Endo physiology L intro 2022

Question 1

Learning Objective

Answer 1

Be able to understand the consequences of common endocrinological diseases
Be able to understand the effects of hormones on multiple organ systems within the body to achieve growth, reproduction and maintain homeostasis (energy and mineral metabolism).

Question 2

Neuroendocrine integration

Answer 2

The endocrine and nervous systems may share the same signalling molecules and are integrated in their control of physiological processes.

Question 3

paracrine secretion

Answer 3

Question 4

Neurotransmitter secretion

Answer 4

Question 5

Hormonal secretion

Answer 5

Question 6

Neurohormone secretion

Answer 6

Question 7

Hormonal control of physiological functions

Answer 7

Energy metabolism:
Mineral metabolism:
Growth
Reproduction

Question 8

Energy metabolism:

hormones

Answer 8

insulin, glucagon, cortisol, adrenaline, thyroid hormone and growth hormone.

Question 9

Mineral metabolism:

Answer 9

parathyroid hormone, calcitonin, Vitamin D, angiotensin, renin and aldosterone.

Question 10

Growth:

Answer 10

growth hormone, thyroid hormone, insulin, oestrogen and androgens and a large number of growth factors.

Question 11

Reproduction:

Answer 11

oestrogen, androgens, progesterone, luteinising hormone (LH), follicle-stimulating hormone (FSH), prolactin and oxytocin.

Question 12

Reproduction:

Answer 12

oestrogen, androgens, progesterone, luteinising hormone (LH), follicle-stimulating hormone (FSH), prolactin and oxytocin.

Question 13

why aren’t hormones simple?

Answer 13

Fertility linked to BCS (body condition score)
So fertility also impacted by energy metabolism and partitioning of nutrients
Genetic selection for increased production (eg milk yield) will favour animals that partition nutrients to production may be at cost of BCS, decreasing fertility
Related to complex interplay of many hormones in the body, nutritional status, production status, welfare, etc

Question 14

So what do hormones do??? Proteins….

Answer 14

Proteins can be structural, receptors, messengers, transporters etc.
Different proteins play different roles.
Hormones influence their production

Question 15

Concept 1: Amplification of signal

Answer 15

Eg. One chemical messenger receptor on a target cell increased enzyme function
Increased production of multiple mRNA molecules to form enzymes, or
Production of cAMP which can also activate enzymes.

In such a way, very low levels of hormones (ng/100ml) in the blood stream can cause significant biological effects in cells which may be prolonged, lasting minutes to days.

Question 16

Concept 2: Lipophilic versus Hydrophilic hormones (4)

Answer 16

Chemical structure
Steroid hormones -> lipophilic
Protein hormones -> hydrophilic
Tyrosine hormones -> thyroid hormones lipophilic/amphipathic
Fatty  acid hormones -> lipophilic

Consider the properties that being lipophilic or hydrophilic conveys to a hormone

Answer 17

Question 18

Concept 3: Hormone synthesis and storage A. Amino acid hormone synthesis

Answer 18

Protein and polypeptide hormones 
Preprohormones
cleaved in the RER to form prohormones 
modified by Golgi to form active hormone
Most of hormone produced is stored in granules before being released by exocytosis
Exocytosis triggered  by ATP and Ca++

Question 19

B. Steroid hormone synthesis

Answer 19

Synthesised from triglycerides and cholesterol (synthesised by the liver) -> lipid soluble
TG or Cholesterol may be stored in the endocrine cell (lipid droplets) but steroid hormones are released as they are synthesised
Production controlled by production of enzymes in pathways
The formation of pregnenolone from cholesterol is the first step in formation, however final hormone produced depends on the enzymes produced by that cell type

Question 20

Concept 4. The transport of hormones in the blood - proteins

Answer 20

hydrophilic
carried in plasma in dissolved form
May travel as multiple, single or as subunits of the biologically active molecule
May have binding proteins that affect their half-life or activity

Question 21

Concept 4. The transport of hormones in the blood- steroids and thyroid hormones

Answer 21

Lipophilic
carried in plasma in association with both specific and nonspecific binding proteins
amount of unbound, active hormone relatively small

Question 22

Concept 5: Plasma membrane receptors

Answer 22

Protein hormones have specific receptors on target cells plasma membranes
Hydrophilic – wont cross PM unaided
Formation of reversible noncovalent bonds
Hormone-receptor complex may be degraded internally by the cell
Available receptor concentration may change
Due to other hormones
Due to agonist with greater affinity
Due to pathological elevation of hormone

Question 23

Concept 6: Postreceptor cell responses

Answer 23

Steroids act directly with the cell nucleus through the formation of a complex with its cytosolic receptor
Results in mRNA being produced
Protein hormones need a second messenger as they cannot enter the cell (hydrophilic)
Best known is cAMP which is formed from the activation of adenyl cyclase by the hormone-receptor complex.
cAMP can then phosphorylate protein kinases which are responsible for biological actions

Question 24

Hydrophilic hormone action on target cells .
Eg. TSH, adrenaline.

Act on membrane receptor as cannot diffuse through cell membrane

Answer 24

Question 25

Lipophilic hormone action on target cells.

Answer 25

Eg. Oestradiol.

Act on specific receptors within the cytoplasm or nucleus after diffusing through cell membrane.

Question 26

Concept 7: Metabolism of hormones

Answer 26

Steroid hormones are metabolised by conjugation with sulphates and glucuronides, which makes them water soluble.
Largely done in liver
Thyroid hormones are de-iodinised during metabolism
Protein hormones are cleaved by peptidases
Metabolites are generally less biologically active but not always
Dihydrotestosterone more potent than testosterone
Oestrone, metabolite produced from adipose tissue is more potent than its precursor oestradiol-17β

Question 27

Concept 8: Rate of hormone clearance

Answer 27

Generally, rate of synthesis reflects rate of clearance
Exceptions occur, eg:
Decrease clearance during pregnancy as a result of increased hormone-binding proteins
Increase clearance due to liver disease as a result of decreased hormone-binding proteins

Question 28

Concept 9: Feedback control mechanisms

Answer 28

The most important feedback control for hormones is the negative feedback system in which increased hormone concentrations result in less production of the hormone, usually through an interaction with the hypothalamus or pituitary gland
Allows for maintenance of optimal hormone concentrations

Question 29

Concept 10: Influence of pineal gland

Answer 29

Endocrine secretary patterns can be influenced by factors such as sleep or light, and can produce diurnal patterns (circadian rhythms) or seasonal patterns.
Through the action of the pineal gland which receives neural input regarding light
day/night patterns.
Increasing day length -> seasonal patterns

Question 30

Endocrine diseases

Answer 30

Too little or too much hormone activity

Question 31

endocrine diseases too fillet hormone activity

Answer 31

Hyposecretion
Increased clearance
Tissue resistance

Question 32

Too much hormone activity

Answer 32

Hypersecretion
Reduced plasma protein binding
Reduced clearance
Excessive response at target tissue

Question 33

Compare and contrast the general concepts of amino acid based hormones to fatty acid and cholesterol based hormones

Answer 33