Endocrine System Flashcards
How do the nervous and endocrine system interact?
The hypothalamus-pituitary axis, HPA
What is the pituitary gland?
The “master gland” however the hypothalamus is actually in charge.
Small recap of nervous system
-electrical impulses transmit signals quickly over short distances (movement of ions across membranes)
-neurotransmitters at synapses to communicate with other neurons or target cells (muscles or glands)
-rapid responses to immediate changes in internal or external environment (muscle contraction or reflexes)
Small recap of endocrine system
-Hormones: chemical messengers released into bloodstream by endocrine glands or cells
-hormones travel to specific target cells and bind to specific receptors, initiating a response
-acts more slowly but have longer lasting effects (adrenaline seconds to minutes, steroids days to weeks)
-regulate processes that require gradual adjustments (homeostasis, growth, development, metabolism, and reproduction)
How do hormones travel?
Through blood
Can female elephant seals have testosterone?
Yes, they just have a significantly lower amount that males.
What does it mean if a hormone is Lipophilic (fat soluble)
It needs a protein carrier through blood
What type of hormone is a testosterone?
A steroid hormone
What is endocrine signalling?
Secreted molecules (H) travel with blood and trigger responses in specific target cells in the body.
What is paracrine signalling?
Secreted molecules diffuse locally and trigger a response in neighbouring cells. (not with blood)
What is autocrine signalling?
Secreted molecules diffuse locally and trigger a response in the cells that secrete them (not with blood)
What are prostaglandins?
They promote inflammation and pain sensation; their synthesis can be blocked by aspirin and ibuprofen (COX inhibitors).
What does nitric oxide do in the body?
Signals low oxygen levels in blood by causing vasodilation (the widening of blood vessels) Viagra enhances NOs effects by prolonging the relaxation of blood vessels, increasing blood flow.
Paracrine and Autocrine signalling signals through…
Local regulators.
What is synaptic signalling?
when neurotransmitters diffuse across synapses and trigger responses in target tissues (neurons, muscles, or glands)
What is neuroendocrine signalling?
when neurohormones diffuse into bloodstream and trigger responses in target cells anywhere in the body (oxycotin) or locally (HPA) via portal veins.
Where does neuroendocrine signalling occur?
hypothalamus-pituitary axis (HPA)
What is an exocrine gland?
a gland the releases secretions into external environment through ducts ( saliva, sweat, milk)
What is an endocrine gland?
glands that are ductless and secrete hormones into the blood stream.
What do portal veins do?
carry neurohormones to 2nd capillary bed in anterior pituitary.
what are the advantages of a portal system in the HPA?
-portal veins carry a tiny amount of blood
-only a small amount of neurohormones from few neurons is needed to control the secretion of anterior pituitary gland
-short distance = rapid response and no unwanted effects on rest of body.
how does testosterone work?
-it diffuses across the lipid layer of the cell membrane.
-once inside a cell it binds to the androgen receptor (AR) in the cytoplasm.
-after binding the testosterone-receptor complex transolcates to the nucleus.
-it then binds to specific DNA sequences hormone response elements (HRE)
-this activates or represses the transcription of specific target genes.
-the resulting mRNA is translated into proteins that mediate testosterones effects, promoting muscle growth, secondary sexual characteristics, or sperm production.
What hormones are secreted by the anterior pituitary?
tropic/ trophic hormones
what hormone is produced by the adrenal gland?
adrenaline
how is adrenaline controlled?
by the sympathetic nervous system.
What are three levels of the endocrine system?
Hypothalamus
Anterior Pituitary
Peripheral Endocrine Glands
What are the types of hormones?
Releasing hormones and inhibiting hormones
Stimulating hormones
What do complex endocrine systems regulate?
Body temperature
Blood glucose
Blood pressure
Methods for studying hormones
-Remove gland to observe deficiency effects
-Reintroduce hormone/ gland to observe recovery
-Increase hormone levels artificially to observe excess effects.
What are the 3 classes of hormones?
Peptide (short amino acid chains to large glycoproteins)
Steroid (derived from cholesterol)
Amine (derived from tyrosine/tryptophan)
What can hormones be released by?
endocrine glands, isolated endocrine cells, neurons, and cytokines
what is normal blood glucose?
4.8mmol/L
Why must insulin action be terminated?
if it isnt, blood glucose drops causing brain malfunction.
how is insulin action terminated?
insulin is broken down by the liver/ kidney and excreted.
how is hormone secretion regulated?
with negative and positive feedback mechanisms.
What is the dominant feedback system?
Long loop negative feedback
Whats the primary regulation method to maintain homeostasis?
negative feedback
What is long loop negative feedback?
when the final hormone (from peripheral gland) inhibits hormone release at the hypothalamus and/or pituitary.
EXAMPLE = CORTISOL REGULATION
what is short loop negative feedback?
The pituitary hormone inhibits the hypothalamus.
EXAMPLE = ACTH REGULATION
what is ultra short loop feedback? (negative)
Hormones act as autocrine or paracrine signals to regulate their own secretion.
Found in the hypothalamus and anterior pituitary.
what is positive feedback?
when hormones enhance their own secretion
EXAMPLE = OXYTOCIN DURING CHILDBIRTH
Rough endoplasmic reticulum has…
presence of ribosomes
protein synthesis and processing
smooth endoplasmic reticulum has…
no ribosomes
synthesis of lipids
how are peptide hormones synthesised and secreted?
-TRANSCRIPTION: in the nucleus mRNA is transcribed from the hormone gene.
-TRANSLATION: in the RER peptide chains are synthesised on ribosomes attached to the RER as preprohormones.
-PROCESSING: in the ER and golgi cleavage, folding, and modifications convert preprohormones into inactive prohormones and then active hormones
-STORAGE: mature hormones are stored in secretory vesicles until needed.
-SECRETION: exocytosis releases hormones into the bloodstream.
examples of peptide hormones
insulin
growth hormones
post secretion characteristics of peptide hormones
Water-soluble → Dissolves in extracellular fluid
Short half-life → Needs continuous secretion
Lipophobic → Binds to membrane receptors
Activates signal transduction pathways (fast response)
examples of steroid hormones
cortisol
estrogen
testosterone
what are steroid hormones produced by?
Adrenal cortex (cortisol)
Gonads (testosterone, estrogen)
Skin (vitamin D)
Placenta (during pregnancy)
how are steroid hormones synthesised?
Derived from cholesterol, synthesized in the smooth ER
Produced on demand (not stored in vesicles)
Lipid-soluble → Diffuses through cell membrane
whats the transport and mechanism of steroid hormones?
Not water-soluble → Must bind to carrier proteins in blood (e.g., albumin)
Carrier-protein complex cannot enter cells → Only free steroid hormone diffuses inside
Acts on intracellular receptors (nuclear receptors) → Directly affects gene transcription
Slow onset but long-lasting effects
examples of genomic and nongenomic effects of steroid hormones.
Genomic: Estrogen activates genes for vitellogenin (yolk protein in egg-laying animals)
Nongenomic: Cortisol rapidly increases blood pressure by binding to membrane glucocorticoid receptors (mGRs)
Where are amine hormones derived from?
Derived from Tyrosine:
Catecholamines (Adrenaline, Noradrenaline, Dopamine) → Act like peptides
Thyroid hormones (T3/T4) → Act like steroids
Derived from Tryptophan:
Melatonin (Pineal gland) → Regulates sleep-wake cycle
Examples of amine hormone functions
Adrenaline/Noradrenaline (Fight-or-flight response)
Increases heart rate
Mobilizes glucose from the liver
Vasodilation in muscles (for oxygen delivery)
Thyroid Hormones (T3/T4)
Regulate metabolism, growth, and development
Transported in blood via carrier proteins
Bind to intracellular receptors → Long-lasting genomic effects
How do peptide hormones signal?
bind to membrane receptors Activate G-proteins or tyrosine kinase receptors → Second messenger systems
how to steroid and thyroid hormones signal?
bind to intracellular receptors to affect gene transcription
how does melatonin affect our sleep?
Produced at night in response to darkness
Helps regulate seasonal rhythms in animals
Teenagers experience delayed melatonin release, affecting sleep patterns
