L1: intro to the endocrine system

Question 1

What are the endocrine glands of the body?

Answer 1

Hypothalamus, pineal gland, pituitary gland, thyroid, parathyroid, thymus, heart, pancreas, adrenal, kidney, digestive tract, testis, ovaries

Question 2

What is a hormone?

Answer 2

Substances secreted by glands that have an action on another tissue. Controlling molecules. Carried in the blood to receptors on target organs. Present in minute concentrations in the blood and bind specific receptors in target cells to influence cellular reactions.

Question 3

What is the endocrine system?

Answer 3

A system of ductless glands and cells that secrete hormones. Regulates metabolism, homeostasis and reproduction.

Question 4

What is an endocrine gland?

Answer 4

Releases secretions (hormones) into the blood directly from cells.

Question 5

What is endocrinology?

Answer 5

The study of hormones

Question 6

Differences between nervous and endocrine systems

Answer 6

N - few neurotransmitters; E - many hormones
N - generally rapid speed of effect; E - generally slow speed of effect
N - short-lived response; E- long-lasting response
N - localised (cell-to-cell) effect; E - widespread effect in the blood

Question 7

What is an intracrine signal?

Answer 7

A signal generated by a chemical acting within the same cell

Question 8

What is an autocrine signal?

Answer 8

Signals in which a chemical acts on the same cell.

Question 9

What is a paracrine signal?

Answer 9

A paracrine signal is a signal between neighbouring cells within a tissue or organ.

Question 10

What is a general endocrine/neuroendocrine signal?

Answer 10

A chemical released by a specialised group of cells into the circulation and acting on a distance target tissue.

Question 11

What is an axis?

Answer 11

An axis is how glands interact with each other

Question 12

What is a feedback system?

Answer 12

Feedback is the process by which body sense change and respond to it,

Question 13

What is negative feedback?

Answer 13

The process by which the body senses change and activates mechanism to reduce it. The final product of an endocrine cascade acts to inhibit the release of hormones higher up the cascade.

Question 14

What is positive feedback?

Answer 14

Process by which body senses change and activates mechanism to amplify it.

Question 15

What are the 3 main groups of hormones?

Answer 15

Protein/peptide hormones - amino acids loaded together to make a protein, e.g. insulin
Steroid hormones - all made from cholesterol, e.g., cortisol
Amine hormones - all have tyrosine residues in them

Question 16

Protein and peptide hormones

Answer 16

• most common type of hormone
• mainly from hypothalamus and pituitary
• made up of chains of amino acids
• hydrophilic - so can travel in the blood without a transporter
• can be stored in cells because they can be stored in membrane bound vesicles ready for release by exocytosis
• produced on the RER as large precursor molecule - pre-prohormone
• pre-prohormone prohormone hormone means that only a small part of that protein is the actual active hormone with lots of other signalling parts which need to be cleaved off

Question 17

Protein and peptide hormone synthesis

Answer 17

• mRNA comes in, producing the protein of interest, e.g. a preprohormone which has the signalling sequence on
• signalling sequence is cleaved off and places the prohormone in the correct area
• prohormone can get into a transport vesicle
• moves into a Golgi complex and is modified e.g. by glycosylation
• secretory vesicles might cleave up the prohormone to release the active hormone leaving fragments
• when a release signal occurs it is all released and the hormone travels to its target cells and fragments get metabolised

Question 18

How are TSH, LH, FSH, hCG related?

Answer 18

All have the same alpha subunit attached to a beta subunit which is the active one, which confers specificity. All are released from the anterior pituitary gland.

Question 19

Steroid hormones

Answer 19

• all made from cholesterol
• hormones of the adrenal cortex and sex hormones
• cholesterol is initially converted by CYP11A (rate limiting step) into pregnenolone
• hydrophobic - repel water, so cannot be stored in cells
• lipophilic so will diffuse straight out of cells as soon as they are synthesised, not stored
• transport proteins needed for blood transport

Question 20

Steroid hormone synthesis

Answer 20

• signal tells the cell to hydrolyse esters and release cholesterol
• cholesterol is transported to the mitochondria (controlled by steroid acute regulatory protein StAR) where it is converted to pregnenolone
• pregnenolone is processed in the SER depending on the cell
• once synthesised they diffuse out of cell

Question 21

Secretion and excretion of steroid hormones

Answer 21

• newly synthesised steroid hormones are rapidly secreted from the cell, with little if any storage
• increases in secretion reflect accelerated rates of synthesis
• steroid hormones are eliminated by inactivating metabolic transformations and excretion in urine or bile

Question 22

Amine hormones

Answer 22

• tyrosine derivatives bound together

- small, non-polar molecules - therefore hydrophobic molecules which are soluble in plasma membranes

Question 23

How are steroid and amine hormones transported in the blood?

Answer 23

Steroid and thyroid hormones require carrier proteins. These bind to the hormones, increasing solubility in water, increase their half-life, and act as a reservoir of the hormone in the blood. There are specific binding proteins for this.
There are also non-specific binding proteins e.g. albumin, which has loose binding.

Question 24

Site of action of protein/peptide hormones

Answer 24

Chemical structure of the hormones changes how they will act at their target tissue.
Protein/peptide hormones have cell-surface receptors, which activate second messenger cascade to cause a change in cellular function.

Question 25

Site of action of steroid hormones

Answer 25

Steroid hormones have intracellular receptors, in the cytoplasm or nucleus. The hormone-receptor complex binds to HRE (hormone response element on DNA).
Each hormone has their own _ response element.