a short club root
185
What is the nail? What is it's function?
A plate of hardened and densely packed keratin
| Protects the finger or toe tip and facilitates grasping and tactile sensitivity in the finger/toe pulp
186
What is the lunula?
The visible part of the nail matrix
187
What is the hyponychium?
The thickened epidermis that underlies the free margin of the nail
188
Why do cells need to communicate with each other? (4)
1) Process information (sensory stimuli)
2) Self preservation (identify danger-take action: reflexes
3) Voluntary movement; getting from A to B, completing daily tasks)
4) Homeostasis (thermoregulation, glucose)
189
What physiological response occurs to hypoglycaemia? (2)
Glycogenolysis
| Gluconeogenesis
190
What hormone stimulates a response to hypoglycaemia? What is the process that occurs?
Glucagon
Secreted by α-cells of islets of Langerhans (in pancreas) travels out in blood vessels to the liver to stimulate glycogenolysis and gluconeogenesis
191
What cells release glucagon in the islets of Langerhans?
α-cells
192
What is the physiological response to hyperglycaemia?
Glucose uptake
Reduced glycogenolysis
Reduced gluconeogenesis
193
What hormone stimulates a response to hyperglycaemia? What is the process that occurs?
Insulin
Secreted by β-cells in the islets of Langerhans.
Has a paracrine (nearby cells) effect: inhibiting glucagon secretion and endocrine effect on the liver
194
What are the types of cellular communication? (4)
Endocrine
Paracrine
Autocrine
Membrane attached proteins
195
What is the process of signalling between membrane-attached proteins in e.g. Hepatitis C?
1) Hep C detected in blood stream by antigen presenting cell (APC)
2) APC digests pathogen- expresses MHC class II molecule on surface
3) Circulating T-lymphocyte engages with MHC molecule through TCR interaction
196
What protein do CD4 receptors on T lymphocytes interact with in HIV?
GP120 glycoprotein
197
Bacterial cell wall components are detected by what haematopoietic cell receptor?
Toll-like receptors
198
```
What type of signalling does adrenaline produce?
Endocrine
Paracrine
Membrane-attached proteins
Autocrine
```
Endocrine
199
```
What type of signalling does bacterial cell wall components produce when they bind to haematopoietic cells?
Endocrine
Paracrine
Membrane-attached proteins
Autocrine
```
Membrane-attached proteins
200
```
What type of signalling does endothelin-1 (made by endothelial cells) produce?
Endocrine
Paracrine
Membrane-attached proteins
Autocrine
```
Paracrine
201
```
What type of signalling does acetylcholine produce?
Endocrine
Paracrine
Membrane-attached proteins
Autocrine
```
Autocrine
202
What enzyme metabolises acetylcholine for recycling?
Cholinesterase
203
What activates an ionotropic receptor? What passes through it? Give two examples
Ligand binding opens ion-permeable pore traversing the membrane. Ions with a certain charge can pass through
e.g. Nicotinic Acetylcholine, GABAa
204
How many times does a G-protein coupled receptor traverse the membrane?
7 times
205
What activates a G-protein coupled receptor? What occurs when it binds?
Ligand binding
| Activates intracellular G-protein
206
What are the signal transduction events of a G-protein coupled receptor?
1) Receptor and G-protein are inactive
2) Ligand binding= conformational change of receptor
3) G-protein bound to the receptor exchanges GDP for a GTP
4) G-protein dissociates into two active components that bind to their target proteins:
α-subunit- with attached GTP
βγ-subunit
5) α-subunit dephosphorylates GTP to GDP
6) α-subunit dissociates from target protein (now inactive)
7) Receptor remains active as long as ligand is bound
207
What is the nicotinic acetylcholine receptor involved in?
Skeletal muscle contraction
208
What is the GABAa receptor important for?
Reducing neuronal excitibility
209
Give three examples of physiological processes regulated by G-protein coupled receptors
1) β1-adrenergic receptor- stimulates adenyl cyclase
Converts ATP to cAMP. cAMP activates PKA
2) M2-muscarinic receptor- inhibits adenyl cyclase
Reduces levels of PKA
3) AT-1 angiotensin receptor- stimulates phospholipase C
Converts PIP2 to IP3 and DAG. IP3 stimulates CA2+ release. DAG activates PKC
210
What binds extracellularly and intracellularly to G-protein coupled receptors?
Extracellularly: Ligand
Intracellularly: G-protein
211
What is the most common enzyme inside the membrane in enzyme-linked receptors?
Tyrosine kinase
212
What is the enzyme-linked reeceptor mechanism of action?
1) Ligand binding causes receptor clustering
2) Clustering activates enzyme activity
3) Cross phosphorylation occurs of enzyme on receptor
4) Signalling proteins bind to enzymes in the cytoplasmic domain
5) Signalling proteins recruit other signalling proteins- a signal is generated in the cell
213
Give 4 examples of enzyme-linked receptors, their ligand and physiological effect
1) Insulin receptor (CD220 antigen), ligand= insulin, effect= glucose uptake
2) ErbB receptor, ligand= epidermal growth factor/ transofrming growth factor β, effect= tumour genesis
3) Guanylyl-cyclase linked receptors (NPRA), ligand= atrial/ brain natriuretic peptide, effect= vasodilation, ↓ blood pressure
4) Ser/Thr-kinase linked receptors (TβR1), ligand= TGFβ, effect= apoptosis
214
What are the two types of intracellular receptor?
Cytoplasmic and nuclear
215
Explain the mechanism of cytoplasmic intracellular receptor action
1) Located within the cytosolic compartment
2) Associated with chaperone molecules (heat shock proteins, hsp)
3) Hormone binds to receptor and hsp dissociates
4) Two hormone bound receptors form a homodimer
5) Homodimer translocates to the nucleus and binds to DNA
216
Explain the mechanism of nuclear intracellular receptor action
1) Located within the nucleus
| 2) Hormone ligand binds and causes transcriptional regulation
217
What activates intracellular receptors?
Chemical messangers that are able to cross the cell membrane (e.g. steroid hormones)
218
What effect do intracellular receptors usually have?
Alter protein synthesis
219
Give two examples of intracellular receptor, it's ligand, the physiological effect and agonist?
1) Glucocorticoid receptor, ligand= cortisol and corticosterone, effect= ↓ immune response, ↑ gluconeogenesis, agonist= glucocorticoids
2) Thyroid hormone receptor, ligand= thyroxine (T4), triiodothyronine (T3), effect= growth and development, agonists= thyroid hormones
