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hormonen en homeostase
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Hormones and HomeostasisInhoud
General principles.................................................................................................................................... 1
HC 1+2 Principles and definitions ........................................................................................................ 1
WC 1 .................................................................................................................................................... 8
Hypothalamus – Pituitary ........................................................................................................................ 9
HC 3+4 Hypothalamus and Pituitary Gland (hypophysis) ................................................................... 9
WC 2 .................................................................................................................................................. 18
Growth regulation ................................................................................................................................. 20
HC 5+6 Growth regulation and disturbance...................................................................................... 20
WC 3 .................................................................................................................................................. 25
E-module WC 3 .................................................................................................................................. 26
WC 4 .................................................................................................................................................. 27
Energy homeostasis............................................................................................................................... 28
HC 7+8 Energy homeostasis .............................................................................................................. 28
WC 5 .................................................................................................................................................. 38
Microscopy 1 Pituitary....................................................................................................................... 39
Microscopy 2 Pancreas ...................................................................................................................... 40
Adipose tissue ....................................................................................................................................... 41
HC 9+10 Adipose tissue as an endocrine organ ................................................................................ 41
E-module tutorial 7............................................................................................................................ 44
WC 7 .................................................................................................................................................. 46
MTE........................................................................................................................................................ 47
General principles
HC 1+2 Principles and definitions
Homeostasis: response to disturbances
• Situation
o All functions of body being in equilibrium
o Chemical and physiological balance
• Activity
o Self-regulation
o The body’s ability to maintain internal stability
1
,Homeostatic set-point:
Fixed set-points
- Body temperature
- Concentrations in blood
Variable set-points
- Ontogenesis (growth)
- Temporal cycles
o Day/night
o Ovarian cycles, seasonal reproduction
Homeostasis is maintained by the endocrine and nervous system (jointly)
Hormones involved in:
• Maintaining internal balance
• Reaction to physical and emotional stress
• Response to environment
Hormones regulate:
• Internal environment
• Growth and development
• Metabolism
• Reproduction
Hormone= compound that:
• Is produced by a gland not connected to the outside world
• Is secreted into the blood
• Has a physiologic or morphogenetic function in the body, usually distant from the site of
production
o Physiologic= change in cell→ ion-channel, characteristics etc.
o Morphogenetic= change in shape→ differentiation
But:
- Signalling molecules can also be synthesized by organs/tissues having a different primary
function
- Compounds such as Na, glucose, NO and CO2 can act as signalling molecules
- Transport medium is not limited to blood
o Intercellular fluid
2
,Hormone= chemical secreted by a cell or group of cells into the blood for transport to a (distant)
target, where it exerts its effect at low concentrations
- Receptor has high affinity for ligand (hormone) so a low hormone concentration is enough
Endocrinology= study of hormones (internal secretion)
Endocrine glands
Pineal gland→ melatonin: high during night, low during day
- Connected to roof of mesencephalon
- Connection from optical nerves to brain
- Regulates day-night cycles
Hypothalamus→ releasing/inhibiting hormones (neurosecretory neurons)
- Ventral part of diencephalon
- Stimulate or inhibit secretion of other hormones such as hormones from pituitary gland
- 3 lobes, produce/release different hormones
ADH and oxytocin are produced by the hypothalamus and stored in the pituitary gland (neural lobe)
Calcitonin and PTH have a role in calcium metabolism
Adrenal glands cortex→ steroid hormones
Adrenal glands medulla→ adrenalin/epinephrine
Pancreas→ insulin, glucagon…
Ovaries/ testes→ reproductive hormones
3
, Placenta only produces hormones in animals with longer pregnancies
Testosterone from testes goes to the brain and is there converted to estrogen which has the effect
- Females produce estrogen directly
Often hormones in the blood are precursors and are activated in the target tissues
Classification of hormones:
• Site of production
o Glandular
o Tissue
o Growth factors
o Pheromones
• Receptor type
o Membrane
o Nuclear
• Biochemistry
o Steroids (cortisol)
o (Poly)peptides (insulin)
o Glycoproteins (gonadotropins: LH/FSH/TSH)
o Amino acid derivatives (epinephrine)
Response loops:
1. Stimulus or change→ trigger
2. Endocrine cell/tissue evaluates stimulus→ may lead to hormone
release
3. Cells or tissues that recognize the hormone carry out specific response
Endocrine and nervous system collaborate in regulation of body functions
Paracrine: hormone to extracellular fluid
Endocrine: hormone to blood, effect on distance
Autocrine: hormone acts on the cell that secreted it
Negative feedback: leads to homeostasis
Positive feedback: does not lead to homeostasis
- Requires external interference to prevent
resonance catastrophe
- Negative feedback mechanisms can be activated when new, desired
level of activity has been reached
4
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