Endocrine system I Flashcards
(39 cards)
1
Q
Analysis of body composition
A
- 6%: minerals, hormones, vitamins, neurotransmitters
- 60%: liquid
- 18%: protein
- 16%: fat
2
Q
Intercellular communication
A
- despite the vast extent of the communication network requires, there are only a few mechnisms for communication
3
Q
Direct communication
A
via gap junctions or direct linkup of cell surface markers
4
Q
Indirect communication
A
via an assortment of chemical messengers or signal molecules
e.g. paracrine, neurotransmitters, hormones, neurohormones
5
Q
Direct communication via gap junctions
A
- gap junctions link adjacent cells together
- connexons form channels that link the cytosol of adjacent cells permitting transfer of ions between the two cells
- e.g. where gap junctions are crucial to survival is in the heart
6
Q
Direct linkup of cell surface markers
A
- complementary surface markers = surface receptors
- e.g. to activate an immune cell
7
Q
Indirect chemical messengers or signal molecules
A
- secretory cell released chemical messenger into EFC
- messenger binds to specfic receptor on the ‘target’ cell
- binding of messenger to receptor triggers a response in the target cell
8
Q
Paracrines (local)
e.g. (3)
A
- local chemical messengers
- exert effect only on neighbouring cells in immediate environment of secreiton site - secreted by once cell and diffuse to nearby target cell
Histamine: released in damaged tissue and causes inflammatory response
Epidermal growth factor: stimulates cell division
Vascular endothelial growth factor: stimulates growth and branching of blood vessels
9
Q
Autocrines (self)
e.g. (1)
A
- bind to receptors and exert their effects on the same cell that secreted them
- often autocrines also function as a paracrine or other messenger
e. g. growth factor
10
Q
Cytokines
A
- secreted by cells of the immune system
- e.g. interleukins and interferons = groups of small proteins released from white blood cells
11
Q
Neurotransmitters
E.g. (3)
A
- released from neurons to axon terminal
- short range chemical messengers
- diffuse across narrow space to act locally on adjoining target cells = synpatic signalling (another neuron, a muscle or a gland)
- released from axon terminals of nerves
- E.g. acetylcholine: involved in triggering contractions of skeletal muscle
Dopamine: precursor of norepinephrine
Serotonin: especially active in constricint smooth muscles, contributing to wellbeing and happiness
12
Q
Hormones
A
- Long range chemical messengers
- secreted by endocrine glands into the blood
- exert effect on target cells some distance away from release sight
13
Q
Endocrinology
A
study of hormones and endocrine organs
14
Q
Hormones II
A
- represent a very small percentage of the body
- effects exerted at very low concentrations
- chemical messengers secreted directly into the blood
- circulatory syste, transports them to distant target organs
- hormones bind to cell receptors and trigger a response
- same hormone can cause different responses in different cell types
- acts with nervous system to coordinate and integrate activity of body cells
- responses slower but longer lasting than nervous system responses
15
Q
Endorcrine system controls and integrates
A
- maintenance of electrolyte, water and nutrient balance of blood. e.g. in kidney
- regulation of cellular metabolism and energy balance e.g. insulin
- growith and development e.g. growth hormone
- mobilisation of body defences e.g. histamine
- reproduction e.g. testosterone
16
Q
Exocrine glands
A
- produce non-hormonal substances
- have ducts to carry secretion to membrane surface
- e.g. sebaceous glands, salivary glands
17
Q
Endocrine glands
A
- typically have a rich vascular and lymphatic drainage for rapid dispersal of hormones throughout body
- produce hormones
- lack ducts (secretion into blood)
- e.g. pituitary, thyroid gland
18
Q
Example of endocrine and hormones
A
- Pituitary gland: FSH, LH, prolactin, GH
- Thyroid gland: thyroid hormones, calcitonin
- Parathyroid gland: parathyroid hormones
- adrenal glands: aldosterone, cortisol, epinephrine, norepinephrine
- pineal glands: melatonin
- gonads: ovaries and testes: progesterone, oestrogen, testosterone
19
Q
Combines exocrine and endocrine
A
- hypothalamus is neuroendocrine organ
- some have exocrine and endocrine functions (pancreas, gonads, placenta)
- other tissues and organs that produce hormones
- adipose cells, thymus and cell inwalls of small intestine, stomach, kindneys and heart
20
Q
Mechanism of hormone action
A
- for hormones to exert their effects, they must bind to a specifc receptor
- target cell receptors are located outside the cell in/ on the cell membrane, in the cytosol or in the nucleus
- receptors bind ligands (hormoens) -> then translate ‘message’ of signal ligand into a cellular response = cell signalling
21
Q
Cell signalling usually involves
A
- activation of transcriptio factors in the nucleus of the cell -> increased production of proteins and other substances
- activate or deactivate enzymes
- induce secretory activity
- stimulate mitosis
22
Q
Receptors and their regulation
A
- the amount of receptors on target tissues is not static
- amount of hormones can influence number of receptors for that hormone
23
Q
Upregulation of receptors
A
Number of receptors increases on the target cell when hormone levels are low
24
Q
Down regulation of receptors
A
Number of receptors decreases on the target cell when hormone levels are high
de-sensitised the target cells to prevent them from overreacting to persisttently high levels of hormones
25
Hormone release
- blood levels of hormones
- controlled by negative feedback systems
- increased hormone effects on target organs can inhibit further release
- levels vary only within narrow, desirable range
26
Hormone release is triggered by
Endocrine gland stimuli
| Nervous system modulation
27
Control of endocrine activity
When hormone concentrations are either too high or too low -> disease -> precise control circulating concentraton of hormones is crucial
the concentration of hormone as seen by target cells is determined by 3 factors
28
Rate of production
- synthesis and secretion of hormones are the most highly regulated aspect of endocrine control
- control mediated by positive and negative feedback circuits
29
Rate of delivery
an example of this effects if blood flow to a target organ or group of target cells - high flow delivers more hormone than low blood flow
30
Rate of degradation and elimination
hormones, like all biomolecules, have characteristics rates of decay -> metabolised and excreted from the body through several routes
Shutting off secretion of a hormone that has a very short half-life causes circulating hormone concentration to plummet
- if a hormone's biological half-life is long, effective concentrations persist for some time after secretion ceases
31
Mechanisem of hormone action
- in most cases, cells release chemical messnegers to casue an effect on a nearby target cell
- hormones have the advantage of being transported in the blood
- secretion of hormones can occur in two ways bases on their solubility properties
Dissolved in the blood (hydrophilic messenger, highly water soluble, low lipid solubility)
Attached to a carrer protein (hydrophobic messenger, high lipid solubility, low water solubility)
32
Mechanisms of hormone action
- lipophilic hormones diffuse across cell membrane and bind to cytosolic or nuclear receptors
- lipophobic hormones bind to cell membrane receptor
- binding of hormone to intracellular receptor leads to hormone response element int the mucleus, altering gene expression
33
Surface receptors
- binding of extracellular messenger to matching receptor leads to response by:
1. opening or closing of channels
2. activating receptor enzymes
3. activating second messenger systems
34
the 3 types of cell surface receptors
- different types of cell surface receptors can result in different outcomes:
1. channel linked receptors
2. enzyme linked receptors
3. G-protein linked receptors
35
Opening or closing of channels
- channel linked receptors
- involved in rapid signalling/electrical transmission
- neurons have a cation linked receptor
36
Activating receptor enzymes
- enzyme linked receptors
- most common are tyrosine kinases
- hormones and growth factors bind to receptor, causing intracellular signalling to occur (e.g. insulin)
37
Activating second messenger systems
- activation of second messenger pathway via G protein coupled receptors
- G protein linked receptors
- odorant molecules, hormones and neurotransmitters
- cause cAMP signalling or PI singalling (e.g. epinephrine, ADH)
38
Amplication of signal
very little messenger necessary to bind target ce;; and cause large effect
39
The downsife of G proteins - Cholera
- affects the small intestine and causes violent diarrhoea
- transmitted by contaminates water/food
- caused by bacterium Vibrio cholera
- secretion of chlorea toxin - choleragen (complex)
- results in the activation of chloride channel proteins, which leads to ATP- mediated efflux of chloride ions and leads to secretion of H2O, Na+, K+, HCO3- into the intestinal lumen
- entry of Na+ and consequently the entry of water into enterocytes are diminished
