Physiology Flashcards
(148 cards)
1
Q
What are the four types of receptors?
A
Ligand Gated
G protein coupled
Tyrosine-kinase
Nuclear
2
Q
What agonists work on ligand gated ion channels/
A
Neurotransmitter
Hormones
3
Q
What is the difference between a neurotransmitter and a hormone?
A
They can be the same substance, neurotransmitters are released across synapse from a nerve.
4
Q
What occurs after agonist binds to the ion channel?
A
Conformational change in structure.
Ions allowed to pass through membrane.
5
Q
How quick is the response in ligand gated ion channels?
A
Milliseconds
6
Q
How quick is the response in G protein coupled receptors?
A
Seconds
7
Q
In a G protein coupled receptor describe the structure of the G proteins?
A
Alpha subunit attached to a GDP
Beta and Gamma subunits bound in a dimer
8
Q
In B2 adrenoreceptor what. type of G protein is present?
A
Gs alpha
9
Q
Upon binding of adrenaline to B2 adrenoreceptor what occurs?
A
Conformational change of the receptor.
GDP is swapped for charged GTP on the alpha subunit.
Alpha subunit breaks away and binds to adenyl cyclase
10
Q
What does adenyl cyclase do?
A
Converts ATP to cAMP
11
Q
What is cAMP?
A
A cell signalling molecule?
12
Q
In B2 adrenoreceptors what does an increase intracellular cAMP do?
A
PKA is activated
Inhibits MLCK activity
Bronchodilation
13
Q
In G coupled protein receptors why does the reaction stop?
A
Weak bond between agonist and receptor.
GTP is hydrolysed breaking bond between alpha submit and adenyl cyclase
14
Q
In A2 adrenoreceptors what is the difference in adenyl cyclase?
A
Adenyl Cyclase is active before activation
15
Q
What G protein alpha subunit is present in A2 adrenoreceptors?
A
Gi (Inhibits)
16
Q
What occurs after agonistic binding to receptor in A2 adrenoreceptors?
Alpha subunit only
A
Alpha subunit is activated by GTP.
B
Alpha subunit binds to adenyl cyclase inhibiting it.
17
Q
What occurs after agonistic binding to receptor in A2 adrenoreceptors?
Beta and Gamma subunits only
A
The dimer binds to K+ channels
Cell membrane becomes hyperpolarized
18
Q
What is the resultant action upon A2 adrenoreceptor activation?
A
Smooth muscle relaxation especially in GI tract
19
Q
In alpha 1 adrenoreceptors what G subunit is present
A
Gq
20
Q
What does the activated alpha subunit do in A1 adrenoreceptors?
A
Activates phospholipase C
21
Q
What is the function of phospholipase C in regards to A1 adrenoreceptors?
A
Converts PIP2 into DAG and IP3
22
Q
What does an increase in intracellular DAG and IP3 result in?
A
Increase in intracellular Ca2+
Vasoconstriction
23
Q
Where are A1 adrenorecpetors commonly present?
A
Within the vasculature
24
Q
In regards to G coupled reactions what kind of response do they evoke?
A
Amplification a large reaction from smaller stimuli
25
In regards to Tyrosine Kinase what kind of response do they evoke?
Divergent reaction, lots of different responses from the same stimuli.
26
What are the agonists of tyrosine kinase receptors?
Hormones e.g. insulin
27
What is the structure of a tyrosine kinase receptor?
They are a dimer
28
Upon binding of the agonist to the tyrosine kinase receptor what occurs?
It undergoes a conformational change bringing the two pieces together.
Intracellular tyrosine molecules are activated by ATP (phosphorylated)
Relay proteins bind to tyrosine triggering different cellular responses.
29
What are relay proteins?
These are individual proteins which bind to the tyrosine molecules present on the intracellular extension of the receptor, each one triggers a different response within the cell.
30
How long is the response in tyrosine kinase receptors?
Up to a few hours
31
How many folds pass across the membrane in a G protein coupled receptor?
7 times
32
Autocrine regulation
Self limiting
| Chemical released by the cell bind to receptors on the same cell
33
Example of autocrine regulation
Somatostatin released from D cells
34
Paracrine regulation
Chemicals released by cell bind to receptors on cells located proximally
35
Example of paracrine regulation
Somatostatin released by D cells binds to parietal cells to inhibit release of HCL
Both located in stomach
36
How is endocrine regulation divided?
Negative and positive feedback
37
Endocrine Regulation
Chemicals released by cells into the circulatory system where they travel and bind to receptors on target cells.
38
Example of endocrine regulation
Insulin released by B cell in pancreas and target cells in liver.
39
Negative feedback
Primary Mechanism of maintaining homeostasis by resisting fluctuations away from physiological set point.
40
Positive feedback
Initial stimuli initiates a response which exaggerates the initial change
41
Examples of positive feedback
Oxytocin in childbirth
| Blood clot cascade
42
What makes up intrinsic regulation?
Autocrine and Paracrine
43
What makes up extrinsic regulation?
Nervous system and endocrine
44
Example of negative feedback ?
Cortisol stress cycle
| Cortisol is the final product but high levels of cortisol inhibits ACTH and CRh production all of which are precursors.
45
What is the function of GLUT2 receptors?
Censorship of blood glucose levels
| Allows diffusion of glucose into the B cells in the pancrease.
46
What enzyme is responsible for monitoring blood glucose and how does it complete its function?
Glucokinase
An enzyme responsible for glycolysis
Increased glucose increases ATP conc
47
As a result of high ATP levels in the B cells due to high glucose levels what happens?
ATP sensitive K+ channels close
Voltage Gated Ca 2+ channels open
Excretion of insulin via exocytosis
48
What is the structure of insulin?
Polypeptide dimer held together by disulphide bridges
49
How is insulin produced then activated
Produced in RER of B cell
| Cleaved to form active form
50
What can be used to monitor inulin production?
C protein
| A by product of the cleaving of insulin to form active enzyme
51
Describe insulin release
Its biphasic
1st phase is dependant on dose larger dose = larger spike
2nd phase smaller as vesicles need to be prepared
52
What is the 1st phase of insulin release called?
Readily Released Pool
| Insulin already packaged in active vesicles so quick response
53
In type II diabetes what happens to the phases?
They weaken and flatten
54
Why in type II diabetes does the pattern of release change?
As glucokinase activity is downregulated
55
Why in type II if enough weight is lost can they symptoms of diabetes disappear?
As B cells still producing insulin however, Blood glucose concentration is higher than the KM of glucokinase so its working at capacity basically.
By loosing weight glucose conc can be brought below KM of glucokinase.
56
What kind of receptor are the ATP sensitive K+ channels?
Inward rectifier - ion channel
Contain a sulphonylurea receptor - regulatory unit
Octomeric structure - 8 subunits
57
What is the function of K+ ATP channels and what stimulates them?
They inhibit insulin release by preventing Ca2+ entry
| Diazoxide
58
What are the two main thyroid hormones?
T4 and T3
59
What is T3
Tri-iodothyronine
60
What is T4
Thyroxine
61
What is the basic functional unit of the thyroid?
Follicle
62
What makes up a follicle?
Colloid surrounded by cuboidal follicular cells
63
What is dispersed between follicles?
Parafollicular cells or C-cells
| Neuroendocrine cells
64
What do C - cells excrete?
Calcitonin
65
What is the function of calcitonin?
Reduces blood calcium by opposing the action of parathyroid hormone
66
What do follicular cells produce?
Thyroglobulin
67
What is thyroglobulin?
Tyrosine packed full of proteins
68
What occurs within the follicular cells before formation of MIT and DIT?
Uptake and concentration of Iodide I-
Oxidation of Iodide I- to iodine I
Iodination of Thyroglobulin
69
What is MIT
Mono-iodotyrosine unit
| Tyrosine bound to 1 unit of iodine
70
What is DIT
Di-iodotyrosine unit
| Tyrosine bound to 2 units of iodine
71
How is T3 formed?
MIT + DIT
Mono + Di
1 iodine units + 2 iodine units = Tri-iodotyronine
72
How is T4 formed?
DIT + DIT
Di + Di
2 iodine units + 2 iodine units = Thyroxine
73
When synthesised where are T3 and T4 stored?
They are stored within the colloid thyroglobulin
74
What percentage of thyroid hormone produced T4?
90%
75
Which is the most potent thyroid hormone?
T3 is 4x more potent than T4
76
Where is T4 converted into T3?
Liver and the kidney
77
What is cycle leading to T3 and T4 secretion?
Hypothalamus stimulates pituitary gland
Anterior pituitary gland secretes Thyroid stimulating hormone
TSH causes stored T3 and T4 to be secreted
78
What does excess free T3 and T4 trigger?
Negative feedback
| Inhibits at the hypothalamus and pituitary
79
What hormones are secreted by the anterior pituitary?
```
Growth Hormone GH
Thyroid stimulating Hormone TSH
Adrenocorticotropic Hormone ACTH
Follicle Stimulating Hormone FSH
Prolactin PRL
Luteinizing Hormone LH
```
80
Where do the majority of thyroid hormones find themselves bound to in transport?
Serum proteins
81
What serum proteins are relevant in thyroid hormone transport?
Thyroxine binding globulin. TBG 70%
Thyroxine binding pre albumin TBPA 20%
Albumin 8%
82
How else can thyroid hormones be transported?
Free within the blood
83
In what form can thyroid hormones enter the cells?
Only when free and unbound
84
What % of T3 is unbound?
0.33%
85
What percentage of T4 id unbound?
0.015%
86
Why does T3 have a more rapid onset of action?
As it is less avidly bound by TBG and TBPA than T4
87
What are some affects of thyroid hormones
Increased Metabolic rate and glucose uptake
Increased Glycogenolysis and Gluconeogenesis
Increased lipolysis
Decreased Gylcogenesis and lipogenesis
Increase breathing, heart rate and force of contraction
88
What is the metabolic affect of hyperthyroidism?
Increased number and size of mitochondria
Increased oxygen use and ATP hydrolysis
Increased synthesis of respiratory chain enzymes
89
What percentage of patients with hyperthyroidism have heat intolerance?
30%
90
What is the affect of hypothyroidism on growth?
Stunted growth
91
Why does hypothyroidism result in stunted growth?
As thyroid hormones required for growth hormone releasing hormone production and secretion
92
What are the three types of thyroid hormone degrading enzymes?
D1
D2
D3
93
Where is D1 found?
Found within the liver and kidneys
94
Where is D2 found?
```
Found in : Heart
Skeletal Muscle
CNS
Thyroid
Pituitary
```
95
Where is D3 found?
Foetal placenta and brain
96
What is the main function of thyroid hormone degrading enzymes?
Conversion of T4 into the more metabolically active T3
97
What does the thyroid usually weigh?
15-25g
98
Where does the thyroid hormone originate from?
Foramen caecum
99
From what week does the thyroid develop
4th week
100
Where does the thyroid descend down?
Thyroglossal duct
| Descends past the larynx
101
Where do the c cells originate from?
Originate around area where thyroid descends to
102
Where should thyroid be found?
C5 level of thyroid cartilage
| T1 Fifth tracheal ring
103
What hormones are produced in the anterior pituitary?
```
ACTH
TSH
GH
Prolactin
FSH
LH
```
104
What hormones are stored in the posterior pituitary?
ADH
| Oxytocin
105
Where are hormones stored in the posterior pituitary produced?
Hypothalamus
106
What are the precursor hormones for Cortisol?
CRH (hypothalamus)
ACTH (Pituitary)
Cortisol (Adrenal glands)
107
What are the precursor hormones for testosterone?
GnRH (Hypothalamus)
LH FSH (Pituitary)
Testosterone (Testes)
108
What are the precursor hormones for growth hormone?
GHRH (Hypothalamus)
| GH (Pituitary)
109
What is different about Prolactin?
Dopamine inhibits Prolactin
110
What are the precursor enzymes for thyroxine?
Thyrotropin Releasing Hormone (Hypothalamus)
Thyrotropin TSH (Pituitary)
Thyroxine (Thyroid)
111
How does the hypothalamus communicate with the anterior pituitary?
Portal system hormones travel within the blood
112
How does the hypothalamus communicate with the posterior system?
Hormones travel down nerves within axoplasm
113
What is the paired hormone of ACTH?
Cortisol
114
What is the paired hormone of TSH?
Thyroxine
115
What is the paired hormone of LH/FSH?
Testosterone or Estradiol
116
What is the paired hormone of GH?
IGF-1
| Insulin like Growth Factor 1
117
Which nerves run close to the pituitary that control eye movement?
3
4
6
118
Which branches of which nerve run close to the pituitary?
5 Facial Nerve
Ophthalmic division
Maxillary division
119
What nerve makes up the optic chiasm?
2 Optic
120
What are the two types of dynamic test?
Too much - test suppresses hormone
| Too little - test stimulates hormone
121
In a normal patient how should they react to a dynamic test for too much hormone?
levels of the hormone should drop
122
In a normal patient how should they react to a dynamic test for too little hormone?
Levels of hormone should rise
123
Give an example of a too little test used in measuring cortisol level ?
Insulin stress test
IV insulin given to induce a hypoglycaemic event
Cortisol and GH levels should rise
124
Give an example of a too much test used in measuring cortisol level test?
SynACTHen test
IV synthetic ACTH
Cortisol levels measured at 0, 30, 60 mins
125
In the synACTHen test how should the cortisol levels change?
Should rise by 150 and reach around 500 in a healthy patient.
126
Where is the anterior pituitary derived from?
Rathkes pouch
127
What is the posterior pituitary?
Extension of neuronal tissue formed from modified glial cells and axonal bodies.
128
What cells secrete GH?
Somatotroph
129
What cells secrete PRL?
Mammotrophs
130
What cells secrete ACTH?
Corticotrophs
131
What cells secrete TSH?
Thyrotrophs
132
What cells secrete FSH and LSH?
Gonadotrophs
133
What three zones make up the adrenal cortex?
Glomerulose
Fasciculata
Reticularis
134
What is produced in the glomerulose layer?
Mineralocrticoids
135
What is produced in the fasciculata?
Glucocorticoids
136
What is produced in the Reticularis?
Adrenal androgens
137
What makes up the medullary zone?
Chromaffin cells
Medullary veins
Splanchnic nerves
138
What does the medullary zone produce?
Catelcholamines
139
What is th starting point for all steroid synthesis?
Cholesterol
140
Under what control is aldosterone under?
Renin-angiotensin system
141
What is released when a low blood pressure is detected in the kidneys?
Renin
142
What is the function of renin?
Fist step in the cycle
| Converts Angiotensinogen to Angiotensin 1
143
What enzyme is responsible for the second step in the renin angiotensin system?
ACE
| Converts Angiotensin I in II
144
What is the third and final step in the Renin angiotensin cycle?
Angiotensin II causes aldosterone to be released by the adrenal glands
145
What is the function of aldosterone ?
Causes Reabsorption of Sodium and water.
| Increases blood volume and in turn BP.
146
As well as acting as a triggering the release of Aldosterone what other affect does Angiotensin II have?
Causes vasoconstriction
Increases systemic resistance
Increasing BP
147
Where are mineralocorticoid receptors mainly located?
Kidney
Salivary Gland
Gut
Sweat Glands
148
What is the main role of mineralocorticoids?
Regulates BP extracellular volume and Na+ retention
