Introduction to endocrinology Flashcards
What do hormones control?
- the rate of enzymatic reactions
- transport of ions or molecules across cell membranes
- gene expression and protein synthesis
How are hormones terminated?
Enzymes that are always present in the plasma can degrade peptide hormones bound to cell membrane receptors
Intracellular enzymes can metabolise hormones in cells
In some cases the receptor hormone complex is brought into the cell by endocytosis
What is endocytosis?
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalised is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material
Inactive broken down metabolites are then excreted in the bile or urine
What is the half life of a hormone?
Indicates length of activity- amount of time required to reduce a hormone concentration to half
What are the 3 main types of hormone?
Peptide/protein hormones
Steroid hormones
Amine hormones
What are amine hormones derived from?
Derived from amino acids= either tryptophan or tyrosine
What is an example of a amine hormone made of tryptophan?
Melatonin, made in the pineal gland
What hormones are tyrosine amine hormones and how do they differ?
Catecholamines which have a one ring structure and thyroid hormones which have a two ring structure
What are examples of catecholamines?
Adrenalin, noradrenalin and dopamine
Where do catecholamines and thyroid hormones bind to?
- Catecholamines= bind to membrane structures
- Thyroid hormones= bind to intracellular receptors that activate genes
How are catecholamines and thyroid hormones formed?
Where are steroid hormones derived from?
Cholesterol
Where are steroid hormones produced and what are examples?
The adrenal cortex (outer portion of adrenal gland). Aldosterone and cortisol
Gonads= oestrogen, progesterone and androgens
What do cells that produce steroid hormones usually have?
A large amount of smooth ER (endoplasmic reticulum) which is responsible for synthesis of cholesterol
How do steroid cells move in and out of cells?
They are lipophilic and can move via simple diffusion
What is the rate of action for steroid hormones?
Slow- half life can be years
Where do steroid hormones bind to?
They bind to cytoplasmic or nuclear receptors. Control DNA synthesis
In what case can steroid hormones initiate a faster pathway?
- Several steroid hormones, including oestrogen and aldosterone have cell membrane receptors linked to signal transduction pathways (like peptide hormones)
- These allow steroids to initiate rapid non genomic responses in addition to their slower genomic effects
How are steroid hormones transported around the blood?
Steroid hormones are lipophilic and thus, are usually transported in the plasma bound to a serum binding protein, such as albumin- or sex hormone–binding globulin
What do peptide or protein hormones start as?
They start as a preprohormone (large and inactive). Once they undergo post-translational modification they are changed into prohormones and later become peptide hormone
How are peptide hormones formed?
Step 1.5- the pro hormone is contained within a transport vesicle which then fuses to the Golgi complex
What is the half life of a peptide hormone?
Short half life- minutes
Are peptide hormones water soluble?
Yes
What do peptide hormones bind to?
Binds to membrane receptors- unable to diffuse through and enter cells.
Most initiate a response through cyclic AMP messenger systems
What are examples of peptide hormones?
ADH, CCK, oxytocin and leptin
What is the order of hormone reflex pathways?
Stimulus ⇒ Afferent signal ⇒Integration of the signal⇒ Efferent signal (the hormone) ⇒ Physiological action ⇒ Negative feedback
What is the reflex pathway for parathyroid hormone?
What is the hormone reflex pathway for insulin?
What is a neurohormone?
A chemical secretion released into the blood from a neurone