Introduction Flashcards
Peptide hormones
- Water solubility
- Oral activity
- Receptor activity
Very water soluble
Orally active- broken down my proteases (digestive enzymes in the mouth)
Receptors are membrane bound
- Requires membrane proteins to cross membrane
- Not lipid soluble
Peptide hormones
- Speed of action
- Plasma half life
Rapid speed of action
- Seconds, minutes
Short plasma half life
- Protease activity
Steroid/thyroid hormones
- Water solubility
- Oral activity
- Receptor activity
Not water soluble, but lipid soluble
Not orally activity
Binds to intracellular receptors
- Lipid soluble, can cross plasma membrane and nuclear membrane.
Steroid/thyroid hormones
- Transport
- Speed of action
- Plasma half life
Transported in the blood via plasma proteins
- Not water soluble
Mostly slow acting
- Hours, days.
Slow plasma half life
- Only active when unbound
Hormone definition [4]
- Chemical messenger released by a ductless gland
- Transported in the blood
- Acts on specific receptors on target tissues
- One hormone can affect multiple target tissues
Endocrinology
Physiology of glands and hormones
Endocrine
Method of cell signalling
- Chemical messenger (hormone) acts on target tissue far away from signalling cell.
Paracrine
Method of cell signalling
- Chemical messenger acts on target tissue in close proximity to signalling cell.
Autocine
Method of cell signalling
- Signalling cell secretes chemical messenger that acts on itself.
Pituitary gland
- Location
- Anatomy
- Main function
Located at the base of the brain
- Sits in a bony case, sella turcica
Anatomy
- Connected to the hypothalamus via the infundibulum
- Portal system: hypothalamico-hypophyseal vessels—> Anterior
- Hypothalamico-hypophyseal tract—> Posterior
Function- master gland, secretes hormones to all glands.
Hormones of the pituitary gland
Anterior
- Prolactin
- FSH
- LH
- ACTH
- GH
- TSH
Posterior
- Oxytocin
- ADH
Thyroid + Parathyroid
- Anatomy
- Function
In the neck
- Below the larynx
- Controls metabolic rates
- Calcium homeostasis
Adrenal glands
- Anatomy
- Function
On top of the kidneys
Functions
- Stress
- Blood sodium and glucose regulation
Steroid hormone receptors
- Structure
- Mechanism
- Speed of action
Located in the cytoplasm or on nuclear membrane
Mechanism
1. Hormone binds to receptor to form hormone-receptor complex.
- Complex binds to hormone-response element.
- Hormone-response binds to DNA and affects gene transcription
Speed
- Slow acting, days of action.
Endocrine organs
Pituitary gland Thymus Thyroid and Parathyroid Adrenal gland Pancreas Gonads (Testes, ovaries)
Tyrosine-kinase receptor - Action
- Speed
- Examples
Action: Receptor contains membrane bound enzyme
- Hormone binds to receptor
- Triggers phosphorylation of the receptor.
- The receptor leads to cellular events that phosphorylates other intracellular proteins.
Speed: Very slow
- Used for growth and development
Example
- Prolactin
- Growth hormone
G-protein coupled receptors
- Action
- Speed
- Examples
Action:
- Hormone binds to 7 transmembrane receptor.
- Secondary messenger is produced (cAMP, IP3)
- Secondary messenger causes phosphorylation or influences other intracellular activity.
cAMP= smooth muscle relaxation IP3= smooth muscle contractrion
Speed:
- Very fast action
Example:
- Adrenaline (adrenergic receptors)
- Calcitonin
- FSH
Thyrotrophin releasing hormone [TRH]
Hormone released from the hypothalamus.
Triggers the release of thyroid stimulating hormone [TSH] from the anterior pituitary gland.
Thyroid stimulating hormone [TSH]
Released from the anterior pituitary gland.
- Thyrotophic cells
Transported in the blood to the thyroid.
Stimulates the release of thyroxine.
Corticotrophin releasing hormone [CRH] and adrenocorticotrophic hormone [ACTH]
CRH is released from the hypothalamus to the pituitary.
- Via hypothalamico-hypophyseal vessels.
- Triggers the release of ACTH from corticotropic cells
ACTH is released from the anterior pituitary.
- Transported in the blood to the adrenal cortex.
- Stimulates the released of cortisol.
Gonadotrophin releasing hormone [GnRH] and Follicle stimulating hormone [FSH]
GnRH is released from the hypothalamus to the anterior pituitary gland.
- Triggers the release of FSH from gonadotropic cells.
FSH travels to the ovaries
- Stimulates the release of oestrogen
Growth hormone releasing hormone [GHRH] and GH
- Secretion
- Action
GHRH is released from the hypothalamus to the anterior pituitary gland.
- Stimulates the release of GH from somatotropic cells
GH travels to the bones and stimulates linear growth.
Luteinising hormone [LH]
- Secretion
- Action
LH is released from the anterior pituitary gland
- From gonadotropic cells
- Stimulates the ovaries to secrete progesterone
- Triggers ovulation
Feedback control of hormones
Hormones can negatively inhibit the release of releasing and stimulating hormones.
- Cortisol inhibits CRH and ACTH.
- Progesterone inhibits LH.
- T3 and T4 inhibits TRH and TSH.
Variation of cortisol release
Diurnal variation
- Peak in the morning, after waking. 9am.
- High Cortisol inhibits ACTH release
Drop in cortisol as the day progresses
- Allows increase in ACTH
- Cortisol lowest at night/sleep, 12am.
Variation of oestrogen release
Monthly variation, overly roughly 28 days–> Menstruation cycle.
- Drop in oestrogen and progesterone allows disinhibition of hypothalamus to allow releasing of FSH and LH.
