Endocrinology 1 Flashcards
What are the main endocrine glands?
- Hypothalamus/Pituitary gland
- Pancreas
- Thyroid Gland
- Parathyroid gland (situated behind the thyroid gland)
- Adrenal gland (on top of the kidneys)
- Testes/Ovaries
What is the role of the anterior pituitary gland?
Produces hormones:
- Thyroid stimulating hormone (TSH) Stimulates the production of thyroid hormones
- Adrenocorticotrophic hormone (ACTH) Stimulates the adrenal gland to produce the steroids
- Growth hormone (GH) - for skeletal growth
- Gonadotrophins (Follicle stimulating hormone, FSH, and Luteinising hormone, LH) Stimulates the testicles and ovaries to produce sex hormones
- Prolactin - stimulates breast milk production (Prolactin is under an inhibitory activity)
What is the role of the posterior pituitary gland?
Stores Oxytocin (helps uterine contractions during labour) and ADH (Stimulates water reabsorption by the kidneys).
What hormones are secreted by the hypothalamus? What do they do?
- Growth hormone releasing home (GHRH) stimulates the release of GH at the pituitary
- Corticotrophin Releasing hormone (CRH) stimulates the secretion of ACTH at the pituitary
- Gonadotrophin Releasing hormone (GnRH) stimulates the release of LH and FSH at the pituitary
- Thyrotrophin Releasing hormone (TRH) stimulates the release of TSH at the pituitary
What is different about the control of Prolactin? What will happen if there is a lesion between the hypothalamus and the pituitary?
Prolactin is under inhibitory control. Once the inhibitory effect is removed, prolactin secretion is increased. If there is a lesion between the hypothalamus and pituitary, the hypothalamus cannot stimulate the pituitary to produce hormones but also means that the Prolactin levels increase as it is no longer under inhibitory control.
How is the pituitary hormones switched off?
- Cortisol, made in the adrenal cortex, switches off ACTH and CRH.
- Sex hormones such as testosterone and Oestrodiol, made in the sex organs, with off LH, FSH and GnRH
- T4 and T3, made in the thyroid, switch off TSH and TRH.
- Growth hormone switches of GHRH and GH
This is known as negative feedback. This prevents continual secretion of endocrine hormones.
Using the example of steroid hormones, how is secretion controlled?
The hypothalamus secretes CRH onto the pituitary. This stimulates the thyroid to produce ACTH. This works on the adrenal gland to cause it to produce steroids such as cortisol. Cortisol can then act on the ACTH and CRH to reduce their sectretion.
Which glands are not controlled by the pituitary?
- Adrenal medulla - adrenaline and noradrenaline secretion
- Parathyroid glands which controls calcium levels
- Pancreas
- Gut hormones
- Some parts of the adrenal cortex e.g. Aldosterone secretion is not controlled by the pituitary but instead the renin-angiotensisni system.
Describe the thyroid gland
Found in the back off the neck, usually not visible. Can be visible in teenagers, pregnant ladies and some clinical conditions. Composed of a right lobe, left lobe and a midline isthmus.
The thyroid cells are arranged in follies and produced thyroid hormones.
There are C cells in the thyroid, which produce Calcitonin. Calcitonin is not under the control of the pituitary - they are involved in calcium metabolism.
How is Calcium controlled?
Calcium metabolism is mainly controlled by the parathyroid gland. It is also controlled by:
- Kidney - calcium excretion and active vitamin D production
- Gut - absorption of calcium
- Bone - storage of calcium
- Thyroid (C cells that produce Calcitonin)
What are the different aspects of the adrenal gland?
Adrenal Medulla (inside) Secretes adrenaline, noradrenaline and dopamine. Not controlled by the pituitary.
Adrenal Cortex (outside) 90% of the gland - secretes androgens (male hormones). In females the made hormones secreted by the adrenal medulla - in male sit is mostly the testes. secretes also corticosteroid (cortisol) and mineralocorticoids (aldosterone - this is controlled by renin-angiotensin system not the pituitary).
What is the function of Cortisol?
Cortisol is a steroid hormone, in the glucocorticoid class of hormones. It is released with a diurnal cycle and its release is increased in response to stress and low blood-glucose concentration. It functions to increase blood sugar through gluconeogenesis, to suppress the immune system, and to aid in the metabolism of fat, protein, and carbohydrates.It also decreases bone formation.. A loss of cortisol can be fatal.
How is female hormone secretion controlled?
The hypothalamus secretes GnRH episodically. The pituitary secretes LH and FSH. This stimulates the ovary to produce Oestrodiol, Inhibin and Progesterone. Inhibin is the main hormone that feedbacks to the pituitary to switch of FSH and LH production. Oestrodiol has dual functionality and acts on the hypothalamus and pituitary. In the first part of the cycles, there is mainly Oestrodiol and FSH produced. Oestrodiol switches off FSH and stimulates LH secretion. Once there is enough LH, progesterone is produced. Towards the end of the cycle, there is mainly progesterone.
What is the function of the different cells in the testes?
Intestinal cells - Produce testosterone
Seminiferous tubule - made up of germ cells producing sperms
Sertoli cells (found between tubules) - help in sperm production and produce inhibin.
How is males hormone secretion controlled?
The hypothalamus produces GnRH which stimulates the pituitary to produce FSH and LH. FSH increases the production of the sperm and inhibin. LH increases the production of testosterone. Testosterone switches of FSH, LH and GnRH production.
