Flashcards in Unit 5 Deck (22):
What is a hormone?
a chemical messenger secreted into the blood by specialized cells
How do hormones act on target cells?
Regulate enzyme activity, regulate ion transport, and regulate gene expression
What are some features of "classical" hormones?
They are secreted by cells derived from epithelial tissues, they are secreted into the blood, they traveller distances, and they act at very low concentrations
What classifies a cell as a target cell for a hormone?
They have to have a receptor for that hormone.
What is needed to transmit a signal from a peptide or protein hormone?
They need a membrane receptor
What are amine hormones derived from?
From either tryptophan or tyrosine
What two types of hormones arise from tyrosine?
Thryoid hormones (T3 and T4)
Which is the main thyroid hormone?
What do all steroid hormones have in common? (x3)
They are all derived from cholesterol. They can easily cross membranes and they are chemically stable
Why are steroids madden demand and not made and stored? How do they circulate?
They easily cross membranes and therefore cannot be easily contained. They circulate bound to proteins (carriers or albumin)
What re the 5 steps of classic hormone action? Are these effects fast or slow?
1. Circulation bound to protein carriers and can only cross membranes once they are unbound
2. "Classic" steroid receptors are within the cytoplasm or within the nucleus
3. Receptro-hormone complexes bind to the DNA and activate or repress gene expression
4. Gene transcription mRNA and shuttled out f the nucleus
They are slow
What type of factors are steroid receptor proteins?
Ligand-activated transcription factors.
What two specialized groups can secrete neurohormones?
Adrenal Medulla and the hypothalamus
What is the pathway of a neurohormone released in the posterior pituitary? What are two examples of hormones released from here?
1. Neurohormone is made and packaged in neuron cell body within the hypothalamus
2. Vessicles are transported down the cell to the posterior pituitary
3. Vessicles containing neurohormone are stored in the posterior pituitary
4. Neurohormones are released into the blood
Oxytocin and vasopressin
What is the pathway of a neurohormone released through the anterior pituitary?
1. Neurons synthesizing neurohormones within the hypothalamus release them into the first pituitary bed
2. Portal veins carry the neurohormones directly into a second capillary bed in the anterior pituitary
3. Endocrine cells release peptide hormones into the second set of capillaries, and peptides exit via the venous drainage
Why is it important that the peptides released in the anterior pituitary small and only travel short distances?
This is because they an then reach their final destination very high concentrations and they will not be broken down
What types of hormones are released out of the anterior pituitary? (in relation to the target tissue)
Trophic hormones. Mammary glands, musculoskeletal system, thyroid gland adrenal cortex and the gonads.
What are the 3 tiers of hypothalamic/pituitary axis?
The hypothalamus, the anterior pituitary and the target organs.
What are the three tiers for the TRH, CRH and GnRH?
Thyroid Releasing hormone
3. thyroid gland > T3 and T4
Coritcal Releasing Hormone
3. Adrenal cortex > Cortisol
Gonadotropin Releasing Hormone
2. FSH and LH
3. Endocrine cells of the gonads > Androgens and Estrogen/progesterone
What acts as the feedback signal in hypothalamic-pituitary axes? Why?
The hormones themselves (cortisol, androgens/estrogen/progesterone and T3 and T4. Because rather than having the hypothalamus keep track of the levels of all the hormones, having direct feedback from the hormone itself is way more efficient
What do the hormones (that act as negative feedback) act on?
they feed back to both the anterior pituitary and the hypothalamus