Endocrine system I

Question 1

Analysis of body composition

Answer 1

• 6%: minerals, hormones, vitamins, neurotransmitters
• 60%: liquid
• 18%: protein
• 16%: fat

Question 2

Intercellular communication

Answer 2

• despite the vast extent of the communication network requires, there are only a few mechnisms for communication

Question 3

Direct communication

Answer 3

via gap junctions or direct linkup of cell surface markers

Question 4

Indirect communication

Answer 4

via an assortment of chemical messengers or signal molecules
e.g. paracrine, neurotransmitters, hormones, neurohormones

Question 5

Direct communication via gap junctions

Answer 5

• gap junctions link adjacent cells together
• connexons form channels that link the cytosol of adjacent cells permitting transfer of ions between the two cells
• e.g. where gap junctions are crucial to survival is in the heart

Question 6

Direct linkup of cell surface markers

Answer 6

• complementary surface markers = surface receptors

- e.g. to activate an immune cell

Question 7

Indirect chemical messengers or signal molecules

Answer 7

• secretory cell released chemical messenger into EFC
• messenger binds to specfic receptor on the ‘target’ cell
• binding of messenger to receptor triggers a response in the target cell

Question 8

Paracrines (local)

e.g. (3)

Answer 8

• local chemical messengers
• exert effect only on neighbouring cells in immediate environment of secreiton site - secreted by once cell and diffuse to nearby target cell
  Histamine: released in damaged tissue and causes inflammatory response
  Epidermal growth factor: stimulates cell division
  Vascular endothelial growth factor: stimulates growth and branching of blood vessels

Question 9

Autocrines (self)

e.g. (1)

Answer 9

• bind to receptors and exert their effects on the same cell that secreted them
• often autocrines also function as a paracrine or other messenger
  e. g. growth factor

Question 10

Cytokines

Answer 10

• secreted by cells of the immune system

- e.g. interleukins and interferons = groups of small proteins released from white blood cells

Question 11

Neurotransmitters

E.g. (3)

Answer 11

• released from neurons to axon terminal
• short range chemical messengers
• diffuse across narrow space to act locally on adjoining target cells = synpatic signalling (another neuron, a muscle or a gland)
• released from axon terminals of nerves
• E.g. acetylcholine: involved in triggering contractions of skeletal muscle
  Dopamine: precursor of norepinephrine
  Serotonin: especially active in constricint smooth muscles, contributing to wellbeing and happiness

Question 12

Hormones

Answer 12

• Long range chemical messengers
• secreted by endocrine glands into the blood
• exert effect on target cells some distance away from release sight

Question 13

Endocrinology

Answer 13

study of hormones and endocrine organs

Question 14

Hormones II

Answer 14

• represent a very small percentage of the body
• effects exerted at very low concentrations
• chemical messengers secreted directly into the blood
• circulatory syste, transports them to distant target organs
• hormones bind to cell receptors and trigger a response
• same hormone can cause different responses in different cell types
• acts with nervous system to coordinate and integrate activity of body cells
• responses slower but longer lasting than nervous system responses

Question 15

Endorcrine system controls and integrates

Answer 15

• maintenance of electrolyte, water and nutrient balance of blood. e.g. in kidney
• regulation of cellular metabolism and energy balance e.g. insulin
• growith and development e.g. growth hormone
• mobilisation of body defences e.g. histamine
• reproduction e.g. testosterone

Question 16

Exocrine glands

Answer 16

• produce non-hormonal substances
• have ducts to carry secretion to membrane surface
• e.g. sebaceous glands, salivary glands

Question 17

Endocrine glands

Answer 17

• typically have a rich vascular and lymphatic drainage for rapid dispersal of hormones throughout body
• produce hormones
• lack ducts (secretion into blood)
• e.g. pituitary, thyroid gland

Question 18

Example of endocrine and hormones

Answer 18

• Pituitary gland: FSH, LH, prolactin, GH
• Thyroid gland: thyroid hormones, calcitonin
• Parathyroid gland: parathyroid hormones
• adrenal glands: aldosterone, cortisol, epinephrine, norepinephrine
• pineal glands: melatonin
• gonads: ovaries and testes: progesterone, oestrogen, testosterone

Question 19

Combines exocrine and endocrine

Answer 19

• hypothalamus is neuroendocrine organ
• some have exocrine and endocrine functions (pancreas, gonads, placenta)
• other tissues and organs that produce hormones
• adipose cells, thymus and cell inwalls of small intestine, stomach, kindneys and heart

Question 20

Mechanism of hormone action

Answer 20

• for hormones to exert their effects, they must bind to a specifc receptor
• target cell receptors are located outside the cell in/ on the cell membrane, in the cytosol or in the nucleus
• receptors bind ligands (hormoens) -> then translate ‘message’ of signal ligand into a cellular response = cell signalling

Question 21

Cell signalling usually involves

Answer 21

• activation of transcriptio factors in the nucleus of the cell -> increased production of proteins and other substances
• activate or deactivate enzymes
• induce secretory activity
• stimulate mitosis

Question 22

Receptors and their regulation

Answer 22

• the amount of receptors on target tissues is not static

- amount of hormones can influence number of receptors for that hormone

Question 23

Upregulation of receptors

Answer 23

Number of receptors increases on the target cell when hormone levels are low

Question 24

Down regulation of receptors

Answer 24

Number of receptors decreases on the target cell when hormone levels are high
de-sensitised the target cells to prevent them from overreacting to persisttently high levels of hormones

Question 25

Hormone release

Answer 25

• blood levels of hormones
• controlled by negative feedback systems
• increased hormone effects on target organs can inhibit further release
• levels vary only within narrow, desirable range

Question 26

Hormone release is triggered by

Answer 26

Endocrine gland stimuli

Nervous system modulation

Question 27

Control of endocrine activity

Answer 27

When hormone concentrations are either too high or too low -> disease -> precise control circulating concentraton of hormones is crucial
the concentration of hormone as seen by target cells is determined by 3 factors

Question 28

Rate of production

Answer 28

• synthesis and secretion of hormones are the most highly regulated aspect of endocrine control
• control mediated by positive and negative feedback circuits

Question 29

Rate of delivery

Answer 29

an example of this effects if blood flow to a target organ or group of target cells - high flow delivers more hormone than low blood flow

Question 30

Rate of degradation and elimination

Answer 30

hormones, like all biomolecules, have characteristics rates of decay -> metabolised and excreted from the body through several routes
Shutting off secretion of a hormone that has a very short half-life causes circulating hormone concentration to plummet
- if a hormone’s biological half-life is long, effective concentrations persist for some time after secretion ceases

Question 31

Mechanisem of hormone action

Answer 31

• in most cases, cells release chemical messnegers to casue an effect on a nearby target cell
• hormones have the advantage of being transported in the blood
• secretion of hormones can occur in two ways bases on their solubility properties
  Dissolved in the blood (hydrophilic messenger, highly water soluble, low lipid solubility)
  Attached to a carrer protein (hydrophobic messenger, high lipid solubility, low water solubility)

Question 32

Mechanisms of hormone action

Answer 32

• lipophilic hormones diffuse across cell membrane and bind to cytosolic or nuclear receptors
• lipophobic hormones bind to cell membrane receptor
• binding of hormone to intracellular receptor leads to hormone response element int the mucleus, altering gene expression

Question 33

Surface receptors

Answer 33

• binding of extracellular messenger to matching receptor leads to response by:
  1. opening or closing of channels
  2. activating receptor enzymes
  3. activating second messenger systems

Question 34

the 3 types of cell surface receptors

Answer 34

• different types of cell surface receptors can result in different outcomes:
  1. channel linked receptors
  2. enzyme linked receptors
  3. G-protein linked receptors

Question 35

Opening or closing of channels

Answer 35

• channel linked receptors
• involved in rapid signalling/electrical transmission
• neurons have a cation linked receptor

Question 36

Activating receptor enzymes

Answer 36

• enzyme linked receptors
• most common are tyrosine kinases
• hormones and growth factors bind to receptor, causing intracellular signalling to occur (e.g. insulin)

Question 37

Activating second messenger systems

Answer 37

• activation of second messenger pathway via G protein coupled receptors
• G protein linked receptors
• odorant molecules, hormones and neurotransmitters
• cause cAMP signalling or PI singalling (e.g. epinephrine, ADH)

Question 38

Amplication of signal

Answer 38

very little messenger necessary to bind target ce;; and cause large effect

Question 39

The downsife of G proteins - Cholera

Answer 39

• affects the small intestine and causes violent diarrhoea
• transmitted by contaminates water/food
• caused by bacterium Vibrio cholera
• secretion of chlorea toxin - choleragen (complex)
• results in the activation of chloride channel proteins, which leads to ATP- mediated efflux of chloride ions and leads to secretion of H2O, Na+, K+, HCO3- into the intestinal lumen
• entry of Na+ and consequently the entry of water into enterocytes are diminished