Lecture 7 - Endocrine System Part 1 Flashcards
What is the function of the endocrine system and what does it consist of?
Regulates long term processes - growth, development, reproduction and coordinates multiple organs together
Consists of hormones (chemical messengers to relay info between cells)
Glands (secrete hormones)
What are the organs of the endocrine system?
Hypothalamus - produces ADH, oxytocin / regulatory hormones
Pituitary gland - Anterior - FSH, LH Posterior - ADH, oxytocin released
Pineal gland - Melatonin - sleep
Parathyroid glands - PTH - posterior of thyroid
Thyroid - Thyroxine
Adrenal glands - medulla - Catecholamines - Cortex - cortisol
Pancreatic Islets - Insulin, glucagon
What are the secondary organs of the endocrine system?
Heart
Thymus
Adipose tissue
Digestive tract
Kidneys
Gonads - Testes and Ovaries
What is the mechanism of endocrine communication?
Through the blood
What are endocrine glands?
Ductless glands compromised of endocrine cells
Have good blood supply
Secrete hormones directly into the blood stream (capillary)
What are hormones?
Organic chemical messengers produced and secreted by endocrine cells into the blood
Bind to receptors in target cells to form hormone-receptor complexes
This stimulates gene expression/ protein synthesis to regulate, integrate and control a wide range of physiologic functions
Outline anabolic steroid hormones
Steroids have receptors in muscle that stimulate muscle protein production
Not all all steroid hormones build muscle - they have specific effects
What are the risks of anabolic steroids?
Teens - early skeletal and sexual maturation - stunted growth
Liver and CV system damage + increased cholesterol
Males - reduced sperm count, infertility, baldness, risk of prostate cancer
Females - facial hair, cessation of menstrual cycle
Effects will be different in different tissues
What are the 3 types of hormones?
Amino acid derivatives - small molecules, structurally similar to amino acids
Peptide hormones - Consists of chains of amino acids, largest class of hormones
Lipid derivatives - 2 classes - steroid hormones and eicosanoids
What are the lipid soluble hormones?
Thyroid hormones (a/a derivative)
Steroid hormones
These don’t transport well but can get inside cells
What are the water soluble hormones?
Catecholamines
Glycoproteins
Short polypeptides and small proteins
Eicosanoids
What are the 2 locations of hormone receptors?
On the cell membrane - includes receptors for non lipid soluble hormones - catecholamines, peptide hormones and eicosanoids - triggers signal in the cell involving G proteins
Inside the cell - Receptors for all steroid and thyroid hormones
Outline the hormonal action via cell membrane receptors
Hormone binds to receptor to activate the G protein on the membrane
This then activates the enzyme adenylate cyclase
Adenylate cyclase converts ATP to cAMP
cAMP activates kinase enzymes
These kinases affect the target cell
Outline how the same hormone can have different effects in different cells with different receptors
Can activate different responses in different target cells
Adrenaline binding to beta receptors - increases cAMP
Adrenaline binding to alpha receptors breaks down cAMP via phosphodiesterase
Outline the hormonal action via the intracellular receptors for steroid hormones
Diffusion through membrane lipids
Hormone binds to cytoplasmic or nuclear receptors
Binding of hormone-receptor complex to DNA
Gene activated
Transcription and mRNA production
Translation and protein synthesis
Alteration of cellular structure or activity
Outline the hormone action via intracellular receptors for thyroid hormones
Transport across the cell membrane
Binds to receptors on the mitochondria (this can increase ATP production) and nucleus
Binding of hormone- receptor complex to DNA
Gene activation
Transcription and mRNA production
Translation and protein synthesis
Alteration to cellular activity
What happens to hormones after secretion?
Free hormones - functional for less than an hour , bind to target cell receptors or broken down in liver, kidney by enzymes
Thyroid/steroid - Circulate much longer but bound
Enter the bloodstream - more than 99% become attached to special transport proteins
Outline the role of the hypothalamus and the pituitary glands
Hypothalamus - interface between nervous and endocrine, regulatory hormones affect pituitary function
Pituitary glands - Anterior pituitary - hormones that control other endocrine organs Posterior - Oxytocin and ADH release
What are the 3 ways of communication in the hypothalamus?
Production of ADH and oxytocin - travel through neurons to the posterior pituitary
Secretion of regulatory hormones - circulate to the anterior lobe of the pituitary
Control of sympathetic output to adrenal medulla - neurons with long axons that travel to the adrenal medulla via the preganglionic motor fibres - stimulates the production of catecholamines
Outline the structure of the pituitary gland structure?
Posterior pituitary - neural tissue located in the sphenoid - well protected
Anterior - Pars tuberalis, Pars distalis, Pars intermedia - secretes melanocyte stimulating hormone
Outline the hypophyseal portal system
Neurosecretory neurons at median eminence secrete regulatory factors - enter fenestrated capillaries in capillary bed in hypothalamus - entering portal veins - capillary bed in anterior pituitary
What are the anterior pituitary hormones?
ACTH - Adrenal medulla
TSH - Thyroid
GH - Liver - somatomedins
Prolactin - Mammary glands
FSH and LH - Gonads - inhibin, test, estrogen, progesterone
MSH - Melanocytes
What is the negative feedback control for releasing hormone with the example of TRH?
Releasing hormone (TRH) stimulates the anterior lobe of the pituitary which stimulates hormone 1 (TSH)
This stimulates the endocrine target organ (the thyroid) and then stimulates hormone 2 (thyroid hormones)
Hormone 2 inhibits RH
How is prolactin regulated?
Hypothalamus produces releasing factor (PRF) and inhibiting hormone (PIH)
PRF stimulates the anterior lobe of the pituitary which stimulates PRL and then the mammary glands
This then inhibits PRF and stimulates PIH
How is Growth hormone regulated?
The hypothalamus produces releasing hormone (GH-RH) and inhibiting hormone (GH-IH)
GH-RH stimulates the anterior lobe which stimulates the GH which stimulates the liver to release somatomedins for skeletal muscle growth
These inhibit the GH-RH and stimulate GH-IH
What are the effects of growth hormone?
Acts on the liver to promote the release of somatomedins e.g. insulin like growth factors (IGFs) which stimulate tissue growth and increase a/a uptake / protein synthesis
GH acts directly on tissues to stimulate cell division in epithelial and connective tissue, triglyceride breakdown in adipocytes and liver glycogen breakdown
