Lecture 1 Flashcards
Hypothalamic / Pituitary / Gonadal Axis (Hormones)
- Hypothalamus = GnRH
- Pituitary = FSH / LH
- Target Organ = ovary / testis
- Target Organ Hormone = estradiol / testosterone.
Hierarchal arrangement of endocrine glands allows…
Amplification - of hormone levels / activity at each level.
Propagation - from one level to another
Integration - feedback from each level tells the components further up in the hierarchy to produce more or less hormones.
Pituitary ANTERIOR lobe input / output
Input = humoral -> a connection via the blood stream ( a portal system).
Output = Gonadotrophins to the gonads
Pituitary POSTERIOR lobe input / output
Input = neural -> axons / impulses.
Output = Oxytocin to various target organs
Sex Hormones
Produced by the gonads. Go to other target organs or feedback to the hypothalamus and pituitary.
Inputs to the hypothalamus from other centres of the brain.
- Light - seasonal breeding
- Smell - pheromones - menstrual cycle coordination unfounded.
- Touch - oxytocin release from posterior pituitary.
- Sound - oxytocin release from posterior pituitary.
- Psycho-social - pain (severe pain decreases cycles), stress (amenorrhea - stop cycle).
- Nutritional Status - less than 47kg (shut down the axis).
Neurosecretion
Nerve cells can produce hormones.
Manufactured in the cell body then transported down the axon, usually in the form of granules then released into the bloodstream.
Receptor specificity
Need to have the right receptors on the right cells before you can respond.
Why every cell in the body doesn’t respond to a hormone circulating in the bloodstream.
Feedback Loops
To each level of the system.
Feed back upwards.
Pulsatile secretion
Hormones are not released at a steady level.
They are released in discrete bursts.
e.g. every 1-2 hours for LH in males.
Information is contained in both amplitude and frequency.
Hypothalamus - origin
Develops from the hindmost part of the forebrain - the diencephalon.
Hypothalamus - location
Base of the forebrain in a region called the diencephalon.
About 4 grams of tissue.
Funnel shaped structure (filled with CSF) leading to a downward extension - a stalk composed of neural tissue (Note: stalk is a part of the pituitary).
Hypothalamus - composition
Cell bodies + axons of hypothalamic neutrons.
Axons and terminals of other neurones who’s cells bodies are outside the hypothalamus (e.g. feedback neurones).
Axons passing through.
Glial cells (CT).
Blood vessels, especially in median eminence.
Hypothalamic nuclei
Cell bodies of the hypothalamic neurones are clustered into distinct groups called nuclei, embedded in the funnel shaped wall of the hypothalamus.
The sites where hormones are produced.
Supraoptic Nuclei and Paraventiruclar Nuclei
Both paired. Hypothalamic nuclei.
Magnocellular (large) neurosecretory cells.
Axons travel to pars nervosa of the posterior pituitary.
Release vasopressin (ADH) and oxytocin into the bloodstream then travel to the target organs.
