MMED1005 Study Guide - Final Guide: Cartilage, Megakaryocyte, Digestion
7 Jun 2018
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Endocrine glands:
- They secrete hormones into the blood or into interstitial fluid
- Hormones, once secreted, travels in the blood to its distant target cells where it
regulates or directs a particular function. This latter effect is dependent on the
presence of a specific receptor on the target cell for a specific hormone
- Endocrine cells receive three types of input:
o Ions (or nutrients), neurotransmitters, and hormones
o These inputs stimulate or inhibit hormone secretion
Endocrine signalling:
- Autocrine: hormones released then attach to receptors on the
cell and inhibit further release of that hormone
- Paracrine: where cells surrounding the cell affected by the
release of the hormone are also affected (same cell type or
different cell type)
- Hormones: enter blood stream to affect distant targets.
Specificity depends on receptors – if othe ells dot hae the
right receptor, the hormone ot have any effect. Same
concept as neurotransmitters
- neurohormones:
Long distance communication may be electrical or chemical:
- the endocrine system communicates by using hormones, which are chemical signals
that are secreted into the blood
- (the Nervous system uses a combination of chemical signals and electrical signals to
communicate over long distances. This patha is alled euoie
o neurotransmitter: when the neurocrine molecule diffuses from the neuron
across extracellular space to the target cell
o neuromodulator: when the neurocrine molecule acts more slowly as a
paracrine or autocrine signal
o neurohormone: when the neurocrine molecule is released from the neuron
and diffuses into the blood for distribution (e.g. vasopressin, oxytocin)
Three main classes of hormones:
- Steroids/steroid-like: cholesterol is the parent compound
- Amino acids: tyrosine is the precursor
- Proteins/peptides
How do hormones travel through the body?
- Some hormones (e.g. steroids, thyroxine) are bound to specific carrier proteins
(cortisol binding globulin, sex hormone binding globulin and albumin)
- Whilst other hormones may circulate unbound and free (e.g. insulin)
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How do they work?
- Depends whether they are hydrophobic or hydrophilic
HYDROPHILIC hormone actions:
- These hormones are generally polar and therefore cannot pass through the cell
phospholipid membrane
- They therefore act on the outside of the cell membrane where there is a target
receptor
not just their physical shape that matters, but
also their chemical nature
(diagram on right shows the amino acid sequence
of the protein) →
Specificity of hormone binding to its receptor
→ three ligands/hormones that have similar structures
→ receptor-protein Y has a high degree of specificity
and is only able to bind ONE ligand/hormone effectively
HYDROPHOBIC
- hydrophobic/lipophilic hormones enter the cell to exert their effects
- most hydrophobic steroids are bound to plasma protein carriers. Only unbound
hormones can diffuse into the target cell
1. steroid hormone receptors are in the cytoplasm or nucleus
a. some steroid hormones also bind to membrane receptors that use second
messenger systems to create rapid cellular responses
2. the receptor-hormone complex binds to DNA and activates or represses one or more
genes
3. activated genes create new mRNA that moves back to the cytoplasm
4. translation produces new proteins for cell processes
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Summary of mechanism of action for hormones:
- hydrophilic hormones
o act on target receptors on the cell surface/membrane
o include peptides, proteins, amino acids (catecholamines)
- hydrophobic (lipophilic) hormones
o act by passing through the cell membrane and binding to receptors inside the
target cell
o include steroids and thyroxine
Terminology:
- hypersecretion: increased, elevated, higher
- hyposecretion: decreased, below, less
- negative feedback control: when the output of a system counteracts a change in the
input to that system
- down regulation: is a negative feedback mechanism that stops target cells
overreacting (desensitization)
- up regulation: is a positive feed forward mechanism that helps target cells increase
activity (sensitization)
The hypothalamic-pituitary system (hypothalamus – pituitary connection) (hypothalamus is
the brain component of this system and the pituitary is the endocrine component)
Two lobes of the pituitary gland (also known as hypophysis):
- Posterior lobe (also known as neurohypophysis, neuro=nerve): neural
o Neurones originate in the hypothalamus. These cell bodies synthesise
vasopressin and oxytocin and release them through nerve endings into the
posterior pituitary area, where these hormones enter the circulation
- Anterior lobe (also known as adenohypophysis, adeno=glandular): glandular, non-
neural
o Neurones in the hypothalamus secrete release factors into arterial blood flow
→ anterior pituitary through the hypothalamic-hypophyseal portal system →
anterior pituitary releases hormones
o Made up of ell tpes tophs ad akes hooes TSH, ACTH, PRL,
FSH&LH and GH)
Vasopressin:
1. Stimuli e.g. high osmolarity, decreased atrial stretch due to low blood volume, low
blood pressure
2. Sensory neurones → hypothalamus
3. Hypothalamic neurones that synthesise vasopressin
4. Vasopressin released from posterior pituitary
5. Vasopressin → collecting duct → insertion of aqua pores → water reabsorption
Oxytocin:
- During delivery of a baby, cervical stretch → brain → hypothalamus → posterior
pituitary → oxytocin release → uterine contraction → cervical stretch → et.…
- Birth and production of milk both examples of positive feedback loops
**Note: vasopressin and oxytocin are neurohormones!!!!
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
They secrete hormones into the blood or into interstitial fluid. Hormones, once secreted, travels in the blood to its distant target cells where it regulates or directs a particular function. This latter effect is dependent on the presence of a specific receptor on the target cell for a specific hormone. Endocrine cells receive three types of input: Ions (or nutrients), neurotransmitters, and hormones: these inputs stimulate or inhibit hormone secretion. Autocrine: hormones released then attach to receptors on the cell and inhibit further release of that hormone. Paracrine: where cells surrounding the cell affected by the release of the hormone are also affected (same cell type or different cell type) Hormones: enter blood stream to affect distant targets. Specificity depends on receptors if othe(cid:396) (cid:272)ells do(cid:374)(cid:859)t ha(cid:448)e the right receptor, the hormone (cid:449)o(cid:374)(cid:859)t have any effect. Some hormones (e. g. steroids, thyroxine) are bound to specific carrier proteins (cortisol binding globulin, sex hormone binding globulin and albumin)
