Terence (Endocrinology and the hypothalamic pituitary axis) Flashcards
Endocrinology
- Endocrinology is the study of hormones
- Classically hormones are chemical messengers secreted into the blood and exert their effect on a distal target
- Hormones exert their effects at low concentrations
- Hormones are important in maintaining homeostasis
- Hormones regulate many diverse functions including growth, development, metabolism, temperature, H2O balance, reproduction
They hypothalamic pituitary axis
- Forms a complex functional unit that serves as a major link between the endocrine and nervous system.
- The hypothalamus is located below the thalamus and the pituitary gland is located below the hypothalamus in a bone socket at the base of the skull called the Sella Turcica. The sella tunica is part of the sphenoid bone.
- The hypothalamus synthesises neurohormones that regulate the endocrine activity of the pituitary gland or are released by the pituitary.
- The pituitary gland is often referred to as the master gland as it controls the function of many other endocrine glands and tissues
The anterior pituitary
The hypothalamus secretes 7 different tropic hormones that act on other endocrine glands and control/stimulate the gland to synthesise/release a hormones from the anterior pituitary.
Connected via the hypophyseal portal system.
The anterior pituitary is a true endocrine organ. It synthesises and secretes hormones.
- Neurons synthesising trophic hormones release them into capillaries of the portal vein
- Portal vessels carry the trophic hormones directly to the anterior pituitary
- Endocrine cells release their hormones into the second set of capillaries for distribution to the rest of the body
Hypothalamus
The hypothalamus plays an important role is the synthesis and release of pituitary hormones. 7 of these regulate the synthesis and release of hormones from the anterior pituitary.
Hypothalamic hormone- Thyrotropin releasing hormone
TRH is released from the hypothalamus and causes thyroid stimulating hormone (TSH) to be released from the anterior pituitary which then acts on the thyroid.
Hypothalamic hormone- Prolactin release inhibiting hormone/dopamine
Prolactin release inhibiting hormone/dopamine is released from the hypothalamus and causes prolactin to be released from the anterior pituitary which then acts on the breast.
Hypothalamic hormone- Gonadotropin releasing hormone
GnRH is released from the hypothalamus and causes FSH and LH to be released from the anterior pituitary which then acts on the gonads.
Hypothalamic hormone- Growth hormone releasing hormone
GHRH is released from the hypothalamus and causes growth hormone (GH) to be released from the anterior pituitary which then acts on the liver/tissues
Hypothalamic hormone- Growth hormone inhibiting hormone/ somatostatin
Growth hormone inhibiting hormone is released from the hypothalamus and causes growth hormone (GH) to be released from the anterior pituitary which then acts on the liver/tissues
Hypothalamic hormone- Corticotropin releasing hormone
CRH is released from the hypothalamus and causes adrenocorticotropic hormone (ACTH) to be released from the anterior pituitary which then acts on the adrenal cortex
Hypothalamic hormone- Prolactin releasing hormone
PRHis released from the hypothalamus and causes prolactin to be released from the anterior pituitary which then acts on the breast
6 hormones synthesised and secreted from the anterior pituitary
TSH- Thyroid stimulating hormone- stimulated secretion of thyroid hormone from thyroid gland
ACTH- Adrenocorticotropic hormone- stimulates secretion of cortisol from the adrenal cortex
LH- Luteinising hormone- acts on gonads and stimulates production and secretion of sex hormones/ovulation
FSH- Follicle stimulating hormone- act on gonads and stimulates the development of egg and sperm and secretion of sex hormones
PRL- Prolactin- stimulates milk secretion
GH- Growth hormone- stimulates growth and energy metabolism (tropic as acts on liver to stimulate IGF1)
Endocrine axis-driven feedback loop
This is where the hormone is regulated by the concentration of the hormone in the blood and not the response to the hormone.
Long loop- last hormone in pathway feedback to hypothalamus/anterior pituitary
Short loop- pituitary hormone feedback to hypothalamus
The posterior pituitary
The posterior pituitary does not make hormones. It is not a true endocrine organ.
Neurones in the hypothalamus make 2 hormones
- oxytocin
- antidiuretic hormone (ADH)
These hormones are transported down nerve cell axons to the posterior pituitary and stored in the posterior pituitary until they are released (upon electrical stimulation) into the general circulation to act on distal targets.
- Hormone is made and packaged in cell body of neuron
- Vesicles are transported down the cell
- Vesicles containing hormone are stored in posterior pituitary
- Hormones are released into blood
Hypothalamic hormone- Oxytocin
- Neuropeptide/hormone
- Controls uterine contractions during labour (positive feedback loop)
- Promotes milk flow in nursing mothers- the let down relflex
- Promotes bonding/social interaction
- Sometimes referred to as the ‘love hormone’