Endocrinology Flashcards
What is a Hormone?
A chemical messenger secreted directly into blood stream from endocrine gland
What are the four types of intercellular messengers in the body?
1) Endocrine
2) Autocrine and Paracrine
3) Neuroendocrine
4) Neurotransmitter
What are the different types of hormones?
-Peptide hormones (chains of amino acids)
-Steroid hormones
(derived from cholesterol)
-Hormones derived from tyrosine
How are peptide hormones synthesised?
Similar to normal protein synthesis
Preprohormone = The result of the peptide forming after ribosome
Prohormone = The hormone in the golgo complex where it is packaged into the finished product
Hormone = a secretory granule that is stored until released upon arrival of a stimulus, then leaves the cell by exocytosis
How are steroid hormones synthesised?
A cholesterol-based precursor molecule is bound to a biosynthetic enzyme which breaks down the substrate into a hormone that is NOT STORED and is released by simple diffusion
-These hormones bind to plasma proteins in the blood
What is the half life?
The time taken for the initial concentration to fall by 50%
What are some differences between peptide and steroid hormones?
Peptide Hormones:
- Hydrophilic
- Free Hormones so biologically active
- Half life is a few minutes
Steroid hormones
- Lipophobic
- Bound to plasma proteins
- Half life can be hours or days
How does peptide hormone action occur?
Hormone binds to a receptor on cell membrane. This then activates G Proteins and Effectors
-This then leads to signal transduction which produces a physiological response such as altered activity of enzymes or ion channels
How does steroid hormone action occur?
Hormone binds to Cytosolic receptor or Nuclear receptor to eventually increase or decrease gene expression
How are hormones metabolised?
Most hormones are metabolised by enzymes in liver, kidney and/or blood
- Small proportion by target tissues
- Small proportion made by target tissues
- Eventually excreted in urine and/or faeces
How are the release of hormones regulated?
1) Feedback regulation
- Negative feedback (consequence negatively controls process)
- Positive feedback (consequence enhances or amplifies process further)
What is the endocrine axis?
Interactions between the hypothalamus, the pituitary and peripheral endocrine glands showing feedback regulation
What are some endocrine disorders?
1) Hormone excess (hypersecretion)
2) Lack of hormone (hyposecretion)
3) Decreased target-cell responsiveness
How to treat certain hormone disorders?
If hormone deficiency - hormone replacement
If hormone excess - drugs to block production
If decreased target-cell responsiveness - drugs to enhance cellular response to hormone
If tumour - radiotherapy or surgery
What are the primary endocrine organs?
Hypothalamus (Brain)
Pituitary (Brain)
Pineal (Brain)
Thyroid (Throat)
What is the order of the endocrine axis?
- Hypothalamus
- Releasing hormone
- Anterior pituitary
- Tropic hormone
- Peripheral endocrine gland
- Peripheral hormone
- Target cell response
What hormones are made and what to do they do within the body?
- Gonadotropin-releasing hormone (Sex Hormones)
- Growth hormone (IGF-1)
- Thyrotropin-releasing hormone (Thyroid hormone)
- Dopamine/prolactin (Breast tissue)
- Corticotropin-releasing hormone (Cortisol)
What occurs in the Posterior pituitary?
- Neuroendocrine cells synthesise vasopressin and oxytocin
- Hormones are transported along the neurons, stored in the axon termini, in the posterior pituitary
What does Vasopressin do?
- Vasoconstriction in Blood Vessels
- Kidney to increase permeability and reabsorption of water
What is Oxytocin released by?
Release stimulated by suckling, and by cervical stimulation
What are the actions of Oxytocin?
- Stimulate ‘milk let-down’, expression of breast milk
- Uterine smooth muscle contraction
- Maternal behaviour / sexual behaviour / social bonding
What does the pineal gland secrete?
Melatonin
What is melatonin involved in?
Melatonin is involved in control of the body’s circadian rhythm in synchrony with the light-dark cycle
- Promotion of sleep
- Seasonal fluctuations of melatonin are important triggers for seasonal breeding, migration and hibernation
What do the thyroid glands secrete?
- Thyroxine (T4)
- Tri-iodothyronine (T3) Calcitonin
Most of T4 is converted to T3 in the periphery
-most actions of thyroid hormones are by T3
