Basics (L1) Flashcards
Three features of classical endocrine glands
Ductless
Secrete directly into the bloodstream/extracellular space
Entire organ is dedicated to endocrine function
Non-classical endocrine organs (6)
Brain Kidney GI Adipose Heart Liver
Hormones released by the kidney
EPO, vitamin D, renin
Hormones released by the GI system
Ghrelin, serotonin
Possible symptoms of endocrine dysfunction
Weight/appetite changes Fatigue Hair loss/Hirsutism Cognitive changes (memory loss, confusion) Dizziness Moodiness
Free vs. bound hormone
A hormone is often carried on a carrier protein to increase half life. However, only free hormones are biologically active
Which hormones are the ones that typically need a carrier protein?
Lipophilic steroid hormones
IGF-1, GH, and T3/T4
What types of compounds usually circulate freely?
Proteins/peptides and amines
SHBG
Sex hormone binding globulin
Binds estrogens and testosterone
CBG
Corticotropin binding globulin
Binds cortisol/corticosterone
TBG/TTR
Thyroid binding globulin, transthyretin
Both carry/bind thyroid hormone
Non-specific hormone carrier
Albumin - can bind most lipophilic compounds
Two different methods of steroid delivery at target cell
- Released at membrane, diffuses in
- Protein complex binds to megalin, endocytic vesicle is formed, and then the hormone dissociates and is released from the vesicle
How are cell surface receptors inactivated?
Internalization of the receptor or release of the ligand
How are internal cell receptors inactivated?
Ubiquitination
Measurement of affinity
Kd: Ligand concentration that takes up 50% of the receptors
What is the relationship between Kd and affinity?
Smaller number means higher affinity
Measurement of specificity
Ki: ability to displace ligand at 50% of maximum activity
What is the relationship between Ki and specificity?
The smaller the number, the greater the specificity
Lipophobic receptors
Bind to cell surface
Coupled to second messenger pathways
Rapid internalization or degradation
G-protein coupled receptors are used often with __
most protein hormones
Receptor-linked kinases are used often with __
growth hormone, prolactin, and EPO
Receptor kinases are used often with __
insulin, ANP
Lipophilic receptors
Mainly bind to intracellular receptors that cause SLOW responses (up/downregulation of transcription)
To what are lipophilic receptors bound in the cytoplasm?
Large chaperone proteins that serve as heat-shock proteins
Describe the thyroid hormone receptor
Thyroid hormones bind to the receptors in the nucleus
When they are NOT bound, NO transcription takes place
Transcription is activated by thyroid hormone presence
What happens to the chaperone proteins when the hormones bind?
They dissociate
What is special about the thyroid hormones?
They belong to the steroid superfamily, though they are not actually steroids
Four factors affecting hormone bioavailability
Hormone transport, target tissues, hormone sythesis/release, and regulatory mechanisms
Hormone transport’s effect on hormone bioavailability
- If the hormone is bound or free
- Half-life
Target tissue’s effect on hormone bioavailability
Desensitization, up/downregulation, mutation of receptors
Chaperone/heat shock proteins present
Regulatory mechanisms’ effects on hormone bioavailability
Feedback, circadian rhythms, age, pulsatility, and metabolism
