The endocrine system Flashcards
What do hormones help to regulate?
Extracellular Fluid Metabolism Biological clock Concentration of cardiac and smooth muscle Glandular secretion Immune functions
What are the two types of glands?
Exocrine- secrete products into ducts which empty into body cavities or body surfaces
Endocrine - Secrete products into interstitial fluid, diffuse into blood
Examples of Endocrine glands?
Pituitary, thyroid, parathyroid, adrenal, pineal
What is down-regulation?
Excess hormone leads to a decrease in number of receptors
Receptors undergo endocytosis and are degraded
This decreases the sensitivity of target cell to hormone
What is up-regulation?
Deficiency of hormone leads to an increase in the number of receptors
Target tissue becomes more sensitive to the hormone
What are the two types of hormones?
Circulating hormones - circulate in blood throughout the body
Local hormones - act locally
What are the two divisions of local hormones
Paracrine - act on neighbouring cells
Autocrine - act on the same cell that secreted them
What are the chemical classes of hormones?
Lipid-soluble - use transport proteins e.g. steroid, thyroid and NO
Water-soluble - circulate in ‘free’ form e.g. amine, peptide, eicosanoid
What does the responsiveness of a target cell depend upon?
Hormone’s concentration
Abundance of target cell receptors
Influence exerted by other hormones
How is hormone secretion regulated?
Signals from nervous system
chemical changes in the blood
other hormones
How do lipid-soluble hormones act?
Diffuse through phospholipid bilayer and into the cell
Bind to specific receptor turning on/off specific genes
New mRNA is formed and directs synthesis of new proteins
New protein alters cell’s activity
How do water-soluble hormones act?
CANNOT DIFFUSE THROUGH PLASMA MEMBRANE
Hormone binds (first messenger) to receptor on cell membrane
The activated receptor activates a membrane G-protein which turns on adenylate cyclase
Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases
Protein kinases phophorylate enzymes which catalyse reactions that produce the physiological response
Where does the hypothalamus receive input from?
cortex, thalamus, limbic system and internal organs
Which gland does the hypothalamus control?
Pituitary gland with 9 different releasing and inhibiting hormones
What do together the hypothalamus and pituitary gland regulate?
Growth, development, metabolism and homeostatis
How are the hypothalamus and anterior pituitary connected?
Hormones transported via blood
How are the hypothalamus and posterior pituitary connected?
Hormones transported via axons of hypothalamic neutrons and then stored in posterior pituitary
What is the human growth hormone known as?
Somatotrophin
How does somatotrophin act?
Indirectly on tissues by promoting the synthesis and secretion of small protein hormones called insulin-like growth factors
How is human growth hormone regulated?
Low blood sugar stimulates release of hGH from anterior pituitary
This causes more glycogen broken down into glucose by liver cells
What are the clinical uses of human growth hormone?
Growth hormone deficiency
Overactivity of growth hormone
What does adrenocorticotrophic hormone (ACTH) stimulate?
Cells of the adrenal cortex to produce glucocsorticoids
What are the functions of glucocorticoids?
Help regulate metabolism Increase rate of protein catabolism & lipolysis Conversion of amino acids to glucose Provide stress resistance Raise BP by vasoconstriction Anti-inflammatory effects
What are the action of gonadotrophin releasing hormone?
GRH is secreted by neutrons in hypothalamus
Travels venous stream to anterior pituitary and activated receptors on the gonadotroph cells
Gonadotroph cells the secrete FSH and LH
What are the reproductive functions of FSH?
Initiates the formation of follicles within the ovary
stimulates follicle cells to secrete oestrogen
stimulates sperm production in testes
What does LH stimulate in females?
Secretion of oestrogen
Ovulation of 2nd oocyte from ovary
Formation of corpus luteum
Secretion of progesterone
What are the clinical uses of FSH and LH?
Assisted reproducion
Ovulation induction
Male infertility
What is the role of Prolactin?
Initiates and maintains mile secretion by the mammary glands
What are the features of the posterior pituitary gland?
Does not synthesise hormones
Consists of axon terminals of hypothalamic neutrons
Neurons release two neurotransmitters into capillaries
What are the 2 neurotransmitters released from the posterior pituitary gland?
Oxytocin
Antiduiretic hormone
What are the target tissues of oxytocin?
Uterus and mammary glands which are both involved in neuroendocrine reflexes
What role does oxytocin play after delivery of baby and placenta?
Stimulates contraction of the uterus and ejection of milk from the breasts
Nursing stimulates oxytocin release promoting uterine contractions and the expulsion of the placenta
What is the role of antidiuretic hormone?
Stimulates water reabsorption by the kidneys and arteriolar constriction
Decreases urine volume and conserve body water
Controlled primarily by osmotic pressure of the blood
What is the stress response?
3 stages
Initial fight or flight
Slower resistance reaction
Exhaustion
What are the effects of prolonged exposure to stress?
Wasting of muscles
suppression of immune system
ulceration of GI tract
Failure of pancreatic beta cells
